Home Stuck/ Course in Bird Biologq

An invaluable reference book on modern ornithology, the Handbook of

Bird Biology also serves as the textbook for the popular Home Study Course
in Bird Biology, created and administered by the Education department at
the Cornell Lab of Ornithology.

The Home Study Course is a self-paced, distance-learning course that

provides a comprehensive, college-level education about the major topics
in ornithology. The course is open to anyone with a serious interest in bird
biology. Students receive guidance from professional ornithologists and
an assessment of their understanding of the information in this book. After
successfully completing 10 exams, students receive a certificate signed by
the director of the Cornell Lab of Ornithology.

Please inquire about further details, including current pricing information.

We offer special rates for individuals, groups (classrooms, bird clubs, and
learning groups), and course sharing (friends and family sharing the same
textbook). Enrollment is simple—just sign up on our web site, by phone,
or by mailing the enrollment card included with this book.

www.birds.cornell.edu/homestudy
800-843-2473 (United States calls)
607-254-2452 (International calls)

"The Home Study Course in Bird Biology has deepened my awe

of our winged friends. Every day while watching birds,
I'm reminded of something I've learned from the course."
-SANDY MADDOX, LOUISVILLE, KENTUCKY

"I am enjoying the course immensely.

It is one of the best investments I have ever made."
-PAT ROBSON, CHRISTCHURCH, NEW ZEALAND

"I wish I could just go on with the course forever. It inspired me to

embark on a master's degree in natural sciences
so I can keep on learning!"
-DIANE TUCKER, WEST HARTFORD, CONNECTICUT
U

Throughout the 1970s and '80s the course underwent several revi-
sions to reflect new findings in ornithology and related disciplines. By the
mid-1990s, however, minor revisions no longer were sufficient to reflect
new and relevantornithological findings in vibrant research areas such as
animal communication, conservation biology, animal behavior, and evo-
lutionary biology. Therefore, in 1998 the Lab of Ornithology temporarily
stopped enrolling new students in the Home Study Course so that science
education staff at the Lab could begin the challenge of overhauling the
course from top to bottom and expanding its coverage by engaging some
of the most knowledgeable professional ornithologists to bring the Home
Study Course into the modern era of ornithology.
The second edition contains new text, photographs, illustrations,
graphs, and tables. It covers all of the major topics addressed in the first
edition, from anatomy and physiology to ecology and behavior. In addi-
tion, we've added a complete chapter on bird identification and another
on conservation to make it more useful for birders and to introduce the
Table of Contents
relatively new science of conservation biology. We've also added a chap-
ter on vocal communication, which, in keeping with the Lab's tradition
of recording and producing media using high-quality animal sounds for
education and research, is accompanied by an audio CD of bird vocaliza-
tions that are used to illustrate the many elements of bioacoustics.
We are confident that you will find the Handbook of Bird Biology
to be an essential resource for all of your bird-related questions.

Home Studtj Course and Certificate of Completion BIRDS AND HUMANS: A HISTORICAL PERSPECTIVE
In addition to serving as a general ornithology reference, this book is Birds as Food H•3
meant to accompany the Home Study Course in Bird Biology (HSC) Use of Skins and Feathers H•4
administered by the Lab of Ornithology Education staff. To successfully Birds in Literature, Culture, and Religion H•6
complete the course you must read each chapter at your own pace Art H•6
Religion H•9
and complete an open-book exam (paper or online) for each of the 10
Folklore H•10
chapters. Exams are graded and returned so that students can review
Literature H•11
their answers and keep track of their performance. Questions and com-
Music and Dance H•13
ments can be submitted to the course instructor, who will help guide
Music and Dance of Indigenous Cultures H•13
students through the most challenging material. After completing all 10
Music and Dance of Western Cultures H•18
chapters and exams with passing grades, you will receive a certificate
The Evolution of North American Ornithology H •19
of completion signed by the Louis Agassiz Fuertes Director of the Lab of
The Early Years: From Aristotle to the 17th Century H•19
Ornithology. We are constantly working to incorporate new informa-
The 18th Century H•23
tion, supplemental materials, and distance learningtools on our web site
The 19th Century H•25
to keep the HSC content current, provide additional resources, and cre-
The American Ornithologists' Union and the
ate an environment that will keep students engaged and motivate them H•32
U. S. Biological Survey
through completion and certification. Please visit our web site <www. H•33
The First Audubon Movement
birds.cornell.edu/homestudy> for the latest HSC information. To enroll H•34
The Second Audubon Movement
call us at 800-843-BIRD (outside the United States at 607-254-2452),
The 20th Century and the Expanding Role
sign up on our web site, or mail the card inserted into this book. H•35
of the Bird Watcher
Whether you acquired the Handbook of Bird Biology to use as a The Development of the Field Guide H•36
general ornithology reference or received it as a part of your enrollment Academic Training in Ornithology H•37
in the Home Study Course, we wish you the very best in your quest Bird Conservation, Bird Watching,
for more knowledge and awareness about the many interesting facets and the Age of Technology H•39
that characterize the science of ornithology. We hope that this book Suggested Readings H•42
provides you with an accessible gateway to the information you seek,
and that it functions as a top-notch reference for years to come.

Cornell Laboratorg of Ornithologg

iv V

CHAPTER 1- INTRODUCTION: THE WORLD OF BIRDS Sidebar 2: The Evolution of an Idea: Darwin's Theory 1.34
1.3 Sidebar 3: Latin and Greek Roots of Biological Terms 1.48
Ornithological Terms
The Form of a Bird 1.3
I
Bill 1.6
Head and Neck 1.7 CHAPTER 2 - A GUIDE TO BIRD WATCHING
Trunk 1.9 How to Identify Birds 2.4
Wings 1.9 Shape 2.5
1.12 I Postures and Flight Patterns 2.5
Tail
Hind Limbs 1.12 Behaviors 2.7
Diversity in Bird Form 1.15 Size 2.7
The Bill 1.16 Comparing Body Features 2.9
The Wings 1.18 Field Marks 2.10
The Tail 1.19 Head 2.10
The Feet 1.20 Bill Shape and Color 2.11
Feathering 1.23 Wings 2.12
Internal Anatomy 1.24 Tail 2.12
Diversity in Bird Movement 1.24 Legs 2.13
Movement on Land 1.24 Colors and Plumage Patterns 2.13
Movement in Water 1.28 Songs 2.14
Naming and Classification of Birds 1.32 Habitat 2.18
History 1.32 Range and Abundance 2.19
Methods Used to Classify Birds 1.40 Time of Year 2.19
Binomial Nomenclature and Classification System 1.45 Sorting Out Birds 2.23
The Species 1.53 Closing the Distance 2.23
The Formation of Species 1.55 Sitting Quietly 2.23
Orders and Families of World Birds 1.61 Pishing and Squeaking 2.26
Orders and Families of North American Birds 1.64 Mobbing 2.26
How Naming and Classification Can Help You 1.64 Playback Songs 2.28
The Use of Common Names 1.64 Bird Blinds 2.29
Evolution of Birds and Avian Flight 1.66 Viewing Birds 2.29
Bird Distribution 1.66 Using Binoculars 2.29
Distribution of Land Birds 1.69 Pointing Out Birds to Others 2.32
Palearctic Region 1.69 Selecting Binoculars 2.34
Nearctic Region 1.71 Magnification Power 2.34
Neotropical Region 1.72 Light-gathering Capacity 2.35
Afrotropical Region 1.81 Field of View 2.37
Oriental Region 1.88 Resolution 2.37
Australasian Region 1.91 Alignment 2.38
Island Distribution 1.97 Binocular Designs 2.38
Distribution of Marine Birds 1.98 Mini Binoculars 2.39
Northern Marine Region 1.99 Binoculars for Eyeglass Wearers 2.40
Southern Marine Region 1.100 How to Shop for Binoculars 2.40
Tropical Marine Region 1.101 How to Clean Binoculars 2.41
Plankton and Bird Distribution F101 Protecting Binoculars 2.41
The Importance of Biodiversity 1.106 Selecting a Spotting Scope and Tripod 2.42
Appendix A: Orders and Families of World Birds 1.107 How to Shop for a Spotting Scope 2.44
Appendix B: Orders and Families of North American Birds 1.111 Recording Observations 2.44
Appendix C: Geological Time Scale 1.113 Checklists 2.46
Journals 2.47
Reporting Rare Birds 2.54
Sidebars Listing Birds 2.54
Sidebar 1: Which Way is Up? 1.4 Counting Birds 2.55

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Conclusion 2.57 Age Recognition 3.66

The Birder's Essential Resources 2.58 Sex Recognition 3.67
Individual Recognition 3.67
(
Flock Attraction 3.68
Sidebars
Sexual Selection 3.68
Sidebar 1: Attracting Birds to Your Yard 2.24
Sidebar 2: How to Calibrate Binoculars For Your Eyes 2.30
Sidebar 3: Sketching Birds in the Field 2.50 SIDEBARS
Sidebar 1: Feather Detective 3.6
Sidebar 2: Feather Facts 3.11
CHAPTER 3 - FORM AND FUNCTION: THE EXTERNAL BIRD
3.2 Sidebar 3: Iridescence 3.56
Feather Tracts
Feather Form and Function 3.3
Feather Structure 3.3 CHAPTER 4 - WHAT 'S INSIDE: ANATOMY AND PHYSIOLOGY
Types of Feathers 3.4 The Skeletal System 4.3
Contour Feathers 3.5 Axial Skeleton 4.10
Down Feathers 3.16 Skull 4.10
Semiplumes 3.17 Hyoid Apparatus 4.13
Filoplumes 3.17 Vertebral Column 4.14
Powder Downs 3.18 Appendicular Skeleton 4.18
Care of Feathers 3.18 Pectoral Girdle 4.19
3.18 Bones of the Wing 4.21
Preening
Oiling 3.20 Sternum 4.23
Head-Scratching 3.20 Pelvic Girdle 4.24
Bathing 3.21 Bones of the Hind Limb 4.24
Sunning 3.22 The Muscular System 4.26
Anting •3.22 Skeletal Muscle 4.26
Ectoparasites 3.23 Smooth Muscle 4.28
Development of Feathers 3.26 Cardiac Muscle 4.31
Molts and Plumages 3.28 The Nervous System 4.31
Annual Molt and Wear Cycles 3.29 The Neuron 4.32
Subadult and Definitive Plumages 3.30 Sensory and Motor Neurons 4.33
Plumage Naming Systems 3.33 Central Nervous System 4.35
The Progression of a Molt 3.34 Brain 4.36
Nonfeathered Areas 3.39 Spinal Cord 4.38
3.39 Peripheral Nervous System 4.40
Eyes
Bill 3.39 Cranial Nerves 4.40
Legs and Feet 3.43 Spinal Nerves 4.42
Other Unfeathered Areas 3.46 Autonomic Nervous System 4.43
3.48 The Senses 4.45
Colors
Pigments 3.50 Vision 4.45
Abnormalities and Variations in Pigment Colors 3.52 The Structure of the Eye 4.46
Structural Colors 3.54 How Birds See 4.50
Functions of Color and Color Patterns 3.60 The Ear and Hearing 4.54
Cryptic Coloration and Patterns 3.60 Structure and Function of the Ear 4.56
Blending In 3.61 Hearing Ability 4.61
3.62 Olfaction 4.62
Disruptive Coloration
3.63 Taste 4.65
Countershading
Skin Senses 4.69
Behaviors that Aid Concealment 3.63
The Endocrine System 4.69
Conspicuous Markings and Predation 3.64
Pituitary Gland 4.72
Reduction of Glare for Foraging 3.64
Thyroid Glands 4.74
The Role of Color and Pattern in Social Behavior 3.65
Parathyroid and Ultimobranchial Glands 4.74
Species Recognition 3.66
Adrenal Glands 4.74

Cornell Laboratoni of Ornithologq Handbook of Bird Biologq

 ix

4.75 Respiratory Rate 4.156

Gonads
4.75 Water and Salt Regulation 4.157
Pancreas
4.76 Life Span and Senescence 4.158
The Circulatory System
4.77 Major Anatomical Differences between Birds and Mammals 4.161
The Heart
4.78 Skeleton 4.161
Heart Valves
4.79 Muscles 4.161
Blood Supply to the Heart Tissue
4.79 Nervous System 4.161
Conducting System of the Heart
4.80 Ear 4.162
Location of the Heart
4.81 Eye 4.162
Blood Vessels
4.81 Circulatory System 4.162
Capillaries
4.82 Respiratory System 4.162
Arterial System
4.84 Digestive System 4.163
Venous System
4.86 Urogenital System 4.163
Blood
4.88 Suggested Readings 4.163
Lymphatic System
The Respiratory System 4.89
Nostrils and Nasal Cavities 4.90 Sidebars
Pharynx 4.91 Sidebar 1: The Amazing World of Avian ESP 4.66
Larynx 4.91 Sidebar 2: Bird Song: From Oboe and Trombone to
Trachea 4.92 Orator and Soprano 4.94
Syrinx 4.93
Lungs and Air Tubes 4.98 CHAPTER 5 - BIRDS ON THE MOVE: FLIGHT AND MIGRATION
Air Sacs 4.100 The Flight Syndrome 5.2
Breathing and Gas Exchange 4.100 Functions of the Flight Muscles 5.7
The Digestive System 4.103 How Do Birds Fly? 5.8
Oral Cavity 4.103 Forces Acting on a Bird in Flight 5.9
Bill 4.103 Gravity 5.10
Tongue 4.111 Lift 5.10
Salivary Glands and Saliva 4.111 Drag 5.16
Pharynx 4.112 Thrust 5.16
Alimentary Canal 4.113 Function of the Tail 5.21
Esophagus 4.113 Landing 5.21
Stomach 4.118 Hovering 5.26
Small Intestine 4.120 Complex Control of Flight 5.30
Colic Ceca 4.123 Wing Loading 5.31
Large Intestine 4.123 Turbulence 5.33
Cloaca 4.123 Variations in Wing Shape and Flight Style 5.36
Liver 4.124 Elliptical Wings 5.37
The Urogenital System 4.124 High-speed Wings 5.38
Urinary System 4.125 Slotted High-lift Wings 5.39
Genital System 4.127 High-Aspect-Ratio Wings 5.42
Male Genitals 4.127 Some Flight Facts and Figures 5.45
Female Genitals 4.128 Air Speed 5.45
Copulation and Fertilization 4.133 Wingbeat Frequency 5.45
Sex Determination 4.133 Flocking and Flying in Formation 5.45
Hormones and Secondary Sex Characters 4.137 Loss of Flight 5.48
Factors Bringing Birds into Breeding Condition 4.140 Migration 5.51
Metabolism 4.144 Patterns of Migration 5.52
Body Temperature 4.146 The Origin and Evolution of Migration 5.57
Countercurrent Heat-Exchange Systems 4.148 Controlling and Synchronizing the Annual Cycle 5.61
Cooling 4.152 The Physiology of Migration 5.63
Torpor 4.153 Daily Timing of Migration 5.65
Heart Size and Heart Rate 4.154
Handbook of Bird Biologq
Cornell Laboratorq of Ornithologq
x xi

The Altitude of Migration 5.66 Antipredator Behavior: Why Do Some Birds

Flight Speed and the Progress of Migration 5.68 Mob Predators? 6.50
Weather and Migration 5.69 Nest Spacing: Why Do Some Birds Nest in Large Colonies?6.58
Migration Routes 5.73 Reproductive Behavior: Why Are There Different Kinds
Site Fidelity 5.75 of Avian Mating Systems? 6.68
Orientation and Navigation 5.79 Reproductive Behavior: Resource-defense and
Compass Mechanisms 5.84 Female-defense Polygyny 6.73
Sun Compass 5.84 Reproductive Behavior: Lek Polygyny 6.75
Star Compass 5.86 Reproductive Behavior: Polyandry 6.77
Magnetic Compass 5.89 Mate Choice: Extrapair Copulations in Birds 6.79
Navigational Maps 5.92 Mate Choice: Why Do Some Birds Display
Sunset Cues 5.92 Elaborate Ornaments? 6.81
Suggested Readings 5.99 Mate Choice: Why Cooperate in Courtship Displays? 6.85
Parental Behavior: Why Do Some Birds Ignore Lethal
Aggression Among Their Nestlings? 6.87
Sidebars
5.22 Parental Behavior: Why Are There "Helpers at the Nest"
Sidebar 1: Flapping Flight
5.76 That Care For Someone Else's Offspring? 6.88
Sidebar 2: Showdown at Delaware Bay
5.94 How to Study Bird Behavior Yourself 6.91
Sidebar 3: Polarized Light
Suggested Readings 6.98
EVOLUTION OF BIRDS AND AVIAN FLIGHT
Archaeopteryx and Other Urvogels E•2 Sidebars
The Descent of Birds E•7 Sidebar 1: Bird Brains 6.16
Flight Origins E•13 Sidebar 2: Play 6.19
Ground-Up (Cursorial) Theory E•14 Sidebar 3: Defense Behavior 6.52
Trees-Down (Arboreal) Theory E•18 Sidebar 4: Living in Groups 6.60
Early Bird Flight E•19 Sidebar 5: Length of the Pair Bond 6.72
The Early Fossil Record of Birds E•20 Sidebar 6: Bird Families as Models for
Palaeognathous Birds E•21 Understanding Ourselves 6.92
Bird Evolution's Big Bang E•25
Appendix A: Bird Evolution Theories and Early CHAPTER 7- VOCAL BEHAVIOR
Diapsid Reptiles E•27 What is Sound? 7.3
Appendix B: Hypothesized Relationships Among Ancient and Seeing Sounds: Sonagrams and Oscillograms 7.4
Modern Bird Groups •29 Use of Tape or CD with Chapter Text 7.6
Appendix C: Index to Fossil Organisms •31 Understanding Complex Songs 7.9
Figure Credits for Appendix C E.34 Vocal Repertoires 7.10
The Problem of Meaning 7.11
CHAPTER 6 - UNDERSTANDING BIRD BEHAVIOR Song 7.14
Questions About Behavior 6.2 The Structure and Function of Sounds 7.19
The Proximate Basis of Bird Behavior 6.4 Vocal Development 7.23
Ethology, Ornithology, and Instincts 6.7 Vocal Development in Songbirds 7.25
Learned Behavior 6.8 Vocal Development in Nonsongbirds 7.30
A Comparison of Instincts and Learning 6.14 Songbird Diversity 7.34
Ultimate Causes of Bird Behavior 6.15 Control of Song 7.37
Territoriality, Dominance Hierarchies, Variation in Space and Time 7.41
and Ritualized Aggression 6.22 Species Differences 7.42
The Evolution of Ritualized Displays 6.30 Individual Variation 7.42
Courtship Displays 6.34 Song Dialects 7.53
The Use of Darwinian Evolutionary Theory 6.42 Geographic Variation in Suboscine Vocalizations 7.57
Feeding Behavior: Why Do Birds Generally Restrict Their The Diversity of Geographic Patterns in Songbirds 7.58
Diets, Ignoring Some Edible Foods in Favor of Others? 6.43 Song Change Over Time 7.63
Dialects Over Broad Regions 7.64

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xii
The Functions of Song 7.66 Incubation Period 8.96
Dawn Chorus 7.75 Start of Incubation 8.97
Duetting 7.78 Role of the Sexes 8.99
Mimicry 7-81 Patterns of Attentiveness 8.99
Flight Songs 7.84 Behavior During Incubation 8.101
Song Repertoires 7.85 Changes in Incubation Behavior 8.103
Suggested Readings 7.91 Feeding the Mate 8.103
Appendix A: Descriptions of Tape / CD Tracks 7.93 Development of Young 8.104
Hatching 8.104
Development at Hatching 8.106
Sidebars Typical Altricial Young 8.107
Sidebar 1: Winnows, Snaps, and Spring Thunder-
Typical Precocial Young 8.117
Nonvocal Sounds 7.15
Recognition Between Parents and Young 8.125
Sidebar 2: Listen Up! 7.44
Caring for Young 8.130
Sidebar 3: Pushing the Limits: New Computer Techniques
Feeding the Young 8.131
for Studying Bird Song 7.48
Defending the Young 8.134
Sidebar 4: Do Birds Think? 7.67
Nest Sanitation 8.136
Sidebar 5: "Call Notes" and Their Functions 7.72
Brood Parasites 8.139
Sidebar 6: Listening on Your Own 7.88
Evolution and Adaptation Among Obligate
Brood Parasites 8.143
CHAPTER 8 - NESTS, EGGS, AND YOUNG: Brood Parasite Ploys 8.143
BREEDING BIOLOGY OF BIRDS Host Counterploys and Coevolution 8.146
8.3 Evolution and Adaptation in New World Cowbirds 8.148
Survival
8.10 Conclusion 8.152
The Timing of Breeding
Breeding Territories 8.13 Suggested Readings 8.152
Functions of Breeding Territories 8.14
Nests and Nest Building 8.15 Sidebars
Functions of Nests 8.18 Sidebar 1: Neat Nesting Facts 8.16
Diversity of Nest Sites 8.20 Sidebar 2: Social Weavers 8.40
Seasonal Changes in Nest Sites 8.22 Sidebar 3: Oology: From Hobby to Science 8.80
Nest Site Selection 8.23 Sidebar 4: Creches 8.126
Diversity of Nests 8.24
The Evolution of Nest Construction 8.44 CHAPTER 9 - INDIVIDUALS, POPULATIONS, AND
Nest Lining 8.47
Nest-building Behavior 8.50 COMMUNITIES: THE ECOLOGY OF BIRDS
Sex Roles in Nest Building 8.56 Birds as Individuals 9.7
Duration of Nest Building 8.57 Habitat Selection: Choosing a Place to Live 9.8
Nest Appropriation and Reuse 8.57 Thermoregulation: Coping with Heat and Cold 9.13
Eggs 8.59 Water: A Matter of Economy 9.18
Egg Structure 8.59 Foraging Ecology: Meeting Energy and
Egg Size 8.70 Nutritional Demands 9.23
Egg Shape 8.72 How Much Food Does a Bird Need? 9.23
Egg Surface Texture 8.74 What Types of Food are Eaten? 9.25
Egg Color 8.75 Where and How to Forage 9.28
Egg Laying 8.77 Do Birds Always Forage Optimally? 9.31
Clutch Size 8.78 Coping with Environmental Fluctuations 9.31
Patterns in Clutch Size Variation 8.78 Relationships with Other Individuals 9.38
The Evolution of Clutch Size 8.79 Types of Intraspecific Competition 9.39
Egg and Clutch Replacement 8.90 Life History Strategies: Putting it All Together 9.43
Number of Broods per Season 8.91 Birds in Populations 9.48
Incubation 8.93 Characteristics of Bird Populations 9.49
Incubation Patch 8.94 Geographic Distribution Patterns 9.49

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xiv

Population Size 9.58 Ivory-billed Woodpecker and Bachman's Warbler-

How Do We Determine Population Size? 9.60 Demise of the Southeastern Forests 10.16
What Affects Population Size? 9.62 Brief History of Bird Conservation in the United States 10.18
What Regulates Population Size? 9.67 Are North American Birds Disappearing? 10.25
Extinction: The Death of the Last Individual The Forested Northeast 10.29
in a Population 9.75 Grasslands 10.30
Structure of Bird Populations 9.80 Southwestern Riparian Habitats 10.36
Bird Communities 9.82 Shorebirds 10.37
Characteristics of Bird Communities 9.82 Conservation Problems: The Ecology of Extinction 10.38
Patterns of Species Richness 9.85 Birth Rates and Death Rates 10.39
Effects of Latitude 9.85 Population Increases 10.40
Effects of Habitat Complexity and Productivity 9.92 Direct Exploitation 10.48
Effects of Habitat Size 9.95 Introduced Predators 10.49
Habitat Patches as "Islands" 9.97 Chemical Toxins 10.51
Patterns of Relative Abundance 9.101 Indirect Chemical Pollution 10.56
Ecological Niches 9.102 Introduced Disease 10.58
Are Bird Communities Organized in Optimal Ways? 9.104 Habitat Loss 10.59
Birds as Components of Ecosystems 9.109 Habitat Specialization and the "Six Forms of Rarity" 10.61
Ecological Distribution of Birds in the Major Terrestrial 1. Widely distributed, small local populations,
Ecosystems of North America 9.109 broad habitat tolerance 10.62
Tundra 9.114 2. Widely distributed, large local populations,
Coniferous Forest 9.116 narrowly specialized habitat requirements 10.63
Deciduous Forest 9.117 3. Widely distributed, small local populations,
Grassland 9.118 narrowly specialized habitat requirements 10.64
Southwestern Oak Woodland 9.120 4. Small geographic range, large local populations,
Chaparral 9.120 broad habitat tolerance 10.65
Pinyon-Juniper Woodland 9.121 5. Small geographic range, large local populations,
Sagebrush 9.121 narrowly specialized habitat requirements 10.65
Scrub Desert 9.122 6. Small geographic range, small local populations,
Two Important Ecotones 9.122 narrowly specialized habitat requirements 10.66
The Role of Birds in the Food Chain 9.123 Unique Problems on Islands 10.67
What if Birds Disappeared? 9.126 Habitat Fragmentation: Mainland Habitats as Islands 10.71
Conservation Genetics 10.74
Conservation Solutions: Tools and Prescriptions
Sidebars for Stabilizing Populations 10.76
Sidebar 1: The Winter Banquet 9.32 DNA Fingerprinting and Genetic Augmentation 10.76
Sidebar 2: The House Finch Hot Zone 9.71 Population Viability Analysis and Metapopulations 10.77
Sidebar 3: Ant Followers 9.88 Preserve Design 10.78
Sidebar 4: From Blackberries to Beeches: Habitat Management 10.81
Ecological Succession in Eastern Deciduous Forests 9.110 Ecosystem Management 10.83
Sidebar 5: Sapsuckers, Swallows, Willows, Aspen, and Rot ... 9.128 Adaptive Management 10.84
Translocation 10.89
CHAPTER W - BIRD CONSERVATION Legal Protection 10.90
Historical Context 10.4 Endangered Species Act 10.91
Global Spread of Humans Begins the Extinction Era 10.5 Clean Water Act, Section 404 10.93
Early Extinctions in North America and the Caribbean 10.6 CITES 10.93
Modern Extinctions on Mainland North America 10.9 Bringing Birds Back from the Brink 10.94
Labrador Duck-the Mystery Extinction 10.10 Wood Duck-Regulated Hunting and
Passenger Pigeon-Market Hunting at its Worst 10.11 Adaptive Management 10.95
Carolina Parakeet-Removal of a Menace 10.12 Whooping Crane-Protected Habitat and
Eskimo Curlew-Three Strikes in the Wink of an Eye.. 10.12 Captive Rearing 10.97

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Peregrine Falcon—Pesticide Regulation and
"Soft Release" Reintroduction 10.100
California Condor—Wild Capture,
Captive-rearing, and Study of "Surrogates" 10.102
Maui Parrotbill and Akohekohe-
Protected Habitat and Feral Mammal Control 10.103
Why Protect Birds? 10.104
Direct Benefits 10.105
Food 10.105
Clothing 10.105
Other Utilitarian Uses 10.105
Recreational Hunting 10.105
Bird Watching 10.106
Indirect Benefits 10.106
Ecological and Evolutionary Roles
Environmental Services
10.106
10.107
Birds and Humans:
Biological Indicators 10.108
10.109

A
Genetic Information
Scientific Study
Aesthetics and Spiritual Values
What Can Each of Us Do?
10.109
10.110
10.110
Historical Perspective
Backyard Conservation 10.110
Be a Citizen Scientist 10.112
Adopt a Place 10.112
Local Vigilance and Grassroots Activism 10.113
Environmental Education 10.114
Sandy Podulka, Marie Eckhardt, and Daniel Otis
Take a Child Birding 10.114
Contribute to Conservation Organizations 10.115
Never Give Up 10.116 The relationship between birds and humans undoubtedly
began as soon as people appeared on the scene. By the
Sidebars time the first ancestral human beings appeared, some
Sidebar 1: A Summer Without Bobolinks 10.31 14 million years ago, birds had been flying and running
Sidebar 2: The Best Laid Plans: What Happens When about for 136 million years. Modern humans with skeletons much like
Conservation Efforts Work Too Well? 10.44 ours first appeared 125,000 years ago, and the countrysides where they
Sidebar 3: Hawk Deaths Spur Action 10.54 lived were also home to birds. Humans evolved in a world saturated
Sidebar 4: Conservation Planning at Ecoregional Scales 10.86 day and night, summer and winter, with birds.
Knowing and appreciating birds as we do today, we can read-
SPECIES TABLE 1 ily surmise how strongly they impressed themselves on the minds
of our ancestors—how their forms, colors, and sounds appealed to
GLOSSARY 17 the senses, how their flight spurred imagination, how their periodic
absences, timed to the seasons, aroused curiosity. They accordingly
ABOUT THE AUTHORS 61 became a pervasive part of our heritage—a prehistoric and historic
influence on our language and literature, our religion and mythology,
REFERENCES 65 our art and our music.
More recently, birds have been a focus of scientific inquiry,
INDEX 81 and it is the science of birds that is the focus of this course. Science,
however, is a recent innovation. Only in the last few hundred years,
and particularly in the last century, has it evolved as one of our most
effective tools for understanding the world. Before this great burst of
scientific discovery, birds and humans had coexisted for eons. Hunt-

Cornell Laboratoni of Ornithologq

H.2 Sandy Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.3
ers, foragers, and farmers, observing the birds that passed through their of birds on the diverse facets of human life can't help but enrich our
lives, asked some of the same questions as modern scientists. Based on scientific appreciation of birds.
their own understanding of how the world works, they also gave their
own answers. Often these explanations are charming and ingenious,
reflecting an odd mix of careful observation and astute deductions with Birds as Food
wild rumor, conjecture, and supernaturalism.
Typical of prescientific interpretations are many of the accounts
■ For early humans, the greatest attraction of birds was probably gus-
tatory. Beside the recently discovered bones of a Neanderthal man,
in Aristotle's Historia Animalium. Aristotle (384-322 B.C.) knew, for
who lived some 50 to 90 thousand years ago, lay the bones of a Great
instance, that Common Cuckoos of Europe lay their eggs in the nests
Auk, possibly the remains of his last meal.
of other birds, and that the consequences for the other nestlings were
Although our common sense tells us that humans feasted on birds
usually dire; in this he is in accord with modern science. He departs
in prehistoric times, we have little tangible proof. Fragile bird bones do
from the modern view, however, by attributing this practice to the
not fossilize well, especially on land, and the few scraps of bird bones
cuckoo's wisdom in recognizing its own character defects: "This bird
that turn up in digs often rest in storage sheds, sometimes for years,
is pre-eminent among birds in the way of cowardice; it allows itself to
while the paleontologists study larger, more dramatic finds.
be pecked at by little birds, and flies away from their attacks." (A mod-
In spite of this neglect, we know that early humans hunted birds
ern scientist might suggest that the cuckoos were being driven off by
and that their weapons became increasingly sophisticated, progressing
parent birds trying to protect their own genetic inheritance.) "The fact
from stones and clubs that they held in their hands, to sticks, darts, and
is, the mother-cuckoo is quite conscious of her own cowardice and of
spears that they threw, and on to snares, bolas, traps, and bows and
the fact that she could never help her young one in an emergency, and
arrows that required ingenuity to construct and skill to use (Fig. H 1).
-

so, for the security of the young one, she makes of him a... child in an
At the same time, they must have relied, as primitive people do even
alien nest." In other words, he believed that the bird behaves like any
today, on the eggs and nestlings of birds. Until recently, the Bushmen
other responsible person who is unable to care for a child.
of the Kalahari Desert in South Africa gathered the eggs of weavers
More accurately, Aristotle unambiguously asserts that certain
as part of their food. Flightless, molting waterfowl may have been
birds migrate with the seasons, something European naturalists were
another seasonal staple; they are easily captured if one knows their
still arguing about 2,000 years later. Some creatures stay put in winter,
hiding places.
he says, but "others migrate, quitting...the cold countries after the au-
Humans eventually learned that taming and rearing birds en- Figure H-1. Trapping Waterfowl for
tumnal equinox to avoid the approaching winter, and after the spring Food in Ancient Egypt: This wall paint-
sured a reliable food supply, and several species were domesticated.
equinox migrating from warm lands to cool lands to avoid the coming ing from the tomb of the Egyptian Kh-
In the Old World, specifically Asia, the most notable triumphs were
heat. In some cases they migrate from places near at hand, in others num-Hotpe (about 1900 B.C.) shows the
the domestic chicken, duck, and goose. The chicken is probably a operation of a trap designed to capture
they may be said to come from the ends of the world."
form of the Red Junglefowl (see Fig. 1-80), which still lives in the wild various species of geese, ducks, and
Although the myriad observations on bird life woven into every grebes. Additional waterfowl, including
in southeastern Asia. Already domesticated in India as early as 3200
aspect of human culture rarely meet today's standards as objective recognizable pintails, flock nearby. In
B.C., chickens appeared in Egypt about 1500 B.C. and somewhat later
"scientific" facts, they are fascinating in themselves. If they don't reveal the surrounding shrubbery are a hoopoe,
in Europe. The domestic duck, a form of Mallard, and the domestic a redstart, a dove, and several shrikes.
reliable truths about how and why birds function as they do, they tell us
goose, a form of the Greylag Goose of Eurasia, were domesticated at Photo: All rights reserved, Metropolitan
about something equally real—the intimate, ancient, and continuing
least as early as the chicken. Museum of Art (33.8.18).
relationship between people and birds.
In the following chapters, we present the current scientific knowl-
edge on bird anatomy, inside and out. We consider bird evolution
and the geographic distribution of birds over the face of the earth. We
explain bird movements during migration, their use of song, and many
other aspects of their behavior. We look at their life cycles, nesting
practices, and the threats birds face in a world utterly dominated by our
species. But before we begin our science-based examination of birds,
we want to briefly note the influence of birds in other realms of human
culture. We also consider the origins and early development of the
field that has become ornithology. The account, roughly chronological
and roughly organized by theme, might be considered a brief history
of ornithology's predecessors and offshoots. We can only cover a few
of the major highlights, but even a scanty knowledge of the influence

Cornell Laboratory or Ornithology Handbook of Bird Biology

H.4 Sandq Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.5

Figure H-2. Ancient Duck Decoys: These waterfowl decoys, dating from 1000 A.D., were discovered in 1924 during an ar-

chaeological excavation of Lovelock Cave, Nevada. The decoys were formed of bulrush stems and either painted or stuffed. a.
The body of the decoy was formed by binding together bundles of bulrush stems. Note the careful and accurate shaping of the
head, which was constructed separately and sewn to the body. b. A painted decoy representing a Canvasback drake. Black and
reddish-brown pigments were used to color the head, neck, and tail; then white feathers were tied to the body using fine hemp
cord. "Stuffed" decoys (not shown) were topped with the stuffed head of an actual duck, and sometimes part of the duck's body
skin was stretched over the bulrush body. From Lovelock Cave, by Llewellyn L. Loud and M. R. Harrington, 1929, published by
the University of California Press.

It is noteworthy that throughout much of history, most people

were intimately acquainted with the habits of birds, albeit domestic
ones, because most people lived in the countryside. Only in the past a
half-century has a chicken dinner meant a trip to the grocery store
rather than a trip to the chicken coop. As our scientific understanding plucking the contour feathers to leave only the down, they sewed the Figure H-4. Hawaiian Feather Cloaks:
of birds proliferates as never before, people outside the ranks of bird skins together, edging them with the colorful feathers from the head of Elaborate feather work was already being
used in ceremonial garments for high-
watchers have less personal experience with birds than ever before. the male birds. Each blanket required more than 100 skins.
ranking Hawaiian chiefs when Captain
In the New World, the NativeAmericans in southern North Amer- Bird skins and feathers have served as ornaments in many soci- Cook visited the Hawaiian Islands in
ica domesticated the resident Wild Turkey, though no one knows how eties, i ncludi ng our own.The royalty in a number of NewWorld Indian the late 18th century. The red and yellow
early. The Cortes expedition in 1519 found the domestic turkey already tribes wore capes, cloaks, and headdresses fashioned from feathers feathers of Hawaiian honeycreepers
and honeyeaters—small, endemic for-
widely distributed in Mexico and Central America. Soon thereafter (Fig. H 3). We are all familiar with the flowing headdress of eagle
-

est birds—were especially revered. Most

the explorers took these domesticated turkeys to Europe, and later the feathers, the glory of the Native American chief of the plains, at least important were the completely red liwi
colonists brought them back to North America. Thus, the domesticated in the movies. To the Crees, Cherokees, Natchez, Zunis, and many of and Apapane, and two black species,
turkey that we eat at Thanksgiving came to us from southern North the Great Plains tribes, the eagle was sacred. On the Missouri River in the Hawaii Oo and the Hawaii Mamo,
America by way of Europe; it is not a direct descendant of the Wild Tur- 1742, Pierre de la Verendrye found Assiniboine Indians trading with which have yellow feathers under their
wings, thighs, or tail. During harvesting,
keys the pilgrims found in the woods near Plymouth, Massachusetts. the Mandans for deer skins "carefully dressed with fur and feathers"
the latter two species were freed after
In the New World outside of Mexico and Central America, people and for "painted feathers;" he noticed also that the Mandans "worked removing their sparse yellow feathers. a.
depended on wild birds much longer than in the Old World and be- very delicately in hair and feathers." These full-length cloaks of red and yel-
came very skilled at capturing them. By 1000 A.D., the Native Amer- Parrot feathers were highly esteemed by the prehistoric pueblo low feathers, made in the early 1800s,
once belonged to the chiefs Kiwalao,
icans were using decoys to attract ducks. Explorations of Lovelock dwellers of New Mexico, who traded for them with peoples from the
Kalaniopuu, and Kamehameha. The
Cave, Nevada, yielded two types of decoys ingeniously wrought of south. Macaw feathers, especially, seem to have been a status symbol. cloak on the far right is constructed from
rushes, one of which had a stuffed skin for a head (Fig. H 2). From sites
- The aborigines of Australia wore feathers of cockatoos and Emus in approximately half a million Hawaii
on St. Lawrence Island, Alaska, occupied from about 900 A.D. to the their hair until recently. The Alaskan Eskimos and the Aleuts decorated Mamo feathers, representing 80,000 to
late 19th century, have come decoys of 45 identifiable bird species. their rain garments with tufts of brightly colored feathers sewn in par- 90,000 birds. b. A tattooed officer wears
a feathered cloak and headdress in this
allel seams; the Porno Indians decorated their baskets with feathers.
engraving from 1817. Both photos cour-
Figure H 3. Sitting Bull Wearing Feath- In the Pacific, the Hawaiians made exquisite cloaks from the feath- tesy of the Bishop Museum, Honolulu,
Use of Skins and Feathers
-

ered War Bonnet: Photographed around ers of honeycreepers; samples can be seen in the Bernice P. Bishop Hawaii.
1885, the famous Sioux chief, Sitting
Bull, is shown here wearing a war bon-
■ The people of many societies used the feathers and skins of wild Museum in Honolulu (Fig. H 4). The natives of Borneo made similar
-

cloaks from the feathers of the Rhinoceros Hornbill (see Fig. 1-82). And
netof eagle feathers. In traditional Native birds for warmth, and some still do so today. Eagle feathers were units
to the north, the Chinese fashioned jewelry from feathers.
American society, the number of feathers of currency in some North American Indian tribes. The Eskimos used
in a chief's headdress symbolized his im- In the United States in the late 19th century, plumes were a fash-
waterfowl feathers for pillows and coverlets and skins for coats. In
portance. Photo copyright Corbis. ionable appendage to women's hats, which led to the decline of egret
Greenland, the Eskimos made blankets from the skins of eiders. After

Cornell Laboratorq of Ornitholo,9 Handbook of Bird Biologu

14.6 Sandq Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective 7

Figure H-5. Woman Wearing Hat Deco- other animals done about 6,000
rated with Egret Plumes: Photographed years ago on the walls of Tajo Se-
in Manhattan around 1886, a woman
gura in Spain. The Lascaux and
wears a hat typical of the fashions of late
19th century America and Europe. Ob- other paintings suggest that even
taining plumes for the millinery trades of at this early date, birds may have
London, Paris, and New York became a assumed some kind of symbolic
lucrative occupation. Plume harvesting
meaning in the human mind, and
ended in North America when the pub-
lic was made aware of the numbers of
the pictures represent more than
herons, egrets, and other wading birds they actually portray.
being killed for their feathers in Florida In the historic period, birds
rookeries. The resulting outcry led to the are present in the visual art of
beginnings of the conservation move-
virtually every culture in every
ment with the establishment in 1896 of
the first Audubon Society in Massachu- part of the world. In the Arctic,
setts (see Chapter 10). Photo courtesy of the Eskimos carved birds in wal-
the National Audubon Society. rus ivory. For the Senufo of the
western Sudan, a bird was a tribal
emblem used to decorate masks and other objects. The court paint- Figure H-6. The Bird-man of Lascaux:
ers of Mughal India painted birds exquisitely, both as incidental el- In this detail of a well-known Paleo-
lithic cave painting from Lascaux Cave
ements in court and landscape scenes and as the main subjects in
in southern France, a bird-headed man
natural history paintings. The Aborigines of Australia painted Emus on (perhaps wearing a bird-shaped mask) is
rocks. The standards of Roman armies bore the image of eagles. Birds depicted with a charging bison. Nearby
decorated the gold cups of kings in Mycenae in ancient Greece and is a bird, variously interpreted as being
the musical instruments of the Anatolian kingdoms of what is now long-legged or perching on a pole or
spear-throwing device. Photo by Charles
Turkey. Stone-carved birds sit in stone-carved trees in Angkor Wat
and Josette Lenars / Corbis.
in Thailand. The image of the eaglelike "thunderbird" was often por-
trayed by the Native Americans of North America, to whom it was an
important element of mythology, capable of producing rain, thunder,
and lightning (Fig. H 7). The Navaho could make an owl playing the
-

cat's cradle game with string; the Pomo of California could construct a
and other wading bird populations (Fig. H 5). One of the strands of
- hummingbird. Bird motifs appear often in the art of the Inca and Aztec.
early conservation movements coalesced around opposition to this From China, an ancient ceramic pot almost 5,000 years old depicts a
capricious waste of bird life. stork holding a fish at the tip of its bill. By 3000 B.C., the Egyptians began

Figure H-7. Thunderbird Totem Pole:

Birds in Literature, Culture, andReliBion The eaglelike thunderbird is an impor-
tant mythological figure to native cul-
tures throughout North America. They
believe it has the power to produce rain,
Art thunder, and lightning. Certain Native
If birds have been important materially, as tangible creatures, in American groups of northwestern North
America believe the thunderbird created
our diets and as sources of materials for warmth and decoration, the
the world, and its carved image appears
idea of the bird has perhaps been just as i mportant from our prehistoric frequently on totem poles and masks.
beginnings. The paintings made by the Cro-Magnon people on the Here, a thunderbird sits atop a totem
walls of Lascaux Cave near Montignac, France, include an occasional pole in Stanley Park, Vancouver, British
bird among the other animals. In one of these paintings made about Columbia. Photo by The Purcell Team /
Corbis.
17,000 years ago, one of the few humans depicted in cave art has a
mask or birdlike face; nearby is a long-legged bird, or perhaps a bird at
the top of a stick or spear-throwing device (Fig. H 6). Most authorities
-

agree that the paintings, because of their secluded location, probably

had a sacred or ritualistic purpose rather than being merely decorative.
The same may be true of the drawings of human beings, birds, and

Cornell Labomtorq of Omithologq Handbook of Bird Biolojq

 ScndH Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.9
H.8
Figure H-8. Shrike and Bamboo: Painted
Other painters use birds Figure H 9. The Phoenix: The phoenix,
-

more as a means to an end, a fabulous mythical bird that under-

by Li An-chung, an artist at the Hsuan-ho
goes regular rebirth by fire, appears in
PaintingAcademy during the reign of Em- to express the multitude of
the myths of numerous human cultures
peror Hui-Tzung of the North Sung Dy- qualities we associate with throughout history. Its physical appear-
nasty "Shrike and Bamboo" is typical of
them. Brancusi's highly ab- ance and story vary greatly among cul-
the "bird-and-flower" genre of Chinese
Painting. The bird is re-created in exqui- stract "Bird in Space" has tures. According to one current version
of the myth, every 500 years the phoe-
site detail in a simple setting of bamboo an aerodynamic grace. In a
nix, sensing its own death approach-
leaves and branches. The medium is few Georgia O'Keefe paint- ing, builds its own funeral pyre and sets
color and ink on silk. Painting courtesy
ings, crows appear as black fire to itself, being reborn out of its own
of The National Palace Museum, Taipei,
Taiwan, Republic of China.
blurs slicing through the sky. ashes. Its first appearance is in ancient
The birds in Van Gogh's last Egypt in the guise of the sacred, heron-
like "Benu" bird, which re-creates itself
painting, "Wheat Field with
daily in the rays of the rising sun. The Chi-
Crows," seem rather ominous. nese version of the phoenix, often seen
Birds may also appear as styl- in paintings, is a fanciful creature called
ized, iconic elements, as in the "Feng-Huang," whose elaborate
plumage resembles that of a peacock.
Paul Klee's "Landscape with
In western cultures, the phoenix is an
Yellow Birds" and "Twittering eaglelike bird, often depicted in medi-
Machine." Finally, in some eval illustrations or on coats of arms as
paintings the fact that it is a arising out of flames. Christians adopted
bird that is being portrayed may be almost incidental—it is the form the phoenix as a symbol of resurrection
and immortality. The symbolism of re-
that interests the painter. Or, the use of a bird may be deliberately in-
birth is important even in modern times:
congruous, as in the work of some of the surrealists. the illustration shown here is adapted
using paintings and sculptures of birds to adorn the friezes of buildings from the logo of the Phoenix Assurance
Company, symbolizing the need for fire
and the tombs of royalty. One picture from a tomb depicts five species ReliBion insurance. From Symbols, Signs and
of geese, three so faithfully drawn as to be identifiable. Their Meaning and Uses in Design, Sec-
From about 1300 B.C., the polytheistic religion of the Egyptians
Noteworthy among the world's ornithological art are the bird ond Edition, by Arnold Whittick, 1971.
embraced both real and imaginary birds. To them the embodiment of
paintings of China. Even a thousand years ago they were so popular Published by L. Hill, London.
the sun was the fanciful phoenix, a beautiful bird that burned itself up
thatthey constituted an entire genre known as "bird-and-flower paint-
every five hundred years and rose from its own ashes youthful again,
ing" (Fig. H 8). Although the artists took pains to observe birds with
-
a symbol of immortality (Fig. H 9). The Egyptians held the very real
-

great care and paint them with extraordinary accuracy, the paintings
ibis so sacred that in many a royal tomb they buried an embalmed ibis
often had a symbolic dimension as well, different birds representing
wrapped in cloth and painted.
certain Buddhist or Confucian qualities and ideals. Far from being
Modern historians regard the first events of the Bible as taking
stiff, analytical case studies, these paintings present lively, graceful,
place in about the 20th century B.C.AI most 40 species of birds are men-
harmonious scenes of perhaps slightly idealized birds in natural sur-
tioned—the doves most frequently—in ways that show a knowledge
roundi ngs. The serene portrayal of birds in a carefully selected context
of their habits and an appreciation for their grace and beauty. Indeed,
of a few flowers, vines, grasses, and rocks continues today as a motif
it doesn't seem farfetched to suggest that the idea of the angel owes
in Chinese painting. something to observations of birds, which often appear as symbols of
The array of uses to which birds have been put in Western art is
transcendence and as messengers from the gods.
much broader. Of the legions of Western artists who have portrayed
Like Aristotle in our earlier anecdote, the writer in Job 39:1 3 1 7
-

birds in some fashion, we can only mention a few.The depictions reflect

sees accurately but reports somewhat anthropomorphically: "The
an extraordinary range of human ingenuity. Some painters have been
wings of the ostrich wave proudly; but are they the pinions and plum-
intrigued by the birds themselves and portray them with varying degrees
age of love? For she leaves her eggs to the earth, and lets them be
of realism, and sometimes birds are incidental elements in landscapes,
warmed on the ground, forgetting that a foot may crush them, and that
as in Breughal's "The Return of the Hunters." Albrecht Durer had clearly
the wild beast may trample them. She deals cruelly with her young, as
studied bird wings carefully; the wings of some of the angels and cher-
if they were not hers; though her labor be in vain, yet she has no fear;
ubim floating about in his paintings are strikingly realistic. In the United
because God has made her forget wisdom, and given her no share in
States, among those who have painted birds is Andrew Wyeth, who
understanding."
painted two dead crows dangling against a white woodshed wall in
In the religious festivals of many peoples throughout the ages,
bright sunlight; he seems equally interested in the abstract pattern of the
feathers were used as symbols, and participants often wore feather gar-
corpses against the wall and in the crows as dead creatures.

Cornell Laboratorq of Ornitholo9 Handbook of Bird Biologq

 Birds and Humans: A Historical Perspective H.11
Sandq Podulka, Marie Eckhardt, and Daniel Otis
H•10
ments on these special occasions Like the owl, both the raven and crow have dual char-
(Fig. H-10). The Plains Indians acters—good and evil. For the crow, there was a chant: "One
carried dried bird skins in their for sorrow, two for mirth, three for marriage, four for birth." In
medicine bundles and decorated most folklores, the black-plumaged birds are threatening, their
the calumet, the sacred "peace once-white feathers blackened by the gods for their evil deeds.
pipe," with feathers, heads, or skins According to one legend, the gods caught the pure white raven
—red for war, white for peace. The stealing water and punished it by turning its feathers black. To
Plains (Sioux)
Pueblo Indians fastened feathers to some people, a raven's harsh call foretells death; to others it
their wands and prayer sticks. Sev- means that the bird is carrying a message to the gods. One has
eral North American tribes still use only to see a raven fly croaking into the distance to sympathize
feathers of eagles and other raptors with early humans fearing that the raven had seen their misdeeds
in ceremonial displays. and was on its way to report them to the gods.
Throughout Europe, the noisy, conspicuous cuckoo fore-
cast coming events—rain, the arrival of spring, or portents in
Folklore the affairs of men. In Japan, outings to hear the first notes of the
Peoples whose cultures seem cuckoo were once a popular spring entertainment.
Yuchi quite unrelated often have simi- Other species of birds figuring prominently in folklore in-
lar legends and folklore motifs. clude the loon for madness, the dove for peace, the swan for
The Old Testament story of Noah pride, the goose for confusion, and the swallow for travel. As with Figure H-11. Eastern Screech-Owl:
sending forth a dove to find land, the crow, a single magpie meant sorrow and two portended joy. Even With their ghostly screeching and hoot-
for instance, has many parallels, ing calls given under cover of darkness,
the behavior of the bird was sometimes important—in Germany, a
it is not surprising that owls have fea-
including the Delaware Indian be- woodpecker flying to the right was a sign of good luck. Indeed, a bird's tured prominently in folklore through
lief that a loon led the survivors of behavior could even influence the destiny of nations. Pliny the Elder the centuries. They are often considered
a flood to dry land. On a similar (23-79 A.D.) tells of special Roman fighting cocks whose manner of omens of bad fortune or symbols of mys-
theme, according to the Crow Indi- eating grain was thought to foretell the likelihood of success of state tery. Yet, because of their large eyes and
intelligent expression, owls also sym-
ans of Montana, diving ducks sent endeavors and to influence whether they were actually undertaken.
bolize wisdom. Photo courtesy of Mike
by the Creator dove down under In India, among the Jai ns, a sect noted for its extreme reverence for Hopiak/CLO.
primeval waters and brought up life in all its forms, it is considered an act of virtue to free a caged bird.
mud to make the Earth. Paradoxically, a trade has grown up of capturing birds and bringing
Cherokee Symbols, too, are often the them to the market so the Jai ns can free them. The Jai ns also operate
114 same in different cultures. Large
a hospital for sick and injured birds; carnivorous birds such as hawks
raptors are almost always symbols of power and strength. Thus, the and owls are treated, but only as outpatients.
Figure H-10. Types of Wands used in
Native American Eagle, Calumet, and eagle feather was fitting for the headdress of a Native American chief, Folklore also recounts how certain birds got some of their char-
Feather Dances: Calumet (ceremonial and the bird itself was thought fitting to represent Zeus. Owls were acteristics. According to legend (seeTurner 1985, p.233, in Suggested
pipe) and Eagle Dances were used by symbols of mystery, appropriate companions of witches (Fig. H-11). Readings), the Red Crossbi I I (see Fig. 4-119) "twisted its beak on the
many Native American tribes to greet
Because of the owl's ghostly habit of hooting at night, they portended nails of the Cross," and the European Robin (see Fig. 21 b) "scorched its
strangers, to create ceremonial friend-
ships, to bring success in hunting or war, disaster. On the other hand, the eye of an owl, worn about the neck, breast bright red while stealing fire from the sun." The Yel low-bellied
to bring good luck or counter bad luck, to warded off evil spirits; a cure for failing eyesight was to eat the eye of Sapsucker is said to have "acquired its many hues as consolatory gifts
cure sickness, or to make peace between an owl; owl soup was considered helpful with whooping cough. Owls from other birds because it had been too tipsy on birch juice to attend
warring tribes. The original calumet was also symbolized wisdom. Because of the binocular vision that gives the official distribution of colors."
a pipe decorated with a fan of eagle
feathers. Over time, it became merely a
the owl a knowing expression, a number of stories feature the "wise
wand with featherdecorations, as shown old owl." Literature
by the four examples here. The Plains All the nightjars, the family to which the Whip-poor-will,
(Sioux) wand is also decorated with Pi- Chuck-will's-widow, and Common Poorwill (see Fig. 4-128) belong, At the foundation of many societies' cultural heritage are epic
leated Woodpecker scalps. From Indian poems and stories based partly on ancient fact and passed on by word
are nocturnal and have very large eyes and low calls that in some soci-
Dances of North America by Reginald of mouth and later in writing. Some tales tell of the origin of the people,
and Gladys Laubin. Copyright 1977 by eties spell doom. The call of the Whip-poor-will foretold a death to a
their early way of life, and their beliefs; others are amusing. Many in-
the University of Oklahoma Press. Re- New England settler. The calls of its relatives foretold the length of life
clude birds in one way or another.
printed with permission. to a South American Indian. Even today, the natives of certain parts of
By the 16th century B.C., the Greeks had a written language, partly
South America and the West Indies believe that the calls of the nightjars
hieroglyphic and partly alphabet. The Miadand The Odyssey, the two
are the voices of lost souls or ghosts.

Handbook of Bird Biologq

Cornell Laboratorq of Ornithologq
 Sandy Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.13
H.12
great works attributed to Homer, were written in Minor Bird," and "On a Bird Singing in Its Sleep." In "Dust of Snow,"
THE CRoW &THE he wrote
l . PITC1 ER. 1) the 9th century B.C. These epic poems poetically im-
imiow-rk. ...fling ow.
rin Crow toi his drink mortalized the Greek gods, many of whom were
The way a crow
associated with birds—an owl with Athena, god-
Winn 'twas low in Tin shook down on me
pilaus, jog' rhink dess of wisdom; a dove with Aphrodite, goddess of
a dust of snow
Dontsay that lit spilkd it! beauty; a falcon with Apollo, god of the sun; and
WiTh rilidts
from a hemlock tree
an eagle with Zeus, king of the gods.
`1111 iin wato Ton I r. has given my heart
ikt ("rink.
Aesop's fables, originating orally about the 6th
YOUR W , TS a change of mood
century B.C. and appearing in early English in the and saved some part
•THE' EAGLE • AND THE CROW
Illy HE Eellt fitto off wifk A Iamb; 9th century A.D., contained many bird characters, of a day I had rued.
:a VI; ThEn -Mt Crow tko“ekt to lift- An olol including the cock, crane, swallow, stork, jay, pea-
In kis tAtlisl, cormcif,
'nt wool teAnikid ftit cock, goose, nightingale, eagle, and crow. Each Many writings for children deal with birds, including Edward
find tht sktiaktroi lad hold oirkt skAm. fable had a moral to it, such as "Use your Wits" Lear's "The Owl and the Pussycat," Robert McClusky's Make Way for
oEwARE of
OVE.RA , N. v0.01 OWWPoWEAS

or "Little by Little Does the Trick" from "The Crow Ducklings, and E. B. White's classics The Trumpet of the Swan and
and the Pitcher." The story involves a crow, dying Stewart Little. (Stewart himself is a mouse, but his romantic interest is
of thirst, who finds a pitcher with a little water in a small songbird named Margalo.)
the bottom. He cannot reach far enough into the If we venture yet further into the realm of popular culture we
pitcher to get the water, so he drops pebbles into again find swarms of birds—literally, in the case of Hitchcock's famous
Figure H 12. Birds in Aesop's Fables: the pitcher, one by one, until the water is at the top. He then drinks the
-
movie The Birds. And we mustn't forget Daffy and Donald, Foghorn
A variety of bird characters appear in water and is saved (Fig. H-12). Leghorn, Heckle and Jeckle, Roadrunner, and Tweetie-Bird, although
Aesop's Fables, ancient tales with a Birds as a literary device to hold a group of stories together orig- we'll admit that they probably don't often attract the attention of seri-
moral. Two fables are shown here. In
inated as early as the 11th century A.D., when "Suka Saptati," 70 tales ous ornithologists.
"The Crow and The Pitcher," the reader
is encouraged to use his or her wits to
of a parrot, appeared. In this Indian collection, translated as "The
overcome an obstacle. In "The Eagle and Enchanted Parrot," a parrot tells 69 tales poking fun at women to keep
The Crow," the reader is warned against her philandering mistress from taking several lovers while her husband
Music and Dance
overrating his abilities. Illustration from Birds, with their tremendous diversity of plumage, displays, hab-
is away from home.
Baby's Own Aesop, by Walter Crane, its, songs, and calls, have inspired the imagination and wonder of
In a number of ancient tales, the authors used birds to explain
1887. Photo copyright Corbis.
natural phenomena. In the Middle East, for example, the Garuda, a people throughout time—and have thus been included in some form
giant bird of prey, carried the sun from east to west each day. Vikar, in many ceremonies, dances, and musical compositions.
another bird of prey, stirred up the winds by beating its wings.
Music and Dance of Indigenous Cultures
William Shakespeare (1564-1616) enlivened passage after pas-
Music and dance are today considered forms of entertainment by
sage in his plays with vivid bird analogies and metaphors. No one
most people, but to traditional native peoples, both past and present,
knows how much of his knowledge of birds stemmed from his read-
they may be powerful forces in the human experience. Their power
ing and how much from boyhood memories of woodlands along the
comes from the fact that music and dance are often important compo-
Avon. He did, however, draw from the Greek and Roman classics and
nents of rituals and ceremonies that have great spiritual significance.
medieval bestiaries, and from scriptures, fables, and epic poems. His
Birds, because they were often seen as intermediaries between the
birds, it would seem, are symbolic rather than real: the raven and crow
physical and spiritual worlds, were often represented in many cere-
meant blackness and evil; the dove and swan, whiteness and purity;
monies. But the way many indigenous cultures think about their re-
the nightingale, evening; the lark, the dawn.
lationship with birds and the spiritual world is so different from the
In later centuries birds remained an occasional focus of poets
way western cultures view these things that it is extremely difficult
and novelists. Japanese haiku master Issa (1763-1827) felt a spe-
to adequately explain their beliefs in this brief passage; indeed, most
cial affinity for sparrows. In Europe, we have, among many others,
westerners may find the concepts nearly impossible to grasp without
Shelley's "To a Skylark," Keats' "Ode to a Nightingale," Wordsworth's
long-term study.
"The Sparrow's Nest," and Yeats' "Leda and the Swan." Poets of the
To many indigenous peoples, the land is a source of life. But it
New World were not slow to immortalize native birds—the Bobo-
is more than just a source of food and livelihood, for there is a core
link in Bryant's "Robert of Lincoln," the Black-capped Chickadee in
perception that al I aspects of existence—including spirituality, culture,
Emerson's "The Titmouse," and the mockingbird in Whitman's "Out
and social life—are inseparably connected to the inanimate world
of the Cradle Endlessly Rocking." More recently, Wallace Stevens,
of mountains, rivers, skies, and rocks and the living world of people,
in what may be his most famous poem, told of 13 ways of looking at
other animals, and plants. Spiritual meaning, including a connection
a blackbird. Robert Frost's bird poems include "The Oven Bird," "A
Handbook of Bird Biologq
Cornell Laboratory of Ornitholooi
 H•14 Sandi Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.15
Figure H-13. Feathered Ceremonial Figure H-14. The Seneca Eagle Dance:
H Costumes of Indigenous Peoples: a. A In this painting from around 1900 by
Native American dance costume fea- Ernest Smith of the Tonawanda Reser-
turing an elaborate bustle is worn by a vation, New York, four dancers perform
dancer performing at the Yakima Indian the Seneca Eagle Dance. Each wears an
Nation Powwow in White Swan, Wash- Iroquois-style costume, including leg-
ington. Photo by Jay Syverson/Corbis. gings, a decorated breechcloth or kilt,
b. A New Guinean tribesman at Mount armbands, and a close-fitting cap with
Hagen, Papua New Guinea wearing an a single eagle feather. Notice, also, the
ornate ceremonial headdress composed feathered wands. Members of the Sen-
of many feathers of birds-of-paradise eca branch of the Iroquois Nation still
and other species. Photo by Quadril- perform an Eagle Dance to this day.
lion/Corbis. Originally it was associated with peace
and war, but in modern times it is per-
formed to celebrate friendships, cure
disease, bring rain, uplift the down-
hearted, and as a thanksgiving. Recent
performances have had two dancers, but
accounts from the early 1900s, such as
this painting, show four dancers. Smith-
sonian Institution, Bureau of American
a Ethnology.

to the past (ancestors), the present, and the future is found in many of in hunting. Although it evolved fronn ceremonies about peace and war,
the connections within this complex web. Ceremonies, rites, songs, it now serves to celebrate existing friendships, to heal illness, and as a
and dances were created to maintain harmony and balance within this giving of thanks (Fig. H 14).
-

web—and these often incorporated birds because of their spiritual or Because they noticed birds performing certain behaviors at the
ecological significance. Sometimes just the physical appearance of time of year when rain falls, many traditional peoples assumed that the
birds was imitated or represented, but at other times their displays, birds were able to bring rain. Thus they developed dances to imitate
vocalizations, and other behaviors were incorporated as well. The these behaviors so that they, too, could bring rain. For example, the
specific beliefs, legends, and ceremonies are as varied as the cultures. Tarahumara Indians of Mexico perform two springtime dances that im-
Bird spirits were invoked to render strength, to provide guidance and itate the strutting courtship ritual of the
wisdom, to heal the sick, to communicate with ancestors, to enhance male Wi IdTurkey a display that occurs
—

fertility, and to provide food and rain. In the following paragraphs are during the rainy spring season. Similarly,
just a few examples of the many ways birds were, and often still are, the Zuni and Hopi of the southwestern
incorporated into the music, dance, and other types of ceremonies of United States try to bring rain by invoking
indigenous peoples. the hummingbird as the mediator be-
Birds frequently appeared in ceremonies in the form of feathers tween humans and the gods (because
or physical images (real or mythical). Familiar to most people are the hummingbirds migrate back from their
feathered headdresses and bustles that mimic the spread tai I feathers of wintering grounds and appear in the
strutting birds (Fig. H 13). Feathers are also used to adorn ceremonial
- southwest during the rainy springtime).
objects such as the prayer sticks of the Zuni of Arizona and New Mex- Bird activities were also associated
ico. Each prayer stick is decorated with a specific type and number with hunting and food. In one ceremony
of feathers, each feather having a special meaning (Bol 1998). Bird in the Torres Strait, between New Guin-
images are re-created in ceremonial masks, totem poles, and other ea and Australia, dancers mimic the Torresian Imperial-Pigeon, which Figure H-15. Torresian Imperial-Pi-
objects. The Tlingit people of Alaska, for example, often used the im- swings its head up and down during one of its displays (Fig. H 1 5). The
-
geon: In a ceremony in the Torres Strait
between New Guinea and Australia,
age of the raven because of its significance in their traditions. Many ceremony serves as a young man's initiation and recognition, as well
dancers imitate the head-bobbing dis-
birds are represented as kachinas (dolls representing ancestral spirits) as an appeal for an abundant food supply (the pigeon is an important plays of the Torresian Imperial-Pigeon.
in Hopi and Pueblo tradition. source of food in the region). Detail of plate by Lilian Medland, from
One bird that is represented in traditional native dances all across Birds with elaborate courtship displays were often imitated by Birds of New Guinea, by Tom Iredale,
the North American continent is the eagle. To many North American 1956. Melbourne, Australia: Georgian
traditional cultures. Of particular interest were birds that displayed
House.
tribes, it is the greatest and most powerful of birds, ruler of the air and in leks (see Ch. 6, Reproductive Behavior: Lek Polygyny): in these
the creatures in it; powerful, fierce, and fearless. The Iroquois Eagle species, males gather at traditional sites and perform showy displays,
Dance, still performed today, was used throughout time to bring luck competing with each other for the attentions of the females, who visit

Cornell Laboratorg of Ornitholom Handbook of Bird Biologq

H .20 Sandy Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.21
Figure H-20. Falconers with Falcons:
Shown here is a drawing from The Art
of Falconry by Emperor Frederick II of
Hohenstaufen. Written in 1248, the
book provided detailed information on
the husbandry of falcons, and the tech-
niques and trappings of falconry. This
important early book provided much
information about the natural history of
game birds and is the first scientific work
known to contain bird illustrations.

doing the same in the 5' century B.C. The "Dialogues of the Buddha"
mention it as being a habit of the seagoing merchants. The Polynesians
Figure H-19. Birds in a Garden Mural from Pompeii: Excavations at the city of Pompeii, which was buried and yet preserved may have been following the migration routes of birds, possibly the
by the volcanic eruption of Vesuvius in 79 A.D., have provided a window into ancient Roman life. Murals from the many walled Long-tailed Koel, when they journeyed to the Hawaiian Islands and
gardens show how important nature was to the inhabitants. Shown are three panels (as a composite image) of one such garden New Zealand.
mural. In the left panel, a jay is shown among plants such as lilies, poppies, morning glories, and a palm. The small center panel
shows what has been described as a bustard. The right panel shows (from bottom to top) a Rock Partridge and a male and female
Christopher Columbus crossed one migratory pathway of North
Eurasian Golden Oriole. Photos courtesy of Foto Foglia, from The Gardens of Pompeii, by Wilhelmina Feemster A. Jashemski, American birds at just the right time and followed the ever-moving
1993. Published by Aristide D. Cavatzas, New Rochelle, New York. stream south to the Bahamas. In the journal of his first voyage in 1492,
he wrote:
courage to carefully analyze and experiment with the natural world.
The book, in addition to details and directions for falconry, gives much October 8—There were many small land-birds and
factual information about birds and is the first scientific work known [the sailors] took one which was flying to the
to contain bird illustrations (Fig. H 20). -
south-west. There were jays, ducks, and a pelican.
Until nearly the end of the Dark Ages, substantive material about
October 9—All night [the sailors] heard birds passing.
birds had been scarce. With the coming of the Renaissance in the
14th century and the invention of the printing press in 1448, a surge For over 300 years after Columbus' notation in his diary—prob-
of interest in birds swept western Europe. In the next two centuries, ably the first written comment on North American birds—the knowl-
with new opportunities for inquiry and knowledge and for scientific edge of the birds of this continent came piecemeal. The colonists and
and literary expression, birds received their share of attention. Three explorers, most of them untrained observers, spent more time in pro-
natural history encyclopedias, published in Zurich, Paris, and Bologna, viding for their own survival than in noticing birds. When they did
recorded current information about birds, including the fanciful as observe birds, they thought of them in terms of their native European
well as the factual. species. The common name of the familiar American Robin is one ex-
With the intellectual expansion came the urge to broaden phys- ample. The early settlers named it after the smaller, brighter, European
ical horizons. Explorers set out from all parts of Europe. Many were Robin, which is a very different bird (Fig. H 21). The same is true for
-

bird watchers, albeit mostly for practical reasons. Navigators followed New World cuckoos, named after the Common Cuckoo of Europe. The
migrating birds to land, or they took land birds to sea and released American Redstart is also named after a similar European species.
them, hoping that the birds would lead them to new territories and Nevertheless, there are some early records: Cabeza de Vaca, in
new riches. Florida in 1 528, probably in the state's northwestern lake country,
The use of birds in navigation was not new. The Norse tale of the writes in his La Relacion (1542): "Geese in great numbers. Ducks,
discovery of Iceland in 874 A.D. described the practice of sending a bird mallards, royal ducks, flycatchers, night herons and partridges abound.
from shipboard to find land. Earlier, Pliny had written of the Ceylonese We saw many falcons, gerfalcons, sparrowhawks, merlins." On the

Cornell Laboratorq or Ornithologq Handbook of Bird Biologq

H.22 Sandq Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective 1-1.23
Figure H-22. Waterfowl from The Orni-
The 18th Centurq thology of Francis Willughby: Willughby
With the 18th century came was an English naturalist known espe-
important American scientific cially for his early classification work
on birds and fishes. He toured Europe
events. From 1712 to 1719 and
with John Ray, collecting material for
1722 to 1726, Mark Catesby, a his book Ornithologia (1676, in Latin),
young Englishman, roamed the translated into English by Ray as The Or-
shores and woods of the south- nithology of Francis Willughby (1678).
eastern colonies and islands. His The illustrations, more accurate than any
previously printed, were reproduced us-
ambitious plan was to paint, de-
ing engraved plates, permitting fine de-
scribe, and name every bird, and tail. Shown here is a plate of waterfowl
other vertebrates as well, that that includes Canada Goose, Common
occurred "between the 30th and Shelduck, and Black Scoter. Note that
both the scientific and most frequently
45th degrees of latitude."
a used common names of the latter two
Short of funds, he published
Figure H-21. European and American Robins: Early European settlers in North America, not well-versed in avian taxonomy, species have changed since Wil lughby's
tended to name the birds they encountered after Old World species that looked similar. For instance, the American Robin (a) was his book in sections from 1731 to time. Courtesy of Blacker-Wood Library,
so called because its chestnut-red breast reminded them of the familiar European Robin from back home. The European Robin (b) 1743. Physically, the complete McGill University.
is a compact, chatlike bird, which systematists currently place in the family Muscicapidae (Old World flycatchers). TheAmerican volume, The Natural History of
Robin is a larger and more strongly built bird in the family Turdidae (thrushes). Photo a courtesy of J. R. Woodward /CLO; photo
Carolina, Florida, and the Ba-
b by John Cancalosi /VIREO.
hama Islands, is luxurious, nearly
14 by 20 inches (35 by 50 cm) in
Pecos River in 1535, apparently near theTexas/New Mexico border, he
size, with 220 hand- painted engravings, all
feasted on quail brought in by native archers for the evening meal. Cas-
but two of which Catesby did himself (Fig.
tenada, writing of the Coronado expedition of 1541 to 1542, observed
H 23). Scientifically, the illustrations and
-

turkeys and tame eagles in Arizona and cranes, wild geese, crows, and
the accompanying discussions earned for
blackbirds in New Mexico, reports that must surely be among the first
the author the well-deserved title "Founder
ornithological observations made in the continental United States. As
of American Ornithology." Catesby, for his
early as 1585, John White, a member of Sir Walter Raleigh's second
time, was remarkably unbiased and insisted
expedition to Roanoke Island, Virginia, painted a series of watercolors
on verifying hearsay with personal obser-
of American birds. The paintings, well drawn, accurately tinted, and
vation. His drawings and descriptions were
more important, the results of first-hand observations, were first pub-
the basis for over one-third of the American
lished in 1590 in de Bry's Virginia; they may be enjoyed today in all
birds that Linnaeus later described. Artisti-
their glowing colors in Stefan Lorant's The NewWorld(1946). Between
cal ly, Catesby provided several innovations:
1630 and 1646, William Bradford, governor of the Plymouth colony,
he painted living birds, naturally posed in
wrote that wild turkeys and waterfowl had been abundant in 1621, but
their native habitats. He also considered
that waterfowl decreased thereafter. In 1674, John Josselyn noted that
shading and composition, using bold pat-
young turkeys were once abundant in the woods, "But...the English
terns of light and dark in some of his paint-
and the Indians [have] now destroyed the breed, so that tis very rare to Figure H-23. Mockingbird by Mark
ings. The best were unsurpassed for over 100 years.
meet with a wild turkie in the woods." Catesby: In the early 1700s, English nat-
In 1758, Linnaeus published his Systema Naturae, which laid
Although the explorers and colonists sent "home" living and dead uralist and artist Mark Catesby set out
the groundwork for modern binomial nomenclature and kindled in to paint, describe, and name every bird
specimens of birds during this period, the investigation of American
travelers the desire to find and name different kinds of organisms, and other vertebrate in the southeastern
bird life had to wait for the further development of science in Eu-
including birds. American colonies and islands, even-
rope. In 1678 appeared The Ornithology of Francis Willughby, by tually to be published in his book The
Specimens of plants and animals flooded into Europe from the
Willughby and his friend John Ray. This publication was a scientific Natural History of Carolina, Florida, and
New World. Aviaries with pet birds from the colonies were much the Bahama Islands. His paintings, based
landmark, the first major work based on careful observation of both
in vogue. In England, George Edwards, Thomas Pennant, and John on personal observation as well as spec-
the structures and habits of birds. The authors adopted the most valid
Latham, important "armchair" ornithologists, compiled great volumes imens, presented birds naturally posed
classification and species concepts of the day, and the illustrations in native habitats, as exemplified by
on birds from specimens of species they never saw alive. Their com-
were far more accurate than any previously printed. In preparing the this lively mockingbird perched amidst
ments, however, based on second- or third-hand information, were
illustrations, the artists used engraved plates that permitted far more dogwood. This illustration is Plate 27 in
not always reliable. Edwards' A Natural History of Birds (1743-1751) Volume I of Catesby's book, published
delicacy of detail than the woodcuts used previously in the early en-
was worldwide in scope; Pennant's Arctic Zoology(1784-1785) dealt in 1731.
cyclopedias (Fig. H 22).
-

Cornell Laboratorq of Ornitholo9q Handbook of Bird Biologq

 Sandi Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.25
H .24
primarily with North American birds; and Latham's A
General History of Birds (1821-1828) included the
first attempt to systematically treat all the birds of the
world.
In the 1790s, Thomas Bewick devised a new
method for producing illustrations by using end-grain
woodcuts that increased detail to a degree formerly
impossible in wood and eliminated the need for cost-
A
ly copper engravings. His A History of British Birds
(1809) was the first well-illustrated bird book avail-
HISTORY
able to everyone (Fig. H 24).
-

OF In 1791 appeared Travels Through North and

South Carolina, by William Bartram, a professional
BRITISH BIRDS. bird watcher and son of a famous Philadelphia nat-
uralist. Although Bartram's notes on birds and their
habits were, at times, more poetic than scientific, he
THE FIGURES ENGRAVED ON WOOD BY T. BEWICK. stands out as one of the first Americans to contribute
to ornithological knowledge. Lou isViei I lot, a French-
man, was the first to point out variations in plumage with season and Figure H-25. Great Seal of the United
PART I.
sex in his L'Histoire Naturelle des Oiseaux de L'Amerique Septentrio- States: The eagle has been the official
CONTAINING THE
nale (1807). John Abbot, an Englishman, worked from 1804 to 1827 symbol of the United States since the na-
HISTORY AND DESCRIPTION OF LAND BIRDS. tion's beginning. Its form, however, has
on several drafts of a manuscript that contained notes on life histories varied over the years. In 1776, congress
and illustrative paintings of the birds of Georgia. Unfortunately, none rejected the two-headed bird proposed
of his work has ever been published. as the national symbol, final lyaccepting
In the New World through the 18th and into the 19th centuries, a crestea, stylized eagle in 1782. Since
then, the crest has been omitted, and
most people, still recovering from the American Revolution and intent
the shape and color modified so that
on establishing a new nation, were concerned with more practical today's symbol more closely represents
affairs than studies of birds. Almost from the beginning, however, the an actual Bald Eagle. The eagle clutches
eagle in one form or another was a symbol of the United States. The arrows and an olive branch—symbols,
respectively, of war and peace. The style
two-headed eagle, first proposed as the national symbol of the United
of eagle currently used in the Great
States in 1776, resembled the imperial German eagle and was not ac- Seal, as shown here, was first adopted
cepted. Congress considered a number of other designs and finally, around 1885. The Great Seal is used in
in 1782, chose a crested, stylized eagle for the official seal. Since that numerous official ways, such as to seal
time, minor alterations in the seal have included the elimination of certain government documents, on cer-
tain letters and envelopes, and on the
the bird's crest and modifications in form and color so that the bird
NEWCASTLE: one-dollar bill. The lithograph shown
on the seal today more closely resembles the Bald Eagle than did the here was created by Andrew B. Graham
PRINTED BY EDWARD WALKER, FOR T. BEW1CX : SOLD BY 11111 2 A N A
original (Fig. H 25).
- sometime around the turn of the 20thcen-
LONGMAN AND CO. LONDON.
The selection of the Bald Eagle as the American symbol did not tury. Courtesy of Library of Congress.
please everyone. Benjamin Franklin thought that the eagle "does not
1,809.
get his living honestly...too lazy to fish for himself, he watches the la-
bor of the fishing-hawk, and when that diligent bird has at length taken
a fish...the bald eagle pursues him and takes it from him." Franklin
much preferred the Wild Turkey, which, though a little "vain and silly,"
was "a bird of courage." Today ornithologists try to avoid judging birds
by human standards of morality.

Figure 1-1-24. Title Page and Illustrations from A History of British Birds, by Thomas Bewick: In the 1790s, Bewick developed a
new printing method for illustrations. He used end-grain woodcuts, eliminating the need for expensive copper plates yet allow- The 19th Century
ing fine detail. His 1809 A History of British Birds was the first bird book readily available to the general public. The illustrations In a century that included many gifted "literary scientists," Henry
show, from top to bottom, Common Cuckoo (the model voice for the popular cuckoo clock), European Goldfinch, and Northern
David Thoreau was perhaps the finest. Although his works were often
Lapwing (called in the original by its colloquial name "Pee-Wit").

Cornell Laboratortj of Ornitholom Handbook of Bird Biolo94

H.26 SandH Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective .27
Figure H-26. John Burroughs and John Young People, St. Nicholas, and The Youth's
Muir: As an essayist and naturalist, John Companion, entreated their young readers
Burroughs inspired a generation of to protect birds. Birds, a magazine started in
American nature-lovers and conserva-
1896, served as a guide to nature education in
tionists in the late 19th and early 20th
centuries. Nicknamed "John 0' Birds," the schools, as did four books by women: The
Burroughs (right) imbued his bird writ- First Book of Birds by Olive Thorne Miller, Birds
ings with emotional and poetic descrip- ofVillage and Field by Florence A. Merriam, Cit-
tions, while his excellent birding skills izen Bird by Mabel Osgood Wright, and How to
assured the accuracy of his observations.
John Muir (left), shown here visiting Bur-
Attract Birds by Neltje Blanchan.
roughs for the latter's 75th birthday cele- Meanwhile, the ornithologists were ac-
bration, was a naturalist, conservationist, cumulating, assimilating, and beginning to
and bird enthusiast from the western publish vast amounts of information. Lacking
United States. Nicknamed "John 0'
modern photography, the artists among them
Mountains," Muir became well known
as a proponent of creating national parks portrayed the species as they saw them.
and conserving forests. Photo courtesy Alexander Wilson, poet, artist, and weaver,
of Library of Congress. arrived in America from Scotland in 1794 and
within 14 years had completed the first volume
in a projected 10-volume work on American
birds that would earn for him the title, "Father
of American Ornithology." Short of funds and
forced to depend on an inadequate number of
subscribers for the entire set of American Orni-
thology, Wilson walked through New England
emotional and philosophical, he was an exceedingly acute and ac-
and south along the coast to Georgia, carrying
curate observer, and he is considered by many to be the first truly great
Volume I (1808) and collecting, painting, and
American nature writer. Thoreau had little interest in what we would
studying birds as well as seeking subscribers. He
call laboratory studies of birds. In his words, ornithology at its best was r Nark threat/4f Warbler

took a second walk westward, down the Ohio IF Yo/ifehy Fiv4,44eiler

a "window opened wide to nature." and Mississippi Rivers to Natchez, and then east
In the last half of the 19th century, John Burroughs (Fig. H-26), a
across the country to Philadelphia. Figure H-27. Plate from American Orni-
serious student of birds with a critical and inquiring mind, was perhaps thology byAlexander Wilson:This plate,
He found support for this project in Philadelphia: William Bar-
the most widely read and loved of the nature writers in spite of the fact from Volume I of the nine volume set,
tram and Charles Wilson Peale encouraged and helped him; Peale's
that he did not hesitate to personalize birds, as in his "Wake Robin." demonstrates the crowding of several
museum supplied him with specimens. He remained near Phila- species on a single plate as a means of
The John Burroughs Society, established in his honor, continues today
delphia for the rest of his life, writing, painting, and collecting. When reducing publishing costs. Shown here
and each year honors the author of the most outstanding nature book
he died in 1813 at the age of 47, he had completed eight volumes. The are Pine Siskin, Rose-breasted Grosbeak,
published in the preceding year. ninth, edited by George Ord, was published in 1814. Black-throated Green Warbler, Yellow-
At the end of the 19th century three authors of books on birds rumped Warbler, Cerulean Warbler,
The nine volumes that appeared in just over six years contained
stand out. John Muir (see Fig. H-26), naturalist, conservationist, and and Blue-headed Vireo. Note that some
illustrations of 320 species-39 that had never been illustrated be- of these species' names have changed
also bird enthusiast, wrote about the Water-Ouzel in his book The
fore on 76 full-page engravings (Fig. H 27). Looking at them today,
- since this book was published.
Mountains of California. The approach of Bradford Torrey, writer and
we adrn i re the skillful drawing and forget, if we can, the awkwardness
ornithologist, varied from the anthropomorphic in Birds in the Bush
caused by crowding too many birds on one plate as an economy mea-
to a detailed study of species in The Foot-Path Way. Frank Bolles had
sure. The text raised the level of ornithology by including accurate
a brief career but showed great promise in his last book, At the North
first-hand observations, measurements of specimens, and notes on
of Bearcamp Water. the fresh colors of the bill, irises, and other soft parts that fade quickly
The nature writers of the 19th century wrote charming, pleasant
once the bird is dead.
books for a general audience, and they contributed much information
The paintings of John JamesAudubon, however, were soon to sur-
about birds, often mixing the information with philosophy and humor.
pass those of Wilson even though Wilson may have inspired Audubon
Popular magazines also did their part. The Atlantic Monthly, Harper's,
to publish his work. The two men met in Louisville, Kentucky, and
and Scribner's Monthly all carried nature essays and articles about reports of this meeting are numerous and conflicting. Later there was
birds, as did Appleton's Journal, Harper's Bazaar, The Independent, ill feeling between the two artists.
and MacMillan's Magazine. Several children's periodicals, Harper's

Cornell Laboratorq of Ornithology Handbook of Bird Biologq

 H.28 Sandi Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.29
Audubon, born in 1785, grew Figure H-29. Spotted Forktails from
H up in France and painted birds from Birds of Asia, by John Gould: Author
of many books and scientific articles,
childhood. His early inclination be-
English ornithologist and painter John
came an obsession as he hunted and Gould (1804-1881) aspired to illustrate
studied birds in the Ohio and Missis- all the birds of the world. He eventually
sippi Valleys of the New World. In published 41 folio volumes, in which
the illustrations were reproduced by
1824, he journeyed to Philadelphia in
the relatively new method of lithogra-
search of a publisher. But Wilson was phy. His artistic wife contributed greatly
dead and those of his friends who were by handling the technical aspects of
still alive refused to support this young the lithographic process, and several
challenger to Wilson's fame. Audubon other artists contributed plates. Gould's
monographic works included the birds
found a publisher in England—Havells of Australia, Asia, Europe, Great Britain,
of London. From 1827 to 1838, Have- and New Guinea, and his Monograph
lls published The Birds of America in of the Troch i I idae (hummingbird family)
four elephant-folio volumes with 435 (1849-1861) is considered his master-
piece.
aquatinted copper engravings by Robert
Havel!, engravings that retain a remark-
able fidelity to the original paintings
(Fig. H 28). Robert Havel!, Jr., and oth-
-

ers, including Audubon's son John, oc-

casionally completed the background
details of the paintings—the vegetation
or landscape. Three of Audubon's birds
are line copies of Wilson's drawings.
Nevertheless, Audubon was the dom-
inant spirit behind the spectacular ac- was the case with the Lewis and Clark Expedition. Without a trained
complishment and deserves credit for a zoologist to guide them, the captains relied on designations in com-
remarkable achievement. mon use in the East, naming new birds in terms of species with which
Audubon painted from fresh spec- they were familiar. As a result, they called the California Quail "a bird
imens arranged in natural poses, just as of the quail kind" and McCown's Longspur a "small bird resembling
Catesby had done 100 years before. a lark," but the vivid descriptions of the two species leave little doubt
Some earlier artists had painted a sin- about their identity. So well and in such detail did Lewis and Clark
gle species on a plate, life-size against record their observations of new species that later ornithologists were
a natural background; others had con- able to place the proper technical names with these descriptions.
sidered the artist's composition of the Nevertheless, very little ornithological renown has been bestowed
Figure H-28. Osprey by John James paintings. Audubon absorbed all their ideas and created something on the captains, even though their expedition returned with obser-
Audubon: Born in the Caribbean in uniquely his. His Ornithological Biography, however, shows that he vations of about 130 birds, many, such as the Clark's Grebe, Tundra
1785 and raised in France, Audubon was not as acute an observer of birds as Wilson. Swan, Lewis' Woodpecker, Sage Grouse, Broad-tailed Hummingbird,
began painting birds as a child. His dra-
Meanwhile, in England, painter John Gould had a far more am- and Western Tanager, new to science. True, "Clark's Grebe," "Clark's
matic paintings of birds from the New
World were first published by an English bitious plan—to illustrate all the birds of the world. By painting from Nutcracker," and "Lewis' Woodpecker" memorialize their names, but
engraver, Havells of London. Between bird skins rather than living birds and by organizing others to help these ascriptions reveal little of their achievement. One searches the
1827 and 1838 Havells produced the him, Gould produced nearly 50 sumptuous volumes, illustrated with lists of alternative common names in vain for mention of Lewis and
four elephant-folio volumes of The
over 3,000 plates by a relatively new method, lithography (Fig. H 29).
- Clark. The American Ornithologists' Union Check-list, at least, refers
Birds of America, containing a total of
The volumes were monographs on taxonomic groups of birds and at- to two names the captains first used, the "Whistling Swan" (Tundra
435 plates, using the technique of aqua-
tinted copper engraving. Typical of this tempted to show the relationships among the species covered. Swan) and the "Prairie Hen" (Sharp-tailed Grouse). Later naturalists
artist's portrayal of action is this Osprey In the 19th century, knowledge of the North American avifauna generously availed themselves of the captains' patient labors, almost
carrying its catch. increased rapidly with the exploration of the West. The members of always without a shred of acknowledgment.
government expeditions, though mostly untrained in science, did Some expeditions were fortunate in having ornithologists whose
their best to record the natural history of the areas they visited. Such careful records contributed a great deal to the expedition's data. Titian

Cornell Laboratorq of0mithologq Handbook of Bird Biologq

H.30 Sandq Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.31
Peale accompanied the Long Expedition of 1819-1820, painted sev- ployed as "professional" ornithologists were among the directors and
eral birds, and no doubt laid the groundwork for his later illustrations curators of the early natural history museums. They held no degrees in
in Charles Lucien Bonaparte's extension of Wilson's American Orni- ornithology, and in fact, many had no college education at all. Instead,
thology, published in four volumes in 1825. From Peale's brush came they were either self-taught or apprenticed under someone knowl-
all but one of the illustrations in Volume One, including the plate of edgeable in the field. Expertise was gained by firsthand experience
Say's Phoebe, first described by his fellow traveler on the Long Expe- in the field, collecting and observing birds. A personal collection of
dition, Dr. Thomas Say. Peale also went on the Wilkes Expedition of bird specimens was considered essential for those serious about bird
1838-1842 from Virginia to Rio de Janeiro, around Cape Horn to study. Along with the "professionals," there was a well-to-do upper
Peru, Antarctica, New Zealand, the northwestern United States, the class who enjoyed learning about birds and had the financial means
Philippines, and back to NewYork by way of the Cape of Good Hope. to spend time in the field creating their own personal collections. They
The data from this voyage, compiled and edited by ornithologists who also relied heavily on the work of collectors, taxidermists, and sport
had not made the journey, became the first major publication on birds hunters to expand their collections of bird specimens.
sponsored by the government. John Cassin compiled several of the The professional ornithologists affiliated with the early Ameri-
volumes, among them Illustrations of the Birds of California, Texas, can museums played a critical role in advancing ornithology. Notable
Oregon, British and Russian America ... and a General Synopsis of among this group were Robert Ridgway, curator of birds from about
North American Ornithology (1853-1856). 1881 until his death in 1929 at the United States National Museum in
Several naturalists joined the railroad explorations that moved Washington, D. C., and Frank Chapman, curator of birds at the Ameri-
west from the Mississippi River to the Pacific between 1853 and can Museum of Natural History in New York City. Robert Ridgway
1856. Their data, added to information from private collections, were (1850-1929), a founder and president of the American Ornithologists'
edited chiefly by Spencer Fullerton Baird, assistant secretary of the Union, served as curator of birds at the United States National Museum
Smithsonian Institution, and became the second part of the ninth (USNM) for over 50 years and was the author of two important works in
volume of Reports of Explorations and Surveys to Ascertain the Most ornithology: A Manual of North American Birds (1887) and a series of
Practicable and Economical Route for a Railroad from the Mississippi volumes known as Birds of North and Middle America (1901-1919).
River to the Pacific Ocean (1858), one of the Frank Chapman (1864-1945), was considered the Dean of American
most important federal publications of the Ornithology (Fig. H 31). He was a pioneer in bird photography, a
-

century. This purely ornithological section, lecturer, and a prolific writer with over 225 articles and 17 books. His
known as Baird's General Report for political Handbook of Birds of Eastern North America, published in 1895, was
reasons, included descriptions of 738 species the most widely used guide of its time.
of birds and was the first book on the birds of By the late 1800s, regional bird clubs, societies, and organiz-
the entire continental United States. Later, the ations were sprouting up all over the country, and some remain active
section was reissued privately as The Birds of to this day. The Nuttal I Ornithological Club, created in the early 1870s,
North America (1860). Although the infor- was the first ornithological club in the United States. The requirements
mation was more detailed and accurate than for joining this group were minimal—you had to be male and have a
any yet published, the book lacked the charm special interest in birds.The club soon included a diverse group of men,
and spontaneity of the works by Wilson and
Audubon.
Figure H-31. Frank Chapman: Although
Natural history inventories and the col- he had no formal ornithological training,
lection of natural history objects (including Chapman was a gifted writer, lecturer,
birds and their eggs) led to the creation of and scientist. He served as the curator of
birds at theAmeri can Museum of Natural
Figure H-30. Smithsonian Institution many natural history museums in the United
History and bridged the gap between
Bird Gallery: This 1885 photograph de- States in the 1800s. Among these were the American Museum of Nat- amateur and professional ornithologists
picts taxidermic mounts and study skins ural History in New York City; the United States National Museum with hundreds of articles, 17 books, and
atopa longcaseofspecimen drawersatthe
Smithsonian Institution in Washington,
(Smithsonian) in Washington, D. C. (Fig. H 30); theAcademy of Natu-
- a popular magazine, Bird-Lore, which
ral Sciences in Philadelphia; the Museum of Comparative Zoology in eventually becameAudubon magazine.
D. C. Many natural history museums
Negative number 12930, courtesyof the
centered on bird collections were Cambridge, Massachusetts; the Field Museum of Chicago; and the
Department of Library Services, Amer-
established in the United States during Carnegie Museum in Pittsburgh. Although there were many private ican Museum of Natural History.
the 1800s. Negative number 96-3532.
collectors, these early museums soon became centers for the study
Smithsonian Institution Bird Gallery,
1885. Smithsonian Institution Archives, of birds.
Record Unit 7006, Alexander Wetmore In the 19th century, ornithology was still a descriptive science. No
Papers, Box 195. formal academic training was available and the few fortunate men em-

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

H.32 Sandy Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.33
including Theodore Roosevelt, who was a fresh- birds and mammals. This later became the U. S. Fish and Wildlife
man at nearby Harvard University (Fig. H-32).The Service within the Department of the Interior. From the work of one U. S. DEPARTMENT OF AGRICULTURE.
DIVISION OF ECONOMIC ORNITHOLOGY.
Nuttal I Ornithological Club—still in existence (but committee, the foundation for a federal agency with a mandate at least BtaaraN No. 2.

now accepting women)—soon became embroi led partly in ornithology was created, and the first study of birds using data
REPORT
in the controversy surrounding the introduction of collected from a large number of volunteer participants—Merriam's OP

House Sparrows into the United States, a program bird migration study—was carried out.
begun in the early 1850s. Known as the "Sparrow The other original AOU committee, the Committee on Clas-
BIRD MIGRATION
Wars," the controversy ultimately led to negative sification and Nomenclature, developed the first "Code of Nomen- MISSISSIPPI VALLEY
publicity and a temporary decline of the club. clature"—a standardized list of common and scientific names for
Another organization of this era was The Li n- North American birds. This was a significant step because before the THE YEARS 1884 AND 1885,

naean Society of New York. It formed in 1878 as a "Code" there were two competing lists of North American birds. Stan- W. W. COOICE.
local (New York City area) natural history society dardizing bird names was essential for any accurate inventory of bird
whose main interest was birds. An offshoot of this distributions. The Committee on Classification and Nomenclature has .Drren PPP RIPSPSED BY PP. C. PPM IdEPPIPM.

group was the Bronx County Bird Club, perhaps also been responsible for determining which groups of birds consti-
the most enthusiastic group of bird watchers any- tute species: whether certain groups traditionally considered separate WASHINGTON:
POYMPENT raleixxxo PHIaL

where. Although these organizations contributed species should be put together as one (lumped) or whether certain 7385—Boll. Nab.
N
1888.

to the growing interest in bird studies, the estab- species should be divided into several (split). These issues are often
lishment of the first national organization—the fiercely debated. Each year at the annual AOU meeting, this committee Figure H-33. Bird Migration Report
Figure H-32. Theodore Roosevelt and American Ornithologists' Union—really laid the foundation for 20th reviews new research concerning the taxonomy of North American Shown here is a report on bird migration
John Muir: This photo, circa 1906, century ornithology. birds, determining which species to split and which to lump, as well from the U. S. Department of Agricul-
shows two conservation pioneers in
as deciding on any name changes for species. The AOU regularly pub- ture's Division of Economic Orni-thol-
California's Yosemite Valley. While at
The American Ornithologists' Union and the U. S. Biological Survey ogy. Through the urging of C. Hart Mer-
Harvard University, Theodore Roosevelt lishes updates of the Check-list of North American Birds. Anyone who
Twenty-three men were present at the founding of the American riam and the American Orni-thologists'
(left) was a member of the nation's first thinks taxonomy is a stagnant science, should consider that there were Union, congress authorized the estab-
birding club, the Nuttall Ornithological Ornithologists' Union (AOU) in 1883. Although there were many
over 150 changes between the sixth edition published in 1983 and the I ishment of the Division of Economic Or-
Club. As president of the United States regional natural history organizations and bird clubs at the time, this nithology in 1885. Although the original
(1901-1909), Roosevelt championed
seventh edition published in 1998.
was the first national organization and its creation was a turning point intent of the division was to study the ef-
many wildlife conservation issues. John By the late 1800s, there was growing concern over declines of
for ornithology. Two important committees were created at the first fects of birds on agricultural production,
Muir, like Roosevelt, was a strong pro- many bird species. Habitat destruction and market hunting for plumes over the years the scope broadened to in-
ponent of creating national parks and meeting: the Committee on Bird Migration and the Committee on
and meat had taken their toll on a number of species, including the now clude the general study of birds. By 1896
conserving forest lands. Copyright Bet- Classification and Nomenclature.
extinct Passenger Pigeon and Carolina Parakeet. The AOU Committee the Division of Economic Ornithology
tman/Corbis. C. Hart Merriam, the first chair of the Committee on Bird Mi-
on Protection of North American Birds, created in 1884, played an im- had become the U. S. Biological Survey,
gration, immediately began an ambitious program to study bird mi- which eventually became the U. S. Fish
portant role in fostering bird protection in America. Their first priority
gration. He was interested in learning arrival and departure times, the and Wildlife Service within the Depart-
was to alert the public to the decline of birds. They also proposed leg- ment of the Interior.
influence of weather, and many other aspects of this poorly understood
islation, which was passed in some states, making it illegal for anyone
behavior. Merriam accomplished his goal by setting up an information
to kill, purchase, or sell non-game birds or their nests and eggs.
network. He sent a circular to 800 newspapers soliciting the support of
all interested people—sportsmen, ornithologists, field collectors, and The First Audubon Movement
nature enthusiasts—to help gather information on these topics. The re- At the same time the AOU was publishing its first bulletin on
sponse was overwhelming. Merriam and theAOU petitioned congress bird protection, George Bird Grinnell was creating the first Audubon
to create a Division of Economic Ornithology within the Department Society. Editor-in-chief of Forest and Stream, and at one time a student
of Agricu Iture (Fig. H-33). Because the public was eager to categorize of Lucy Audubon, the widow of John James Audubon, Grinnell was
the effects of different types of birds on agriculture as either beneficial a leading voice in condemning the commercial exploitation of wild-
or harmful, Merriam and theAOU were able to gain federal support by life. He was also one of the founding members of the AOU. Grinnell's
emphasizing the economic value of bird migration data. Of necessity, long-term goal was to create a national society organized into local
the division's early publications, such as The Hawks and Owls of the chapters and he named his new organization after the legendary bird
United States in their Relation to Agriculture, and numerous bulletins artist John James Audubon. Grinnell's Audubon Society enjoyed early
on the food of different bird species, were oriented toward farmers. In success, but unfortunately it wasn't sustained. By 1888, the work of
1885, the Division of Economic Ornithology was authorized as a unit both the AOU bird protection committee and Grinnell's Audubon
within the Division of Entomology. By 1886, it was separate from the Society had stalled. Although short-lived, Grinnell's Audubon Society
Division of Entomology, and in 1896 it became the U. S. Biological strengthened the public's growing concern about bird destruction and
Survey, whose focus was to study the geographic distribution of both established a public arm to the bird protection movement.

Cornell Laboratory of Ornithology

Handbook of Bird Biology
 Ir
1-1.34 Sandq Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.35
Women, initially excluded from the male-dominated "profes- Figure H-34. Bird Lore: One of the first
-

H popular bird magazines, Bird-Lore, be-

sional organizations," were instrumental in popularizing the study FEBRUARY, 1899
. - gun in 1898 by Frank Chapman, intro-
of birds and bird protection. In 1886 Florence Merriam (the sister of ,..ti duced a new generation of people to the
C. Hart Merriam) created a local Audubon chapter while she was a study of birds and served as the voice of
student at Smith College. In 1887 she began writing a series of articles ---iviiv-- the National Association ofAudubon So-
("Hints to Audubon Workers: Fifty Birds and How to Know Them") (s,
9'. ‘P
irt) 6, orr. cieties. Bird-Lore was renamed Audubon
Magazine in 1941, and the name was
for Grinnell's Audubon Magazine. At the conclusion of the series in shortened to Audubon in 1953. Today,
-1,4; 1888, she included a field key incorporating color, bill shape, song 4.I■ 'a ....,„, , A..,. , 3, iiQ, Audubon serves as the primary publi-
type, behavior, habitat preference, and nesting habits as characters cation of the National Audubon Society.
; ,
to help identify the fifty species. In 1889 she published her first book, ..., . ._ Courtesy of the National Audubon So-
ciety.
Birds Through an Opera Glass, in which she expanded her field key , .

to seventy species. It became a bestseller, inspiring thousands to take

-, .... ......=.
up bird watching. Many similar publications by other authors soon 4,..,....
I
. „..

„1
followed. ,,,,

The Second Audubon Movement

„........

The bird protection movement was revitalized in 1896 by two !Rh N1C 11 CHAPMAN

Zbc acmillan Company

Boston women, Harriet Hemenway and her cousin Minna Hall, who 13;i7ca lit!
were instrumental in creating the Massachusetts Audubon Society.
4
reirkal; 4'1,1r 41141'i,ZW,41 ,41.4 •-•:/e',,Ee'-•
Inspired by horrific accounts of birds slaughtered only to adorn
women's apparel, the mission of the organization was to discourage
the use of feathers for ornamentation and to promote the protection
of birds. Concerned people in other states soon established similar but many others were produced by private publishers. The literature
organizations. included state and regional works on birds and, most importantly, Elliot
At about the same time, the AOU bird protection committee Coues' Key to North American Birds, the classic that first introduced
was strengthened as William Dutcher became its chairman. Dutcher ornithology to many thousands of people (Fig. H 35). -

was dedicated to establishing state Audubon societies and promoting

bird protection through public education. In 1905, Dutcher created The 20th Centurq and the
the National Association of Audubon Societies. Having a national as-
sociation relieved the AOU of much of its role in bird protection—a Expanding Role of the Bird Watcher
role that was increasingly divisive among its members, as many were The growing number of bird watchers in the late 19th century
actively collecting birds. The AOU did not revive its bird protection presented both challenges and opportunities to professional ornitholo-
activities until 1930. gists. As bird collecting became more restricted, many ornithological
Meanwhile, the American Museum of Natural History was pro- societies focused more on field studies and cooperative research,
foundly affecting ornithology. Frank Chapman, first hired by the mu- especially in the areas of geographical distribution, migration, and
seum in 1888, eventually became curator and served in that capacity life history studies. Lynds Jones, a founding member of the Wilson
until 1945. Although he had no formal education, Chapman was a Ornithological Society, and his student, William Dawson, advocated
gifted writer, lecturer, and scientist (see Fig. H-31). In a field that was systematically keeping detailed checklists of birds observed at different
becoming increasingly divided, Chapman formed a bridge between locations and times of the year. The value of such lists, they lobbied,
the professional and amateur. He created the popular bird magazine was that they could be used to estimate bird abundance. Dawson and
Bird-Lore in 1898, in part to supplement his income, but also to assist Jones soon had hundreds of observers competing to compile the lon-
the AOU bird protection committee in distributing information on gest lists. Getting out into the field to count birds replaced collecting
Figure H-35. Elliot Coues: Coues' Key
bird protection to the public. (Fig. H 34). Bird-Lore introduced a new
- in numerous ways, providing many of the same benefits without killing to North American Birds was the most
generation of people to the study of birds and it served as the voice birds. The competitive aspect also attracted the interest of a whole new influential of the numerous American
of the emerging National Association of Audubon Societies. The Na- breed of bird watchers. Observers were encouraged to submit their ornithological publications that prolif-
tional Audubon Society assumed the publication of Bird-Lore i n 1941, lists for publication in the Wilson Bulletin, the journal of the Wilson erated during the late 19th century. Its
two illustrated volumes contained infor-
renaming it Audubon Magazine. In 1953, the name was shortened to Ornithological Society.
mation about the structure and classific-
Audubon, the publication familiar to us today. The idea of counting birds inspired Frank Chapman to propose ation of living and fossil birds as well as
During the last quarter of the 19th century, ornithological publica- a Christmas Bird Count in 1900. Chapman encouraged people to a manual on collecting, preparing, and
tions began to proliferate. Some were sponsored by state governments, count birds instead of participating in the traditional Christmas Day preserving bird specimens.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 H.36 Sandq Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective 1-1.37
Hunt, promising to publish the results in Bird-Lore. From this modest a system of arrows to indicate key field marks,
H H beginning, the Christmas Bird Count has become a major ornitho- and shortening the text to the minimum needed e nKr.r 1,111 nr. CY!, vorc Kum -rls,

logical tradition, collecting valuable information on bird abundance to identify a bird, Peterson produced a reference
throughout the United States to this day. book that revolutionized bird watching. His first
By the early 1900s, the U. S. Biological Survey had amassed an field guide, A Field Guide to the Birds: Giving
enormous amount of data on bird migration in addition to data on bird Field Marks of all Species Found in Eastern North C.A:5r1INIA KOVAL- III
abundance from the surveys. This information was used by A. C. Bent America, was published in 1934 (Fig. H-37). In
to compile his monumental Life Histories series (Fig. H-36) and by 1980, range maps reflecting the seasonal move-
111 1. 1 1.1.,

the AOU to prepare their Check-lists of North American Birds. While ments of each species were added to the guide. 1.1 1,1 1 X-

1,1 1

the U. S. Biological Survey's census programs waxed and waned, the A Field Guide to the Birds was the first of a series CABOT`fi GULL - 1St I I

National Audubon Society began its own spring count in 1937, the of field guides that would make publishing his-
"Breeding Bird Census." Still held each June throughout the United tory. More than anyone else in the world, Peter-
States, the Breeding Bird Census is a major effort to count birds in the son introduced an enormous number of people
1111,

breeding season. to birds—an achievement that far surpasses the

NOLIIN'T
Bird banding was quickly gaining momentum as people realized commercial success of his series. As species rec- 131 ,AC

Figure H-36. Arthur Cleveland Bent: it was useful for studying bird movements. At the 1909 AOU meeting, ognition is the first step toward preservation, his
During the early 1900s, A. C. Bent pro- banding enthusiasts organized the National Bird Banding Associa- work also has been pivotal to the 20th century
duced a series of texts on the life histories
tion (NBBA), which was administered through several different orga- conservation movement.
of many groups of birds, such as the Life
H istories of North American Birds of Prey
nizations before its demise. In its wake, regional organizations were
formed to fill the void: the New England Bird Banding Association in Academic Training in Ornithology
and the Life Histories of North Amer-
ican Shorebirds. Bent obtained much of 1922 (renamed the North American Bird BandingAssociation in 1924), Ornithology became increasingly profes-
the information for his books from the the Inland Bird Banding Association (1922), the Eastern Bird Banding sional in the early part of the 20th century. Al-
newly founded U. S. Biological Survey though no formal degree programs were yet
Association (1923), and the Western Bird Banding Association (1925). 1111 t.1
r 1
and by corresponding with other keen
As a result of the growth of bird banding in the 1920s and '30s, the available, a number of academic institutions
bird watchers. To this day, Bent's texts are IC
used by birders and ornithologists as a U.S. Biological Survey (now the Biological Resources Division of the offered classes in ornithology as part of zool-
source of life history information. Photo U. S. Geological Survey) began to coordinate banding activities. This ogy or nature study programs. A period of rapid
courtesy of D. L. Garrison.
organization and its Canadian counterpart have overseen the activities expansion soon followed, with more students
of dedicated North American bird banders ever since. interested in ornithology, and more in-depth, sci-
entifically-based studies of birds being carried
The Development of the Field Guide out. As the field grew, graduate degrees became
While bird watchers were amassing all kinds of information about standard requirements for serious researchers. TERNS "n 51411-111ERS

birds, the scientific community was becoming increasingly skeptical Biology itself was rapidly transforming from a
about the accuracy of many reports. With no specimens to back them descriptive discipline to an experimental one, with a number of spe- Figure H-37. Plate from an Early Peter-
up, reports of questionable birds were hard to verify and thus were cialized fields such as genetics, embryology, and the field-based stud- son Field Guide: Roger Tory Peterson rev-
olutionized bird watching in 1934 when
of little scientific value. Yet, as collecting became more restricted by ies of ecology and animal behavior.
he published A Field Guide to the Birds:
law, scientists had to rely increasingly on observational reports. One During the early 20th century, Cornell University was the leading Giving Field Marks of all Species Found
scientist who believed that just about anyone with an interest in birds institution for graduate training in ornithology. From its beginning, in Eastern North America. This plate of
could learn to accurately identify them was Ludlow Griscom, an orni- Cornell had a strong program in zoology, but once Dr. Arthur Allen terns and skimmers from a 1939 edition
thologist at the American Museum of Natural History. arrived it earned a reputation as an important center for bird studies. of the book shows the unique system of
arrows Peterson used to indicate impor-
Griscom, an early Ph.D. student of Arthur Allen at Cornell Uni- Allen wasn't the first person to earn a Ph.D. by studying birds, but his tant field marks on each bird. Today, Pe-
versity, was instrumental in promoting the field identification of birds research was the first to be widely publicized. His Ph.D. dissertation, terson guides are the standard by which
based on characteristics that could be easily observed in wild birds. The Red-winged Blackbird:A Study in the Ecology of the Cattail Marsh, all other field guides are judged. "Terns
His book Birds of the NewYork City Region, published in 1923, was an published in 1914, set a new standard for documenting the ecology and Skimmers" from A Field Guide to
the Birds: Giving Field Marks of All Spe-
inspiration to many young bird watchers. It was especially important and life history of a bird species. A year after he graduated, Allen was
cies found East of the Rockies. Copyright
to the young enthusiasts of the Bronx County Bird Club, a local group offered a position as an instructor of zoology at Cornell. In 1915 he 1939 by Roger Tory Peterson. Reprinted
that regularly watched birds in the New York City region during the was promoted to assistant professor of ornithology and developed the by permission of Houghton Mifflin Com-
1920s and '30s. One member of this group was the now-legendary first graduate program in ornithology in America. pany. All rights reserved.

Roger Tory Peterson. An artist and teacher, Peterson had an uncanny Many ofAllen's students, including Ludlow Griscom, John Emlen,
ability to recognize birds in the field, and he took Griscom's ideas to Peter Paul Kellogg, Olin S. Pettingi II, Jr., and George M. Sutton, went
the next level. By organizing groups of birds in similar poses, using on to become leaders in emerging biological disciplines. In addition

Cornell Laboratorq of Omitliologq Handbook of Bird Biologq

1-1.38 Sandq Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective 1-1.39

Figure H-38. Peter Paul Kellogg, Arthur ogy programs. Among these were Case Western Reserve in Ohio, the
A. Allen, and James Tanner: Seen here University of Kansas, and the University of Mich igan.Today over thirty
with photographic and sound recording universities in North America offer graduate degrees with the oppor-
equipment, Peter Paul Kellogg (left) and
tunity to pursue advanced studies of birds.
Arthur Allen (center) were leaders in de-
veloping the technology to record bird As academic research has expanded, so has the body of knowl-
sounds. The success of this technology, edge concerning birds. Beyond classification and life history studies,
along with the belief thatthe public could birds have served as models for studies in a diversity of biological fields,
contribute to the professional study of
including biogeography, evolution, mating systems, population dy-
birds, led Allen to found the Cornell Lab
of Ornithology and its Library of Natural
namics, ecology, animal communication and learning, neurobiology,
Sounds. Photo courtesy of Cornell Lab of and conservation. In this way, birds have helped us develop a better
Ornithology Archives. understanding of the natural world.

Bird Conservation, Bird Watching, and the Age of Technology

Birds and bird watchers have been critical to the field of wild-
life conservation. Because birds are relatively accessible to observers,
they are important warning flags for the wide-scale environmental
changes caused by people. Growing public concern about the fate of
birds has been key to passing federal legislation protecting birds and
other wildlife. The Lacey Act of 1900 was the first federal legislation
offering some protection for birds, and it came about largely through
the efforts of the AOU bird protection committee, the U. S. Biological
Figure H-39. Aldo Leopold: Considered
to his impressive list of academic progeny, Allen was one of the first Survey, and Audubon supporters. These groups also helped to create
the father of modern wildlife manage-
professors to teach courses in wildlife conservation and management. the first national wildlife refuge—Pelican Island in Florida—home to a ment, Aldo Leopold is shown here pre-
He also was a leader in popularizing birds—offering many courses to colony of nesting Brown Pelicans. The Audubon Society also played a paring to weigh an American Woodcock
the public on bird identification and photography, and writing many key role in passing the Federal Migratory Bird Treaty Act of 1918, a law as part of his field research. Leopold's
articles for Bird-Lore and National Geographic. Through the work of 1949 book, A Sand County Almanac,
that for the first time protected all migratory birds in America. The En-
focused on environmental stewardship
ArthurAl len and Peter Paul Kellogg, along with the financial support of dangered Species Act of 1973, re-authorized in 1988, gave even more and the ethical use of land. Photo by
Albert Brand, Cornell became a leader in developing the technology to weight to securing the future of endangered and threatened birds. The Robert Ockting, courtesy of The Aldo
record bird sounds (Fig. H-38). This tradition continues to grow today Wild Bird Conservation Law, passed in 1992, banned the import of all Leopold Foundation Archives.
with the Library of Natural Sounds and Bioacoustics Program at the birds listed by CITES (the Convention
Cornell Lab of Ornithology. on International Trade in Endangered
Close on Allen's heels, academically, was Joseph P. Grinnell of Species of Wild Fauna and Flora). For
the Museum of Vertebrate Zoology at the University of California at more information on legislation af-
Berkeley. Annie Alexander, a wealthy naturalist and collector, founded fecting birds, see Chapter 10.
the museum in 1909 and appointed Grinnell its first director. Grinnell Twentieth century nature writ-
earned his Ph.D. in 1913 at Stanford University by studying the mam- ers and artists have done their part to
mals and birds of the Lower ColoradoVal ley; a study now considered a instill an environmental ethic in the
classic in biogeography. After he earned his degree, Grinnell's appoint- American public. Among the classics
ment was expanded to include a professorship in the Department of are Aldo Leopold's A Sand County
Zoology at U.C. Berkeley. Grinnell raised ornithology to new scientific Almanac (1949), which focused on
levels by setting new standards for collecting expeditions—empha- the ethical use of land (Fig. H-39),
sizing careful note-taking and record keeping, and accurate labeling and Rachel Carson's Silent Spring
of specimens. He also placed considerable emphasis on accumulating (1962), which indicted the use of pes-
and carefully documenting data on each species. Li keAl len at Cornel I, ticides. There are many more each
Grinnell produced an impressive academic line, including students book nudging the reader forward to
such as Alden Miller, Frank Pitelka, Ned Johnson, Charles Sibley, and greater awareness and appreciation
Robert Storer. of the natural world. Among the 20th
Although Cornell University and the University of California at century artists, Louis Agassiz Fuertes
Berkeley were the most prolific academic institutions in the 1920s stands out for his ability to capture,
and '30s, several other universities also established active ornithol- with pen and brush, the essence of

Cornell Laboratorq of Ornithology Handbook of Bird Biologti

H.40 Sandq Podulka, Marie Eckhardt, and Daniel Otis Birds and Humans: A Historical Perspective H.41

Mean number of birds

reported at a site.

Figure H-40. American Kestrel by Louis the living bird (Fig. H--40). Although he died in 1927, his work is still
Agassiz Fuertes: Fuertes' ability to cap-
unsurpassed and his influence is apparent in the paintings of many art-
ture the essence of a bird's character is gives birders and researchers all over the world a chance to view and Figure H-41. Abundance and Distribu-
exemplified by this American Kestrel
ists working today. Other great bird artists of the 20th century include
interpret the results instantaneously. Other web sites, such as one tion of Downy Woodpeckers as Record-
feeding on a grasshopper. This painting George Miksch Sutton, Roger Tory Peterson, Larry McQueen, Robert ed by Great Backyard Bird Count Par-
hangs in the halls of the Cornell Lab of Bateman, and Don Eckleberry. operated by the United States Geological Survey's Patuxent Wildlife
ticipants in February 2000: The power
Ornithology in Ithaca, New York, and is Today, bird watching has become big business. Bird feeders, Research Center, also function as a clearinghouse for information on of the Internet is shown in this example
one of the most popular among the gen- bird populations. At this one site, birders and researchers can access from the Great Backyard Bird Count
bird foods, bird baths, binoculars, telescopes, field guides, books,
eral public. Courtesy of Cornell Lab of (GBBC), an annual continentwide sur-
magazines, audio and video tapes, computer software, guided bird- data and other information from a variety of sources, including the
Ornithology. vey that occurs during a four-day period
ing tours, checklists, and birding festivals all contribute to a multi-bil- North American Breeding Bird Survey, hawk migration counts, night
each February. This map, which depicts
lion dollar industry. Binoculars and telescopes, once engineered for bird monitoring, marsh bird monitoring, and the Colonial Waterbirds the late-winter distribution of Downy
military use, are now tailored to the needs of bird watchers. Beyond Inventory and Monitoring Program. Woodpeckers throughout North Amer-
fueling the growth of this lucrative industry, however, volunteer bird Because the Internet can handle bird distribution and abundance ica, is based on 22,500 individual re-
data from huge numbers of observers so rapidly—analyzing and dis- ports submitted over the Internet during
watchers have become vital to the science of ornithology—counting,
the GBBC of February 2000. The GBBC
atlassing, monitoring, studying, and conserving North America's bird playing in minutes data sets that previously might have taken years
is a joint project of the National Audu-
populations. to input and process—it is a powerful conservation tool (Fig. H 41).
-
bon Society and the Cornell Lab ofOrni-
Today, computer and Internet technologies are poised to revolu- Having instant access to large amounts of data permits scientists to thology. Copyright BirdSource.

tionize bird watching and the role of the volunteer bird observer once evaluate changes in bird populations over time, allowing conserva-
again. An unprecedented amount of information is available on the tion biologists to take action while species are still relatively common.
Internet to help people identify birds by sight and sound, and under- When bird watchers take part in these on-line counts and other bird
stand more about their life histories. For example, BirdSource—an in- watching programs, their observations are making valuable contribu-
teractive web site administered by the Cornell Lab of Ornithology and tions to bird conservation.
the National Audubon Society—allows users to submit and retrieve
massive amounts of data collected through several different programs,
such as Project FeederWatch and the Christmas Bird Count. Using Suggested Readings
a complex database and associated computer software, BirdSource Barrow, Mark V. Jr. 1998. A Passion for Birds, American Ornithology after
can generate geographical distribution maps and other sophisticated Audubon. Princeton, New Jersey: Princeton University Press.
graphics and tables almost immediately. Such rapid data processing

Cornell Laboratorg of Ornithology Handbook of Bird Biologu

 H.42 Sandq Podulka, Marie Eckhardt, and Daniel Otis

Buxton, E. J. M. 1985. "Birds in Poetry." pp. 475-478 in A Dictionary of Birds,

H ed. by B. Campbell and E. Lack. South Dakota: Buteo Books. 670 pp.
Feld, Steven. 1990. Sound and Sentiment; Birds, Weeping, Poetics, and
Song in Kaluli Expression, Second Edition. Philadelphia, PA: University of
Pennsylvania Press.
Hal l-Craggs, J. M. and R. E. Jel I is. 1985. "Birds in Music." pp. 369-372 in A
Dictionary of Birds, ed. by B. Campbell and E. Lack. South Dakota: Buteo
Books. 670 pp.
Lambourne, L. 1985. "Birds in Art." pp. 23-25 in A Dictionary of Birds, ed. by
B. Campbell and E. Lack. South Dakota: Buteo Books. 670 pp.
Laubin, Reginald and Gladys. 1976. Indian Dances of North America; Their
Importance to Indian Life. OK: University of Oklahoma Press.
Roseman, Marina. 1991. Healing Sounds from the Malaysian Rainforest,
Temiar Music and Medicine. Berkeley and Los Angeles: University of
California Press.
Stresennan, Erwin. 1975. Ornithology, From Aristotle to the Present. Cam-
I ntroduction:
bridge, MA: Harvard University Press.
Turner, G. E. S. 1985. "Birds in Folklore." pp. 233-234 in A Dictionary of Birds,
ed. by B. Campbell and E. Lack. South Dakota: Buteo Books. 670 pp.
The World of Birds
Kevin J. McGowan

Every child knows what a bird is. Birds exist on every

continent, in every climate, and over every body of water.
Everyone has seen them and recognized them. But what
exactly makes a bird a bird?
Like fish, amphibians, reptiles, and mammals, birds are verte-
brates. That is, they are supported along the back by a series of small
bones, the vertebral column. Like many vertebrates, birds lay eggs.
Only reptiles and birds lay eggs with a tough shell that allows the
embryo within to remain alive out of water. Like some reptiles (croc-
odiles and alligators) and all mammals, birds have four chambers in
their hearts; like mammals, they are endothermic ("warm-blooded").
Endothermic animals can regulate their body temperatures physio-
logically, and thus are less dependent on ambient temperatures for
survival than ectothermic, or "cold-blooded," animals. Using the heat
energy they produce by burning (digesting) their food, endothermic
animals keep their bodies relatively warm—at the optimal temperature
for the chemical reactions necessary for life. Being endothermic al-
lows birds and mammals to be active on days so cold that ectothermic
animals such as snakes and insects could not move. Endothermy has
its costs, however; most significant is the large amount of energy, and
therefore the great volume of food, that is required to produce heat. An
ectothermic snake needs to eat only once every few weeks, whereas
an endothermic bird would starve in just one day without food.
Cornell Laboratorq of Ornithology
1.2 Kevin J McGowan
. Chapter 1— Introduction: The World of Birds 1.3
Figure 1-1. Barn Swallow: Feathers are
unique to birds. Here, a Barn Swallow Ornithological Terms
stretches its right wing, providing an ex-
cellent view of the individual feathers. ■ Ornithology, the scientific study of birds, embraces a vast store
Photo by Marie Read. of knowledge acquired by many thousands of researchers. Over the
years, these scientists have developed a terminology for certain struc-
tures, processes, and concepts that may strike nonscientists as being
unnecessarily technical. For some terms this may be true, but many
other technical terms are used because no adequate or concise substi-
tutes exist in everyday language. Technical terms also help scientists to
convey very specific information with a minimum of confusion, in the
same way that legal wording allows members of the legal profession
to avoid ambiguity in contracts. This Handbook of Bird Biology nnini-
mizes the use of technical terms, using them only when necessary to
clearly explain the material. To get you started, a few basic directional
terms are described in Sidebar 1: Which Way is Up?

The Form of a Bird

■ Undoubtedly, you know what "a bird" looks like. But how closely
and carefully have you really looked at a bird? Have you ever noticed
Unique to birds are feathers, outgrowths of the skin that cover the scales on the legs? Have you seen the small, whisker-like feathers
and streamline the body (Fig. 1-1). Another special feature of birds, around the bills of insect-eating birds? Do you know where a bird's
perhaps the most obvious, is their ability to fly (Fig. 1-2). Although knee is, or its ankle? One goal of the first section of this chapter is to
flight is not exclusive to birds—bats, for example, have also evolved help you understand the basic form of a bird. This knowledge provides
true flapping flight—no other vertebrate is so thoroughly modified for a framework within which you will be able to identify, describe, com-
proficiency in the air. Most birds can fly, and those that cannot, such pare, and eventually classify the different kinds of birds.
as penguins, evolved from ancestors that were capable of flight. A live bird in the hand is an ideal aid for studying bird form. Any
pet bird such as a parakeet, finch, domestic fowl, or Rock Dove (pi-
geon) will do, but a fresh road or window casualty also can be used.
In the United States and Canada, however, the only casualties that can
be legally removed from the road or window sill for personal study
are non-native species: Rock Dove, House Sparrow, and European
Starling. All other North American birds are protected by the Migratory
Bird Treaty Act (see Chapter 10); it is illegal to possess a carcass, a
living specimen, a nest or egg, or even a feather of protected species
without the appropriate permits. To study some avian features, even a
whole chicken or turkey from the grocery store can be helpful. If you
can get one with the head and feet still on it, great, but you can learn
a few things even from one that is ready to cook. If you prefer to learn
Figure 1-2. Northern Harrier in Flight: from live, wild birds, you might go to the park and study the pigeons,
Although not alone in their ability to House Sparrows, or ducks that come to the bread you throw out, or
fly, birds are thoroughly modified for watch the birds at a feeder next to your window. In any way you can,
proficiency in the air. Northern Har-
get up close to birds and observe the details.
riers—slender, long-tailed hawks with
long wings and a conspicuous white For descriptive purposes, the bird's body is arbitrarily divided
rump patch—typically fly low over into seven major regions; each of these, and their major parts, are
-
open fields and marshes, gliding and
tilting from side to side with the wings
, a
f1h r
kW/
004:tett 11:_11c finairi considered in turn. On your subject bird, first note the shape of the
body—how it tapers at both ends, perfectly streamlined for flight. Then
held in a shallow V, as they search for 71
identify the seven main parts: beak, head, neck, trunk, wings, tail, and
meadow voles and other prey. Drawing
by Orville 0. Rice.
27.2' ice hind limbs (Fig. 1-3).
(Continued on p. 1.6)

Cornell Laboratorg of Ornitholom Handbook of Bird Biolo,

 1.4 Kevin& McGowan Chapter 1 — Introduction: The World of Birds 1.5

Sidebar 1: WHICH WAY IS UP?

Kevin J. McGowan
Left or right? Whose left, yours or mine? Behind or in front? Right: Always refers to the animal's right side, not that of
1 Of you or me? Directions can be confusing when they the observer.
use arbitrary reference points. When face to face, my left
is your right, and vice versa. When discussing anatomy, Caudal: Toward the tail.
keeping directions straight is imperative. Unfortunately, Cranial: Toward the head.
many directional terms used in everyday speech are not The body is always caudal to the head; the neck is
specific enough when dealing with parts of the body. Such always cranial to the tail.
words as "lower" or "upper" and "back" or "front" can
be confusing when trying to discuss parts of an animal. When you reach the head or neck and still want to
For example, stand up straight with your hands hanging describe forward positions, what do you do? Use the
at your sides. Are your fingers above or below your el- following:
bows? Hold your hands over your head. Now where are
your fingers in relation to your elbows? What if you were Rostral: Toward the beak. For positions on the head and
standing on your head? It is useful to have terms that can neck.
be understood no matter what the orientation of an animal The nasal opening is rostra) to the ear opening.
Although rostra! is the official term for directions
is, just as it is useful to have similar terms for a boat (port
toward the beak on the head and neck, in much of
and starboard, fore and aft). Whether your bird subject is the literature and in everyday language, cranial and
upside down, on its back, or on its belly, you need one anterior are often used. This course uses the terms in-
term to indicate the direction "toward the head" and an- terchangeably, when their meaning is clear.
other to indicate "toward the tail;" you also need a way to
indicate whether the position of one structure compared Anterior: Toward the front.
to another is closer to, or more distant from, the middle of Posterior: Toward the back.
the body. Such terms exist, and the following list defines Anterior and posterior can be confusing, because
those used throughout the Handbook of Bird Biology to they use an outside frame of reference—the earth.
describe the positions of anatomical structures (Fig. A). For a standing penguin or person, the belly is anterior
and the back is posterior. On a swimming penguin,
however, the head is anterior and the tail, posterior.
Dorsal: Toward the back (the vertebral column). Officially, the terms anterior and posterior should be
Ventral: Toward the belly. used only within the eye and inner ear of a bird. In
These terms do not depend on the orientation of the much of the literature and in everyday language, how-
body. The breast of a penguin is ventral to the back ever, anterior and posterior are used interchangeably
whether the bird is tobogganing along the snow or with cranial and caudal. In places where anterior and
standing upright. posterior are not confusing, this course uses them
interchangeably with cranial and caudal.
Lateral: To the side of the body; away from the midline.
Medial: Toward the midline of the body. Transverse Plane: A vertical plane through a bird, di-
Median: On the midline of the body. viding the body into cranial and caudal portions.
The beak of a bird is median. A bird's outer tail feathers Frontal Plane: A (usually) horizontal plane through a bird,
are lateral to the inner tail feathers. dividing the body into dorsal and ventral portions.
Sagittal Plane: A vertical plane through the long axis of
Distal: Away from the center of the body or from the a bird, extending from head to tail. It divides the body
into left and right portions. Figure A. Anatomical Directions: Researchers use specific terms to refer unambiguously to directions and relative locations on
origin of the structure.
These terms refer to planes of sectioning through an the bodies of animals, as illustrated here. Toward the back is termed dorsal, and toward the belly is ventral; toward the midline of
Proximal: Toward the center of the body or toward the
animal, and are used in the Handbook of Bird Biology the body is medial, toward the side is lateral, and something positioned on the midline of the body is median; toward the center
origin of the structure. of the body is proximal, and away from the center is distal. To describe directions toward the head or tail, cranial and caudal
to describe the perspective from which various sec-
The elbow is distal to the shoulder, but the elbow is tional views of a bird's internal anatomy are shown. are generally used, respectively; but anterior and posterior may be used as well, although their use is sometimes limited to sites
also proximal to the wrist. The tip of a feather is distal within the inner ear and eye. To refer to something in the direction of the tip of the beak, from a point of reference on the head
to its base (the base of a feather is where it attaches to (see inset), the term rostra! is used. The terms left and right refer to the animal's own left and right, not those of the observer. It is
the bird). On a tree, the ends of the branches are distal Now, if you stand straight up with your hands hanging at also useful, for certain anatomical sectional views, to refer to planes cut through an animal. For a bird in the position illustrated,
to the inner branches. your sides, your fingers are distal to your elbows. With a sagittal plane extends vertically from head to tail, a transverse plane extends vertically from side to side, and a frontal plane
----- your hands held over your head, they are still distal. Even extends horizontally. Reprinted and adapted from Manual of Ornithology, by Noble S. Proctor and Patrick J. Lynch, with permis-
Left: Always refers to the animal's left side, not that of when you stand on your head, your fingers remain distal sion of the publisher. Copyright 1993, Yale University Press.
the observer. to your elbows. ■
Cornell Laboratorq of Ornithologg Handbook of Bird Biologq
1.6 Kevin J . McGowan Chapter 1— Introduction: The World of Birds 1.7
Figure 1 —3. Bird Topography: Birds have Head Figure 1-4. Regions of the Head and
seven main topographic regions: beak, Nostril Neck: The head and neck regions are
head, neck, trunk, wings, tail, and hind Upper subdivided into a number of smaller
Neck Beak Crown
limbs. To facilitate identification and Trunk areas. These subdivisions allow re-
Superciliary Line
description, ornithologists divide many searchers and birders to give precise
of these regions further. Drawing by Back descriptions of a bird. Note that the
Lower Beak Forehead
Charles L. Ripper. superciliary line is also called the eye-
Throat brow stripe, or simply the "eyebrow";
Auriculars
and a stripe in the malar region may be
Lore Nape called a malar stripe, a mustache, or a
Rump Breast Malar Region whisker stripe. The close-up view of the
eye shows the upper and lower eyelids
Side of fully open. A third eyelid, termed the nic-
the Neck titating membrane, is partially covering
Uppertail Chin
Coverts Wing the eye, as it sweeps to close from left to
Gular Region right. This translucent, inner eyelid pro-
tects the eye while still permitting birds
Side Jugulum to see. Drawing by Charles L. Ripper.

Belly Upper Eyelid

1;41:4
Flank
Nictitating
Hind Limb Membrane
Undertail
Coverts
\, Iris

Lower Eyelid

Bill Head and Neck

The bill has two parts, the upper beak and the lower beak; the As you read this section, refer to the profile of the head and neck in
upper beak slightly overlaps the lower beak when the bill is closed. Fig. 1-4, as well as Fig. 2-8. Caudal to the upper beak are theforehead,
As you study birds, you undoubtedly will come across other terms for crown, and nape. The nape is actually part of the neck. Running back
the upper and lower beak, such as the "maxilla" (upper) and "man- from the upper beak and below (ventral to) the boundary of the fore-
dible" (lower), or the "upper and lower mandible." Because "maxilla" head and crown is the eyebrow stripe or superciliary line (also called
technically refers to a specific bone, and "mandible" can have various simply the "eyebrow"), which is distinctively colored in some birds.
meanings, this course follows the use by Lucas and Stettenheim (1972) The eye is very large. Only the dark pupil and surrounding col-
of "upper and lower beak" to refer to the bird's jaws. The bones that ored iris show; much more of the eyeball lies under the skin. In most
make up the beak are the premaxilla (upper beak) and dentary (lower birds, the combined size of the eyes is larger than the brain! In some
beak) (see Figs. 3 33 and 4-8).
-
species, the eye changes color as the bird ages. American Crows
Although today the terms "bill" and "beak" are used inter- have grayish blue eyes while in the nest, but their eyes quickly turn
changeably, the term "beak" was originally used to describe the de- the same dark brown as adults' eyes within a month or so. (Oddly,
curved (downwardly curved) bills of birds of prey. Each half of the Australian crows and ravens start out with dark eyes that turn to pale
jaws has a bony core that is attached to (and generally considered white as adults.) Birds have three eyelids: the upper eyelid, the lower
a part of) the skull, and a horny outer covering, or sheath, called the eyelid, and a "third eyelid," the nictitating membrane—a thin, trans-
rhamphotheca (see Fig. 3-33). The rhamphotheca—which also makes lucent fold that sweeps across the eye sideways from front to back.
up the tip and sharp, biting edges of the beak—grows throughout the The nictitating membrane moistens and cleans the eye and protects
life of a bird, like claws and fingernails, but continual abrasion during its surface. All birds blink from time to time, but most blink regularly
feeding normally keeps its length constant. Birds in captivity often do only with the nictitating membrane. In raptors and other predatory
not get enough to chew on to wear the rhamphotheca down properly, birds, the nictitating membrane protects the eyes as the bird pursues
so the bill grows too long and must be trimmed.Toward the base of the prey through heavy cover, such as a blackberry thicket. Birds close
upper beak, on each side, is a nostril or naris. Its shape varies among their eyes—usually by raising the lower lid—when they sleep or when
different species of birds; in some it is partially concealed by a tuft of their eyes are threatened by something. If you have a live bird, gently
feathers, and in others it may be absent. move your finger toward the eye and watch the response. Does the

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

1.8 Kevin J . McGowan Chapter 1 — Introduction: The World of Birds 1.9
Figure 1-6. Bird Neck: All birds have
long necks. Their necks do not appear
long because they are folded in an S
shape and concealed beneath feathers.
Even birds such as quail, chickadees, and
the hummingbird pictured here, which
appear to have little or no neck, actually
have relatively long necks. The large dark
area in this diagram is the skull, and the
long, thin, dark structure curving down
from it indicates the chain of vertebrae
that make up the neck. Adapted from Gill
Hummingbird (1995, p. 94).

Auricular
Feathers
Trunk
The rather compact trunk of birds is divided into the back, rump,
Ruffed Grouse breast, belly, sides, and flanks (see Fig. 1-3). Often the sides and flanks
are partly concealed by the wings and visible only when the bird is
in flight.

Figure 1-5. Auricular Feathers of a nictitating membrane react first, or one of the eyelids? Around the eye
Wings
Ruffed Grouse: The auricular feathers many birds have a circle of differently colored feathers or skin referred
cover the external opening of the ear. The wing of a bird (Fig. 1-7) is structured like the forelimb of any
to as the eye ring.
Unlike most feathers, the auriculars amphibian, reptile, or mammal, with the same three divisions: the
The small space between the eye and the base of the upper beak
have an open texture, providing a upper arm, or brachium (pronounced BRAKE-e-um); the forearm, or
protective screen from wind noise and is the lore. In some birds the lores are distinctively colored; in a few
antebrachium; and the hand, or manus. To understand the wing, com-
debris, while at the same time helping birds they are unfeathered. The small space caudal to the base of the
pare it to the human forelimb as you go along (Fig. 1-8). If you have a
to channel sounds into the ear—much lower beak is the cheek or malar region. A malar stripe is sometimes
like the external ear flaps of mammals. chicken wing, boil it until the meat comes off and look at the bones.
referred to as a mustache or whisker stripe.
In many birds, the auriculars are only vis-
ible upon close inspection. Inset shows
Birds, obviously, have no external ear flaps. Below and behind
detail fora domestic chicken, with many the eye l ies a patch of feathers, the auriculars, which conceals the ear
auricular feathers cropped near the base opening (Fig. 1-5). The feathers are specially formed, having an open
to reveal the external ear opening. From Carpels Manus
texture that provides a protective screen, yet helps to channel sounds
Lucas and Stettenheim (1972, pp. 99 Radiale Ulnare
into the ear, much like the ear flaps of mammals.The auricular feathers
and 100). Brachium
also act like a wind screen on a microphone, reducing the noise of the
Phalanx of Digit 1
wind in the ear opening. Antebrachium

Under the lower beak is a very small area, the chin, followed Phalanges of
backward by the gular region, and finally the jugulum, which is the Digit 2
lower part of the neck. When describing plumage, people often com-
bine the gular region and jugulum into the "throat." Lying on each side
between the jugulum and the nape is the side of the neck. Carpometacarpus
Ulna
All birds have long necks. Although some birds, such as swans Phalanx of
Digit 3
and herons, obviously have long necks, even birds that appear to have Radius
no necks at all, such as quail or chickadees, in fact have long necks.
These birds typically keep their neck folded in an S shape, and the Figure 1-7. Bones of the Wing: The wing of a bird, like the forelimb of any amphibian, reptile, or mammal, is divided into three
covering of feathers hides the details (Fig. 1-6). If birds were mammals, sections: the brachium (upper arm), the antebrachium (forearm), and the manus (hand). The brachium is supported by a single
none would have necks relatively shorter than a deer or horse. When a long bone, the humerus; the antebrachium, by two long bones of unequal size, the thicker ulna and the smaller radius. The manus
consists of a series of bones that vary in number and size. Notice that the bird "hand" has fewer bones than the highly dexterous
bird dies, the muscles relax and the long neck becomes apparent. The
human hand (see Fig. 1-8) because many bones are absent or are fused to form a rigid structure important for flight. In birds, the
long, floppy neck of dead birds has given rise to the misconception that carpals (wrist bones) are reduced to two bones, the radiale and ulnare, and the metacarpals (palm bones) are fused with some of
birds commonly die by breaking their necks. (In fact, most birds that the carpals to form a single, large carpometacarpus. The finger bones (phalanges) of only the first three digits remain, with only
strike windows die of head trauma or other internal bleeding.) digit 2 having more than one bone. Drawing by Charles L. Ripper.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

1.10 Kevin J. McGowan Chapter 1— Introduction: The World of Birds
Manus Bend of Figure 1-9. Patagia of the Wing: A fold
Human Arm
the Wing of tough skin, the patagium, extends
Brachium Patagium
from the brachium to the antebrachium,
connecting the shoulder to the wrist.
Antebrachium
Covered with feathers, it forms the
leading edge of the inner wing during
flight. A smaller fold of skin, the humeral
patagium, extends from the brachium to
the trunk. During flight, the long wing
feathers must be able to withstand the
I force of the air moving by them. A band
of tough, tendinous tissue, the postpa-
Carpals tagium, surrounds the bases of the flight
Bird Wing Postpatagium feathers, supporting and holding them in
Metacarpals
Brachium ) place. Adapted from Proctor and Lynch
Phalanges Humeral (1993, p. 101).
n fel)/ .1( lot Patagium

Manus
Spread outthe wing of your specimen and, by feeling underneath,
identify the big bones under the skin. Observe the fold of skin, the
patagium, that extends from the brachium to the antebrachium, essen-
tially connecting the shoulder to the wrist (Fig. 1-9). The patagium is
covered with feathers, and forms the leading edge of the inner wing in
flight. A smaller humeral patagium extends from the brachium to the
trunk. The prominent angle at the wrist is commonly called the bend
Fiume, u
of the wing. Gently open and close the wing, observing the action at
each main joint. The wing of a bird is not as mobile as your arm. Note
Primaries that the wing cannot rotate in a full circle at the shoulder as your arm
can, nor can the manus rotate at the wrist as yours can.The joints of the
Secondaries
wing are formed only for specific movements in flight, whereas those
in your arm are designed for a multitude of differentfunctions. Chapter
5 describes precisely how a bird uses its wings in flight.
Figure 1-8. Bird Wing Compared to In both the wing and human arm, note that the brachium is sup- Refer to Fig. 1-10 as you work through the following information
Human Arm: Although the wing and ported by one long bone, the humerus; the antebrachium, by two long on the feather groups of the wing. The longest wing feathers are the
arm have the same three main sections,
bones of unequal size, the radius and the larger and thicker ulna; and flightfeathers, or remiges (singular, remex), the long, stiff quills that ex-
the manus and antebrachium make up a tend distally from the bones. The rem iges are stiff feathers that form the
larger portion of the bird wing, providing
the manus, by a series of bones that vary in number, size, and thick-
a long attachment site for the primary ness. These are wrist bones, or carpals; palm bones, or metacarpals; predominant air-catching portion of the wing. Above these feathers are
and secondary flight feathers. These two and finger bones, or phalanges (singular phalanx). Observe that the the coverts, the smaller feathers that overlap the flight feathers at their
sections are what you normally see as wing has fewer bones than the human arm because many are fused bases like evenly spaced shingles on a roof. From two to six (usually
the wing when you watch a bird in flight, three) alular quills (pronounced AL-you-lar; a quill is a feather) project
or absent, leaving two carpals, the radiale and ulnare; one big, fused
as the brachium is short and close to the
palm bone, the carpometacarpus; and four phalanges, all the bones from the phalanx of the first finger (the bird's "thumb"; see Fig. 1-8) at
body—the division between it and the
antebrachium is generally obscured by that remain of the first three fingers. Only the middle finger, with two the bend of the wing. The alular quills make up the alula, sometimes
feathers. The large muscles that move the of the four phalanges, is still large. known as the "bastard wing," which can be spread apart from the rest
wings attach to the humerus, moving the
The skeleton of the wing is significantly lighter than that of the of the wing and is used for fine control of airflow over the wing.
entire wing by moving the humerus. The The rem iges emerging from the man us are the primaries and
alular quills—a small group of feath-
forelimb of any terrestrial vertebrate. The long bones are actually hol-
ers attached to the first digit—form the low; the humerus is even invaded by an air sac from the respiratory those from the antebrachium are the secondaries. By feeling their bases
alula, which helps to keep air flowing system (see Fig. 4-82). Furthermore, compared to your arm, most under the wing, you will find (in flying birds) that all are firmly attached
smoothly over the upper surface of the wings are additionally lightened by having no large muscles. Their to the skeleton by ligaments—the primaries to the bones of the man us
wing. Drawing by Charles L. Ripper. and the secondaries to the ulna. A tough band of tendinous tissue, the
principal movements are controlled by tendons coming from huge
muscles on the breast. This arrangement takes weight away from the postpatagium, also holds the remiges firmly in place and supports each
wing and brings it nearer to the bird's center of gravity—a more stable quill (see Fig. 1-9). Each individual within a species normally has the
arrangement for a creature that must fly. same number- of rem iges. Overlying each remex on the upper surface

Cornell Laboratorti of Ornithologq Handbook of Bird Biologii

1.12 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.13

of the wing is one greater primary covert or greater secondary covert.

Overlying the greater coverts are the median coverts, and overlying Blue Jay
Scapulars
them are the lesser coverts. All are in distinct rows. The remaining
feathers that complete the forward roofing of the wing are the marginal
coverts. Finally, note again the al u lar quills overlying the bases of the
greater primary coverts. - ,

Uppertai I Coverts
Other features of the feathering that you should note are the - Scapulars
Marginal Coverts
scapulars, a group of feathers emerging from the upper surface of the
brachium and shoulder, but not attached to the bone; the underwing
coverts, often collectively called the "lining of the wing"; and the axil-
laries, a cluster of feathers in the "armpit" that are recognizably longer Greater Secondary Coverts
than those lining the wing. Alular Quills

Greater Secondaries
Primary Coverts
Tail
Rectrices
The tail of a bird is technically a small bony and fleshy structure (Tail
Primaries Remiges
marking the end of the vertebral column, but most people, including Feathers)
(Flight Feathers
ornithologists, use the term "tail" to mean the feathers arising from the of the Wing)
"official" tail. The long, stiff flight feathers of the tail are the rectrices
(singular, rectrix); the shorter feathers overlying their bases, above
and below, are the coverts (called the uppertail coverts and undertail
coverts, respectively). The rectrices are paired, one member of each
Marginal Coverts
pair on each side of the tail, with no feather in the middle (see Fig. 3 - 7).
Median Secondary Coverts
Most birds have five or six pairs, but some, like the Ruffed Grouse, have
Greater Secondary
Primaries
more. Like the flight feathers of the wing, the number is the same in Coverts

each species (with only the occasional mutant). Note that when the Lesser Secondary Coverts
Alular Quills
tail is not spread, each rectrix is overlapped by the one next to it; the Alular Quill Coverts
exception is one of the middle pair, which lies on top. Because the
middle (or "deck") feathers protect the other feathers, they often are Alular Quills
Underwing
Coverts
the most badly worn of the rectrices.

Hind Limbs
As in the wing, the structure of the bird's hind limb is similar to
that of a human, with three divisions: the upper leg, or thigh; the lower
Secondaries
leg, or crus; and the foot. Unlike the hind limb of a human, however,
the foot has been elongated and modified into two functional sections,
more like the hind limb of a horse or dog.
In most birds, the thigh bone is rather short and often hidden by
body feathers. Because of the elongated lower leg and foot, a bird has
three elements to the leg, not just two as in the human leg. Note that Great Egret
birds' knees bend in the same direction that yours do, but the actual
location of the knee can be confusing. Just as the length of the neck is
hidden by posture and feathers, so, too, is the thigh hidden from sight,
making the ankle appear to be the knee.
The hind limb of a bird and human are compared in Figure 1-11. Figure 1-10. Feathers of the Wings and Tail: The major groups of feathers are illustrated in dorsal view on a Blue Jay, and in ventral
First, notice that in both, the thigh is supported by one long bone, the view on a Great Egret. Note that the details of feather arrangement—such as number, size, and shape—vary dramatically among
femur. Next, note that in humans the crus (lower leg) is supported by different species, but that the same main groups of feathers are present in most birds. The inset, a dorsal view of a Rock Dove
two long bones, the tibia and fibula, and the foot is composed of a se- wing, shows a detailed view of the secondary coverts. See text for a description of each feather group. Blue Jay and Great Egret
reprinted from Manual of Ornithology, by Noble S. Proctor and Patrick]. Lynch, with permission of the publisher. Copyright 1993,
ries of bones: the ankle bones (tarsals), the instep bones (metatarsals),
Yale University Press. Inset adapted from Proctor and Lynch (1993, p. 59).

Cornell Laboratorq of Ornithologq Handbook of Bird Biologti

1.14 Kevin J . McGowan Chapter 1 Introduction: The World of Birds 1.15
and the toe bones (phalanges). Compare these bones with those in the
bird and you will see numerous differences.
In the crus of a bird there is only one long bone, the tibiotarsus,
extending between the knee and heel (this is the chicken's "drum-
stick"). The tibiotarsus is a fusion of the tibia with two or more of the
tarsal bones. What there is of the fibula is a needlelike bone (perhaps
you have noticed it when gnawing on a drumstick) running two-thirds
of the way down the side of the tibiotarsus. In some birds, such as the
turkey, the tendons that connect the leg muscles with the toes are
calcified (stiffened by deposited calcium salts, like those in bone) and Figure 1-12. Primitive Foot: The feet of
may appear to be small, thin bones. the earliest terrestrial vertebrates had five
The foot of a bird contains one long bone, the tarsometatarsus, forward-pointing toes, numbered from
Femur medial to lateral. The four (at most) toes
and the phalanges of the toes. The tarsometatarsus—sometimes called
of birds are thought to correspond to toes
Knee simply the metatarsus—represents a fusion of tarsals (ankle bones) one through four of these vertebrates.
and metatarsals (instep bones) and forms the skeleton of the tarsus,
Tibiotarsus
(Fused Tibia, the general name for the section of the foot between the heel and toes.
Fibula, and Some Birds have, at most, four toes, and each one bears a claw. The toes are
Tarsal Bones)
given numbers to correspond with those of birds' ancestors. The ear-
Crus
liest vertebrates had five toes, all of them pointed forward (Fig. 1-12),
Ankle
Heel Joint numbered (by researchers) from the inside out (medial to lateral). In
birds, the first toe (if present) projects backward and is called the hallux.
Tarsometatarsus Crus
Thus, the second toe of early vertebrates is the innermost toe of birds.
(Fused Tarsals and Meta-
tarsals)
Many species of birds have no hallux, with only three forward-facing
Hallux
toes. Ostriches have only two toes (Fig. 1-13). Because the tarsus is
elevated, with the toes attached to the distal end, a bird walks on its
Metatarsals
toes only, keeping its heel off the ground.
Foot
A bird's leg and foot, like the wing, have been structurally light-
ened. The femur, like the humerus, receives an air sac from the respi-
Tarsals ratory system. The toes and most, if not all, of the tarsus have only a
(Ankle Bones) thin, scaly covering. Movements of the toes are controlled by tendons
3
4 extending from muscles in the crus.
Foot
If you have a live bird or a freshly killed specimen, slowly extend
its hind I imb to ful I length, then flex it closeto the body, while watching
the movement of the toes. You will observe that when you extend the
limb the toes open, and when you flex it, the toes close into a position
for grasping. The toes close because of tension placed on the tendons Figure 1 13. Ostrich Foot: In many fast-
-

running animals, natural selection has

as the heel bends (Fig. 1-14). When a bird squats on a perch to sleep,
reduced the surface area contacting the
the toes thus automatically grip the perch and stay locked onto it until ground. Just as the feet of horses are re-
Figure 1-11. Comparison of Human Leg and Bird Leg: The leg sections. The upper section consists of a single long bone, the
the bird awakens and stands up. duced to hooves, the feet of Ostriches
of both birds and humans has three main divisions: the thigh tarsometatarsus (also called simply the metatarsus), formed by
are reduced to two short, stout toes, one
(upper leg), the crus (lower leg), and the foot. In both birds and the fusion of the remaining tarsals and metatarsals. The lower
poorly developed. On the bottoms of
humans, the thigh is supported by a single bone, the femur. section consists of the phalanges. Birds have four toes, at most,
Two bones, the tibia and fibula, support the crus in humans. In although their arrangement differs from species to species. Diversity in Bird Form both toes aresoft, elastic pads, which pre-
vent the feet from sinking into soft sand.
birds, however, the crus is supported by a single long bone, the
tibiotarsus—the familiar "drumstick" of a cooked turkey. The
One common arrangement, shown here for a bird's right foot,
is with the first toe, termed the hallux, pointing back, and three ■ Now that you are familiar with the form of a bird and have become The flightless Ostriches rely on their abi I-
ity to maintain a steady running speed
tibiotarsus is formed by the fusion of the tibia with two or more toes in front, numbered from medial to lateral. At first glance, acquainted with the names for the different parts, you are prepared
of about 31 miles (50 km) per hour—to
of the tarsal (ankle) bones. The fibula is present, but reduced the sections of a bird's leg can be confusing. The thigh is short to take a broad look at the ways birds differ from one another in form escape predators in the open savannas
to a fine, needlelike bone running about two-thirds of the way and, along with the knee, usually hidden by the body feathers.
and appearance. This step is essential before learning how birds are and deserts of Africa. From Birds: Read-
down the side of the tibiotarsus. In addition to the tarsal (ankle) Thus, the joint that appears to be a knee bending backward is
bones, the human foot consists of metatarsals (instep bones) actually the ankle. A bird's knee bends in the same direction as
classified and named. ings from Scientific American, edited by
Although the ability to fly imposes certain restrictions on size and Barry W. Wilson. Copyright 1980 by W.
and phalanges (toe bones). The bird foot, however, is quite dif- a human's. Birds walk up on their toes, with their heel in the air,
H. Freeman and Company. Used with
ferent. It has been elongated and modified into two functional as do horses and dogs. Drawing by Charles L. Ripper. weight, the range in birds is astonishing—from the male Bee Hum-
permission.

Cornell Laboratorq of Ornitholooq Handbook of Bird Biologq

1.16 Kevin ,J. McGowan Chapter 1— Introduction: The World of Birds 1.17

Knee

Figure 1-15. Bird Sizes: Birds range

in size from the tiny male Bee Hum-
mingbird with a wingspan of 2.6 inches
(65 mm) to the Wandering Albatross
with a wingspan of over 11.5 feet (3.5
m). Here, a hummingbird perches on a
flight feather from the wing of a large
a. Decurved Bill bird. Drawing by Charles L. Ripper.
White Ibis

b. Tubular Nostrils c. Spoon-shaped Bill

Sooty Shearwater Spoonbill

Figure 1-14. The Mechanics of Perch- mingbird with a wingspan of 2.6 inches (65 mm) and a weight of less
ing: In the legs of tree-dwelling birds, than 1/14 ounce (2 gm) to the Wandering Albatross with a wingspan d. Crossed Bill e. Recurved Bill
the tendons from certain muscles extend Red Crossbill American Avocet
of over 11.5 feet (3.5 m) and a weight of as much as 19 pounds (8.6
down the leg behind the ankle to attach
to the tips of the toes. When a perched kg) (Fig. 1-15). The heaviest birds cannot fly; the flightless Ostrich
bird bends its ankle to lower itself onto may weigh 345 pounds (156.5 kg); the Emperor Penguin, 100 pounds
a branch, the bending automatically (45.3 kg). The heaviest of flying birds—the Mute Swan, Wild Turkey,
creates tension on these tendons, which
Kori Bustard, and Great Bustard—weigh up to 20 to 30 pounds (11 to
pulls on the toes, forcing them to close
around the branch. Thus, when the bird
15 kg), with extreme individuals of the large bustards reported up to
is at rest, its toes tightly grasp the perch. 44 pounds (20 kg).
From Birds: Readings from Scientific Perhaps because of their adaptations for flight, all birds are similar
American, edited by Barry W. Wilson. Figure 1-16. Bill Diversity: The bills of birds have been molded broad, flat bill through shallow water from side to side to search
in general configuration, and all are immediately identifiable as birds. by natural selection into a great variety of shapes and sizes, each for small aquatic animals such as crustacea and mollusks. In
Copyright 1980 by W. H. Freeman and
Within these general limits the external form of birds varies widely, suited to a particular foraging strategy. In addition to gathering murky water, however, the spoonbill sweeps its bill just above
Company. Used with permission.
reflecting their specific adaptations both to the habitats in which they food, birds use their bills for fending off predators, courting, the bottom, the curved dorsal and flat ventral surfaces creating
live and to their methods of acquiring food. The following sections nest building, and preening. a. Decurved Bill of White Ibis: The swirling currents that pull prey up off the bottom and into the
White Ibis uses its long, decurved (downward curved) bill to water, where they can be captured more easily. d. Crossed Bill
describe some of the more common variations in the bill, wings, tail,
probe mud and sand for invertebrates. Italso sweeps its bill from of Red Crossbill: The crossed tips of crossbill bills allow them
and feet. side to side in the manner of the spoonbill (see c). b. Tubular to efficiently pry seeds from deep within open or closed cones
Nostrils of Sooty Shearwater: Many birds that spend much of pines or other conifers. e. Recurved Bill of American Avocet:
of their time at sea, and thus must drink salt water, have their The American Avocet sweeps its long, sensitive, recurved (up-
The Bill nostrils at the ends of long tubes on top of the bill. These tubular ward curved) bill from side to side in water, in a similar manner
The bills of birds have different shapes for reaching, picking up, nostrils help with the elimination of excess salt (see Fig. 3-34b). to that of the spoonbill. Drawings by Charles L. Ripper.

and manipulating different types of food (Fig. 1 1 6). Bills can be short,
-
c. Spoon-shaped Bill of Spoonbill: The spoonbill sweeps its

Cornell Laboratori of Omithologq Handbook of Bird Biologq

1.18 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.19

long, stout, thin, pointed, or blunt. Bills may curve up or down, or may The shape of birds' wings is not arbitrary—each is suited to its own Figure 1-18. Tail Shapes: Like beaks
specific purpose. The shape of a wing directly affects the way a bird can and wings, bird tails come in a variety
be faintly or conspicuously notched, spoon-shaped, or crossed. Bills of shapes and lengths. Although the
can be specialized for cutting flesh, filtering small organisms from fly, affecting such things as the amount of lift and drag thatthe wing cre-
functions of different tail shapes are
water, stabbing, grasping, hammering, picking up small insects, or ates when movingthrough the air. Long, narrow, pointed wings are best not well understood, the tails of birds
opening large, hard fruits (see Ch. 4, Oral Cavity, Bill). suited to long-distance flying and soaring over the seas; long, broad, are important in flight and various types
Figure 1-17. Wing Diversity: Wings rounded wings to long-distance flying or soaring over land; short, of displays. Tail shape is determined by
The nostrils (pares) also may have various shapes: oval, circular,
have evolved a tremendous diversity of the relative lengths and shapes of the
or slit-like; sometimes they have bony tubercles in their centers or are rounded wings to short flights in forests and fields; rounded, concave
shapes, each suited to a different flight rectrices (tail feathers). All tails shown
located at the ends of elongated tubes; sometimes they lack a septum wings for quick take-off and rapid escape over short distances; and here are viewed from below. a. Round
style. The four examples here are viewed
from above. In a and b the curves labeled between the two sides (you can look in one and out the other!); and pointed, flat wings for quick wing action and swift flight. Wing shape (American Crow): The rectrices become
"wing curvature" are cross sections sometimes they are surrounded by a fleshy cere or overarched by a and its effect on flight is discussed in more detail in Chapter 5. slightly longer from the outside in (lat-
through the outstretched wing from eral to medial). b. Graduated (Black-
fleshy operculum (see Fig. 3-34). Some birds, such as boobies and billed Cuckoo): The rectrices become
the leading, cranial edge (thicker part
gannets, lack external nostrils altogether. In some cases the function The Tail abruptly longer from the outside in.
of curve, at left) to the trailing, caudal
edge (thinner part of curve, at right). of the peculiarities is known; in many cases, it is not. Nostrils and their c. Forked (Common Tern): The rectrices
The tail is considered long if it is obviously longer than the trunk, become abruptly longer from the inside
They represent the curvature of the various forms are discussed further in Ch. 3.
or short if it is the same length or shorter than the trunk. It is practically out. d. Pointed or Acute (Ring-necked
top and bottom surfaces of the wing.
a. Flat Wings of a Swallow: Swallow absent in a few birds, such as grebes. Usually the tail owes its shape Pheasant): The middle rectrices are
wings have little curvature and are The Wings to the relative lengths of the rectrices and the way they terminate at much longer than the others. e. Emar-
ginate or Notched (Pine Siskin): The
considered flat. b. Concave Wings of the trailing margin (Fig. 1-18). Thus, the tail is square at the end if
The wings are considered long when the distance from the bend rectrices become slightly longer from
a Grouse: Grouse wings are curved
of the wing to the tip is longer than the trunk of the bird, or short when the rectrices are all about the same length (for example, Clark's Nut- the inside out. f. Square (Sharp-shinned
below, and are considered concave.
c. Round Wings of a Hawk: In some this distance is the same or less. Wings are rounded when the middle cracker); rounded, if they become slightly longer from the outside in Hawk): The rectrices are all about the
hawks, the middle primary feathers are primaries are longest, or pointed when the outermost primaries are (for example, American Crow); graduated, if they become abruptly same length. Drawings by Charles L.
Ripper.
the longest, creating a rounded wing tip. longest. They are considered narrow when all the rem iges are short, or longer from the outside in (for example, Black-billed Magpie); pointed
d. Pointed Wings of a Gull: In gulls, the
outermost primary feathers are the lon-
broad when all the remiges are long; concave when the curvature of
gest, creating a pointed wing. Drawings the wing's underside is extreme, orflat when the curvature is unusually a. Round b. Graduated c. Forked
by Charles L. Ripper. slight (Fig. 1-1 7). American Crow Black-billed Cuckoo Common Tern

a. Flat b. Concave
Swallow Grouse

ALL TAILS VIEWED

FROM BELOW

Wing Curvature

ALL WINGS VIEWED d. Pointed or Acute

FROM ABOVE Wing Curvature Ring-necked Pheasant
c. Round
Hawk

d. Pointed
Gull

f. Square
e. Emarginate or Notched Sharp-shinned Hawk
Pine Siskin

Cornell Laboratorc of OrnitholoBq Handbook of Bird Biologq

1.20 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.21
Figure 1-19. Forms ofthe Podotheca:The a. Booted b. Scutellate
tough skin covering the tarsus, termed Thrush Tanager TYPE OF FOOT TOE CONFIGURATION Figure 1-20. Toe Arrangements: Al-
the podotheca, has different forms in (Right Foot) though most birds have four toes, their
different types of birds. The functions arrangement differs among different
of these forms, if any, remain unknown. Anisodactyl groups of birds. Most birds, including
a. Booted (Thrush): In thrushes the nearly all perching (passerine) birds
podotheca is smooth, divided into long, such as the Blue Jay, have an anisodac-
continuous, nonoverlapping scales. b. tyl foot, with three toes directed for-
Scutellate (Tanager): In most birds with Blue Jay ward and a hallux directed backward.
bare legs, such as the songbirds, the Woodpeckers, cuckoos, toucans, owls,
podotheca is broken up into overlapping Osprey, turacos, most parrots, and some
scales. c. Reticulate (Osprey): In some other birds have a zygodactyl foot, in
birds, such as falcons, plovers, and the which two toes point forward and two
Osprey, the podotheca is divided into point backward. (In each schematic,
a network of small, irregular, nonover- Zygodactyl which represents the right foot, the back-
lapping plates. d. Scutellate/Reticulate ward-directed digits are at the bottom;
(American Woodcock): Different sides thus in the zygodactyl foot, toes 1 and
of the feet and legs may have different 4 point backward.) Note that the fourth
forms of podotheca in some species. In c. Reticulate d. Scutellate / Reticulate
toe of some birds with zygodactyl feet,
the American Woodcock, for example, Osprey American Woodcock
such as owls and Osprey, is reversible,
the front of the leg and top of the foot allowing the bird to use it in either a
is scutellate, and the back and bottom Gray-headed Woodpecker Owls and
Osprey forward or backward position. The zy-
surfaces are reticulate. Drawings by godactyl feet of many of the different
Charles L. Ripper. Heterodactyl
bird groups appear to have evolved
independently, and thus are considered
convergent structures. Trogons also
have two toes reversed, but in their feet,
ElegantTrogon
termed heterodactyl, toes 1 and 2 point
backward. Anisodactyl, zygodactyl, and
heterodactyl feet are all well-adapted to
grasp branches. In the syndactyl feet of
many kingfishers and hornbills, the toes
are arranged as in the anisodactyl foot,
but toes 2 and 3 are fused for part of
their length. In the pamprodactyl feet of
or acute, if the middle rectrices are much longer than the others (for some swifts, such as the Chimney Swift,
example, Mourning Dove); emarginate or notched, if the rectrices all four toes point forward, allowing
them to cling to vertical surfaces such
become slightly longer from the inside out (for example, Violet-green
as the inside walls of chimneys and hol-
Swallow); or forked, if they become abruptly longer from the inside Belted Kingfisher low trees (see Fig. 1-28). They can also
out (for example, Swallow-tailed Kite). use toes 1 and 2 against toes 3 and 4 in
a pincerlike fashion, to grasp plants or
I- nest material. Reprinted and modified
Pamprodactyl
The Feet from Manual of Ornithology, by Noble
The tough skin covering the tarsus, the podotheca, has differ- S. Proctor and Patrick J. Lynch, with
permission of the publisher. Copyright
ent forms in different types of birds (Fig. 1 19). It may be smooth
-
1993, Yale University Press.
(booted), broken up into overlapping scales (scutellate), or divided
into numerous small, irregular plates (reticulate). Sometimes the tar-
Chimney Swift
sus is booted only in the back and scutel late in the front, or scutellate
in front and reticulate in back. The functions, if any, of these different
forms are not known.
Most birds have four toes with one toe (the hallux) directed back-
ward, the others, forward. This arrangement is known as anisodactyl
(Fig. 1-20). In a few birds, however, either the second or fourth toe
joins the hallux in its backward direction. In birds with zygodactyl
feet, such as woodpeckers, cuckoos, parrots, and others, the reversed
toe is the fourth. (In some, such as the Osprey and owls, the outer toe

Cornell Laboratorg of Omithologq Handbook of Bird Biolo51,1

1.22 Kevin J. McGowan Chapter 1 — Introduction: The World of Birds 1.23

is reversible—the bird can use it pointing forward or backward. Only all seem to do this equally well—so any ecological advantages that
trogons have heterodactyl feet, with the second toe reversed. In the the different toe arrangements might confer remain a mystery. Toes for
pamprodactyl feet of some swifts, all four toes, including the hallux, perching in trees, climbing, capturing prey, and carrying and manipu-
point forward. Swifts can use their small feet as hooks to hang from lating food are equipped with sharply curved and pointed claws. Toes
the inside walls of chimneys, caves, and hollow trees. In addition, for running and scratching are robust with strong, rather blunt claws
they can grasp plant material or nest material with a lateral, pi ncerl i ke (as in turkeys, quail, grouse, and others). Toes for swimming may be
motion, using toes one and two against toes three and four. Kingfish- webbed, either involving just the three forward toes (ducks and gulls)
ers have three toes forward and one behind, but their feet are termed or including the back one as well (pelicans and cormorants); or all the
syndactyl because the inner and middle toes are united for much of toes may be lobed, as in grebes and coots. In some birds, the toes bear
their length—the ecological advantages, if any, of this arrangement peculiar features whose functions, if any, are unknown. For example,
are not known. Mousebirds (Coliidae)—small, long-tailed, African the hallux claw of larks and some other open-country birds is very
birds—have highly versatile feet, which, although often classified as long, and the forward toes of some shorebirds (such as the Semipal-
pamprodactyl, can actually be used in a variety of configurations: mated Sandpiper) may be partly webbed, even though the birds do
all four toes pointed forward, toes one and four pointed back, or any not normally swim.
combination in between these positions.
The form of the feet of many birds clearly suits their habits and
Feathering
environment (Fig. 1-21). Having one or two toes reversed helps a bird
I n addition to variations in the feathering of the wings and tail that
to grasp perches, but anisodactyl, zygodactyl, and heterodactyl feet
may distinguish different birds, some of the rem iges may be notched or
greatly narrowed and stiffened (as in theAmerican Woodcock), where-
a. Lobed Toes of Grebe b. Webbed Toes of Pelican c. Perching Foot
for Swimming for Swimming of Crow
as the rectrices may be noticeably stiffened and pointed (woodpeckers) Figure 1-22. Female Northern Flicker:
(Fig. 1-22), or may feature partly bare shafts (motmots). Elsewhere on The stiff, pointed tail feathers of wood-
different birds, the feathering may be just as distinctive, if not more so. peckers, such as the Northern Flicker
pictured here, actas a prop when the bird
On the head, the feathers may form crests (cardinals, titmice), discs
is perched vertically or ascending a tree
about the face (owls) (Fig. 1-23), and bristles at the base of the bill trunk. They also brace the woodpecker's
(many flycatchers), or they may be absent on parts or all of the head body while drumming, excavating a nest
(vultures). Feathers on the head, neck, back, rump, and even the flanks cavity, or pecking for insects—allowing
the head and neck to pound forcefully
against a tree trunk. Although it drums
on trees and excavates nest cavities, the
Northern Flicker forages primarily on the
ground, consuming ants and beetles.
Photo courtesy of Isidor Jeklin/CLO.

d. Stout Toes and Strong, Blunt e. Long Hallux Claw of Lark

Claws of Grouse for Running
and Scratching

Figure 1-23. Barn Owl Facial Disc: As

nocturnal predators, owls rely heav-
Figure 1-21. Foot Diversity: The form of a bird's foot reflects its behavior and habitat. Feet modified for swimming have a large ily on sounds to help them locate prey.
surface area to push against the water. This may be accomplished by having lobed toes, as in coots and grebes (a), or by having The facial disc of feathers on many
webbed toes. In birds such as ducks and gulls, only the three forward toes are webbed, but in others, such as cormorants and owls—heart-shaped in the Barn Owl
pelicans (b), all four toes are webbed. Feet for perching in trees, climbing, capturing prey, and carrying and manipulating food illustrated here—enhances the owl's
commonly have toes with sharp, curved claws, as in crows (c). Birds such as grouse (d) that spend a great deal of time on the sensitive hearing by focusing sounds
ground, often running and scratching in the dirt for food, generally have stout toes with strong, blunt claws. Some foot adap- into the ear openings, which are located
tations are not well understood, such as the long claw on the hallux of larks and some other open-country birds (e). Drawing by posterior to the eyes. Photo courtesy of
Charles L. Ripper. J. Robert Woodward/CLO.

Cornell Laboratorq of OrnitholoBq Handbook of Bird Biolom

1.24 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.25
may be greatly lengthened and modified to form conspicuous plumes
or adornments (birds-of-paradise, peafowl).
The colors of feathers not only enhance adornments but quite American
Redstart
obviously provide color patterns that characterize different birds. Thus,
some birds have spotted plumage, others, streaked. Some birds have
color patterns that make them inconspicuous, whereas others have
gaudy patterns. The same species may have colors that conceal it on its
nest and other colors that it uses to attract attention when displaying.
Although birds may seem to have feathers growing from all parts
of the body, feathers in most birds grow from tracts separated by bare Downy
areas. The bare areas are usually concealed, because the feathers from Woodpecker
White-breasted
the neighboring tracts overlap and hide them. Feathers and other ex- Nuthatch
ternal features of birds are discussed in detail in Chapter 3.

Internal A natomq Figure 1-24. Movement in Trees: Many

The diversity of birds is no less apparent in their internal sys- birds are well-adapted to perch and
move about in trees. Most perching (pas-
tems—skeletal, muscular, nervous, circulatory, respiratory, digestive, serine) birds, like theAmerican Redstart,
and urogen ital. Indeed, some birds differ more sharply internally than have anisodactyl feet, allowing them to
they do superficially, thus providing a sound basis for distinguishing easily grasp a branch. Woodpeckers,
them. The internal anatomical differences among species are dis- creepers, and nuthatches have long,
curved claws that act as climbing hooks,
cussed in detail in Chapter 4.
helping them to creep along tree trunks.
Brown Woodpeckers and creepers hitch them-
Creeper selves up tree trunks, using their toes and
Diversitti in Bird Movement tail for suppor t as they move. Nuthatches
either work their way up at an angle, or
■ Birds are masters of the air, but many of them also move quite well descend headfirst, often keeping one
on land: walking, hopping, or running on the ground; or climbing in foot high for suspension and the other
trees. Many species have become proficient around water: swimming, low for support, since their tails are not
modified to act as props. The claw of
diving, or plunging for food. Here, the different methods that birds
their hallux is larger and more strongly
use to move on land and in water are briefly discussed. Bird flight is curved than the claws of their forward-
explored at length in Chapter 5. but their fledglings hop; and the American Robin hops, walks, and runs facing toes, providing the strong grip
that allows them to descend headfirst.
between pauses when foraging for earthworms on a lawn (Fig. 1 25). -

Drawings by Robert Gi I lmor.

Movement on Land For walking in water, some birds—herons, cranes, Limpkins, and
many shorebirds—have long legs with the accompanying requirement
The first birds were probably tree-dwellers; when not flying from
of long necks for reaching far down to feed, and for counterbalancing
tree to tree, they moved from branch to branch by hopping—that is,
the long legs during flight. For walking in mud and on aquatic vege-
moving by a series of jumps with feet together. Later, some of the tree-
tation, some species have exceptionally long toes (gal I inules) (see Fig.
dwellers, such as woodpeckers and creepers, achieved an ability to
3-39e) and claws (jacanas), which prevent them from sinking down
climb by hitching themselves up, using their tail feathers as supports,
(Fig. 1 26).
-

or, like the nuthatches, by jerking themselves up at an angle or climb-

Penguins, because of their torpedo-shaped bodies and stubby
ing down headfirst, keeping one foot high for suspension and the other
legs set far back from their center of gravity, must walk upright with a
low for support (Fig. 1 24).
-

short-stepping gait (Fig. 1 27). If hard pressed to move fast, penguins

-
When many birds left the trees for life on the ground, they began
resort to "tobogganing" on their bellies, propelling themselves vigor-
moving by walking and running—moving the legs alternately. The
ously with both their flipperlike wings and their feet.
changeover from hopping to walking and running was gradual, and
Extremes in the ability to move on land are best represented by
gradations still can be seen. Among the cuckoos, for example, are the
the powerful Ostrich, which can run as fast as 43 miles (70 km) per
awkwardly hopping, arboreal Yellow-billed and Black-billed cuckoos,
hour, and by the swifts, the most aerial of all birds, which cannot hop
and the fast-paced, terrestrial Greater Roadrunner. Although most
or run, and can use their weak feet only for clinging to vertical surfaces
passerine species still hop much of the time, crows and the European
(Fig. 1 28).
-

Starling ordinarily walk; adult larks, pipits, and wagtails walk and run

Cornell Laboratoru of 0 rnithologq Handbook of Bird Biologq

1.26 Kevin j . McGowan Chapter 1— Introduction: The World of Birds 1.27
Figure 1-25. Movement on the Ground: Figure 1-27. Penguin Locomotion on
The first birds probably lived in trees, fly- Land: The flightless penguins, highly
ing or hopping from branch to branch. specialized for swimming, move awk-
As some birds adapted to life on the wardly on land. a. Emperor Penguin
ground, they gradually evolved from Walking: Because the penguin's feet are
hopping (moving both legs at the same set way back on its body to aid in swim-
time) to walking or running (moving Greater Roadrunner •
ming, it is limited to walking upright,
the legs alternately). For example, the with a slow, shuffling gait. b. Emperor
--
Greater Roadrunner runs quickly along Penguin Tobogganing: When they must
the ground, but when its arboreal rela- move quickly on land, penguins resort to
tives—Yellow-billed and Black-billed tobogganing on their bellies, propelling
cuckoos—venture to the ground, they •(G their torpedo-shaped bodies across the
hop. Although most passerines hop, the o t snow and ice by vigorously beating their
• 7., 71
Ins /-1/?-
European Starling walks when on the stubby, flipperlike wings as well as their
ground. Most birds either hop or walk American Robin feet. Drawing of penguin tobogganing
and run, but watch an American Robin &NM/ /g/eup. by Robert Gillmor.
for any length of time and you will no
doubt see that it uses a combination
of movements: walking, hopping, and
running as it searches a lawn for earth-
a. Walking
worms. Drawings by Robert Gillmor.

■ •••••••■•■•■

European Starling

b. Tobogganing

Figure 1-26. Walking in Water: Some

birds—especially herons, cranes, Limp-
kins, and a number of shorebirds—have Great Blue Heron Figure 1-28. Chimney Swift Clinging
long legs for wading in water, the length to a Vertical Surface: Chimney Swifts
reflecting the water depth in which they spend most of their time in the air—for-
may feed. The Great Blue Heron, with aging, courting, and even copulating in
its long legs and neck, usually stalks flight. These streamlined "flying cigars"
fish in shallow water, but sometimes are highly specialized for an aerial life,
wades belly deep along the shorelines with feet so weak that they cannot walk,
of oceans, as well as freshwater lakes, run, or hop. Their feet, with all four toes
streams, and marshes. The Black-necked forward, can be used like small hooks to
Stilt, with somewhat shorter legs, favors cling to vertical surfaces of chimneys,
shallower water and flooded fields, trees, barns, and other structures. Swifts
where it searches mainly for aquatic in- can also move toes 1 and 2 against toes 3
sects. Other birds, notably jacanas and and 4, pincerlike (see Fig. 1-20), to grasp
Northern Jacana
some rails, have long toes that distribute plants and nest material. Although they
their weight over a large surface area, once nested primarily in hollow trees,
like snowshoes, allowing them to walk an increasing number of Chimney Swifts
across muddy areas and floating vege- now nest and roost in chimneys. At dusk
tation such as lily pads. The Northern on a late summer evening, hundreds
Jacana, like other jacanas, has long of Chimney Swifts may gather to roost
claws as well as long toes. Drawing by in a single chimney. Photo courtesy of
Robert Gillmor. Black-necked Stilt Michael Hopiak/CLO.

Cornell Laboratory of Ornithology Handbook of Bird Biology

1.28 Kevin J. McGowan Chapter 1 — Introduction: The World of Birds 1.29

Mallard

Tundra Swan
Backward
Backward Lesser Scaup
Stroke Forward
Forward Stroke
Stroke
Stroke
)
',.. .., ,..., Figure 1-30. Foraging in Water: Birds
Horned Grebe ) -.4
search for food in water in a number of
,:::;:,!:-0:47-
,-,--„,---•-' different ways. Swans, geese, and the so-
Figure 1-29. Horned Grebe Swimming: Movement in Water „,.
-.".-,--.:- --,,
-•-•-r--
-

cal led "dabbling ducks" may dip just the

To increase the surface area that pushes head and neck below the surface to nib-
Although the ancestors of birds were terrestrial and most birds still
against the water, many swimming ble on aquatic plants, or may turn "bot-
birds have either webbed or lobed toes.
depend on land for nesting, many species have adapted so strongly to tom-up" (as in the Mal lard pictured here)
Coots and grebes, such as the Horned an aquatic existence that they spend much of their time swimming. A to reach deeper vegetation. Other birds
Grebe pictured here, have lobed toes. To great number also dive. dive from the water's surface, using the
swim, they move their legs alternately, Most birds swim by alternately moving their feet in the water. wings, feet, or both to propel themselves
as in walking. On the backward stroke, through water in search of plants, fish, or
Swimming birds commonly are aided by either webbed or lobed toes
which generates power, the lobes push other small aquatic animals. Surface div-
the bird forward like oars or paddles. On although some birds, such as moorhens and phalaropes, are excellent ers include penguins, shearwaters, div-
the forward recovery stroke the lobes of swimmers despite having no special toe modifications. Both webs ing-petrels, loons, grebes, cormorants,
coots are folded and the foot of grebes is and lobes act as paddles, pushing against the water on the backward anhingas, mergansers, alcids, coots,
turned, both actions'presenting the least and the "diving ducks"—such as the
(power) stroke, then folding or turn i ng to resist as I ittle water as possible
possible amount of resistance to the wa- Lesser Scaup illustrated here. Drawing
ter. Drawing by Robert Gillmor.
on the forward (recovery) stroke (Fig. 1 29).
-
by Robert Gillmor.
The size of the feet in proportion to body size is commensurate
with the importance of swimming in a bird's l ife. Storm-petrels have
small feet because they swim infrequently; conversely, pelicans have
enormous feet because they spend much of their time swimming. In
most birds, swimming is further aided by broad, almost raftlike bod-
ies that give stability, and by a dense feather coat that holds air for
buoyancy.
Swimming is the principal movement in the water for albatrosses,
shearwaters, petrels in the genus Pterodroma, gulls and other aquatic
scavengers, and phalaropes—all of which gather food on or just below Figure 1-31. Diving fromAir: Many birds
the water's surface. But more than swimming is required of birds that "plunge dive" into water from the air,
obtain food under water. Swans, geese, and the dabbling ducks—teal, the height of the dive depending on the
bird's size and the depth to be attained.
Mallard, Northern Pintail, Wood Duck, and so on—tip up in shallow
The heavy-bodied Northern Gannet
water, reaching down to forage on the bottom (Fig. 1 30). -
scans for schools of fish and then may
Osprey, Brown Pelicans, boobies, gannets, and terns plunge into plummet from as high as 100 feet (30.5
the water from the air, gaining momentum as they descend. The height m) to reach underwater depths of 10 to
of the dive depends on their size and the depths to be attained. The 12 feet (3 to 3.7 m). The lighter-bodied
tern dives from much lower, barely going
heavy-bodied gannets may plummet from 100 feet (30.5 m) to reach
below the water's surface. Terns hover
depths of 10 to 12 feet (3 to 3.7 m). An adaptation consisting of many in place before diving, watching for fish
minute air sacs under the skin acts as a shock absorber when they strike near the water's surface. Osprey, Brown
the water. The lighter-bodied terns plunge from only a few feet, because Pelicans, boobies, and kingfishers also
dive into water from air. Drawing by
they go no deeper than a few inches (Fig. 1 31). -

Northern Gannet Tern Robert Gillmor.

Cornell Laboratorg of Ornithologg Handbook of Bird Biolvi

i 1 30
. Kevin J. McGowan Chapter 1— Introduction: The World of Birds
Not surprisingly, the master divers of the
1.31

bird world are the penguins. Many species

I regularly dive deeper than 65 feet (20 m). The

two largest species, the Emperor and King
penguins, are the undisputed champions. The
large King Penguin has been recorded (with
depth gauges) to dive up to 1,059 feet (323
m), and the even larger Emperor Penguin has
been recorded to a fantastic 1,752 feet (534
m). Even the smallest penguin, the Little Pen-
Arctic Loon guin of Australia, which normally dives to less
than 6 feet (2 m), has been recorded diving to
88 feet (27 m). To dive this deeply, penguins
can hold their breath for long periods, up to
Gentoo Penguin
15.8 minutes for the Emperor Penguin, which
regularly stays under water for 2 to 4 minutes.
Birds diving for such long periods actually stay
under water longer than would be predicted by
the amount of oxygen in their bodies. Penguins
have a number of complex physiological ad-
Long-tailed Duck
aptations, not all completely understood, that
al low them to accomplish these long and deep
Figure 1-32. Swimming Underwater: Penguins, shearwaters, diving-petrels, loons, grebes, cormorants,
Birds specialized for underwater swim- dives.
anhingas, diving ducks, mergansers, alcids, and coots dive from the
ming have streamlined, torpedo-shaped A few other birds, not water birds per
water's surface (Fig. 1 32; see Fig. 1-30). Lacking the momentum of
-
bodies with the feet located far back on se, exploit the food resources of inland wa-
the body. In this position, the feet can an aerial plunge, they power their dives with their feet or wings, or
terways by expertly diving or swimming. The
generate much power and also act as ef- sometimes both. Their feet are suitably located near the rear of the
fective rudders. Loons, grebes, cormo-
Belted Kingfisher is skilled in plunging for fish,
body, just as a ship's propeller is located at the stern. They are heavier
rants, anhingas, and coots use primarily although it cannot swim; the American Dip-
than land birds of similar size because their bones are less pneumatic
their feet to propel themselves through per, residing along swift mountain streams
water. Mergansers and diving ducks, in- (air-filled). Furthermore, to reduce their buoyancy during a dive, they
in western North America, swims—actually
cluding the Long-tailed Duck, may use compress their feather coat and internal air sacs to reduce the air con-
flies—under water and walks on the stream
just the feet while foraging along the bot- tent. Penguins, shearwaters, diving-petrels, and alcids use only their
tom, keeping their wings at their sides, bottom to take insect larvae attached to rocks.
short, bladelike wings to propel themselves through water. Loons,
but use both wings and feet to swim Neither species has specializations for maneu-
to great depths. Although they usually
grebes, cormorants, anhingas, and coots mainly use their feet, which
vering in water.
feed within 30 feet (9 m) of the surface, are large and powerful. The diving ducks and mergansers can use
One more unique, water-related behavior
Long-tailed Ducks have been observed both their feet and wings. This versatility is particularly characteristic
is often observed and is worth noting. When mildly alarmed, some Figure 1-33. Pied-billed Grebe Sinking:
as deep as 200 feet—deeper than any of the diving ducks that frequent the sea. For example, a Long-tailed
grebes, particularly Pied-billed Grebes, may squeeze air from their When mildly alarmed, the Pied-billed
other duck! Penguins, however, are
Duck foraging on the bottom propels itself only with its feet, keeping Grebe may squeeze air from its feathers
the champion avian divers. Like alcids, feathers and air sacs, thus increasing their density, and slowly sink
its wings at its sides, but when diving to reach great depths, it powers and air sacs, decreasing its buoyancy and
shearwaters, and diving-petrels, they straight down into the water (Fig. 1 33). They may remain completely
-
thus slowly sinking straight down into
use only their short, paddle-like wings itself by both wings and feet.
submerged, or with the eyes just peering out across the water, until all the water. It may submerge to various de-
to "fly" through the water. They regu- Twenty feet (6 m) is probably the limit to which most birds dive,
danger has passed. grees, sometimes remaining completely
larly forage at depths of 65 feet (20 m) or
although there are numerous records of birds going much deeper. underwater, sometimes leaving the neck
more, the large Emperor Penguins going Often, birds can capably perform certain movements to which
as deep as 1,752 feet (534 m). Drawing
The Common Loon can descend to 90 feet (27 m) and the Long-tailed and body partly visible, and sometimes
they are not primarily adapted. Ducks and gulls have webbed feet, and leaving just the eyes and nostrils above
by Robert Gil Imor Duck to about200 feet (61 m). Although diving birds usually stay under
coots lobed feet, for swimming, yet these birds can forage successfully the surface, to check for danger. Photos
water for a minute or less, the Long-tailed Duck has been timed under
on dry land far from water. Under compelling circumstances, prac- by Tom Vezo.
water for three minutes or more. Most diving birds can extend sub-
tically all swimmers can dive to some extent, and many species can
mergence—if frightened, for instance—by relying on some residual
swim even though they lack webbed or lobed feet. This is true of all
air in the air sacs and large amounts of oxygen stored in the muscles.
gal li nules, rails, and shorebirds. Watch a Spotted Sandpiper attacked
The length of a bird's endurance, if forcibly held under water, is about
by a predator and do not be surprised to see it take to the water and
15 minutes.
dive repeatedly!

Cornell Laboratoni of Ornithologu Handbook of Bird Biologq

1.32 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.33
Figure 1-34. Significant Steps in the History of Bird Classification
Naming and Classification of Birds
■ Have you ever looked in a field guide and wondered why the brightly 384-322 B.C. Aristotle groups birds into three categories: those that live on land, those that live in water,
colored orioles and meadowlarks are all lumped together in the same and those that live at the edge of water.
family (Icteridae) with the mostly black grackles and Red-winged
Blackbirds, whereas the soot-black starlings and crows are not? Why Mid 1500s Pierre Belon separates birds into six groups: raptors, waterfowl with webbed feet, marsh
are the coots put in with the rails and cranes and not with the ducks, birds without webbed feet, terrestrial birds, large arboreal birds, and small arboreal birds.
which they resemble so much when swimming around in a pond?
Why are the swifts and swallows that look and act so similar not listed 1676 Francis Willughby and John Ray are the first to use morphological characters to classify
together? And why are the cranes on different pages than the sim- birds.
ilar-looking herons? What these simple questions really translate to is
"How, and why, do people classify birds?" Mid 1700s Carolus Linnaeus devises system of binomial nomenclature for classifying organisms.

Histort1 1859 Charles Darwin publishes his theory of evolution in his book On the Origin of Species by
Means of Natural Selection. From this time on, researchers try to classify birds based on
At least since Aristotle (384 to 322 B.c.), and probably from time
common ancestry.
immemorial, people have been giving names to birds and trying to put
them into logical groups, that is, making classifications (Fig. 1-34).
Humans love to put things into pigeonholes, whether they go easily 1888 & 1892 Maximilian Furbinger (1888) and Hans Gadow (1892) each devise modern classifications
of birds based on a host of anatomical characters. For the first time, all passerine songbirds
or not. Exactly how people arrange birds into categories however, de-
are grouped together, swifts are separated from swallows, and cuckoos are separated from
pends on what the categories are supposed to represent. For example,
woodpeckers.
in some primitive societies, birds might be divided into two groups:
edible and inedible. (Even today some people tend to think of "useful"
1930-1960 Alexander Wetmore uses new information to adjust the classifications of Gadow, including
and "harmful" birds.) Aristotle and other early Western thinkers trying
organizing the songbirds. Wetmore's publications are responsible for the ordering of
to group "similar" birds based their classifications on such things as
groups found in most American field guides.
habitat (for example, water versus land), locomotion, food habits, and
obvious physical characters (for example, bill size and shape). Aristotle
1980s Charles Sibley and Jon Ahlquist propose a major rearrangement of the orders and families
divided birds into three categories: those that live on land, those that
live in the water, and those that live at the edge of water. In the mid
16th century, Pierre Belon, following the ideas of Aristotle, classified
birds into six groups: raptors, waterfowl with webbed feet, marsh birds
without webbed feet, terrestrial birds, large arboreal birds, and small
arboreal birds. (His classification lumped Ostriches, chickens, and relationships—of organisms, whereas phylogeny refers to the actual
larks into the same terrestrial category!) Morphological characters evolutionary relationships that the taxonomist hopes to represent.) Just
(the actual form of body structures) were first used as a basis for clas- what characters to use and where to draw the boundaries have been,
sification by Francis Willughby and John Ray in 1676, and their work and continue to be, subjects of great debate.
was one of the primary sources used in the mid 1700s by a Swedish The first modern, evolutionary classifications of birds were pro-
naturalist, Carolus Linnaeus, in his classification of animals, the Sys- posed by Maximilian Fi_irbinger in 1888 and Hans Gadow in 1892,
tema Naturae, discussed in more detail later in this chapter. based on a host of anatomical characters. Finally, all the songbirds
Various systems of classification based on differing ideas of were grouped together, and the swifts (because of such features as their
habitat, behavior, and physical similarities floated around for the next unusual wing structure) were separated from swallows, and cuckoos
hundred years or so, with no consensus on what to represent. With from woodpeckers. Subsequent bird classifications were heavily based
the understanding of evolution by natural selection as expounded on these works, and few major changes were made in the first half of
by Darwin in 1859 (Sidebar 2: The Evolution of an Idea: Darwin's the 20th century.
Theory), the classifications based on some vague "natural" or "logi- Especially relevant is the work of Smithsonian researcher Alex-
cal" order were replaced with ones that grouped organisms because of anderWetmore. Although his classifications published between 1930
common ancestry. In other words, organisms thought to be related to and 1960 differed little from Gadow's, he did incorporate some new
one another were put in the same group. The classifications, therefore, information. He also organized the songbirds, a group that Gadow
were an attempt to represent the phylogeny, or evolutionary history, of viewed as uniform, and had left largely undifferentiated. Wetmore's
birds. (Note that taxonomy is the classification—assigning names and (Continued on p. 1.38)

Cornell Laboratorq of Ornithoiogq Handbook of Bird Biolo8q

1.34 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.35
basis for natural selection: the individuals with the Doves, more of the faster individuals should survive
Sidebar 2: THE EVOLUTION OF AN IDEA: DARWIN'S THEORY advantageous traits survive; in essence, they've been and reproduce. If flight speed is hereditary, the next
"selected by nature." generation should have a greater percent of faster
Sandq Podulka individuals, and so on. (In evolutionary jargon, the
(2) Some of the variation between individuals is he- faster birds are said to have a greater fitness—the
In 1859, Charles Darwin rocked both the scientific and possibly be the one best starting point from which to build
reditary. likelihood of producing offspring that will survive to
nonscientific world with his radical theory on how spe- appendages for flying, swimming, walking, running, and
Although the idea of receiving traits through our reproduce—relative to the others; being fast is con-
cies change overtime. His book, On the Origin of Species handling objects. Third, during his voyage on the H. M.
genes is common knowledge today (indeed, it is sidered an adaptation—a genetically controlled trait
by Means of Natural Selection, set forth the idea of evolu- S. Beagle, Darwin observed oddities in the distribution
now "fact," rather than "inference"), Darwin lived at that increases an individual's relative fitness.)
tion by natural selection, which remains a cornerstone of of species around the globe. In particular, he noted that
biology to this day. It addressed many puzzling aspects the flora and fauna of temperate South America more a time when nothing was known about inheritance. This simple example assumes that flying fast carries
of living things, such as their tremendous diversity, their closely resembled the species in nearby tropical South He proposed his theory long before chromosomes no disadvantages, which is undoubtedly false—high
origins and relationships to one another, their similarities America than they did the species of temperate areas of and genes were discovered, and just before the work speed brings energetic, aerodynamic, and maneu-
and differences, their bewildering geographical distri- Europe. Thus, he reasoned, the similarities must result of Gregor Mendel, an Austrian monk working with verability concerns. Thus in reality, the flight speed
bution, and their startlingly appropriate adaptations to from common ancestry, and not because species were pea plants, provided the basis for modern genetics. of Mourning Doves results from a compromise: it has
their own environments. It also unified the field of bi- created to fit certain habitats. Fourth, Darwin saw that been honed by natural selection to meet an array of
ology by beautifully fitting together the array of scattered plant and animal breeders were able to produce changes (3) When more individuals with certain (advantageous)
concerns. Natural selection, a truly simple process,
observations and facts that previously had composed the in domestic organisms—such as chickens, pigeons, or traits survive and reproduce, more of the advan-
is intriguingly complex in its application.
discipline. It is, indeed, the one grand theory through roses—through the generations, even though no one un- tageous traits appear in the next generation.
One further assumption was essential to Darwin's
which much of the natural world can be understood. derstood how these changes came about. He assumed Over many generations, the characteristics of a spe- theory: that enormous spans of time are available for
Darwin's theory had two main parts—both revolu- that if humans could cause changes, then changes could cies may change. Through this process, evolution slow, gradual change. In Darwin's time, people believed
tionary ideas for the time: occur naturally as well. occurs. For example, if flying faster allows a Mourn- that the earth was created a few thousand years before
ing Dove to more easily avoid becoming a meal fora the birth of Christ. But Darwin's friend, geologist Charles
(1) Organisms Change through Time (Evolution) Natural Selection: The Mechanism of Change Cooper's Hawk, then in any generation of Mourning
By definition, evolution is any change over time. Figuring out the mechanism of change was more
Just as an idea or fashion trend can evolve, so can involved, but again, Darwin got a hint from domestic
living things. But when biologists speak of evolution, breeders. From a group of offspring with a variety of
they generally mean a change in the most common traits (say, different feather colors in pigeons), they would
characteristics of a species or population over many choose those individuals with the desired traits and breed
generations, not a change in an individual over its them again, repeating this process through the genera-
lifetime. The idea that organisms change had been tions until all or nearly all of the offspring had the desired
around for a while, but was not accepted by most coloration. Through these and other observations, Dar-
people. Darwin provided a great deal of scientific win noted two important facts about natural populations,
evidence to support it. which formed a basis for natural selection:

(2) Natural Selection is the Mechanism by which Or- (1) In any generation of a species, many more young
ganisms Change are born than will survive to reproduce. (Recently,
someone calculated that if all the offspring of all the
The process of natural selection, detailed below, was
house flies on earth survived, in just six months the
a completely new concept.
entire planet would be 47 feet deep in house flies.)

The Evidence for Evolution (2) Variation exists among the individuals of a species:
Although Darwin lived at a time when most people they are not identical in all of their characteristics.
believed in Divine Creation, a number of different ob-
From these facts, Darwin inferred the following:
servations, including the following, convinced him that
organisms did indeed change. First, Darwin recognized (1) Individuals with certain traits have a better chance
that the fossil record held many species that no longer of surviving and reproducing than individuals with
existed, and different species were found in different rock Figure A. Vertebrate Forelimbs: The forelimbs of all vertebrates constructing appendages for flying, swimming, running, and
other traits, because they compete better.
are constructed from the same basic bones, although they have handling delicate objects. Note that the bat's palm and finger
layers. In some places, organisms preserved in adjacent
Because essential resources such as food, water, been modified through natural selection to carry out widely bones are greatly elongated to support the membranous wing,
layers showed only slight differences, indicating a pattern
and suitable habitat are not usually superabundant, different functions. In this drawing, corresponding bones are and the whale's bones are shortened and thickened to form a
of gradual change through time. Second, Darwin noted
individuals must compete for them—whether di- shaded similarly for each animal. Darwin noticed the similarity strong flipper. Both the cat and horse walk up on their toes,
the strong resemblances between certain aspects of liv- among vertebrate forearms, and reasoned that it must result with the palm bones elevated—the horse, on one toe, the hoof
rectly or indirectly. They also "compete" in their
ing things, such as the bones of the forearm of a number from each being modified from the same common ancestor. being modified from the claw of just one toe. Reprinted and
ability to avoid predators, to obtain mates, to locate
of different vertebrates (Fig. A). He reasoned that they Otherwise, if the structures were unrelated, each "designed" adapted from Inquiry into Life, 5th Edition, by Sylvia S. Mader.
appropriate breeding sites, to produce and rear off-
must be so similar because they all were modified from from scratch, one would have to accept the unlikely theory Copyright 1988, William C. Brown, publisher. Reproduced
spring, and so on. This "survival of the fittest" is the
a common ancestor—the same basic design could not that the same basic set of bones was the best starting point for with permission of the McGraw-Hill Companies.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

1.36 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.37

Lyell, provided him with evidence that the earth was dation by Cooper's Hawks became a survival factor, or The Effects of Natural Selection
much older. Today we know that the planet has existed for (2) a mutation increasing flight speed arose randomly in a Natural selection does not always result in change. referred to as macroevolution. In contrast, the frequency
at least 4.5 billion years, and life of some form has been Mourning Dove, allowing it to more readily escape hawk Some organisms, such as cockroaches and horseshoe of certain characteristics in a population can change
present for at least 3.5 billion. Because natural selection predation. Once the variability exists, natural selection crabs, have changed only slightly over vast stretches of relatively quickly—a type of evolution termed micro-
often acts on minute differences between individuals, proceeds in a very nonrandom fashion, but the type of geologic time, whereas others, such as mammals, have evolution. Some changes are so rapid that humans can
producing slight changes from one generation to the variability that arises in the first place is random. changed dramatically. If a species is well adapted to observe them in their lifetimes—the evolution of drug-
next, long time spans are necessary to explain the kinds The random nature of mutations explains why evo- its environment, natural selection may act against any resistance in certain strains of bacteria, for example.
of changes evident in the fossil record. lution is often so slow. Nearly all mutations are detri- mutation that would change it. For example, if Mourn- The words "evolution" or "natural selection" often
mental. As Cornell astronomer Carl Sagan explained to ing Doves already fly at the optimum speed, selection bring to mind the expression "survival of the fittest," but
How Natural Selection Acts his students: "Think of any living thing as a finely tuned will act against mutations that would make that speed this phrase can be very misleading. Although the fittest
Although species or populations evolve, natural se- watch. What is the chance that dropping your watch will either faster or slower. This type of selection, termed do indeed survive, and the natural world can be a pretty
lection does not act directly on them as a whole. Natural improve its function?" Natural selection proceeds slowly stabilizing selection, works to keep the species at the gory place, evolution is responsible for a number of more
selection acts onlyon individuals—each individual lives because it has no predetermined purpose: it is not goal- optimal middle point. Only when conditions change pleasant aspects of life as well. In some circumstances,
or dies accordingly—but it results in the evolution of oriented. Natural selection works on the random efforts (for example, Cooper's Hawks become less abundant) the fittest individuals are those who cooperate with oth-
populations and species. Furthermore, natural selection of a "blind watchmaker" (Dawkins 1987), but natural and the former traits are no longer optimal, does natural ers of their own species. Many social birds, including
acts on the whole individual. Because each individual selection itself is anything but random. With time, it can selection produce changes. American Crows, Florida Scrub-Jays (Fig. C), and White-
is the sum of many different genetic traits, the relative produce a masterpiece of adaptation: from the colorful, When studying living things, it is easy to forget that what fronted Bee-eaters, as well as humans, fit this model. In
advantage of each trait depends on its genetic context. elaborate feathers in a peacock's train to the sharp, fish- you see is not a finished product. Natural selection is an these species, individuals benefit by cooperating with
For example, a trait increasing the growth rate of a tree's catching beak of a Black Skimmer (Fig. B). Natural se- ongoing process that will continue into the future, further others, and very complex social systems have evolved.
trunk and branches is useless, possibly even detrimental, lection did not, however, have to produce anything like modifying the organisms alive today as conditions change. Such admired human traits as motherly love, courage,
unless accompanied by a trait to increase the growth of birds or humans—both are the result of natural selection, Evolution can occur on several different levels. The compassion, and honesty all can, in various social sit-
the roots. at each step along the way, merely responding to the evolution of new species over thousands of years is often uations, act to increase an individual's relative fitness.•
conditions at hand.
The Source of Genetic Variation
The variability between indi-
Figure C. Cooperative Breeding in Florida Scrub-
viduals of the same species ul-
Jays: Found only in patches ofstunted scrub oak in
timately arises from mutations:
central Florida, the threatened Florida Scrub-Jay
actual changes in the basic struc- has evolved a cooperative breeding system. These
ture of DNA. Mutations can arise jays live year round in extended family groups
spontaneously, but also are induced of up to eight birds, consisting of a permanently
by radiation and certain chemicals. mated pair plus offspring produced in previous
Although mutations can occur in any years. Young Florida Scrub-Jays delay their own
cell in the body, only those in the cells dispersal for up to six years, remaining with their
parents as "helpers." In this photo, a three-year-
that produce sperm and eggs can be
old daughter (on nest, at right) helps to defend the
passed on to an individual's offspring.
nest of the breeding pair (her four-year-old stepfa-
Over hundreds and thousands of
ther, at top; and her eight-year-old mother, at left).
generations, many mutations arise. Two nestlings are visible beneath the daughter.
Neutral and advantageous ones may All three adults have drawn near the nest, joining
persist, while disadvantageous ones forces against the photographer. Helpers assist
may die out. Over time, much vari- significantly with territory defense, nest defense,
ability may be produced in a popu- and nestling care, increasing the chance of nesting success. ity. Young scrub-jays that disperse in their first year face great
lation (for example, green, blue, and Although helpers delay their own breeding to help, these difficulty competing for breeding opportunities, and often die
long-lived birds may actually increase their lifetime genetic before succeeding. Besides providing a safe "home base," de-
brown eyes; blond, black, and red
contributions to successive generations by doing so. The Flor- laying their dispersal allows helpers to contribute some of their
hair) from neutral or near-neutral
ida Scrub-Jay's habitat is rare and patchy—the jays can occupy own genes to future generations by rearing their own siblings
mutations.
only those areas that recently have been burned by wildfire. As (who have some of the same genes as the helper because they
A key point, misunderstood by a result, nearly all suitable areas are constantly being defended share parents), while they wait for a chance to become breed-
Figure B. Black Skimmer Foraging: The beak of the ternlike skimmers is highly spe-
many people, is that mutations are vigorously by breeding birds. Thus, a newly fledged male seek- ers themselves.
cialized for their unique, fish-catching technique. With its beak open, a Black Skim-
random. They arise by chance, not ing a territory on his own stands little chance of success. Be- As remarkable as it may seem, natural selection can pro-
mer (as pictured here) flies low over a river or ocean, its lower beak slicing through
for a purpose. In the previous hypo- the water. When it contacts a fish, it snaps the upper and lower beak together, grasping
cause bigger groups can defend larger territories, a male that duce cooperative breeding systems even more complex than
thetical example, the variation in the remains with his parents can increase the size of their territory, the Florida Scrub-Jay's, simply because helpers benefit more by
its prey tightly. Natural selection has modified the lower beak to a vertically narrow,
flight speed of Mourning Doves did which he may inherit when they die, or from which he may helping their parents than they would by attempting to breed
knife-like blade, which creates minimal friction as it moves through the water. It
"bud off" a territory of his own. Similarly, female helpers benefit early on their own. See Ch. 6, Parental Behavior: Why are there
not develop because a need for faster also contains many sensory receptors, allowing it to detect precisely when a fish is
from having a "home base" from which to search a wide area for "Helpers at the Nest" that Care for Someone Else's Offspring.
birds arose, but because either (1) by contacted. Furthermore, the lower jaw can open widely to allow the lower beak to
an unpaired territorial male—a rare and ephemeral commod- Photo courtesy of John W. Fitzpatrick.
chance, an array of flight speeds penetrate below the water's surface in flight, while the upper beak also opens widely
existed in the population before pre- to avoid touching the water. Also see Figures 4-87 and 4-88. Photo by Tom Vezo.

Cornell Laboratorq of Ornithologq Handbook of Bird Biolopi

1.38 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.39
publications are responsible for the ordering of groups found in most Although a few odd reorganizations occasionally have been
American field guides. For example, as a result of Wetmore's work, the proposed, none has gained much support in the ornithological com-
lobe-footed, short-billed coots are shown with the rails and not with munity. In fact, inertia has played a great part in maintaining the clas-
the web-footed, spatulate-billed ducks, which they most superficially sification of birds throughout the past century. Unless strong evidence
resemble when swimming (Fig. 1 35). - to the contrary has been available, bird relationships have stayed just
where Gadow put them. Species get moved around regularly, and
Figure 1-35. Wetmore's Classification some families have emerged while others have been discarded, but
of Coots, Rails, and Ducks: For many
very little movement of families among orders (the next category of
years, coots were grouped with the
ducks because, like ducks, they swim classification above families—see Fig. 1-41) has taken place.
on the water's surface and dive for food. In the 1980s, Charles Sibley and Jon Ahlquist proposed an en-
Alexander Wetmore was the first to rec- tirely new and somewhat radical phylogeny of birds. Sibley had long
ognize that the coots, with their long,
been interested in the higher groupings of birds and was a pioneer
lobed toes, medium-long legs, and short,
thick bills should be grouped with the in using chemical (instead of physical) methods to explore bird rela-
rails (see Sora photo)—who have similar tionships. The studies of Sibley and Ahlquist resulted in the first major
characteristics (but whose long toes are rearrangement of the orders and families of the world's birds in nearly
unlobed). Wetmore published his classi- half a century. Many of the relationships they proposed were familiar
fications between 1930 and 1960. Coot
(ducks and geese still went together, as did hawks and falcons), many
and Mallard photos by Marie Read. Sora
photo courtesy of Lang Elliott/CLO. corroborated previous "heretical" revisions proposed by others (New
World vultures and condors are really modified storks and not hawks),
and still others were surprisingly novel (frigatebirds, penguins, loons,
and tubenoses formed a group). Perhaps one of the most unexpected
findings was that the numerous passerine land birds native to Australia
American Coot were not related to the warblers and thrushes they resembled, but were
related to each other in a remarkably diverse array of forms at least as
spectacular as the better-known marsupial mammals.
Unfortunately, this work was not without controversy. Some of
the results were tainted by suspect methods and unexplained cor-
rection factors. As a result, acceptance of the new ordering of birds has
been slow and guarded. Gradually other researchers are testing the
proposed novel relationships, and generally finding corroboration for
most. It will take a while, however, for the dust to settle and for any ar-
rangement of birds of the world to become universally accepted again.
The American Ornithologists' Union, the largest body of professional
ornithologists in North America, in its 7th edition of the Check-list
of North American Birds (commonly called the "AOU Check-list"),
Sora used the following philosophy regarding taxonomy: "Because of
wide acceptance of the Check-list as an authoritative standard, the
Committee responsible for its preparation feels it necessary to avoid
hasty decisions that risk quick reversal, thereby fostering instability....
Our general stance has been conservative and cautious when judg-
ing recently published proposals for novel classifications, schemes of
relationship, and species I imits.... The Committee established a policy
for this edition whereby changes in classification of major groups re-
quire concordant evidence from two or more independent data sets."
In the future, as more of the relationships are examined and more
information is gathered, the placement of some species may change.
Taxonomy is not a static endeavor, but rather, like much of science,
ideas change as more information becomes available.

Mallard

Cornell Laboratorq of Ornithologg Handbook of Bird BioloBq

1.40 Kevin j. McGowan Chapter 1— Introduction: The World of Birds 1.41
survival and reproductive success of the individual bird, and conse-
Methods Used to Classifq Birds
quently can be rather easily modified by natural selection. As a result,
Through the years, a large number of physical characters have
the bill and overall shape of birds, which are often striking, may be of
been used to classify birds. Some of the obvious external characters,
little help in discovering true phylogenetic relationships.
such as color, bill shape, and foot shape, have turned out to be of little
More useful in determining relationships are characters that
use because of the problem of convergence, one of the most troubling
vary among groups but that are not so easily changed by natural se-
problems for biologists. Researchers now realize that some animals
lection—using these often minimizes the confusion resulting from
(and plants) resemble each other not because they are related, but
convergence. Internal characters often have been used because they
because they evolved to do the same thing; that is, they independently
are considered (whether rightly or wrongly) to be more evolutionarily
developed a similar solution to a similar problem.This pattern of evolu-
conservative than external characters. Examples of such characters
tion is called convergent evolution. For example, horses and antelope
are the shapes of feather tracts, the shape and construction of the oil
both have long legs not because they came from the same ancestor, but
gland at the base of the tail, the shapes of many different bones in the
Figure 1-36. Convergence of Swifts because they both use the strategy of running fast to escape predators,
skull, the shapes of bones of the inner ear, the arrangement of muscle
and Swallows: At first glance, swifts and and long legs are good for that. Both swifts and swallows have long,
and tendon attachments, the construction of the syrinx (voice box), the
swallows are very similar in appearance. pointed wings and short bills because they both chase flying insects
Specialized for life in the air, they both arrangement of the blood vessels, the construction of the intestines, the
and capture them in their mouths, and their wing and mouth shapes
have streamlined bodies; long, pointed presence of specialized feathers, the number of feathers in the wing,
wings; and short bills with which they
help them to do that. On examination of other characters, such as
and various aspects of behavior (especially reproductive behavior). Al I
capture insects in midair. A closer their toes, wing bones, and voice box structure, it becomes apparent
of these have been used to classify birds.
examination, however, reveals many that swifts and swallows look alike only on the outside; inside they are
significant anatomical differences. The discovery of the structure of DNA in 1953 by James Wat-
very different (Fig. 1 36). They have independently converged on the
-

Swallows have a more complex syrinx son and Francis Crick helped researchers to understand the "genetic
same overall body plan because they each have evolved to do the same
(voice box) than swifts, a different toe code"—how the genes provide instructions for making proteins. Pro-
arrangement (anisodactyl, compared to thing. Because they did not start from the same point (in other words,
teins are complex molecules composed of strings of amino acids. They
the pamprodactyl feet of swifts (see Fig. they had different ancestors), their exact "solutions" are somewhat
act both as structural material in the body and as enzymes, chemicals
1-20]), and different wing proportions. different: antelope have two toes at the end of their long, running legs,
In swallows, the wings are long as a re- that catalyze (assist) chemical reactions. Understanding the process
whereas horses have only one; swallows have long wings owing to a
sult of the long radius and ulna (in the of protein synthesis from DNA codes allowed researchers to see how
forearm, or antebrachium), whereas the
very long radius and ulna (an elongated antebrachium), whereas in
information is passed from parent to offspring, and how it is modified
swift's long wings result from an elon- swifts the long wings result from an elongated manus.
in the process of natural selection. An organism's traits (both internal
gated manus (hand). These anatomical Sometimes separating similarity owing to lifestyle from similar-
differences indicate that the similarities and external) are determined by the sequence of merely four different
ity due to common descent is relatively easy, but often it is difficult.
between the two bird groups are due to chemical bases in the DNA molecule (Fig. 1 37). These bases are the
-

Certain physical characters are subject to very strong selection, espe-

convergence—the evolution of similar "letters" and, taken three at a time, the "words" in the instructions for
features in response to a similar envi- cially characters that help birds find food or escape enemies. A bird
building an organism. Each "word" of three bases codes for a specific
ronment and lifestyle—rather than to with a stronger bill can open larger seeds; a bird with an efficient wing
common ancestry.
amino acid, and the sequences of amino acids produced determine
shape for its flight style uses less energy. All these differences affect the
the types of proteins created. The proteins direct the production of all
the other molecules needed, thereby determining the characteristics
of the organism. DNA is truly a blueprint for making an organism.
Most organisms, including humans and birds, have two copies
Swift Swallow of each gene. (Precisely defined, a gene is the sequence of base pairs
Simple Syrinx Complex Syrinx
that codes for one specific protein.) You received one copy from your
mother, and the other from your father. Because you are using some
of the same blueprints to construct yourself that your parents used,
some of your constructed parts resemble those of your parents. (Note
that you don't have your mother's eyes, you have her recipe for eyes.)
Sometimes, when copies are being made to put in the sperm or egg,
the instructions get garbled; such a change in the base sequence of
Long Wings due to
Pamprodactyl Feet Elongated Antebrachium DNA is called a mutation. This change will then be passed on to the
(Four Toes Forward)
Anisodactyl Feet offspring. Physical modifications of the body made during the life-
(Three Toes Forward, time of an organism do not get passed on—only changes in DNA. For
One Toe Backward)
example, for hundreds of years, farmers cut the horns off domestic
Long Wings due to
Elongated Manus
cattle to make them safer to be around. Each of those de-horned cows,
though, gave birth to offspring that would grow horns. At some point,

Cornell Labomtorq or Ornitholvi Handbook of Bird Biologg

1.42 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.43
just by chance, a mutation cropped up that changed the DNA code for
making horns, and a cow grew up hornless. It passed this mutation on
The Four Different Bases to its offspring, and those cattle with the new hornless gene were able
One Base Pair That Make Up DNA to produce hornless young.
I With the understanding of DNA and the development of mo-
lecular techniques, systematists (scientists who study how organisms
are related to one another) began to look in different places for useful
DNA Double Helix characters to construct classifications.They began to look at the chem-
(Segment) A
ical makeup of birds, not just their outward (or internal) appearance.
Because DNA molecules are very small, direct observation of the se-
quences of bases is not possible. Researchers using chemical methods
to classify birds started by looking at things one step removed—not
at the blueprints, but at the building blocks of organisms, the pro-
teins. Certain proteins can be chemically isolated from an organism.
T A C CG TATG Different types of animals make slightly different forms of the same
DNA "Unzips" for --
Protein Synthesis C A A protein (the forms all have the same function), and these differences
can be detected. One important tool used to compare protein forms is
electrophoresis. By watching how far each form of a protein migrates
up a gel in an electric current (somewhat the way ink "bleeds" up a
Intermediate Steps Involving RNA strip of paper), different forms of the same protein can be separated
(Fig. 1-38). Smaller or differently charged forms travel at different

Amino Acids Met Lys Phe

1 1 I
Gly "Stop" Met Arg Tyr
speeds than do others. This method was one of the first ways to look at
chemical differences quite apart from (and thus unbiased by) external
morphology.
Although proteins are the main building blocks of animals, they
are still a step away from DNA. Ideally, what should be examined to Figure 1-38. Gel Electrophoresis of
determine relationships are not the products of protein synthesis as Proteins: Because protein molecules
are too small to see, even under a pow-
translated from DNA, but the actual sequences of bases in the DNA
erful microscope, scientists must use
molecules themselves. indirect means to determine their form.
Proteins Met Lys Phe Gly Met Arg Tyr
DNA molecules, however, are too small for their structure to be Gel electrophoresis separates large mol-
"seen" directly, so various indirect methods are used to determine ecules, such as protein molecules with
*Protein #1 *Protein 42 different lengths, by their rate of move-
their base sequences. A number of different techniques have been de-
ment through a thin slab of gel in an
veloped to look at DNA, and each is useful fora different level of corn-
*In reality, proteins are much longer chains of amino acids. electric field. To create the electric field,
electrodes (one negative and one posi-
tive) are attached to opposite ends of the
Figure 1-37. The Genetic Code and Protein Synthesis: The paired bases break temporarily, so that a portion of the DNA Cathode ( ) gel, and the electric current is turned on.
Protein -

main genetic material, DNA, contains within its structure the molecule, in effect, "unzips" to create a single chain. The key molecules Researchers treat the protein molecules
instructions for making proteins, which in turn determine every to the genetic code is the sequence of base pairs of DNA. so that they carry a negative charge, and
AK ) thus the proteins are attracted to the pos-
characteristic of an organism. DNA is composed of subunits Through a multitude of complex biochemical steps involving
called nucleotides, which differ only in the type of nitrogenous another type of genetic material, RNA, each set of three ad- itive electrode, migrating slowly toward
DSG
(nitrogen-containing) base they contain. (A base is a type of jacent bases is translated to indicate a particular amino acid. Larger it when the current is on. Because larger
chemical, such as ammonia, which acts in an opposite manner The cell then bonds the amino acids together into long chains, Molecules molecules are slowed down more by
in the sequence indicated, to form proteins. The sequence of the gel, they will not migrate as far in a
to an acid in solution.) The nucleotides of DNA each contain
amino acids determines the type of protein. Since there are given amount of time. Thus, if a sample
only one of four types of bases, adenine (designated by the
only 20 types of amino acids, and 64 possible sequences of Gel — of protein molecules of different lengths
letter A), guanine (G), thymine (T), and cytosine (C). The DNA
three bases, there is some redundancy: several different codes is applied to the gel, they will appear
molecule is composed of two long chains of nucleotides, with
may indicate the same amino acid, and some codes indicate Smaller as separate "locations" on the gel after
their attached bases. Each base in a chain is paired with one
"stop" (the end of one protein) and "start" (the beginning of Molecules migration. Originally, electrophoresis
base in the other chain, A only with T, and C only with G; this Anode (+)
another protein). For simplicity, proteins are indicated here as was used only to separate proteins, but
double chain is twisted to form a double spiral known as a
short chains of amino acids, but in reality they are much longer. a. Protein Applied b. Electrodes Attached c. Molecules Migrate more recently it also has been used to
"double helix." Only a short section of a DNA double helix is
to Slab of Gel. to Both Ends of Gel; Along Gel According separate DNA molecules of differing
shown here, since an entire DNA molecule is many millions Amino acid abbreviations used here are met (methionine), lys
Electric Current to their Size. lengths. Adapted from Campbell (1990,
of base pairs long. (lysine), phe (phenylalanine), gly (glycine), arg (arginine), and
Turned On. p. 403).
During protein synthesis, the bonds between some of the tyr (tyrosine).

Cornell Laborator,1 of Omithologg Handbook of Bird Biolom

1.44 Kevin J . McGowan Chapter 1— Introduction: The World of Birds
1.45
parison. For example, the information needed to distinguish the more Again, problems were encountered. Mitochondria are not passed
closely related two out of three chickadee species is different from the from both parents to their offspring, but instead are transmitted intact
information needed to determine which two out of three groups, say, from mother to offspring. Therefore, all your mitochondria came from
ducks, hawks, and sparrows, are more closely related. Here, a brief your mother, and all of hers came from her mother, and so on back
overview of the techniques that are currently most important for clas- through time. Although useful for many studies, maternal-only inher-
sifying birds is presented. itance presents some problems for understanding evolution. Never-
Through a variety of techniques, past researchers were able to theless, examining mDNA remains an important tool in exploring
actually read the sequence of bases in DNA, a process termed "se- evolution and the relationships of organisms, especially at the popu-
Figure 1-39. Nuclear Versus Mito- quencing." One major problem was that a single DNA molecule for lation level (a population is a group of individuals of the same species
chondria! DNA: DNA is found in both a relatively simple organism, such as a nematode worm, contains that live in the same general area).
the nucleus and mitochondria of animal
millions of base pairs in its DNA. Sequencing takes time, and no one Systematists recently have turned to sequencing nuclear DNA,
cells. In the nucleus (command center),
could possibly read the entire sequence and make sense of it. So, the but still are limited by how little of the whole DNA molecule they can
individual DNA molecules exist as ex-
tremely long, thin, coiled strands known first techniques used to read DNA did not concentrate on the DNA sequence. Most researchers, therefore, are restricting their work to
as chromosomes. Bird chromosomes contained in the nucleus (command center) of a cell, where the plans specific regions of the DNA molecule, sequencing single genes for
vary widely in size and their lengths for the whole organism lie. Instead, they took advantage of the fact that comparisons between organisms. This technique creates the same
are not fully known, but they are on the
little structures within the cytoplasm (material outside the nucleus) problems thatfaced earlier systematists who used morphological traits
order of tens of millions of base pairs (see
Fig. 1-37) long. In the close-up view, the of each cell, the mitochondria (singular: mitochondrion) have their to classify birds, namely that a single character is used to determine a
chromosome is shown as two identical own DNA, which is much smaller and simpler than that found in relationship.Togetaround this problem, many systematists use a num-
DNA strands held together in the middle. the nucleus (Fig. 1-39). The mitochondria are the "powerhouses of ber of known DNA sequences together with morphological characters
This is the form DNA takes just before the cell," where most of the energy generation takes place. They are to investigate the relationships among groups of birds.
cell division (in which the two strands
probably ancient bacteria that somehow got incorporated into cells Another technique using DNA for detecting relationships, espe-
pull apart and one goes to each new
cell), and is the usual way chromosomes at a very early stage of evolution. Part of the evidence supporting the cial ly at the higher levels of comparison, is DNA-DNA hybridization.
are illustrated. Mitochondria are small bacterial origin of mitochondria is thattheir DNA is very similar to that This technique was used by Sibley and Ahlquist to construct their
structures in the cytoplasm, the cellular of bacteria: relatively short and arranged in a circle—unlike the long, new phylogeny. They collected and analyzed tissue samples from an
material found outside the nucleus. Their
complex strands of DNA, termed chromosomes, found in the nuclei astonishing one-sixth of the bird species of the world—the largest set
single chromosome is much shorter (an
average of 16,000 base pairs long in ver- of most cells. Researchers were able to isolate the mitochondrial DNA of DNA comparisons made for any group studied to date.
tebrates) and in the form of a ring. (mDNA) and sequence specific regions of it. In the process of DNA-DNA hybridization, the double-stranded
molecules of purified DNA (which look roughly like incredibly small
but very long, twisted zippers) from two species are "unzipped" (Fig.
1-40). That is, the molecules are chemically broken apart down the
middle, between the millions of base pair combinations. Because a
DNA molecule is more stable double-stranded (zipped) than single-
Animal Cell stranded (unzipped), the doubled-stranded molecules will tend to
reform. If unzipped DNA from one species is put in contact with
Cytoplasm unzipped DNA from another species, the molecules will try to fuse
with one another. Of course, some of the "words" in the genetic code
Nucleus

Mitochondrion
I of one species will be different from those in the other species (some
of the zipper teeth will not fit together), so the base pairs of the hybrid
DNA molecules will not be perfectly matched. The key is that the fit
of those DNA strands that are most similar will be most stable, and
that the stability can be measured. The more stable the hybrid DNA
molecules, the more closely the two species are related.
Nuclear DNA in Form of Chromosome
(Tens of Millions of Base Pairs Long in Birds)
Binomial Nomenclature and Classification System
Early in the 1 8th century, the time of great explorations to all
parts of the globe, expeditions returned to Europe bearing new plants
Mitochondrial DNA "Ring" and animals by the score. Naturalists in different countries gave them
(16,000 Base Pairs Long, on Average, in Vertebrates)
different names; there was no uniformity, no standard followed by all
naturalists in all countries. How long this chaotic situation might have

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1.46 Kevin J . McGowan Chapter 1— Introduction: The World of Birds 1.47
Figure 1-40. DNA-DNA Hybridization: DNA Samples from Two Species are continued is anybody's guess, had it not been for Swedish naturalist
DNA-DNA hybridization is used to de- Collected and Purified Carolus Linnaeus (1707 to 1778). A genius at organization, he set
termine the degree of similarity between
up a system, binomial nomenclature, for all plants and animals. This
two different samples of DNA. At the top
of this schematic, a short section of DNA method was so useful that it soon became the standard system and
from two different species is illustrated; biologists have used it ever since.
in the actual process, however, the entire Linnaeus designated each plant or animal by two Latin names,
molecules would be used. The different
the first denoting the genus (plural genera; always capitalized) and the
shapes along the line down the middle of
each represent the different nitrogenous
second, the species (plural also species; never capitalized). He chose
bases. For example, the square "peg" Latin because it was the universal language of scholars, and he used
might be adenine, and the square two names because there were not enough single names in the lan-
"hole," thymine (see Fig. 1-37); and, the
guage for all the species. Thus, although the second word is officially
triangular "peg" might be cytosine, and
called the "species" designation, both the genus and species must be
the triangular "hole," guanine. First, the
DNA samples are heated to break the Species 1 Species 2 written together to indicate a unique organism, because there may be
bonds between the base pairs, disassoc- DNA Strands DNA Strands more than one unique organism with the same "species" designation
iating (separating) each double-stranded (for example, the Least Flycatcher, Empidonax minimus, and the Bush-
molecule into two separate strands
tit, Psaltriparus minimus). To allow easy recognition of these two-word
(middle drawing)—a process termed
"melting." Because DNA is more stable The DNA is Heated to Disassociate the Latin (or "scientific") names for species, they are always underlined
in the double-stranded form, single DNA Molecules into Individual Strands. The or placed in italics.
strands in the same sample will bond Samples are then Combined to Form The indisputable value of Linnaeus' system can be demonstrated
together to form double strands, unless Hybrid DNA.
today by examining all the common names for a certain large bird of
kept apart by high temperatures. There-
fore, "melted" samples from each spe-
prey that ranges widely over much of the world. The "official" English
name is Osprey, while in some parts of both the United States and

11
cies are combined, and held at a lower
temperature, allowing double-stranded Canada it is known as the Fish Hawk. The Swedes call it Fiskgjuse;
molecules to form. Although many of the the Germans, Fischadler; the Dutch, Visarend; the South Africans,
single strands will bond with another
Visvalk; the Burmese, Wun-let; and the Argentines, Sangual. But to
strand from the same species, some of
the strands will "hybridize," bonding all ornithologists, regardless of the language they speak, the bird is
with the DNA of the other species (bot- Pandion haliaetus. This illustrates why guides to identification and
tom drawing). Because hybrid double other authoritative treatises give the scientific names after the common
strands do not have perfectly matched
names—to eliminate any doubt in anyone's mind about the identities
base pairs, they are less stable, and thus
separate more readily when reheated.
of the birds mentioned.
Furthermore, the greater the difference Every scientific name means something (Sidebar 3: Latin and
between the base sequences of the two Greek Roots of BiologicalTerms). The names are concocted from Latin
The Hybrid DNA is
species' DNA, the lower the melting or Greek roots, or at least made into the form of Latin words. Although
then Reheated and
temperature of the mixture of reformed,
the MeltingTempera- some names may have been created to honor a person, many of the
double-stranded DNA molecules—giv- ture is Analyzed
ing researchers a quantitative measure translated roots are descriptive, and usually provide some informa-
of the degree of similarity between the tion about the organism. For example, the familiar American Crow is
DNA molecules from the two species. known as Corvus brachyrhynchos. Corvus comes from the Latin for
Adapted from Proctor and Lynch (1993, Mismatched "crow," and brachyrhynchos means "short beak," which a crow has,
p. 23). Areas are
Weak and compared to a raven.
More Readily Linnaeus used very few higher categories to express the orga-
Disassociate
nizational affinities of genera. But as more organisms were described
when Heated
and fitted into the classification scheme, new categories had to be
added to supplement and organize the Li n naean categories of genus
and species. Each type or form of animal or plant is described by
placing it in a hierarchy of categories. As mentioned previously, since
Hybrid DNA
the work of Darwin, classifications generally have been attempts to
from Both Species reflect evolutionary relationships. Individuals of a recognizable type
are considered members of the same species. Different species that are

(Continued on p. 1.52)

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1.48 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.49

Sidebar 3: LATIN and GREEK ROOTS of BIOLOGICAL TERMS Root Meaning of Root Example and Definition

Marie Eckhardt chrom color chromatophore: a pigment-bearing cell

cide killing pesticide: an agent used to destroy pests
Students new to the field of biology may find the terminology daunting. Many biological terms and names, how-
ever, are derived from Latin or Greek roots. Once you become familiar with these roots, you will find that biological circa about, approximately circadian rhythm: a biological rhythm of about one day
terms are more comprehensible. You may already be acquainted with some of these terms. Many are present in our circum around circumnavigate: to go or travel completely around something
everyday language as prefixes or suffixes embedded in familiar words.
cloac a sewer cloaca: in birds, the chamber in which fecal material, urine, and
The Latin and Greek roots presented here are each spelled in a form that is commonly encountered in biological eggs or sperm collect before being discharged from the body
words, but these are not necessarily the original forms.
cran skull cranial: belonging to the skull
Additional information may be found in Jaeger (1955) and Pough et al. (1996).
dactyl finger, toe anisodactyl: the toe arrangement in songbirds and many other
Root Meaning of Root Example and Definition perching birds

a, ab away from abductor muscles: muscles that draw bones away from the center de removal of, off dehydration: an abnormal loss of body fluids
of the body derm skin, covering epidermis: the outer skin of vertebrates
a, an without, lacking, not abiotic: not living; apteria: areas of bird skin that lack feather di, diplo two, double dimorphic: occurring in two distinct forms
tracts
e, ex out of, from, without excretion: elimination of metabolic waste products from the body
ad to, toward, attached to adductor muscles: muscles that draw bones toward the center of
the body eco, oikos house, home ecology: the study of the relationship between organisms and
their environment
aeros the air aerodynamics: branch of science dealing with the motion of air
and objects in air ect outside ectoparasite: a parasite living on the outside of the body

al, alula a wing alula: feathers attached to the first digit in a bird's wing end within, internal endoparasite: a parasite living inside the body

alb white albino: lacking color pigmentation epi upon, above epidermis: the outermost layer of skin in vertebrates

all, allo other allopreening: the preening of one bird by another extra beyond, outside extrapair copulation: copulation with someone other than your
mate
aqua water aquatic: living primarily in or on water
frug fruit frugivorous: fruit-eating
amphi both, double amphibian: a class of vertebrates that spend part of their lives in
water and part on the land gallus poultry gallinaceous birds: chicken-like birds in the order Galliformes,
including quail, pheasants, turkeys, domestic chickens, grouse,
andro male polyandry: mating system in which a single female mates with and guineafowl
several males in a breeding season
gastr belly, stomach gastrointestinal tract: digestive tract
ante before antebrachium: the forearm of a bird—the part before the
brachium gen origin genetics: the study of genes, which are essentially an organism's
"origin"
anthro human anthropomorphic: ascribing human qualities to nonhumans
geo earth geology: the study of the earth
arch beginning, first time Archaeopteryx: the earliest known fossil bird
gloss tongue entoglossal process: a bone in the tongue of birds
audi to hear auditory: related to hearing
gon seed gonads: sexual reproductive organs
av a bird avian: relating to birds
gul throat gular fluttering: rapid vibration of muscles and bones in the
bi, bis two bipedal locomotion: walking on two feet throat, which helps birds cool down in hot weather
bio related to life biology: the study of life gyn female polygynous: mating system in which a single male mates with
blast bud, sprout blastodisc: flattened sphere of cells that is the first stage of devel- multiple females within a single breeding season
opment in the bird embryo hemi half hemisphere: half of a spherical body
brachi arm brachial artery: main artery of the human arm and bird wing hepat the liver hepatic veins: large veins that carry blood from the liver to the
carp flesh carnivorous: meat-eating caudal vena cava

caud tail caudal vertebrae: bones of the tail hetero different, other heterogeneous: consisting of ingredients or constituents that dif-
fer from one another
ceno new, recent Cenozoic: the most recent geological era
homo alike homologous: having the same relative value, position, structure,
cord guts, a string spinal cord: cable or thick "string" of nerves running the length of or origin
the vertebral column
hydr, hydro pertaining to water hydrophil ic: having a strong affinity for water
chorio skin, membrane chorion: membrane surrounding the embryo, yolk sac, amnion,
and allantois in a bird egg hyper above, excessive hypersensitive: abnormally sensitive

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1.50 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.51

Root Meaning of Root Example and Definition Root Meaning of Root Example and Definition

hypo below, insufficient hypothermia: subnormal temperature of the body phyl tribe, race phylum: one of the primary divisions of the animal kingdom

inter between interspecific: occurring or existing between different species plasm formative substance cytoplasm: formative substance in cells
intra within, inside intracellular: occurring or functioning within a cell pod foot megapode: a ground-dwelling bird that uses its large, strong feet
to construct mound nests
leuc, leuk white leukocyte: white blood cell
poly many polygyny: having more than one female mate at one time
kin movement cranial kinesis: the ability of birds to raise the upper beak while
simultaneously depressing the lower beak post after postnuptial: occurring after breeding

klepto to steal kleptoparasitism: robbing another bird species of its prey pre before, in advance of precocial: young bird that hatches in an advanced state of matu-
rity—capable of much independent activity before (at an earlier
mela black melanin: a dark brown or black pigment
age than) altricial young
meso middle mesobronchus: main air tube running down the middle of each prim first primary feathers: outermost feathers of a bird's wing
bird lung
pro before, favoring proventriculus: the glandular or true stomach of birds that is situ-
meta to change metabolism: all the physical and chemical processes of an organ-
ated before the gizzard
ism, including those by which food is converted to energy or
body structures pter wing, feather pterosaurs: extinct flying reptiles

micro small microclimate: the local climate of a small site or habitat PYg the rump pygostyle: the last bone in the tail of a bird, formed by the fusion
of several tail vertebrae
milli a thousand millennium: a period of 1,000 years
soma body somatic cells: the body cells, in contrast to the sex cells (the eggs
mono one, single monogamous: having just one mate in a given period of time
and sperm)
morph shape morphology: the study of the form and structure of something
sonus sound sonagram: an image produced by sound
nephro kidney nephron: the excretory unit of the vertebrate kidney sub below, under, smaller subordinate: occupying a lower rank, class, or position
neuro nerve neurotoxin: a poison that acts on the nervous system supra above, over supracoracoideus: a principle flight muscle that is attached to the
nidi nest nidicolous: reared in a nest humerus, a bone located above the coracoid
nomen a name nomenclature: a system of naming sym, syn together, with sympatric: occurring in the same area

not the back notochord: a flexible, rod-like support running along the back of tax arrangement of taxonomy: the classification of organisms
all chordate embryos tele far off, distant telescope: a tubular optical instrument for viewing distant ob-
omni all omnivorous: feeding on both animal and vegetable materials jects

00 pertaining to an egg oocyte: an immature egg cell therm heat thermometer: an instrument that measures temperature
ology study of ornithology: the study of birds tri three Foramen triosseum: a hole formed by the junction of three bones
in the shoulder joint of birds
opercul a cover, lid operculum: a protective flap partly covering the nostrils of some
birds such as starlings, pigeons, and chickens troph nourishment trophic level: level in the food chain at which an organism seeks
its nourishment
optic eye optic lobes: the portions of the brain that process visual infor-
mation ultra beyond ultraviolet: a portion of the light spectrum beyond the blue and
violet wavelengths
ornith bird ornithologist: one who studies birds
uni one, single uniform: consistent, having a single form, manner, or degree
os bone ossicle: a small bone or bony structure
ura, oura tail or urine uropygial gland: oil gland at the base of the tail in birds
ov, ovi pertaining to an egg ovary: female reproductive organ that produces eggs
vas a vessel vas deferens: duct that carries sperm in vertebrates
paleo ancient paleontology: the study of past geological periods as known from
fossils ventr the belly ventral: anatomically, the lower or abdominal side of the body
par, para beside parasite: an organism that lives at the expense of another species, verm worm vermivorous: worm-eating
often in or upon it
viv live viviparous: giving birth to live young
parous bearing, giving birth to oviparous: producing eggs that develop and hatch outside the
vor to devour herbivorous: plant-eating
female's body
xer dry xeric habitat: a habitat with very little moisture
path disease pathogen: disease-causing agent
zoo animal zoology: the study of animals
peri around peripheral vision: the outer part of the field of view
zyg union, coupling zygote: the cell formed by the union of the sperm and egg cells of
pheno visible phenotype: the visible properties of an organism
animals

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1.52 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.53
somewhat similar are grouped within the same genus. Similar genera recognizable as similar to the American Crow: they are large, mostly
are placed within a family, similar families within an order, similar black, omnivorous, intelligent birds. Crows and ravens, together with
orders within a class, similar classes within a phylum, and finally, jays and magpies, make up the family Corvidae. Most corvids are
similar phyla within a kingdom (Fig. 1-41). large, omnivorous birds with feathers covering the nostrils on their
To help understand the classification system, look again at the stout beaks. Corvidae is just one family in the order Passeriformes, a
crow. The species American Crow, Corvus brachyrhynchos, lives over group containing all of the familiar songbirds. Passeriformes are rec-
most (but not all) of North America, from British Columbia to Mexico ognized by their overall perching physique (three toes forward, with
and Florida. It can be separated from other species of crows and ravens a well-developed hallux), and especially by the uniquely complex
by its calls, the size of its body parts, its tail shape, and the shape of the structure of their syrinx (voice box). The 31 orders of living birds make
back and throat feathers. All crow and raven species are placed in the up the class Ayes, or birds. Among living organisms, birds are instantly
genus Corvus. Although not all of the 50 species of crows and ravens recognizable by their feathers.Together with the various other animals
found throughout the world are entirely black, most would instantly be (fishes, mammals, reptiles, amphibians, and the strange lancelets and
tunicates) whose embryos share certain characteristics such as a noto-
chord (a rod-like support along the back) and gill slits, birds make up
Classification of the the phylum Chordata, within the kingdom Animalia.
CATEGORY American Crow Other Examples of Category Linnaeus' basic system of classification is still in use today, albeit
with many changes in names and positions of the organisms. It is, of
KINGDOM Animalia All Other Kingdoms: Plantae, Fungi, Monera course, his system that is important, not necessarily the classifications
(Bacteria), Protista (Misc. Simple Organisms) he made. For example, he lumped whales in with fish, even though
two thousand years earlier Aristotle already had realized that they
PHYLUM Chordata (Chordates) Examples of Other Animal Phyla: Porifera
were different. Linnaeus' classification of birds was based heavily on
(Sponges), Nematoda (Roundworms), Arthropoda
(Arthropods), Mollusca (Mollusks) the structure of bills and feet, and consequently grouped together such
odd bedmates as parrots, woodpeckers, crows, and orioles.
CLASS Ayes (Birds) All Other Chordate Classes: Agnatha (Jawless Fish),
Chondrichthyes (Cartilagenous Fish), Amphibia,
Reptilia, Mammalia The Species
The species is the basic unit of classification of living organisms.
ORDER Passeriformes (Perching Birds) Examples of Other Avian Orders: Anseriformes
Species serve as the basis for describing and analyzing biological di-
(Waterfowl and Screamers), Columbiformes
1 (Pigeons and Doves), Apodiformes (Swifts and versity. By the prevailing Biological Species Concept (BSC), a species
Hummingbirds) is a group of potentially interbreeding individuals that share distinctive
characteristics and are unlikely to breed with individuals of other spe-
FAMILY Corvidae (Crows, Ravens, Jays, Magpies) Examples of Other Passerine Families: Tyrannidae cies. Although most species are recognizable by obvious structural
(New World Flycatchers), Vireonidae (Vireos),
and behavioral peculiarities—how else could they be identified as
Turdidae (Thrushes), Parulidae (Wood-Warblers)
different species in the field?—the ultimate criterion for defining them
GENUS Corvus (Crows and Ravens) Examples of Other Corvid Genera: Nucifraga is whether they are reproductively separate. To retain its distinctive-
(Nutcrackers), Cyanocorax (Certain Neotropical ness and thus its "species" status, a group of organisms must not breed
Jays), Cyanocitta (Blue Jay and Stel ler's Jay) with other species; that is, there should be no gene flow (movement
of genetic material, as between generations) between species. There
SPECIES Corvus brachyrhynchos American Crow Examples of Other Species in the Genus Corvus:
Corvus monedula (Eurasian Jackdaw), C. corax are exceptions to this general criterion for defining species, however.
(Common Raven), C. frugilegus (Rook), C. caurinus Hybrids between different but closely related species do occur in na-
(Northwestern Crow) ture. Notable examples include the Blue-winged and Golden-winged
warblers and the Mallard and Black Duck. In such cases, ornithologists
Figure 1-41. Classification System for Living Organisms: Scientists classify all living organisms using the hierarchical system have concluded that the frequency of hybridization is insufficient to
pictured here. Each species is designated by a unique, two-word scientific or "Latin" name, according to the system developed
consider calling the birds the same species.
by Carolus Linnaeus in the 18th century. The first word of the name is the genus, and the second, the species. Both are underlined
or italicized, and the genus (but never the species) is capitalized. For example, the scientific name of the bird species commonly When just one region is considered, species seem easy to identify,
called the American Crow is Corvus brachyrhynchos. There are other species within the genus Corvus, and each has a different but when the entire range of organisms across the globe is considered,
word for the "species" designation. As shown for the American Crow, related genera are placed within the same family, related the boundaries between species become murky. Life is complex, and
families within the same order, related orders within the same class, and soon. Note that for the kingdoms and chordate classes,
organisms do not always fall into the neat little categories that people
all possibilities are shown, but for the other categories, only a selection of examples is given. People use various mnemonics to
remember the levels in the classification scheme, but one effective one is: "King Philip Came Over For Good Spaghetti," in which desire. The main criterion for the BSC, that individuals of two differ-
the first letter of each word gives the first letter of each category, in the proper sequence. ent species will not interbreed, is often useless in practice. Similar

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1.54 Kevin J . McGowan Chapter 1— Introduction: The World of Birds 1.55
birds may live in quite separate localities and thus have no chance of separate evolutionary histories than interbreeding individuals. If two
interbreeding (for example, American Crows and the similar looking forms became different (either morphologically or chemical ly) because
Carrion Crows of Eurasia). Are they different species? What would they diverged genetically at some point in their evolutionary history, the
happen if they came into contact? How could anyone begin to guess? PSC considers them separate species. The PSC is not based on hybrid-
And does it really matter if a few individuals interbreed? Would that ization or guesses about whether species will interbreed, but is con-
mean that the two forms share most of their genes, or just that they do cerned only with discrete, recognizably different forms with separate
not recognize each other as different forms? Because of dissatisfaction evolutionary histories. Under this concept, the number of bird species
with problems such as these, a number of people dislike the BSC, and recognized in the world would be approximately double the number
have proposed other definitions of species. recognized by the BSC. For example, consider two forms of the North-
One species concept that has gained much support is the Phy- ern Flicker—the Red-shafted and Yellow-shafted flickers—named for
logenetic Species Concept (PSC). This idea is more concerned with the brightly colored feather shafts of the wing and tail. In addition to
shaft color, a number of differences in the color patterns of the plumage
distinguish the two groups. The red-shafted form is found throughout
western North America and the yellow-shafted form, throughout east-
ern North America, but they interbreed within a narrow north-south
Aleutian Subspecies zone through the Great Plains, extending northwestto southern Alaska.
Melospiza melodia maxima
The BSC would proclaim these forms a single species (their current
QIcr
(F"
official designation), because of the extensive interbreeding. The PSC,
•N.S0 however, would declare them separate species, considering the distinct
plumage differences to indicate separate lines of evolution.
Like the human species, all bird species show individual varia-
tion. If a species ranges widely over geographical areas that encompass
shifts in environmental conditions, such as from warm to cold or humid
to arid climates, it is likely to show a gradual change (called a cline)
o
Pacific Northwest Subspecies
in certain characters from one population to the next. The variations
Melospiza melodia morphna between populations may be in one or more of a number of characters,
Figure 1-42. Song Sparrow Cline: Song including coloration, body size, bill size, song, or number of eggs laid;
Sparrows found on the Pacific coast of these variations are roughly correlated with changes in geographical
North America show a gradual change areas (Fig. 1-42).
(termed a dine) in body size, plumage
Sometimes the changes in characters are abrupt, especially if
coloration, and song characteristics,
when considered from north to south. physical barriers such as a large body of water, a mountain range, or
The large, dark Aleutian subspecies a desert separate the populations. Whether gradual or abrupt, popu-
appears dramatically different from lations in certain geographical areas may be sufficiently distinct to
the small, pale subspecies of the California Coastal Subspecies
Melospiza melodia heermanni warrant the designation subspecies, sometimes cal led race (Fig. 1-43).
Southwestern desert region, with the
Pacific Northwest and California coast When a subspecies is formally described in the scientific literature, it
subspecies showing intermediate char- receives a third name after the binomial. For example, the common
acteristics. Reprinted from Manual of American Crow in New York is Corvus brachyrhynchos brachyrhyn-
Ornithology, by Noble S. Proctor and chos, whereas the smaller form common in California is known as
Patrick J. Lynch, with permission of the
Desert Southwest Subspecies Corvus brachyrhynchos hesperis.
publisher. Copyright 1993, Yale Uni-
_Melospiza melodia saltonis A subspecies is defined as a population of a species that has some
versity Press.
unique characters and some that are shared with other populations,
and which can interbreed with other populations when they meet. Sub-
species, then, are separated only geographically, not reproductively. In
practice, reproductive isolation is difficult to detect, so under the PSC
many geographically isolated forms would be considered full species.

The Formation of Species

As discussed above, widespread species are composed of popu-
An Example of a Cline:
Pacific Coast Subspecies of the Song Sparrow lations that, through geographical separation, may become sufficiently
(Melospiza melodia) distinct to warrant their designation as subspecies. If the isolating fac-

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1.56 Kevin J . McGowan Chapter 1— Introduction: The World of Birds 1.57
Figure 1-43. Races of the Dark-eyed tors continue operating, the subspecies may eventually develop still
Junco: Familiar for its pale beak and stronger distinctions until their populations, unable to interbreed,
white outer tail feathers, flashed con-
become species (Fig. 1 44). Evolution of this sort (termed divergent
-

spicuously in flight or during displays,

the Dark-eyed Junco has a number of evolution because one group "diverges" into two or more) results in
different subspecies or races. Males of the generation of new species—a process known as speciation. The
three of the races are pictured here. All geographical separation that leads to speciation is frequently caused
breed mainly in coniferous or mixed
coniferous/deciduous forests. The Figure 1-44. Speciation through Geo-
Slate-colored race is widespread in graphic Isolation: When populations of
North America, but much more com- a species become geographically iso-
mon in the east. Males are dark gray, lated from one another, speciation (the
with a contrasting white belly that gives formation of new species) may occur. As
them a "hooded" appearance. Females an example, consider the population of
are brownish gray, with a similar pat- "white" birds shown in (a). It becomes
tern. The Pink-sided race, found in the divided into two populations that do not
central Rocky Mountains, has pinkish- interbreed because they are geographi-
brown sides, a blue-gray hood, black cally isolated by the formation of a large
lores, and a white belly. The Oregon river (b). Over time, each population is
race of western North America is quite exposed to different ecological factors,
variable, with paler colors found in which cause natural selection to favor
Slate-colored
the more southerly populations. In all different traits in each—represented by
Oregon forms, the black hood of the the black versus white plumage in (c),
male contrasts sharply with the brown and the two populations "diverge" in a
back, pinkish to buff sides, and white process known as divergent evolution.
belly. The hoods of females are gray. Such ecological factors might include
Some researchers consider the Pink- slightly different food supplies, pred-
sided race a pale version of the Oregon ators, habitats, nesting materials, and
race. Not shown, are Gray-headed competitors. If the two populations
and White-winged races. Where their become so different that they can no
ranges overlap, the Dark-eyed Junco longer interbreed, they are considered
races interbreed frequently, producing separate species. In (d), the two popu-
offspring with intermediate coloration. lations have reestablished contact with
Hybrids between the Slate-colored and one another (due to range expansion or
Oregon races are particularly common, removal of the geographic barrier), yet
especially in the Great Plains. The fact they have retained their separate iden-
that the Dark-eyed Junco races are, in tities—demonstrating that they are prob-
general, separated geographically but ably not interbreeding and are, indeed,
not reproductively is evidence that the separate species. Adapted from Mader
different forms, once each considered (1988, p. 522).
separate species, are actually races of
a single species. Slate-colored race
photo by Marie Read; Pink-sided and
Oregon race photos courtesy of Ted
Pink-sided
Willcox/CLO.

Oregon

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 V

1.58 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.59

AMAZON RIVER isolated islands is colonized, natural selection may proceed differently
KEY
on the different islands, eventually producing an array of new spe-
Dusky Antbird
cies that all evolved from the same founding species (Fig. 1 46). The
-

0 Individual Record formation, from a common ancestor, of a variety of different species

adapted to different niches and behaviors, usually showing different
Range
Ii Dusky
morphologies (sometimes drastically different), is known as adaptive
Antbird radiation (or simply "radiation").
Blackish Antbird Although adaptive radiation is not restricted to islands, very iso-
lated island chains present some of the most striking examples. The
• Individual Record
Galapagos, a cluster of islands 600 miles (965 km) off the west coast
Range
a Figure 1-46. Adaptive Radiation on
Islands: New species frequently evolve
•

„lit D
when a small population of birds col-
• onizes a distant island and gene flow

Figure 1-45. The Role of Geographic

Mainland
cf) with the parent population becomes
minimal or nonexistent. When a group
of islands is colonized, natural selection
Isolation in Antbird Speciation: In the may proceed differently on the different
rain forests of South America, the vast islands, eventually producing an array of
Amazon River marks the boundary new species in a process termed adap-
between the ranges of many similar tive radiation. a. In this hypothetical
b
species, including the Dusky and Black- Blackish example, species A from the mainland

D
ish antbirds. These two species appear Antbird colonizes the closest island. b. Over
very similar, except that the plumage of
the male Dusky Antbird is a lighter gray
than thatof the male Black ish Antbird, as
)11hP cfi) time, different selection pressures (fac-
tors that favor one trait over another) on

c,
the island cause the founding population
illustrated here. What role the Amazon to evolve enough differences to become
River played in the divergence of these a new species, indicated as B. Species
species is not clearly understood. Per- B spreads to the next closest island. c.
haps the Amazon, instead of serving as by physical barriers. The formation of new mountain ranges, the for-
Over more time, the population of B
an absolute barrier to the intermingling mation of new large bodies of water, or changes in climate and the c
on the second island adapts to its new
of the two groups, maintained slightly consequent changes in the distribution of specific habitats can be environment, evolving into new species
different ecological conditions or sets C, which spreads to the next island as
responsible for separation of bird populations and the formation of
of competing species on its two banks,
new species (Fig. 1 45).
-
BC well as to the first, where it is unable to
which, together with the partial water interbreed with species B and remains
barrier, discouraged a mixing of the Because populations exist at every conceivable intermediate Cf3 as a separate species. d. Eventually, spe-
individuals from the two sides. Where stage between recently isolated populations and completely separate cies C on the third island evolves to be
the two species occur together, on the
northern bank of the Amazon and in
species, decisions on how to draw the artificial "species/subspecies"
Wel" C) a new species, D, which spreads to the
last two islands and back to the second
line are usually controversial. Often, there simply is not enough infor-
the coastal lowlands of the Guianas, d island, where it remains separate from C.
they occupy slightly different habitats. mation to determine exactly where on this continuum the forms lie.
e. Finally, the populations of species D
From Neotropical Ornithology, edited In some cases, future work may shed light on how different the forms on the last two islands each adapt to the
by P A. Buckley, Mercedes S. Foster, Eu- are and how much gene flow exists. In other cases, the distinctions BC conditions on their own island, forming
gene S. Morton, Robert S. Ridgely, and
are more a matter of perspective: different people would categorize D two new species, E and F Adapted from
Francine G. Buckley. Ornithological Campbell (1990, p. 468).
the populations differently. In some cases "superspecies"—groups of
Monographs No. 36, published by the
American Ornithologists' Union, 1985. closely related species—can be described, such as the Great Blue
D D
Reprinted by permission of the American Heron of North America, the Gray Heron of the Old World, and the
Ornithologists' Union. White-necked Heron of South America. Differentiating between su- e
perspecies and groups of subspecies always will be contentious.
New species also frequently evolve when a small population of
birds colonizes a distant island, and further gene flow with the parent
population is minimal or nonexistent. Over time the founding popu-
lation evolves to be better adapted to the local environment: some traits
0 IA
disappear, while others become more widespread. Mutations occur,
and if advantageous, spread across the island. When a whole group of
D
11*
Cornell Laboratorq of Ornithologq Handbook of Bird Biolog
1.60 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.61

Figure 1-47. Adaptive Radiation in of Ecuador, are a veritable laboratory of recent speciation. Never con- Ground-Finches: The Small, Medium, and Large ground-finches use
Darwin's Finches: The Galapagos nected to one another or to South America, the small volcanic islands their strong, conical beaks to crack and eat seeds—their names re-
Islands are home to a group of finches flecting the relative sizes of their beaks. Smaller species are restricted
were at first without life. Gradually, they acquired habitats that could
known as "Galapagos Finches" or
support the animals that reached them accidentally from overseas. to eating smaller and softer seeds. The Sharp-beaked Ground-Finch
"Darwin's Finches." Now placed
within the family Emberizidae, the 14 The separate forms of mockingbirds and tortoises found on each island has a longer, more pointed beak, which it uses to probe flowers for
species are a classic example of adap- provided an important stimulus to Charles Darwin as he developed nectar and leaf-litter for insects and seeds. On some islands, birds
tive radiation, as they are all thought to
his theory of evolution. of this species have even longer beaks, which they use to draw and
have evolved from a common ancestor drink the blood of large seabirds (see Fig. 6-30m) and to break open
The Galapagos also are host to an array of finches. These "Gala-
that reached the islands from South
pagos finches" (order Passeriformes, family Emberizidae) are a classic seabird eggs and drink the contents. The Small, Medium, and Sharp-
America. Although they are similar in
appearance—gray, brown, black, or example of divergent forms evolved from a common ancestor. These beaked ground-finches also remove ticks from iguanas and tortoises.
greenish, sparrow-sized birds with short birds are commonly known as Darwin's Finches, although Darwin did The Common Cactus-Finch has a longer, thinner beak that it uses in
wings and tails—the shape and relative a variety of ways, most notably to extract nectar, pollen, and pulp
not notice their similarities until the eminent ornithologist John Gould
size of their beaks differ from species to
pointed them out while viewing Darwin's collected specimens. The from prickly pear cacti. The Large Cactus-Finch has a large, heavy
species. Beak shape is not an infallible
identification aid, though, as it varies 14 species found today probably radiated from a single ancestral finch beak that allows it to feed on larger seeds and insects than most
widely among individuals within some species that arrived on the Galapagos relatively recently from South other ground-finches.
species, especially among populations America. Limited dispersal, isolation, and adaptation to different types
of the same species on different islands.
Warbler-like Finches:These two species have distinctively thin, pointed,
of foods found on the islands eventually produced an array of spe- warbler-like beaks used for picking insects and spiders from flow-
Based on feeding habits, the finches fall
roughly into three groups, the ground- cies with notably different beak types—although most are still clearly ers, leaves, and twigs, as well as for probing flowers for nectar. The
finches, the warbler-like finches, and variations on the typical seed-eating finch beak (Fig. 1-47). Based on Cocos Island Finch is found only on Cocos Island, 390 miles (630
the tree-finches, but there is consider- feeding habits, the finches fall roughly into three groups: km) northeast of the Galapagos, where being the only Darwin's
able diversity within the groups. See
text for details. From Pough, F. H., J. B. Finch, its foraging methods and diet have diversified tremendously.
Heiser, and W. N. McFarland, Vertebrate But, interestingly, instead of individual birds each using a variety
Life, 4th Edition. Copyright 1996 Pren- of foraging techniques, different individuals within the population
tice-Hall. Reproduced by permission of
have adopted different specific foraging methods.
Prentice-Hall, Inc.
Tree-Finches: These birds spend significantly more time foraging in
trees than do the ground-finches. The Vegetarian Finch has a short,
broad beak for crushing and eating fruits, leaves, and buds. The
Darwin's Finches Small, Medium, and Large tree-finches have conical, somewhat
parrot-like beaks, which are able to apply force at the tip, and are
used primarily to probe into decaying wood to extract insects. The
Woodpecker Finch Woodpecker Finch has a long, stout, tanager-like beak for prying
Common Cactus-Finch
I Woodpecker-like l large insects from bark and soft wood. The Mangrove Finch, found
in dense mangrove swamps, has a similar, but smaller, beak, used
to capture insects and spiders. Woodpecker and Mangrove finches
are famous for their ability to use "tools"—using cactus spines or
Mangrove Finch
twigs to pry insect larvae and pupae from holes in dead branches
(see Fig. 6-10a).
Small Ground-Finch

Cocos Island Finch

Even more spectacular, however, are the Hawaiian honeycreepers.
(Cocos Island only) The Hawaiian Islands, the most isolated group of islands in the world,
Insectivorous
once was home to an extensive bird fauna, now mostly extinct. From a
Medium Tree-Finch goldfinch-like ancestor arose several dozen species of small birds that
Ground- Sharp-beaked Warbler-like
show a remarkable array of bill sizes and shapes, all of which evolved
Finches Ground-Finch Finches
Tree- to exploit different niches on different islands (Fig. 1-48).
Small Tree-Finch Finches

Orders and Families of World Birds

The living species of birds in the world total about 9,600. All
Vegetarian Finch Ancestral Seed-Eating
Ground-Finch are named in accordance with the binomial system established by

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

1.62 Kevin J . McGowan Chapter 1— Introduction: The World of Birds 1.63
Linnaeus and now controlled by the International Commission of
Zoological Nomenclature. Through its code, the Commission stipu-
lates how the names shall be written, makes decisions on accepting Apodiformesl
t
or rejecting names proposed, and sometimes authorizes changing or Hummingbirds,
Swifts
otherwise altering names already in use. AppendixA lists the 31 orders Pelecaniformes
Cormorants, Boobies,
and all families of living birds. Figure 1 49 depicts the 31 orders in
- / Pelicans, Gannets, Caprimulgiformes
\ Anhingas, Frigatebirds Nightjars, Oilbird
their primary habitats.
Ciconiiformes Coliiformes Mousebirds
Sphenisciformes
Penguins Herons, Storks, Ibises, Cuculiformes
New World Vultures, Cuckoos,
and Allies Roadrunners,
j. Ula-ai-hawane (Ex.) Anis
f. Kona Grosbeak (Ex. ) h. Hawaii Amakihi W Opisthocomiformes
Procellariiformes Hoatzin
Albatrosses,
e. Laysan Finch Phoenicopteriformes Galliformes
Shearwaters, Petrels
Anseriformes Flamingos Grouse, Pheasants,
g. Lesser Akialoa (Ex.) Ducks, Geese, Swans, Turkeys, Megapodes,
Screamers Guans, Curassows,
k. Apapane and Allies
d. Ou (Probably Ex.) i. Akohekohe Upupiformes
Falconiformes Hoopoes,
Hawks and Allies,
Musophagiformes Woodhoopoes
Turacos
Old World Vultures,
Secretary-Bird
Coraciiformes
\Kingfishers,
c. Nukupuu Motmots,
(Probably Ex.) Podicipediformes Gruiformes Hornbills,
Grebes Cranes, /Rollers, Bee-Eaters,
NBustards,
-4. Todies Tinamiformes
m. Black Mamo (Ex. I R u si taradsd
Rails, n Tinamous
b. Akiapolaau

dij
Passeriformes
Psittaciformes
vl sects and Necta Perching Birds
Macaws, Parrots, A
Parakeets
Beris TrogTorongiofonsrmesc
a. Maui Parrotbill n. Hawaii Mamo (Ex.) Charadriiformes Columbiformes
Auks, Pigeons, Doves
Shorebirds,
Gulls
Ancestral
Drepanidinae
'-
Strigiformes
Rheiformes Owls
Rheas 13iciformes
Figure 1-48. Adaptive Radiation of Hawaiian Honeycreepers: way, the Akiapolaau chisels, woodpecker-like, into soft wood 4\Toucans,
Illustrated here are 14 of the 32 known species of Hawaiian with the lower beak, then uses the long upper beak as a probe Woodpeckers,
Honeycreepers, a subfamily (Drepanidinae, within the family to reach insects. Jacamars,
Barbets,
Fringillidae) of small, often colorful birds with a bewildering The beaks of some Hawaiian Honeycreepers are short and Puffbirds,
variety of beak shapes. Extinct species are noted with (Ex.) after stout. The thick, powerful beak of the Kona Grosbeak (t) was Honeyguides
the name. The ancestral honeycreepers were probably a flock used for cracking the small, extremely hard fruits of naio trees;
of cardueline finches from North America that strayed out over and the thick, parrot-like beak of the Maui Parrotbill (a) is used
the Pacific Ocean and landed on one of the Hawaiian Islands.
They subsequently spread to the other islands, radiating into
to search for insect larvae and pupae by ripping into decaying
wood, small twigs, ripe fruits, and plant stems. Other beaks 41 1/
t il
Casurifome
numerous species with a dramatic diversity of beak shapes and are slender and decurved, adapted for gathering nectar from
Cassowaries, Emu Dinornithiformes
feeding habits. flowers, as in the liwi (I), the Black Mamo (m), and the Hawaii Kiwis
Struthioniformes
Three members of the same genus (b, c, and g) illustrate Mamo (n). Still others, not shown, are slender and warblerlike Ostrich
the correlation between beak shape and specific function. for gleaning insects and probing flowers for nectar.
The Lesser Akialoa (g) had a long, slender, decurved beak for The most abundant and widespread Hawaiian Honey-
picking insects from bark crevices as the bird hopped along creeper, the Apapane (k), may resemble the ancestral form. It
tree limbs. The Nukupuu (c) has a long, slender, strongly de- uses its long, slightly decurved beak to glean insects and probe
curved upper beak and a shorter, thicker lower beak; the lower ohia flowers for nectar. It is well-known for its long-distance
beak is used alone to chip and pry away loose bark as the bird flights in search of flowering ohia trees. Figure 1-49. Living Orders of World Birds: The world's 31 orders of living birds are shown here in their primary habitats—
searches for insects on tree trunks. In the bizarre beak of the Adapted from Ecology and Field Biology, Second Edition, by water, shore, open ground, trees, or air. This schematic only approximates the real world, however, because some groups actu-
Akiapolaau (b), the lower beak is straight and stout, whereas Robert Leo Smith (1974, p. 476). Copyright 1966 and 1974, by ally contain members in several different habitats, and because subtle variations among different types of each major habitat are
the upper beak is slender, sickle-shaped, and nearly twice as Robert Leo Smith. Reprinted by permission ofAddison-Wesley not shown. The evolutionary relationships among the different orders are not well established and remain highly controversial
long. Holding its beak open to keep the upper beak out of the Education Publishers, Inc. among ornithologists. Note that the bird silhouettes are not drawn to scale.

Cornell Laboratorq of Ornithologg Handbook of Bird Biologg

1.64 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.65
Figure 1-50. Vermivora and Mniotilta
Orders and Families of North American Birds Wood-Warblers: By noting the scien-
Appendix B lists the living orders and families of birds that occur tific names of bird species, and which
in North America north of Mexico, including Hawaii. ones are placed in the same genera,
you may gain useful information on the
relatedness among similar species. For
How Naming and Classification Can Help You example, among the numerous species
of New World wood-warblers (family
Now that you have read the information on the naming and clas- Parulidae), the Black-and-white Warbler
sification of birds, peruse the latest edition of your field guide. In most Black-and-white Warbler is distinct enough to warrant its own ge-
guides the names and sequence of taxa are roughly in accordance nus, Mniotilta, whereas the Tennessee,
with the lists in Appendices A and B. In your guide, be sure to note the Orange-crowned, Nashville, Virginia's,
Colima, and Lucy's warblers are more
following:
similar to one another than to other
(1) The sequence of orders and families. Try to learn as much of the warblers, and thus are placed in the
same genus, Vermivora. The Vermivora
sequencing as you can. Besides helping you to crackthe book quickly
warblers have slender, finely pointed
at the right place for a particular group of birds, the sequence will bills for picking insects from leaves
give you recent scientific thinking on evolutionary relationships and branches; muted colors—usually
among the groups. olive, green, brown, gray, white, and/or
yellow; and songs that include trilled
(2) The sequence of species within a family. Although purely con- notes. The Black-and-white Warbler
Tennessee Warbler Orange-crowned Warbler
jectural, the sequence is an attempt to put related species close is most distinctive in its foraging be-
together. havior: it creeps like a nuthatch along
tree trunks and large branches, probing
(3)The scientific names of species in a large family or subfamily, such into bark for insects and spiders with its
as the wood-warblers, Parulidae.The words, when translated, may slightly decurved bill. Its placement in
in the Handbook of Bird Biology, alphabetical by common name, is a separate genus is based primarily on
be helpful by describing the bird's appearance, behavior, range, or
located after the references. For any species that occurs both in North anatomical adaptations for this foraging
habitat. They also may be useful to you by expressing relationships. style: it has a much longer hallux, shorter
America and in other countries where it has a different common name,
For example, the Black-and-white Warbler is so different from all tarsus, larger feet, and stronger legs than
the North American name is used. For example, Common Loon is used
the other warblers that it warrants its own genus, Mniotilta; theTen- other warblers. Its genus name, Mniotilta
when speaking of the same species in Europe, where the English name (literally, "moss-plucking"), also reflects
nessee, Orange-crowned, Nashvi I le, Vi rgi n ia's, Colima, and Lucy's
is Great Northern Diver. this habit and its species designation,
warblers are so much more like one another than like the rest of the varia ("variegated"), refers to its bold,
So that you will recognize when the common name of a particular
warblers that they share one genus, Vermivora (Fig. 1-50). Know- black-and-white striped plumage. The
species is mentioned, it is capitalized—for example, "YellowWarbler."
ing this, you can better understand why these birds are so similar Black-and-white Warbler also com-
Therefore, a Yel low Warbler is a specific species, Dendroica petechia, monly forages among foliage, gleaning
in color patterns, in the way they nest, and in many of their songs
and a yellow warbler is any warbler that is yellow. insects I ike other wood-warblers. Photos
and calls.
Throughout the Handbook of Bird Biology, the following terms of Tennessee and Black-and-white war-
are used to cover particular groups of birds: blers courtesy of Bill Dyer/CLO. Photo
of Orange-crowned warbler courtesy of
The Use of Common Names Ratites: All birds lacking a keel on the sternum. Includes the flightless Donald Waite/CLO.
Unlike so many groups of organisms—plants, worms, insects, and Ostrich, rheas, Emu, cassowaries, and kiwis, as well as the ti namous,
soon—all bird species have common names in English. Unfortunately, which are fully capable of flight.
not everyone agrees on just which common names should be "official,"
so reference to the scientific names is still important. In North America,
Waterfowl: Ducks, geese, and swans. Thus, refers only to the family
Anatidae.
the common names are so well established and familiar, thanks to
consistent following of the AOU Check-list, that both professionals Water Birds or Aquatic Birds: All species with webbed feet that com-
and amateurs speak of species by their common names, confident that monly swim, including the Anatidae; also, all deep-water waders
everyone will know which species they are referring to. belonging to the order Ciconiiformes, such as herons and storks.
In this course, therefore, birds are referred to by their common
Seabirds or Marine Birds: All species directly associated with the open
names. The common names given in the 42nd Supplement to the AOU
seas and consistently dependent on the seas for food.
Check-list(AOU 2000) are used for all species covered by that list. All
species not covered by the AOU Check-list are referred to by the Eng- Shorebirds: Oystercatchers, plovers, snipes, sandpipers, curlews,
lish names provided by James Clements in his Birds of the World: A phalaropes, and sheathbi Ils. Ornithologists in Britain and the British
Checklist(2000). A list of the scientific names of all species mentioned Commonwealth, except Canada, speak of shorebirds as "waders."

Cornell Laboratory of Ornithology Handbook of Bird Biology

1.66 Kevin j. McGowan Chapter 1— Introduction: The World of Birds 1.67
Land Birds or Terrestrial Birds: All species not included in the aquatic and Asia, but most species have somewhat limited distributions. A
groups above. few, such as the Kirtland's Warbler and Guadalcanal Honeyeater, are
restricted to very small areas. Similarly, some bird families, such as the
Gallinaceous Birds: Grouse, quails, turkeys, pheasants, and all other
swallows (Hirundinidae) and larks (Alaudidae), have representatives
Gal I 'formes; includes domestic chickens.
on most continents, whereas others are found on just one or two.
Raptors:All diurnal and nocturnal birds of prey, namely Falcon iformes The earth has not always looked as it does today, and appreciating
and Strigiformes. why birds are distributed in these ways requires an understanding of
Perching Birds, Passerine Birds, or Passerines: All species of Passeri- historical changes in climate and the movements of the continents,
formes. as well as past speciation, dispersal, and extinction patterns in differ-
ent lineages of birds. For a chart of the major geological time periods,
Songbirds: All passerines in the suborder Passeri. These birds have and a summary of the changes in the global climate, the arrangement
particularly complex voice boxes. of the continents, and the diversity of living things, see Appendix C:
Geological Time Scale.
Occasionally, for lack of a suitably inclusive name for a group Two hundred forty-five million years ago, a single land mass
of birds, the ordinal or familial name will be shortened; for example, known as Pangea formed. It then broke apart into two large masses:
"charadriiform birds" for the order of shorebirds, gulls, and auks; "al- Laurasia, in the north, and Gondwanaland, in the south. These even-
cids" for the family of auks, dovekies, guillemots, murres, and puffins. tually fragmented into separate continents (Fig. 1-51). Attached to
If the names are unfamiliar to you, refer to the list of orders and families great plates that float on the molten rock of the earth's mantle, the
in Appendices A and B. continents slowly drifted into different arrangements—a process that
continues to this day. Over time, continental collisions and volcanic
activity have created mountains, and erosion has lowered them; huge
Evolution of Birds and Avian FliBht basins have filled with water, and others have drained; and the output
■ Did birds evolve 230 million years ago from small, arboreal reptiles of energy from the sun has varied—causing dramatic changes in the
called thecodonts, or 150 million years ago from terrestrial theropod global climate.
dinosaurs? Did feathers, which probably first evolved as insulation, The early diversification of birds took place on a very different
then enlarge to promote gliding from trees, leaping on the ground, or earth; neither the arrangement of the continents nor the distribution
insect-catching? And what were the few birds like that survived the of climates resembled those of today. During the time that modern or-
massive extinctions at the end of the Cretaceous period—to become ders of birds were evolving, in the early Tertiary about 50 to 60 million
the wellspri ng of all modern birds?The answers to all of these questions years ago, Gondwanaland already was breaking apart: South America
remain elusive, but the debates rage on. had separated from Africa and India had split from Antarctica and was
These complex and controversial topics are beyond the scope moving north to collide with Asia. North America, Europe, and Asia
of this course, but we have included an in-depth discussion of them remained joined as Laurasia, however.
in an optional section located at the beginning of Part 2. This is an During much of the Tertiary period the world's climates were
exciting area of research because so many fossil birds continue to be warm from pole to pole, and birds moved through the tropical-sub-
discovered—as you may hear through the news media. These new tropical or warm temperate forests that covered Eurasia and North
findings compel researchers to alter their theories, so our view of the America. At first, movement was easy across a broad North Atlantic
relationship between birds and reptiles is continually evolving. land bridge. After the separation of North America from Europe dur-
ing the Eocene, however, the Bering land bridge between Siberia and
Alaska became the main corridor for faunal exchange between Eurasia
Bird Distribution and North America.
Similarly, the warm climate of Gondwanaland allowed much ex-
■ Although birds are found nearly everywhere on earth, their distri- change of fauna amongAfrica, South America, and Australia. Dispersal
bution is quite uneven. Some habitats, such as tropical rain forests,
between Australia and South America was possible via the temperate
have numerous species, whereas others, such as deserts and alpine
climates and forests of Antarctica. The early flightless ratites may have
zones, have few. Even among similar habitats the distribution is un-
taken advantage of this dispersal route, resulting in Ostriches in Africa,
even—the rain forests of the Amazon Basin in South America host
Emus in Australia, and rheas in South America. Penguins, too, may
many more species per square mile than those of the Congo Basin in
have moved among all three continents via Antarctica.
Africa, for example. Furthermore, species' ranges vary tremendously
At the close of theTertiary, the earth's climates cooled, especially
in size: some species, such as the Northern Harrier and Tundra Swan,
in the polar regions, and became more strongly seasonal.Tropical birds
are found throughout the northern portions of North America, Europe,
became restricted to equatorial latitudes. During the Pleistocene, cli-

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

1.68 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.69
Figure 1-51. Continental Drift:Attached matic changes and glaciers drastically altered the distributions of birds
to plates that float on the molten rock of throughout the world. Dry, cool climates alternating with wet, warm
a. Triassic
the earth's mantle, the continents slowly
ones split the geographic ranges of birds and promoted both speciation
have drifted into different arrangements
over time—a process that continues and extinction. Remnant or relict populations are one major conse-
today. a. Triassic: Around 245 million quence of historical habitat changes. For example, Ostriches, now
years ago, at the end of the Paleozoic restricted to Africa, once roamed throughout Asia, and todies—tiny,
Africa
era, all the continents came together to South
America
colorful kingfisher relatives found only on the Greater Antilles of the
form one large supercontinent called
Pangea, which persisted throughout the West Indies—once lived in Wyoming and France.
Triassic period. b. Jurassic: Around 200 Antarctica
million years ago, during theJurassic pe-
riod, Pangea split into two large masses, Distribution of Land Birds
a northern Laurasia, consisting of pres- Birds can be a window on the world in many ways. Knowing that
ent-day North America, Europe, and
some North American birds migrate south for the winter, you can use
Asia; and a southern Gondwanaland,
consisting of South America, Africa, b. Jurassic
them to tell the seasons. For instance, if you saw a picture or a film
Madagascar, India, Australia, New Zea- from Ithaca, NewYork, and it included a Rose-breasted Grosbeak, you
land, and Antarctica. During this time, L wa s would know that the picture must have been taken between May and
the earliest birds evolved. c. Cretaceous: October. Similarly, you can observe geography using birds as a lens.
During the late Cretaceous period, Gond-
If you were blindfolded and whisked away to some distant part of the
wanaland fragmented—South America Africa
split from Africa and India split from South globe, and if you knew your birds of the world well enough, you could
America
Antarctica and drifted north toward Asia. tell where you were, within perhaps a thousand miles or so, simply by
Laurasia remained more or less intact. observing birds.
This is the approximate configuration Antarctica
Scientists looking at the fauna of the world, including birds, have
of the continents during the time period
when most of the modern orders of
divided the globe into six general regions, with boundaries where the
birds evolved, in the very early Tertiary. distributions of many different types of animals all seem to change.
d. Eocene Epoch ofTertiary: At this time, These regions roughly mirror the continents, but many boundaries
North America separated from Eurasia, are climatic rather than physical (Fig. 1 52). The following sections
c. Cretaceous -

but a land bridge between Alaska and

describe the avifauna (set of bird species) of each region.
Asia remained, allowing the exchange
Liu rasia
of fauna. The components of the former
Gondwanaland continued to drift apart, Palearctic Region
heading toward their current positions. The Palearctic region encompasses most of the large landmass
Just 10 million years ago, India collided of Eurasia, as well as northern Africa and most of the Sahara desert.
South
with Asia, forming the towering Hima- America It stretches from the Atlantic to the Pacific and from the Arctic to the
layas. Adapted from Gill (1990, p. 470).
Himalayas, and is by far the largest region. The major physical fea-
Antarctica tures and habitats run roughly in east-west belts and are, from north
New
to south: the arctic tundra, the boreal forests (also known as conifer-
Zealand ous forests, or taiga), a chain of deserts stretching from the Sahara in
Africa east to the Gobi in Mongolia, and a nearly continuous chain
of mountains (from the Pyrenees and Alps east to the Himalayas). The
climate ranges from the high arctic to the subtropical, stopping short
d. Eocene Epoch of Tertiary
of the true tropics.

■
North
Eurasia Because so much of this region is either temperate (free from ex-
America
treme heat and cold, but experiencing some of both) or arctic, a large
proportion of the avifauna migrates south to winter in the tropics or be-
South
America
Africa
I — Madagascar

Australia
yond. In winter, insect food is scarce, but a small number of birds, such
as the titmice (chickadee relatives), woodpeckers, and nuthatches,
have adapted to remain and continue their insect diet throughout the
Antarctica year. When winter is over and the northern lands warm again, insect
populations increase rapidly, and the food available for insectivorous
New
Zealand
birds becomes tremendous. Migrants return in the spring and take
advantage of the abundant insects to raise their young.

Cornell Laboratorq of Ornithologg Handbook of Bird Biologu

1.70 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.71

Other typical Palearctic birds include larks, Old World fly-

catchers, pipits, and wagtails (Fig 1-54).

Nearctic Region
-4"
The Nearctic region includes arc-
tic, temperate, and subtropical North
America, reaching south to the northern
Nearctic border of tropical rain forest in Mexico; it also
Region
includes Greenland. Although it contains many of the me
"-:%••••••• same physical features as the Palearctic, the major moun-
Oriental Region tain ranges of the Nearctic (the Rocky Mountains in the
lib /.
3
west and the smaller Appalachians to the east) run north-
Neotropical "*.... south, adding a layer of complexity to latitudinal climate belts. As Figure 1 53. Dunnock: Formerly called
-

................. .......
.....
Re ion Afrotropical in the Palearctic, east-west belts of arctic tundra and boreal forest exist, the Hedge Sparrow, the Dunnock is the
Region best-known representative of the only
Australasian Re ion with patches of deciduous forest extending southward wherever there
V bird family endemic to the Palearctic
is sufficient rainfall to support it (as in the southeastern United States). region, the Prunellidae. Although the
The center of the continent, with lower rainfall, consists of prairie-cov- Dunnock is common in gardens, wood-
ered plains; areas further west, with even less rainfall, are semi-arid lands, scrublands, and cultivated areas
and desert. The southern tip of Florida and the extreme southwestern throughout western Europe, in central
and eastern Europe, it breeds mainly in
United States and northern Mexico are subtropical.
mountainous areas. It is brownish above
As in the Palearctic, a large proportion of the bird species are and grayish below, and generally spar-
migratory, taking advantage of the abundance of spring insects to raise row-like in appearance, but has a more
their young, but leaving northern Nearctic areas after breeding—many slender, pointed bill than most sparrows.
Drawing by Robert Gillmor.
to winter in the Neotropics.These birds, termed Neotropical migrants,
Figure 1-52. The Six Major Zoogeo- The land bridge across the Bering Strait once allowed the ex- include wood-warblers, tanagers, and orioles. The springtime return of
graphic Regions: Scientists studying change of species between Eurasia and North America, and the similar multitudes of these colorful birds is one of the most spectacular birdi ng
the world's fauna have divided the land
avifaunas of the two continents reflect this connection—although the events of the region.
areas of the globe into six major regions.
At the boundaries of the regions, distri- Palearctic also shares many species and higher taxa with the other re- Despite the diversity of Nearctic habitats, no avian families are
butions of many different types of ani- gions it borders. Many Palearctic birds would be familiar to a visiting endemic to the region. Instead, the Nearctic is more distinctive for its
mals, including birds, change. Many of North American, as approximately 13 percent of Palearctic species blend of Palearctic and New World groups, which reflects the conti-
the boundaries are climatic rather than
and 35 percent of the genera also are found in the Nearctic. In fact, so nent's varied history: periods of isolation as well as periods when land
physical, but the regions generally mirror
the continents. In some cases, different many groups of birds (for example, loons and alcids) occur in these bridges connected with South America or Eurasia (either via Green-
researchers divide the globe differently. two regions and nowhere else on earth that some authorities prefer to land or the Bering Strait).
For example, Greenland may be includ- group the Palearctic and the Nearctic regions into one, the Holarctic.
ed with the Palearctic region instead of The Holarctic has the fewest bird species per land area of any of the
with the Nearctic; Madagascar and New
regions, presumably owing to the harsh climatic conditions found in Figure 1 54. White Wagtail: Inhabiting
Zealand may each be placed in separate -

regions; and the islands of Oceania in many areas. Birds characteristic of, but not limited to, the Holarctic farmlands, grasslands, and other open
the mid and southern Pacific Ocean, include hawks, owls, grouse, woodpeckers, swallows, thrushes, king- areas throughout Eurasia, often near
including Hawaii, may constitute a water, wagtails (family Motaci I lidae) are
lets, tit-mice, creepers, crows, jays, and many shorebirds and water
separate region. In some cases, the slender, titmouse-sized birds with long
birds that breed in the Arctic. tails. Their habit of frequently wagging
Afrotropical region is referred to as the
"Ethiopian" region, and theAustralasian Perhaps surprisingly, despite its size, the Palearctic region has but their tails gives them their name. Aided
region as the "Australian." Drawing by one family that is endemic (found only in that region), the Prunellidae by their strong legs and long toes, wag-
Charles L. Ripper. (accentors and Dunnock)—sparrow-I Ike birds with slender, pointed bills. tails typically run across the ground in
pursuit of insect prey, and occasionally
Twelve of the thirteen species of this family inhabit high mountains—
snatch insects from the air. The White
ranging from northwest Africa and western Europe as far east as Japan. Wagtail shown here (formerly called
The other species, the Dunnock (Fig. 1-53), breeds at somewhat lower the Pied Wagtail) is common and well-
elevations in Europe, and is a familiar garden bird in Great Britain. known because it often lives near hu-
mans, running along roads and rooftops
Bird groups with a great array of species in the Palearctic include
after insects. It breeds in northwestern
the buntings (genus Emberiza), Old World warblers (family Sylviidae), Alaska as well as Eurasia. Photo by T. J.
and cardueline finches (family Fri ngill idae, subfamily Carduelinae). Ulrich/VIREO.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

1.72 Kevin J. McGowan Chapter 1— Introduction: The World or Birds 1.73
World barbets), Furnariidae (ovenbirds), Dendrocolaptidae (wood-
creepers), Thamnoph i I idae (antbirds), Form icari idae (antthrushes and
antpittas), Conopophagidae (gnateaters), Rh i nocryptidae (tapacu los),
Cotingidae (cotingas), Phytotomidae (plantcutters), Pipridae (mana-
kins), Oxyruncidae (Sharpbill), Dulidae (Palmchat), and Coerebidae
(Bananaqu it).
The tremendous avian diversity of the region results partly from
the types of environments found there—particularly the extensive trop-
ical rain forest of the Amazon Basin, which covers about one-third
of South America. Rain forests, with their complex structure, warm
climate, and abundant resources, contain more species per land area
than any other habitat on earth. There are also vast grasslands—some
north of the Amazon River, but even more extensive ones to the south,
the pampas, stretching from Mato Grosso in Brazil south to Patagonia.
These grasslands host numerous species of birds and other wildlife.
Within the southern grasslands, extending across parts of Brazil, Par-
aguay, and Bolivia, is an expansive region, the Pantanal, which is trans-
Figure 1-55. Great Tit: A member of Bird groups shared with the Palearctic, in addition to those formed each year into a huge marsh by torrential rains. The Pantanal
the same family, Paridae, as the familiar already listed under the Palearctic region, include larks, pipits, nut- has one of the greatest concentrations of wildlife on the continent,
North American chickadees and titmice, including numerous waders and other water birds, as well as the few
hatches, cranes, pigeons and doves, shrikes, and kingfishers. Although
the Great Tit, with its yellow breast, is
the particular species represented may differ in the two regions, they remaining Hyacinth Macaws. South America narrows so much to-
a bit more colorful than its New World
relatives. Found throughout much of often are similar in ecology and basic appearance. For example, a ward the south that not much land area is found within the temperate
the Palearctic and Oriental regions, the GreatTit (Fig. 1 55) or a BlueTit might come to a bird feeder in Europe,
-
zone—a climate that typically contains fewer species. To the west,
Great lit readily breeds in nest boxes, the towering Andes, adding an array of habitats at different altitudes,
instead of a Black-capped Chickadee or a Tufted Titmouse, but any
and thus has been the subject of many
North American birder would notice the similarities in behavior and run the length of the continent. Along the Pacific coast south
detailed, long-term studies. It is very
similar in behavior to the chickadees appearance immediately. of the equator, the cold and fish-laden Peru (Humboldt)
of North America. Drawing by Robert The New World families—those occurring in both the Nearctic current flows northward from the Antarctic, supporting a
Gillmor. and Neotropical regions but nowhere else—include the New World rich diversity of oceanic birds (see Fig. 1-102). This cold
vultures, NewWorld quail, Limpkin, hummingbirds, tyrant flycatchers, current sets up a temperature inversion by cooling a layer
mockingbirds and thrashers, vireos, blackbirds and orioles, and wood- of air directly above the ocean, which is overtopped by
warblers. Only one of the 78 species of wrens (Troglodytidae) occurs the warm, tropical air typical of most of the area. The lay-
outside the New World—the Winter Wren, known simply as the ering creates the Atacama Desert along the Pacific coasts of
"Wren" in Great Britain (Fig. 1 56). The distinctive turkeys (family
-
Ecuador, Peru, and northern Chile, because fog and clouds often form, Figure 1-57. Wild Turkey: Native to
but rarely rain. Although the Atacama is one of the driest deserts on North America, the Wild Turkey inhabits
Phasianidae, subfamily Meleagridinae) also are restricted to the New
mature forests, roosting high in trees at
World (Fig. 1-57). earth and thus has few bird species, it covers a relatively small portion
night, and by day scratching the ground
of the Neotropical region. for nuts with its large, strong feet. Turkeys
Neotropicat Region The historical isolation of the Neotropics also contributes to its also eat grass seeds, buds, bulbs, berries,
The Neotropical region includes South America, Central America extraordinary avian diversity. Over much of the last 60 million years, and some small animals. Wild Turkeys
north to the northern edge of tropical forests in Mexico, and the West are the only native New World birds to
the Central American land bridge between North and South America
be widely domesticated. Explorers in the
Indies. It has by far the greatest diversity and the greatest number of bird was transformed into a series of islands by high water levels. As a result, 1500s found them al ready domesticated
Figure 1-56. Winter Wren: The small, species per area of any of the faunal regions, hosting approximately South America was effectively a huge island, its only connection with in Mexico and Central America, and
spunky wrens are almost entirely a New one-third of all bird species found on earth. About one-third of the fam- another faunal region reduced to the island "stepping-stones" across took these birds back to Europe. Colo-
World family, but the tiny, stubby-tailed nists eventually brought them back to
ilies found here are endemic: Tinamidae (tinamous), Rheidae (rheas), Central America. During this time, a huge array of new birds evolved
Winter Wren of North America is also North America. When displaying to fe-
found throughout much of the Palearctic Anhimidae (screamers), Cracidae (curassows, guans, and chachal- in South America, resulting in the numerous endemic groups found
males, the males raise and fan their tails,
region—where it is known as the "Eu- acas), Eurypygidae (Su nbittern), Psophiidae (trumpeters), Cariamidae today. assuming a posture familiar to every
ropean Wren" or simply as the "Wren." (seriemas), Pluvianellidae (Magellanic Plover), Thinocoridae (seed- A further factor contributing to the plethora of Neotropical spe- schoolchild. They also lower and spread
In North America, it breeds mainly in
snipes), Opisthocomidae (Hoatzin), Steatornithidae (Oilbird), Nycti- cies is the fluctuating climatic conditions (the series of "Ice Ages") their wings, raise their back feathers, and
moist, coniferous woods, often near give loud gobbles, while the bare skin
streams, but it frequents a wide variety of
biidae (potoos), Todidae (todies), Momotidae (motmots), Bucconidae during the Pleistocene, which created habitat "islands" within both
of their head turns red, blue, and white.
Palearctic habitats. Drawing by Charles (puffbirds), Galbulidae (jacamars), Ramphastidae (toucans and New the Andes mountains and the lowland areas of the Amazon Basin. In Drawing by Charles L. Ripper.
L. Ripper. the Andes, many of the high forests have cool temperatures year round,

Cornell Laboratorg of Ornithologg Handbook of Bird Biologq

1.74 Kevin J . McGowan Chapter 1— Introduction: The World of Birds 1.75
and many bird species are restricted to these forests and elevations. Figure 1-58. Paramo "Islands" of the
During the previous ages when the world was cooler, the forests on High Andes: In the high northern Andes
of South America, areas above the tree
the main chain of the Andes were connected by low-lying cool forest
line but below the zone of permanent
to the forests on peaks lying out away from the main chain. Each time snow (glaciers) are covered by a habitat
the world heated up, the cool forests retreated to the higher elevations, called paramo—humid grasslands with
and those on the outlying peaks became isolated, separated from the some shrubs, dotted with lakes and bogs.
Currently, paramo and glacier-covered
others by a vast expanse of hot lowland forest, as they are today. Al-
land areas (shown in black) exist as
though no obvious physical barriers existed, cool forest specialists chains of isolated islands on the higher
found their desired habitats isolated from similar ones on "sky islands." Aw K, Venezuela peaks, separated by areas of lowland
These mountain islands acted as genuine islands, and many new spe- or mountain forest. During the Pleis-
•
cies evolved in these very restricted areas. New species continue to tocene, however, the cool, dry climate
accompanying each period of glaciation
be discovered in these areas even today, as scientists explore the most
allowed the glaciers and paramo to ex-
remote of these mountaintop islands. Similarly, periods of glaciation pand, creating long, continuous regions
caused areas of the high Northern Andes above the tree line that are of paramo connecting the islands. The
covered by glaciers and a humid grassland habitat termed paramo ,
greatest extent of this continuous par-
Y amo habitat is shown by dashed lines.
to become connected, allowing a greater exchange of species (Hg.
v/' The alternating warm and cool climates
1-58). In the Amazon Basin, the cool periods (which were also dry) r ' 0,1
7
during the series of Ice Ages caused the
4
caused the extensive rain forests to shrink to isolated patches known e r k f• is/ glaciers and paramo islands to shrink
as refugia. These refugia were widely separated by grasslands. Existing and expand repeatedly—creating con-
species thus were fragmented into a number of isolated populations, ditions highly favorable for speciation.
Many new forms or species could evolve
many of which experienced different selection pressures and evolved
4117 Colombia in the isolated islands during warm peri-
into new species. When warmer conditions returned, these new spe- ods, and then come in contact with one
cies expanded their ranges with the expanding forests. In this way,
i
,
%.
.,. N .r_..../... another during cooler periods. When
..... similar species or forms come together,
formerly widespread species evolved into a number of different spe- c.....`01
natural selection often causes them to
cies that had either more limited ranges or overlapping ranges, or some t 1-• rapidly diverge to reduce competition
combination .The current distribution of certain toucan species reflects (
/ .1, for similar resources. The result of these
a um lor
this pattern of speciation (Fig. 1-59). i (....,
./ alternating conditions, then, is a great
:
Of the many endemic bird families in the Neotropics, some 4.... number of endemic bird species, many
.e./
,e miles with quite restricted ranges. In a similar
contain just a few species, but others have radiated into numerous
o 100 200 way, the distribution of high forests in
species. Some of the smaller, but more extraordinary, families include I
0 100 200 300 the Andes alternated between islands
the following: Kilometers and larger, connected areas, also fa-
voring large-scale speciation and the
rheas (2 species): large, flightless ratites of the temperate open Current Distribution of Paramo j
CS
Greatest Area Covered by Paramo evolution of numerous endemic spe-
country and Glacier-covered Land t..) During Past Glacial Periods cies with restricted ranges. Reprinted
tinamous (46 species): primitive, grouse-like birds whose eerie calls with permission from Vuilleumier, Beryl
haunt both forests and pampas (see Fig. 7-21); tinamous are the only Simpson, 1971. Pleistocene Changes in
the Fauna and Flora of South America.
ratites capable of flight
Science, Vol. 173, Number 3999. Copy-
screamers (3 species): heavy-bodied, goose-like birds with far-reaching right 1971, American Association for the
calls (see Fig. 4-1 8a) seriemas (2 species): fast, long-legged, grassland birds that chase down Advancement of Science.
Hoatzin (Fig. 1-60) (1 species): an odd-looking, leaf-eating bird whose their reptile prey on foot
young clamber about in trees on all fours, aided by small claws on
their wings (see Fig. 3-41) One of the most important features of the Neotropical avifauna
seedsnipes (4 species): ptarmigan-like birds that nest both in southern is the extensive radiation of the suboscines (Tyranni). This suborder of
lowlands and in high mountains the huge order Passeriformes is distinguished from the other suborder,
Oilbird (1 species): a large, nocturnal frugivore, related to nighthawks, Passeri (oscines or songbirds), by the relatively simple syrinx. No re-
that uses echolocation to reach its nest deep within caves (see Fig. gion on earth has as many suboscines as the Neotropics; in fact, most
4-53) regions have none or only a few. Fully a third of the Neotropical bird
trumpeters (3 species): large, hump-backed, chicken-like birds that species are suboscines. In general, the Neotropical families with the
roam the rain forest floor in flocks, sometimes following army ants most species tend to be suboscine, including the following:
for the arthropod prey they disturb

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

1.76 Kevin J . McGowan Chapter 1— Introduction: The World of Birds 1.77
Figure 1-59. Amazonian Rain Forest Refugia and the Distri- relationships remain unclear. Clements (2000) considers Ptero-
bution of Aracaris: In the Amazon Basin, the cool, dry glacial glossus inscriptus humboldti a subspecies of the Green Aracari,
a. Hypothesized Dispersal of Three Aracaris
periods of the Pleistocene caused the extensive rain forests to instead of a subspecies of the Lettered Aracari, as shown here.
from Amazonian Refugia
shrink to isolated patches separated by grasslands. These iso- a. Hypothesized Dispersal of Three Aracaris from Amazonian
lated patches are known as refugia. Existing species thus were Forest Refugia: Colored areas indicate the presumed locations
fragmented into a number of isolated populations, many of of large forest refugia in tropical South and Central America dur-
Guiana Refuge which experienced different selection pressures and evolved ing the cool, dry glacial periods of the Pleistocene. Dark areas
Green Aracari into new species. When warmer conditions returned—be- indicate mountains above 6,600 feet (2,000 m). Researchers
tween the Ice Ages, and in the time since the last glacial hypothesize that a single aracari species was fragmented into
Belem Refuge period—the new species expanded their ranges with the ex- populations in the Guiana Refuge, the Belem Refuge, and a
Lettered Aracari (P. i. inscriptus) panding forests. In some cases, such as the aracaris illustrated third site in the upper Amazon (possibly a group of refuges
here, a widespread, ancestral species apparently evolved into known as the Eastern Peruvian Refugia). In isolation, they each
a number of species with more limited ranges. Aracaris are evolved into new forms. As the forests expanded during warmer
slender, small to medium-sized toucans. The three forms dis- times, the new forms expanded their ranges as indicated by the
cussed here, the Green Aracari and two subspecies of the Let- arrows. b. Current Ranges of Three Amazonian Aracaris: The
Eastern Peruvian
tered Aracari (considered subspecies because they interbreed current ranges of these three forms, indicated by the different
Refugia
Lettered Aracari
along their common boundary), differ mostly in the color of types of shading, overlap very little. After Haffer (1974). Copy-
(P. i. humboldti) the bill. These three aracaris are so similar that their taxonomic right Nuttall Ornithological Club.

b. Current Ranges of Three

Amazonian Aracaris
_

Vp

Lettered Aracari (P. i.

Letterecl Arac-ari (P. i. inscriptus) Figure 1-60. Hoatzin: The bizarre,

chunky, pheasant-sized Hoatzins, with
their blue, bare facial skin, bright red
eyes, and ragged crest, appear to be
caught in a perpetual bad-hair day.
Found in noisy groups crashing around
the foliage along slow-moving streams
and oxbow lakes of theAmazon and Ori-
noco Basins, Hoatzins place their crude,
communal nests low in branches over-
hanging streams. Nonbreeding adults
assist the breeding pair in tending the
eggs and young. To escape danger, the
nestlings may drop into the water. They
climb back to the nest using small claws
on their wings (see Fig. 3-41). Hoatzins
are among the few bird species that eat
mostly leaves, including many con-
taining toxic compounds; the leaves are
digested and detoxified by bacteria in
VP
their gut. Drawing by Robert Gi I lmor.

Cornell Laboratorq of Ornithologq Handbook of Bird Biolcvi

1.78 Kevin J . McGowan Chapter 1— Introduction: The World of Birds 1.79
woodcreepers (51 species): similar-looking, rust-colored
birds with a wide array of beak shapes (Fig. 1-61); they
forage in bark much like the unrelated Brown Creeper
of North America
antbirds (197 species): small, insectivorous, forest birds;
some specialize on following columns of army ants
to prey on the insects and other arthropods stirred up
by the numerous moving ants (Fig. 1-62; also see Fig.
7-28 and Ch. 9, Sidebar 3: Ant Followers)
antthrushes and antpittas (60 species): small, drab birds
with loud, ringing songs; many haunt the rain forest
floor and may follow army ant swarms
ovenbirds (240 species): a diverse group, especially nu-
merous in temperate South America, named for the
oven-shaped, clay nests of some species (see Fig. 4-118) Figure 1-62. White-plumed Antbird:
Antbirds are small, often boldly pat-
tapaculos (52 species): antbird relatives with cocked tails, frequenting
terned birds that frequently move
more southerly, open, and dry areas than antbirds through the rain forest in mixed-species
----- foraging flocks. Most species pick insects
The most numerous of all subosci nes are the flycatchers. Although and other arthropods from foliage, with
different species feeding at different lev-
many "fly-catching" birds around the world are called "flycatchers,"
els in the forest. The group gets its name
the huge family Tyrannidae (tyrant flycatchers) is entirely restricted from a few species, informally termed
to the New World. Only a handful of the nearly 400 tyrannid species the "professional antbirds," which spe-
make it to the Nearctic, and they are all rather similar, generalized, cialize on following columns of army
ants as they march across the forest
aerial insectivores (see Figs. 2-15 and 7-43). In the Neotropics, the
floor. These antbirds prey on arthropods
tyrant flycatchers have evolved to fill a large number of ecological stirred up by the movi ng ants. The White-
roles, specializing into a diverse assemblage (Fig. 1-63). plumed Antbird, striking with its white
The Neotropical avifauna also includes many bird groups that are face and crest, black head, blue-gray
shared with the Nearctic or Holarctic regions. In the near future, DNA back and wings, and chestnut breast
and tail, is among the most common
comparisons may provide useful clues on the origins of these groups,
of the professional antbirds in northern
but for now scientists can only speculate based on the distribution of Amazonia. Photo by Doug Wechsler/
species. The overwhelming number of species of both hummingbirds VIREO.
and tyrant flycatchers in the Neotropics compared to the Nearctic
suggests that both these groups originated in the Neotropics and
later reached the Nearctic. Other shared groups include New World
Figure 1-61. Woodcreepers: Found in forests, forest borders, and to slender and strongly downcurved, as in the scythebills vultures, waterfowl, hawks, New World quail, pigeons, owls, wood-
and mangroves throughout Central and South America, the sub- (16 and 17). These bill variations undoubtedly reflect subtle peckers, vireos, jays, wrens, thrushes (Turdidae), New World war-
oscine woodcreepers (family Dendrocolaptidae) resemble the differences in foraging methods. A few species, notably the blers (Parulidae), tanagers, cardinals (Cardinal idae), and blackbirds
unrelated oscine creepers (family Certhiidae: Brown Creeper Plain-brown Woodcreeper, are regular followers of army
and New World orioles (Icteridae). Regardless of where these groups
of North America and treecreepers of Eurasia) in both appear- ants, capturing the insects flushed as an ant swarm passes by
ance and habits. Using its stiff tail as a brace, a woodcreeper (see Ch. 9, Sidebar 3: Ant Followers). Species shown here are originated, most of them radiated in the Neotropics to such an extent
hitches its way along branches and up tree trunks, peering and (1) Ruddy Woodcreeper, (2)Tawny-winged Woodcreeper, that they currently contain many more Neotropical than Nearctic spe-
probing for insects and other small animals under bark, in tree (3)Plain-brown Woodcreeper, (4) Olivaceous Woodcreeper, cies. Two important families, the fruit-eating tanagers and the closely
crevices, or among mosses and epiphytic plants (plants, such (5) Wedge-billed Woodcreeper, (6) Spot-crowned Wood-
related, insect-eating New World warblers, contain numerous species.
as orchids and bromeliads, that grow on other plants). The tail creeper, (7) Streak-headed Woodcreeper, (8) Buff-throated
is well-adapted to wedge into irregularities in the bark as the Woodcreeper, (9) Long-tailed Woodcreeper, (10) Spotted A few members of each migrate to the Nearctic to breed, but these are
bird climbs, because the feather shafts extend beyond the vanes Woodcreeper, (11) Straight-billed Woodcreeper, (12)Strong- essentially Neotropical groups. Although both titmice (Paridae) and
and curve downward. The 51 species are remarkably similar billed Woodcreeper, (13) Black-banded Woodcreeper, nuthatches (Sittidae) are widespread throughout the rest of the world,
to one another in appearance, their rufous or olive plumage (14) Amazonian Barred-Woodcreeper, (15) Black-striped they have no Neotropical members.
usually barred or spotted with lighter colors in the head and Woodcreeper, (16) Red-billed Scythebill, and (17) Brown-
breast regions. However, as can be seen from this plate of 17
Most of the non-endemic bird families of the Neotropics are
billed Scythebill. Painting by John A. Gwynne (adapted), from
species from Panama, bill shape varies widely, from short and A Guide to the Birds of Panama by Robert S. Ridgely and John shared only with the Nearctic or Holarctic, but several groups, such
pointed (bird #5); to long, strong, and woodpecker-like with A. Gwynne, 1989, Plate 19. Published by Princeton University as the parrots and trogons (Fig. 1-64), are found in tropical regions
varying amounts of curvature (for instance, 7, 12, 13, and 14); Press. Used with permission.

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1.80 Kevin j. McGowan Chapter 1 — Introduction: The World of Birds 1.81
throughout the world. Birds dis- Figure 1-64. Slaty-tailed Trogon: Tro-
a. Vermilion tributed in this way are said to be gons are chunky, colorful birds that tend
b. Cliff Flycatcher
Flycatcher
pantropical. to perch on branches in a characteristic,
c. Cock-tailed upright posture with their long, square
Tyrant Because so much of the
tail pointing down. They often remain
Neotropical region is covered perfectly still for long periods of time.
by lowland tropical forest, Thus, in spite of their brilliant colors,
fruits and flowers are particu- they can be difficult to see, but their
frequent "cow, cow, cow" call may give
larly abundant, and frugivory
away their location. These fruit- and
(specializing on eating fruit) is insect-eaters dig their nest cavities in
particularly common. Entire dead trees or in active termite or wasp
g. Long-tailed
Tyrant families of frugivorous birds nests. Although most trogon species live
have evolved, such as the in the Neotropics, they are also found in
tropical Africa and Asia. The Slaty-tailed
cotingas, manakins, most of
Trogon is found in rain forests from Mex-
e. Spectacled
the tanagers, and the toucans ico to Ecuador. Photo by Marie Read.
Tyrant (Fig. 1 65). Abundant flowers
-

f. Short-tailed feed the large number of hum-

Pygmy-Tyrant mingbirds, a successful group
k. White-crested Spadebill
h. Sharp- containing more than 300 spe-
tailed Tyrant I. Boat-billed Flycatcher cies, all but a dozen of which
are found only in the Neotropics. Easy food, such as abundant fruits,
allowed many Neotropical birds to evolve a mating system in which
the males take no part in rais-
ing young, but instead display Figure 1-65. Choco Toucan: Toucans,
instantly recognizable with their enor-
elaborately for mates—often
j. Royal mous, gaudy bills, live in Neotropical
congregating in traditional forests, nesting and roosting in tree cav-
Flycatcher
i. Many- display areas that females ities. In body shape and some aspects of
colored
Rush-Tyrant
visit. The colorful Neotropical their ecology, they are convergent with
manakins (see Figs. 6-42 and the Old World hornbills (see Fig. 1-82).
n. Short-tailed
Toucans use the tips of their large, light-
Field-Tyrant 6-47) and cotingas—including
weight bill to reach out and grab ripe
the fantastically plumaged urn- fruits. They then flip back their head and
m. Ringed
Antpipit brellabirds (Fig. 1 66) and the
- toss the fruit down their throat. Although
gaudy cocks-of-the-rock (Fig. primarily frugivorous, toucans also eat
small animals, including the eggs and
1 67) are challenged only by
- —

nestlings of other birds. The Choco

Figure 1-63. Tyrant Flycatcher Diversity: The suboscine family Tyrant flycatchers live in nearly every habitat—from rain for- the New Guinean birds-of-par- Toucan—striking with its yellow and
Tyrannidae (tyrant flycatchers), found only in the New World, est and savanna to the high, treeless paramo; and forage atevery adise for having the most elab- chestnut beak, yellow face and front,
has more species than any other family of birds. Of the nearly forest level—from the ground, understory, and forest edge, to orate plumages and displays in black back, white rump, and red under-
400 species, just over three dozen regularly breed in the Ne- the canopy and above. Like the Nearctic-breeding tyrannids, tail coverts—lives in wet forests on the
the avian world.
arctic. Most of these—including most Empidonax flycatchers, many Neotropical tyrannids sally out to grab flying insects from Pacific slopes of western Colombia and
some kingbirds, the Great Crested Flycatcher, wood-pewees, an exposed perch, but numerous variations exist. Some have Ecuador. Photo by S. Holt/VIREO.
and phoebes—are similar in general shape and aerial insect- even evolved to eat fruit, fish, young birds, or frogs. Some fly-
Afrotropical Region
catching behavior. In the Neotropics, however, the tyrant catchers reach for insects while perched or hovering, whereas The Afrotropical region
flycatchers have radiated into a wide array of ecological roles, others fly out to grab insects from branches, foliage, or even the includes Madagascar, southern
making up roughly 10 percent of all bird species, and 20 to surface of water. The Cliff Flycatcher (b) looks and behaves like Arabia, and all of Africa south of
25 percent of the passerines. Some of the more spectacular a swallow, perching on cliffs to search for aerial insects. The
the Sahara. Isolated by water as well as by sand—the vast Sahara and
tyrant flycatchers pictured here are: the brightly colored Ver- Boat-billed Flycatcher (I) has a huge, wide beak with which it
milion Flycatcher (a) and Many-colored Rush-Tyrant (i), the may capture large insects, and the tiny White-crested Spadebill Arabian Deserts—the region has many endemic families and is second
long-tailed Strange-tailed Tyrant (d) and Long-tailed Tyrant (g); (k) uses its wide, flat beak like a shovel, scooping insects off only to the Neotropical region in the number of species. Although
the bizarre Royal Flycatcher (j), which flashes its fan-shaped the undersides of leaves. The long-legged Ringed Antpipit (m) much of the region is relatively warm, it is also dry, receiving only about
orange crest only during alarm or aggression; the Cock-tailed walks on the rain forest floor, looking up at the undersides of half as much rain as South America. As a result, a greater proportion of
(c) and Sharp-tailed (h) tyrants, with modified tail feathers; the leaves and then hopping up to grab any insects it finds. The
the region is covered by desert, scrub, grassland, and savanna, and the
miniature Short-tailed Pygmy-Tyrant (0; and the Spectacled Short-tailed Field-Tyrant (n) is also terrestrial. Original paint-
Tyrant (e), with its conspicuous yellow eye wattle. ing by John W. Fitzpatrick, from Traylor and Fitzpatrick (1982). areas of tropical rain forest are somewhat more restricted than those of
Reprinted with permission of John W. Fitzpatrick. the Neotropics. Although mountainous regions are present, there is no

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1.82 Kevin . McGowan Chapter 1— Introduction: The World of Birds 1.83
Figure 1-66. Long-wattled Umbrel- region is above 3,000 feet, compared to less than 17 percent of the
labird: Like other members of the sub- Neotropical region. Around the equator, in the western two-thirds of
oscine family Cotingidae, umbrellabirds
the continent, is the lowland tropical rain forest of the Congo Basin. As
are large, stocky fruit-eaters of the Neo-
tropical forests. Many cotingids are in the Amazon Basin, the dry, cool glacial periods of the Pleistocene
beautiful and interesting, with bizarre created a series of refugia here, which are thought to have served as
courtship rituals. The Long-wattled Urn- centers for species diversification across the east-west axis of today's
brellabird, a bit larger than an American
equatorial tropical forests.
Crow, is black with a bluish gloss. Males
have a large, umbrella-shaped crest on Farther from the equator, and in parts of the plateau regions, are
the head and a long, fleshy, inflatable vast areas of open woodlands, savannas, and grasslands. Characteristic
wattle—covered with feathers—hang- birds of the grassy areas are cisticolas (small, drab, insectivorous war-
ing down from the throat. Females are blers), weavers (a diverse group of colorful seed-eaters, many of which
similar with a smaller wattle. Males dis-
weave large, complex nests), and waxbills (another group of colorful
play in the rain forest canopy by spread-
ing their crests, inflating their wattles, seed-eaters; seeAustralasian region for more information). Deserts and
and jumping from branch to branch semi-arid scrublands, with sparse vegetation and scattered trees such
while giving a long, low grunt. Drawing as acacia (and in the east, baobab), are found in three main areas: (1) in
by Robert Gi I lmor.
the Sahel region, just south of the Sahara, (2) in the northeast, between
the Gulf of Aden and northern Tanzania, and (3) in the southwest—the
Kalahari Desert region. Typical birds of these open areas are larks,
Figure 1-67. Guianan Cock-of-the- bustards, and coursers. Bustards are large, heavy-bodied, flat-headed
rock: Another cotingid (see Fig. 1-66), birds with long legs and necks (Fig.1-68). They often assume bizarre Figure 1-68. Kori Bustard: Stout birds
the flicker-sized, male Guianan Cock-
postures during their elaborate courtship displays. Coursers are slen- with long legs and necks, the ground-
of-the-rock is among the gaudiest of dwelling bustards frequent a variety of
Neotropical rain forest birds. It is almost der, plover-like ground nesters that sometimes cool their eggs or young
open habitats, from semi-desert and
entirely vivid, day-glo orange, with some by partially burying them in sand or by bringing water to the nest in grassland to dense scrub. They eat a
white and black markings. A large, disk- their breast feathers. In addition, the trees support a great diversity of variety of plant and animal foods rang-
like crest nearly hides the beak. Females
other species, including many Palearctic migrants. ing from shoots, flowers, and berries to
are dull, olive brown, with a smaller
Families endemic to the Afrotropical region include the fol- insects, frogs, and small mammals. Al-
crest. Males display in groups of up to
though most species live in Africa, a few
40 or 50 birds at traditional sites, usually lowing:
are found in the Oriental, Australasian,
near rocky outcrops. Each male clears
Struthionidae (Ostrich): the largest living bird, this familiar ratite of and southern Palearctic regions. The
leaves and debris from a small area of
long-lived Bustards range in size from
ground to form his own display "court." deserts and savannas is almost entirely herbivorous; Ostriches breed
as small as a Ring-billed Gull to as large
When a female arrives to choose a mate, communally, with several females laying eggs in the same nest as a Tundra Swan. They have strong legs
the males erupt into a cacophony of calls Balaenicipitidae (Shoebill): a large, stork-like water bird with a huge, and feet designed for running, with three
and displays, but much of their "show-
shoe-shaped, hooked bill for seizing big fish (Fig. 1-69) forward-facing toes and no hallux. Their
ing off" consists of static posturing di- plumage is cryptically colored in buff
rected toward the female. Typically just or brown overall. Some of the smaller
a few males do most of the mating. The species perform dramatic aerial court-
female performs all of the nesting activi- ship displays: males of the Buff-crested
ties—sticking her cup nest of mud to a Bustard fluff their feathers and fly straight
rock wall near the entrance to a cave, up into the air, sometimes as high as 100
incubating for approximately 40 days, feet (30.5 m), then parachute back down
and then feeding the young exclusively to earth. The large Great Bustards and
on fruit. Kori Bustards (pictured here), display on
major chain comparable to the Andes, with its tremendous diversity the ground. These courting males cock
their outspread tails forward, inflate their
of altitudinal zones. All of these factors undoubtedly contribute to
gular (throat) sacs, retract their heads,
the lower species diversity of the region compared to the Neotropics and elevate the light-colored neck and
(1,560 versus 3,300 species). The drier climate hosts relatively few undertail feathers—creating a feathered
water birds, but a great diversity of terrestrial and seed-eating birds. entity that only barely resembles a bird!
The different climate zones of Africa exist roughly as a series of lat- Drawing by C.J. F. Coombs, from A Dic-
tionary of Birds, edited by Bruce Camp-
itudinal belts that become more open and dry farther from the equator.
bell and Elizabeth Lack, p. 75. Copyright
The eastern and southern thirds of the continent, however, are raised 1985, The British Ornithologists' Union.
into wide plateaus 3,000 feet (1,000 m) or more above sea level, too Reproduced with the kind permission of
dry to support forests. Approximately 37 percent of the Afrotropical the British Ornithologists' Union.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

1.84 Kevin . McGowan Chapter 1 — Introduction: The World of Birds 1.85
Figure 1-69. Shoebill: The only member Scopidae (Hamerkop): a stork-like water bird whose shaggy, crested
of its family, the Shoebill (also known nape and stout, tapering bill make the head appear hammer-shaped
as the Whale-headed Stork) has a huge,
(see Fig. 8-38)
shoe-shaped bill with a prominent,
hooked nail at the tip. Standing nearly Sagittariidae (Secretary-bird): a long-legged bird of prey that stalks
4 feet (1.2 m) tall, the Shoebill hunts the savannas on foot for snakes, other small vertebrates, and large
freshwater swamps of central and east- insects (Fig. 1-70)
ern Africa by waiting motionless for long
Coliidae (mousebirds or colies): long-tailed birds about the size of
periods, watching the water for unwary
fish, amphibians, aquatic snakes, and a Mourning Dove that climb through vegetation using their stout,
small birds. Its nest is a large, flattened hooked beaks; they frequently perch in "chin-up position," hanging
mound of grass on floating plants, hid- vertically down from a branch (Fig. 1-71)
den among dense vegetation. Nesting Musophagidae (turacos): noisy, arboreal relatives of cuckoos that run
Shoebills regularly bring water to the
nest in their large bills, pouring it onto
squirrel-like along branches; the plumage is soft green (one of the
their eggs and downy young to cool few green pigments known from birds), blue, or gray, often with red
them. Photo by A. MorrisNIREO. on the wings (Fig. 1-72)
Phoeniculidae (woodhoopoes): sociable birds with glossy, dark plum-
age and long tails; woodhoopoes nest in tree cavities and breed
cooperatively—with additional adult birds helping the parents to
tend the nest
Lybiidae (African barbets): small, colorful, stocky birds with large,
sometimes serrated, beaks; they dig their nest cavities in trees, earthen
banks, or termite nests
Picathartidae (rockfowl): dull-colored birds with colorful, bare heads;
they hop along the rain forest floor in rocky areas and nest colonially
in caves
Promeropidae (sugarbirds): two long-billed, long-tailed, nectar-feed-
ers that specialize on Protea plants on the mountainous slopes of
South Africa Figure 1 71. Speckled Mousebirds: The
-

----- grayish or brownish mousebirds (also

known as colies) get their common
Also endemic to the Afrotropical region are the guineafowl, six
name from their long, drooping tails
species that form subfamily Numidinae within the pheasant family and habit of scurrying along the tops
(Phasianidae). These gregarious, chicken-like birds have distinctively of branches, mouse-like. They clamber
spotted and striped plumage that often lands them in zoos (Fig. 1-73). through vegetation with great agility,
and often cling upside down, like par-
They have loud, harsh calls and are often domesticated.
rots, to feed on fruits, foliage, and nec-
The Afrotropical region shares many families with the Oriental tar. Strong claws and reversible first and
region, as well as about 30 percent of the genera. But, only about two fourth toes aid their acrobatic abilities.
percent of the species are shared, probably reflecting how long the Highly gregarious, mousebirds live year
birds of the two regions have evolved independently. A significant round in groups of a dozen or more,
breeding cooperatively, and constantly
annual event is the huge influx of migrants that occurs as roughly
chattering and whistling as they forage
one-third of the Palearctic species, mostly insect-eaters, move south in the wooded savannas and scrublands
to overwinter throughout Africa. of sub-Saharan Africa. They roost in tight
Many Afrotropical birds are passerines, including larks, weav- clusters, often dust-bathing and playing
together, preening each other, or perch-
ers, shrikes, and sunbirds (Fig. 1-74). All these groups have numerous
ing breast-to-breast for warmth—as
species in the Afrotropical region. Other passerine groups that are pictured here. The Speckled Mousebird
well-represented include thrushes, cisticolas, starlings, bulbuls, bush- is the most widespread species, rang-
Figure 1-70. Secretary-bird: The sole member of its family, the gray and black Secretary-bird is distinctive with its elongated shrikes, and waxbills. ing throughout eastern, central, and
central tail feathers and long, loose crest of quills. Over 3 feet (1 m) tall, this long-legged bird-of-prey hunts by striding through the southeastern Africa. Drawing by lan
Important nonpasserine components of the avifauna include
savannas and grasslands, stamping its feet to scare potential prey—large insects, reptiles, rodents, and other small animals—out Willis, from The Birds of Africa, Vol. 3,
of hiding. It is known for capturing snakes and then crushing them against the ground with its blunt talons. Despite being ground hawks, hornbills (see Oriental region), bee-eaters, and rollers. Bee- p. 252. C. H. Fry, S. Keith, and E. Urban,
hunters, Secretary-birds fly and soar well, performing spectacular aerial courtship displays with undulating dives and croaking eaters are brightly colored birds with long, slender beaks. They catch editors. Copyright 1988 Academic Press
calls. Their nest, used year after year, is a large platform of sticks in the top of a shrub or tree, often in the flat-topped acacia trees stinging bees, wasps, and ants flycatcher-like, beating them to remove Limited. Used with permission.
common throughout the African savannas. Drawing by Robert Gillmor.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

1.86 Kevin J. McGowan Chapter 1 — Introduction: The World of Birds 1.87
Figure 1-72. Schalow's Turaco: Together with plantain-eaters and go-away- Figure 1-75. Red-billed Oxpeckers on
birds, turacos make up the family Musophagidae. These crow-sized, long- a Black Rhinoceros: The bluebird-sized
tailed, arboreal birds are weak fliers, preferring to run along branches much oxpeckers inhabit savannas throughout
like squirrels. Their outer toe can be rotated forward or back, but is often used much of eastern and southern Africa,
at right angles to the main axis of the foot—allowing them to nimbly traverse feeding on ectoparasites that infest the
branches in search of fruit, foliage, and buds. Their harsh, barking calls are fa- skin of large mammals. They forage
miliar sounds in the African forests. The forest-dwelling turacos and plantain- in small flocks, hopping and climb-
eaters are usually soft green, violet, blue, or some combination of these colors, ing over the bodies of grazing zebras,
with crimson on the wings. They also have colorful crests, eye rings, and bills. giraffes, buffalo, rhinos, warthogs,
The gray and white go-away-birds inhabit more open, dry woodlands. This antelopes, and even domestic cattle.
family of birds is famous for its unique pigments, found in no other animals. The mammals are usually indifferent
The reds are produced by a copper-containing pigment called turacin, and to, and indeed benefit from, the birds'
the greens, by turacoverdin. Schalow's Turaco, found in the humid forests of gleanings. Oxpeckers have short legs;
south-central Africa, is mostly green, with crimson primaries, a scarlet eye sharp, curved claws; and stiff tails that
ring, and a green crest tipped with white. Photo by P. DaveyNIREO. act as braces—all adaptations helping
them to cling to their hosts. Their bills
are laterally flattened, and the birds open
and close them rapidly in a scissor-like
action as they push them through the
fur or over the naked skin of a mammal,
removing ticks and other skin parasites.
They sometimes capture flies that land
upon the host's skin and drink fluid from
around the host's eyes. Oxpeckers breed
cooperatively and, like their starling rel-
atives, roost communally at traditional
the venom before eating them. Some species are cooperative breeders sites. Photo by Marie Read.
that live in complex societies. Rollers, named for their rolling or rock-
ing dives during courtship flights, appear somewhat like bee-eaters,
but with more muted plumage colors mainly in shades of blue, pink,
olive, or chestnut. They often forage like bluebirds, perching and then
flying to the ground to grab large arthropods.
Particularly interesting in their habits are the oxpeckers (members
of the starling family, Sturnidae) and the nonpasserine honeyguides.
The sociable oxpeckers, also called "tickbirds," climb upon large Af-
rican mammals as they graze, removing ticks, insects, and the scabs
Figure 1-73. Vulturine Guineafowl: The
of skin wounds—a relationship benefitting both the birds and their
large, chicken-like guinea fowl have dark
plumagedistinctivelyspottedandstriped hosts (Fig. 1-75).The honeyguides are peculiar in their ability to digest
with white. The bare skin of the head and wax, especially beeswax, in addition to their insect prey. At least two
neck is often brightly colored and may species use distinctive calls and behaviors to lead humans, baboons,
be adorned with wattles. Some species
or honey-badgers to bees' nests—feeding on the wax and larvae once
have bony casques or feathered crests
on the head. Guineafowl are gregarious the mammalian helper has opened the nest for its honey.
when not breeding, often gathering into The island of Madagascar, off the east coast of Africa, deserves spe-
flocks of 50 or more birds. Their raucous cial mention. Although it shares most of its fauna with mainland Africa
voices can be heard from nearly every Figure 1-74. Mount Apo Sunbird: The tiny sunbirds—some smaller than a Ruby- at the family level, it has been isolated long enough to have evolved a
African habitat—from dense forest to throated Hummingbird—have long, slender, downcurved bills, and the males of many
semi-desert. The Vulturine Guineafowl
number of unique families and a host of endemic species. Its habitats,
species are brilliantly colored, often iridescent. Most of the 124 species inhabitAfrica
has particularly beautiful plumage, in- although much denuded by humans, vary from dry woodlands and
and Madagascar, frequenting a variety of habitats. Some, however, are found in the
cluding brilliant blue on its breast and Oriental, Australasian, and southern Palearctic regions. Although the family name scrub in the west, through central highlands, to rain forest in the east.
back. It occurs in dry, scrubby regions (Nectariniidae) hints that sunbirds feed on nectar, they also eat insects. Short-billed Families unique to Madagascar and the surrounding islands include:
of eastern Kenya, Somalia, and Ethiopia. species tend to eat more insects than nectar, whereas long-billed species primarily
Photo by Marie Read. feed on the nectar of tubular flowers—much like the unrelated hummingbirds. Like mesites (Mesitornithidae): rail-like, ground-dwelling birds, about the
hummingbirds, sunbirds act as pollinators of flowers, and their bills have evolved to size of a Mourning Dove
match the shape of the flowers they visit. Unlike hummingbirds, however, sunbirds ground-rollers (Brachypteraciidae): solitary, terrestrial insect-eaters
cannot hover to feed on the wing. Instead they cling, often upside down, to a flower
with stout bills, short wings, and moderately long legs and tails
as they probe for nectar. Shown here is a Mount Apo Sunbird from the Philippines.
Photo by Doug WechslerNIREO.
(Fig. 1-76)

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1.88 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.89
Cuckoo-Roller (Leptosomatidae): a single, crow-sized, arboreal spe- larger, feeding primarily on figs and other fruits (Fig. 1-78).
cies with a stout, broad bill The Asian barbets are chunky birds slightly smaller than
asities and false sunbirds (Philepittidae): suboscines, the asities feed a Belted Kingfisher, with thick bills and gaudy, clashing
on fruits, and the false sunbirds, on insects and nectar colors; many are green with red, blue, or yellow markings.
vangas (Vangidae): a diverse passerine group of 14 shrike-like species; They feed mostly on fruits and insects (Fig. 1-79). The four
most are gregarious and noisy, gleaning insects and other small species of ioras are small, arboreal songbirds that search
animals as they move through the trees (Fig. 1-77) leaves, often in dense foliage, for insects. Males of some
----- species perform elaborate courtship displays with vertical
Madagascar was the home of the Giant Elephantbird (Aepyorni- leaps and parachuting flights.
thidae), a huge, flightless creature long extinct, which weighed half Birds of the Oriental region—especially in and near
a ton and laid two-gallon (eight-liter) eggs (see Fig. 5-48). The Dodo India—resemble those of tropical Africa more than they
(Raphidae), a flightless bird the size of a turkey, lived only on the island resemble any other faunal group, reflecting the long period in geologic Figure 1-78. Asian Fairy-bluebird:
of Mauritius, east of Madagascar; it has the unhappy distinction of be- history that India spent attached to Africa via Madagascar. The fact Together with the leafbirds, fairy-blue-
ing one of the first birds known to be eliminated by "civilized" humans, that many families (for example, hornbills, honeyguides, broadbills, birds make up the Irenidae, a family
of songbirds endemic to the Oriental
in the 17th century (see Fig. 9-75). bulbuls, sunbirds, and weavers), but few species, are shared between
region. Male fairy-bluebirds have bril-
the Oriental and Afrotropical avifaunas indicates the long period of liant, metallic blue plumage with con-
Figure 1-76. Long-tailed Ground-Roll-
Oriental Region time—about 85 million years—that they have been evolving sepa- trasting areas of velvety black; females
er: The five species of ground-rollers
make up the family Brachypteraciidae, The Oriental region includes all of Asia south and east of the rately. are similar, with somewhat du I ler colors.
which is endemic to Madagascar. These Himalayan Mountains (India and Southeast Asia), as well as southern Particularly well-represented in the Oriental region are members Slightly larger than orioles, fairy-blue-
birds inhabit the canopy of tall, semi-
stocky, ground-dwelling birds have large China and the islands of Indonesia and the Philippines. Although the of the family Phasianidae: Old World quai I, pheasants, partridges, and
heads and eyes, stout bills, short wings, deciduous or evergreen forests, where
H imalayas form a clear boundary with much of the Palearctic region, grouse—as well as the spectacular peafowl (see Fig. 3-6). The domestic they roam widely in search of fruiting
and relatively long tails and legs. All are
the distinction is less clear in China, where some mixing of the Oriental chicken has descended from the Red Junglefowl of this family (Fig. trees, especially figs. Drawing by C. E.
insectivorous, occasionally preying on
small lizards, snakes, or snails. They and Palearctic faunas occurs, with thrushes, accentors, dippers, and 1-80). Additional families with numerous species include pigeons, Talbot-Kelly, from A Dictionary of Birds,
nest in tunnels dug into the side of a tits being shared between the two regions. Similarly, the Australasian by Bruce Campbell and Elizabeth Lack,
corvids, sunbirds, several families of finches, and the following:
bank. Like most other birds of Mada- p. 201. Copyright 1985, The British
and Oriental faunas grade into each other in Indonesia. The boundary
gascar, their populations are in severe Ornithologists' Union. Reproduced
has been chosen somewhat arbitrarily, just to the east of the islands with the kind permission of the British
decline due to human-induced habitat
destruction. The Long-tailed Ground- of Timor and Sulawesi, where the proportions of the two faunas are Ornithologists' Union.
Roller, shown here, is about the size of a roughly equal. The Oriental region is mostly tropical and subtropical,
magpie and is mottled brown and black much of it in rain forest, although there are smaller areas of drier hab-
above, with blue on the wings and outer
itats such as dry forest, scrub, savanna, and desert.
tail feathers and a black band across
the pale breast. It inhabits desert scrub,
Less isolated than the other avifaunal regions, the Oriental hosts
whereas the other four species live in only three endemic families, the Irenidae (arboreal songbirds called
dense evergreen forests. Drawing by leafbirds and fairy-bluebirds), the Megalaimidae (Asian Barbets), and
N. A. Arlott, from A Dictionary of Birds, Figure 1 79. Red-crowned Barbet:
-

the Aegith in idae (ioras). The oriole-sized leafbirds, mostly green and Stocky and colorful, Asian barbets
edited by Bruce Campbell and Elizabeth
yellow, feed mainly on insects and fruit. The two fairy-bluebirds, (family Megalaimidae) are one of just
Lack, p. 257. Copyright 1985, The Brit-
ish Ornithologists' Union. Reproduced named for the brilliant blue and black plumage of the males, are slightly three families endemic to the Oriental
with the kind permission of the British region. They have stout, sharp beaks
Ornithologists' Union. with which they pluck fruits and insects,
and excavate their nest holes. Asian
barbets were once placed in the same
Figure 1-77. Helmet Vanga: The vanga family (Vangidae) consists family with African barbets and South
of 14 species, all endemic to Madagascar. Gregarious, shrike-like American barbets, but the three groups
birds, vangas move through the trees in noisy flocks, capturing are now considered separate families
insects. Most species have heavy bills, which are hooked in some. (with the South American barbets in
Their plumage is boldly patterned and sometimes glossy, and varies the same family as toucans). The Red-
in color—being black and white, blue and white, or a combination crowned Barbet, pictured here, is mostly
of black, rufous, and gray. The HelmetVanga, shown here, has bold glossy green with a red crown, and has
black-and-rufous plumage and a greatly enlarged bill, which it uses red, yellow, and blue facial markings.
to capture insects as well as tree frogs and small reptiles. Drawing Its prominent rictal bristles—the large
by C. E. Talbot-Kelly, from A Dictionary of Birds, edited by Bruce "hairs" visible projecting from the base
Campbell and Elizabeth Lack, p. 619. Copyright 1985, The British of the bill—are characteristic of all bar-
Ornithologists' Union. Reproduced with the kind permission of the bets, and give them their common name.
British Ornithologists' Union. Photo by Tim Laman/VIREO.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

1.90 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.91
Figure 1-80. Red Junglefowl: The fam- Figure 1-82. Rhinoceros Hornbill at
ily Phasianidae—pheasants, partridges, Nest Cavity: Found throughout the
grouse, turkeys, peafowl, and Old World Oriental and Afrotropical regions,
quail—is particularly well-represented hornbills have long tails and strong,
in the Oriental region. Most species decurved bills with a distinctive casque
are ground-dwelling seed-eaters, and on the top. Many species have black-
many—particularly the pheasants and and-white plumage, but the bill is often
peafowl—have elaborately patterned, colorful, and the head may have brightly
colorful plumage. Many of the species colored areas of bare skin or feathers.
are important game birds, and some Hornbill species are found in a variety of
have been domesticated. The Red Jun- habitats, and vary from 2 to 4 feet (38 to
glefowl of Southeast Asia is thought to 126 cm) in length. They eat large insects
have given rise to the domestic chicken. and other arthropods, small vertebrates,
Although the exact date and location of and fruit. Most interesting is their breed-
domestication are not known, domestic ing behavior: the female (sometimes
chickens were recorded in India as early with help from the male) seals herself
as 3200 B.C. The male Red Junglefowl, into the nest cavity, where she remains
shown here, is glossy red and orange throughout incubation and much of the
above, with dark, iridescent underparts nestling period, receiving all of her food
and an elaborate tail. Drawing by Robert from her mate through a narrow slit in
Gillmor, from Lack (1968). the mud-sealed entrance. During this
time, females of many species undergo
a rapid molt and are flightless. The Rhi-
babblers: a diverse group of gregarious, insectivorous birds, many of noceros Hornbill, one of the largest spe-
cies, inhabits Malaysia and Indonesia.
whom have complex social systems and breed cooperatively
In this photo, a male brings food to a
pittas: secretive, stocky birds of the tropical forest floor with long legs Other birds characteristic of the region include owls, parrots, female in the nest cavity. Photo by M.
and short tails; many are brightly colored below and cryptic above; woodpeckers, shrikes, thrushes, warblers, mynas, and Old World Strange/VIREO.
pittas use their heavy bills to catch a variety of insects and other small flycatchers. In addition, many Palearctic migrants overwinter in the
animals, especially snails (see Fig. 7-28) Oriental region.
flowerpeckers: small, often-colorful songbirds, much like sunbirds in Two particularly bizarre bird famil ies found in the Oriental region
their busy, noisy behavior as they forage high in the trees on berries, are the hornbills (Bucerotidae) and the frogmouths (Podargidae). The
nectar, and insects hornbills have huge, down-curved bills topped by a peculiar casque
broadbills: chunky, brightly colored forest birds most closely related (Fig.1 - 82), and are famous for their unique nesting behavior, in which
to cotingas and tyrant flycatchers, they use their wide, flat, colorful the female seals herself inside the nest cavity with the eggs and young
bills to snatch up large insects; 10 of the 15 species of broadbi I Is are nestlings, and depends on the male to bring food (see Figs. 3 - 32,
found in the Oriental region (Fig.1 - 81) 8 -44 and their associated text
Figure 1 83. Papuan Frogmouth: Found
-

sections). The frogmouths re-

in forests of the Oriental and Austral-
semble their nightjar relatives asian regions, the frogmouths resemble
Figure 1-81. Black-and-red Broadbill:
Found throughout the Old World trop- in both cryptic appearance their smaller nightjar relatives in both
and behavior (Fig. 1-83). cryptic appearance and behavior. They
ics, the broadbills are stocky, brightly
have mottled gray or brown plumage
colored, suboscine birds with large, These nocturnal forest birds
and heavy bills with an enormously
wide, colorful bills. They occur in a sally out from a branch and wide gape. From an exposed perch, they
variety of forest and scrub habitats, and
use their wide, "frog-like" wait for suitable prey—large insects or
feed by grabbing insects from foliage or
beaks to snatch up small an- other arthropods, frogs, or lizards—to
out of the air. Some species are large
appear, and then swoop down to snatch
enough to take large grasshoppers and imal prey—including mice,
them from the ground or branches with
small lizards. Broadbill nests are elab- frogs, and small birds—from their wide bills. If disturbed during the
orate, pear-shaped bags, camouflaged
the ground or branches. day, the nocturnal frogmouths assume
with many tendrils, plant fibers, spider
a cryptic pose, freezing with the neck
webs, and lichens hanging below them
like a beard. They are often hung from Australasian Region outstretched and bill angled upward,
The Australasian region resembling a broken branch. Here,
an inaccessible vine or branch across an
open space or above water. The Black- a Papuan Frogmouth shows its large,
encompasses the islands south
and-red Broadbill of Southeast Asia, night-adapted eyes and its wide gape. It
and east of the Oriental region, inhabits northeastern Australia and New
Sumatra, and Borneo is black above and
crimson below, with a blue and yellow
including the Moluccas, New Guinea, and islands in between. Photo
bill. Photo by Doug WechslerNIREO. Guinea, Australia, Tasmania, by W. PeckoverNIREO.

Cornell Laboratory of Ornithology Handbook of Bird Biology

 r-

1.92 Kevin J . McGowan Chapter 1— Introduction: The World of Birds 1.93

Figure 1-84. Varied Sittellas: Because New Zealand, and the numerous smaller islands in the mid-Pacific (logrunners), Pomatostomidae (pseudo-babblers),
theAustralasian region has been isolated Ocean (Micronesia, Melanesia, and Polynesia—including Hawaii). Corcoracidae (White-winged Chough and Apostle-
from other land masses for so long, many
The region, about half tropical and half temperate, is relatively flat, bird), Paradisaeidae (birds-of-paradise), Cracticidae
of its birds are unrelated to those in other
regions. Through convergent evolution, with mountainous areas mainly in New Guinea (tropical) and New (butcherbirds, Australasian Magpie, and currawongs),
however, many have come to resemble Zealand (temperate). Cal laeidae (wattlebirds), Gral I inidae (mudnest build-
other bird groups. One example is the The region is somewhat restricted in total bird species, probably ers), Melanocharitidae (berrypeckers and longbi I Is),
sittellas, which—as their common name
as a result of at least three factors: (1) The large number of islands. As Paramythiidae (Tit Berrypecker and Crested Berr-
reflects—resemble nuthatches (Sittidae)
in appearance and behavior. The two
discussed earlier, islands tend to have fewer species than continental ypecker).
species of sittellas, however, differ from regions, although the species they have may be unique. (2) The rel- Prominent nonpasserines in the Australasian
nuthatches in subtle ways (such as leg atively small land mass compared to the other avifaunal regions. (3) avifauna include parrots, pigeons and doves, and kingfishers (es-
musculature and bill form), as well as in The relatively arid climate. Although the region has some species-rich pecially in New Guinea). In addition, many songbird families have
breeding habits, and are placed in the
tropical rain forest (mostly in New Guinea and northeastern Australia), had extensive radiations here, including the birds-of-paradise, the
family Pachycephalidae, with whistlers.
Also known as "treerunners," the forest- compared to other regions a greater percentage of the land is occupied whistlers and allies, the monarch flycatchers, the honeyeaters, and
dwelling sittellas explore tree branches by drier habitats—woodland, savanna, grassland, scrub, and desert. the Australo-Papuan warblers. Compared to temperate areas of
in tight spirals, working from tip to trunk, Fully 70 percent of Australia is desert, the harsh conditions hosting Europe and North America, the temperate Australasian habitats
and move headfirst down trunks, prying
fewer than two dozen species of birds, including the nomadic Bud- have fewer small seed-eaters (some parrots fill this role) and many
under bark and probing into crevices for
gerigars (see Fig. 4-132). more nectar-feeders, many of which act as pollinators. Notably absent Figure 1 85. Emu: At roughly six feet
-
insects and other arthropods. They oc-
The region is rich, however, in endemic forms—second only to (two meters) tall, the flightless Emu is
casionally use a twig or bark chip as a from the avifauna are Old World vultures, pheasants, woodpeckers,
the second largest living bird, next to the
probing tool. The Varied Sittella shown the Neotropics in the number of endemic families. Australia has been trogons, cardueline finches, and emberizids. Relatively few Palearctic Ostrich. The only member of its family, it
here is common in open Eucalyptus and isolated from other land masses for so long that its fauna include many migrants overwinter in the region—mostly waders and a scattering of has powerful legs with three toes; coarse,
Acacia woodlands of Australia, and is
lineages that originated and radiated there. From their DNA-DNA other birds—although many of the Australasian species have complex loose, drooping feathers; and bare blue
uncommon in New Guinea, where it
hybridization work, Sibley and Ahlquist (1985) suggested that many migratory patterns within the region. skin on the face and upper neck. It is
inhabits moist mountain forests. Unlike
common in open areas throughout Aus-
nuthatches, which nest in cavities, the Australasian songbird families, although resembling birds from other Some of the more spectacular or peculiar birds of the region in-
tralia, occupying habitats ranging from
Varied Sittella builds a deep cup nest in regions, actually result from a huge radiation of a lineage of crow rela- clude the ratite Emu (Fig. 1 85) and cassowaries (see Fig. 3-44, and Fig.
-
near desert conditions to scrub, wood-
a tree fork. Composed primarily of spider
tives—often referred to as parvorder Corvida (see Fig. 7 22).Th is group
- 17 in Evolution of Birds and Avian Flight); the chicken-like megapodes, lands, and alpine pastures. It eats a wide
webs and cocoons, it is camouflaged on
the outside with bark and lichens. The
diversified in the region in the early Tertiary, taking on the ecological in which the males care for eggs from several females in huge, warm variety of foods, including insects such
roles of unrelated birds in other parts of the world. Thus, the Austral- as grasshoppers and caterpillars, fruits,
Varied Sittella is highly social—living, mounds of decaying vegetation (see Fig. 6-36); the strange, flightless
seeds, grains, flowers, and grasses. It
roosting, and breeding in groups. All asian avifauna provides many examples of convergent evolution, such Kagu (Fig. 1 86) a single species, presumably related to the cranes
- —
has adapted well to living in agricultural
group members help to build the nest as the Australo-Papuan warblers of the genus Gerygone, which closely and rails, which lives on the verge of extinction in the forest underbrush areas, where it may come in conflict with
and feed the young, although normally
resemble and behave like the unrelated Sylviid and Parul id warblers of New Caledonia, tapping the ground to locate its earthworm prey; humans by damaging fences and crops.
only one female lays and incubates the
of Eurasia and the Americas, respectively. Similarly, the sit- the diverse, forest-dwelling birds-of-paradise—unsurpassed for male The male Emu, alone, incubates the
eggs. Drawing by N. W. Cusa, from A
eggs and raises the young (for four to six
Dictionary of Birds, edited by Bruce tellas (Pachycephalidae) have a striking resemblance to
months), while the female either remains
Campbell and Elizabeth Lack, p. 539. nuthatches (Fig. 1 84). When Australia drifted closer
-
nearby or leaves to mate with another
Copyright 1985, The British Ornitholo-
to Southeast Asia during the late Tertiary, some of the male. Drawing by Robert Gillmor.
gists' Union. Reproduced with the kind
permission of the British Ornithologists'
crow relatives—including the crows and jays of
Union. family Corvidae—presumably dispersed to Asia
and eventually to other regions, radiating further
in these areas.
The Australasian region has a number
of endemic bird families: Casuariidae
(cassowaries), Dromiceidae (Emu), Ap- Figure 1 86. Kagu: The few remaining
-

Kagu live on the verge of extinction in

terygidae (kiwis), Rhynochetidae (Kagu),
the dense, forest undergrowth on New
Aegothelidae (owlet-nightjars), Acan- Caledonia, a large island northeast of
thisittidae (New Zealand wrens), Cli- Australia. The only member of its family,
macteridae (Australasian treecreepers), the Kagu can run quickly on its strong
Menuridae (lyrebirds), Atrichornithidae legs and feet, and although flightless,
can glide down slopes. It taps the ground
(scrub-birds), Ptilonorhynchidae (bower-
to locate its primary food, earthworms,
birds), Mal uridae (fairywrens), Eopsaltri- and digs up any discovered prey with
Male idae (Australasian robins), Orthonychidae its strong beak. Drawing by Robert
Gillmor.

Cornell Laboratoru of OrnitholoBli Handbook of Bird Biolojt

1.94 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.95
Figure 1-87. King Bird-of-paradise: The ornamentation (Fig. 1-87; also Figure 1-89. Red-collared Myzomela-
birds-of-paradise, found mostly in New see Fig. 3-10); and the bower- a Honeyeater: The 181 species of hon-
Guinea, are famous for their spectacular, eyeaters form the diverse Australasian
birds—builders of remarkably
colorful plumages and displays. In the family Meliphagidae. These active, gre-
complex bowers, which they garious nectar feeders vary widely in col-
past, they were hunted intensively to
provide feathers for European hats. They
decorate to attract females or, size (from as small as a hummingbird
inhabit wet forests at a variety of alti- (see Fig. 6-41). Rivaling the to nearly as large as a magpie), shape,
tudes, and the numerous species differ plumage and constructions of and lifestyle. In an adaptive radiation
significantly in diet, size, and matingsys- nearly as impressive as that of marsupial
the previous two groups are
tem. Males of the King Bird-of-paradise mammals in the same region, they have
the songs and calls of the two spread to every habitat that contains
display solitarily from trees. Photo by W.
PeckoverNIREO. species of lyrebirds. Named for flowering trees and shrubs, evolving
their elaborate, harp-shaped into nectar-feeding species whose form
and behavior resemble birds as diverse
tails (Fig. 1-88), these large
as flycatchers, titmice, nuthatches,
passerines are fantastic mim- woodpeckers, hummingbirds, and jays.
ics, including in their songs Despite their variety, all honeyeaters
mechanical sounds as well as have a specialized tongue that differs
from the tongues of other nectar feeders.
the songs of other birds. They
The tip of this "brush-tongue" is divided
are reported to give convincing lengthwise into four sections, each with
imitations of a passing flock frayed edges, that together form a brush-
of cockatoos, complete with Members of another large family, the whistlers, are known for their like structure with which the bird rapidly
wing noise and doppler effect licks up nectar. They also have a special-
explosive, often-beautiful songs. These large, round-headed birds with ized digestive system, which allows the
(the drop in pitch when calls arrive from a receding bird), and also may stout, slightly hooked bills have evolved a variety of foraging behav- easily-digestible nectar to bypass the
mimic logging trucks and chain saws. iors—searching trunks, branches, leaves, or the ground for insects.The stomach and continue straight to the
Some bird families are represented by numerous species in the numerous Australasian robins are actually more like flycatchers—al- intestines, where it can be absorbed
region. The 181 species of honeyeaters, for example, have diversified quickly. Although honeyeaters also may
though they usually snatch food from the ground—but the orange, eat insects and fruit, their primary food
into nearly every habitat (Fig. 1-89). These arboreal, relatively dull- pink, or yellow breasts and dull-colored backs of many of them are is nectar. They are extremely important
colored birds have medium-length, curved bills, and busily feed on reminiscent of both New and Old World robins. Other species-rich pollinators of flowers, and many spe-
nectar, insects, and fruits, often congregating at flowering trees. They families include the fairywrens—cooperatively breeding wren like cies are nomadic, congregating in large
are important pollinators, and have a distinctive brush-tipped tongue birds with long, cocked tails (see Fig. 6-43)—and waxbills, estrildid
numbers around flowering trees. The
that they move in and out up to 10 times per second, lapping up nectar. male Red-collared Myzomela shown
finches including the well-known cage bird, the Zebra Finch. here, from mountainous regions of New
Figure 1-88. Superb Lyrebird: Among Other characteristic Australasian birds include the following: Guinea, is black with a crimson collar.
the largest of songbirds, the two pheas- Photo by W. Peckover/VIREO.
ant-sized lyrebird species live in the rain pseudo-babblers: noisy, busy, social ground-feeders with a long, curved
forests of Australia. Although they can beak and long, towhee-like tail
run quickly, their flight is limited to short cracticids: a distinctive family with stout, straight beaks; loud, me-
distances and gliding. They roost high in
trees that they ascend by jumping from
lodic calls; and a generalist, crow-like diet of small vertebrates,
branch to branch. Lyrebirds forage for eggs, insects, and fruits. It includes the voracious, shrike-like
insects and other arthropods by digging butcherbirds named for their habit of wedging prey into a tree fork
and scratching in soil and rotting logs and dismembering it; the large, crow-like currawongs; and the
with their strong feet and claws. Their
Australasian Magpie—a crow-sized, black-and-white bird that is
voices, often used to mimic various
sounds, may be the most powerful of common, widespread, and familiar because it has adapted well to
any songbird. Male lyrebirds were killed open areas with trees, such as orchards, golf courses, gardens, and
in great numbers in the 19th century for other suburban areas.
yf
their stunning tail plumes. The family is -----
,

mudnest builders: two striking, black-and-white, robin-sized birds

named for the two outer tail feathers of
the Superb Lyrebird, which, when raised
named for their large, cup-shaped mud nests. The Magpie-lark is
and spread as shown here, resemble the widespread, abundant, and well-known throughout open areas in
frame of a lyre. Male Superb Lyrebirds much of Australia (Fig. 1-90); and theTorrent-lark inhabits fast-flow-
display to females from mounds on the Superb Lyrebird ing streams in the mountainous areas of New Guinea.
ground by arching the tail forward and
corcoracids: the large, blackbird-like White-winged Chough and
turning slowing, all the while vocal-
izing dramatically. Drawing by Robert smaller, seed-eati ngApostlebi rd. Both are cooperative breeders that
Gillmor. range over agricultural fields in huge flocks when not breeding.

Cornell Laboratorq of Omithologq Handbook of Bird Biolojq

1.96 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.97
Figure 1-90. Magpie-larks: The Mag- Figure 1-92. Wattlebirds: Three species
pie-lark of Australia, together with the Male Huia of wattlebirds, one of which has recently
Torrent-lark of New Guinea, form the become extinct, form the family Cal laei-
family Grallinidae, commonly known dae, endemic to New Zealand. Named
as "mudnest builders" or "mudlarks." for the pair of colorful, fleshy wattles,
Magpie-larks are common in a wide which develop from a fold of skin at the
range of open areas throughout much of base of their bill, wattlebirds are dark-
Australia, including farmlands and city colored forest birds somewhat resem-
suburbs. Their striking black-and-white bling slender grackles. The mostly black
markings, loud calls and songs (in- Huia, eliminated by 1910 as a result of
cluding duetting between a mated male overhunting, feather collecting, and
and female), and conspicuous behavior habitat destruction, had orange or yel-
render them one of the best-known birds low wattles. The bills of male and female
in Australia. Magpie-larks forage on the Huias differed greatly: the female had a
ground for insects, spiders, snails, frogs, long, thin downcurved bill with which
and seeds. Pairs mate for life, both mem- she probed insect tunnels for larvae and
bers actively and aggressively defendi ng adults, whereas the male had a straight-
the territory year round. er, shorter bill, used to chisel out insect
They are particularly common near prey (also see Fig. 9-28). The stocky,
water sources where they can obtain black Saddleback has a chestnut brown
mud to build their large, bowl-shaped back and red wattles, and feeds on fruits
nests, which are placed far out on a and insects—the latter, by probing and
horizontal branch, often over water. In tearing apart rotten wood. The large, gray
dry years, when mud is in short supply, Kokako (shown in both side and ventral
breeding may be curtailed, but in wet views) has blue or yellow wattles, and
years, two or occasionally three broods maximus, stood 14 feet tall. Being flightless, the moas were easy marks eats mostly young leaves and fruit. Like
may be raised. for predatory humans, and all have been extinct for more than 200 other species that were once widespread
The black-and-white head patterns years (see Fig. 20 in Evolution of Birds and Avian Flight). in New Zealand, both the Kokako and
of Magpie-larks differ by sex and age. the Saddleback are severely declining as
Note how the head pattern of the male a result of predation by introduced mam-
(bottom) differs from that of the female
(center). The juvenile (top) has a pat- cuckoo-shrikes: a diverse group of arboreal songbirds that are slender Island Distribution mals such as rats. Conservationists have
been successful in establishing viable
tern intermediate between those of its like cuckoos, with a shrike-like bill, but related to neither Islands, as long as they are adequate in size and have suitable populations of both species on small,
parents. Drawing by N. W. Cusa, from woodswallows: small, chunky birds with a graceful, swallow-I ike flight, habitats and food, almost invariably support breeding populations nearby islands that contain no preda-
A Dictionary of Birds, edited by Bruce known for huddling together on branches or in tree cavities in groups of land and freshwater birds from the adjacent continents. The more tory mammals. Drawing by Sir Charles
Campbell and Elizabeth Lack, p. 335. Alexander Fleming, from A Dictionary
of up to 50 or more birds remote the islands, the fewer kinds of birds they support, because
Copyright 1985, The British Ornitholo- of Birds, edited by Bruce Campbell and
gists' Union. Reproduced with the kind the chance of stragglers, or "pioneers," reaching them in sufficient
Elizabeth Lack, p. 645. Copyright 1985,
permission of the British Ornithologists' New Zealand separated from Australia so long ago (in the late numbers to found colonies decreases with increased distance from The British Ornithologists' Union. Re-
Union. Cretaceous) that its fauna is quite distinctive. Indeed, some researchers the mainland. In general, the species that colonize the more remote produced with the kind permission of
believe that New Zealand should be considered a separate zoogeo- islands are not necessarily the best flyers, but the ones that can best the British Ornithologists' Union.

graphic region. Currently, three bird families are endemic there: the adapt to restricted cover and food resources. Some of the weakest
Figure 1-91. Rifleman: The Rifleman is flightless, and almost wingless, ratite kiwis—grouse-sized, nocturnal flyers—for example, rails and gallinules—have been the most suc-
one of four known species of the family cessful colonizers, whereas strong flyers such as swallows have rarely
birds that probe the soil with their long beaks, using their keen sense of
of tiny, suboscine New Zealand wrens.
smell to locate earthworms (see Figs. 4-54c and 5-48); the tiny, nearly colonized distant islands.
One of these species, the Stephen Island
Wren, became extinct at the end of tailless New Zealand wrens The kinds of birds on islands close to a continent are little dif-
the 19th century. New Zealand wrens (Fig. 1-91); and the odd, for- ferent from those on the mainland, because they have not been suf-
build domed nests inside tree cavities est-dwel I i ng wattlebirds, aptly ficiently isolated to develop distinctions as separate species. They
or rock crevices, and augment their
named for the fleshy wattles at clearly belong to the avifauna of the continent and its zoogeographic
insectivorous diet with some fruit. Just
three inches (eight centimeters) long, the the corners of their mouths region. However, birds on remote islands and archipelagos have often,
Rifleman is three-quarters of the size of (Fig. 1-92). Not so long ago at through long isolation, developed distinctions so peculiarthatthey not
a kinglet. The female, illustrated here, is least 22 species of moas (ratites only have the status of endemic species, but their origins are blurred as
slightly larger than the male, and differs well. A classic example is the avifauna of the Hawaiian Islands, which
in the family Dinornithidae)
from him in appearance. The Rifleman is
roamed the open foothills and includes 52 endemic species: one goose, two ducks, one hawk, two
most abundant in mountainous forests,
where, creeper-like, it extracts insects tussock lands of interior New rails, one coot, five honeyeaters, one crow, one Old World flycatcher,
from bark crevices and from mosses and Zealand. The smallest was tur- one Old World warbler, five thrushes, and the endemic subfamily of
lichens growing on trees and shrubs. key-sized, the largest, Dinornis Hawaiian honeycreepers (Drepanidinae) containing 32 species. Of

Cornell Laboratorq of Omithologq Handbook of Bird Biologii

1.98 Kevin . McGowan Chapter 1 — Introduction: The World of Birds 1.99
these birds, at least four honeyeaters, one thrush,
•
and nine honeycreepers recently have become ex-
tinct. Some Hawaiian bird families appear to have Northern
Marine Region
originated in the Nearctic, and some in the Austral-
asian region, but the origin of others remains un-
known. Hawaiian birds are generally placed in the 35°N

114111... \-A•4111111
Australasian zoogeographic region based on their
Tropical
location, but some researchers place them in other
Marine Region
regions, or in a separate region with other islands of
the middle and southern Pacific Ocean. \350,
Bird species native to islands normally have
small populations. Sedentary and without predators,
many have become flightless and tame (Fig. 1 93).
-
Southern
Marine Region
Figure 1-93. Weka: Dark, tame, flight- They are consequently vulnerable to extinction from human-imposed
less rails a bit larger than a crow, Wekas causes: direct killing, destruction of habitat, and the introduction of
inhabit the scrublands and forest edges
dogs, cats, rats, goats, and other human symbionts. Until humans
of New Zealand, foraging on a variety
of foods as well as scavenging among
began eliminating them, dozens (perhaps even hundreds) of species
kelp on beaches and from garbage bins. of flightless rails existed on different islands around the world. Many
Wekas have strong beaks and feet and of these are known only from fossil or skeletal specimens, and disap- and have long incubation, fledging, and "adolescent" periods, many Figure 1-94. Marine Faunal Regions:
species taking 5 to 10 years to reach reproductive age. Like land areas, the seas have been
can run very fast, but typically walk peared as soon as humans colonized their islands. Nine flightless rails divided by biologists into major faunal
slowly, flicking their tails. Photo by D. Like the land areas, the seas have been divided by biologists into
have gone extinct over the past 150 years, and at least six more are in regions. The Northern Marine region
HaddenNIREO.
danger of extinction—all as a result of humans! major faunal regions, as follows (Fig. 1 94): -
extends from the cold Arctic waters
south to the Subtropical Convergence
(1) Northern Marine Region: The frigid waters of the Arctic south to
of the Northern Hemisphere at about
about 35 degrees north latitude. The water temperature rises rap-
Distribution of Marine Birds 35 to 40 degrees north latitude, where
idly between 35 and 40 degrees north latitude, an area termed the the water temperature rises rapidly.
Marine birds, or seabirds, are directly associated with the ocean, The Southern Marine region extends
Subtropical Convergence of the Northern Hemisphere.Th is change
consistently depending upon it for food. They are generally divided from the cold Antarctic waters north
in water temperature has important ecological consequences that
into pelagic and coastal species. Pelagic birds roam the open ocean, to the Subtropical Convergence of the
affect bird distribution, as discussed below. Southern Hemisphere, at about 35 to
feeding primarily on small animals such as fish, squid, crustacea, and
(2) Southern Marine Region:The frigid waters around Antarctica north 40 degrees south latitude. The Tropical
carrion at the surface or just below it; they come to land only to nest.
Marine region includes the warm equa-
Many pelagic birds are in the large order Procellariiformes (tubenosed to about 35 degrees south latitude. In the Subtropical Convergence
torial seas between the two Subtropical
seabirds), which includes albatrosses; shearwaters, fulmars, and typ- of the Southern Hemisphere, between 35 and 40 degrees south Convergences. Adapted from a drawing
ical petrels; storm-petrels; and diving-petrels. The remaining pelagic latitude, the water temperature rises rapidly, as in the north. by Charles L. Ripper.
groups are the tropicbirds, some penguins, the boobies and gannets, (3) Tropical Marine Region:The warm equatorial waters between the
most of the alcids, the skuas and jaegers, the noddies, the kittiwakes, Subtropical Convergences of both hemispheres.
Sabine's Gull, and some terns—notably the Sooty Tern. Coastal spe-
cies primarily occupy the shallower waters around oceanic islands Northern Marine Region
or above the continental shelf, feeding mainly on fish, crustacea, and This region is characterized by the familyAlcidae, which includes
mollusks, which they find on or near beaches and other shorelines. 24 species of auks, auklets, mu rres, mu rrelets, guillemots, and puffins,
They frequent land—usually coastal areas—in the nonbreeding season most of which live in the colder waters of the higher latitudes (Fig.
as well as for breeding. These include most penguins, cormorants, pel- 1 95).The medium-sized, black-and-white alcids are excellent swim-
-

icans, frigatebirds, gulls, terns, and skimmers. Shorebirds, waders, and mers, pursuing their fish prey by flapping their wings underwater, and
waterfowl, many of which depend more heavily on land for feeding are well-known for their upright, penguin-like stance. The family is
and rarely venture far from coastal areas, are not considered marine almost completely restricted to the Northern Marine region, but sev-
birds. The exceptions are eiders, scoters, and some phalaropes, which eral species venture south along the coast of southern California—the
are usually grouped with the coastal seabirds. Craveri's Murrelet all the way to Mexico, breeding on islands in the
Many marine birds, especially the pelagic species, are quite Gulf of California. Because many more alcid species are found in the
long-lived. The Northern Fulmar, for example, once it has survived to North Pacific than in the North Atlantic, the fami ly may have originated
breeding age, lives an average of 44 years. Marine birds also tend to there. Other birds of the Northern Marine region include numerous
nest colonially, often on islands; lay only one or sometimes two, eggs; gulls and terns, both kittiwakes, three species of albatross, and an

Cornell Laboratortj of Ornithologg Handbook of Bird Biology

1 1 00 Kevin J . McGowan Chapter 1 — Introduction: The World of Birds 1-101
assortment of typical petrels, shearwaters, Tropical Marine Region
cormorants, and gannets. The warm, nutrient-poor, tropical waters of this region are low in
plankton, and thus cannot support a rich array of the marine animals,
Southern Marine Region such as fish, squid, and crustacea, which ultimately depend on plank-
This region is by far the richest of the ton. Most fish are found in schools close to land, and consequently
three regions, not only in the array of species, most distinctive birds of this region—tropicbirds, boobies, frigatebirds,
but also in the numbers of individuals. Even and several species of terns—keep to the inshore waters. Only three
the most disinterested sailors will notice the albatross species, several typical petrels and shearwaters, and a num-
steady increase in birds as their ship heads ber of storm-petrels (Fig. 1-98) find the plankton supply sufficient for
southward into the higher southern latitudes. them to occupy the open tropical seas. The tropicbirds, boobies, and
The birds that they see are mainly albatrosses, frigatebirds (Fig. 1-99) are found only in this region. Most Tropical
shearwaters, and petrels. The high density of Marine birds feed by hovering and plunging quickly into the water
plankton, the base of the ocean food chain, ac- after prey, or skimming prey from the water's surface while hovering.
Figure 1-95. Common Murres: Like counts for the presence of so many of these birds, as described below. The region hosts notably few gulls.
other members of the family Alcidae, Figure 1 97. Snowy Sheathbill: Named
-
The almost constant winds of the region are favorable to the albatross's
the crow-sized, black-and-white Com- for the horny, yellow-green sheath cov-
style of long-distance, soaring flight (see Fig. 5-42), and 10 of the 14 Plankton and Bird Distribution
mon Murres are designed for swimming. ering the base of the stout bi I I and nostrils,
albatross species are found here (see Fig. 5-1). Other bird families The abundance of marine birds in different oceanic regions is the two species of sheathbil Is are white,
Their streamlined bodies and feet set
back on the body give them an upright, characteristic of the region include penguins (only 3 of the 17 species directly related to the supply of plankton. As the base of the ocean food pigeon-like shorebirds with bare faces
chain, plankton are consumed by numerous small marine animals, and fleshy wattles around the eyes and
penguin-like stance. These adaptations are found outside the region) (Fig. 1-96); the auk-like diving-petrels
al low them to pursue fish expertly under base of the beak. Sheathbills live on or
(3 of 4 species are found here); and the two sheathbi I Is (Ch ion ididae), which are, in turn, prey for larger animals, in a chain of consumers
water. As shown here, Common Murres near shores in the Antarctic region of the
aberrant, all-white shorebirds (Fig. 1-97)—the southernmost birds in that often ends in seabirds. Where plankton are plentiful, so, too, Atlantic and Indian Oceans, often in as-
nest in dense colonies on ledges of rocky
cliffs throughout much of the northern the world without webbed feet! The region also hosts numerous spe- are fish and seabirds. Plankton consists of microscopic plants and sociation with penguin or seal colonies.
Holarctic. Drawing by Robert Gil lmor, cies of shearwaters and typical petrels, as well as gannets, terns, gulls, animals termed phytoplankton and zooplankton, respectively. Just They scavenge any type of food they can
find and are quite tame, frequenting hu-
from Lack (1968). and cormorants. The large number of shearwater and albatross species like terrestrial plants, phytoplankton use the sun's energy to convert
man campsites in the region. Reluctant
suggests that these groups originated here. simple inorganic molecules into carbohydrates; and, like terrestrial to fly, they escape predators by running
plants, they require a supply of nutrients to survive. Although sunlight quickly. The Snowy Sheathbill is found
is plentiful in the open ocean, nutrients are usually very limited: when in Southern Argentina and Chile, the
organisms die they tend to sink to the ocean bottom, decomposing into Falkland Islands, and the Antarctic Pen-
insula—a long, thin finger of Antarctica
their component nutrients very slowly. There they remain for centuries,
extending toward South America. Photo
unless something happens to bring them to the water's surface. Coastal by Tom VezoNIREO.
areas, including the relatively shallow waters over the continental

Figure 1-98. Wilson's Storm-Petrel:

Found throughout most of the world's
oceans, the starling-sized, pelagic storm-
petrels are among the few bird species
that find the low number of plankton and
other tiny organisms of the open oceans
of the Tropical Marine region sufficient
to live on. They fly low over the water's
surface, treading their feet in the water
Figure 1-96. Chinstrap Penguin: and fluttering their wings somewhat
Flightless seabirds found mostly in the like butterflies, as they search for prey.
Southern Marine region, the streamlined Storm-petrels are tubenosed seabirds of
penguins with their strong, stiff flippers the order Procellariiformes, and breed
and feet set well back on the body are colonially on islands, digging their own
highly specialized for swimming. Just nest burrows. The tiny Wilson's Storm-
2 feet (40 cm) tall, the feisty Chinstrap Petrel, thought to be one of the most
Penguin of the Antarctic region is named abundant seabirds on the globe, breeds
for the thin, black line extending around in the Antarctic and ranges the northern
its throat from ear to ear, like the strap oceans, except the northern Pacific, in
of a helmet. Photo by 0. S. Pettingi I I/ winter. Drawing by Robert Gi I Imor, from
VIREO. Lack (1968).

Cornell Laboratoru of Ornitholo9u Handbook of Bird BioloBq

1.102 Kevin j. McGowan Chapter 1— Introduction: The World of Birds 1.103
Figure 1-99. Birds of the Tropical Ma- shelf, tend to be rich in nutrients, as some are carried from land to the Figure 1-100. Coastal Upwelling: When
rine Region: Tropicbirds, boobies, and
ocean by rivers, and others are brought to the surface by the action of marine organisms die, they usually sink
frigatebirds, found only in the Tropical
Marine region, are all pelican relatives in
tides, waves, winds, and coastal currents (Fig. 1-100). and decay very slowly in the cold envi-
In the Tropical Marine region, the sun heats the upper layers of ronment of the ocean floor. There, vast
the diverse order Pelecaniformes, whose
amounts of nutrients, released from the
members are distinguished by having water so much that a significant temperature stratification develops,
decaying organisms, build up over time.
all four toes joined by webbing. a. Red- with cold, dense water below the warmer, lighter surface layers. This In coastal areas, winds blowing from
billed Tropicbird: The tropicbirds have
layering, much like a temperature inversion in the atmosphere, is an land to sea (a common nighttime oc-
two long, central tail feathers, which
effective barrier to mixing between the layers: the cold, dense water currence) move the surface water away
render them unmistakable in flight.
from shore, causing cold water from the
With short legs set far back on the body, stays below, as do the associated nutrients. The dramatic layering ex-
ocean bottom to replace it by moving
tropicbirds cannot support the weight of plains why the open oceans of tropical latitudes are so low in plankton upward and toward shore, carrying dis-
their body on land, and usually nest co-
and other marine life. solved nutrients. This process—cold,
lonial ly on steep cliffs—from which they
In the Northern and Southern Marine regions, layering is less nutrient-rich water from the ocean
can take off without walking. The flicker-
bottom rising to the surface—is called
sized (excluding the long tail) Red-billed marked, and thus nutrients, plankton, and other marine life are more
upwelling. The nutrient-rich coastal wa-
Tropicbird, found in most tropical seas plentiful. The growth of phytoplankton is seasonal, however, with a ters support numerous phytoplankton
around the world, plunge-dives into the burst of growth in spring—a time when sunlight is more available (microscopic plants), which are eaten
water from air in search of small fish a and just after winter storms have disturbed the water sufficiently to by zooplankton (tiny animals), which
or squid. Photo by T J. UlrichNIREO.
bring up nutrients from deep in the seas. A number of bird species in in turn support an abundance of fish
b. Masked Booby: Large birds with long,
and other marine life—all components
narrow wings and torpedo-shaped bod- these regions are migratory, and some shearwaters and storm-petrels
of the highly productive coastal ecosys-
ies, the boobies catch fish and squid move back and forth across the equator to take advantage of spring tem. Upwelling also occurs in certain
by either plunge-diving or diving from
and summer in both hemispheres. (Birds with this habit are termed areas where ocean currents meet.
the water's surface. Boobies breed in
huge colonies on islands, and incubate transequatorial migrants.) From Owens/Chiras/Regangold, Natural
Resource Conservation 7/e, copyright
their eggs by placing them under the In certain areas where ocean currents meet or where deep cur-
1998. Reprinted by permission of Pren-
webbing of their feet. The pantropical rents are forced upward by the topography of the sea floor, large-scale tice-Hall, Upper Saddle River, NJ.
Masked Booby eats mainly flying fish.
upwelling of deep water occurs, bringing abundant nutrients to the
c. Magnificent Frigatebird: The dark,
eagle-sized frigatebirds, with their long,
surface. One example is the Antarctic Convergence at roughly 60 de-
narrow wings and deeply forked tails,
can both soar and maneuver skillfully in
flight. They rarely settle on water, as their
plumage wets quickly. They frequently
WIND
harass other seabirds, forcing them to
drop or disgorge recently eaten fish.
The frigatebirds then catch the dropped 7
item in midair. They also follow schools
of tuna or dolphin to grab the flying fish
b
that they scare into the air, swoop over
nesting colonies and snatch untended - _
— —
=
-

chicks (even of their own species), and Movement of Surface Water—

rsherman 460
%,=.1i
scavenge items such as jellyfish, eggs, _ _ _- -_
and baby turtles from on or near the _ - --7-
water. Frigatebirds nest colonially on
islands, building flimsy stick nests in
dense vegetation such as mangroves,
where they can perch, as their small,
sharply-clawed feet are ineffective for Fish
;$11.=.

walking or swimming. In courtship, 7 *I •ra •

males inflate their bright red throat Zooplankton--,.

pouch, vibrate their wings, and rattle
.-?..-
their huge, hooked bills. Booby and Phytoplankton
frigatebird photos by Marie Read.
• NUTRIENTS

.. •

Decaying Organisms
on Ocean Floor

Cornell Laboratoru of Omithologq Handbook of Bird Biologu

1.104 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.105
Figure 1-101. Plankton and Seabird grees south latitude, an area extremely rich in seabirds (Fig. 1 101). - 180°
Abundance in the South Atlantic: The Other notable upwellings occur along the western coasts of several
graph on the left shows the average
continents, where currents flowing toward the equator from north and
plankton abundance in the upper 55 41-.)
yards (50 m) of water, in thousands of south tend to bend away from shore because of the earth's rotation (a
organisms per liter, at different latitudes phenomenon called the Coriolis effect), drawing deep, nutrient-rich
60
in the Atlantic Ocean. On the right, the water upward near the coastline (Fig. 1 102). The south-flowing Cali-
-

relative abundance of certain species of

fornia and north-flowing Humboldt (or Peru) currents, along the west if
pelagic seabirds is illustrated for three
coasts of North and South America, respectively, create such upwell-
or cd North I:I:*
different latitudes. Between about 50 Current *
•Nik 4
and 60 degrees south latitude, in a region i ngs; along the west coast of Africa, the Canary and Benguela currents •

known as the Antarctic Convergence,

cold north-flowing and warmer south-
act similarly. Although many tropical, pelagic seabirds are worldwide
in distribution, the areas of upwelling in tropical seas create isolated NNth Equa toria l e • \ •1/4,/,
- *T.
flowing currents meet, resulting in large- Equatorial Counter Current
patches of abundant food. Many bird species that specialize on these •■► ■► ■•■•►
scale upwelling of nutrient-rich water -11.

from the ocean's depths. The plethora of resources have very limited ranges—for example, the Peruvian Booby 'k) CiCr, 0
'___„_
•---* ..:z.

0 41
---0
nutrients supports tremendous numbers and Humboldt Penguin of the Peruvian coast; and the Jackass Penguin South Equatorial CurreM • "1".mm-7•7:. V:
of plankton, which support higher levels and several cormorant species of western Africa. Upwelling also oc- West : il
of the food chain, including a great di- "1 Australian : ..1
curs in the Arabian Sea from May to September, owing to the action of Current
versity and abundance of seabirds. The 7t7 40
nutrient-poor water near the equator
monsoon winds on the water, which brings a seasonal abundance of ■I o,„
supports few plankton, and thus few sea- plankton and marine birds to an area that hosts few birds during the ...••• •.•••• • •
Antarctic Convergence ■•■ :' ; ;
•••• :••• :.•.•••
birds, but the numerous, small storm-pe- rest of the year. • :
••••• •• • • •• . • • ••• • • •• • • •
,1„: • • •
trels find the plankton supply adequate. Undoubtedly the most famous upwelling site is the southwest Antarctic Circumpolar Current
Plankton data originally from Hentschel
(1933) and seabird data originally from
coast of Peru. Here the rich water supports a tremendous population I I I I
Spiess (1928). Figure from The Life of of anchovies, a virtual banquet for millions of seabirds, as well as the
'''mm•lo• Ocean Current Upwelling Areas
Birds, 4th Edition, by Joel Carl Welty and basis for an extensive fishing industry (the 1969 to 1970 catch was over
Luis Baptista, copyright 1988 by Saun- 10 trillion fish). Many of the seabirds nest on offshore islands, where,
ders College Publishing, reproduced by "guano birds"—especially the Guanay Cormorant, Peruvian Booby, Figure 1-102. Major Ocean Currents
because of the arid conditions, their droppings (known as guano) ac-
permission of the publisher. and Peruvian Pelican—historically reached depths of more than 300 and Areas of Upwelling: The water in
cumulate in massive quantities (Fig. 1 103). Droppings from these
-
the world's oceans circulates continu-
feet (90 meters), but have been mined extensively for use as fertilizer
ally, the patterns resulting from differen-
since at least the days of the Incas. In 1972, a combination of particu- tial heating and cooling of water masses
larly strong effects of El Nino (triggered by atypical atmospheric con- in different parts of the globe, combined
ditions, this warm, south-flowing surface current of Ecuador extends with the rotation of the earth and the ac-
Plankton Abundance
tion of persistent winds. In certain areas,
southward to flow along the coast of Peru every two to ten years, warm-
10-20 ° the patterns of currents cause large-scale
Seabird Abundance ing the upper water layers and preventing upwelling) and overfishing upwelling of deep water. Upwellings
Latitude 3° S.
caused anchovy and thus seabird populations to plummet to around bring abundant nutrients to the surface,
0-1°
one million birds, down from a high of 27 million in the late 1950s. and support large, but localized, seabird
Although fish and seabird populations have increased since their de- populations. In addition to massive up-
0-10° welling just north ofAntarctica, between
cline, they have not returned to their former levels.
50 and 60 degrees south latitude (see
Latitude 22° S. Fig. 1-101), upwellings occur along the
10-20°

20-30°
z '"'"44.000■
Now that you have a feel for the great diversity of birds in the
world, as well as the remarkable similarities from one region to an-
western coasts of Africa, the Americas,
and Australia.There, currents flowing to-
ward the equator from north and south
other, you may find that paying attention to birds increases your en-
tend to bend away from shore due to
joyment of travel—whether around the world or across the country. the Coriolis effect, drawing deep, nutri-
30-40°
If you live in Vermont and travel to Utah, for example, most birds you ent-rich water upward along the coasts.
Latitude 55°S. encounter will be quite different. The common, large, blue bird at the The California and Peru (Humboldt)
40-50°
m""Neu".' oftee' feeder will no longer be the Blue Jay, but the Steller's Jay. The juncos, currents off the Americas, the Canary
••••—
eir instead of being all gray on top, will have black caps and rusty brown
and Benguela currents off Africa, and
50-60° the West Australian current off Australia
.• • sides, being the Oregon rather than the Slate-colored form. Open any create such upwellings. Upwelling also
^r-■ -se•
60-70
field guide that covers all of North America and examine the range occurs in the Arabian Sea from May to
0 20 40 60 80 100
maps. You will find that many species are restricted to the western part September, due to the action of monsoon
Plankton
winds on the water. Adapted from Gra-
(Thousands/Liter) of the continent, some are restricted to the eastern, and others can be
Albatross Cape Other Storm-Petrel hame (1987).
Petrel birds found all over.

Cornell Laboratorq of Ornitholo9u Handbook of Bird Biolo9q

1.106 Kevin J. McGowan Chapter 1— Introduction: The World of Birds 1.107

Appendix A:
Figure 1-103. Peruvian Booby Nest
Colony on Ballestas Islands, Peru: Along
the southwest coast of Peru, the north-
flowing Peru (Humboldt) current bends ORDERS AND FAMILIES OF WORLD BIRDS
away from shore as it approaches the Below are listed the 31 orders and all families of living birds. The list was compiled using Clements
equator, pulling nutrient-rich water to (2000), Sibley and Monroe (1990), and Sibley and Ahlquist (1990), but for North American species fol-
the surface in a massive up welling. This
lows the 7th edition of the Check-list of North American Birds (1998), prepared by the Committee on
upwelling supports a huge population
of anchovies—a virtual banquet for mil- Classification and Nomenclature of the American Ornithologists' Union.
lions of seabi rds. The seabirds, including Ornithological names are pronounced following the rules listed in any standard English diction-
the Peruvian Boobies shown here, form ary. Note that all order names end in "-iformes," all family names in "-idae," and all subfamily names in
huge nesting colonies on islands in the
"-inae." The names of orders and families are shown in boldface type. Those in color are represented by
region, such as the Ballestas. Their drop-
pings accumulate to great depths in the species occurring in North America north of Mexico, or near its coasts, including Hawaii. The number of
arid environment, and are mined by living species in each family is given in parentheses; it includes some species that have gone extinct very
Peruvians for use as fertilizer. Photo by recently. Several orders and families of birds that recently went extinct are included in square brackets.
Sandy Podulka. With the 7th edition of the Check-list, the AOU took the bold step of making several groups incertae
sedis, that is, having "no certain affinity." Instead of putting a confusing bird somewhere justto give it a home,
as has been the general practice in the past, the committee, in effect, admitted that they don't know where
these birds fit in. Future studies may shed more light on the real relationships of these "orphaned" taxa.

The Importance of Biodiversittj Tinamiformes Vultures, and Allies

Tinamidae—Tinamous (46) Ardeidae—Herons, Egrets, and Bitterns (65)
■ Much of this chapter has described the great diversity of birds—di- Rheiformes Balaenicipitidae—Shoebi II (1)
versity in bills, wings, tails, feet, and feathers—as well as the diversity of Rheidae--Rheas (2) Scopidae—Hamerkop (1)
taxonomic groups that use an array of behaviors to exploit nearly every Struthioniformes Threskiornithidae —Ibises and Spoonbills (33)
habitat on earth. Birds are just one component of biodiversity the — Struthionidae—Ostrich (1) Ciconiidae—Storks (19)
great wealth of living organisms that occur on earth. As scientists con- Casuariiformes—Cassowaries and Emu Cathartidae—New World Vultures (7)
tinue to study natural systems, they are becoming increasingly aware Dromiceidae—Emu (1) Phoenicopteriformes
of the importance of each component, and of the complex ways these Casuariidae—Cassowaries (3) Phoenicopteridae—Flamingos (5)
[Aepyornithiformes (extinct)] Anseriformes—Screamers and Waterfowl
components are related to one another. The study and preservation of
[Aepyornithidae—Elephantbirds (extinct)] Anhimidae—Screamers (3)
biodiversity are major focuses of contemporary scientists around the
Dinornithiformes Anatidae—Ducks, Geese, and Swans (161)
world. [Dinornithidae—Moas (extinct)] Falconiformes—Vultures and Diurnal Birds of Prey
The earth's biodiversity, including birds, provides direct benefits Apterygidae—Kiwis (3) Sagittariidae—Secretary-bird (1)
to humans in such forms as food, clothing, recreation, and aesthetic ex- Gaviiformes Accipitridae—Kites, Eagles, Hawks, Old World
periences; but biodiversity is more than that. Maintaining biodiversity Gaviidae—Loons (5) Vultures, and Allies (237)
is crucial to sustaining the healthy, functioning ecosystems on which Podicipediformes Falconidae—Caracaras and Falcons (64)
all life depends. These ecosystems maintain a balance among organ- Podicipedidae—Grebes (22) Galliformes—Gal I inaceous Birds
isms, purify and cycle water, recycle nutrients, and ensure adequate Sphenisciformes Megapodiidae—Megapodes (21)
reproduction of living things. Spheniscidae—Penguins (17) Cracidae—Curassows, Guans, and Chachalacas
Procellariiformes—Albatrosses, Shearwaters, and (50)
As you continue through this course, try to interpret each topic
Petrels Phasianidae—Pheasants, Partridges, Grouse,
and example in the context of biodiversity. For example, ask yourself,
Diomedeidae—Albatrosses (14) Turkeys, Old World Quail, and
"In terms of conserving biodiversity, why is it important to identify Procellariidae—Shearwaters, Fulmars, and Typical Guineafowl (177)
and count birds? Why study the shapes of hummingbird bills? Why Petrels (76) Odontophoridae—New World Quail (30)
determine the exact migration routes of birds?" Hydrobatidae—Storm-Petrels (21) Gruiformes—Cranes, Rails, and Allies
Birds are beautiful, fascinating, and intriguing. Having chosen to Pelecanoididae—Diving-Petrels (4) Turnicidae—Buttonquai I (17)
pursue this course, you are undoubtedly already drawn to birds. But Pelecaniformes—Pelicans, Cormorants, and Allies Rallidae—Rails, Gal I i nules, and Coots (144)
birds in all their diverse forms are also vital components of the world Phaethontidae--Tropicbirds (3) Heliornithidae—Finfoots (3)
around us, and as you read the following chapters, your respect and Sulidae—Boobies and Gannets (9) Rhynochetidae—Kagu (1)
appreciation for them will likely grow. Pelecanidae—Pelicans (8) Eurypygidae--Sunbittern (1)
Phalacrocoracidae—Cormorants (38) Mesitornithidae—Mesites (3)
Anhingidae—Anhingas (4) Aramidae—Limpkin (1)
Fregatidae—frigatebirds (5) Gruidae—Cranes (15)
Ciconiiformes—Herons, Ibises, Storks, New World Psophiidae—Trumpeters (3)

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1.108 Kevin J. McGowan Chapter 1 — Introduction: The World of Birds 1.109
Cariamidae—Seriemas (2) Todidae—Todies (5) Paradisaeidae—Birds-of-Paradise (46) Mimidae—Mockingbirds and Thrashers (35)
Otididae—Bustards (25) Momotidae—Motmots (9) Artamidae—Woodswal lows (14) Sturnidae—Starlings (114)
Charadriiformes—Shorebirds, Gulls, and Auks Alcedinidae—Kingfishers (95) Cracticidae—Butcherbirds, Australasian Magpie, Prunellidae—Accentors (13)
Burhinidae—Thick-knees (9) Meropidae—Bee-eaters (26) and Currawongs (10) Motacillidae--Wagtai Is and Pipits (63)
Charadriidae—Plovers and Allies (66) Coraciidae—Rollers (12) Oriolidae—Old World Orioles (29) Hypocolidae—Hypocolius (1)
Haematopodidae—Oystercatchers (11) Brachypteraciidae—Ground-Rollers (5) Campephagidae—Cuckoo-shrikes and Minivets (82) Bombycillidae—Waxwings (3)
Recurvirostridae—Avocets and Stilts (10) Leptosomatidae—Cuckoo-Roller (1) Dicruridae—Drongos (24) Ptilogonatidae—Silky-flycatchers (4)
Jacanidae—Jacanas (8) Bucerotidae—Hornbills (55) Monarchidae—Monarch Flycatchers (139) Dulidae—Palmchat (1)
Rostratulidae— Painted-Snipes (2) Bucorvidae—Ground-Hornbills (2) Malaconotidae—Bushshrikes and Allies (93) Promeropidae—Sugarbirds (2)
Scolopacidae—Sandpipers and Allies (88) Piciformes—Woodpeckers and Allies Vangidae—Vangas (14) Dicaeidae—Flowerpeckers (43)
Dromadidae—Crab Plover (1) Bucconidae—Puffbirds (33) Callaeidae—Wattlebirds (3) Nectariniidae—Sunbirds (124)
Glareolidae—Coursers and Pratincoles (17) Galbulidae—Jacamars (18) Grallinidae—Mudnest Builders (2) Melanocharitidae—Berrypeckers and Longbills (10)
Chionididae--Sheathbil Is (2) Indicatoridae—Honeygu ides (17) Picathartidae—Rockfowl (2) Paramythiidae—Tit Berrypecker and Crested
Pluvianellidae—Magellanic Plover (1) Megalaimidae—Asian Barbets (26) Alaudidae—Larks (91) Berrypecker (2)
Pedionomidae—Plains-wanderer (1) Lybiidae—African Barbets (42) Hirundinidae—Swal lows (91) Peucedramidae--Olive Warbler (1)
Thinocoridae—Seedsnipes (4) Ramphastidae—Toucans and New World Barbets (55) Paridae—Chickadees and Titmice (58) Parulidae—New World Warblers or
I bidorhynchidae—lbisbi II (1) Picidae—Woodpeckers and Allies (217) Remizidae—Verdins and Pendul ine Tits (14) Wood-Warblers (115)
Laridae—Gulls, Terns, Skuas, and Skimmers (106) Passeriformes—Perching or Passerine Birds Aegithalidae—Bushtit and Long-tailed Tits (8) Coerebidae—Bananaquit (1)
Alcidae—Auks, Murres, and Puffins (24) Suborder Tyranni, Suboscines Sittidae—N uthatches and Allies (25) Thraupidae—Tanagers (252)
Family INCERTAE SEDIS = "Family with No Order" [as Acanthisittidae—New Zealand Wrens (4) Certhiidae—Creepers (7) Emberizidae—Seedeaters, New World Sparrows,
by AOU; or Pteroclidiformes? or Charadriiformes?] Pittidae—Pittas (31) Troglodytidae—Wrens (78) and Buntings (323)
Pteroclidae—Sandgrouse (16) Eurylaimidae—Broadbills (15) Cinclidae—Dippers (5) Cardinalidae—Cardinals and Allies (44)
Columbiformes—Pigeons and Doves Philepittidae—Asities and False Sunbirds (4) Pycnonotidae—Bulbuls (130) Icteridae— Blackbirds and New World Orioles (99)
[Raphidae—Dodo and Solitaires, (3) extinct] Furnariidae—Ovenbirds (240) Regulidae—Kinglets (6) Fringillidae—Finches and Hawaiian Honeycreepers
Columbidae—Pigeons and Doves (314) Dendrocolaptidae—Woodcreepers (51) Sylviidac Old World Warblers and Gnatcatchers (291) Fri ngill inae, Chaffinches (3)
Psittaciformes Thamnophilidae—Antbirds (197) Muscicapidae—Old World Flycatchers (118) Carduelinae, Finches (135)
Psittacidae—Parrots, Parakeets, Lories, and Formicariidae—Antthrushes and Antpittas (60) Turdidae—Thrushes (182) Drepanidinae, Hawaiian Honeycreepers (32)
Macaws (359) Conopophagidae—Gnateaters (8) Timaliidae—Babblers (267) Catamblyrhynchidae—Plush-capped Finch (1)
Coliiformes Rhinocryptidae—Tapacu los (52) Panuridae—Parrotbil Is (20) Passeridae—Old World Sparrows (35)
Coliidae—Mousebirds (6) Tyrannidae—New World Flycatchers or Tyrant Rhabdornithidae—Rhabdornis (3) Ploceidae—Weavers (117)
Musophagiformes Flycatchers (398) Cisticolidae—Cisticolas (117) Estrildidae—Waxbills and Whydahs (159)
Musophagidae—Turacos (23) Cotingidae—Cotingas (61) Zosteropidae—White-eyes (95)
Cuculiformes Phytotomidae—Plantcutters (3)
Cuculidae—Cuckoos, Roadrunners, and Anis (142) Pipridae—Manakins (44)
Opisthocomiformes Oxyruncidae—Sharpbi II (1)
Opisthocomidae—Hoatzin (1) Suborder Passeri, Oscines
Strigiformes—Owls Climacteridae—Australasian Treecreepers (7)
Tytonidae—Barn Owls (17) Menuridae—Lyrebirds (2)
Strigidae—Typical Owls (170) Atrichornithidae—Scrub-birds (2)
Caprimulgiformes—Oilbird and Goatsuckers Ptilonorhynchidae—Bowerbirds (20)
Steatornithidae—Oilbird (1) Maluridae—Fairywrens (26)
Podargidae—Frogmouths (14) Meliphagidae—Honeyeaters (181)
Aegothelidae—Owlet-Nightjars (8) Pardalotidae—Australo-Papuan Warblers (68)
Nyctibiidae—Potoos (7) Eopsaltriidae—Australasian Robins (44)
Caprimulgidae—Goatsuckers (82) Irenidae—Leafbirds and Fairy-bluebirds (10)
Apodiformes—Swifts and Hummingbirds Aegithinidae—Ioras (4)
Hemiprocnidae—Treeswifts (4) Orthonychidae—Logrunners (2)
Apodidae—Swifts (101) Pomatostomidae—Pseudo-Babblers (5)
Trochilidae—Hummingbirds (329) Laniidae—Shrikes (30)
Trogoniformes Vireonidae—Vireos (52)
Trogonidae—Trogons (39) Cinclosomatidae--Whipbirds and Quail-thrushes (15)
Upupiformes—Hoopoes and Woodhoopoes Corcoracidae—White-winged Chough and
Upupidae—Hoopoes (2) Apostlebird (2)
Phoeniculidae—Woodhoopoes (8) Pachycephalidae--Whistlers and Allies (58)
Coraciiformes—Kingfishers and Allies Corvidae—Crows, Magpies, and Jays (115)

Cornell Laboratort of Ornithologq Handbook of Bird Biolo,9ti

1110 Kevin ,J. McGowan Chapter 1— Introduction: The World of Birds 1.111

Appendix B:
ORDERS AND FAMILIES OF NORTH AMERICAN BIRDS
Below are the living orders and families of birds that occur in North America north of Mexico, or near
its coasts, including Hawaii, as listed in the 7th edition of the Check-list of North American Birds (1998),
prepared by the Committee on Classification and Nomenclature of the American Ornithologists' Union.
Included here are some bird groups that are accidental to this area (marked with an A) and some that have
been introduced (marked with an I). Bird groups that, within this region, are found only on Hawaii, are marked
with an H. For each family (and some subfamilies), the number of species known to occur in this region is
given in parentheses; it includes some species that have gone extinct very recently. The names of orders are
shown in boldface type. Endings and pronunciation guidelines are the same as for the world list.

Gaviiformes Galliformes
Gaviidae—Loons (5) Cracidae—Curassows, Guans, and Chachalacas (1)
Podicipediformes Phasianidae—Pheasants, Partridges, Grouse, Tur-
Podicipedidae—Grebes (7) keys, Old World Quail, and Guineafowl (15)
Procellariiformes Phasianinae—Partridges and Pheasants (11)
Diomedeidae—Albatrosses (8) Tetraoninae—Grouse (10)
Procellariidae—Shearwaters, Fulmars, and Meleagridinae—Turkeys (1)
Petrels (27) Numidinae—Guineafowl (1) I, H
Hydrobatidae—Storm-Petrels (12) Odontophoridae—New World Quail (6)
Pelecaniformes Gruiformes
Phaethontidae—Tropicbirds (3) Rallidae—Rails, Gallinules, and Coots (17)
Sulidae—Boobies and Gannets (5) Aramidae—Limpkin (1)
Pelecanidae—Pelicans (2) Gruidae—Cranes (3)
Phalacrocoracidae--Cormorants (6) Gruinae—Typical Cranes
Anhingidae—Anhingas (1) Charadriiformes
Fregatidae—Frigatebirds (3) Burhinidae—Thick-knees (1) A
Ciconiiformes Charadriidae—Lapwings and Plovers (16)
Ardeidae—Herons, Egrets, and Bitterns (16) Vanellinae—Lapwings A
Threskiornithidae—Ibises and Spoonbills (5) Charadriinae—Plovers
Threskiornithinae—Ibises (4) Haematopodidae—Oystercatchers (3)
Plataleinae—Spoonbills (1) Recurvirostridae--Stilts and Avocets (3)
Ciconiidae—Storks (2) Jacanidae—Jacanas (1) A
Cathartidae—New World Vultures (3) Scolopacidae—Sandpipers, Phalaropes, and Allies (64)
Phoenicopteriformes Scolopacinae—Sandpipers and Allies
Phoenicopteridae—Flamingos (1) A Phalaropodinae—Phalaropes
Anseriformes Glariolidae—Coursers and Pratincoles (1) A
Anatidae—Ducks, Geese, and Swans (62) Laridae—Gulls, Terns, Skuas, and Skimmers (57)
Dendrocygninae—Whistling-Ducks and Allies Stercorariinae—Skuas and Jaegers
Anserinae—Geese and Swans Larinae—Gulls
Tadorninae—Shelducks and Allies Sterninae—Terns
Anatinae—True Ducks Rynchopinae—Skimmers
Falconiformes Alcidae—Auks, Murres, and Puffins (22)
Accipitridae—Hawks, Kites, Eagles, and Allies (30) Family INCERTAE SEDIS = "Family with No Order"
Pandioninae—Osprey (1) Pteroclididae—Sandgrouse (1) I, H
Accipitrinae—Kites, Eagles, and Hawks (29) Columbiformes
Falconidae—Caracaras and Falcons (10) Columbidae—Pigeons and Doves (20)
Micrasturinae—Forest-Falcons (1) A Psittaciformes
Caracarinae—Caracaras (1) Psittacidae--Lories, Parakeets, Macaws, and Parrots (6)
Falconinae—True Falcons and Laughing Falcons (8) Platycercinae—Australian Parakeets and
Rosellas I

Cornell Laboratort of Ornitholosti Handbook of Bird BioloBq

 1.112 Kevin J. McGowan Chapter 1 — Introduction: The World of Birds 1.113

Psittacinae—Typical Parrots I Vireonidae—Vireos (16)

Arinae—New World Parakeets, Macaws, and Corvidae—Crows, Jays and Magpies (21) Appendix C:
Parrots Monarchidae—Monarch Flycatchers (1) H
Cuculiformes Alaudidae—Larks (2)
GEOLOGICAL TIME SCALE
Cuculidae—Cuckoos, Roadrunners, and Anis (8) Hirundinidae—Swallows (14) To understand the significance of the fossil record of birds and other organisms, it is essential to place
Cuculinae—Old World Cuckoos (2) A Hirundininae—Typical Swallows them in geological time—time that begins with the formation of the earth and continues to the present.
1 1
Coccyzinae—New World Cuckoos (3) Paridae—Chickadees and Titmice (11) Geological time is measured in millions, even billions, of years—a magnitude difficultfor humans to com-
Neomorphinae—Ground-Cuckoos and Remizidae—Pendul ine Tits and Verdi n (1) prehend. This enormous span of time is subdivided into progressively shorter units termed eras, periods,
Roadrunners (1) Aegithal idae—Long-tai led Tits and Bushtit (1) and epochs. Within the rock layers laid down sequentially throughout geological time, fossilized plants
Crotophaginae—Anis (2) Sittidae—Nuthatches (4) and animals succeed one another in a recognizable order, which reflects the evolution of living organ-
Strigiformes Sittinae—Nuthatches isms through time. The ages of rock layers and fossils are determined by radioactive dating techniques. To
Tytonidae—Barn Owls (1) Certhiidae—Creepers (1)
read this table in chronological order, begin at the bottom of the table with the formation of the earth and
Strigidae—Typical Owls (20) Certhiinae—Northern Creepers
proceed upward. Modern humans first appear in this sequence approximately 200,000 years ago.
Caprimulgiformes Troglodytidae—Wrens (9)
Cinclidae—Dippers (1)
Large-scale extinctions of many species, termed extinction events, have occurred throughout earth's
Caprimulgidae—Goatsuckers (9)
Chordeilinae—Nighthawks Pycnonotidae—Bulbuls (2) I history. Although the cause of each event is not well understood, scientists attribute the extinctions to
Capri mulgi nae—N ightjars Regulidae—Kinglets (2) either catastrophic events, such as meteorite or asteroid showers, or a major shift in earth's environmental
Apodiformes Sylviidac Old World Warblers and Gnatcatchers (11) conditions due to volcanism, glaciation, global climate change, or changes in the salinity or oxygen level
Apodidae—Swifts (10) Sylviinae—Old World Warblers (7) of the ocean. Five major and many lesser extinction events have occurred in the last 600 million years.
Cypseloidinae—Cypseloidine Swifts Polioptilinae—Gnatcatchers and Gnatwrens (4) Best known is the K-T event at the Cretaceous-Tertiary boundary 65 million years ago, which claimed
Chaeturinae—Chaeturine Swifts Muscicapidae—Old World Flycatchers (6) A dinosaurs, marine reptiles, pterosaurs, and many marine invertebrates. However, the most extensive mass
Apodinae—Apodine Swifts Turdidae—Thrushes (32) extinction in earth's history, the Permian Extinction, occurred atthe Permian-Triassic boundary 245 million
Trochilidae—Hummingbirds (23) Timaliidae—Babblers and Wrentit (4)
years ago. At this time, 90 to 95 percent of marine species and many terrestrial species were eliminated.
Trochilinae—Typical Hummingbirds Zosteropidae—White-eyes (1) I, H
Adapted from Pough et al., (1999).
Trogoniformes Mimidae—Mockingbirds and Thrashers (12)
Trogonidae—Trogons (2) Sturnidae—Starlings (4) I
Trogon i nae—Trogons Prunellidae—Accentors (1) A
Upupiformes Motacillidae—Wagtails and Pipits (11)
Upupidae—Hoopoes (1) A Bombycillidae—Waxwings (2)
Coraciiformes Ptilogonatidae—Silky-flycatchers (2)
Alcedinidae—Kingfishers (3) Peucedramidae—Olive Warbler (1)
Cerylinae—Typical Kingfishers Parulidae—New World Warblers or Wood-Warblers (57)
Piciformes Coerebidae—Bananaquit (1) A
Picidae—Woodpeckers and Allies (25) Thraupidae—Tanagers (6)
Picinae—Woodpeckers Emberizidae—Towhees and New World
Jynginae—Wrynecks A Sparrows (61)
Passeriformes Cardinalidae—Cardinals and Allies (13)
Tyrannidae—Tyrant Flycatchers or Icteridae—Blackbirds and New World Orioles (25)
New World Flycatchers (42) Fri ngillidae—Fi nches and Hawaiian
Elaeniinae—Tyrannulets, Elaenias, and Allies Honeycreepers (57)
Fluvicolinae—Pewees, Empidonax Flycatchers, Fringillinae—Chaffinches (2) A
and Phoebes Carduelinae—Finches (23)
Tyranninae—Kingbirds and allies Drepanidinae—Hawaiian Honeycreepers (32) H
Genera INCERTAE SEDIS = "Genera with No Family" Passeridae—Old World Sparrows (2) I
Pachyramphus—Becards (1) Ploceidae—Weavers (3) I
Tityra—Tityras (1) A Ploceinae—Typical Weavers
Meliphagidae—Honeyeaters (5) H Estrildidae—Waxbills and Whydahs (10) I, H
Laniidae—Shrikes (3) Estrildinae—Waxbills

(Open)

Cornell Laboratoru of Ornithologq Handbook of Bird Biolo9u

 .
V2I3 314/11
PERI OD EPOCH * eA ui
MAJ OR EVENTS
,
Rise an d expa ns ion ofhu man c iv i lizatio ns. Pas ser in es a re t he most diverse a n d a b
Ho lo cene
g roup of mode rn birds. Human activities cause many b irds, particu lar ly is land b
( Rec en t) go extinct.

C:)
7;
Q UAT ERNARY
Time of repeated g lac iat io n, c ha ng ing sea leve ls, an d w i desp rea d ext inct ions c l
m any bir ds an dlarge ma mm a ls. Hom in i ds sp read g lo ba lly. Mode rn humans first
P le istoc e ne
in the foss il reco rd app rox imate ly 200, 000 years ago. Most mo de rn spec ies c
evo lve.

1.
.
Lower lat itu des rema in wa rm, whi le hig her lat itu des coo lfurther. Mou n ta in bu i l
auaDo gd western North an d Sou th Ame r ica; Pa naman ian la n dbr i dge for ms. Sea leve ldrc
te ns ive grass lan ds an ddese rts deve lop as forests co n trac t. Hom in ids (early hu man
app ear. B irds reach their max imu m species diversity.

If
C limate co n t inu es to dry an d coo l. The A lps an d H ima layas fo rm, a n d g rass lan ds do
Mioce ne the p la ins of As ia an d N. Amer ica. Passer ines dive rs ify explos ively and spread
n iches. Modern bird genera begin to appear.

C4
C lima te beg ins to dry an d coo l, espec ia lly at po les; g reat forests sp read to cover me

JIOZONiJ
>-.
CC

ILI
i'
=
<
O ligoce ne masses. Orde r Passer iformes evo lves late Eo ce ne to ea rly O ligocene. Near ly al lf
of nonpasser ines are p resent.

j:3
M
G lo ba l c lima te m i ld an dhu m i d. N. Amer ica a n d Europe separate. Ma m ma ls di
Epoch of greatest diversification ofb irds: most modern orders are p resen t by 5 0 m
Eoce ne most mode rn fa m i lies are p resent by beg inn ing of next epoc h. S ho rebir ds, flam in
birds, ra i l- li ke birds, an d crane li ke birds are diverse an d a bu n da n t.
IT.)

Mi ld c limate wo r ldw i de. S ha llow con t inen ta l seas disapp ear. First pr im itive pri
Lit ho rn ithi ds (mediu m-s ized, fly ing birds poss i b ly ancestra l to ra t ites ) appea r in N.
Pa le oce ne sp here. Gian t, flig ht less, p redatory birds appea r: Dia tryma in N. He m isp here an dr
rhac i ds in S. Ame r ica. Many modern o rde rs of birds beg in to appear.
vv. • 'I T T p ip
1

•• • .
L1
Z

Warm trop ica l a n d su btrop ica l c limate; s lig ht coo ling at e n d of p eriod. Gon dwa
frag men ts a n d most of wor ld is cove red by s ha llow seas. F lowering p lan ts (angiosl
ap pear and soo n become the dom inant lan d p lants. Ma r ine rep ti les suc h as p ies '
flou r is h in the s ha llow seas. D inosau rs dom inate the land, while sma l l ma mma ls,
CRETAC EOU S
saurs, and m ediu m- sizedb irds diver sify. The dom inant birds are the enantior n
(opposite birds). Dro maeosau rs appear. B irds p rese nt in c lu de the toothed birds I-
ornis an dlchthyornis; an d the ea r liest toot hless bird, Con fu ciusornis (125 mya ).
extinction at the en d of the pe r iod c laims d inosaurs, pte rosau rs, mar ine repti le
many mar ine inverte brates.
Cr

Pa ngea sp lits in to Lau ras ia a n d Go n dwan a lan d. At la nt ic Oc ean forms fro m r i fts in tl
JU RASSIC t inen ta l crust. C lima te wa rms wor l dw i de. Lus h veg etat ion do m inatedby gy mnos
D inosau rs d ive rs ify whi le mamma ls rema in small. The first b irds, lizards, and sa lmi)

3IOZOSIW
appea r. Archaeopteryx foss ils appear 15 0 mya.
I

MASS EXT INCTIONS

Pa ngea is e levated a n d s ha llow seas dra in. Exte ns ive deserts. The lan d a n ima ls tf
v ived the Perm ian ext in ct ion dive rs i fy a n d sp read to vacan t n ic hes. Thecodo n ts
TR I ASS IC therapsids as the dom inan t ve rtebrates. By end of period, d inosau rs, pterosaurs, '
rept iles, croco diles, lep idosa urs (a ncestral sna kes andl iza rds), frogli ke amp hi bian
fish, an d true ma mma ls appear.
RALIMOIA110011LCOFILLIWIN -- 1 IROMLI M11 01.111 [1101:1101W11 A I 111: I KIM
rt
Lin

Co ld c lima te wa rms throug hout per io d; w i desp read a r i dity. A s ing le wo r ld co n fine'
PER MIAN gea, fo rms at en d of per iod. Cone- bear ing p lants (gy m nospe rms ) rep lace spore-p ro
p la n ts. Early reptiles and mam mal- li ke repti les (therapsids) diversify anddom in
land. Most exte ns ive extinct ion eve nt in ea rth 's history occu rs o n bothlan d an d in
at the per iod 's e n d, de fin ing the e n d of the Pa leozo ic Era.
c7.
©

Age of Amp h ibians. Maj o r g lac iatio n in secon dha lf of pe r iod. Coa l swamp s p rev
lN N N
1—

trop ica l a reas, do m ina tedby spo re-p roduc ing p la n ts su c h as mosses an dferns. Amp l
CARBO NIFEROU S an dfis hes divers i fy a n d sp rea d. Insects divers ify greatly on land, p rov iding a food
that spu rre d the radiat ion of ter restr ia l vertebrates. A maj o r evo lut iona ry adva nc
a mn iotic (terre str ia l) egg, w hic hfrees a ncestra l rept i les from a depen dence o n wat
reptiles appear; mam ma l- li ke rept i les are p res en t by en d of per iod.
I

MASSEXTINCTIONS
NVINOMO
Age of F ish. Maj o r moun ta in bu i lding in N. Amer ica a n d Europ e. C limate coo ler.
do m inated by reef- bu i lding orga n isms (cora ls ). F irst fo rests and amp h ib ia ns. Fis he
s i fy but many go ext inct at en d of per iod.
310Z011Vd
©
CT

NV11:111 11S
I

MASSEXTINCTIONS
a)
A rt d r.
m

NV IDIA0C1110
tin ents. Moderate c lima te u nt i l g lac iat io n at en(
rine an ima ls, inc lu d ing first jaw less fish, dive r!
rt
CT
0

Age of Mar ine Invertebrates. Co n t ine nta l masses brea k up an d are coveredby s
CAM BRIAN seas. C ho rdates an d inverte brates w ith s he lls fir st appea r. F irst vertebrates may ap
en d of pe r iod.
rr
If)
Lin

c•i'

Large land mass es form. Oxygen firs t appears in atmosp he re. Mu lticellu lar org
ItC (a lgae, fu ng i, invertebrates) appear a n ddive rs i fy.
tri
©

Format ion of the ea rth. Va ria b le c lima te. F irst foss ils kn own from 3. 5 bi llio n year!
"tC

c4..
CC*mya = million years ago
d

NVININVANdl
I
C.g
1.114 Kevin J . McGowan

A Guide to
Bird Watching
Stephen W. Kress

When you see something new for the first time—a bright
green beetle, a startling yellow flower, or a warbler with
a golden head and breast—your first question is usually
"What is it?" To make sense of the bewildering variety of
living things, and to think about how they relate to each other, we need
names. Using names helps us to separate the jumble of bird voices and
fleeing brownish blurs into distinct species with habits of their own,
and opens doors to the wonders of courtship, nesting, migration, and
other aspects of bird biology.
The ability to recognize birds also can help efforts in bird con-
servation. Much of what ornithologists know about bird numbers and
distributions, and about how they change in response to alterations
in our environment, comes from bird watchers who report sightings
in their local areas. In fact, there are many organized conservation
projects in which birders can participate (see Ch. 10). But to help
scientists follow trends in wild bird populations and develop conser-
vation plans, you must know how to identify bird species. So, one of
the first steps in becoming a better earth steward is to learn the cast of
bird characters inhabiting our planet.

Cornell Laboratorq of Ornithologq

2.2 Stephen W. Kress Chapter 2 —A Guide to Bird Watching 2.3

1: Belted Kingfisher, 2: Mallard, 3: woodpecker, 4: quail, 5: mockingbird, 6: kingbird, 7: nuthatch, 8: screech-owl, 9: jay,
Figure 2 1. Using Silhouette to Identify Bird Groups: Birds in the same taxonomic group typically have the same body shape
-
10: vireo, 11: cardinal, 12: European Starling, 13: grackle, 14: warbler, 15: dove, 16: finch, 17: swallow, 18: kestrel, 19: crow,
and proportions, although they may vary in size. Silhouette alone offers many clues to a bird's identity, and may allow a birder 20: wren, 21: shrike, 22: Killdeer, 23: meadowlark.
to assign a bird to the correct group or even the exact species. European Starling and Belted Kingfisher, for example, both can be
identified by silhouette.

Cornell Laboratorg of Ornithologq Handbook of Bird Biologq

2.4 Stephen W. Kress Chapter 2 — A Guide to Bird Watching 2.5

How to Identifq Birds Shape

■ Novices invariably are awed by how quickly an experienced birder Although birds in the same general group can vary dramatically
in size, they usually have the same body shape and proportions. For
can differentiate similar-looking birds zipping overhead or dashing
example, doves have chunky bodies, whereas blackbirds are more slen-
through dense tangles. Learning to identify birds is actually similar
der. Having a knowledge of bird shapes and silhouettes allows you to
to getting to know your human neighbors. When you move into a
assign birds to the correct group (Fig. 2 1). Sometimes shape can even
-

new community, at first everyone is a stranger. But soon you learn to

reveal the exact species. For instance, the European Starling and Belted
distinguish your neighbors as you unconsciously build a catalog of
Kingfisher can be identified by their silhouettes alone.
pertinent details. One neighbor wears Bermuda shorts all summer,
Shape is not infallible as an identification clue, though. Once I
another emerges only for church on Sunday, a third is always sur-
spotted a "fat-bodied" bird with a long tail sitting at the top of a smoking
rounded by a gaggle of children. One shuffles along slowly, another is
chimney. Thoughts of rare exotics floated past as I waited for the bird to
always in a hurry. Some jabber constantly, others never utter a peep.
move. When it flushed from its warm perch, it flashed white patches on
As their habits, silhouettes, styles of walking, and "habitats" become
the wing—a Northern Mockingbird fluffed up against the frigid winter.
more familiar, you learn to recognize your neighbors in a flash—even
at a distance.
In a similar manner, paying attention to differences will help you Postures and Flight Patterns
identify your bird neighbors. You can recognize many birds simply by Similarities of postures and flight
observing their shapes and postures. Rapid assessments of this sort are patterns can also help to place birds in
based on jizz, a birding term that harkens back to the "general impres- their proper groups. If you watch one
sion of size and shape" (G. I. S. S.) that British observers used during common member of the thrush family,
World War II to distinguish between enemy and friendly aircraft. As an the American Robin, strut across a yard,
example, in their book Hawks in Flight, Pete Dunne, David Sibley, and you'll see that the bird takes several steps,
Clay Sutton share a tip for using jizz to separate two similar-looking Red-eyed Vireo
then adopts an alert, upright stance with
falcons. They write, "A Merlin is to a kestrel what a Harley-Davidson L east Flycatcher
its breast held forward. Hermit and Wood
is to a scooter." Of course, to get to the point at which you can identify thrushes have similar postures. Other birds
falcons from general impressions, you must look closely at many fal- that strike vertical poses include hawks,
cons of each kind, so a mastery of jizz can take years to develop. flycatchers, and larks, whereas birds that
Beginners should start by learning to identify the general groups usually perch horizontally include shrikes,
of birds. These groups, such as warblers and flycatchers, contain crows, and vireos (Fig. 2 2).-

birds whose members all share certain similarities. Warblers, for in- Many bird groups also have charac-
stance, are generally small, brightly colored birds that glean insects teristic flight patterns (Fig. 2 3). Finches
-
Loggerhead Shrike
from leaves and twigs; flycatchers usually perch upright on exposed exhibit a steep, roller-coaster flight; American Robin
branches, making frequent sorties to capture flying insects. Examples woodpeckers generally fly in a pattern of
of other groups include woodpeckers, which extract insects from tree moderate rises and falls. Accipiters such as
trunks and large branches, using their tails as props; kinglets, which Sharp-shinned Hawks, Cooper's Hawks,
hover near branches while picking off tiny insects; and wrens, small, and Northern Goshawks typically make
energetic, brown birds that dart through underbrush with upright tai Is. several wing flaps followed by a glide,
The differences among groups, and among species within groups, can unlike buteos such as Red-tailed Hawks,
be daunting at first but will become clear with experience. which are usually seen soaring.
During the initial phase of birding, you will see many birds that Posture and flight pattern can some-
you don't recognize. As you begin learning what they are, focus on the times help to identify a bird's species. The
features described in the following sections. Remember, though, that American Crow flies with regular, flapping
American Crow
in most cases several features must be considered together to make a wingbeats, whereas the similar-looking Red-tailed Hawk
final identification. Common Raven flaps occasionally and
Remember also thatthe following section presents only a general frequently soars like a hawk. Soaring Tur-
overview of identification features. To explain all there is to know about keyVultures look a lot like hawks, but they Figure 2-2. Using Posture to Identify Bird Groups: Posture can be a clue to
identifying birds would take an entire book, in fact, several books. placing a bird in its correct group. Flycatchers, thrushes, and hawks usually
typically hold their wings in a shallow V
stand or perch with an upright stance. Vireos, shrikes, and crows usually
Fortunately, such books exist, and many of these "field guides" are shape over their backs, whereas most perch horizontally. Distant perched crows and hawks may look similar, but
excellent. An annotated list appears at the end of this chapter. hawks and eagles hold their wings flat. noting their different postures may help to distinguish them.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

2.6 Stephen W. Kress Chapter 2—A Guide to Bird Watching 2.7

a b

Finch Red-tailed Hawk

Turkey Vulture

Bald Eagle
Woodpecker

Black Vulture
Northern Harrier

Behaviors

Accipiter Sometimes a bird's behavior is your best clue for determining Figure 2-3. Using Flight Patterns as
Identification Clues: Many bird groups
its group. For instance, warblers and vireos have similar postures and
have diagnostic flight patterns. a: Finch
shapes, but the two groups are readily differentiated by behavior. flight is steeply undulating, whereas
Watch them feed and you'll see that warblers are quick, energetic woodpecker flight has more moderate
birds that constantly dart from place to place as they pick tiny insects rises and falls. Accipiters typically fly

Nkik from leaves and branches. In contrast, vireos often perch for several
minutes in one place, waiting until they see a large insect, and then
they dash forward to snatch up their prey. A close view of warbler and
with several wingbeats followed by a
glide, unlike buteos, which usually soar.
Flight pattern also can help to distinguish
similar species: the American Crow has
vireo beaks helps to explain this behavioral difference. Warblers have deliberate, flapping wingbeats, whereas
trim, pointed beaks—ideal tools for eating insects such as mosquitoes the Common Raven often alternates
Buteo flapping with hawklike soaring. b:
or aphids. Because these prey are so small, it takes a lot of them to
Head-on flight profiles also may give
make a meal fora bird, so warblers are always on the move.Vireos have identity clues: Soaring Turkey Vultures
stouter beaks with a distinct hook at the tip, so they can subdue and resemble hawks, but hold their wings in
hold much larger prey—hence their wait-and-attack behavior. a shallow V-shape, whereas most hawks
and eagles hold their wings out flat.
You can also differentiate the various groups of ducks by observing
Black Vultures also have a flatter, more
their behavior. Dabbling ducks such as Mallards and Gadwalls tip their hawk-like profile. Northern Harriers
tails up to feed in shallow water, whereas Canvasbacks, Redheads, and hold their wings in more of a V shape,
other diving ducks completely disappear in search of bottom-dwelling but their hovering behavior generally
fish and plants. gives away their identity. Note how the
American Crow Bald Eagle's profile is even more flat than
Behaviors can also help distinguish individual species. For in- that of a typical hawk, such as the Red-
stance, Fox Sparrows scratch the leaf litter looking for spiders and tailed Hawk.
insects; Song Sparrows pump their tails in flight as they dash from one
shrub to the next. Or, consider Mourning Doves and American Kestrels.
These two birds are about the same size, have similar silhouettes and
postures, and perch on telephone lines in open farm country. However,
kestrels tend to pump their tails frequently while perched, and doves
do not (Fig. 2-4).
Common Raven Gliding

— — — — Flapping Size
Once you have assigned a bird to the correct group by observing
its shape, posture, flight pattern, and behavior, you can use several

Cornell Laboratoni of Ornithologii Handbook of Bird Biologq

2.8 Stephen W. Kress Chapter 2—A Guide to Bird Watching 2.9
other clues to determine its species. One important consideration is ing hot weather birds may hold their feathers tightly to their bodies,
size. Birders often use familiar birds such as American Crows, Amer- which makes them look smaller. Conversely, on frigid days they may
ican Robins, and House Sparrows as references when fluff themselves up to provide better insulation, so a chickadee might
they are trying to determine or describe the size of look I ike a mockingbird.
a new bird they have seen (Fig. 2 5). Size com-
- Also, birds of the same species sometimes differ in size. Male
parisons are most useful when you see an un- gulls, turkeys, and pheasants are larger than females, but female
known bird side-by-side with a reference bird, but hawks, eagles, and owls are larger than males. And when young birds
with some practice you will be able to remember the leave the nest they can be bulkier than their parents. Exercise soon
approximate sizes of common birds and use them as trims them to adult size.
comparisons. For example, a bright, yellow-and-black
finch at your feeder could be an American Goldfinch,
Comparing Bock' Features
which is a little smaller than a House Sparrow, or an
American Evening Grosbeak, which has similar colors and You can sometimes identify species of birds by taking a careful
Kestrel look at their body features, especially extremities such as beaks, heads,
Mourning patterns but is nearly as large as a robin. A wood-
Dove and tails. As an example, consider the Hairy and Downy woodpeckers,
pecker the size of a crow would be a Pileated;
two similar-looking species that often live in the same woodlot and
one the size of a sparrow might be a Downy or
frequently appear at feeders. At first glance, the two species—which
a Ladder-backed woodpecker. Sometimes you can use two reference
have nearly identical plumage patterns—look hopelessly similar. The
Figure 2-4. Distinguishing Birds by birds for comparison. For example, waxwings are larger than sparrows
Behavior: Similar-looking species may but slightly smaller than robins. Jays are larger than robins, but smaller Hairy Woodpecker is noticeably larger than the Downy Woodpecker,
be distinguishable by behavior. For in- but what if you see one of these birds alone? The key is to note the
than crows.
stance, American Kestrels and Mourning proportions of the bird's beak relative to its head (Fig. 2 6). On careful
Doves are about the same size, have sim-
Like shape, size is also fallible as a bird-identification clue. Ap- -

inspection, you can see that the Hairy Woodpecker's wood-drilling

ilar silhouettes and postures, and choose parent size can be affected by lighting conditions and distance, and
beak is nearly as long as its head. However, the beak of the smaller,
similar perches in their open-country size may be especially hard to judge in rain or fog and at dusk or dawn
habitats. Perched kestrels, however, fre- bark-picking Downy Woodpecker is only as long as the distance from
when, in silhouette, perched blackbirds can look like crows and crows
quently pump their tails up and down,
can look like hawks. Birds also can change their apparent size. Dur- the base of its beak to the back of its eye, or about half as long as its
whereas doves do not. head. This may seem like a subtle distinction, but it works!
Once you are tuned in to this type of proportional difference in
size and shape, similar species become much easier to sort out. Other
examples abound: the nearly identical Cooper's and Sharp-shinned
hawks can be distinguished when flying overhead because the Coo-
Figure 2-5. Using Familiar Birds as per's Hawk head protrudes far ahead of its wings, whereas the head
Size References: Use the sizes of well- of the smaller Sharp-shinned Hawk barely extends beyond its wings
known birds, such as the American (Fig. 2 7). Greater and Lesser scaups look similar—the Greater Scaup
-

Crow, American Robin, and House House Sparrow American Goldfinch

Downy Woodpecker is bigger, but size is hard to judge when you're looking at birds halfway
Sparrow, as references when trying to
identify an unfamiliar bird. For instance, across a lake—so look at the head: the Greater Scaup has a rounded
a crow-sized woodpecker would be a head whereas the Lesser Scaup's head is more peaked.
Pileated, but one the size of a sparrow
might be a Downy or a Ladder-backed
woodpecker. A yellow-and-black finch 1 bill about Figure 2-6. Using Body Proportions
smaller than a sparrow is probably an Evening Grosbeak 1 bill length 1 bill length to Distinguish Similar Species: Pay
American or a Lesser Goldfinch; Evening American Robin Cedar Waxwing length 2 bill lengths >1< attention to body features, especially
Grosbeaks have similar colors and pat- 1, <
beaks, heads, and tails, to tell similar
terns but are almost robin-sized. Some- species apart. The Hairy and Downy
times you need two reference birds for woodpecker, for instance, have almost
comparison. For instance, a waxwing is identical plumage patterns and habi-
bigger than a sparrow but smaller than tats. The best way to tell them apart is to
a robin. A Blue Jay is larger than a robin compare the length of each bird's beak
but smaller than a crow. to the length of its head. The Downy
Woodpecker's beak is only about half
American Crow as long as its head, whereas the Hairy
Woodpecker's beak is proportionately
much longer, almost the same length
Pileated Woodpecker Downy Woodpecker Hairy Woodpecker as its head.

Cornell Laboratorg of Ornithologq Handbook of Bird Biologu

 /"-

2.10 Stephen W. Kress Chapter 2—A Guide to Bird Watching

2.11

Field Marks useful. For example, the black eyel ine of a Red-breasted Nuthatch sep-
arates it from the White-breasted Nuthatch, which completely lacks
Birds display a huge
an eyeline (Fig. 2-9). This field mark can actually be more diagnostic
variety of patterns and
than color—many female Red-breasted Nuthatches have very light
colors, which they have
breasts, and in dim light or backlighting the colors can be difficult to
evolved in part to recognize
see. As another example, the Ruby-crowned Kinglet has a white eye
other members of their own
ring, whereas the similar Golden-crowned Kinglet has a white eye-
species for mating. Fortu-
brow stripe. And as one more example, Field and Chipping sparrows
nately, bird watchers can
both have rufous caps and plain gray breasts. But the Chipping Sparrow
Sharp-shinned Cooper's use the same features to
help distinguish species. For has a crisp, black eyeline and white eyebrow stripe, whereas the Field
Hawk Hawk
Sparrow shows at most a hint of a brown eyeline with an indistinct
instance, the three different
grayish eyebrow area.
but similar-looking species
of sea ducks known as sco-
Bill Shape and Color
ters are easy to differentiate
Bill shape can help to identify both general bird groups and indi-
by the pattern of white patches on the tops of their heads. Among adult
vidual species. Most members of the family that includes blackbirds,
males, the White-winged Scoter has one white patch under the eye,
Figure 2-7. Sharp-shinned Hawk Versus orioles, and meadowlarks, for example, have long, pointed beaks.
Cooper's Hawk Flying Overhead: The the Surf Scoter has white patches on the forehead and nape, and the
Flycatchers have beaks that are flattened with a hook on the end,
Sharp-shinned Hawk and the Cooper's Black Scoter has an all-black head.
which improves their ability to grip large insects; warblers generally Figure 2-9. Use of Field Marks in Bird
Hawk are almost identical in ap- When identifying an unknown bird, the following features are
have pointed beaks that lack a hook; and vireos have beaks intermedi- Identification: Prominent field marks
pearance and their size ranges partially
particularly important. You may find it useful to review the parts of a often facilitate bird identification.
overlap; thus, if you see a lone bird flying ate between warblers and flycatchers, thickened from the sides with
overhead, it can be difficult to identify. A
bird illustrated in Fig. 1-3. For instance, the black eyeline of the
a hook for holding large, squirming insects. Considering individual Red-breasted Nuthatch (left) readily
good distinguishing characteristic is the species, study the beaks of the similar Greater and Lesser yellowlegs
Head distinguishes it from the White-breasted
length of the head. The Cooper's head
and you'll see that the beak of the greater tilts slightly upward whereas Nuthatch (right), which completely
protrudes far ahead of its wings, whereas Check whether the bird's head has a crest (tuft), which will narrow
the lesser has a shorter, straight beak. lacks an eyeline. Under difficult lighting
the Sharp-shinned Hawk's head barely the list of possible species dramatically. Also check for a stripe over conditions this field mark can be more
extends beyond its wings. Beak color is most helpful for identifying individual species. The
the eye (eyebrow stripe), a line through the eye (eyeline), or a ring of diagnostic than the birds' coloration.
yellow lower beak of the Eastern Wood-Pewee distinguishes itfrom the Photographs by Marie Read.
color around the eye (eye ring) (Fig. 2-8).These field marks can be very
Crown
Stripe

Eyebrow
Stripe Eye Ring

Upper
Beak

titt:*3‘
Eyeline
Whisker
Mark

White-throated Sparrow Ruby-crowned Kinglet

Figure 2-8. Field Marks on the Head: The following features of the head, if present, serve as good field marks: A stripe over the
eye (eyebrow stripe), a line through the eye (eyeline), a stripe in the midline of the head (crown stripe), a ring of color around the
eye (eye ring), and a throat patch. Pay attention to the colors of the upper and lower beak, and the area between the base of the
bill and the eye, known as the lore. Red-breasted Nuthatch White-breasted Nuthatch

Cornell Laboratorti of Ornithologu Handbook of Bird Biologu

2.12 Stephen W. Kress Chapter 2—A Guide to Bird Watching 2.13
Eastern Phoebe. Field Sparrows have pink beaks, whereas the similar ers. In towhees, juncos, meadowlarks, mockingbirds, and Vesper
American Tree and Chipping sparrows have black ones. Snowy Egrets Sparrows, for example, the feathers on the outside of both
have black beaks, whereas Great Egrets have bright yellow beaks. sides of the tail are white—an especially prominent American Crow
field mark when the bird flies. House and
Wings Winter wrens are quite similar
Check for wing bars or wing patches (Fig. 2 10). If the warbler
- in both appearance and be-
you see has a large white wing patch, you can be sure it is either a havior, skulking in dense
Cape May, Blackburn ian, or Magnolia warbler; or a Painted Redstart. vegetation with their
Just a glimpse of a small white dot on the wing announces a Black- tails pointed up-
throated Blue Warbler, even in fall. In fact, wing bars are so useful in ward. But the
identifying warblers and vireos that some field guides separate each of short, stubby tail
Common Raven
these groups into birds with and without wing bars. The orange-brown of the Winter
wing bars of the Blue Grosbeak distinguish it from the similar all-blue Wren immediately
Indigo Bunting. distinguishes it from the House Wren.
Wing Bars
When viewing a perched or standing bird, note the length of the At first glance, flying crows and ravens
wings compared with the tip of the tail. With this information you look very similar—both are big, black
will be able to distinguish certain terns, gulls, and sand- birds. But pay careful attention to the
pipers more readily. For example, the wings of the less shape of their tails, and you will be able
common Baird's and White-rumped sandpipers ex- to distinguish them. Crows have tails that are smoothly rounded or Figure 2-12. Raven Versus Crow Tail
tend a bit beyond the tail, whereas those of the similar straight across the end, whereas the raven's tail is "wedge-shaped," Shape: In flight, an American Crow ap-
but more common Least, Western, and Semipalmated coming to a broad point in the middle (Fig. 2 12). pears similar to a Common Raven, but
-

the two species can be distinguished by

sandpipers are about the same length as the tail. Bird-
tail shape: the crow's tail is smoothly
ers determined to find an unusual species may spend Legs
rounded or straight at the end, whereas
hours scanning a distant flock of these "peeps" to pick Note the length and color of the legs, two features especially use- the raven's tail is wedge-shaped.
outthe one or two different birds. Comparing wing-to-tail ful in identifying shorebirds, gulls, and egrets (see Ch. 3, Nonfeathered
lengths also will help you differentiate perched Red-tailed Areas, Legs and Feet, for examples). Keep in mind, however, that no
Hawks from Swainson's Hawks (Fig. 2 11).- matter how bright yellow a Least Sandpiper's legs are, they will still
Figure 2-10. Field Marks on the Wing: look brown after it walks in mud!
Check for wing patches and wing bars. In
Tail
a few groups, most notably the warblers
and vireos, wing markings can provide Check the length and shape of the tail. Note if the end is notched,
positive identification even if the bird is rounded, or straight, and look for any white spots or white outer feath-
Colors and Pluma8e Patterns
in nonbreeding plumage. Although color is often useful in bird identification, it also can
be misleading. A bird's apparent color often varies with the angle of
view, time of day, and lighting direction. The Indigo Bunting presents
a dramatic example: in direct light this bird flashes a brilliant indigo
glow, but if it is lit from behind, it appears jet black. Color is especially
difficult to see over water. Most ducks have spectacular colors, but they
can be difficu It to see because of glare from surrounding water. Instead,
look for the distinctive dark and light patterns of their plumage.The first
edition of Roger Tory Peterson's Field Guide to the Birds didn't even
show duck colors, and it worked fine for identification.
Figure 2-11. Wing Versus Tail Length:
In perched or standing birds, the length
As another example, puffin beaks display a rainbow of brilliant
of the folded wing compared to the colors that you can sometimes use to identify the birds, but you must
tip of the tail is a useful distinguishing see the beak in just the right light to enjoy the display. Rather than
character, particularly for challenging counting on seeing a colorful beak, first learn to recognize puffins
groups such as terns, gulls, and sandpip-
as members of the auk family, a group of plump seabirds with bold
ers. Comparing wing-to-tail length also
may help differentiate perched buteos: black-and-white patterning. Each auk species has a slightly different
notice how the wings of the Swainson's black-and-white pattern that helps birders (and probably birds, too)
Hawk (right) extend beyond the tip of recognize it at a distance (Fig. 2 13).The shape of a puffin's beak—ver-
-

its tail, unlike those of the Red-tailed

tically broad—is the second clue to its identity. The beak's flashy colors,
Hawk (left). Red-tailed Hawk Swainson's Hawk

Cornell Laboratort of Ornithology Handbook of Bird Biologq

2.14 Stephen W. Kress Chapter 2 — A Guide to Bird Watching 2.15
would otherwise overlook, because they are far away, skulking in dense
vegetation, or otherwise hard to see. Knowing bird songs also helps in
bird-monitoring projects, when it's not practical to observe all birds in
an area by sight. Hearing a bird tells you as clearly as seeing it that the
species is present, and population estimates based on counting calls
and songs are vital in assessing the health of wild bird populations.
Becoming familiar with bird songs usually comes after learning
to recognize species by sight, and it takes a great deal of practice in
the field. The best way to begin is to focus on one or two species at a
time. Whenever possible, track down singing birds to discover their
identities. Watching a bird sing its song will improve your memory of
that song. Another good approach is to accompany a knowledgeable
V98
'MN!
birder who can identify the singers—but you still should try to watch
■Nise the birds sing, to establish the visual connection. Listening to record-
lei.
gob. ings of bird songs can also be useful and, unlike listening to wild birds,
you can replay the songs as often as you want. Recordings are most
Figure 2-13. Plumage Patterns of like the body colors of ducks, are less useful for field identification than useful, however, as reviews for songs you have al ready heard outdoors.
Alcids: Because of glare, the true col- the black-and-white body pattern. For novice birders, videos of singing birds may be more helpful than
oration of birds is especially difficult
Land birds, too, have distinctive contrasting patterns that are more audio tapes, as they allow you to see and hear a bird at the same time.
to see accurately over water, hindering
the identification of distant, swimming
useful than colors for identification. Patterns such as striped breasts In addition, CD-ROM field guides and birding games are now widely
birds such as ducks and members of the (Ovenbird, waterthrushes), dark caps (Eastern and Say's phoebe, available, giving you the added advantage of interactive learning while
auk family (the alcids). When identify- Blackpoll Warbler), and light-colored rumps (Northern Flicker) are seeing and hearing birds vocalize.
ing these birds, distinctive light and dark visible under most lighting conditions, and are often conspicuous even Bird songs come in a huge variety. Winter Wrens, for example,
plumage patterns are often more useful
at a considerable distance (Fig. 2 14).
- have the longest song of any North American bird—each song includes
than plumage color. Notice the different
black-and-white patterns of the Black Trying to identify birds by color can present another problem: the about 40 notes and can last more than 10 seconds. The high-pitched,
Guillemot (top left), Atlantic Puffin (top amount of color an individual bird displays often varies with age, sex, musical notes ring through the forest in a rapid, ever-changing, pic-
right), Razorbill (bottom left), and An- diet, and time of year. And each fall, many birds such as shorebirds, colo-like run. The singer of a song fitting this description, heard in a for-
cient Murrelet (bottom right).
tanagers, and warblers undergo complete body molts—they lose all est, is easy to identify—and it's a good thing, because these mouse-like
their bright, breeding-color feathers as they change to more somber birds are seldom seen. At the other extreme is the Henslow's Sparrow,
winter plumages (see Ch. 3). whose song once was described by Roger Tory Peterson as "a feeble
Comparing living birds with color plates in field guides will show hiccup."
a final problem: color reproductions can only approximate bird colors, Many bird watchers learn new songs most easily by associating
Northern Flicker and the quality of the color can vary from one printing to the next. To them with songs they already know. So, mastering a few basic songs
get a feel for the extent of color variability in pictures, look up the same will give you a framework for comparison. When you hear a new song,
bird in several field guides and compare the colors of the different think whether it is similar to one with which you are already familiar. Is
paintings and photos. it faster, slower, higher, lower? How do the rhythm and tone differ?The
Despite these limitations, color can be helpful when you American Robin, for example, has a clear, musical song consisting of
are observing birds nearby and in direct light (not backlighting). a string of short phrases delivered as one song, with very short pauses
White The similar Least and Sem ipal mated sandpipers, for instance, are very between the phrases. The Scarlet Tanager, though not related to the
Rump
much alike in size and behavior, but Least Sandpipers have brown robin, has a similar song—the rhythm is almost exactly the same—but
backs and straw-colored legs, whereas the semipalmated has black it has a raspier quality. And the Rose-breasted Grosbeak—again no
legs and a gray back. Male Orchard and Baltimore orioles can also be relation—also sounds much like a robin, though it strings its phrases
distinguished through color; the orchard's chestnut body is strikingly together more closely, and has a whistled tone, like "a robin with a
different from the vivid orange Balti nnore.The females differ, too, the Or- cold in a hurry." Rose-breasted Grosbeaks also may utter a very sharp,
Figure 2-14. Conspicuous Plumage Pat- chard Oriole being more yellow, the Baltimore Oriole more orange. high-pitched peek it could be mistaken only for a tree squeaking in
—

terns of Land Birds: Bold plumage pat- the wind—in the middle of the song or between songs.
terns such as breast stripes, dark caps,
and white rumps—as in the Northern
Not only do unrelated birds often sound alike, but related birds
Songs
Flicker—are visible under most lighting can sound very different. In fact, members of a single family often
Experienced birders can identify most birds by their songs or calls
conditions and are often conspicuous, produce a diverse array of songs. The 57 species of North American
even at a distance. alone, and knowing bird vocalizations can help you find birds you
warblers present a good example. Although none of them actually

Cornell Laboratorg of Ornithologu Handbook of Bird Biologq

2.16 Stephen W. Kress Chapter 2— A Guide to Bird Watching 2.17
warble, some produce insect-like buzzes (Blue-winged Warbler), learn to recognize the bird's voice—the speed, duration, pitch, and
some trill (Pine and Worm-eating warblers), and others sing loud, tonal quality of notes (buzzy, whistled, raspy, screechy, harsh, musical,
rollicking songs (Hooded and Kentucky warblers). The different song chirpy). Song Sparrows, for example, sing from 5 to 15 different songs,
characteristics may have a lot more to do with the kind of habitat in and many individuals sing their own unique songs. Even so, you can
which a bird lives than with its particular family (see Fig. 7-20). recognize the voice of these common songsters quickly because they
Certain terms are useful for describing and mentally organizing start each type of song with the same two or three clear introductory
songs. The Chipping Sparrow, Swamp Sparrow, Dark-eyed Junco, Pine notes. Thoreau noted that the people of New Bedford, Massachusetts
Warbler, and Worm-eating Warbler, for instance, have similar songs described the bird's song as maids, maids, maids—hang on your tea-
that are best described as trills, in which a single note or note cluster kettle-ettle-ettle-ettle-ettle. Whereas the tea-kettle-ettle part is debat-
is repeated again and again. To tell these similar-sounding birds apart able, the two or three maids followed by a variable jumble of notes is
takes a very practiced ear. A few birds make buzzy sounds, somewhat nearly always diagnostic.
like a very loud bee. By counting buzzes, you can distinguish the Recognizing patterns can help birders distinguish many other
slow, lazy bee-buzz of the Blue-winged Warbler from the bee-buzz- songs as well. Brown Thrashers hold the record as the most varied
buzz-buzz of the Golden-winged Warbler. Some of our most melodic singers in eastern North America: an individual bird can sing 2,000
songsters whistle, producing clear tones one pitch at a time. Northern different songs, many of which mimic phrases from other birds. Still,
Cardinals, Black-capped and Carolina chickadees, Tufted Titmice, Brown Thrasher songs are easy to recognize once you focus on the pat-
Eastern Meadowlarks, Baltimore Orioles, and Broad-winged Hawks tern—they usually repeat each phrase twice, in couplet fashion, going
all whistle their songs. These are some of the easiest songs for us to on and on in a harsh voice, and changing phrases continually. Buteven
mimic—a whistled two-note imitation of the Black-capped Chickadee though patterns are helpful, you still must learn tones. For example,
song in spring will nearly always prompt a response if a male is within other birds also sing in couplets, including the Indigo Bunting—whose
earshot. Other songs are not as beautiful to our ears. Kingfishers pro- song is shorter, sweeter, and more emphatic than the thrasher's and is
duce a harsh trill we term a rattle, Common Grackles squeak, parrots exactly the same in every rendition that a particular bird sings—and
squawk, and herons, gallinules, coots, grebes, and mergansers give the Yellow-throated Warbler, whose song has a much sweeter, fluid
hoarse croaks. quality. All of these birds could possibly be found singing in the same
Some birders use mnemonic devices, such as associating phrases location.
from human speech with the songs of particular birds, to help them re- As another example of pattern, consider the vireos. Most of these
member bird songs more easily. It doesn'ttake too much imagination to treetop birds sing similar songs consisting of whistled notes delivered
picture a Barred Owl chanting Who cooks for you, who cooks for you- in short phrases—but the quality and pacing of the songs vary. Red-
all?or an Eastern Wood-Pewee whistling pee-a-wee (although it helps eyed Vireos have a chanting, repetitive song often paraphrased as Here
if someone slowly mouths the words for you while you listen to the I am, way up high, over here, look at me, the phrases continuing on
bird's song). But other commonly used mnemonics can be misleading. and on, in no particular order, with no long pauses. Yellow-throated
Olive-sided Flycatchers supposedly say quick-three-beers, and Wh ite- Vireos sing a similar song in a similar phrasing, often paraphrased as
eyedVi reos reportedly say pick-up-the-beer-check-quick, but making three-eight, eight-three, three-eight, eight-three and so on, but their
these connections takes some creativity (and perhaps a cold beer on a song has a raspy quality akin to the burry voice of a Scarlet Tanager.
hot day). Muddling matters further is the tendency for different authors Blue-headed Vireos also fol low the general pattern, but compared with
to produce strikingly different mnemonics for the same call. In his the Red-eyed Vireo's, their song has a more pure, whistled quality, is
journals, for instance, Henry David Thoreau transcribed the call of the often slower, and includes a pause after every two or three phrases—all
Olive-sided Flycatcher as whip-ter-phe-ee and cited an authority who characteristics that give away their identity as they perch hidden in the
paraphrased the call of the White-eyed Vireo as tshippewee-wa-say. leafy canopy of a deciduous forest.
However, even when mnemonics don't sound exactly like the song, Some birds are actually easier to identify by song than by sight. For
they may still help you remember a song's general features. instance, song is one of the best ways to distinguish the Alder, Willow,
Although different mnemonics usually result from a listener's Least, and Acadian flycatchers. These small birds look so much alike
idiosyncrasies in hearing, sometimes the calls or songs of one species that it's hard to tell them apart even in the hand (Fig. 2 15). Indeed, the
-

can vary between regions (see Ch. 7, Song Dialects). Donald Borror, birds themselves probably recognize members of their own species
an important figure in the field of bioacoustics, became so familiar by song rather than appearance. Although all four have short, harsh,
with the local dialects of White-throated Sparrows migrating through emphatic songs, they differ enough that a little practice will allow
central Ohio that he could tell his students where individual birds you to tell them apart. The song of the Willow Flycatcher has a sharp,
were heading! Songs can also vary among individuals, sometimes abrupt beginning: FITZ-bew. The alder's song has a softer beginning:
even in the same bird. For this reason, learning song patterns can be free-BEE-er. The acadian's song is more shrill than the others: PI-zza.
important. That is, rather than learning precisely what the bird says, And the Least Flycatcher—unlike the other birds who sing their song

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 Stephen W. Kress Chapter 2—A Guide to Bird Watching 2.19
2.18
just once—repeats his song over and loons sometimes land on wet highways during rainstorms, presumably
over in a long series: che-BECK, che- mistaking the broad, winding, slick surfaces for rivers. (This is a serious
BECK, che-BECK. mistake—with their small wings and heavy bodies, these birds need
a water runway and can't take off from land, so they're stuck.) Tired
bitterns sometimes land in grassy backyards; so accustomed are they
I Habitat to hiding among cattails that they still hold their heads in their charac-
che-BECK,
che-BECK....
free-BEE-er Each species of bird is predictably teristic vertical posture (Fig. 2 17).
-

found in a particular habitat, and each

plant community—a spruce-fir forest,
a meadow, a freshwater marsh—con- Range and Abundance
Least Flycatcher Alder Flycatcher
tains a predictable assortment of birds. Although birds can travel fast and often show up in out-of-the-
For example, Swamp Sparrows and way places, each species usually stays within a certain geographic
King Rails are usually found in fresh- area called its range. You can find information about bird ranges in any
water marshes. In a salt marsh, the North American field guide; those with maps are easiest to use in the
Swamp Sparrow would be replaced field. Some maps show both breeding and wintering ranges and give
by a sharp-tailed or Seaside sparrow, dates for the arrival of migratory species.
and the King Rail by a Clapper Rail. Range maps are invaluable for determining which of several sim-
Learn which birds to expect in each ilar species might appear in your region. For instance, suppose you
habitat and, faced with an unfamiliar are sure that you've seen a titmouse, but you're not sure which of the
bird, you'll be able to eliminate from four North American species it may be. Range maps will show you that
consideration species that usually live in most parts of the continent you can figure this out by range alone,
FITZ-bew Pl-zza
in other habitats (Fig. 2 16).
-
because the species scarcely overlap (Fig. 2 18).
-

As an example, knowledge of Knowing the relative abundance of the different species in your
breeding habitat would help you iden- area is also helpful. Some species are common, others are rare. Learn
tify three birds mentioned earlier that the common birds first, then you'll be more likely to spot unusual birds
sing similar trilled songs: the Dark-eyed that look different. Checklists showing the relative abundance of birds
Willow Flycatcher Acadian Flycatcher Junco, Chipping Sparrow, and Swamp are available in many regions.
Sparrow. Their ranges overlap, and— A warning: when using range and abundance as guides, re-
Figure 2-15. Empidonax Flycatcher especially in the Northeast—all three may appear in the same region. member that the birds have not seen the maps or read the books.
Identification by Song: Some birds are But their habitat preferences differ, and taking habitat into account Ranges change, and wandering individuals occur in most species.
easier to identify by song than by sight. when you hear a trill can help you decide which bird you are hearing. In fact, your alert observations can help to document these events,
Least, Alder, Willow, and Acadian fly-
A slow trill emanating from a mass of cattails or a wet, shrubby area improving our understanding of regional, national, or global changes
catchers (all of the genus Empidonax)are
mostly drab olive in color, with faint eye is almost certainly a Swamp Sparrow. Chipping Sparrows are more in climate and habitat.
rings and wing bars, and are notoriously likely to be suburbanites, favoring lawns, parks, grassy fields, and for-
difficult to distinguish by plumage. est edges. And juncos are most common in the interior of coniferous
However, each has a short, distinctive Time of Year
or mixed woods. But be careful: Chipping Sparrows and juncos do
song that is easy for birders to paraphrase Some birds, such as nuthatches, chickadees, titmice, and most
and recognize in the field. overlap in habitat, so you'll need to catch a glimpse to be certain which
woodpeckers, are year-round residents, staying in the same general
bird you are hearing.
area throughout the seasons. By contrast, most flycatchers, thrushes,
Breeding habitat can also help distinguish the similar-looking
tanagers, warblers, and vireos spend the breeding season in northern
Northern and Louisiana waterthrushes. Both species nest on the
latitudes but winter in the southern United States, Mexico, or Central or
ground, have similar, harsh chip notes, and true to their names, are
South America. During migration, they pass through areas in between.
usually found near water. (Untrue to their names, they are warblers, not
Knowing which birds live in or visit your locale at different times of
thrushes.) Nevertheless, they are rarely found together except during
year can help distinguish similar-looking species.
migration. The Northern Waterthrush sticks to the quiet, slow-moving,
For example, some closely related and similar-appearing species,
or stagnant waters of woodland bogs or swamps, whereas the Loui-
such as American Tree and Field sparrows, neatly divide the year with
siana Waterthrush lives in wooded ravines or gorges with streams.
only a little overlap (Fig. 2 19). During late spring and summer, Amer-
-

Although having a knowledge of bird habitat preferences is one of

ican Tree Sparrows breed in the northern tundra, while Field Sparrows
the best ways to sort out which birds you are most likely to encounter,
are breeding throughout southern Canada and the northern United
surprises do occur. During spring and fall migrations, for example,
States. In late fall and winter, American Tree Sparrows migrate south
birds often settle down when they get tired, regardless of habitat. And

`Cornell Laboratoru of Ornithologu Handbook of Bird Biologq

2.20 Stephen W. Kress Chapter 2—A Guide to Bird Watching 2.21

tiNIIIINdllul _ it

441.61;eos •
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Figure 2-16. Common Birds of Common Plant Communities: Each bird species requires a certain combination of habitat com- Sparrow, Winter Wren, Northern Goshawk, Black-throated Green Warbler. c: Sonoran Desert Inhabitants: Black-throated Spar-
ponents, and each plant community supports a predictable assortment of species. By knowing which birds to expect in each row, Cactus Wren, Harris' Hawk, Lucy's Warbler. d: Cattail Marsh Inhabitants: Swamp Sparrow, Marsh Wren, Northern Harrier,
habitat, you may be able to identify an unfamiliar bird by the process of elimination. a: Abandoned Field Inhabitants: Field Spar- Common Yellowthroat.
row, House Wren, Red-tailed Hawk, Blue-winged Warbler. b: Mixed Deciduous/Coniferous Forest Inhabitants: White-throated

Cornell Laboratorq of Omithologg Handbook of Bird Biologq

 2.22 Stephen W. Kress Chapter 2 — A Guide to Bird Watching 2.23
into the breeding range of Field Sparrows, but Field Spar-
rows head for the southern United States. Therefore,
these potentially confusing species are seldom seen
together. Field marks, such as the American Tree
Sparrow's black chest spot and the Field Sparrow's
pink bill, will confirm an identification.
You can profit from the birding experience of others
by seeking out local bird checklists produced by Audubon
Society chapters and other bird clubs, or the staffs of county, ...

state, and national parks and forests, national wildlife ref- American Tree Sparrow
2
2 uges, nature centers, and similar organizations (see Fig. 2-34). Such
checklists tell approximately when each species occurs in an area and
describe its relative abundance; sometimes they provide arrival and
41W/If departure dates. It's worth studying the list for any area in which you
.....
......... are birding, whether you're a traveler, a new resident, or a long-
Pt,"
..... time resident but beginning bird watcher.

Sorting Out Birds

The process of bird identification begins when you
/::••,• •
••;■ lo•
• note the features—shape, posture, and behavior—that
•, 01,.
Field Sparrow
t1,14.&• -
permit placing a bird in the correct group. Identify-
ing the group greatly reduces the number of pos-
".klilkagifLiell'4041A• ••••,,id
sibilities; you need only consider which members 1191
,44WIAA4,400at,,:T.U:att Ak44(e''''''444"4441).-
"S•t(4.“.‘14.8, • •
...
of the group are likely to be in that habitat at that
time of year. Then, look for field marks and listen to the bird's song to Figure 2-19. Time of Year as an Identi-
Figure 2-17. Habitat Surprises: During make your final identification. With attention to these details, you'll fication Clue: Knowing which species
spring or fall migration, exhausted birds are found in a given location at different
soon be able to identify your bird neighbors as quickly as you do your
may land anywhere, regardless of hab- times of year can help sort them out.
itat. A tired American Bittern, landing in
human neighbors. The American Tree Sparrow breeds in
a backyard, will automatically assume the northern tundra, whereas the sim-
its typical vertical posture if approached; ilar-looking and closely related Field
this behavior renders it nearly invisible
when performed in its normal habitat of
Closing the Distance Sparrow breeds in southern Canada
and the northern United States. In late
dense marsh vegetation, but provides
Juniper
Titmouse ■ Most birds are wary of approaching people; usually they fly off or fall and winter, American Tree Sparrows
little concealment in a backyard. retreat into dense vegetation. Nevertheless, you can close the distance migrate south into the breeding range of
the Field Sparrow, which in turn heads
between you and the birds with a few tricks (also see Sidebar 1: At-
for the southern United States. So even
tracting Birds to Your Yard). though the two potentially confusing
species overlap in range, they do not
overlap much in time, and are seldom
Sitting Quietlii seen together.
One of the best ways to observe birds up close is also one of the
simplest: just sit quietly in a likely location until the birds no longer
Figure 2-18. Titmouse Range Maps: In notice you—try it for at least 10 minutes, but preferably half an hour.
most parts of the United States, titmice You'll be pleasantly surprised by the birds and other animals you will
can be identified to species by range Tufted
Titmouse
notice in almost any location—forest, field, or even a yard—but you
alone, because the ranges of the four
will see even more if you choose a site that is especially attractive to
North American titmice barely overlap.
Shown are three western species—the birds, such as a marsh, pond, or streamside, or the edge where several
Juniper, Oak, and Bridled titmouse— different habitats meet.
and the eastern Tufted Titmouse with On atypical nature walk, many of the behaviors you see are those
its "black-crested" form (the latter two Bridled Titmouse
of birds alarmed by your intrusions, not birds going about the ordinary
were considered separate species until Tufted Titmouse
recently). "Black-crested" form (Continued on p. 2.26)

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

2.24 Stephen W. Kress Chapter 2 — A Guide to Bird Watching 2.25

Sidebar 1: ATTRACTING BIRDS TO YOUR YARD

Sandq Podulka Selected References on Attracting Birds
If you already enjoy watching and strategy is to select an as- Feeding Birds Landscaping Putting Up Nest Boxes
identifying birds, you can add a new sortment of plants with Henderson, Carrol L 1995. Wild Henderson, Carrol L 1987. Land- Henderson, Carrol L. 1992. Wood-
dimension to your relationship with a variety of food types About Birds: The DNR Bird scaping for Wildlife. Minnesota working for Wildlife. Minnesota
them by enticing them to visit and (tasty buds, seeds, nuts, Feeding Guide. Minnesota De- Department of Natural Resources, Department of Natural Resources,
nest in your yard. Birds, like humans, cones, and fruits), fruit- partment of Natural Resources, 144 pages. If not at bookstores, or- 111 pages. If not at bookstores, or-
have a few basic needs that, when ing seasons, heights, and 278 pages. If not at bookstores, der from Minnesota's Bookstore: der from Minnesota's Bookstore:
missing, limit their ability to live in cover types (evergreen order from Minnesota's Bookstore: 117 University Ave, St. Paul, MN 117 University Ave, St. Paul, MN
an area. At a minimum, all must and deciduous trees and 117 University Ave, St. Paul, MN 55155. (800) 657-3757. 55155. (800) 657-3757.
have food, water, cover, and nest shrubs, thorny bushes, 55155. (800) 657-3757. A comprehensive guide to bring- Detailed plans for constructing
sites; some also need song perches, unmowed grasses, brush
An excellent, thorough guide to ing wildlife to your yard or a larger nest boxes, shelves, platforms, and
foraging perches, dust-bathing sites, piles, hedgerows, and so
feeding birds. Includes sections piece of land. Contains everything roost boxes, as well as information
and specialized nest materials. on).
on specific birds and how to at- from landscape plans to tips on on how to locate and maintain the
The simplest way to attract birds is Water also will entice
tract them, as well as sections building brush piles, bird feeders, structures.
to put out bird feeders. The key is to birds to your yard. A
that focus on each different type and frog ponds. Detailed charts of Stokes, Donald and Lillian. 1990.The
provide a variety of food types (suet, simple birdbath can at-
of bird food, on bird feeder types plants and their use by wildlife.
black oil sunflower seed, cracked tract a surprising number of birds, "deserts") or timber plantations result Complete Birdhouse Book. Bos-
and how to build them, and on Most applicable to the Midwest ton: Little, Brown and Company,
corn, niger seed, and so on) and especially in areas where there is in a monotony of birdlife. Similarly,
troubleshooting. The best all- and Northeastern United States. 95 pages.
feeding situations (ground, hanging, little suitable natural water, as in in suburban areas natural habitats
round reference to bird feeding. Kress, Stephen W. 1995. The Bird
and platform feeders) throughout many suburban and urban areas. If are often replaced with sterile lawns Gives several basic nest-box
the year. you have more space and ambition, and pavement. Wild habitats that Dennis, John V. 1983. A Complete Garden. London: Dorl ing Ki nder- plans, with dimensions and mod-
Bird feeding is a good way to lure you can construct a small built-in are not obliterated are often de- Guide to Bird Feeding. NY: Alfred sley Limited, 176 pages. ifications for most cavity nesters
birds close enough to see them well pool or even a pond. For birds, an graded by pollution or chopped into A. Knopf, 288 pages. Produced bytheNationalAudubon in North America. Also includes
and to study certain types of behavior, essential component of any of these isolated fragments too small to meet Discusses different types of feed- Society. Discusses many ways to information on buying, locating,
and it is invaluable as a way to share water resources is a shallow area one the needs of many species. ers, nontraditional foods to offer attract birds to your backyard, from and maintaining nest boxes, as
your love of birds with friends or to to two inches deep for bathing. Although public nature preserves, birds, and problems at feeders. bird feeders and nest structures, to well as on the nesting behavior of
interest children in nature. Whether Nest boxes are effective in at- wildlife refuges, and parks are superb Gives information on the behavior ponds and gardens. For each re- the birds.
or not feeding actually benefits birds tracting hole-nesting birds, because ways to provide high-quality habitats and identification of feeder birds, gion of the United States, contains
significantly is extremely difficult to natural cavities are usually in short for birds, much of the good and po- and the food preferences of spe- a guide to the plants that are most
determine, and there is very little supply around modern-day yards tentially good bird habitat in the cific feeder birds. effective in attracting birds.
clear data on this subject. Bird feed- and gardens. For other species, you United States is on private land. It is Stokes, Donald and Lillian. 1987. The
ing does not appear to harm bird can build nest shelves or platforms. therefore up to each of us, whether Bird Feeder Book. Boston: Little, Providing Water
populations, and it undoubtedly One more way to assist birds is, our "yard" is 100 square feet or 100 Brown and Company, 90 pages. Low, Jim.1992."WettingYourWhis-
increases the survival of some indi- whenever possible, to leave old acres, to improve or preserve the land tiers." Birder's World, June 1992,
Gives basic information on feeder
vidual birds in times of food shortage dead trees (called "snags") standing, under our stewardship. For example, pp. 50-54.
types, feeder maintenance, prob-
or severe weather. But detailed, long- as they supply food, cover, perches, a single small yard may not be able
lems at bird feeders, and bird A thorough discussion on how to
term studies incorporating the many and nest sites for birds. to provide all the space or resources
behavior. Then discusses each provide water for birds, from bird
other factors that affect bird survival Improving your yard habitat is im- a breeding Northern Cardinal needs.
common feeder bird in detail, baths to garden pools and ponds.
and mortality will be needed before portant for birds and other wildlife But together, several neighboring
including information on how
we can fully understand the impact because the biggest obstacle they yards may form the ideal habitat and
to identify and attract it, and its
of feeding on bird populations. face today is the loss of natural hab- may "share" a cardinal or an Amer-
behavior at feeders.
If you want to be sure to assist itat. Fields, forests, and swamps are ican Robin. Adjacent private lands,
wild bird populations, landscaping being rapidly converted to housing, or a combination of private and
to improve the quality of your yard highways, airports, and parking lots. public lands, can form "corridors"
for them is one of the best actions Large farms with few crop types have of suitable habitat critical for the
you can take. The trees, shrubs, replaced brushy fencerows, farm successful migration and dispersal
flowers, and groundcovers you woodlots, and wetlands—varied of birds and other wildlife. So, when
plant can provide cover, food, nest habitats that are essential in main- you landscape your yard for birds,
sites, and perches all year long, at- taining abundant and diverse bird your effect may reach well beyond
tracting a greater diversity of birds populations. Trackless horizons of your own boundaries. ■
than will feeders alone. The best single crop plantings (corn or wheat

Cornell Laboratorq of Ornitholos Handbook of Bird Biolos

2.26 Stephen W. Kress Chapter 2—A Guide to Bird Watchin 2.27

tasks of their daily lives. Once you have settled down for quiet obser-
vation, you may see behaviors you've never noticed before: a Scarlet
Tanager gleaning insects from leaves, an Ovenbird poking about in
the forest debris, a Barn Swallow gathering mud for its nest. If you have
the patience to be completely still, birds may move within a few feet
of you. One day after photographing a BlackTern nest from her canoe,
a friend of mine retreated about three feet to watch the adults return.
In less than 10 minutes, one bird came back and sat on the nest. The
other member of the pair flew about for a little longer, then perched
on the bow of the canoe. After that, each time my friend returned to
track the progress of the nest, the birds sat on her canoe, sometimes
even preening. One bird even perched on her head—the most magi-
cal moment of all.
Becoming part of the environment for even a few minutes will
leave you exhilarated, feeling privileged to have witnessed a few spe-
cial moments in the natural world as an insider. In spring and summer,
be sure to carry insect repellent—swatting bugs will not help you
blend into your surroundings. A cushion to sit on also may increase
your comfort.

Pisking and Squeaking

When alarmed, many land birds give a call to rally nearby birds,
who may collectively chase away a predator such as a snake, owl, or
cat. These alarm calls tend to have a similar sound, a sort of "psh."You
can sometimes bring in birds for closer observation by imitating this
sound with a technique that birders call "pishing." Repeat a syllable
like "psh" or "spsh" in a drawn-out, hissing exhalation. Whilee pishing,
try to be very inconspicuous by standing against the trunk of a large
tree to break up your silhouette, or crouching down to hide the typical
human upright shape. Although pishing is most effective during the
breeding season when birds are protecting their nesting territories and
fledglings, it may work at any time (but not on windy days, because the
birds can't hear it). "Squeaking" is a similar attracting noise produced
by kissing your clenched fist to make a prolonged squeaking sound.
Not all birds are equally attracted by pishing and squeaking.
Skulkers, such as sparrows and Common Yellowthroats, fall for it fre- may be mobbed if they are discovered near active nests. Common Figure 2-20. Attracting Birds Using
mobbers include chickadees, titmice, jays, blackbirds, grackles, and Pishing and Squeaking: Sometimes you
quently; treetop birds respond less often. Success generally depends
can bring in birds for close observation
on a bird's breeding condition and level of excitement when you first crows, and sometimes these birds, which may have overlapping ter-
by imitating their alarm calls, with a
attemptto attract it. When you do succeed in attracting a bird, it usually ritories during the nesting season, will combine their efforts to mob a technique that birders call "pishing":
darts into view, takes one quick look, then disappears again. Chick- common threat (seethe more detailed discussion of mobbing in Ch. 6, repeating a syllable like "psh" or "spsh"
Antipredator Behavior: Why do Some Birds Mob Predators?). in a drawn-out, hissing exhalation. The
adees and some other birds may give their own alarm calls if they get
technique works best for skulking spe-
excited by your pishing and squeaking efforts; these calls will help to Owls spark the most intense mobbing behaviors (Fig. 2 21). -

cies, and is most effective during the

attract additional birds (Fig. 2 20).
-
Screech-Owls and Great Horned Owls often prey upon sleeping birds, breeding season. A squeaking sound,
so small birds that chase owls out of their territories during the day may produced by kissing your clenched fist
be safer at night. You can use this fact to lure birds in for close view: or the back of your hand, has a similar
Mobbing simply play a recorded screech-owl call and watch the reaction. The attractive effect on certain birds. Avid
birders quickly overcome their self-
Small birds often mob potential predators, swooping and dash- owl's trembling whistle usually attracts small birds, which flock to the
consciousness about producing these
ing at the intruders to chase them out of their territories. Owls, hawks, sound, ready to mob. Even a whistled imitation of a screech-owl call sounds in public!
snakes, and even mammalian predators—foxes, cats, or squirrels— may rally a local songbird congregation.

Cornell Laboratorq of Ornitholopi Handbook of Bird Biologq

 Stephen W. Kress Chapter 2—A Guide to Bird Watching 2.29
2.28
You can trigger an even stronger mobbing Bird Blinds
reaction by playing a screech-owl recording in Bird blinds are generally used for
the presence of an owl model. Make an owl close observation and photography of
from papier-mâché strips over a balloon (be nests, but they also are great to set up
sure to give it big yellow eyes), or buy one at near watering places and special feeding
a hardware store (they are often sold to scare spots such as the edges of marshes and
birds from gardens, though they are usually wetlands (Fig. 2-22).
ineffective at this). Mount the model in a con- Most birds apparently recognize
spicuous place, turn on the tape recorder, and the human shape by our distinctive two-
hide nearby to watch the reaction. Note the leggedness, so anything that hides the
calls given by the mobbing birds and how long human form, especially the legs, can
the reaction lasts. Don't overdo this activity— function as a blind. Even a burlap bag
remove the owl after about 15 minutes and let or loose poncho draped over your back
the birds sense a victory over the owl invader. will hide your waist and legs, but find a
Otherwise, you may cause birds to squander comfortable tree for a back prop. Such
important energy reserves. simple blinds, however, are usually un-
satisfactory for long waiting periods;
Playback Songs your "blind" moves when you do, so you must keep completely still, Figure 2-22. A Homemade Bird Blind:
which gets downright painful before too long. To disguise your human shape, sit in a
One function of bird song is to alert males
blind to observe birds near a watering
of the same species that a breeding territory You can construct a simple blind that allows some freedom of
area or feeding spot, such as the edge of
is occupied. A newcomer who begins to sing movement by attaching a skirt to a large umbrella bound to the top a wetland; birds will usually forget their
within an established territory will soon be of a sharpened stake. Or use a lightweight card table as the roof and wariness and approach, allowing close

confronted by the resident male (some females, frame for your blind—just toss a prestitched cover over the top and observation. Photograph by Marie Read.

such as cardinals and orioles, also sing to repel you're ready to hide. A number of commercial blinds are also avail-
other females). Persistent singing by the "chal- able through catalogs and advertisements in nature photography and
lenger" male is usually met with a chase from bird-watching magazines.
the territory's first "owner" (see Ch. 7 for more When setting up a blind near a nest, always keep the best interests
Figure 2-21. American Crows Mob-
on this topic). of the birds in mind. If you choose a commercial blind, look for one
bing a Great Horned Owl: Birds often that you can erect quickly, because prolonged commotion near a nest
mob potential predators, especially You can use this chase response to lure seldom-seen birds into
view. Play a tape recording of a species' song within its territory and can cause birds to abandon it. Stay in the blind for long stints (several
if their nests or young are threatened.
Owls trigger the most intense mobbing the territorial male will quickly appear. Even hard-to-see birds that hours), and never disturb the vegetation near a nest. Overhanging
activity. Birders can take advantage of
live in treetops or dense tangles may come into view to challenge a leaves and branches, which hide the nest from predators and offer
this behavior; try playing a recorded shade to keep the young from overheating, are especially important.
screech-owl call to lure birds in for a newcomer.
close view, but don't overdo this ac- Commercial recordings serve nicely for playback, especially
tivity, because it may cause birds to use those on CDs, which permit you to quickly retrieve the species you
up energy reserves they could put to want by simply punching in the location code. You can also obtain
Viewing Birds
better use. Drawing by Anne Senechal
calls for playback by making your own recordings of the territorial male
Faust, from The National Audubon So-
you are trying to observe. Birds do not recognize their own voices, so Using Binoculars
ciety Handbook for Birders, by Stephen
W. Kress, 1981. a singing male will come to defend his territory against any rival, even Binoculars are a virtual necessity for locating birds. If you don't
his own recorded voice! yet own a pair, you'll find information on selecting and caring for bin-
Although an occasional confrontation with a tape recorder prob- oculars in the next section. For information on adjusting a pair of bin-
ably has little effect on a breeding bird, you should take care to avoid oculars to work best with your eyes, see Sidebar 2: How to Calibrate
excess use. Once the bird you are seeking has appeared, turn off the Binoculars ForYour Eyes. Meanwhile, just a note on using them in the
recorder and let the male sing his song without competition. Never field: Don't get discouraged. Birds are moving targets, and both skill
use tape recordings to attract rare or endangered birds or any bird and practice are needed to find a bird in a binocular's narrow field.
nesting outside its normal range. Such disturbance to a bird already The most important tip is: first spot the bird with your unaided
in precarious circumstances may threaten its breeding success. These eyes and then, holding your head still and keeping your eyes on the
same precautions apply to using pishing and squeaking, as well as owl bird, lift the binoculars to your eyes and look through them. Avoid
calls and models, to attract birds. (Continued on p. 2.32)

Cornell Laboratort of Ornithologq Handbook of Bird Biologq

2.30 Stephen W. Kress Chapter 2 — A Guide to Bird Watching 2.31

Step 3
Sidebar 2: HOW TO CALIBRATE BINOCULARS FOR YOUR EYES Facing the sign, lift the binoculars into position and
Stephen W. Kress cover the end of the right binocular barrel. With both eyes
open, turn the center focusing wheel until the lettering
Most binoculars have a center focusing wheel that adjusts the focus of both eyepieces simultaneously and a separate comes into sharp focus. To be sure you have the sharpest
diopter adjustment that allows you to focus one eyepiece independently, to make up for the differences in vision possible focus, pass the sharpest point and then back up
between your left and right eye. To determine the correct diopter adjustment on your binoculars, stand about 30 feet to find it again.
away from a sign with clear lettering—make sure that it is in the middle of the focal range of your binoculars—and
follow these steps:

Step 1 Hinge Post

Notice that the two binocular barrels pivot on a hinge
post, al lowing the eyepieces to fit your eyes comfortably.
Facing the sign, spread the barrels as wide as you can.
Then, put the binoculars to your eyes and press the bar-
rels together until the two images converge into one. (If
you cannot push the eyepieces close enough together
to see through comfortably, reject those binoculars; the Step 3: Focus left eyepiece with central focusing wheel
"interpupi I lary distance" of that model may be too wide
to accommodate the narrowness of the space between
your eyes.) The number (angle) indicated on the hinge Step 1: Form one image
post will always be the same for your eyes, on any pair
of binoculars. Step 4
Now cover the left barrel (keep both eyes open) and
turn the diopter adjustment ring clockwise to bring the
lettering into focus. Be sure to leave the center focus in ex-
Step 2 actly the same position as before. Pass the point of sharp
Turn the center focusing wheel counterclockwise as focus and then back up to where the lettering is sharpest.
far as it will go. On most binoculars, one of the eyepieces Uncover the left barrel and the binoculars should be in
(usually the right one) is marked with calibrations and can perfect focus and calibrated for your eyes.
move independently. This is called the diopter adjust-
ment ring. Turn this ring in a counterclockwise direction
until it stops. Now both eyepieces should be out of focus.
(Please note: some binoculars have a separate knob in Eyepieces Step 4: Focus right eyepiece by turning the diopter adjust-
the center or another mechanism for diopter adjustments; ment ring
if so, consult the manufacturer's instructions.)

Diopter
Adjustment
Ring

Step 5
Note the diopter setting because it is now adjusted to
Step 2b: Turn diopter your eyes. That setting should remain constant, unless
adjustment ring your vision changes. Some people put a piece of tape
counterclockwise
over the diopter adjustment to prevent it from shifting
until it stops
accidentally. Once this adjustment is set, you need only
adjust the center wheel to focus both eyepieces.

Step 2a: Turn center focusing wheel

counterclockwise until it stops Step 5: Note your diopter adjustment ring setting

Cornell Laboratorq of Ornithologq Handbook of Bird Biologg

2.32 Stephen W. Kress Chapter 2—A Guide to Bird Watching 2.33

Figure 2-23. Pointing Out the Loca- scanning wildly through the trees. Practice locating stationary objects • Refer to the most obvious land- a
tion of a Bird to Other Observers: Use first—birdhouses, feeders, flowers, tree branches. Start with large ob- mark near the bird, then narrow
precise descriptions rather than vague jects, then try to find progressively smaller ones. the field until you come to the bird.
directions. Start with close landmarks
For example, if you spot a hawk in
that all the observers can see, then nar-
a farm field, you might describe its
row the field until you come to the bird.
For example, to describe the location
Pointing Out Birds to Others location this way: "See that large
of the screech-owl pictured here, you
If you are with a group of birders and someone cannot find a bird red barn with the white silo? Look
might say: "See the birch tree that has that you see, describe the location precisely. Vague directions, such as over the top of the silo to the fence
been chewed by a beaver? Beyond it "It's in that tree," "It's over there," and "Look where I'm pointing," are on the hillside behind it. Count
and to the right there's a broken snag no help and only increase the chance that the bird will fly away before
with fungi on it. To the right of that is a eight fence posts to the right and
others see it. Here are a few tips for describing a bird's location: there's the hawk sitting on top of
large maple with a double trunk. Follow
the rightmost trunk up to the second the post. Do you see it?"
branch on the right. The screech-owl
is about halfway out from the trunk on In wooded areas, try referring to
that branch." an unusual-looking tree trunk or
other natural landmark in the fore-
6 _, :411." rc L. ,
ground to make sure everyone is
/ • ",

. C.
looking at the same place. Using
s.
the reference point, successively
indicate trees closer to the bird
until you lead others to your dis-
covery (Fig. 2 23). For maximum
-

b 12
success, check often to make cer-
tain your directions are clear. At
moments of excitement, calmly
sharing a bird discovery takes as
much skill as locating the bird in
the first place.
• For a bird in a tree, use the "clock"
technique to describe its position
(Fig. 2 24). Mentally superimpose
-

an hour hand onto the tree and use

it to point to the bird. This system
works especially well for birds
near the edge of the tree. A bird
in the top of the tree is at twelve
ff. o'clock; a bird halfway down the
right side is at three o'clock. If a
bird is not at the edge, then the
hour designation is only the first
step in describing its position. You
must give additional pointers, such
as "Find two o'clock in the largest
Figure 2-24. The Clock Method for Describing the Location of a Bird: a: For
sycamore, then move in halfway a bird in a tree, mentally superimpose a clock face onto the tree, with twelve
to the center of the tree. The bird is o'clock at the top and six o'clock at the bottom. Then use an imaginary hour
t./4 •- b•-•
in front of the largest branch near hand to point to the bird; in this case the bird is at one o'clock. This system
J05% <=. - • works well for a bird at the edge of the tree. If the bird is not at the edge, the
a large woodpecker hole. See it?"
-
hour designation must be supplemented with additional directions. b: To use
„0—
•••••■ Avoid using distance measure- the clock system when birding from a boat, the imaginary clock face is oriented
ments, such as "20 feet from the with twelve o'clock at the bow, and six o'clock at the stern. In this case the Ross's
top of the tree." Most people find Gull is at seven o'clock.

Cornell Laboratoru of Ornithologq Handbook of Bird Biologq

 Stephen W. Kress Chapter 2 — A Guide to Bird Watching 2.35
2.34
it difficult to agree on exact distances. The best check on your suc-
cess in giving directions is to ask if people see the bird.
• The clock system also works for spotting birds from a moving vehicle,
such as a bus or a boat. For nautical birding, the clock is oriented with
Eyepiece
the twelve at the bow and the six at the stern (see Fig. 2 24). Calling
-

out "Ross's Gull at seven o'clock" would send people rushing back
to search for the bird just to the left of the stern. The clock also can Diopter
Adjustment
be superimposed on land in a horizontal position: twelve o'clock is
+. o • • — •-• Ring
usually north or toward some predetermined landmark. Th is system
is sometimes used to point out migratory hawks at hawk-watching
locations. 11111 11 1 11 1 111111 i

Prisms )
Selecting Binoculars
■ Binoculars are probably the most important tool for watching birds,
but choosing the best type, brand, and model for your needs can be
bewildering. Magnification power, field of view, brightness, lens coat-
ing, size, weight—all are important. So is price: binoculars range in
cost from less than $100 to well over $1,000. You must decide which
features are most important to you and how much you're willing to Hinge
Post
spend. Here are some tips to help you make your selection. Remember,
a wise choice will give you much pleasure and will last for years.
Objective
Lens LIGHT
Magnification Power
Examine the flat upper surface of a binocular housing and you'll
Figure 2-25. Porro Prism Binoculars:
find two numbers—for example, 7x35 (pronounced "seven by thirty- Light-gathering Capacitj Light enters the binoculars through the
five") or 1 0x40. The first number always designates the power of the To a birder, the light-gathering capacity of binoculars is nearly as objective lens, and passes through a se-
binoculars; 7x (pronounced "seven ex") means the binoculars make important as image sharpness. Only a bright image reveals the subtle ries of prisms before leaving through the
subjects appear seven times closer than they would without magnific- exit pupil in the eyepiece and entering
nuances of field marks and the full beauty of bird colors.
the observer's eye. The binocular barrels
ation. (The second number is the diameter of the binoculars' objective Light enters binoculars through the objective lenses (Fig. 2-25). pivot around the hinge post. Binocular
lenses—those farthest from the eye—i n millimeters; see next section.) As mentioned above, the diameter of these lenses in millimeters is the optics can be adjusted to your eyes by
Some birders prefer binoculars as powerful as 10x for viewing birds second number in the binoculars' designation—so 7x35 binoculars means of the diopter adjustment ring
such as hawks, waterfowl, and shorebirds, which are likely to be seen have 35 mm objective lenses. The bigger the objective lens, the more (see Sidebar 2: How to Calibrate Bin-
in relatively open areas. However, the majority of bird watchers prefer oculars for Your Eyes).
light that can be gathered and the brighter the image. Therefore, 7x50
7x or 8x binoculars, for a couple of reasons. First, the more powerful binoculars have the same magnification power as a pair of 7x35, but
your binoculars, the more difficult they are to hold steady for com- the 7x50, with their 50 mm objective lenses, have a significantly
fortable viewing—the effects of "hand shake" are greatly increased in greater light-gathering ability. Just as an owl's large eyes gather suffi-
binoculars with a magnification power greater than 8x. Also, lower- cient light to permit nocturnal vision, binoculars with large objective
power binoculars tend to have greater light-gathering ability and a lenses provide an advantage for bird watching in low light, such as at
wider field of view than more powerful models and generally can be dawn or dusk, or in dark, forested habitats.
focused on closer objects. The best measure of a binocular's brightness is the size of the exit
Although some "zoom" binoculars offer the ability to quickly pupil, the hole that the observer is looking through. You can see the
increase magnification power from 7x to 15x, the convenience is a exit pupil by holding your binoculars at arm's length and looking into
poor trade-off for the bulk and weight: at the higher magnifications the the eyepieces (Fig. 2-26). Depending on the binoculars, the exit pupil
binoculars a're so difficult to hold steady and the image is so dark that may vary in appearance from a dark hole to a brilliant, clear circle. To
it's almost impossible to see important field marks. determine the exit pupil size, divide the size of the objective lens by
the magnification number. Thus, 7x35 binoculars have an exit pupil of
5 mm, whereas 7x50 binoculars have an exit pupil of 7.1 mm, which

Cornell Laboratoru of 0 rnithologq Handbook of Bird Biologq

2.36 Stephen W. Kress Chapter 2—A Guide to Bird Watching 2.37

7 X 35 provides a much brighter image. tive film that helps deliver more than 90 percent of the light gathered
Birders using binoculars on boats will by the objective lenses. Without this nonreflective coating, binoculars
find that an exit pupil of at least 5 mm offers a may lose up to 60 percent of the light that enters the objective lenses.
distinct advantage. When motion causes your Coated optics also are a great aid when you're looking at backlit sub-
binoculars to move in all directions around your jects. Light reflects within uncoated binoculars, causing annoying
eyes, you may experience image blackouts as glare. (But even with coated optics, never look directly at the sun; it
the exit pupil moves away from your eye's pupil. could cause permanent eye damage.) Make sure the binoculars you
5 mm Exit Pupil In bright daylight, when your eye has a pupil purchase have "fully coated" optics. Although most manufacturers
opening of about2 mm, binoculars with a 5 mm coat the exterior lenses, some inexpensive binoculars may have un-
7 X 50
exit pupil provide 3 mm of leeway to adjust to coated internal optics, which will cause a significant loss of light.
the movement.
Although binoculars with larger exit pupils
are better for boating and generally offer bright-
Field of View
er images, they do have drawbacks—principally The term field of view refers to the width of the
the additional size and weight of the objective area you see while looking through your binoculars.
lenses and the larger housing necessary to It is usually described as the width of the area visible
support them. Fortunately, the best binoculars at 1,000 yards from the observer—for example, some
made today offer remarkable brightness with binoculars show an area 400 feet wide at 1,000 yards. If
7.1 mm Exit Pupil moderate weight by using high-quality optical all else is equal, binoculars with a higher magnification
glass and incorporating design improvements. power will have a smaller field of view than those with
Check the following table to determine which exit pupil size a lower magnification power. Sometimes the manu-
Figure 2-26. Exit Pupil Comparison: A
binocular's brightness can be judged by facturer of a particular binocular model expresses the
meets your needs:
the size of its exit pupil: the larger the field of view in degrees. If you wish, you can convert
exit pupil, the brighter the image. Hold degrees to feet simply by multiplying the number of
the binoculars at arm's length and look
Exit Pupil Size Appropriate Situations
degrees by 52.5, the number of feet in 1 degree at 1,000
into the eyepieces to see the exit pupil. Bright-light situations (such as open farmland,
2-4 mm yards. Thus, a 6-degree field of view would show an 1,000 Yards
To calculate the size of the exit pupil,
mountains, shorelines) area 315 feet wide at 1,000 yards (6 degrees x 52.5
divide the size of the objective lens by
the magnification number. For example, 4-5 mm Shaded situations (such as forests) feet/degree = 315 feet) (Fig. 2-28).
7X 35 binoculars have a 5 mm exit pupi I, The wider the field of view, the easier it is to locate
Over 5 mm Dusk and dawn, boating
whereas 7 X 50 binoculars have an exit
birds with your binoculars. Wide-angle binoculars are
pupil of 7.1 mm, providing a brighter im-
age. Drawing by Anne Senechal Faust, especially useful for beginning bird watchers, because
Binoculars with large objective lenses can have poor light-gath-
from The National Audubon Society the larger field of view they provide makes it easier to
ering abilities if the optics are poor. As one test, carefully examine the
Handbook for Birders, by Stephen W. find birds—especially if they are flying or skulking in
Kress, 1981.
edge of the exit pupil to see if it forms a complete, bright circle or if it
dense vegetation. Manufacturers of extra-wide-angle
is shaded in gray, resulting in a bright central area (Fig. 2-27). If only
binoculars expand the field of view by increasing the
the center of the exit pupil is bright, then inferior optics are blocking
size and number of lenses in the binoculars' ocular
some of the light, and the advantages of the large objective lenses are
system. The additional optics increase the cost of the
not being realized.
binoculars and make them heavy and bulky. Because
Figure 2-27. Exit Pupil and Optical
Light entering the objective lens must pass through as many as
producing binoculars that have sharp images across
Quality: Binoculars with poor qual- eight pieces of optical glass in each barrel. At each glass surface some
their entire field of view is difficult and expensive, be-
ity optical components can have poor light is reflected backward rather than passing through the prisms and
light-gathering abilities despite large ware of low-cost, extra-wide-angle binoculars. They
lenses.The optics of well-made binoculars are coated with a nonreflec-
objective lenses. Holding the binocu- are probably only sharp in the center of the field. Most Figure 2-28. Field of View: The field of view is the width
lars at arm's length, examine the edge experienced bird watchers find that a standard field of of the area you see while looking through your binoculars.
of the exit pupil: it should form a com-
view is adequate for most situations and that investing It usually is expressed as the width of the area visible at
plete, bright circle, as in (a). If only the
in extra-wide-angle binoculars is unnecessary. 1,000 yards (which, in this example, is 400 feet). Some-
center of the exit pupil is bright, as in
times a manufacturer gives the field of view in degrees (in
(b), inferior optics are blocking some of this example it is 7.62 degrees). Convert degrees to feet by
the light, counteracting the advantages
multiplying the number of degrees by 52.5 (the number
of large objective lenses. Drawing by Resolution
of feet in 1 degree at 1,000 yards). Binoculars with higher
Anne Senechal Faust, from The National Resolution is a function of the quality of the op- magnification usually have a narrower field of view than
Audubon Society Handbook for Birders,
tical glass used in the manufacture of binoculars. High- those with lower magnification.
by Stephen W. Kress, 1981. a. High Quality Optics b. Low Quality Optics

Cornell Laboratorq of Ornithologj Handbook of Bird Biologq

2.38 Stephen W. Kress Chapter 2—A Guide to Bird Watching 2.39
quality optical glass is extremely expensive, and each lens and prism in line—a feature achieved by placing the two prisms in each barrel
must be professionally ground and mounted with expert precision. close together. Roof prism binoculars offer several advantages over
Top-of-the-line binoculars are finely crafted instruments. Manufac- Porro prism binoculars. Most roof prism models are compact and light-
turers of lesser products cut corners throughout production, often by weight, and they provide excellent image resolution without sacrificing
using less expensive glass and looser quality control. brightness or field of view. Many of them focus internally by moving
High-priced binoculars usually have excel lent optics, producing lens elements back and forth inside the casing to achieve focus, rather
tack-sharp, crisp images from the center to the edge of the field of view. than moving the eyepiece assembly back and forth externally as do
You can check the center-to-edge resolution of a pair of binoculars by most Porro prism binoculars. Internal-focus binoculars can be sealed
focusing them on a map or newspaper tacked to a wall. Stand back more effectively and tend to be more resistant to moisture and dirt. On
about 25 feet and see if you can read the print at both the center and the other hand, roof prism binoculars are usually much more expensive
edge of the field of view. than Porro prism binoculars, their depth perception is not as good, and
they don't focus as well on nearby objects unless they've been specially
A lignrnent designed or retrofitted to improve their close-focusing ability.
Because binoculars consist of two separate optical instruments—
basically, an individual telescope for each eye—it is vitally important Mini Binoculars
that they stay in proper alignment. When binoculars are functioning Palm-sized binoculars are becoming increasingly popular among
properly, both sides focus on the same field of view, but a sharp jolt birders. More than 40 models are currently available, ranging in price
can easily throw them out of alignment so that the two fields no longer from about $50 to more than $600. They generally use a reverse Porro
overlap. Looking through misaligned binoculars, your eyes attempt to prism or roof prism design, and some models deliver quite sharp im-
bring the two views together. If the binoculars are severely misaligned, ages. They appeal to many people because they are small and light-
you will see a double image and the subject will look blurry (when both weight, but birders with large hands and long fingers may find them
your eyes are open). In some ways, binoculars that are only slightly out uncomfortable to hold.
a. Binoculars In Alignment
of alignment may be more of a problem, because your eyes strain to Beware of lower-priced mini binoculars, which often have poor
bring the two images together; this quickly results in eye fatigue and light-gathering capacity. Mini binoculars in the upper price range, how-
a headache. ever, are usually finely crafted instruments with excellent optics. Tested
Inexpensive binoculars are more likely to go out of alignment to withstand the rigors of temperature extremes and sudden jolts, they
than higher-priced models. Prisms and lenses in cut-rate models may are a good option for bird watchers who are already encumbered by
be glued in place rather than securely strapped by metal brackets.Tem- bulky camera gear, tape-recording equipment, and field guides.
perature changes or sl ight jars can easily throw inexpensive binoculars
out of alignment. And realigning binoculars is not a simple task. They
b. Binoculars Out of Alignment
must betaken apart by an experienced technician and recalibrated us-
a. Roof Prism Binoculars b. Porro Prism Binoculars
ing special equipment. It makes far more sense to invest in good binoc-
ulars in the first place than to repeatedly replace or repair inexpensive
binoculars each time they get bumped in the field. (And birding can
be very tough on optical equipment.)Top-quality binoculars are more
likely to withstand the stress of constant field use and, if you treat them
with reasonable care, should last a I ifetime. To check the alignment of
your binoculars, try the simple test shown in Figure 2 29.
-

Figure 2-29. Binocular Alignment: To

check the alignment of your binoculars,
try this simple test. Look at the roof of a
house through them, then, continuing
Binocular Designs
to look through the eyepieces, move You'll find three basic designs in modern binoculars—Porro
the binoculars about eight inches away prism, reverse Porro prism, and roof prism (Fig. 2-30). You can easily
from your eyes. If the binoculars are in recognize standard Porro prism binoculars, the most common, be-
alignment, the horizontal line of the roof
cause their eyepieces are closer together than their objective lenses.
should be at the same level in both fields
(a). If the roofline appears offset (b) the Reverse Porro prism binoculars have an inverted design, with the
Figure 2-30. Binocular Design: a: Roof
binoculars are out of alignment. Draw- objective lenses placed closer together than the eyepieces. (Several
prism binoculars have straight barrels.
ing by Anne Senechal Faust, from The compact binocular models employ this design.) Roof prism binoculars b: Standard Porro prism binoculars have
National Audubon Society Handbook
have straight barrels, with the eyepieces and objective lenses directly thei r eyepieces closer together tha n their
for Birders, by Stephen W. Kress, 1981.
objective lenses.

Cornell Laboratory of Ornithology Handbook of Bird Biology

2.40 Stephen W, Kress Chapter 2 — A Guide to Bird Watching 2.41

first pair to backup status, or better yet, donate them to someone else
Binoculars for Etjeglass Wearers
who will appreciate them. Many bird observatories, clubs, nature cen-
People who wear eyeglasses should always leave their glasses in
ters, and schools are happy to receive donated binoculars.
place when using binoculars. (You'll never be able to find and focus
quickly on a bird if you always have to remove your eyeglasses before
looking through your binoculars.) Of course, eyeglasses do get in the
way: they prevent your eyes from getting as close to the eyepieces as
How to Clean Binoculars
they should to obtain the full field of view. Most binocular manufac- ■ Binoculars should be cleaned frequently, following these sugges-
turers now have rubber eyecups that you can either roll or pop down to tions:
minimize this problem, but some work better than others (Fig. 2 31). -
• Thoroughly wipe off metal parts and lightly brush all lenses with a
If you wear eyeglasses, look through several models and see which wad of lens-cleaning tissue or a soft camel's-hair brush to dislodge
work best for you. particles of sand and grit. Removing this debris keeps you from
scratching the lens and its coating during the cleaning process. Hold
How to Shop for Binoculars binoculars upside down so that dirt will fall away from the lens sur-
Once you've narrowed down your choice of magnification pow- face.
er, objective lens size, and field of view, try the following tests on the • Fold a piece of lens-cleaning tissue so that it is at least four layers
array of suitable binoculars behind the store counter. Save your final thick. This prevents oil from your fingers from soaking through the
decision regarding price until you've examined what's available. lens tissue and onto the lens surface. Use a circular movement to
• Compare binoculars of the same magnification power by holding one gently wipe all lens surfaces.
above the other. Alternately look through each binocular, comparing • If there is a film of oil on the lens, put a drop of lens cleaner on the
them for brightness and clarity. Then compare the best binoculars tissue and repeat the circular wiping movement.
from your first selection with a third group—each time choosing
Figure 2-31. Binoculars for Eyeglass • Look for dirt on all the internal optics by holding the binoculars up
the binoculars with the best characteristics. Continue this process
Wearers: To locate a bird and focus bin- to the light and looking into the objective lenses. Never attempt to
oculars quickly on it, birders who wear of elimination until you have thoroughly examined everything that's
open the binoculars; you can easily disrupt their alignment.
eyeglasses should always keep their available.
eyeglasses in place. Eyeglasses may Although it's expensive, leave internal cleaning to the professionals.
prohibit the full field of view, though,
• Holding the binoculars at arm's length, check the exit pupils to see if
by preventing the eyes from being close they are blocked at the edges by gray shadows. Nearly all binoculars
to the eyepieces. Many binoculars have under $100 have a gray border obstructing the exit pupil.
rubber eyecups that can be rolled or Protectin8 Binoculars
folded down to minimize this problem. • Look into the objective lenses to make sure that all optical surfaces
are coated with an even purple-violet or amber hue. Carefully ex- • Never stroll through the woods swinging binoculars by the strap;
amine the objective and ocular lenses for scratches. banging them on a tree could throw them completely out of align-
ment. Always keep your binoculars around your neck in the field.
• Be sure that all the mechanical parts move smoothly and that the
bridge supporting the barrels does not wobble. • When you have to jump across a ditch, climb a rocky slope, get into
a boat, or do any other active maneuver, always tuck your binoculars
• Outside the store, check alignment by looking at a rooftop or hori-
inside your jacket or secure them under your arm.
zontal power line. Carefully examine the print on a billboard or sign
to see if you can read the lettering at the edge of the field as well as • Never leave your binoculars on your car seat—a quick stop will send
at the center. them flying—a sure way to knock them out of alignment. And never
leave your binoculars out in the open in your car, especially on a hot
• Look at the edge of a backlit sign or building to see if it is fringed
summer day. If thieves don't find them, the sun may soften the lens
with a band of bright color. This fringing indicates an inferior optical
coatings, causing them to crack and separate from the lenses.
system that cannot focus light of different wavelengths to the same
point. • Keep binoculars under cover as much as possible if it starts rain-
After narrowing the field to a few choices, select the highest- ing. Water can leak into the housing, causing internal fogging and
priced binoculars you can afford. Price is often a good measure of carrying in dirt, which can stain the internal optics. Rain guards
craftsmanship and materials. To produce lower-priced binoculars, offer some protection during light rain and drizzle, but they are not
manufacturers have to make compromises with the quality of their adequate protection for heavy rain. If your binoculars do fog up on
products. But even inexpensive binoculars can be good enough to the inside, set them in a warm, dry place, and they will probably
launch your enjoyment of bird watching. You can always retire your dry out in a couple of days. Otherwise, fungus may start growing on

Cornell Laboratorq of Ornithologj Handbook of Bird Biologg

2.42 Stephen W. Kress Chapter 2— A Guide to Bird Watching 2.43

The problems of less light and more vibration that accompany

greater magnification power in binoculars also apply to spotting
1 1014-6. 41Z.- \ -• scopes. High powers magnify the air as well as the subject, often pro-
1111 414ii ui
' 11 11 '
ducing hazy images or distracting shimmering from heat vibrations
- _ over water and other flat expanses.
With good observation conditions and a steady tripod, the extra
magnification power of a good scope will help you to spot birds and
distinguish field marks that may be impossible to see with binoculars.
ll I / When you're scanning an area with a spotting scope, however, it's best
\• \ ~

to start with a low-power eyepiece (or the lowest setting on a zoom

eyepiece), and then switch to a higher power once you've located the
birds you want to examine closely.
Zoom lenses offer the convenience of being able to change mag-
nification power from 20x to 45x or even 60x with a single, simple
adjustment. But viewing conditions are seldom good enough to go
beyond 45x—the image generally becomes too dark to see much detail
as you move toward 60x. The best all-purpose magnification power
Figure 2-32. Binoculars Face Many the lens coating. Alternatively, leave them overnight in a sealed bag is 25x. The top spotting scopes are made with "ED" (Extra-low Dis-
Hazards: Intrepid birders expose their with some desiccant (purchased at a camera store) that will absorb persion) glass or have fluorite-coated lenses. The difference in bright-
binoculars to many perils. Binoculars ness and image clarity between these special scopes and identical
the excess moisture. It is prudentto bring desiccant on birding vaca-
must be rugged enough to withstand
tions to humid climates, where your binoculars may not dry out on non-ED or nonfluorite scopes made by the same manufacturers is very
precipitation, salt spray, impact dam-
age from scrambling over rocky shores their own. noticeable, particularly in difficult, low-light viewing conditions.
and in and out of boats, abrasion from For overall stability when you're using a spotting scope, a tripod
dust and sand, and exposure to extreme
• If your binoculars fall into fresh water, have them professionally
can't be beat. If you don't like the weight or bulk of a tripod, however,
temperatures. cleaned as soon as possible to avoid rusting. If you drop them in salt
you can mount a scope on a modified rifle stock, but don't use a more
water, rinse them thoroughly in fresh water, seal them in a plastic bag,
powerful eyepiece than 15x or 20x—you won't be able to hold it steady
and rush them to a professional service department immediately.
enough. Commercially built stocks for spotting scopes and telephoto
Salt water is amazingly corrosive and can turn fine binoculars into
lenses are available.
junk in just a few days.
A rifle-stock-mounted scope is difficult to share with a group
of bird watchers. If you want to give everyone in your group a good
In bird watching, binoculars face many hazards that they would
look at a bird, you should use a tripod. But buying a good tripod for
never be subjected to at opera houses and football stadiums.They must
birding can sometimes be more difficult than buying a scope. Tripods
be able to withstand precipitation and highly corrosive salt spray, and
come in numerous heights and weights and with a wide assortment
must be rugged enough to accompany birders as they scramble up
of heads. Some tripods are clumsy to use—they may have as many as
rocky slopes, climb in and out of boats, lie down on sandy beaches,
nine different locks and clamps to control the extension of their legs.
and hike through both wet and arid bird habitats (Fig. 2 32). External-
-

Not infrequently, you get the last leg secured just as the bird leaves.
focus binoculars are particularly vulnerable to water and dirt, which
Some tripods are too heavy to carry around in the field, so they end up
may enter through the focusing apparatus. Dirty binoculars provide
getting left at home. Other tripods are just too flimsy.
neither sharp detail nor crisp colors.
For birding, look for a moderate-weight tripod with a minimum
of clamps and twisting parts. The most efficient for birding have "flip

Selecting a Spotting Scope and Tripod locks" to adjust leg length. They're easy to operate because once the
locks are released, the legs fall to their own level and you can fasten
■ Spotting scopes are medium-range telescopes, usually with a them in place with the locks conveniently located at the top of each
magnification power between 15x and 60x. Most of them use in- leg.
terchangeable fixed-focal-length eyepieces or a zoom eyepiece to "Window mounts" are also available that allow you to tempo-
change magnification power or field of view. Telescopes designed for rarily attach your spotting scope to a partially open car window. These
stargazing tend to be much more powerful, butthey usually don't have are particularly useful on long birding trips at locations where you must
sufficient light-gathering ability for effective bird watching. Spotting stay in your car, as at some National Wildlife Refuges, or in situations
scopes provide the magnification necessary to see distant birds and to •
in which getting out of your car would scare or disturb the birds you
admire the detail at closer ranges. are viewing. A car can be an excellent bird blind.

Cornell Laboratory of Ornithology Handbook of Bird Biology

2.44 Stephen W. Kress Chapter 2 —A Guide to Bird Watching 2.45

Although birders use scopes most often for long-distance viewing

of birds that live in expansive, open habitats, spotting scopes also can
provide intimate views of small land birds perched at close range. Such
scope-aided views frequently reveal the intricate beauty of a bird's plum-
age and allow you to observe behavior that might otherwise go unseen.
Even tiny, secretive warblers sometimes sit still long enough to view
with a spotting scope, especially when they're singing on their territories
rather than flitting through the forest canopy in search of insects.

How to Shop for a Spotting Scope

• The best all-around eyepiece for a birding spotting scope is 25x.
Because of the effects of heat distortion and loss of light, eyepieces
larger than 45x usually are useless for birding.

• Ideally, the objective lens (the one farthest from your eye) should be
at least 60 mm in diameter to provide adequate light.

• Zoom lenses that vary in power from 20x to 45x are ideal for most
bird watching. They permit convenient scanning at low power and
then a quick shift to higher power for looking at details. But many
of the less expensive zoom eyepieces are optically poor. The only
good zoom eyepieces I've seen are the ones made by the top optical
companies for their high-quality scopes.

• Don't buy a cheap spotting scope. Inexpensive scopes deliver fuzzy, behind the Miccosukee Restaurant—an entry that immediately recalls Figure 2-33. Male Blue Grosbeak:
distorted images. The shortcuts the manufacturer took to deliver a the smell of coffee and refried beans." But even more important, your Always keep accurate field notes—you
low-cost product wi I I only give you disappointing field performance written records make the benefits of your time in the field available to can never predict when they might have
and splitting headaches. scientific value, such as documenting the
all who have reason to care about the abundance of birds. Rick Bon- occurrence of a species outside its nor-
• Select a rigid tripod with as few leg adjustments as possible. The ney (1991) also wrote this account of how documenting what you see mal range. Photograph by Tom Vezo.
flip-lock design provides a secure mount for your scope and a quick can have scientific value:
way to set the legs on uneven terrain. I remember the morning well. It was early spring 1981,
----- with lifting fog and smell of earth. The season's first bird
Binoculars are best for close-up birding, but for distant birds such songs had lured me out of bed, and I was tramping through
as waterfowl and hawks, spotting scopes can expand your vision at the state forest behind my home looking for early migrants.
least three times beyond that of binoculars. You'll be amazed what a Around 8:00 A.M. I had just started back toward the house
difference that makes. when I heard a strange song, one I knew I'd heard before but
couldn't place. Slowly I crept toward the bird until I could
see it si I houetted against the sky, perched atop a large shrub.
Recording Observations At first I thought it was an Indigo Bunting singing a weird
■ As I discussed at the beginning of this chapter, giving a name to a song, but after a harder look I realized that the bird was a
creature you've encountered in nature opens a door to exploring the Blue Grosbeak, a species I knew well from the South but had
many facets of its life. To keep the door open, to turn your ephemeral never before seen in Upstate New York (Fig. 2 33).-

memories of your daily experiences into a durable record of the natural

world as it existed in a certain place at a certain time, you must record As it turned out, very few people had seen it, perhaps
your observations. only one. For no good reason I didn't think to look up the
This can be a source of personal pleasure; the notes will help you bird's status right away, but several months later I was pe-
r€live your field experiences. In an article about keeping field notes, for rusing Birds of NewYork State byJohn Bull and read this: "As
instance, the Lab of Ornithology's Director of Education, Rick Bonney, far as I am aware, the only Upstate report of a Blue Grosbeak
wrote, "My field notes from a trip to the Everglades in 1986 tell me that with details is that of a male observed near Lake Champlain
on March 15, at 11:05 A.M., I saw a Snail Kite hunting over the marsh on June 17, 1964."

Cornell Laboratorq of Ornithologq Handbook of Bird Biolo8q

2.46 Stephen W. Kress Chapter 2—A Guide to Bird Watchino 2.47
s S FW

T
Wow! I thought. My Blue Grosbeak had been a really he Edwin B. Forsythe National Wildlife Refuge's LOONS — GREBES
good bird. I should have reported it. I should still report it. Brigantine and Barnegat Divisions contain more Red-throated Loon • o u
than 42,000 acres of southern New Jersey coastal /T_Q+Common Loon o r o 0
When had 1 seen it? Let's see, it was late April—or was it habitat. Refuge headquarters and public use facilities, includ- Pied-billed Grebe u o u o
early May? Already I couldn't remember. And not only had ing an eight-mile Wildlife Drive, observation towers and two Horned Grebe • u u
1 neglected to record the date, I hadn't recorded any infor- short nature trails, are at the Brigantine Division. Best
birdwatching opportunities occur during spring and fall SHEARWATERS — PELICANS — CORMORANTS
mation about the bird at all—so even if I could reconstruct
migrations. A "Guide to Seasonal Wildlife Activity" is avail- Sooty Shearwater r r
the timing, I had no documentation that would prove to able in the refuge's general brochure. Northern Gannet r r U
anyone other than myself that a Blue Grosbeak had decided This folder identifies 293 species that have been observed American White Pelican
Brown Pelican
to visit Wil lseyville, New York, in the spring of 1981. at the Brigantine and Barnegat Divisions. Names and order of Great Cormorant
listing are in accordance with the Sixth American Ornitholo- La Double-crested Cormorant u o c u
The moral is quite simple: take field notes. . . . Such ob- gists' Union Checklist.
BITTERNS — HERONS — IBISES
servations have scientific value. My sighting, for example, Most birds are migratory. Their seasonal occurrence is
would have been useful to ornithologist Janet Carroll coded as follows: • American Bittern u o u u
• Least Bittern U u u
when she compiled information on the spread of the Blue j2.• Great Blue Heron c c cu
SEASON
Grosbeak into New York for the state's breeding bird atlas, 2.5-• Great Egret c c c o
s Spring March — May 50.
) Snowy Egret c c c o
published in 1988—that is, it would have been useful had S Summer June — August • Little Blue Heron u u u o
it been properly documented and recorded. F Fall September — November • Tricolored Heron u u u o
W Winter December — February I • Cattle Egret u u u
• Green-backed Heron u u u
Although we all enjoy seeing rare birds, it's not just unusual • Birds known to nest on or near the refuge • Black-crowned Night-Heron u u u u
Italics indicate threatened/endangered species • Yellow-crowned Night-Heron o o o
sightings that warrant documentation. Even lists of birds common to White Ibis r
a certain place are valuable if they include numbers of birds seen and RELATIVE ABUNDANCE ip. • Glossy Ibis a a o o
• White-faced Ibis
are carefully made. Bird populations change constantly, and their ups a abundant a species which is very numerous
and downs often reflect changes in the environment. Only birders c common likely to be seen or heard in suitable habitat SWANS — GEESE — DUCKS
u uncommon present, but not certain to be seen
meticulously recording the numbers of birds seen at various localities o occasional seen only a few times during a season Tundra Swan o u o
can properly document these changes so that scientists can look for ✓ rare may be present but not every year • Mute Swan c c cu
x accidental seen only once or twice on refuge Greater White-fronted Goose o o
patterns and try to explain what the changing populations mean. Snow Goose a o a a
What should you actually write when describing your forays into Ross' Goose r r
NOTES 20+ Brant a o c c
the field?There's a broad range of options. Your choice will depend on 100+ Canada Goose c c c c
the nature of your field excursions, your goals in keeping notes, and Location Fotzvii-H aJ ea I(rAN171 NE- Div. • Wood Duck u o u r
a c
on how much time you can devote to your record keeping. Date PI A1 Iqq`a ,rNme":3 0-1: 00 e rn • Green-winged Teal
6 • American Black Duck
c
a
o
c a a
Observers BRUCE 1404Ci
a i'44/ S 4- • Mallard c U c o
• Northern Pintail c o a u
Checklists Weather Al A CP1P 55 9 N.G NT 2r4, N .
• Blue-winged Teal c u a o
WIND 10 -16 mpt, Li) I TN CrUSTS • Northern Shoveler c o c c
The kind of field record used most often is the checklist, a printed • Gadwall c c CU
list of the birds found in a particular area. Unfortunately, most lists con- To 2530 mph. Eurasian Wigeon r r

tribute little to our understanding of bird distributions and abundance

because observers check off the species they saw on a particular trip resolve to fill out our records "as soon as we get home," and days of Figure 2-34. Filling Out a Bird Checklist:
observations are likely to be lost. A checklist is a printed list of the birds
without indicating how many they saw or exactly where they saw
found in a particular area. Filled out cor-
them. And, in their search for new and unusual species, many birders Your complete daily checklists may be useful in preparing and
rectly and completely, checklists can be
ignore the most common birds. But it is precisely these birds, and not updating local and regional checklists, and their value increases over meaningful sources of data on bird distri-
the solitary wanderer far from his usual haunts, that can be sensitive time because they are an important source of baseline data for de- bution and changing abundance. Don't
indicators of environmental changes. Checklists are much more valu- tecting population changes. Information from a number of observers just checkoff the species; include an ac-
over a broad area can provide an early warning signal that populations tual count or an estimate of the numbers
able when they include an actual count or an estimate of the numbers
of birds of all species seen. Fill out the
for all species (Fig. 2 34). of a formerly abundant species are declining. Your daily records will
-
exact location, number of hours spent in
Most checklists provide space for some other crucial information: become historic accounts that someday could help restore species to the field, and the weather conditions. For
the exact location (compass direction and distance in air miles to the habitats where they once flourished. accuracy's sake, the information should
be filled out in the field. Checklist re-
nearest town), the number of hours you spent in the field, and the
produced with permission, Edwin B. For-
weather conditions. These basics ensure that your checklist will have journals sythe National Wildlife Refuge, United
meaning for anyone who wants to use the data. Most observers, espe- States Fish and Wildlife Service.
Recording field observations in a journal suits the purposes of
cially beginners, find that the best way to keep their checklists up to
many bird watchers willing to spend just a little extra time (Fig. 2 35). -

date is to fill them out in the field; the complications of life thwart our

Cornell Labomtorq of Ornitholojq Handbook of Bird Biologq

2.48 Stephen W. Kress Chapter 2— A Guide to Bird Watching 2.49
As with a checklist, certain information is crucial to note: date, time of
day, location (distance and compass direction to nearest town, name
of county, state, and country if you're abroad), weather conditions, and
. 1.65047.)6K.
tqls icorzom. persons with you, if any. Then, simply write down what you see—spe-
cies, numbers, ages, sexes, and other identifying characteristics.
Underline species names with wavy or double lines, so they will be
i4 5
cavinuocIL.,: easy to locate at a glance. A good technique for recording field marks
is to start by looking at the bird's head and work your way back to the
amliAlAte 11,2- ru-ozs)0 ups v4( tele/ 14- (41,43*
tail. With practice, you can use quick sketches to map field marks and
-rett ,{-01) atri, kuee. fiettioad, capture behaviors (Sidebar 3: Sketching Birds in the Field).
is + Le to d- ea off, ctr) (90aL at 27-w. One benefitoftaking notes is that it improves your powers of obser-
5z4t1;16,, 1604 (a, rt4w.,, vation and memory. Think of a bird you have seen many times, perhaps
rot (Lp a Black-capped, Carolina, or Mountain chickadee. Can you sketch its
aq 30, - b (.14.6 fel, - - 55) r,
black-and-white pattern from memory? Exactly where do the black cap
c,J4tk 10 rim PR 6, mt. ifie.kta-k 04. and bib begin and end? Once you have looked closely at a bird and
14‘A ,71- Kat at- e9 ra), welt, tried to write a description or sketch it, you will notice and remember
12,4" Lae cl),A vtot i more about it.
Besides recording the species you see and their descriptions, you
We- 51-4) ivfOWIA kttiSik 051,J (PitIL I y 01,
may want to describe the birds' behaviors. If you find a nest, observe
Gds I 44,94i VaLf 5 IVw v
k~ 4144 it for a period of time and record the birds' activities. Accurate field
6-(54404A- Ck4-115 , A lso 5 iraK notes about behavior are just as critical as detailed descriptions of bird
61•01,- Ovel1/2 , sightings. For the field biologist, behavioral notes are a source of data
on how a bird relates to its environment, just as laboratory experiments
c‘ot.A. 5 at Iota) b. t
provide the database for a physical scientist.
010,-
?itott.440,1 . (cytioaidde. Take complete notes. You never can tell what seemingly unim-
st) ov,J -i-‘42, i5ia421.). portant facts may later become decisive. Greg Butcher, a former biolo-
gist at the Lab of Ornithology and editor of Birder's World magazine,
1 3 O, 414_ (A.115 -3-2.° F. P100
tells about watching what he thought was a Hooded Oriole (a resident
toz 5c1.001 ovJ of the southwestern United States) singing in N iantic, Connecticut. The
5 , -714, 5a4.,t) (.44_,, song sounded funny, though, so he wrote it down, syllable by syllable.
ii-P-15 we -1)414 ÷I•Q, rxi5114. ktwi.Y6 Later he discovered the exact same description of an oriole's song in
rtapv.
his field guide—and learned that his bird had actually been a first-year
00-t- ip.11(2, ukfake0( 41•6) 4-14 ET
male Orchard Oriole, a common bird in his location.
zli9; fat at A few nuts-and-bolts considerations: you can keep your notes in
-epol- (45 )444ti, rorziei 1a55 affe4Q,b. a loose-leaf notebook or a bound notebook. Waterproof ink is best,
but you can use pencil. If you do use ink, select paper with a high rag
content; it will hold the ink better and will not yellow with age. You'll
5Mrlai Atd, -f- kOtiw,„ also need a technical pen with a tip of approximately 0.35 mm; pens
.g iv/ 444447L. CA) -rte 56- that draw a narrower line are too likely to clog. Such pens are avail-
able at art supply stores. Keep them in plastic bags, especially when
‘Otal Of AtZ-5 10V14 -114fe we'ee- cc-"
ei-dr*5 --hu> -ay in ec G ge, off a -
traveling, to contain leaks.
The cardinal rule, and one that requires a good bit of self-disci-
5 t waee, ipack pline, is to record everything in the field as it occurs. You can't possibly
remember, at the end of a long day, everything that happened. Write
things down at once, before your memories slip away. If you hate writing
in the field, take along a cassette recorder, record your stream-of-con-
Figure 2-35. Keepinga Field Journal: Recording observations in a field journal is worth the extra time and effort. As with a checklist, sciousness account, then transcribe your notes after you get home. Mi-
include exact location, date, and weather conditions, along with detailed information about the birds seen. Underline species crocassette players that fit in a shirt pocket are great for this purpose. Be
names with wavy lines so they will be easy to locate at a glance. Supplement written material with sketches, where needed.
Courtesy of Stephen W. Kress, from The National Audubon Society Handbook for Birders, 1981. (Continued on p. 2.52)

Cornell Labomtorg of Ornithologq Handbook of Bird Biolo9i

 Stephen W. Kress Chapter 2 — A Guide to Bird Watching 2.51
2.50

Sidebar 3: SKETCHING BIRDS IN THE FIELD

Stephen W. Kress
A quick field sketch, with pertinent addition, a sketch will allow you the general proportions of the bird. head and neck, wings, tail, and legs. goal should be to capture shape and then add details to i I lustratedistinctive
to convey your memories to others Regardless of whether you intend to Concern yourself with the proportions posture with as few lines as possible field marks, carefully noting these in
field marks noted, can be invaluable
much more clearly than you could sketch an owl, heron, or robin, they all of the different parts to one another and before the bird flies away. the margins of the page (Fig. B).
when you are trying to recall exactly
how a bird looked or behaved. Be- with just a written record. have oval (egg-shaped) bodies (Fig.A). the position of attachment, always re- Portray most behaviors by chang- Practice by sketching tame birds,
A few basic techniques will allow It is the differences in wings, tails, and ferring to the living bird. ing the posture of the bird's body (po- such as captive parakeets, pigeons,
cause a sketch can replace part of
anyone, no matter how little draw- legs that give each species a distinctive Draw with smooth, flowing lines sition of the oval) and the position of or feeder birds. Perched postures are
your written description, it also
can save you some writing time in ing experience he or she has had, to form. Watch carefully to see at what to achieve an outline sketch of the its appendages. If you see an unusual easiest, but it won't take long before
the field, although it should be ac- make a useful sketch. Start your field angle the bird holds its body, then be- bird. Don't worry about erasing bird or one you can't identify, quickly a few pencil lines will also capture
companied by thorough notes. In sketch with an oval that approximates gin to assemble body parts, outlining mistakes or lines you don't like. The draw a standard perching posture and the movement of birds in flight. ■

14,14/41t,fiNNINNNN
SNowV
BR I GIA NrINE NA/12
_NNE 'a, ilgo LACY 6A CK
0900 cc..c-A PLUM ES
WIAlb• 0-Io me4
51A,

Es L.M...<
BE.A.K

CB Gk TAI23k/S

erg( G,4-4T 0 01-01z.ED

strr IN
BEAD SNAG
AT EDGE OF
WtsT LIKE. TAIL y ELL04 ig'
eLACk PUPIL

PATO4 OF
SK t N
At BASB or BEAK
EAK

Figure A. Use Ovals to Begin your Bird Sketch: The bodies and heads of most bird species are roughly oval in shape, so you Figure B. Sketching for Identification: When you encounter a bird you do not recognize, first make a quick sketch of the general
can begin drawing by placing ovals of the right size in the orientation you wish to portray. Then add the distinctive legs, wings, shape. Then add notes in the margins to detail all the special field marks and features you observe. Drawing by Anne Senechal
tail, and beak for your species. Drawing by Anne Senechal Faust, from The National Audubon Society Handbook for Birders, by Faust, from The National Audubon Society Handbook for Birders, by Stephen W Kress, 1981.
Stephen W Kress, 1981.

Cornell Laboratory of Ornithology Handbook of Bird Biology

2.52 Stephen W. Kress Chapter 2 —A Guide to Bird Watchin 2.53
aware, though, that it's easy to end up with a shelf full of untranscribed
cassettes. If you need to refer back to a specific incident, finding the
right tape can take a while. Still, tapes are better than no record at all.
Ma( iv
Keep in mind, too, that cassette recorders break and batteries fail. Pen-
cil points can always be sharpened with a pocket knife or even with
your teeth in the field.
Finally, regardless of the technology you use to record your obser- wa,ki.
vations, follow these three rules at all times: record your observations WOO: orroX . 3 Pm. cme
as soon as possible after making them; don't consult references before
ceutki ,
writing up your field notes—your impression of what you actually
1,4 .
saw may be influenced by what you think you should have seen, ren-
dering your notes less accurate and useful; and never change your 010t) k•
notes—these are the records of your observations and should remain
as you first made them.
Once you've completed your initial field notes on your excursion
into the field, you have several options. Some observers consider their
recordkeeping done at this point. Others enjoy using their field notes 1105 5 `6( t eLL .0ethod av ca,. 1..e Pcd 01
to compose a more structured set of records, organizing the material ovaL., 6unclicitac ( Kip
in various ways for easy access. The most devoted observers may use
the straightforward, standardized note-taking system established by Jo-
seph Grinnell in the early 1900s, which is described in Herman (1986). d.F-- . 5 af e 51-edia‘v oikJ (e.de{
This system in its entirety is too demanding for most recreational bird- Factfot
ers to use routinely, but aspects of it can be adapted to the needs of the
weekend naturalist.
g ,240-C, 5' .0 ot . ■ jtoiclichti

One enjoyable way to learn a lot about individual species is to 044- 04- do ViciAutwk (4-alzars,

keep species accounts, transferring observations from your field note- 004k Aib< 6,(04t(o. (A.h5k).
book into another notebook that you've organized by species (Fig.
05 :=/ A4) -1-k4m cy.y-
2 36). Then all your observations on, say, the Black-capped Chickadee t
-(le7
,, cAii-iLry of+. or se),
-

will be grouped together. A loose-leaf notebook is the best choice for kyx5 kil 6,64
this effort, because it allows you to add pages to your existing notes on 14 e, c-irc12. 104101#44.- yietii,L) Q ktaki 4:5Ne55
each species. If you follow this procedure for a few species that are of E -t k Were,
particular interest to you, you'll soon become an expert on them.
Now, what are you going to do with all this dutifully recorded
( Ctr arirt) i -20 30 -

information? At first, it's not crucial that the data you've gathered be Led- 0-4--
published. As you learn to observe birds closely, you are learning far iqz.(ct Lt•1104.0 1244? otio
more about the specific bird you are watching than you could ever
6etsi
tkJ ti
c ; e0
114%) ovt It.
learn from a book. But even in the beginning you should get in the habit
of reporting your sightings to your local bird club, which will prob- a+dcSio n:0: fyovifIl Gat, mi5S4
ably use them to update local and regional checklists. You might even
want to file your daily checklists with the club. The value of your lists
a- itfalt 44,
increases with time, providing important baseline data for detecting
population changes. Information from a number of observers—you (U. 5 414Wei, We. I
and your fellow club members—over a broad area can serve as an -1-41 we're, so love Lii•5(
early warning signal that a formerly abundant species is experiencing
a serious population decline.
Also, many journals produced by state bird organizations wel-
come carefully documented reports for publication. Your local bird
club can probably put you in touch with the regional editor for your Figure 2-36. Sample Page from a Species Account: An enjoyable way to learn about particular birds is to organize your obser-
locality. And, if you live near a city, county, state, or national park or vations by species, accumulating them overtime into species accounts. Courtesy of Stephen W. Kress, from The National Audubon
any other sanctuary or refuge, check with officials there to see if they Society Handbook for Birders, 1981.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

2.54 Stephen W. Kress
would like reports of your sightings to maintain their checklists.
r Chapter 2 —A Guide to Bird Watching

will ever attain such lists, although it is fun to try.

2.55

Finally, if you begin keeping detailed species accounts, you will People vary in their attitudes toward life lists. Some derive their
probably accumulate enough information to write short reports on greatest pleasure from just watching fami I iar birds in their own habitat;
those species for publications, particularly if you pick species that have others find great satisfaction in traveling from place to place, checking
not been well studied. You could become the regional expert. off the "lifers." But it is sad when the life list becomes a birder's only
goal, because so many opportunities for enjoyment and contributions
to bird conservation are overlooked. Horace's golden mean—"Mod-
Reporting Rare Birds
eration in all things"—applies to bird watching as well as it does to
If you see an unusual bird, make your notes as detailed as pos-
other human activities.
sible, because validation of such sightings may well depend on your
notes. Record details of color, plumage, and behavior, as well as the
conditions under which you are making the sighting, such as the
lighting and your approximate distance from the bi rd. You might even
Counting Birds
make a quick sketch. If possible, photograph the bird and tape record ■ Counting birds accurately requires lots of practice. It's not hard to
its songs and calls. count a few chickadees or a small flock of crows, of course, but when
When you report a rare bird or even a common bird in an unex- the birds fly past you in multitudes rather than dozens, or when several
pected season (a Blackburnian Warbler in Michigan in winter, for in- species flock together, counting accurately can be very challenging.
stance), your observation may need to be verified before it is accepted How can you judge the size of a mixed flock of Canada and Snow
as part of the official local, state, or national record. Procedures vary geese that stretches from horizon to horizon or a huge, roiling mass
from state to state, but as an example, the New York State Avian Re- of foraging blackbirds? But even difficult, laborious counts are more
cords Committee (NYSARC), a group of experienced birders, reviews useful than "ballpark estimates." The challenge is to give as accurate
the accuracy and completeness of the field description in each report, a count as possible.
then decides whether to accept or reject the sighting. If the lighting is poor or the birds are far away, making an exact
count impossible, presenting round numbers is best. A flock containing
100 or fewer individuals should be rounded off to the nearest 5 or 10
Listing Birds birds; a flock with more than 100 birds may be rounded to the nearest
Many birders enjoy keeping a variety of separate bird lists, not 25 or 50, depending on your viewing opportunities. Trai ned observers
necessarily as checklists. The possibilities are countless—lists of birds usually can give a good estimate of large numbers, and such estimates
at the feeder, in the garden, or on a field trip; daily lists, weekly lists, are better than ranges, which are more difficult to compare than spe-
yearly lists, or a "yard list." Listing is especially fascinating during the cific numbers.
migration periods. A daily list in the spring, for example, follows the Flocks of flying birds, such as waterfowl, shorebirds, and black-
changes from the seed-eaters, such as finches, to insect-eaters, such as birds, are among the most difficult to count. Their speed, movement,
warblers and flycatchers. In species with sexes of different colors, you and habit of flying in dense, three-dimensional flocks contribute to the
can keep separate records for males and females.You can compare the problem of making reasonable estimates. Continued practice and a
lists for different seasons and note which birds migrate and which do few additional techniques will help. To determine the number of birds
not. Remember, the cardinal that nests near your back door may not congregating at a certain point (herons or blackbirds returning to a
be the same one you fed all winter (although it often will be). A yearly roost, for example), count how many pass a tree, house, or other fixed
list may reveal important population trends in your area corresponding point for one-minute periods throughout the time during which the
to habitat changes. birds are returning. Average your one-minute counts and multiply the
Many bird watchers keep a life list—a record of every species average by 60 to find the number of birds passing the reference point
they have ever seen with the date and place of the first sighting. The in one hour. To compute a grand total, multiply the average number of
life list, like solitaire, is your own game in which you make your own birds-per-minute by the total duration of the procession in minutes.
rules concerning which species to count. Few birders would consider Exact counts are usually possible if a flock contains fewer than
the colorless blur that flashed past just as someone called out "juvenile 30 birds. For larger flocks, try a technique called blocking (Fig. 2-37).
Lincoln's Sparrow" an honest candidate for their life list, however. This approach entails counting the birds in a "block" of typical density
The constant challenge of the life list widens the scope of your bird- from the trailing end of the flock (so that birds are not flying into your
watching activities and leads to exciting new experiences with birds. projection) and then visually superimposing this block onto the rest of
Standing as constant goals are the North American life lists of some the flock to see how many times it will fit. If a flock contains about 100
expert bird watchers, a few of whom topped the 700 mark some time birds, count the trailing 20 and fit this onto the remainder of the flock;
ago and are now aiming for 800 North American species. Few of us it should "fit" about five more times. For huge flocks, start by choosing

Cornell Laboratorg of Ornithologg Handbook of Bird Biologq

2.56 Stephen W. Kress Chapter 2 — A Guide to Bird Watchin8 2.57

Figure 2-37. The "Blocking" Method of

Counting Birds: First count the birds in an
imaginary block of typical density from
the trailing end of the flock (this avoids 44. 4- 4
the distraction of birds flying into the At
block). Then visually superimpose the
ot4
block onto the entire flock and estimate A, " A .- -*4
how many times it fits. Finally, multiply
this number by the number of birds in
T- o- P-- JO A
the original block. In this example, the 4. 7' "4

block contains 17 birds and fits into the

flock about 3 times, giving an estimate 4 4-
of 51 birds. There are actually 60 birds
in the flock.

I
b

a group that represents 50 or 100 birds and see how many times this Figure 2-39. Great Blue Heron: The
block fits on the flock as a whole. magical experience of watching a Great
Blue Heron take flight from a misty
Concentrate on memorizing impressions of what flocks of dif-
wetland may be all that a newcomer
ferent sizes look like. Practice by throwing rice grains out on a table- needs to begin a lifetime of fascination
top, making a quick estimate, and then checking your success. With with birds, and with it a concern for the
practice you can develop mental images of different-sized flocks of natural environment. Photomontage by
various shapes (Fig. 2 38).
-
Marie Read.

The estimates of different observers looking at the same birds vary

to a surprising degree, but accuracy is important. Many North Amer-
ican bird censuses and surveys rely on amateur participants, and the
success of these important studies depends largely upon the counting
c 41. skills of participants.

" rile" f pi_ Conclusion

o- ■ We are all teachers. Our fascination with birds is one of the greatest
)1.4cAs. f rft gifts we can pass on to others—friends, neighbors, family, and espe-
cially children. More than 60 million Americans already watch birds,
so it appears that birds themselves may be the ultimate environmental
educators. All we need to do is direct more of the uninitiated into the
realm of birds, closing the critical gap of distance between bird and hu-
man, and let the birds do the rest with their magic. Initiate a newcomer
with a close encounter with a Great Blue Heron lifting out of a misty
Figure 2-38. Practice Flocks: Bird flocks vary widely in size, shape, and density. Use these examples to practice your counting
technique. The actual number of birds in each flock is given at the end of the chapter. wetland, and the conversion starts (Fig. 2 39). You can continue by
-

Cornell Laboratory of Ornithology Handbook of Bird Biology

2.58 Stephen W. Kress

sharing intimate views of elegant waxwings plucking apple blossoms

and bluebirds resplendent in glowing color. "How could I have missed
all of this?" they ask. "No longer," they insist.
Perhaps it is envy of their flight, colors, and stamina, or delight in
their enchanting songs and remarkable behaviors. Perhaps it is awe at
their mysterious migration and boundless vitality. For whatever reason,
birds capture our attention and our imagination, whether we stay at
home and let the migrant flocks flow into our lives and out again, or we
pursue them by foot, bike, plane, or ship. Once people notice birds,
commitment to their well-being usually follows. This connection is at
the soul of birding: the birds' future is intimately tied to our own.

The Birder's Essential Resource Guide

■ There is a mountain of information available these days to birders
Form and Function:
with various levels of interest and experience in the form of field
and audio guides, checklists and travel guides, textbooks, popular
magazines, scientific journals, web sites, general and leisure read-
ing about birds. Due to the volume of information available and the
continual release of new publications of interest to bird watchers
The External Bird
and other enthusiasts, to list just a few of these resources here would
be vastly incomplete. Please visit the Home Study Course website
<www.birds.comell.edwhomestudy> to view the Birder's Essential
Resource Guide online and see what resources, old and new, that George A. Clark, Jr.
we believe might be of interest to you.

One reason people love birds is that they are so beautiful

and so varied. Consider color alone, ignoring for the mo-
ment the many variations in features such as bill length
and feather shape. Birds come in every conceivable hue.
Any experienced birder can easily think of a bird for every color of the
rainbow, even among the birds of North America: Northern Cardinal,
Baltimore Oriole, Yellow Warbler, Green Jay, Eastern Bluebird, Indigo
Bunting, and Purple Martin. In fact, the blues alone vary from the subtle
hues of the Blue-gray Gnatcatcher and Cerulean Warbler to the deeper
tones of the Blue Grosbeak and Steller's Jay. Furthermore, some spe-
cies, such as the Painted Bunting, simultaneously display an amazing
array of these colors. Nearly every color we can imagine can be found
on at least one of the nearly 10,000 species of birds.
Most of the remarkable colors and other aspects of a bird's ex-
terior are specializations of its skin—not only the coverings of the face,
beak, and legs, but even the feathers. Feathers occur on no other living
animal: if it has feathers, it is a bird. Some years ago a mutant breed of
nearly featherless chickens was studied with the idea that these birds
could be sold cheaply because they would need little or no plucking.
It turned out that the extra heating required to keep these birds warm
more than offset the savings on plucking; featherless birds, it would
seem, don't have much of a future.

Cornell Laboratorq of Ornithologq

3.2 George A. Clark, Jr, Chapter 3— Form and Function: The External Bird 3.3
This chapter introduces feathers—their locations, structure, func- Feathers lie on the body and wings with impressive neatness.
tion, care, and development, including their replacementthrough molt- Such orderliness helps to produce the tidy, streamlined cover of feath- Outer Vane

ing. Then we move to other parts of the skin, such as the bill and legs, ers that is crucial to a bird's survival.
where a feathered covering would in many cases be a liability. Each
Leading Edge
part of a bird's exterior contributes to the unified whole, and we give of Wing
special attention to the color and pattern of the entire bird, considering, Feather Form and Function
for example, why some birds have vivid colors but others are dull.
■ From an engineering viewpoint, feathers are mag-
nificent—they accomplish so much with so little ma-
terial. Of their many functions, the most important are (1 )
Feather Tracts insulating and protecting the skin and body, (2) providing
Inner Vane

■ Examine a plucked chicken or turkey ready for the oven.You can see the smooth, streamlined surface area required for effi-
Feather the sites where feathers were attached, known as follicles, as small cient flight, and (3) providing pattern and color, which
Pterylae
Follicles indentations in the skin. In most birds, the feathers are not attached are important in social behavior, as discussed later in
uniformly over the body, but are grouped into feather tracts this chapter and in Chapter 6.
called pterylae (singular: pteryla). Between the tracts are Shaft
regions of bare or less-feathered skin called apteria (sin-
gular: apterium) (Fig. 3-1).
Feather Structure Figure 3-2. Basic Structure of Typical
Pterylosis, the arrangement of feather tracts and bare patches, Examine a feather from the wing or Wing Feather: Stiff central shaft runs
tail of a bird. Note the rather stiff central entire length of feather, with vanes ex-
varies from one taxonomic group to another, and some groups have
tending to either side. Note asymmetry
unique patterns. For instance, the corvid family, which includes ra- shaft and the two broad vanes extending
in vane width, with narrower vane on
vens, crows, jays, nutcrackers, and magpies, has a characteristic ap- from opposite sides of the shaft (Fig. 3-2). In edge of wing that leads in flight—termed
terium in the mid I i ne of the pteryla located on the back. H istorically, birds capable of flight, the outer wing and tail feathers are typically the outer vane. The wider vane is called
asymmetrical, with one vane narrower than the other. This asymmetry the inner vane.
such distinctive patterns have been important in classifying the main
groups of birds. The feather patterns are symmetrical from one side of produces greater rigidity on the leading (narrower-vaned) edge of the
the body to the other and are shared by all members of a species. wing, which is needed to maintain the streamlined shape of feathers Wing
Although we know little aboutthe possible functions of the many during flight. It also causes individual wing and tail feathers to twist as
taxonomic variations in pterylosis, we can deduce that, for any given they move through the air, which is essential for flight (see Figs. 5-1 7
group, strategically locating feathers in tracts may allow birds to get and 5-19).
Figure 3-1. Distribution of Feather
Tracts on Plucked Bird: Dots represent away with fewer feathers overall, thus reducing the baggage they must In general, vane width becomes less symmetrical as you move
feather follicles, sites of attachment of carry in flight. Much as balding men comb their remaining hair to cover farther from the center of the body. Thus, a feather from the middle of
feathers. Groups of dots, often in a linear
a bald spot, feathers from the feather tracts cover the apteria, forming the tail will be more symmetrical than one from the edge of the tail. In Less
pattern, are feather tracts, termed ptery- the same way, the vanes of the innermost flight feathers of the wing may
flight surfaces and providing insulation without requiring a solid mass Symmetrical
lae. Featherless areas between tracts are Vanes
of feathers. Grouping feathers in tracts also may allow the muscles be almost symmetrical, while the vanes from the outermost feathers More Symmetrical
apteria. Vanes
that move them to be smaller and more localized—lightening the bird are quite different in width (Fig. 3-3).
even more. As discussed in Chapter 5, birds have evolved many such When flight has been lost secondarily through evolution, as in
Tail
adaptations to reduce their weight and create an aerodynamic shape. certain rails on isolated oceanic islands, the primaries have lost their
In addition, apteria may aid heat loss, as many birds raise their feathers asymmetry. The asymmetry in the fossilized primary feathers of Ar-
to expose bare skin when becoming overheated. chaeopteryx indicates that this earliest known bird could indeed fly,
A few kinds of birds, most notably penguins, have a continuous but whether it was a strong flier remains controversial.
pterylosis with no apteria. This arrangement helps to prevent water The central shaft is divisible into two sections. The lower portion,
from penetrating to the penguin's skin and chilling it. Penguin feath- part of which lies beneath the skin, is the calamus; it is hollow and
Less
ers are so good at trapping an insulating layer of air near the body that has no vanes. Above the 'calamus lies the rachis, which is essentially Symmetrical
solid (Fig. 3-4). The vanes, extending from the rachis, are made up of Vanes More Symmetrical
the skin stays dry even while the bird is swimming and diving. Adult Vanes
Ostriches from Africa also lack apteria, but their embryos have them. a series of parallel branches called barbs. At right angles to the barbs,
and in the same plane, are branchlets called barbules. The barbules, Figure 3-3. Asymmetry of Vane Width
Because many researchers believe the stages that developing embryos in Wing and Tail Feathers: The narrower
pass through indicate the stages their ancestors evolved through, the by hooking together (the distal barbule of one barb catching upon the
(outer) vane of each feather is located
lack of apteria in adult Ostriches is probably a secondary condition. adjacent proximal barbu le of the next), hold the vane intact.The whole toward the leading edge of the wing,
The ancestors of Ostriches undoubtedly had a more typical feathering effect is somewhat like a series of tiny strips of Velcro. and toward the outside of the tail. Note
Run your fingers down a feather from tip to base, and notice how that asymmetry in vane width increases
and perhaps those of penguins did as well.
farther from the center of the body.
you can separate the barbs by pulling them apart. Now press the barbs

Cornell Laboratorq of Omithologq Handbook of Bird Biologq

3.4 George A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.5
Contour Feathers
The contour feathers are what you see when
you look at a bird. Forming the outer shell of the bird's
Hooklets
feather coat, they are termed contour feathers because
they give the bird its characteristic shape or outline.
Unlike other major types of feathers, most contours
have tightly knit vanes that form a relatively impene-
trable surface. These feathers streamline and shape
Proximal Barbules the wings to provide propulsion and lift in flight. The
of the Next Barb
tightly knit vanes deflect air currents, minimizing the
}

effects of wind and allowing the bird to slice through

Distal Barbules of the air. When beaten against the wind, they also
One Barb
provide strong resistance to air; the bird uses this re-
Rachis \AM }

sistance in aerial maneuvers, and in stopping. Try to

blow through the intact vane of a large wing feather
Barbules and you'll see that only an extremely strong wind can
penetrate such a surface.
Contour feathers also provide insulation against
Barbs extremes of temperature. Because these feathers are
aligned one atop another like shingles on a roof, water
tends to run off. A bird in the rain, therefore, remains
dry at the skin thanks to its feathers. If this protection
becomes disrupted (for example, if the feathers be-
come oil-soaked), the bird can die within seconds
from hypothermia.
Figure 3-4. Structural Detail of a Typical together by stroking from the base toward the tip, and see how neatly
Contour Feather: The feather shaft is di- they fit against one another, forming a smooth, continuous surface. Healthy birds, you may have noticed, always
vided into two segments: the lower, hol- look trim and neat. Each contour feather has a set of specialized mus- Figure 3-5. Common Grackle Display
This motion is exactly what birds do while they preen, to smooth and
low, vaneless calamus; and the upper, with Feathers Erect: Each contour
adjust their feathers, "zipping" them together. The large surface area cles, located beneath the surface of the skin around the follicle, which
solid rachis, to which the vanes attach. feather has a set of specialized muscles
The vanes consist of parallel branches of wing feathers is particularly important in providing lift and thrust for helps to position the feather. Without such muscles to hold feathers
that helps to position the feather, keep-
called barbs, which are likewise flanked flight. The barbules not only hold the barbs together but allow them to in the right positions, the feather coat would be disheveled. In some ing the feather coat smooth and neat.
by parallel branchlets called barbules.
slide relative to one another, contributing to the feather's extraordinary cases, muscle sheets immediately beneath the skin act together with Although birds have only limited con-
Tiny hooklets on each distal barbule the individual feather muscles to coordinate movement of the feath- trol over feather placement, some, like
catch onto each adjacent proximal bar- flexibility. this Common Grackle, take advantage
ers within a tract. Individual feathers usually can't move very much,
bule, holding the barbs together lightly, of that control in their displays. Photo
somewhat like strips of Velcro. Adapted but their movement can be highly conspicuous when, for example, a
from Faaborg and Chaplin (1988, p. 15, Types of Feathers displaying male grackle elevates the feathers over most of his body (Fig.
by Tom Vezo.

Fig. 2-1). When we think of a feather, we often visualize a flight feather 3-5) or when an adult male Red-winged Blackbird displays his bright
from the wing; however, this is just one of the many types of feathers red epaulettes (shoulder patches) (see Fig. 6-38). Even more spec-
that birds possess. A single bird may have delicate and fragile down tacular is a male peafowl spreading his train of feathers (Fig. 3-6).
feathers, largely vaneless bristles, and strong feathers used in flight. The largest contour feathers in many birds are the large flight
Furthermore, each type of feather differs from species to species, and feathers on the wing, called remiges, and the tail feathers, called
within a species, by sex and age. Differences occur in size, shape, rectrices. Because the remiges of all flying birds provide lift and pro-
pattern, color, and microscopic structure. pulsion, it is importantthatthey not be displaced by strong air currents.
Given a single feather, an experienced person with a microscope— Thus, they are attached firmly to the bones of the wing either directly or
and access to a large collection of bird specimens for comparisons—usu- indirectly via ligaments, unlike most other feathers, which attach only
al ly can determine the species, sex, age category, and the feather's original to the skin. The rectrices are connected to one another by ligaments,
position on the body (Sidebar 1: Feather Detective). Information of this sort with only the innermost attaching directly to the tail bone (pygostyle)
can be valuable. Researchers studying the diet of nesting Sharp-shinned via ligaments.
Hawks, for example, cannot kill these protected species to examine their
stomach contents. But by studying feathers of prey that are dropped from
the hawk's nest, they can learn the species, sex, and age of the prey. (Continued on p. 3.10)

Cornell Laboratory of Ornithology Handbook of Bird Biology

3.6 George A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.7
of an employee but no salary," she identify them after they go through
Sidebar '1: FEATHER DETECTIVE explains. something, like a jet aircraft engine,
has worked at it so hard, examining
thousands upon thousands of feath-
Mike Lipske It was not until 1960 that Roxie and they're all chewed up." ers and committing their trademarks
Laybourne's peculiar knack for The first thing she does with the to memory during the 21 years she
(Excerpted from "To Down Detective Roxie Laybourne, a Feather's the Clue," by Mike identifying feathers began to reveal chewed-up feathers that Weaver and has studied the structure of down.
Lipske, in Smithsonian, March 1982. Reprinted with permission from the author and itself. On October 4 of that year a other engineers send to her is wash But even her doggedness, and her
Smithsonian.) turboprop Lockheed Electra took them (Fig. A). "You cannot identify memory for minute variation, would
off from Boston's Logan Airport, dirty feathers." After the feather frag- be insufficient if she did not have ac-
On her way to becoming this in a thick Carolina drawl, and punc- burst into flames and plunged into ments have been soaked in soapy liq- cess to the reference library that is
country's absolute last word on the tuates her conversation with rolling Winthrop Bay with 72 aboard. Eight uid, rinsed and dried, she puts one on the Smithsonian's collection of bird
identification of feathers, Roxie C. hand gestures. passengers and two crew members a slide and under her microscope. skins—"somewhere approaching
Laybourne has not hewn to the tidy Combing quickly through the survived the 47-second flight—cut She is a student of the fine, diag- half a million specimens," according
path. The clutter on her desk at the crammed drawers of her desk, she short by a flock of birds sucked into nostic structures on the barbules of to George Watson, curator of birds.
Smithsonian Institution stands a solid pulls out plastic bags holding bird the Electra's engines. down (Fig. B). These barbules are Stored in drawers in a complex of
six inches deep at the left rear corner remains. From one, she dumps a few The Federal Aviation Adminis- microscopic parts of a feather that cases on the sixth floor of the Natural
and slopes to a depth of two inches bits of mangled fluff recovered from tration turned to Mrs. Laybourne extend from an individual barb. History Museum's EastWing (Fig. C),
near the right front. From mountain an airplane engine following a bird and John W. Aldrich, her supervisor The barbs, in turn, are tiny feather- the collection ranks first for North
to plain spreads a layered mass of strike in Texas last year. Reading the at the time, for help in identifying lets, some small as an eyelash, that American species of birds, but trails
routing envelopes, official letters, scant evidence, she has conjured up fragments taken from the engines. grow from the quill and make up the the American Museum of Natural
scientific texts, seminar proceedings a female American Kestrel. Figure A. Roxie Laybourne Washes "That was our first case," remembers soft vane of a feather. In a six-inch History, in New York City, for birds
and scattered scraps of paper. One "This strike occurred in Turkey," Soon-to-be-identified Feathers. Photo
Aldrich, also a research associate in feather taken from the wing of a city of the world. Possibly a third of the
small brown-and-white feather, she says of the next one, a grayish courtesy of Chip Clark.
the Division of Birds. "And it was a pigeon, about 1,200 barbs and about Smithsonian's skins were collected
pennant on a sinking ship, pokes up wing and one severed foot, sent by of fields and woods to roam in. Most tough one. They were all mangled. 990,000 barbules make up the vane. for the old Biological Survey of the
from the pile. "It's from Thailand, but the U. S. Air Force. "Golden Plover." people don't. But I did. I liked to hunt Finally we did find one whole star- Here, in that 990,000th part of a Department of Agriculture, which
I haven't worked it out," she says of On a microscope slide are and fish." ling feather." feather, is where the scientist goes became today's Fish and Wildlife
the feather. mounted a few tiny, white strands She was graduated in 1932 from The Boston crash caused an im- to work. Service. The Museum's array of bird
On an adjacent table are more of down: "I knew for certain it was a Meredith College in Raleigh, with a mediate scurrying in the industry, skeletons and preserved specimens
papers, more books, her black mi- Buteo (a genus of soaring hawks). It degree in science and mathematics, and a feeling that the effects of birds Feathers Stand Up to Jets is preeminent.
croscope, a plastic bread bag filled turned out to be a Red-tailed Hawk. and went on to work at the North on airplanes was something that had She uses down for her investig-
with eagle feathers, as well as sev- Probably a Red-tailed Hawk. You Carolina State Museum of Natural to be understood. "It was one of the ations because the microscopic
eral small glass bottles containing have to be careful not to overstep History, where she learned taxi- first that ever happened with birds," structures on downy feathers vary
charred bits of down floating in Ivory your bounds." dermy and spent summers at the said one industry employee. "Lives less than do similar structures on
Snow and water. "Remarkable woman," says Doug- federal fisheries station in Beaufort, were lost and a plane came down the barbs of flight feathers. Also,
Feathers, ones in need of a name, las Sutton, at the time a Smithsonian collecting birds, fish and other spec- out of the sky." the downy feathers, which are more
flow steadily to Mrs. Laybourne's tiny post-doctoral fellow for whom she imens for the museum and puzzling The aircraft industry prefers to flexible, stand up better to the sort of
office in the National Museum of was identifying feathers found at out problems in shark identification. remain quiet about its bird strike re- wear and tear that comes of being
Natural History. Aircraft engineers, archaeological sites in Labrador. Graduate study in zoology at North search. "People get hysterical when inhaled by a jet engine.
designing planes to withstand colli- "That work she does with feathers, Carolina State University was fol- we take dead pigeons and throw Why birds have evolved micro-
sions with birds, send her tiny shreds I've never seen anyone do. Bright as lowed by a master's degree in botany them into running engines," says scopic trademarks in their feathers
of feathers scraped from jet engines. hell. Feathers, for God's sake! That's from George Washington University a Pratt & Whitney public relations is something Mrs. Laybourne cannot
An archaeologist in New Mexico a very difficult thing." in Washington, D.C. man. "And we do." say: "All I know is they have it." The
drills a hole in a 500-year-old sealed "I grew up as an ornithologist," She came to work at the Smith- Al Weaver, a Pratt & Whitney en- microscopic process pins identi-
pot, plucks bright yellow and orange says Mrs. Laybourne. "I've been in- sonian in June 1944, intending to gineer who has been sending Mrs. fication down to family in most
feathers from inside, and mails them terested in natural history and birds leave Washington after a year. But Laybourne feather fragments for cases, but Mrs. Laybourne does not
to Mrs. Laybourne in Washington. ever since I could walk. You get used by November 1946, she had trans- ten years, says he is not especially attempt to identify the particular
Feathers come routinely from field to thinking of birds in certain terms. ferred to a job at the Fish and Wild- curious about the species or sex of species through her microscope. In-
agents of the U. S. Fish and Wildlife People who band birds know the life Service, where she has worked birds that fly into engines. But he stead, once she has determined the
Service (FWS) and the Federal Bu- bird from handling it, or seeing it in since, for many years with the Bird does want to know the size and if it is family of birds that a fluff of down has
reau of Investigation. the field. I know birds better when and Mammal Laboratories, now with Figure B. Microscopic Detail of Barn
a flocking bird, like a gull, "or a loner come from, she takes accompanying
A systematic ornithologist and re- they're dead." Owl Down Feather: Magnified 400
the Division of Law Enforcement. As like a hawk." Which is where Roxie feather fragments from the tidbits that
times, the microscopic structure of a
search associate in the Smithsonian's She was born in Fayetteville, a Smithsonian research associate, Laybourne becomes a good person have been sent to her and compares downy feather recovered from the en-
Division of Birds, Mrs. Laybourne is North Carolina. The year, she says, is she has an office and access to the to know. them with feathers from specimens gine of a Boeing 747 reveals it to be from
also a part-time zoologist with the not "pertinent." Her parents moved vast collection of bird skins and "Feathers," she points out, "will in the Smithsonian's skin collection. a Barn Owl. The engine maker, Pratt &
Division of Law Enforcement of the soon after to Farmvi I le, in Pitt County. skeletons in the Museum of Natural take a lot of beating. They're pretty Mrs. Laybourne says the only thing Whitney, sought identification. Photo
FWS. Short, square-faced, she speaks "It was a small town. You had plenty History. "You have all the privileges tough. That's one reason you can special about her method is that she courtesy of Douglas W. Deedrick.

Cornell Laboratorq of 0 rnithologq Handbook of Bird Biologq

3.8 George A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.9

Feather Identification do that all the time? The weeds will So there were more birds being a puzzle—every time you get bird
and the FBI come back. You never win that battle. struck, and since the Air Force orga- remains, you don't know which
The resource is often tapped by This field, I'm just beginning to get to nized its Bird Aircraft Strike Hazard species you have. With every bird
"outsiders" who, in turn, add their where I can go somewhere with it. (BASH) Team, personnel at air bases you're being put to a test. Even if it is
own knowledge. It was, for example, I've just got enough background now became more aware of air strikes and the same species, the feathers could
an FBI microscopist who helped Mrs. to begin learning. You have to know better at collecting feather samples. well be from different parts of the
Laybourne come up with a perma- so much to begin asking yourself The consequence is that she got to do bird. And the date and locality of the
nent slide mounting medium for use questions. I figure in 20 years I might more birds. strike are important. You see, you're
in her feather studies and, more im- learn something." That's how she put it: "I get to do putting a puzzle together, trying to
portant, eased her burden of routine more birds." Sixty-five years after she figure out where the pieces go.
identifications. Douglas Deedrick, graduated from college, and nearly "I warn people, don't come to
a 32-year-old agent working with
15 YEA RS LATER 40 years after she began research on work with me—you may become ad-
hair and fibers in the microscopic feather identification as part of her dicted. When people say to me 'you
Daniel Otis duties at the U. S. Fish and Wildlife don't make much money in museum
analysis unit of the FBI laboratory
In 1997, 15 years after publication Service, her pleasure in her work work,' I always say 'you don't need
in Washington, met Mrs. Laybourne
of the above Smithsonian article, was undiminished. Her persistence as much—you don't need to go on
in early 1978 (Fig. D). Deedrick
Roxie Laybourne was sti II at work full and dedication earned her some no- vacations to enjoy yourself. You've
showed an interest in her work and Figure D. Douglas Deedrick and Roxie Laybourne: Photo courtesy of Chip Clark.
time, still in love with her job, still the toriety; a brochure advertising her enjoyed your day. Your work is your
she, who had been identifying feath-
ultimate authority on bird IDs for the 1996-97 exhibit at the Smithson- recreation."
ers for the FBI for 18 years, saw in the
Air Force and commercial airlines, ian, "Feather Focus," referred to her When I spoke to her in mid- facturers improve the safety of their
young agent the answer to her wish strikes from Britain, Slovakia, and
and still eager to surpass herself at as "world-famous feather detective September, her current recreation aircraft. One use to which her iden-
that someone at the Bureau would elsewhere.
her craft. She had the advantage of Roxie Laybourne." And although you was identifying birds for theAir Force. tifications are put is developing air-
"learn feathers." She had taken on If her own enthusiasm testified to
the long view, and in a phone conver- got the impression that bragging was Planes from a base in North Carolina craft specifications. When designing
as many as a dozen cases a year for the work's addictiveness, her com-
sation I asked her how her job had alien to her character, she couldn't were hitting birds at night—"So it's a windshield for a jet, for instance, it
the FBI, handling feather evidence in ments on the demands of the work
changed over the years. quite conceal her pride in being an migrating birds," she said, fitting a helps to know whether a strike by a
crimes such as robbery, kidnapping emphasized its daunting aspects. She
Not much, she told me, when it acknowledged master. She laughed piece of the puzzle. "They're anxious sparrow or a goose is more likely.
and murder. Criminal convictions took her responsibility very seriously.
comes to bird IDs. Mrs. Laybourne easily and often. Her enjoyment of to know what they're hitting. So far,
seldom hinge on feather identific- Having worked so long to accu- "I try to instill in my students how
still received chewed-up bits of feath- her craft was evident in her tone of I've identified Mourning Doves and mulate her skills, she was determined
ations. But having a scientist testify careful you have to be in this work,
ers from around the world, cleaned voice—eager, careful, kind, like that Killdeer—birds that like the grass- to pass them on to others. "When you
that a feather fragment adhering to a the importance of being absolutely
them off, and tracked down the spe- of a favorite aunt, still rich with the land habitat of airfields. Also three
suspect's knife matches the filling in have some knowledge," she said, "it's accurate," she says. "This is not glam-
cies using the Smithsonian's bird col- cadence of North Carolina. It was bats."The Air Force had compiled in- your responsibly to share it. No sense
the victim's down-lined jacket can- orous, and some people wouldn't
lections as a reference. When I asked also evident from her comments. formation on the birds that live at all in other people having to start at the
not hurt the government's case. like it. The first qualification is per-
if she always used the microscope, "To me, the whole process is like the different bases. If they have bird
The carefully dressed-and-pressed beginning the way I did. They should severance. You have to work hard for
she mentioned that she could some- problems, they may change flight be able to build on what you've
FBI man and the white-coated re- a long time without results. You need
times tell a bird's family by "how its patterns, discourage birds by chang-
search scientist are an unlikely pair learned, and then they'll be able to a good memory. You're thinking all
feather behaves in the cleaning solu- ing habitat, or even move flights to
of crime fighters. Yet she speaks of go on that much further." the time. You've got to know where
tion." So the fact that her approach different airfields. That's another change: she had
Deedrick as a favored nephew, and you're going. You can't just go hunt-
had not changed may be unsurpris- "Overall, the bird hit most often is
the agent is effusive in his praise of more students. One of her first, Doug- ing through the collections trying to
ing. Expertise of this caliber evolves probably the Horned Lark," she told
her: "She's a stand-up person. She las Deedrick, has taken over her work match a feather. It's like heading out
over decades and is not easily ren- me. "In the United States and Europe,
never sits down. She can walk twice for the FBI. In classes she taught at on a cross-country drive—you can't
dered obsolete by technological de- commercial airlines are most likely
as fast as I can. Her memory is sharp. the Smithsonian she had students as just take off, you've got to have at least
velopments. to hit gulls. In Africa and Asia, it's some idea of your destination."
She can associate all the different young as six years old. "It's good to
But the world from which she ob- Black Kites. Air Force planes often
areas she's worked in—botany and get them young," she said. "Because It seems not too presumptuous
tained her birds had changed. "There's hit Turkey Vultures."
birds and animals—and put it all to- to do this, to specialize, you've got to to suggest that her attitude toward
more awareness now—people are The Horned Larks weigh about her work was an important source
gether. She can take something most know birds in the field, have a back-
more interested," she said. "Back when one and one-half ounces (42.5g), so of her achievement. Despite the dif-
people wouldn't find that interesting ground in bird watching. You've got
I started, people weren't paying much like the vast majority of bird strikes, ficulties, she told me, "I am happy
and put herself into it. She's a true to know systematics. Otherwise you
attention to feathers. At the FBI, they they do no damage and endanger no with it, I enjoy it every day, and I still
scientist." Figure C. Smithsonian Institution's don't know where your piece of the
didn't think feathers could be used as lives. Nevertheless, she said, "A strike learn something new every day—it's
Thirty-seven years into her career Bird Skin Collection: Roxie Laybourne puzzle fits." More typical, though,
working at the Museum of Natural
evidence. Now they realize that a tiny
displays just a few of the Smithsonian's is always a serious problem, because are undergraduate and graduate just as true now as it ever was." ■
bit of feather can include a lot of infor- you never know when it will cause
History, and 21 years into her re- numerous drawers of bird skins. The students, postdocs, and profession-
mation. There are more planes flying, collection, used for reference, research, damage." Mrs. Laybourne's years
search on the structure of down, als. She had forensics students from On August 7, 2003, Roxie died peace-
too, and they're faster and quieter. Birds and teaching, contains specimens from of work have helped aircraft manu-
she has no intention of retiring to California and other students of bird fully at her cabin in Manassas, Virginia.
can't evade them the way they could all over the world. Photo courtesy of
Virginia. "I could go out to my farm
when they were slower and noisier." Douglas Deedrick.
and pull up weeds. But who wants to

Cornell Laboratory of Ornithologq Handbook of Bird Biology

3.10 George A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.11
The outermost remiges are
the primaries, recognized by
their attachment to the skeleton
of the "hand" (see Fig. 1-8). To
meet the demands of powered
flight, the primaries must be
strong yet flexible. Depending
on the species, birds commonly
have between 9 and 12 well-de-
veloped primaries.
Projecting rearward from
Figure 3-7. Numbering System for Rectrices and Remiges: The rec-
the forearm of the bird wing is trices are numbered from the central two feathers toward the left and
another row of remiges; these right sides of the bird. The primaries are numbered from the innermost
are known as secondaries. In toward the tip of the wing, and the secondaries are numbered from the
innermost toward the center of the bird. The number of each type of
both flapping and soaring flight,
feather is constant within a species, but varies among species. There
the secondaries provide lift and are typically between 6 and 32 rectrices, between 9 and 12 primaries, 5
thus function like the fixed wing and between 8 and 32 secondaries.
of an airplane. Among birds as
a whole, the number of second-
aries varies more than the number
of primaries, ranging from 8 to 32
(Van Tyne and Berger 1959). The Sidebar 2: FEATHER FACTS
higher numbers occur among
birds with long wings, such as
Sandtj Podulka
albatrosses, which need a large
Number of Feathers addition, aquatic birds tend to have ground, its size is a useful clue to the
wing surface for soaring flight
How many feathers does a bird have? more feathers than terrestrial species size of the bird it came from.
over water. In most flying birds, of a similar size—undoubtedly due Not surprisingly, the smallest
As you might expect, big birds tend
the secondaries attach directly to have more feathers than small to the rapid loss of heat experienced contour feathers known are from the
to the ulna bone in the forearm birds. The record low count (contour by birds in water. world's smallest bird: the feathers
via ligaments. On many isolated feathers only) is 940—from a Ruby- Heat retention is probably also from the eyelids of the Bee Hum-
ulnas, such as might be washed throated Hummingbird (Wetmore the reason smaller birds tend to have mingbird are merely 1/63 of an inch
up on a beach, you can see the 1936). The highest number was more feathers per unit body weight (0.4 mm) long! In contrast, the con-
bony bumps that were points of reported by Ammann (1937), who than do large birds. Like a human, tour feathers forming the peacock's
attachment for the secondaries. (patiently) counted 25,216 contour a bird generates heat through the tail are nearly 4,000 times longer—
feathers on a Tundra Swan. Of these, metabolic reactions that take place up to 5 feet (1.5 m) in length.
The other major set of flight
Figure 3-6. Display of the Male Indian 80% (20,177) were on the head and throughout its body, and it loses
feathers in most birds, the rec-
Peafowl: In a spectacular display of neck. This distribution is not sur- much of this heat across its body Weight of Feathers
feather control, the peacock faces one trices (tail feathers), are particularly important for stability and control surface. Therefore, the more surface Feathers are, indeed, "light as
prising, since swans are so clearly
or more females and lifts and fans his in flight, somewhat like the tail of a child's kite (Thomas and Balmford long-necked, but even short-necked area a bird has relative to its heat- a feather." Although the feathers
"train" while rustling his wing feathers 1995). For instance, forest-dwelling hawks, such as the Northern birds have a high percentage of their generating volume—a comparison of some birds, such as owls, seem
and stamping his feet. The "train" con- Goshawk, use their tails as rudders to help guide them through an to make up half their volume, the
feathers on the head and neck, where known as the surface to volume
- -

sists of nearly 150 uppertail coverts with

obstacle course of trees. Among flying birds the number of rectrices many small feathers are packed ratio the more quickly it will lose
— feather coat commonly accounts
as many "eyes" and is supported behind
ranges from 6 to 32, with the higher numbers occurring in larger birds closely together. heat. Because small birds tend to for only 5 to 10% of a bird's weight.
by the unadorned rectrices. Photo cour-
tesy of Isidor Jeklin/CLO. (Sidebar 2: Feather Facts). To make accurate references to individual Feather number also varies with have a higher surface-to-volume Thus, a chickadee weighing four-
a bird's need for insulation. For ex- ratio, they lose heat rapidly, and thus tenths of an ounce (10 g)—about as
feathers, ornithologists have developed a standardized numbering
ample, birds living in cold climates need more feathers for each unit of much as two quarters—would have
system (Fig. 3-7).
have more feathers in winter than body weight than does a larger bird. a feather coat weighing less than a
Bordering and overlying the rem iges and rectrices on both the
in summer. Wetmore (1936) found dollar bill (four-hundredths of an
upper and lower sides are rows of feathers called coverts, which pro- Size of Feathers ounce 11 g]). And yet, as light as they
that in winter White-throated Spar-
vide insulation, color, and pattern on the wing surface and, perhaps rows have about 2,500 contour Bigger birds not only have more are, a bird's feathers are still usually
most important, contribute to the streamlined shape of the wing and feathers, but in summer they have feathers, they have bigger feathers. 2 to 3 times heavier than its skeleton.
(Continued on p. 3.12) only 1,500—a 40% decrease. In Thus, if you find a feather on the ■
Cornell Laboratori1 of Ornithologq Handbook of Bird Biologq
3.12 George A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.13
tail. Just like aircraft, flying animals need
streamlining to reduce friction with the
air; streamlining greatly reduces the en-
ergy needed to fly.
Some contour feathers have an af-
terfeather, resembling the main feather
but in miniature, growing from the lower
shaft. Well-developed afterfeathers con-
tain a shaft and two vanes (Fig. 3 8a). -

Afterfeathers provide extra insulation

and are especially well developed in
grouse, many of which live in seasonally
cold or arctic regions. In the flightless
Australian Emus, the afterfeathers are as
large as the main feathers (Fig. 3 8g). -

These big, fluffy contour feathers help to

form a thick protective coat that is use-
ful in the dense brush of the Australian
scrublands. The feather coat is so tough that these birds can cross the Figure 3-9. Holy cow! I hope that new
Australian outback's sturdy four-foot-high sheep fences topped with hair replacement stuff works on feathers.

barbed wire simply by running fast, crashing into them, and somer-
saulting over. In the process, they leave behind a pile of feathers hang-
ing on the barbed wire (Fig. 3 9). It's quite a testimony to the protective
-

value of the feather coat—one hates to think what would happen to a

human who tried to cross such a fence by smashing into it!
Some contour feathers have become highly modified for special
functions (see Fig. 3-8). Among the most bizarre are those used in
courtship displays, such as the elaborate ornaments of the male birds-
of-paradise (Fig. 3 10). Motmots, nightjars, and other species have
-

odd feathers with a wirelike rachis for their displays (Figs. 3 8b, 3 11).
- -

Other modifications are more subtle. In most owls, for instance, the
leading edge of the first several primary feathers has a loose fringe, and
the dorsal surface of the inner vanes of most flight feathers has a soft
"pile" (Fig. 3 12). These modifications render the feather coat very
-

soft to the touch. More important, they allow owls to fly very quietly,
creating little noise even in the high-frequency range that their rodent
prey hear so well.
Other special contour feathers include the waxlike tips of some
wing and tail feathers of waxwings (see Ch. 7, Sidebar 5, Fig. A); the
curly feathers in the erectile crests of the Australian cockatoos (Fig. 3-
8i); and the stiff, strawlike crown feathers of the Black Crowned-Crane
Figure 3-8. Examples of Modified Contour Feathers: a: Body feather of a pheasant. It has a smaller afterfeather with all of the
of Africa (Fig. 3 13). Some birds, such as the American Woodcock and
-

barbs free and soft. b: One of the two long, central rectrices of a motmot (Momotidae) from the New World tropics. Along the
terminal half of the shaft the barbs have fallen away, leaving a racketlike tip. c: Rectrix of a Chimney Swift. The tip end is devoid
Common Snipe, have contour feathers modified to produce sounds (see
of barbs and spinelike. d: One of the shorter feathers in the "train" of the male Indian Peafowl. All of the barbs are free except Ch. 7, Sidebar 1, Figs. C and E).
near the tip, where they are hooked together to form a continuous surface for the colorful "eye." e: The plume from the back of Bristles are highly specialized contour feathers in which the rachis
an egret. The few barbs are little more than willowy filaments. h Breast feather of a turkey. The barbs in the vanes toward the tip is stiffened and lacks barbs along its outermost parts (Stettenheim 1 974).
gradually shorten, producing the truncated or squared-off effect. g: Body feather of an Emu. Its afterfeather is so similar in size and
Among the best-known bristles are rictal bristles, which project from
structure to the main feather that it is indistinguishable, thus forming a double feather. All of the barbs are free. h: Body feather
of an Ostrich. The many long, soft barbs with their countless barbules, unhooked and fuzzy, give the feather its characteristic the base of the beak in birds that catch insects, such as flycatchers, night-
fluffiness. i: Crest feather from the Sulphur-Crested Cockatoo of Australia and New Guinea. The curliness results partly from one jars, and some New World Warblers (Fig. 3 14a). Some ornithologists
-

side of the shaft being exceedingly flat. Drawing by Charles L. Ripper. have suggested that rictal bristles might funnel insects into the mouth,

Cornell Laboratory of Ornithology Handbook of Bird Biology

3.14 George A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.15

Figure 3-11. Modified Flight Feathers: a: Two extremely modified remiges adorn the male Standard-winged Nightjar, a small,
nighthawk-like bird from central Africa. The second primary on each wing features a broad vane toward the tip of a very slender
shaft. It is approximately 11 inches (28 cm) long, and extends well behind the other wing feathers. When flying in the twilight
with the shafts of the two feathers practically invisible and their terminal vanes flapping, the starling-sized bird looks as though it
were being pursued by two little bats. Drawing by Charles L. Ripper. b: Two extremely modified rectrices grace the unmistakable
male Marvelous Spatuletail, a hummingbird from the Andes of northern Peru.

Rachises
Pile on Dorsal
Surface of
Inner Vane
Outer
Vane

Figure 3-12. Features of Owl Feathers

that Produce Silent Flight: Owls achieve
very quiet flight with two specializations Fringe
of their feathers. First, a soft fringe on
the margin of the outer vane of the first Inner
two or three primary feathers softens the Vane
contact between the air and the leading
edge of the wing. Second, a velvety pile
is located on the dorsal surface of the in-
ner vanes of all remiges and, to a lesser
extent, the rectrices. This pile, a fur-like,
filamentous component of the barbs and
barbules, is very efficient at deadening Fringe
any scraping sound that may be made as
Pi le on Dorsal
the remiges slide against each other dur- Surface of
Figure 3-10. Display Feathers of Male Birds-of-paradise from New Guinea: a: Wallace's Standard wing. b: Greater Bird-of-par- ing flight. In addition to owls, Northern Inner Vane
adise. c: Blue Bird-of-paradise. d: King-of-Saxony Bird-of-paradise. e: Superb Bird-of-paradise. f: Magnificent Bird-of-paradise. Harriers exhibit this pile on their feathers
Note in b and c, the smoky effect of the long filamentous feathers; in c and f, the long, barbiess "wires;" in e, the erectile cape and and probably benefit greatly from silent
flightas they course or hover over mead- , 97
bib; and in d, the two extraordinarily long crown plumes, which have vanes on only one side, and which are so deeply scalloped
that they suggest a series of tiny pennants. Drawing by N. Tolson. ows in pursuit of rodents.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

3.16 George A. Clark, Jr. Chapter 3—Form and Function: The External Bird 3.17
but little supporting data exist. In Willow Natal downs are present only around the time of hatching. They
Flycatchers, Conover and Miller (1980) are prominent on newly hatched chickens and ducklings, giving these
found that experimentally taping down or birds their soft, fluffy look. These first feathers characteristically lack
removing the bristles did not affect the birds' barbules on the outer portions of the outermost barbs and are prob-
success in capturing insects. By using a wind ably important for insulation, camouflage, and social behavior, as
tunnel, however, these researchers demon- Rictal
discussed below. Natal downs arise from the same follicles that later
Bristles
strated that bristles protect the eyes from fly- produce contour feathers, and are typically carried on the tips of the Common Poorwill
ing insects and other debris. They released growing contour feathers. In contrast, body downs of adults arise from
particles in front of the mouths of Willow follicles that produce only down feathers. a
Flycatchers and found that more particles The old saying "naked as a jay bird" is quite correct for young
struck the eyes of birds whose rictal bristles jays, such as the Blue Jay and Steller's Jay, which have no natal downs
had been removed. Rictal bristles are highly at hatching. The newly hatched young of many other birds, including Rictal Bristle of
American Robin
developed among certain species (such as most passerines, have a much-reduced natal down. Clues from em-
puffbirds—Neotropical relatives of king- bryonic development, however, indicate that the ancestors of these
fishers) that regularly capture scaly moths, birds had a complete coat of natal down. The less down a new nestling
butterflies, and other large, noxious insects; has, the more easily it is warmed by its parent. Therefore, scientists hy-
apparently the bristles protect the face and pothesize that naked chicks save energy both by not producing down
eyes of these birds from their prey (John W. and by quickly absorbing their parents' body heat, which may allow
Fitzpatrick, personal communication). Ric- them to develop more quickly. Chicks that leave the nest promptly
tal bristles also may help birds detect move- after hatching, such as ducks and pheasants, must carry their own
ments of prey held in the beak, functioning insulation from the moment of hatching, and so have kept their down b
Down Feather
like the whiskers of some mammals. coats (see Fig. 8-113).
Many kinds of young that cannot fly for weeks after hatching
Down Feathers have an insulating cover of downy feathers that lasts for much of the
Down feathers are fluffy and soft, typ- flightless period—during which the young grow enormously. Presum-
ically lacking a rachis. If present, the rachis ably, it is most efficient to postpone development of contour feathers
is always shorter than the longest barbs. Be- until the bird requires them for flight. Hawks, for example, have a
cause the barbules lack hooks, each flexible prolonged downy cover in early life. Their coat of natal down is fol-
barb can wave about independently, giving lowed by a second downy plumage, consisting of body downs, which
the feathers their characteristic "downy" transforms the appearance of the young (Fig. 3-15). The gradual
appearance (Fig. 3-14b). Down feathers replacement of natal downs with darker body downs, and eventually
Figure 3-13. Modified Contour Feath- are excellent, lightweight insulators because the barbs and barbules with juvenal contour feathers, makes these hawk nestlings look like
ers of Black Crowned-Crane: The form a loose tangle of air pockets. clean, white snowmen, growing increasingly dirty and angular in the
distinctive crown of this large African
Down feathers include the body downs and the natal downs. winter's afternoon sun.
bird is formed from stiffened, strawlike
contour feathers. Photo courtesy of Body downs, the down feathers of adults, are most common in water
Michelle Burgess/CLO. birds such as penguins, loons, petrels, auks, geese, and ducks, as well Semiplumes
as in hawks—all of whom undoubtedly benefit from the extra thermal The semiplumes (Fig. 3-14c) occur in a continuum of forms be-
insulation. Some birds, notably the woodpeckers, generally lack body tween down and contour feathers. Unlike contour feathers, the bar-
downs. bules lack hooks and thus the barbs do not cling together as a vane,
Many female waterfowl pluck body downs from their bellies to but unlike down feathers, the rachis is longer than the longest barb.
line their nests. Of these, the mostfamous is the Common Eider (see Fig. They lie at the edges of the contour feather tracts, sometimes visible,
4-124a). On islands off coastal Norway, people collect the down from sometimes hidden beneath the contour feathers. Semiplumes provide
nests during incubation and sell it. The harvesters avoid harming the insulation and help maintain the streamlined form in the overlying
birds and leave enough down so that the birds will come back to nest feathers, functioning much like tissue paper stuffed into a pair of good
each summer. Some eiders nest under shelters set up by the harvesters, shoes that are not being worn.
and a few even nest under the residents' houses. Eider down clothing Figure 3-14. Specialized Feathers:
and bedding is notoriously expensive because accumulating just one Filoplumes a: Rictal bristles on a Common Poorwill
and from an American Robin. b: Down
pound requires down from 35 to 40 nests, the down must be gathered Scattered among, and usually hidden by, the contour feathers
Feather. c: Semiplume. d: Filoplume.
by hand, and the supply is limited. Nevertheless, eiders provide the of most kinds of birds are feathers of a third major type known as filo- Drawings b, c, and d by Charles L.
highest quality down used in jackets and sleeping bags. plumes. Hairlike but relatively stiff, filoplumes are simple structures—a Ripper.

Cornell Laboratorq of Ornithologg Handbook of Bird Biologq

3.18 George A. Clark Jr. Chapter 3 — Form and Function: The External Bird 3.19

rachis, usually bare, with barbs, if any, only on its bill, smoothing the barbs so that they will
the tip (Fig. 3-14d). These are the "hairs" that lock together. The bird fluffs the feathers in
you see on a plucked supermarket chicken. the section of the body it is preening and
Unlike contour feathers and body downs, filo- turns and twists in a variety of movements
plumes lack feather muscles.They do, however, which—if one follows them closely—are all
have sensory receptors in the skin next to their quite stereotyped, about the same for each
follicles, which monitor movement within part of the body and each feather every time.
the feather coat (Necker 1985). Why are such Preening keeps the feathers neat, preserving
receptors necessary? Fully grown feathers are their streamlining and insulating effects as
dead structures analogous to human hair and well as their color pattern. Preening also
fingernails; therefore, much of a bird's body is removes external parasites (ectoparasites),
covered by a flexible shell of lifeless feathers. some of which are described below.
To monitor goings-on in this feather coat, the Birds preen even without sensory stim-
bird depends partly on filoplume movements. ulation from the region being preened, as
Birds also have sensory receptors in the skin shown by experiments in which severing
away from the filoplumes, so they receive sensory nerves from certain skin areas did
several kinds of tactile information on events not eliminate preening of those areas (Delius
inside the feather shell. Birds presumably use 1988). Thus, preening and perhaps other
this information to monitor feather positions grooming behaviors are practiced even in
(Brown and Fedde 1993) and to detect changes the absence of a "tickle" or other stimula-
of the type that might be caused by wind or body tion of the skin. The advantage of this kind
movements. Much remains to be learned about of unstimulated preening may be that the
the sensory and neural processes involved in bird routinely cleans and sorts through its
monitoring of this type. feathers, removing ectoparasites and other
disturbances in the feather coat before they
Figure 3-15. Nestling Red-tailed Hawk Powder Downs become problematic, thereby improving the
in Second Coat of Down: In hawks, the Perhaps the strangest of all feathers are the powder downs. They coat's overall sanitation and health.
natal down is followed by a coat of body
are never molted, but grow continually, disintegrating at their tips to Although researchers have notexamined
down that insulates them during much of
their long nestling stage. Photo courtesy produce a fine powder something like talcum powder. The powder closely the seasonal frequency of grooming behaviors for many birds, Figure 3-17. American Oystercatcher
of Jim Weaver/CLO. permeates the plumage, possibly helping to waterproof and prevent temperate-zone birds do appear to groom less in the colder months. Preening: When preening, a bird grasps
a feather-near its base, then nibbles down
staining of the feathers, although its functions are not yet clearly un- During short winter days, small birds must spend much of their time
the shaft toward the tip, removing stale
derstood. In form, powder downs may appear like somewhat fluffy foraging to get enough to eat, so they have less time to groom. Fur- oil and dirt. Photo by Brian Kenney.
contour feathers, or more like body downs (Fig. 3-16).They occur thermore, because ectoparasitic insects and mites are cold-blooded
only in certain taxonomic groups, such as herons and pigeons, (ectothermic), they are presumably less likely to move onto or between
and may be scattered throughout the body downs, or clustered in hosts when it's cold. We would expect birds in tropical regions with
patches (Lucas and Stettenheim 1972). little seasonal change to have more uniform grooming patterns, but
this apparently has not been investigated.
As you might expect, birds groom more often when they are molt-
Care of Feathers ing. Also, birds that have spent the night incubating eggs (for example,
■ Feathers are essential to the health and survival of birds, so birds female passerines) often engage in a prolonged bout of preening just
spend a good deal of time caring for them. Because feathers are dead after leaving the nest for the first time each morning. If you observe this
structures, they have no active circulatory system to maintain them behavior, you know you're watching an incubating bird.
from the inside. Therefore, a bird provides all their care from the out- Certain kinds of birds with strong social ties, such as parrots
side, by preening, water-bathing, dust-bathing, sunning, or anting. and crows, are well known for their allopreening, in which one bird
preens another. Birds often direct their allopreening to the back of the
neck and other areas that the recipient cannot reach with its own bill.
Preening Allopreening presumably helps to remove ectoparasites, to keep the
Figure 3-16. Typical Powder Down
Feather from a Pigeon: Adapted from In preening, a bird grasps a feather near its base, then nibbles plumage in order, and to establish and enhance social bonds between
Lucas and Stettenheim (1972, p. 337, along the shaft toward the tip with a quivering motion (Fig. 3-17), birds. Allopreening also serves as an indication of dominance-subor-
Fig. 227 C). removing stale oil and dirt. The bird may also draw the feather through dinance relationships, as subordinate individuals offer themselves to

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

3.20 George A. Clark Jr. Chapter 3— Form and Function: The External Bird 3.21
be preened by dominant individuals. Allopreening may even occur one of the two techniques, but some birds, such
between different species. For example, Red-winged Blackbirds oc- as Blue Jays, use both methods. Why
casionally al lopreen Brown-headed Cowbirds. Why these birds al lo- different birds use different head- - -
preen is not clearly understood, but the behavior appears to function scratching methods is not known,
more in aggression and dominance interactions between these species so a good research opportunity
than in feather care (Post and Wiley 1992). for a dedicated birder exists a
here. Birds that can't scratch
their heads, either through ac-
Oiling cidental injuries or experimental Mr"
For many kinds of birds, preening includes using the bill to
use of neck collars, tend to have
ito :sv■lik0 spread fatty secretions from the oil gland (also called the uro- Figure 3-19. Head-Scratching Meth-
more ectoparasites living on their
pygial gland or preen gland) over their feathers. The oil gland, ods: Birds scratch their heads either by
heads (Clayton 1991). (a) bringing the leg under the wing, as in
one of the few glands in bird skin, is located on the rump im-
doves, or (b) over the wing, as in many
mediately in front of the rectrices. On a hand-held songbird tyrannid flycatchers. Most species use
ti
you can see the small pimple-like gland by blowing gently in Bathing only one of the two techniques.
this region to part the feathers (Fig. 3-18). Another feather maintenance
Researchers have suggested that oil gland secretions behavior is bathing. Birds may bathe in
might waterproof the feathers, but there is no evidence for water, snow, or even dust.
this. When the oil glands of ducks were removed, their feath- In water, the manner of bathing tends to be
ers did not lose their waterproofing ability. Instead, the results quite consistent within various families. Swal lows
indicated that the secretion is a conditioner that keeps the outer and swifts drop down repeatedly and skim the sur-
surface of the skin supple and prevents feathers and scales from face of a lake, pond, or stream to wet their feathers.
becoming brittle and breaking prematurely (Jacob and Ziswi ler 1982). Terns plunge into the water from the air, and king-
Oil Gland
Actual waterproofing of feathers seems to result primarily from the m i- fishers, from an overhanging branch. Many forest birds
crostructural arrangement of the barbs and barbules, which provide bathe in rainwater or dew that has collected on leaves.
an evenly spaced surface of ridges with narrow gaps between them Most songbirds such as American Robins and European Starlings stand
that sheds water very effectively. Thus, spreading oil gland secretion or squat in shallow puddles, vigorously ruffling the feathers and shak-
seems to facilitate waterproofing only indirectly; feathers provide the ing both wings, creating a veritable shower. Hummingbirds sometimes
waterproofing, but oil gland secretions make feathers last longer. dart in and out and swing back and forth in the spray from a garden
Researchers also suspect that the secretions help both to con- hose on a hot day. Common Nighthawks may bathe on the wing during
trol the growth of undesirable fungi on the feathers and to promote intense downpours, alternately flapping rapidly and ruffling the body
Figure 3-18. Oil Gland of Hand-Held
Blue Jay: By carefully spreading the the growth of favorable fungi that chemically inhibit lice from living feathers amid the deluge.
feathers, and gently blowing on the rump among the feathers. Another suggestion is that, for some species, the A thoroughly wet bird can be quite helpless, and many are unable
area of a hand-held bird, you can see the secretion's strong odor might help deter mammalian predators. The to fly efficiently, making them particularly vulnerable to cats and other
small pimple-like oil gland (also known
cavity-nesting hoopoes and woodhoopoes have particularly noxious predators. Because birds must dry as soon as possible, all have special
as the preen gland or uropygial gland).
Secretions from the gland are used in uropygial odors, making them the bird equivalents of skunks.The birds drying movements. After bathing, a bird typically shakes its body to
preening to keep the skin supple and to cannot spray their secretions, however, so they are repulsive only at throw off extra water, whirs the wings, fluffs its feathers to promote
prevent the feathers and scales from be- close range. It also has been proposed that the oil gland secretions, evaporation, and begins to preen and scratch its head. Similar body
coming brittle.
when exposed to sunlight and then consumed in preening, might be a motions are used in snow. During hot weather, bathing in water might
source of vitamin D for birds, but recent experiments failed to confirm help a bird's body temperature to stay down.
any role for these secretions in vitamin D production. Dust-bathing is most often reported for species that spend much
time on the ground, such as House Sparrows and Wild Turkeys. This
behavior is not a substitute for water bathing; several families of birds
Head-Scratching
do both. In dust-bathing (Fig. 3-20), a bird usually squats or lies down
To oil the feathers that it cannot reach with its bill—those on the
in a dusty area, often a dirt road, and drives fine particles through its
head, for instance—the bird rubs oil on its feet with its bill and then
plumage by rolling its body, fluffing its feathers, wiping with its head
scratches the head and other areas. Birds also scratch their heads
and bill, or even, in the manner of the Greater Rhea of South America,
when not applying secretions. They use two techniques, bringing the
picking up dust and throwing it over its body. The bird removes some
foot forward either under the wing, as in doves, or over the wing, as
of the dust by violent shaking, but often much dust remains, staining
in many tyrann id flycatchers (Fig. 3-19). Vi rtual ly all species use only
the bird's plumage the color of the soil.

Cornell Laboratorq of Ornitholos Handbook of Bird Biolos

 r

3.22 George A. Clark, jr. Chapter 3 — Form and Function: The External Bird 3.23
Presumably all kinds of bathing can
help to control ectoparasites, but this has
not been studied experimentally. Ectopara-
sites breathe through small holes in their
outer skeletons, which are vulnerable to
clogging with dust. Comparing birds with
and without opportunities for dust-bath-
ing has shown that dust-bathing helps to
remove substances coating the feathers,
such as old oil gland secretions.

SunninB
Sunning may also help maintain the
feathers (Simmons 1986). Sunning birds
adopt quite varied and extremely unusual
postures. Commonly the bird's feathers are
fluffed, the tail is spread againstthe ground,
Figure 3-20. Wild Turkey Dust-Bathing: and a wing is extended on at least one side, sometimes both. Sunning
Lying in the dust, a dust-bathing bird rolls birds frequently lie on the ground in a warm place, with the head
and wiggles its body to work the dirt into
lowered and tipped to the side, remaining nearly motionless for many
its feathers, tossing dust up over its back
using its bill or wings. Photo by Sandy seconds or minutes. Although sunning has been described for numer-
Podulka. ous species of birds, few experimental studies have tested its functions.
Suggested purposes include conditioning the feathers by keeping them
supple through limited heating; harming or repositioning ectopara-
sites; and saving energy by taking up solar heat through the feather
coat. The possibility that birds might sun simply because it feels good
is difficult to test.
A number of large birds, including cormorants, anhingas, pel-
up an ant or other chemically potent object, such as a millipede, and Figure 3-21. Anhinga Drying Wings: See
icans, storks, and New World vultures, stand for many moments with text for explanation. Photo courtesy of
deliberately rubs it in the feathers. Objects rubbed in the feathers dur-
their wings extended to the side in a pose known as the spread wing - Isidor Jeklin/CLO.
ing "anting" (in its broad sense) include insects, plant material, and
posture (Fig. 3 21). Although cormorants and anhingas are closely
-

even cigarette butts. Ornithologists presume that the

related, they use the spread-wing postures in slightly different ways.
rubbed materials contain chemicals that are nox-
Both types of birds prey on fish, but the feathers of anhingas are more
ious to ectoparasites. Because birds sometimes
permeable to water.Th is reduces the birds' buoyancy and al lows them to
eat the arthropods used in anting, it's possible
swim for long periods with just their necks and heads above the surface.
that the process also helps rid a potential
Both cormorants and anhingas use the spread-wing posture to dry their
food item of its most noxious chemical
feathers after swimming, but anhingas take longer to dry because their
protection.
permeable feathers take up extra water. Furthermore, anhingas generate
less heat internally, and in cooler areas, they may use the spread-wing
posture to absorb sunlight. The difference in anhinga and cormorant Ectoparasites . —
energy production is reflected in their geographic distributions—cor- Controlling ecto-
morants can live in much cooler regions than can anhingas. parasites is important to a Figure 3-22. Blue Jay Passively Anting:
bird's fitness. Although car- In passive anting, a bird squats among a
rying a few ectoparasites may have little group of ants with its wing (and some-
Antin8 times tail) feathers spread, and lets the
effect on a bird, a heavy ectoparasite load can impair a bird's health
Like bathing and sunning, anting is believed to help control ants run in and out of the feathers and
and reproduction. Scientists believe that many feather-maintenance
ectoparasites. In passive anting a bird simply stations itself among a over its body. Anting is thought to help
behaviors evolved to control these parasites, either physically or chem- in the control of ectoparasites, but is not
swarm of ants, permitting them to run all over its body and move in
ically. Many birds, including hawks, House Sparrows, and European well understood. Drawing by Charles L.
and out among the feathers (Fig. 3 22). In active anting a bird picks
-

Starlings, add pieces of fresh plants to their nests after they complete Ripper.

Cornell Laboratorq of Ornitholo9i4 Handbook of Bird Biologq

3.24 George A. Clark, Jr, Chapter 3 — Form and Function: The External Bird 3.25

construction. Some of these plants either produce chemicals noxious a. Hippoboscid Fly
to ectoparasites, or have antibacterial effects. Clark and Mason (1 985;
1988) found that at least one bird, the European Starling, appears to
choose plants specifically for these properties.
Birds are host to many kinds of bloodsucking external parasites,
especially flies, ticks, fleas, lice, and mites.The habits and life histories
of these parasites are fascinating, although in many cases they remain
poorly studied. c. Bird Louse

Many ground-nesting birds carry the same species of ticks found

on mammals in the same habitat; the Ruffed Grouse, for example,
is often heavily infested with rabbit ticks. In North America certain
birds, especially those that frequent the ground, may carry the ticks
that sometimes contain bacteria that produce Lyme disease, a serious
human health problem.
Another group of ectoparasites that feeds on the blood of mature
birds is the hippoboscid flies, which superficially resemble house flies
but are vertically flattened so they can slip readily between the contour
feathers (Fig. 3 23a). Nestlings, especially those of Tree Swallows,
-

bluebirds, and other cavity nesters, often are infested with the large
b. Blowfly Larvae on Nestling Eastern Bluebird
larvae of another type of fly called a blowfly, which feed on their blood
(Fig. 3 23b).
-
.".........., ....::?.:

Bird lice of the order Mal lophaga feed on feathers and the surface '
...'
• .•••

layers of the skin (Fig. 3 23c). Quite harmless to humans, a few species
-
•-- ,ote +.... .......•,
tAtot..""-• _F..'
do live on mammals, feeding on hair. Many are highly host-specific;
that is, a given species of louse lives only on members of a singlefamily
or genus of birds. Like the hippoboscid flies, most bird lice are flat, and
live among the feathers. Most species are adapted for life on specific d. Feather Mite
portions of a bird's plumage, rarely venturing away from the head,
neck, body plumage, flight feathers, or whatever area the louse calls
home. One very specialized genus of lice l ives in the throat pouches
of pelicans and cormorants.
Several kinds of mites occur on birds, including itch-mites, nasal Blowfly
mites, and red mites. The most specialized are tiny feather mites that Larvae

live among, on, or even within the feathers, feeding on the feather itself
or on the skin (Fig. 3 23d). Some are so specialized that they live only
-

in certain areas of plumage on certain species; one mite species, for

example, lives only on the white areas of the rem iges of the Eurasian
Nightjar.
Feathers provide some protection against nonparasitic biting
insects, such as mosquitoes. Mosquitoes can often get a blood meal,
however, by biting where the feathers are short, such as around the
eyelid, base of the beak, or on the legs. Mosquitoes can transmit en-
cephalitis viruses to birds, and they sometimes carry these viruses from
birds to people. In humans, the disease can be fatal; fortunately, it is
uncommon. Different kinds of birds differ in their resistance to biting
Figure 3-23. Avian Ectoparasites: a: Hippoboscid fly. Note extremely flattened body that allows it to crawl easily between contour
mosquitoes. Active birds such as White Ibises move constantly and so
feathers. Hippoboscids, also called "feather-flies," are bloodsuckers that live on many different species of birds, especially birds
are less likely to be bitten than relatively sluggish birds such as Black- of prey. b: Nestling Eastern Bluebird with two attached blowfly larvae. These are particularly common bloodsuckers on nestlings
crowned Night Herons. Most insect bites, however, occur at night of cavity-nesting birds. c: Bird louse (Order Mal lophaga) from a turkey. These ectoparasites are also flattened, and they feed on
while birds are roosting. bird feathers and skin. d: Feather mite from a passerine bird. Mites live among, on, or within the feathers, feeding on feathers and
skin. Illustrations are not drawn to scale. Drawings c and d by Charles L. Ripper.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 r
3.26 George A. Clark, jr. Chapter 3 — Form and Function: The External Bird 3.27

Development of Feathers Feather Papilla

■ The skin of a bird, like our own, consists of two major parts, the in- a
ner dermis and the outer epidermis. Throughout life, the epidermis
continually renews itself by the growth of new cells in its lower layers
Epidermis
and the hardening, drying, and sloughing off of the outer layers. During
Dermis
embryonic development, the surface of the skin is covered with little
bumps known as papillae (Fig. 3-24a) arranged in the eventual pattern
of the bird's feathers. Each papilla is an outgrowth of dermis forming
a core beneath a rapidly multiplying layer of epidermal cells. As the
Feather
proliferation of epidermal cells continues, outstripping the dermis, the
Papilla Developing
epidermis doubles inward around the papilla, forming an epiderm is- Feather
Feather
Sheath
I ined pit, the follicle (Fig. 3-24b). From each follicle a succession of
b
feathers is produced by the bird during its lifetime.
As the epidermal cells multiply, the papilla elongates into a cone.
The outer cells harden, fuse, and form an epidermal collar that sur-
Follicle
rounds the dermal portion of the original papilla (Fig. 3-24c). Most
conspicuous structures in the fully formed feather originate in this
epidermal col lar.The inner layers of the collar continue to grow toward
the center, forming a tubular series of ridges that eventually solidify to Epidermis
become the rachis and barbs of the feather. Because the feather grows
from its base outward, the outer part is always the oldest, as in a hu-
man fingernail.
The dermal portion of the papilla remains in the follicle for the Developing
Blood Vessels
life of the bird. While each feather is developing, blood vessels extend Barbs

outward from the papilla into the feather shaft, providing a temporary
source of nourishmentfor the growing feather. When the feather is fully
formed, the blood supply is cut off as the vessels are resorbed into the Epidermal
Natal
papilla through a hole at the very end of the calamus. On large feathers, Collar
Down
you can see this hole with the naked eye, although it appears more as
a depression than a hole. d
A growing feather is surrounded by a thin feather sheath, which
acts somewhat like a mailing tube (Fig. 3-24d). When the sheath
breaks open, the feather vanes unfurl from the tubular packing into
the broad, mature feather. The unfurling occurs slowly over many days. Unfolding
Barbs
Packaging feathers in sheaths permits them to grow much more densely
than they could if each feather somehow emerged fully unfolded di-
rectly from the skin.
Growing feathers can be recognized by the intact sheaths, which Juvenal
Feather Sheath Feather
are typically gray or bluish, and look I ike the fat tips of knitting needles
sticking out of a bird's skin (Fig. 3-25). Before the sheaths open, these
growing feathers are termed pin feathers. Look for a pin feather on
a supermarket chicken, and break it open. Notice that the material
inside is soft and moist. This is the developing feather; on a live bird, Figure 3-24. Development of a Feather: a: The skin with a feather papilla beginning to form. b: As epidermal cells multiply more
the cells would be alive and multiplying. As the feather grows, its cells quickly than dermal cells, the epidermis folds inward around the papilla, forming an epidermis-lined pit, the follicle. c: As epi-
dermal cells continue to multiply, the papilla elongates to form a cone, or' pin feather"The dermis remains as the dermal papilla
eventually die and become hardened as the sheath splits and falls
at the base of the developing feather, and is surrounded by a collar of epidermal cells that multiply to produce most structures in
away. In many cases the outer (distal) portion of the sheath dies and the developing feather, including the thin feather sheath, and a series of doughnut-shaped ridges that eventually form the barbs
breaks open, while growth continues in the parts of the feather still in and rachis. The growing feather is nourished via blood vessels that extend into the shaft. d: The feather sheath gradually splits
the sheath. open from the tip and falls away, allowing the feather vanes to begin unfurling. In this case a juvenal feather has developed and
carries out the old natal down on its tip. Drawings a, b, and d by Charles L. Ripper.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

3.28 George A. Clark Jr. Chapter 3 — Form and Function: The External Bird 3.29
When feather development is completed, During a typical molt, growth of a new feather push-
the cells cease to multiply. Yet the original es the old one from its follicle. In juvenile birds, each
papilla, with its dermal core and epidermal natal down feather may be physically attached to the tip
covering, waits deep within the follicle, ready of its successor, the juvenal feather, which is the first true
to restart the process when it is time for a new contour feather; thus the new juvenal feather carries the
feather. Then a new collar, growing upward old natal down out as it grows (see Fig. 3-24d). (Note
Pin Feathers
and outward, will push out the old feather. that the term "juvenal" is applied to feathers and plum-
The hardening of a maturing feather is ages, whereas "juvenile" designates a young bird; the two
caused by formation of the protein keratin, a words often are confused.)The strength of the connection
metabolic product of the dying cells. Indeed, between the downs and the contour feathers varies great-
keratin is the primary structural component ly. In some birds, the down is so delicate that it breaks at
of mature feathers. Originally produced the merest touch, and finding museum specimens that
inside cells, the keratin from one cell may show the connection can be difficult—the down has bro-
bond strongly with the keratin in adjoining ken off either in the nest or during the preparation of the
cells, developing over time into such familiar specimen. In other birds, such as the European Starling and American Figure 3-26. Fledgling Eastern Bluebird:
structures as scales, claws, and feathers. Avian Robin, the connection is very strong, and you can often see the fluffy Note wispy down feathers still attached
keratins differ in their amino acid sequences to the head of this newly fledged bird.
natal downs still attached to the heads of juveniles who have recently
Photo courtesy of the North American
from all other known keratins, including those left their nests (Fig. 3 26).
-
Bluebird Society.
in the scales of living reptiles such as lizards Because producing new feathers takes a lot of energy, birds gener-
and crocodiles, and in the nails and hair of hu- ally molt when they are not engaged in other energetically demanding
mans. Therefore, the evolution of feathers must activities, such as feeding young or migrating. The molting process also
Figure 3-25. Nestling in Pin-Feather have involved major evolutionary innovations reduces flight efficiency, lowering a bird's ability to evade predators
Stage: With each developing feather (Brush 1993). Keratins are not readily digested by any of the chemicals and procure food. Therefore, long-distance migrants may molt before
still completely enclosed in its sheath, ordinarily found in the digestive tracts of animals, so feathers last lon- they migrate, after they migrate, or partly before and partly after. In the
a young bird in the pin-feather stage
ger than most other discarded animal parts. But we are not chest-deep temperate zone, adults of many species of North American songbirds
looks something like a small porcupine
or pin-cushion.
in loose feathers, even though birds drop billions of feathers annually molt during late summer, when they are no longer caring for young but
during molts, so their keratin is broken down somehow. Researchers before fal I migration. Because temperatures are often still warm and en-
assume that bacteria and fungi are responsible, but almost nothing is ergy demands are relatively low, this is a good time to molt. We humans
known about the specific organisms that digest feathers in nature. notice this molt when some of our more colorful birds acquire their
Many environmental factors can influence the development of subdued winter tones: male Scarlet Tanagers become yellow-green;
feather structure. For example, nutritional deficiencies can lead to the bright red head of male Western Tanagers becomes yellow; and
minor changes in barbule structure (Murphy et al. 1989). This infor- many striking male warblers, such as the Chestnut-sided Warbler, Yel-
mation is useful to researchers in the field. For species that periodically low-rumped Warbler, Magnolia Warbler, and Common Yellowthroat,
can be recaptured, researchers can pluck feathers and then, when the lose their bold spring patterns.
bird is captured again, examine the structure of the regrown feather to
determine the bird's nutritional state (Grubb 1995).
Annual Molt and Wear Cycles
Birds vary greatly from species to species in the number, type,
Molts and Plumages and timing of their molts. Some birds, such as American Crows, un-
dergo only one complete molt per year. Mature crows look much the
■ A feather is a dead structure; it cannot be repaired if it becomes same before and after this annual molt; the new feathers are less worn
worn or broken. Yet the feathers of most birds, especially those living
than the old ones, but this is evident only at close quarters. Many
in open, sandy, or grassy areas, become brittle, faded, and frayed in
other North American passerines, such as the American Goldfinch,
just a few months. To restore their feather coats and produce feathers
undergo a complete molt following the breeding season, and then
appropriate to their age and sex, birds regularly must grow new sets of
a partial molt in winter or spring. This partial molt includes all the
feathers. Replacing all or part of the feather coat is called molting. In a
contour feathers except those of the wings and tail, and provides
complete molt, all feathers are replaced; in a partial molt, only some
brighter colors for the breeding season. Only a few species are known
feathers are replaced. If an entire feather is lost between molts, it grows
to have two complete molts per year. Most of these live in harsh hab-
back right away. Damaged, broken, or worn feathers are replaced only
itats that quickly wear out feathers. Examples include Marsh Wrens
during the regular molt cycle, however.
and Bobolinks, which move within abrasive vegetation, and African

Cornell Laboratoru of Omithologq Handbook of Bird BioloBq

3.30 George A. Clark Jr. Chapter 3—Form and Function: The External Bird 3.31
larks that dwell in windy, sandy deserts.
Some passerine species have only one complete molt
per year, but nevertheless change their appearance seasonally
as a resu It of wear on the feathers. For example, after they molt
in mid to late summer, European Starlings have prominent
buff-colored tips on their belly and breastfeathers. By the ti me
they are ready to breed the following spring, the buff-colored
tips have worn off and the underparts are dark (Fig. 3 27). -

Similarly, adult male Purple Finches have dull red heads after
a
their annual molt in late summer, but feather wear slowly
removes the outer barbules, revealing the bright, pink-red
color below. And male Northern Cardinals in fresh fall plum-
age have a grayish cast, especially on the back, which wears
away as winter progresses. By late spring the cardinal is a Adult Breeding
(Alternate)
photogenic bright red, yet has undergone no intervening
molt.

Third Winter
Suhadult and Definitive Plumages (Third Basic)
Young birds also molt; they must replace their feather
coats as they mature. As young birds grow, the small feathers
b produced early in life, such as natal downs, are no longer
large enough or able to carry out the functions necessary for
an older bird. So, young birds pass through one or more sub-
adult (immature) plumages, eventually reaching the definitive
plumages, those of a mature bird. Second Winter
The ages at which birds reach definitive plumage vary. (Second Basic)
Many songbirds take less than a year; thus, a one-year-old
Song or Chipping sparrow may be indistinguishable from
an older one. One-year-old Red-winged Blackbirds, on the
other hand, do not have the brilliant, crisply defined, red-and-
First Winter
yellow epaulettes of older birds; their "shoulders" (actually (First Basic)
located at the wrist, or bend of the wing) are duller, usually
more of an orange-red and buff, with the buff portion often
blurred and marked with black.
In general, long-lived species such as large raptors, gulls,
and pelagic seabirds retain their subadult plumages for a rel-
atively longer period of time. For example, the familiar de-
finitive plumage of the Bald Eagle is not reached until a bird's
fourth or fifth year. Before acquiring a clear white head and
Juvenal
Figure 3-27. The Effect of Wear on tail, young birds go through several subadult plumages that are much Natal Down
European Starling Feathers: a: After less tidy, with a blotchy or mottled brown-and-white appearance.
the fall molt, newly grown European Many gulls also take several years to reach definitive plumage; in
Starling body feathers have pointed,
buff-colored tips. b: The buffy tips of the
a "three-year gull" such as the Ring-billed Gull, birders can distin-
European Starling's fall feathers give it guish first-winter, second-winter, and adult birds. Four-year gulls, such
a mottled appearance. c: By spring, the as the Herring, Great Black-backed, California, and Western gulls,
pointed, buffy feather tips have worn off, sport at least four different plumages on their way to maturity (Fig.
and the starling is a glossy black. Photos
3 28). The male Steller's Eider acquires his definitive plumage in his
-

a and b courtesy of Carrol Henderson. Figure 3-28. Complete Plumage Series of the Herring Gull: Some birds take more than one year to reach their definitive adult
Photo c by Marie Read. third fall; the males of the larger Common Eider and the King Eider, in plumage. After shedding its natal down, the Herring Gull passes through four different subadult plumages before reaching the
their fourth fall. Slowly maturing birds such as albatrosses may take as familiar white and gray definitive plumage of the adult—at four years of age!

Cornell Laboratorq of Ornithologu Handbook of Bird Biologu

3.32 George A. Clark Jr. Chapter 3 — Form and Function: The External Bird 3.33
long as seven or eight years to reach their definitive plumage. Given women's hats—a practice no longer fashionable and now banned
a choice, many birds such as gulls select mates in definitive plumage. in many places. In New Guinea, for example, killing male birds-of-
Sometimes, however, birds in subadult plumage do get a chance to paradise in their spectacular definitive plumages (see Fig. 3-10) was
breed. Breeding by subadults occurs principally among species with so extensive that these males were nearly extirpated from accessible
relatively short life spans, or when birds in definitive plumage are in areas. Ordinarily, females do not mate with males in the duller subadult
short supply. plumages, but they had to when males in definitive plumage became in
In some species, one sex remains in subadult plumage for longer short supply. The delayed plumage maturation of young males therefore
than the other, a situation termed delayed plumage maturation. The proved fortuitous; otherwise, the feather trade might have completely
male American Redstart, for instance, does not wear his orange-and- wiped out some of the showiest bird species in the world.
black definitive breeding plumage until his second breeding season;
his first breeding plumage is nearly identical to that of the adult female,
who has yellowish patches, and who acquires her definitive plumage
Plumage Naming Siptems
by her first breeding season. However, at least some male redstarts In its broadest sense, a plumage is a bird's entire feather coat; thus,
breed at one year of age, despite their subadult plumage. Why plum- you might say, "The plumage of theAmerican Robin is orange and gray."
age maturation is delayed in this species is not known (Morse 1 989); Some authorities, however, use the word to designate the set of feathers
the trait is not shared by most other New World warblers. produced in a particular molt. In this usage, after a partial molt, a bird
How delayed plumage maturation evolved, and the advantages simultaneously wears parts of two different plumages. In this chapter
it brings, is a hot topic of research among ornithologists. A number of we will use the former definition and refer to the bird's entire feather
hypotheses have been proposed to explain why one sex (usually the coat as its plumage.
male) might remain in subadult plumage longer than the other. The Historically, the common practice was to name plumages for the
"female mimicry" hypothesis (Rohwer et al . 1980) suggests that during presumed presence or absence of breeding activity at the time the bird
the breeding season, subadult males may be able to fool adult males by wore the particular plumage. Thus, in spring and summer birds were
mimicking females. Thus disguised, the subadults may be able to de- said to be in nuptial (breeding) plumage, and in fall and winter, in
fend their own territories or may gain access to adult territories, thereby postnuptial or winter plumage. This system was somewhat misleading,
procuring more food resources, or even mating with the adult female however, because different plumages are not necessarily linked with
while her mate is away. In contrast, the "status signalling" hypothesis reproductive activities or seasons of the year. Among birds in the tropics,
(McDonald 1989) suggests that subadult plumages accurately convey where there is no real winter, "winter" plumages may be correlated with
a male's younger age to adults, thus decreasing the amount of aggres- the wet season, a time when few birds breed. Also, some seabirds breed
sion it receives from older, more dominant, males. This hypothesis is either less or more often than once a year, foregoing an annual cycle.
most relevantto species, such as Long-tailed Manakins (see Fig. 6 47),
-
For these reasons, the Humphrey-Parkes nomenclature has come
with well-developed age hierarchies in which younger males rarely into use. Under this system, an adult's main plumage each year, usually
mate, and in which adult males have elaborate plumages or behaviors produced by a complete molt, is termed the basic plumage. Although
that are energetically costly to maintain. Other hypotheses focus on bird enthusiasts in the temperate zone general lythink of a bird's "breed-
potential advantages conveyed by subadu It plumages in winter. For in- ing plumage" as the main plumage—because it is usually the most no-
stance, Butcher and Rohwer (1988) proposed that subadult plumages ticeable and colorful—it is rarely worn for as long as the "nonbreeding"
may either decrease a bird's conspicuousness to predators (the "win- plumage. Thus, the nonbreeding plumage is termed the basic plumage
ter crypsis" hypothesis) or may decrease male-male aggression (the of most birds. The majority of birds, including most jays, chickadees,
"winter status signalling" hypothesis). In either case, subadults might woodpeckers, flycatchers, thrushes, vireos, swallows, hummingbirds,
enjoy higher winter survival rates. Butcher and Rohwer suggested that hawks, and owls, molt only once a year and thus have only a basic
although the advantages are gained in winter, birds might retain their plumage as adults.
subadult plumage through the breeding season to avoid the high en- If a partial molt occurs before breeding, it produces an additional
ergetic costs of spring molt. (Most birds undergo their most extensive plumage, the alternate plumage. This is the plumage that temperate
molt in fall.) Undoubtedly, different species gain different advantages zone birders usually think of as the "breeding plumage." It is this molt
from delayed plumage maturation, but researchers attempting to de- that produces the brilliant red of the male ScarletTanager (Fig. 3-29).
termine which hypotheses apply to which bird species have met with If, in addition to the basic and alternate plumages, the bird pro-
mixed success. duces another, it is termed supplemental; supplemental plumages oc-
The willingness of female birds-of-paradise to mate with males in cur in ptarmigans and certain buntings.
subadult plumage when males in definitive plumage are not available Equivalents for the traditional and Humphrey-Parkes nomencla-
may have saved some species of these beautiful birds. During the early tures for plumages and molts are shown in Table 3-1. Note that molts
20' century, feathers of wild birds were in great demand for decorating are named for-the feathers they produce, not for the feathers they shed.

Cornell Laboratorg of Ornithologg Handbook of Bird Biolou

3.34

Prealternate Molt
George A. Clark, Jr. r Chapter 3— Form and Function: The External Bird

Table 3 1. Plumage Naming Sytems

-
3.35

TRADITIONAL. SYSTEM H UMPHREY-PARKES SYSTEM

Yellow-green Red

NATAL DOWN (IF ANY) NATAL DOWN (IF ANY)

Postnatal Molt Prejuvenal Molt

Breeding (Alternate) JUVENAL PLUMAGE JUVENAL PLUMAGE

Plumage
Winter (Basic)
Plumage Postjuvenal Molt 1st Prebasic Molt

1ST WINTER PLUMAGE 1 ST BASIC PLUMAGE

1st Prenuptial Molt 1st Prealternate Molt

Prebasic Molt

1 ST NUPTIAL PLUMAGE 1 ST ALTERNATE PLUMAGE

Figure 3 29. Scarlet Tanager: The adult

- This naming system was developed because the energy required at
male Scarlet Tanager alternates between 1st Postnuptial Molt 2nd Prebasic Molt
molting and other physiological changes at this time are more related
a brilliant red breeding plumage and a
to producing the incoming feathers than to discarding the old ones.
dull yellow-green plumage during the
Note also that subadult plumages are indicated by numbering them as 2ND WINTER PLUMAGE 2ND BASIC PLUMAGE
nonbreeding season. The wings and
tail remain black in all plumages. After "1st," "2nd," "3rd," and so forth. Once definitive plumage is reached,
the breeding season, the birds undergo these numbers are dropped. 2nd Prenuptial Molt 2nd Prealternate Molt
a prebasic molt of all the feathers, dur- The Humphrey-Parkes system also works well for molt and
ing which the red body feathers are re-
plumage sequences that are highly specialized, such as that of the
placed by yellow-green feathers. In the 2ND NUPTIAL PLUMAGE 2ND ALTERNATE PLUMAGE
prealternate molt just before breeding, Mallard. In early summer after mating, the male Mallard has a com-
only the body feathers are shed, being plete (prebasic) molt, producing a dull-colored basic plumage aptly
replaced by the familiar scarlet feathers termed the eclipse plumage. Most male ducks in eclipse plumage 2nd Postnuptial Molt 3rd Prebasic Molt
of the male.
resemble females (Fig. 3-30). Female Mallards undergo a prebasic
molt a bit later in summer, after their young are independent, although 3RD WINTER PLUMAGE 3RD BASIC PLUMAGE
their appearance does not change at all. The basic plumage of both
sexes is soon lost in a molt of the body feathers—a partial prealternate When a bird reaches its definitive plumage, the numerical designations are dropped. For this
molt—which produces the brightly colored head and other distinc- example, we assume definitive plumage is reached after the 3rd winter or 3rd basic plumage:
tive features of the male. The occurrence of the prealternate molt im-
mediately after the prebasic molt (much sooner than in most species)
Prenuptial Molt Prealternate Molt
is related to the timing of courtship in Mallards, which begins in the
fall. Thus, male Mallards are in basic plumage for only a few weeks of
the year. For field observers, male ducks in alternate plumage are the NUPTIAL PLUMAGE ALTERNATE PLUMAGE
easiest to identify to species. Females or males in the basic (eclipse)
plumage are generally much less distinctive, so duck identification is Postnuptial Molt Prebasic Molt
often more difficult in mid to late summer.
WINTER PLUMAGE BASIC PLUMAGE
The Progression of a Molt
In most birds, especially land birds, molt occurs through an or- ETC. ETC.
derly, sequential replacement of feathers along a feather tract so that

Cornell Laboratort1 of Ornithologui Handbook of Bird Bioloaq

3.36 George A. Clark, Jr. Chapter 3—Form and Function: The External Bird 3.37
Wing Figure 3-31. Typical Progression of Molt
in the Flight Feathers: Most birds molt
only a few flight feathers at one time, in
Female—Breeding (Alternate) an orderly progression. In the tail, the
central feathers usually are lost first, and
1170 4x
as they grow back, successive feathers
toward each side are molted. In this
example, the central tail feathers have
completely regrown, while numbers
A-0• 0 2 and 3 have only partially regrown.
e A sev■ Tail feathers 4 and 5 have not yet been
molted. In the wing, molt begins simul-
taneously in the inner primaries and
the outer secondaries and proceeds in
opposite directions, as indicated by the
arrows.

Male—Breeding (Alternate)

Male—Eclipse (Basic)

Figure 3-30. Mallard Plumages: The

male Mallard in eclipse plumage looks
remarkably like the female, but his bill
is light olive green, whereas the female's
bill is orange marked with black. The
basic plumage of the female is identical
to her alternate (breeding) plumage.
2

a time probably makes these birds more vulnerable to predators, but

in any particular tract, only a minority of feathers are replaced at one they often molt in secluded places, and if they are attacked, most can
time (Fig. 3 31). Thus, you will rarely see a land bird missing more
- escape by swimming underwater. For many male ducks, recall that the
than a few wing or tail feathers. This gradual replacement of feathers prebasic molt in which all the flight feathers are lost produces a dull
spreads out the energetic cost of molting over time, while minimally eclipse plumage; this helps them remain inconspicuous. Furthermore,
impairing the flight, insulation, and other functions of the feathers. the molt in ducks occurs in several stages, such that the flight feathers
In woodpeckers, for example, the stiffened rectrices act as a prop to are retained until after the brightly colored body feathers have been
support the bird while it searches up and down tree trunks. Molting of replaced.
these feathers starts with the second innermost rectrices and progresses A few groups, including pigeons, parrots, and cuckoos, replace
to the outside. The long central pair of rectrices is replaced only after their tail feathers irregularly. In contrast, some of the smaller owls,
the other tail feathers have grown in, so the tail can serve as a sturdy such as the Northern Pygmy-Owl, the Little Owl, and the Burrowing
brace throughout the molt cycle. Owl, molt all the rectrices at once. This is also true of some of the other
Many water birds, including loons, grebes, anhingas, swans, short-tailed birds—the alcids and rails—which use their tails very little
geese, ducks, and even dippers, drop all the remiges simultaneously, in flying. Simultaneous tail molt is most conspicuous in the Boat-tailed
leaving the birds unable to fly during their prebasic molt. These water Grackle; the males of this long-tailed species appear ludicrous during
birds typically have a high ratio of body mass to wing area; thus the their stub-tailed period.
loss of a small amount of wing surface area would seriously impair Females of a number of hornbill species also molt abruptly. In
flight performance. By replacing all the major wing feathers at once, these Old World cavity nesters, the females stay in the tree cavity
they avoid the prolonged period of impaired flight that would result if throughout incubation and the early part of nestling life; while seques-
the remiges were replaced gradually. Being completely flightless for tered they undergo a full molt, including an extended flightless period.

Cornell Laboratoru of Ornithologq Handbook of Bird Biologq

3.38 Geor8e A. Clark Jr. Chapter 3 — Form and Function: The External Bird 3.39
The birds plaster a mixture of mud and saliva around the
entrance hole of the nest, creating a barrier to exclude Non feathered Areas
predators such as climbing snakes and monkeys. The 11111We now consider parts of the bird normally not covered by feathers,
male passes all food to the imprisoned female and young such as the eyes, bill, legs, and feet. Frequently, their peculiarities in
through a small opening; the female and young depend on color or form play a significant role in the bird's life, and are useful in
his survival for their own (Fig. 3 32).
-
identifying particular species.
Occasionally, a bird will shed many feathers all at
once. This shock molt or fright molt has been reported
for dozens of species in numerous taxonomic families, Eqes
but occurs only in unusual circumstances. For instance, a No thorough description of a bird is complete without mention
bird may shed its tail feathers when the tail is grabbed by a of the color of its iris (see Fig. 3-34c). Although most birds have a dark,
predator—clearly an adaptive strategy. It occasionally oc- commonly brown, iris around a black pupil, many species have more
curs during handling by people, and reports say that it can conspicuously colored irises—white, yellow, orange, blue, red, or
be induced by violent natural events such as earthquakes even, as in some grebes, concentric circles of two or more colors. The
and tornados. The mechanism of shock molt has not been Yellow-eyed Junco and the Red-eyed Vireo are named for the color of
determined, but clearly some relaxation of the muscles the iris in adults, as is the White-backed Fire-eye of the Neotropics.
holding each feather shaft must be involved: under normal Iris color may help some birds in species recognition. In Malaysia,
circumstances, a force of roughly one to two pounds is mixed flocks may include several species of bulbuls almost identical
required to pull out a single feather! in size and plumage color, but quite different in eye color—the dif-
The speed of molt varies to some extent with latitude ferences may help both birds and bird watchers to distinguish among
and the extent of seasonal change in climate. Molt is often the species!
more rapid, for example, in Arctic-nesting gulls than in Sometimes the sexes differ in iris color. Mature male Brewer's
closely related gulls of the temperate zone. Birds in the Blackbirds have a yellow iris, but females have a brown iris. The effect
Arctic simply do not have time for a slow-paced molt after of iris color on social behavior has not been studied extensively, but
breeding, as they must soon head south for the winter. The when iris color differs by age or sex, it presumably reflects different
abundance of food and continual daylight for foraging in social positions and, like differences in plumage color, plays a role in
the Arctic undoubtedly help these birds in gathering the social interactions. Commonly, if the adult has a bright iris color, the
Figure 3-32. Male Rhinoceros Hornbill resources they need to molt rapidly. In some tropical species, on the juvenile's iris is duller, so iris color can indicate the age of a bird. For
Bringing Food to Imprisoned Female: other hand, molts may be prolonged. The Rufous-collared Sparrow in example, juvenile Red-eyed Vi reos have brown irises during their first
During the incubation and early nest- fall. This difference may help the birds recognize juveniles, especially
northern South America takes two months to molt. Breeding seasons
ling stages, the female hornbill remains
in the tropics also may last a long time, and the energy demands of when there are no obvious plumage differences.
sealed in her nest cavity, depending
solely on food brought to her by her some species are low enough that they are able to overlap molt and In some species, eye color continues to change as the bird ages.
mate. Photo by M. StrangeNIREO. breeding activity. A Cooper's Hawk begins life with a bright yellow iris, but as the bird
Once in a while, a bird turns up with very few feathers on its head. grows older the eye changes to light orange, Rhamphotheca Premaxilla
The head may be bare, with the ear opening clearly visible, or may then medium orange, then dark orange, and
have a short layer of barely emerging feathers. Generally the entire finally to a deep, dark red. This pattern of color
head from the neck up is bare, but sometimes just patches of feathers change is so predictable that scientists can de-
are missing. These "bald" birds (often Blue Jays or Northern Cardinals) termine the bird's approximate age by eye color
are seen most often in the fall, although they occasionally appear at alone (Rosenfield et al. 1992).
Rhamphotheca Dentary
other times of the year. Most bald birds seen in fall are probably juve-
I„„
niles born earlier in the year undergoing their first prebasic molt. For AO'

unknown reasons, some of these birds drop all of the head feathers at
Bill l%tio

The terms beak and bill are synonymous.

one time and quickly regrow them, rather than losing and replacing
The visible portion of the bill consists of a sheath of skin, the rham- Figure 3-33. Bill Anatomy: The premax-
them a few at a time. Why birds occasionally become bald at other illa and dentary bones, which make up
photheca, which covers the projecting portion of the bony jaws (Fig. 3-
times of year, and why adult birds are sometimes affected, remain a most of the hard, internal structure of
33). In most birds, the rhamphotheca is hard and hornlike; it is softer and
mystery. It's possible that some type of atypical molt causes baldness the bill, are covered by a thin sheath of
more leathery in most waterfowl, sandpipers, plovers, and pigeons. skin called the rhamphotheca. In most
in these birds, or that an infestation of feather lice or feather mites is
Although the outer layers of the rhamphotheca consist of dead birds, the rhamphotheca is hard and
responsible. Whatever the cause, bald birds certainly command the at-
skin worn away by bill-wiping and abrasion during feeding, the in- hornlike, but it is softer and leathery in
tention of birders—their prehistoric, vulture-like appearance reminds most waterfowl, sandpipers, plovers,
ner layers are alive, and they renew the outer cover of skin. At the tip,
us of their ancestral ties to reptiles. and pigeons.

Cornell Laboratorg of Ornitholvi Handbook of Bird Biologq

3.40 George A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.41

growth is almost continuous, but it normally is not noticeable because

of a continual wearing away. If an injury breaks one tip or puts the two a

jaws out of line, such that one is not worn away by contact with the Naris (nostril)

other, the bill may grow extremely long until the bird cannot eat and
Groove
starves to death. Species that feed on a soft diet of insects in summer
and then switch to hard seeds during the cooler months have seasonal
differences in bill length. In House Sparrows, for example, bills are
longer in the summer months and are worn down by the harder foods
and grit taken during winter; these differences in bill length are small,
and can be detected only by detailed measurements. Captive birds may
not eat hard enough foods to wear down their bills properly, so their
owners often give them cuttlefish bone, which provides an abrasive
Albatross
surface to chew on, as well as minerals.
In certain kinds of birds, including ratites, albatrosses, petrels,
pelicans, and cormorants, grooves extend along the rhamphotheca. In
b
many cases, the function of these grooves is unknown. In albatrosses
and pelicans, however, the grooves carry salty fluids emitted from salt- Tubular Nares
excreting glands near the eyes (see Fig 4-131), guiding them from the
nostrils to the bill tip, where they drip away (Fig. 3-34a). (These are not
the types of grooves for which the Groove-billed An i is named.) Iris
The nostrils or nares (singular: naris) are on the upper part of the
bill, usually near its base. The shape of the nares differs along taxo-
nomic lines. The most highly pelagic order of birds, which includes
albatrosses, shearwaters, petrels, storm-petrels, and diving-petrels, is
characterized by tubular nares (Fig. 3-34b), whose function is un-
certain. These birds, often called "tubenoses," excrete large amounts Northern Fulmar
of excess salts in a fluid that is released into the nasal cavities. Some
biologists believe that the protection afforded by the tube reduces heat
and airflow at the point where salty fluid is excreted from the salt gland. d
Thus, evaporation of the salty fluid occurs at a point farther down the
bill, reducing the possibility that salts left behind after evaporation
will clog the gland. Another specialization occurs in some ground-
Chicken
feeding birds such as starlings, pigeons, and domestic chickens. These
birds have a fixed protective flap, the operculum, partially covering
the nares; this flap may help keep out debris (Fig. 3-34c). Perhaps
most bizarre are the kiwis of New Zealand, whose nares are uniquely
situated at the tip of their lengthy bills (see Fig. 4-54c). Kiwis use their
well-developed sense of smell to probe for earthworms at night. The
nares of hawks, pigeons, and some parrots are located in a leathery
band of skin known as the cere, which extends across the base of the
upper part of the bill and presumably protects the nostril openings Red-tailed Hawk
(Fig. 3-34d).
Many land birds, including hummingbirds, woodpeckers, and
passerines, regularly clean their bills by bill-wiping on tree branches, Figure 3-34. Adaptations of the Bill: a: A groove on each side of the albatross bill carries excreted salty fluid from the bird's naris
the ground, or other surfaces, especially after eating messy foods such to the tip of the bill, where it drips away. b: In the Northern Fulmar, like other pelagic birds termed "tubenoses," a tubular structure
covers the site where salty fluid is excreted from the salt gland. The fluid flows through the tube and out the opening in the end.
as oily insects or suet. Other land birds, such as doves, rub off debris by
These tubular [tares may reduce heat and airflow at the salt gland so that evaporation occurs farther down the bill, reducing the
scratching with their toes and never have been reported to bill-wipe. possibility that salts left behind will clog the gland. c: In some ground-feeding birds, such as the domestic chicken, a flap termed
Ducks and many other water birds clean their bills by bathing and the operculum partially covers the nares, probably helping to keep out debris. d: Many parrots, pigeons, and birds of prey, such
rubbing them against their feathers. as this Red-tailed Hawk, have a leathery band of skin termed the cere at the base of the bill, into which the nares open. The cere
is thought to protect the nares.

Cornell Laboratorq of Ornitholo cag Handbook of Bird Biologq

 3.42 George A. Clark J r. Chapter 3 — Form and Function: The External Bird 3.43
Bill color also
may differ by sex. In
Breeding
the European Starling,
(Alternate) Breeding
(Alternate) during breeding sea-
son the basal portion
of the lower beak be-
Horned Puffin comes bluish in males,
and pinkish-brown in
Atlantic females. The bill of the
Puffin Mallard is olive-green
to olive-yellow in the
male (varying with
the season), and bright
orange mottled with
3 Winter
(Basic)
black in the female.
Bill color mark-
ings serve several func-
tions. The red mark on
the lower beak of breeding adult Herring Gulls is a target for begging Figure 3-36. Begging Black-and-white
nestlings. When the chick pecks at this spot, the adult opens its mouth Warbler Nestlings: At the slightest hint
Breeding
(Alternate) that a parent may have returned with
and disgorges food. In the nonbreeding season this region of the bill
food, hungry young birds "open wide,"
becomes dark. Nestling cuckoos, woodpeckers, and passerines have fully displaying the bold oral flanges (see
brightly colored temporary enlargements called oral flanges (Figs. also Fig. 3-37). These temporary swell-
3 36 and 3 37) at the base of the bill, which are targets for adults
- - ings at the side of the mouth actas targets
Tufted Puffin
feeding the young (Clark 1969). Juveniles of cavity-nesting songbirds for adults feeding young. Photo courtesy
of Isidor Jeklin/CLO.
such as starlings typically have bright yellow oral flanges; these remain
visible in the dim light resulting when a parent blocks the nest entrance
)697
on returning with food. Colorful bill markings also may serve a social
Figure 3-35. Puffin Beaks: After breed- Winter function, especially in some highly gregarious birds such as toucans,
ing, puffins molt the brightly colored (Basic) which have bold, colorful patterns on oversized bills.
rhamphotheca and their beaks assume
the more subdued tones of the new Oral
rhamphotheca. Flanges
Legs and Feet
In most birds the bill is black, but bills do occur in virtually ev-
ery color, from the stunning red bill of a Common Merganser to the Typically, the unfeathered part of the leg is the lower portion of
bold sky-blue beak of a breeding male Ruddy Duck. In some birds, the tarsometatarsus, simply called the tarsus by most ornithologists.
including puffins and many toucans, the bill is the most colorful area One exception is the Ostrich, whose entire leg, including the thigh, is
of the body. featherless. Many birds have tarsi and feet of gray, black, or another
The colors of some bills change with the seasons. Atlantic, dark color, but others show a wide variety of colors and patterns.
Horned, and Tufted puffins molt the colorful outer sheath of their bills Bird watchers often use leg and foot color to recognize particular
after breeding (Fig. 3 35). More typically, though, color changes occur
-
kinds of birds: the bright yellow legs of the Greater and Lesser
by a gradual wearing away of the rhamphotheca, exposing the new, yellowlegs are a beacon to the identity of these birds, which
brighter color of the growing skin layers below. The European Starling otherwise look a great deal like many other members of the
and the American Robin have dark brown bills in the fall, but they turn sandpiper family. Leg color also is helpful in distinguishing
yellow in the breeding season; indeed, the increased yellow of the among the white egrets. These all-white waders look sim-
starling's bill in February is one of a birder's signs of spring. The reverse ilar at a distance, and size comparisons may be difficult to judge, Figure 3-37. Oral Flanges of a Nestling:
but their feet and beak colors quickly give away their identities. Great Begging nestling displays its prominent
occurs in the male Bobolink and House Sparrow, whose bills are black oral flanges at the sides of its mouth (see
in the breeding season and yellowish or light brown in the fall, and in Egrets have yellow beaks and black legs; Snowy Egrets, black beaks and
also Fig. 3-36).
the Evening Grosbeak, whose bill turns from bright apple-green in the legs with bright yellow feet; Cattle Egrets, yellow beaks and legs; and
breeding season to olive-yellow in the fall. Most brightly colored bills white-phase Reddish Egrets, pink beaks with a black tip and dark blue
do not attain their full coloration until the bird matures sexually. legs. In many herons and egrets, leg colors become especially bright

Cornell Laboratoru or 0 rnitholoBti Handbook of Bird Biologg

3.44 George A. Clark Jr. • Chapter 3— Form and Function: The External Bird 3.45
urN\ for the breeding season. The bright
„ Knee orange feet of a breeding Green
Heron are unmistakable as it walks a
;i0
• \ I
in mud or along dark logs. Like the
\\
"11))) bill, legs change color through the

4 el'
■ 10\ \, 011. Tibia
sloughing off of dead outer skin
layers to expose the replacement
layer produced underneath.
In certain cavity-nesting
birds such as woodpeckers, nest-
lings have a special enlargement
of the upper end of the tarsus, the Papillae
heel pad (Fig. 3-38). Heel pads
probably reduce abrasion of the
Heel Pad
tarsus caused by the rough lining
of the nest, in the way that elbow
Figure 3-38. Heel Pad of Nestling Tou- pads protect a hockey player. Heel pads are shed at about the time the
can: Many nestling cavity nesters, such young leave the nest.
as woodpeckers and toucans, have an
A few kinds of birds, such as ptarmigans and most owls, have Ruffed Grouse
enlargement at the upper end of the tar-
sus termed the heel pad. It is thought to feathers covering the legs and feet (Fig. 3-39a). Ptarmigans have extra
reduce the abrasion of the tarsus from the feathers on their feet during winter. These provide insulation and offer
rough lining of the nest cavity. a larger surface for support on snow, like a snowshoe. Owls apparently
have feathered feet to help suppress flight sounds that might alert prey.
Unlike the silently flying nocturnal owls, daytime fishing owls lack
feathered feet, and their flight is relatively noisy.
In most birds the outer end of the leg has some type of skin cov-
ering that resists abrasion, and depending on the type of bird, may Summer Winter
include scales, papillae, or leathery skin. Patterns of papillae and folds
on the undersides of the toes often reflect the functions the feet must
perform. The feet of Osprey, for example, have spiny-tipped papillae
on the underside to firmly grip slippery fish (Fig. 3-39b). In Ruffed
Grouse, an enlargement of scales along the sides of the toes creates
supporting winter "snowshoes" (Fig. 3-39c).
In many birds, papillae patterns on the feet vary considerably
and can be used to identify specific individuals (Clark 1 972; Smith et
al. 1993), much as human fingerprints are used to identify individual
people. In the case of rare birds worth tens of thousands of dol lars, such
as certain falcons and parrots, knowledge of papillae patterns could
help identify individuals stolen or illegally taken from the wild.
The claws at the ends of toes often reflect a bird's habits. Species
Northern Flicker Swainson's Thrush
that climb tree trunks, such as nuthatches, Brown Creepers, and Black-
and-White Warblers, have claws more curved than those of nonclimb-
ing species (Fig. 3-39d). These claws help them grasp irregularities on Purple Gallinule
bark without noticeably impairing their ability to perch. It is remarkable
how well nuthatches can climb on vertical trunks without slipping or
falling off. The curved claws of Archaeopteryx are among the character- Figure 3-39. Adaptations of Bird Feet: a: The feet and legs of most owls are covered with feathers, which apparently suppress
flight sounds that might alert prey. b: The undersides of Osprey feet are covered with spiny-tipped papillae to help them firmly
istics indicating that it was arboreal in its habits (Feduccia 1993).
grasp slippery fish. c: In winter, the scales on the toes of Ruffed Grouse enlarge, forming "snowshoes" that provide a larger surface
Ground-dwelling songbirds such as larks and pipits are noted area to help support their weight on snow. Drawing by Charles L. Ripper. d: Climbing birds, such as the Northern Flicker, have
for their long hind claws. These conceivably could help them to avoid claws curved more than those of nonclimbing birds, such as the Swainson's Thrush. e: Purple Gallinules have long toes to help
sinking into mud or other soft surfaces, although this idea remains distribute their weight so they can walk on floating lily pads.

Cornell Laboratorq of Ornithologq Handbook of Bird Bioloo

3.46 George A. Clark, Jr. Chapter 3—Form and Function: The External Bird 3.47

speculative. The Purple Gallinule uses its

long toes in a similar way—they distribute
the bird's weightso it can walk on floating lily
pads (Fig. 3 39e).
-

In a few birds, including Barn Owls,

nightjars, bitterns, and herons, the side of the
middle claw has a comb-like, serrated edge
(Fig. 3 40). This pectinate claw (sometimes
-

called a "feather comb") is used as a preen-

Pectinate Claw
ing tool.
Claws, like beaks, are subject to con-
stant wear, which helps to maintain the nor-
mal length. When wear is reduced, however,
as in captive birds, the skin covers of both
claws and beaks may grow exceptionally
long and must be trimmed.
Embryos and juveniles of many species
Figure 3-40. Pectinate Claw of Heron: bear claws on the wings as well as on the feet. Most remarkable are
The middle claw in some birds, such those of the Hoatzin of Amazonian South America, which builds its
as this heron, has a comb-like, ser-
nest a few yards above quiet water. When disturbed, nestlings leap
rated edge used as a preening tool. The
structure is termed a pectinate claw or a into the water beneath and swim away. When danger is gone, they use
feather comb. their wing claws to climb back up into the vegetation (Fig. 3 41). Wing
-

claws in the embryos or young of most living species, however, are

vestigial: nonfunctional holdovers of an ancestral structure. Archae-
opteryx had well-developed wing claws, which it presumably used to
climb in vegetation.

Other Unfeathered Areas

Areas of unfeathered or sparsely feathered skin occur in birds of
almost every order. These vary from the relatively inconspicuous to the
bold and beautiful. In many species, areas of bare skin function in dis-
play, but they have other uses as well. Carrion-feeding birds, including
the New and Old World vultures and some of the storks, have heads
that are largely bare except for bristles. Th is is reasonable because face
and head feathers—if they had them—would become badly soiled
when the bird reached inside messy carcasses to feed. Among birds
that feed regurgitated, partly digested fish to their nestlings, such as
pel icans,the young tend to have few or no feathers on their faces.
Some vultures also use their unfeathered, highly vascularized
head and neck to help regulate body temperature (Arad, Midtgard, and
Bernstein 1989) (Fig. 3 42). For example,when a Tu rkey Vu lture is too
-

Figure 3-41. Hoatzin Adults and Young:

hot, it stretches out its neck and increases the flow of blood through that
a: The bizarre, pheasant-sized Hoatzins
region. Excess body heat carried by the blood is then given off through ofAmazonian South America build their
the skin, from blood vessels near the skin's surface. When cold, the nest in low branches overhanging quiet
bird retracts its head and reduces blood flow through the superficial water. b: Young Hoatzins bear claws on
blood vessels, thus conserving body heat. the leading edges of their small wings.
When disturbed, they leap from the nest
The unfeathered areas of most birds are on the head and neck.
into nearby vegetation or water, then use
Some of these areas are normally inconspicuous, but become very the claws of al I four appendages to climb
prominent during displays. Certain North American grouse have back up.

Cornell Laboratoru of Ornithologii Handbook of Bird Biologq

3.48 George A. Clark Jr. Chapter 3—Form and Function: The External Bird 3.49
highly colored booming sacs on the To get a sense of the full Figure 3-44. FeatherlessAdornments of
sides of their neck (see Fig. 4-97). In Sage palette of colors and array of the Southern Cassowary: This Australian
bird displays a huge bony helmet—pos-
Grouse, the sacs lie on the breast and are patterns found in the more than
sibly a protection against thorny vege-
inflated by the expansion of the walls of 9,000 species of birds, you need tation and vines in the bird's rain forest
the esophagus. The bare throats of male only skim through a work such habitat; grotesque, floppy wattles tipped
frigatebirds inflate like huge red balloons as Birds of the World, by James bright pinkish red; and cobalt blue bare
skin on the face and neck. These fea-
during courtship displays (see Fig 6-44b). F. Clements. Strikingly named
tures, combined with the bird's coat of
Other bare areas change seasonally: the birds appear on every page, and glossy black body feathers and five-foot
enormous orange knob at the base of the the names suggestthe profusion stature, give this largest of the cassowar-
bill of the male King Eider shrinks after the of colors: Claret-breasted Fruit- ies a truly awesome aspect. Photo by C.
Dove, Silvery-throated Spine- VolpeNIREO.
breeding season, as do the frontal shields
of some coots and other members of the tail, Saffron-breasted Redstart,
rail family. Purple-bearded Bee-eater, Scar-
Bare or sparsely feathered areas of the let-hooded Barbet, Fire-maned
head often have peculiar outgrowths of the Bowerbird, Pink-throated Bril-
Figure 3-42. Turkey Vulture: TurkeyVul- skin, such as the comb and throat wattles of the Domestic Fowl, the liant, Ruby-topaz Humming-
tures and many other bare-headed birds warty bumps on the face of the Muscovy Duck, or the snood of the bird, Violet-necked Lory, Opal-
can eliminate excess heat by stretching crowned Manakin, Cobalt-winged Parakeet, Pearly-breasted Cuckoo,
WildTurkey—a limp, red, fingerlike projection from the forehead. Pen-
out their necks to expand the area of bare
dulous wattles also hang from the heads of New Zealand wattlebirds Buff-throated Purpletuft, Lilac-tailed Parrotlet, Sapphire-rumped Par-
skin and increasing blood flow through
the skin of that region. Photo courtesy of (see Figs. 1-92 and 9-28) and the spectacular Neotropical bellbirds rotlet, Malachite Sunbird, Gilt-edged Tanager, Glistening-green Tan-
Ray Martorelli/CLO. (Fig. 3 43). A number of species have feather-free casques on top of
- ager, Citron-headed Yellow-Finch. As these names imply, the assort-
the head, including the cassowaries of Australia and New Guinea
(Fig. 3 44) and the Maleo, a brush-turkey (megapode) native to the
-

a
Indonesian island of Sulawesi.
Brilliantly colored eyelids occur in birds of many families,
including plovers, pigeons, cuckoos, trogons, thrushes, and White Light
Old World flycatchers. In some, such as the Wattled Broadbi II
and the Yellow-wattled Bulbul—both of the Philippine Is-
lands—the brightly colored eyelid is also enlarged and fleshy.
In some birds, such as toucans and some parrots and honeyeat-
ers, an area around the eye is bare and brightly colored. In many
herons the bare area is between the eye and the base of the bill,
and the color varies with season. Prism

Colors
• The tremendous range of bird colors, on both feathered and White Light
unfeathered parts, suggests immediately that birds have well-
developed color vision. Indeed, experiments have verified that
many birds do see colors, and the structure of their eyes indi-
cates that they may be able to discriminate a greater variety of
colors than can humans. In addition, many birds can see certain
types of ultraviolet (UV) light, which is invisible to the unaided
human eye (Fig. 3 45) (Bennett et al. 1994). What advantages
-

Figure 3-43. Bearded Bellbird: The might this give them? The answer remains a mystery, but for a discus-
Bearded Bellbird, a jay-sized cotinga of sion of this topic, see Sidebar 1: The Amazing World of Avian ESP, in Figure 3-45. Human Versus Avian Visual Spectrum: When white light strikes a prism, the different wavelengths it contains are
northern South America, features a mass
Chapter 4. Altogether, the bird-human differences in visual perception each bent to a different degree, forming a spectrum. Longer wavelengths such as red are bent less than shorter wavelengths such
of slender, fleshy wattles, black in color,
are so great that it is hard for us to understand exactly how birds see as violet. In the atmosphere, water droplets can act as prisms to produce a rainbow. a: The portion of the sun's spectrum visible
which suggests a beard. Photo by C. H.
to humans. This is normally termed "visible light." b: The portion of the spectrum visible to birds that can see UV light in addition
Greenewalt/V1REO. the world (Bennett et al. 1994).
to "visible light."

Cornell Laboratorq of Ornithologq Handbook of Bird Biolos

3.50 George A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.51
ment of patterns is just as spectacular: birds are freckled, chevroned, high speeds or spend a lot of time flying, such as gannets, terns, and
naped, collared, capped, crowned, hooded, shouldered, browed, gulls, including Common and Arctic terns and Ring-billed and Herring
spectacled, mustached, necklaced, speckled, striped, blotched, bor- gulls (Fig. 3-46).
dered, banded, vented, chinned, backed, cheeked, and crested with Carotenoids produce reds as in Northern Cardinals, oranges as in
this amazing array of colors. male Blackburnian Warblers, and many yellows, especially the bright
How are all these beautiful colors produced? To understand this, yellows of birds such as Yellow Warblers, goldfinches, and canaries.
you first need to realize that sunlight is a mixture of many different Unlike melanins, carotenoids are synthesized only by plants. Birds
wavelengths of light. Seen all together they look white, but when a must therefore acquire them preformed in their diet, either by eat-
prism or water droplet in the air bends each wavelength to a different ing plants or by eating something that has eaten plants (Brush 1990;
degree, the wavelengths separate, and we see each as a different Hudon 1991). In some bird species, differences in the specific types
color, as in a rainbow (see Fig. 3-45). When white light strikes an of carotenoids in the diets of individuals inhabiting different locations
object, some wavelengths are absorbed by the object while others are produce regional color variations. This occurs in the European Great
reflected back to our eyes. The reflected wavelengths are what we see Tit, whose young are more yellow underneath when fed on caterpil-
as the object's color. A red ball, a cardinal, or red paint appears red to lars from deciduous rather than coniferous woodlands (Slagsvold and
us because it reflects only red light; the other colors are absorbed and Lifjeld 1985). Some colors, such as the olive-green of the female Scarlet
never get to our eyes. Tanager, result from the interaction of both melanins and carotenoids
Birds employ two different systems to break light apart into its in the same feathers.
component wavelengths—pigments and the microscopic structure The third group of pigments, porphyrins, produce reds, browns,
of feathers. Pigments are colored substances that can, in principle, greens, or pinks in a number of different avian orders. They interact
be extracted from feathers or other parts of the skin. (In practice, their with melanins to producethe browns of many owls, and are also found
actual extraction may be very difficult.) The color of pigments can be in pigeons and gallinaceous birds. In eggshells, they may appear pink
seen even after the physical structure of the material in which they are or red, or they may be masked by melanins. Porphyrins are most strik-
embodied—a green leaf, a red bowl, or a brown feather—has been ing, however, in the brilliant reds and greens of the turacos, a family of
destroyed. In contrast, structural colors depend on the actual physical
structure of the feather to reflect certain wavelengths of light. Destroy
that structure and you lose the color, just as you lose the rainbow if
you destroy the prism.

Pigments
Three main types of pigments are found in birds: melanins,
carotenoids, and porphyrins. Melanins, which usually occur as tiny
granules in the skin and feathers, are the most common. Depending on
their concentration and distribution, melanins can produce any shade
from the darkest blacks through browns, red-browns, yellow-browns,
and pale yellows. Melanin colors the all-black Common Raven and
American Crow, the reddish phase of the Eastern Screech-Owl, and
the yellowish down of a young chicken. Birds synthesize their own
melanins from amino acids, which they obtain from the proteins in
their diet.
Melanin provides more than color for feathers, though. Feathers
containing melanin are stronger and more resistant to wear than feath- -
•- '''' _ -
ers with other pigments. Some researchers suggest that the melanin
granules themselves provide the added strength, but others attribute it
to the higher levels of keratin found in feathers with melanin; indeed,
both factors may be involved. White feathers, which lack any type of _- -
pigment, are the flimsiest. It is no surprise, then, that most birds, espe-
cially white or lightly colored ones, have dark wings or wing tips—ex- Figure 3-46. Light Birds with Dark Wing Tips: Many white or light-colored birds that spend a lot of time flying have dark wing
tips colored with the pigment melanin. Feathers with much melanin are stronger and more resistant to wear than feathers with
tra protection for the feathers most vulnerable to abrasion during flight
no pigments, or other types of pigments. Species from left to right: Northern Gannet, Common Tern, Herring Gull, American
(Burtt 1986). Dark wing tips are especially common in birds that fly at White Pelican, Laysan Albatross.

Cornell Laboratoru of Omithologq Handbook of Bird Biologu

3.52 George A. Clark, Jr. Chapter 3— Form and Function: The External Bird 3.53
colorful African birds related to New World cuckoos. The porphyrin
pigment turacoverdin, which produces the green body plumage of
many turacos, is one of the few green pigments known from birds. Most
greens on birds, as in the parrots, are produced as structural colors that
are modified by overlying carotenoid pigments.
Porphyrins are complex, nitrogen-containing molecules related
to hemoglobin, which birds (and other living things) make by modi-
fying amino acids. Although the exact chemical structure varies from
pigment to pigment, all porphyrins share one significant feature: they
fluoresce bright red under ultraviolet light. If you have ever seen an
exhibit of minerals at a natural history museum, you may recall the
dazzling colors of the fluorescent rocks displayed under ultraviolet (or
"black") light. Feathers with porphyrins glow in the same manner.

Abnormalities and Variations in Pigment Colors

If you take a careful look at the birds coming to your feeder, you
will see that not all individuals of the same species look alike. For ex-
ample, House Finches vary in the amount of streaking on their breasts
and in the extent of the red areas, as well as in the exact shade of red. Downy Woodpecker Baltimore Oriole
Color variations like these are common and normal. But sometimes a
truly unusual individual shows up: perhaps a House Finch with a white
head, or an American Crow with white patches under its wings. These
types of color abnormalities are discussed here.
Figure 3-47. Downy Woodpecker and
Some odd colorations are caused by abnormalities in a bird's Baltimore Oriole with No Melanin:
pigmentation. The most common conditions involve the reduction When a genetic mutation prevents a
or absence of melanin. Birds with reduced melanin are significantly bird from producing melanin, an al-
paler than normal, whereas birds with increased levels are darker—a Plumage colors may be altered by all sorts of environmental fac- bino results. Because other pigments

relatively common example is the dark phase of the Rough-legged tors. Exposure to sunlight, for example, may lighten feather colors. may still be produced, the outcome may
Birds in open areas that receive lots of direct sunlight, such as deserts, be very odd indeed. A Downy Wood-
Hawk, illustrated in most field guides. Sometimes melanin is com- pecker may be pure white with a red
pletely absent from the entire plumage, or from certain parts, as in are especially susceptible. Consider American Kestrels, found in a
cap (produced by carotenoids), and a
the crow example above. Colors produced by other pigments remain, wide range of habitats. Birds from Arizona deserts look very much like Baltimore Oriole may retain its bright
sometimes resulting in odd-looking birds. For example, male Downy birds from Michigan when their feathers are fresh in the fal I. After a few orange or yellow color but lose its dis-
months, however, Arizona birds are so much paler than Michigan birds tinctive black markings.
Woodpeckers lacking melanin are pure white with a red spot on the
back of the head, orioles are white and yellow instead of black and that the two look like different species. Before such color changes were
yellow, and Cedar Waxwings are white with yellow abdomens and understood, museum scientists sometimes classified the sun-bleached
tail tips (Fig. 3-47). and unbleached specimens as separate races or species.
A bird that lacks all melanin is termed an albino. Albinism re- In industrial areas, air pollution may affect feathers, giving birds
sults from a genetic mutation that interferes with the production of a coating of soot that may mask their true colors. When the use of soft
tyrosinase, an enzyme that helps to produce melanin. Birds that lack coal as fuel was restricted in Pittsburgh, Pennsylvania in 1940, the nat-
not just melanin but all types of pigments in the plumage, eyes, and ural history museum began getting telephone calls from bird watchers
skin are rare and are called complete albinos. These birds have white trying to identify "a handsome little bird in chestnut, gray, and white,
feathers, but their unfeathered areas, including the eyes, legs, and feet, with a black bib." Many were disappointed to learn that the "new" bird
usually appear pink due to the hemoglobin within the blood vessels was only the male House Sparrow without a coating of soot. Even in
near the surface of the skin. relatively clean areas, tree-climbing birds such as woodpeckers and
Abnormal pigmentation is usually under genetic control, but creepers may dirty their plumage by contact with bark.
disease, injury, and diet also can be factors. Wild flamingos, Roseate Colorful soils and foods also may stain feathers. Birds that dust-
Spoonbills, and Scarlet Ibis, for example, derive their pink color from bathe in soils of certain consistencies cannot always remove all the
the carotenoids produced by certain crustacea that they eat. When dust by shaking, and may thus acquire the general color of the soil.
held in captivity they eventually become white unless zookeepers add In southern Brazil, for example, certain House Sparrows may acquire
carotenoids to their diet, often in the form of chopped shrimp. a pinkish tinge from the reddish soil of the region—a bit of a change

Cornell Laboratorg of Ornithologq Handbook of Bird Biologq

 3.54 Geor8e A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.55

Light Source Feather appears

blue due to scat-
Wavelength Wavelength tering of blue light
waves
Brown — Feather appears
brown due to
Wave 1A Wave 1B light passing
Blue
Blue through the
brown pigment
Initial Wave Blue
melanin
Heights

Wave 2A Wave 2B
Blue Keratin Sheath

Small air vacuoles that scatter blue light

3 Wavelength Cells, termed "cloudy cells" or "blue-producing

cells," made of keratin, which contain the light-
Wave 3A Wave 3B
scattering vacuoles

Melanin Granules
Resulting
Wave (a+(-b)=c)
Height
(a+b=c)
a b

Hold a Peacock feather and

Figure 3-48. Patterns of Interference from the House Sparrow's usual browns and grays. Some geese, ducks, slowly turn it from side to side,
from Two Light Waves: a and b = initial swans, and cranes that feed in water containing iron oxide (rust) turn and you'll see a series of gl istening
wave heights, which may be positive (+)
reddish as the iron precipitates out on their feathers; this can be espe- colors appear and disappear. This
or negative (-); c = wave height resulting
from interference (determines perceived cially noticeable on the heads of Snow Geese. Birds even acquire a occurs because at different angles
brightness). a: The combination (or "in- few of their colors while eating. Berries may stain the feathers around light waves bouncing off and go-
terference") of two light waves (1A and the face and vent of berry-eating birds; pollen may discolor the faces of ing through the complex layers
2A) in which crests and troughs line up
birds probing flowers for nectar or insects; and half-digested shrimps in the barbules interfere with
perfectly results in a new wave (3A) with
crests twice as high. The wavelength, may turn the pure white fronts of penguins a splotchy pink. each other in different ways: at
which determines the color, remains the each angle, some wavelengths JCF97
same, but the color will appear twice as are brightened and others are Light
bright. b: Waves 1B and 28 interfere, Structural Colors Source
cancelled before they reach your
resulting in wave 38. In this case, how- Two kinds of structural colors occur: iridescent and non irides-
ever, the wave crests and troughs nearly
eye. At each position, you see
cent. Both result from the microscopic structure of the feathers, which
cancel each other out, producing very only the brightened colors (Sidebar 3: Iridescence).
causes only certain wavelengths of light to be reflected. Iridescent
low waves, which will be seen as a dull, Iridescent colors rarely occur on a bird's flight feathers, probably Figure 3-49. Cross Section through a
nearly black, version of the original colors, as on soap bubbles, the "eyes" of a Peacock's plumes, and Blue Jay Feather Barb: When light is
because the flattened barbules required to reflect light would not be
color. Again, the actual color remains the throats of many hummingbirds, are very bright and change with scattered by air vacuoles in the blue-
sturdy enough for flight, and because any wear would change the
the same because the wavelength is the angle of view—so they appear to glisten and shimmer as the producing cells, the feather appears
unaltered. If wave crests and troughs feather structure, destroying its color (Greenewalt et al. 1960). Fur- blue. When light is transmitted through
bird moves. Iridescence is produced when light waves reflected off
overlapped perfectly, the result would thermore, flashing iridescent colors on moving wings might hinder a the feather, the feather appears brown. In
be a straight line, viewed as black. certain structural layers within flattened barbules "interfere" with some birds the keratin layer conta ins pig-
bird's ability to hide from predators.
one another, somewhat the way that widening circles from pebbles ment. For example, many green birds,
Noniridescent structural colors arise when tiny vacuoles (pock-
tossed into a pond interact when they contact each other. Depending such as parrots, have a yellow pigment
ets) of air within cells in the barbs scatter incoming light (Fig. 3-49). here that adds to the scattered blue light
on whether the contacts are wave crests or troughs, the result can be
According to the laws of physics, whenever particles smaller than a to produce green. Adapted from Welty
taller waves, shorter waves, or a complete cancellation of the waves
particular wavelength of light are separated by distances greater than and Baptista (1988, p. 49, Fig. 3-19A).
(Fig. 3-48). The eye interprets these different wave heights as different
that wavelength, all incoming wavelengths of roughly that size or larger
brightnesses of color. Only interference patterns can produce the
will be scattered: absorbed by the particles and re-emitted in a new
"super bright" colors seen on iridescent parts of feathers.
(Continued on p. 3.58)

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

3.56 George A. Clark, Jr. Chapter 3 —Form and Function: The External Bird 3.57

Sidebar 3: IRIDESCENCE Light

Source
Eye of
Observer
Ruby-throated the range of colors produced. Hum-
Hummingbird mingbirds (as mentioned above) are
Sandi./ and Bill Podulka notorious for their quickly disap-
pearing colors—changing from glit-
To understand the details of how dull green to black, as
tering brilliance to black with just a
feather structure can produce iri- the film moves, chang-
slight change in angle. Some, such
descent colors, you must first un- ing the angle at which
as the Ruby-throated Hummingbird,
derstand the physics of how a thin the incoming light hits
Air A can only produce red or black on
film affects light. For this discussion, the film.
the throat feathers, but others may
please refer to Fig. A. When a beam of When sunlight, a mix Thin Film of a
light (1) hits a thin, translucent film, of all colors, strikes a Soap Bubble
//,
-7/ 4
• ,
j # display several colors in addition to
blackness. The colors of a peacock
such as a coating of oil on water, or film, at each angle be-
Air feather are numerous—ranging from
the membrane around a soap bubble, tween the observer and
bronze through blue-green, but they
some of it is reflected (2) and some the film, just one color
never completely disappear to form
enters the film (3). Whenever light will be brightened—the
black. One of the most beautiful
moves between media with different one for which wave
Observer Sees birds in the world, the Resplendent
densities, it is bent (refracted)—as crests meet—and it will Figure A. Reflection and Refraction Bright Red Quetzal of Central American cloud
occurs at point A—and the degree of be seen to the exclusion of the others. from a Thin Film: Light beam striking a
forests, varies between gold-green
refraction depends on the difference This is why you see a series of colors thin film—the skin of a soap bubble. See
and blue-green, with a touch of
between the two densities. Some of as you turn a peacock feather in your text for explanation. Adapted from Simon
(1971, p. 71). violet at times. The intensity and
the refracted light may travel on and hand, changing the angle between
beauty of its colors has placed it as
exit the film (4), but some is reflected your eye and the feather.
Observer Sees the national symbol of Guatemala;
off the bottom surface (5). Since the The iridescent colors of feathers, pancake-shaped granules, and each Dull Red
Observer Sees Black in the past, it was worshiped by the
eye of any observer is much larger like those of a soap bubble, result granule contains a layer of air-filled
Mayans and Aztecs.
than the distance between the paths from light interference created by vacuoles (a vacuole is a parcel of air
Although some of the most
of light waves 2 and 6, they will both thin films. The structural complexity or some other substance, contained Figure C. Angles, Interference, and Iridescence: Schematic representation of how
spectacular iridescent colors occur
be seen atthe same time. When these of iridescent feather barbules, by a membrane). Light waves reflect different angles between the sun, Ruby-throated Hummingbird throat, and observer
produce different interference patterns and thus different brightnesses of red. Angles on tropical species, many North
two light waves meet inside the eye, however, is much greater than that off the upper and lower surfaces of
and resulting interference patterns are not necessarily accurate. American birds also display irides-
the combination produces inter- of a single thin film. Although the the vacuoles. The vacuoles thus serve
cence—and some of these can be
ference, and the type of interference details vary from one group of birds the same function as the top and bot-
light reflecting off the top surface brighten the red wavelengths, and seen at your feeder. European Star-
depends on whether wave crests or to another, all use the same basic tom (or outer and inner ) surfaces of
of the vacuoles in layer 1 interferes the brightness depends on the angle lings, many grackles and cowbirds,
troughs arrive at the eye at the same plan: layers of melanin granules, the skin of a soap bubble.
with light reflecting off the bottom of view. At some angles all wave- Wild Turkeys, Ring-necked Pheas-
time (see Fig. 3-48). Whether crests running parallel to the surface of The key to the barbules' exquisite
surface of the vacuoles in layer 1 in lengths cancel each other out, and ants, and Wood Ducks all glitter
or troughs arrive together depends on the barbule, embedded in keratin. design, however, is that each layer of
exactly the same way as it interferes you see the throat as black (Fig. C). with iridescent hues. But iridescence
the extra distance in the film (A to B In most hummingbirds, as pictured melanin granules (and thus vacuoles)
with light reflecting off the bottom of Variations on this structural theme is not limited to birds. Some snakes
to C) that light leaving in beam 6 has in Fig. B, there are 7 to 15 layers of is the same thickness. As a result,
the vacuoles in layer 2, or 3, or any are as endless as the array of irides- (such as boas), lizards, fish (rainbow
traveled, compared to light leaving in
other layer. Therefore, for a given cent colors they produce. The mela- trout and many popular aquarium
beam 2. That extra distance, in turn,
Top Surface of Barbule incoming light angle, the color that nin may be solid or air-filled, and species such as neon tetras), and in-
depends on three things: the angle at
is brightened is the same not only for may be in flat disks, or in rounded, sects (especially butterflies, moths,
which the incoming light strikes the
each layer individually, but between hexagonal, or flattened rods. Some- and beetles) produce iridescence.
film, the degree of refraction, and the Atierittratral different layers, as well. The total times the melanin granules are tight- Although they use different sub-
thickness of the film. 401204ilk
41P S14.47409r,f4 2 Layers of
In the simplest case, in which
Melanin
Granules
N14---talostM4 I Melanin
brightness you see is the sum of all ly packed, and at other times they stances and structures to form the
,,,fli ettaiff5417*71 FA #A these layers acting together, and the have spaces between them, roughly colors, they still use the principle of
light of only one color, such as
° rio. Granules
,

interference from th in films.

green, is involved, the result seen by .m 2TAPTOVIAPPIt more layers involved, the brighter forming a grid. The colors produced

C=1:211:1
the color. may be as pure and brilliant as the Perhaps the most awe-inspi ring as-
the observer (light waves 2+6) will
be either bright green (when wave
Melanin • ttri0 If you have ever watched a male red throat of a Ruby-throated Hum- pect of iridescence—even beyond the
AO111011160 411111115t r
"
Granules Ruby-throated Hummingbird prob- mingbird or may contain a duller mix beauty of the colors themselves—is
crests meet), dull green (when partial
ing a flower, you may remember his of wavelengths—as in the greens of thatthe purity, range, and brilliance of
crests and/or troughs meet), or black Air ailWki00110
Vacuoles flashing, changing colors, his throat some trogons. Some colors result the colors produced by each species
(when wave crests and troughs meet WO01111111, 6111s diltlf i varying from brilliant red to near from a combination of iridescent are tightly controlled by minute struc-
and cancel each other out). For a sta- Keratin
black. As he moved, he altered the colors—as in the copper (a mix of tures whose size, density, and shape
tionary observer watching a moving
angle formed by your eye, the re- red and yellow-green iridescence) must be highly accurate—sometimes
film (such as a drifting soap bubble), Figure B. Detail of a Hummingbird Feather Barbule: Three-dimensional cross sec- flecting surface, and the light source. on some African sunbirds. to within 4 ten-millionths of an inch
under green light the color will ap-
pear to change from bright green to
tion of approximately one-half of a barbule from a typical hummingbird feather.
See text for explanation. Adapted from Simon (1971, p. 160).
H is throat barbules are structured so The precise arrangement of the (0.00001 mm). ■
that interference patterns can only layers of melanin granules restricts

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

3.58 GeorBe A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.59

Blue di rection. The shorter the wavelength, the more strongly it is scattered.
In a feather, the air vacuoles act as scattering particles, and are so
tiny—smaller in diameter than the wavelength of blue light (about 19
millionths of an inch [0.0005 mm])—that all wavelengths of visible
light are affected. But the shades of blue light (blue, indigo, and violet)
are affected the most, because they have the shortest wavelengths.
The blue can be seen from any angle, because the wavelengths are
scattered in all directions. Scattering of this sort produces the blues of
bluebirds, Indigo Buntings, and Steller's Jays. It also produces the blue
of the sky as dust particles scatter sunlight.
Melanin is also present in blue feathers, just below the layer of
cells containing the light-scattering air vacuoles. It absorbs most of
the longer wavelengths of light, such as red, that are not scattered as
much by the overlying air vacuoles, creating a dark background that
intensifies the blue you see. (These longer wavelengths tend to move
straight through the cell layer that contains the scattering particles,
reaching the melanin below.)
If you hold a blue feather up with a light behind it, or look at a
a
backlit Blue Jay, it looks brown. In these situations the light you see has
Brown passed through the feathers, rather than reflecting off them, so the blue
disappears and you see only the brown of the melanin (Fig. 3 50). In-

a
contrast, if you hold a yellow feather up to light it still looks yellow,
because the color is produced by a pigment, not the structure of the
feather. Blue pigments are rare in birds, occurring in only a few species
such as the Blue-capped Fruit-Dove of New Guinea; most blues are
structural colors.
One more way to demonstrate to yourself the difference between
structural and pigment colors is to crush or grind up a blue feather.
When the blue-producing structure is destroyed, the feather will ap-
pear dark due to the melanin. In contrast, when you crush a pigmented
feather—try this with a yellow or red one—it will remain the same color
when its structure is destroyed (Simon 1971).
In addition to blue, a few other noniridescent colors may be
produced structurally. When the light-scattering air vacuoles are a bit
bigger (bigger than the wavelength of blue light), the result is green
(since blue is no longer scattered, and green wavelengths are now
b
scattered the most), as in some parrots. With even larger air vacuoles,
Figure 3-50. Blue Jay Feather Under
Different Light Conditions: a: When no wavelengths are scattered, but all are reflected, producing white
light reflects off the top surface of a Blue light and thus plumage that we perceive as white; white does not exist
Jay feather, the feather appears bright as a pigment in birds. The feather structure of many birds also reflects
blue due to the detailed structure of
ultraviolet light (Burkhardt 1989), which birds, but not humans, can
the feather. b: When light is transmitted
through a Blue Jay feather, the feather
see. Thus, birds may appear very different to each other than they do
appears brown due to the pigment mel- to us (Andersson 1996) (Fig. 3 51).
-

b
anin. (See text for further explanation.) A few colors result from a combination of pigment and structure.
Photos courtesy of Carrol Henderson. The greens of some parrots are caused by yellow pigment overlying the Figure 3-51. Thrushes Under Different Lighting Conditions: Black-and-white photographs of Old World thrushes. a: Birds il-
blue-reflecting structure of the barbs. When the yellow pigment fails luminated by light conditions visible to humans. b: Birds illuminated only by ultraviolet light (wavelengths 320 to 400 nm). Note
that b does not show the birds as they would appear to a bird whose vision is sensitive to both visible and ultraviolet light, but
to develop, a bird such as theYel low-headed Parrot, which is normally
does show the additional ultraviolet plumage features that might be visible to a bird, but not to a human. The way these plumages
green with a yellow head, is blue with a white head—a rare genetic might actually appear to a bird that sees in both the visible and ultraviolet ranges is probably somewhere in between the images
mutation. When the overlying pigment is red instead of yellow, purples shown in a and b. Species from top to bottom are: male Eurasian Blackbird, Song Thrush, Taiwan Whistling-Thrush, and male
and violets result, as on the heads of some Indian parrots. Blue Whistling-Thrush. Photos courtesy of Staffan Andersson.

Cornell Laboratorq of Omitholos Handbook of Bird Biolos

3.60 George A. Clark, Jr. Chapter 3— Form and Function: The External Bird 3.61

For in-depth explanations and clear illustrations of how struc- is concealment important to prey—we assume, for ex-
tural colors are produced in birds, see Simon (1971) and Greenewalt ample, that ground-nesting meadowlarks are more likely
(1960). to avoid the sharp eyes of hungry hawks if they look like
their grassy surroundings—but the predators themselves
may be more successful if they are hard to detect. For
Functions of Color example, we assume that even a bird as large as a Snowy
Owl can go unnoticed by its lemming prey if it blends
and Color Patterns into the white arctic landscape. The only data to support
this idea, however, come from experiments on captive
■ Feather structure and pigments combine to make birds among the Black-headed Gulls, which became much less effective
most colorful animals on earth. Their bright colors and striking pat- at capturing fish in a tank from the air when the under-
terns are rivaled only by those of coral reef fishes and butterflies. For sides of their ordinarily white wings were dyed black
all animals, including birds, coloration is an evolutionary compromise (Gotmark 1987).
between hiding from predators and being conspicuous for social in- Different predators, however, have different visual capabilities, Figure 3-52. American Woodcock: The
teractions such as territorial defense, courtship, and mate choice. For mottled brown-and-white feathers on
so we must not assume that all prey appear as conspicuous or as cryptic
most animals, however, concealment is the more critical need. Just as to predators as they do to us. For instance, most mammalian pred- the back of an American Woodcock
the dull, cryptic colors of most mammals, reptiles, amphibians, and render it virtually invisible against the
ators such as cats and raccoons, as well as nocturnal avian predators leaf litter of the forest floor. Photo cour-
fish help them to remain inconspicuous, so, too, do most birds sport such as owls, apparently lack color vision. Many bright yellow or red tesy of John Trott/CLO.
earth tones that render them hard to see. Nevertheless, a large number birds may thus be inconspicuous to these predators, which see the
are brightly colored—perhaps because flight allows them to escape
colors as shades of gray. On the other hand, hawks, eagles, and other
most predators, perhaps because bright colors are concealing in some avian predators that are active by day probably have full color vision
habitats (sunlit, fruit-and-flower-laden forest canopies, for instance), or including some ultraviolet wavelengths. Thus, markings on a "prey"
perhaps because colors are so crucial for birds' social interactions.
bird such as a goldfinch may be cryptic for one kind of predator, but
We probably will never know exactly why each bird looks the not for another.
way it does, but we do know that color and pattern, like most other
attributes, result from generations of natural selection. Individuals Blending In
whose colors best meet their needs raise more young and pass to those Birds that spend much time on the ground generally are colored
offspring their favorable colors and patterns. Over time, this "hand of more cryptically than arboreal species; this camouflage probably
evolution" continues to fine-tune each bird's appearance. Thus, when results from heavy predation. The mottled patterns on many birds
we view a bird, we must remember that it is not a finished product, of the forest floor, such as the American Woodcock, Ruffed Grouse,
but one under continuous construction. Some patterns remain a mys- and many of the nightjars including the Whip-poor-will, resemble or
tery to us. Why, for example, is the Bobolink light above and dark mimic the leaf litter beneath them (Fig. 3 52). Nearly all shorebirds,
-

below, not the reverse, like most birds? With careful observation and from Least Sandpipers to Long-billed Curlews, have mottled brown-
interpretation, however, we often can deduce which selective forces ish backs that conceal these ground nesters during incubation as well
produced the colors and patterns we see in birds today. as while they are foraging on beaches, mud flats, or in grasses. Birds
Throughout the following discussion of bird colors and their func- of grasses and reeds—the bitterns, snipes, and grass-loving sparrows
tions, keep in mind that most observations and experiments with birds such as the Savannah Sparrow—often have patterns with longitudinal
have assumed that their color vision, as well as that of their predators, streaks. Among sparrows and thrushes that feed on the ground, such
is similar to ours. Only in the early 1970s did researchers begin to as Song Sparrows and Wood Thrushes, brownish-patterned plumages
realize that birds see some types of UV light, and that some birds may are common. The tundra-dwelling ptarmigans molt from their brown
be able to discriminate a greater number of colors than we do. Our summer plumage to a white garb that blends with heavy snow cover
understanding has thus been hampered by our own perception of the in winter (Fig. 3-53).
colors around us. As we struggle to grasp the way the world really looks Perhaps the most striking adaptations of color and pattern to
to birds and their predators, some of our long-held beliefs about the match their environment occur among some of the Old World larks.
roles of colors and patterns on birds may be challenged. Even within a single species, the birds of different populations re-
semble the different types of ground on which they live—black lava,
reddish brown earth, or white sand. Individuals rarely stray into an
CrLjptic Coloration and Patterns
environment with the "wrong" background, for if they do, they become
Predation is the chief cause of death in many birds, especially
more conspicuous to their sight-oriented predators. Natural selection
smaller ones. Avoiding predation, therefore, appears to be the main
favors those individuals that best resemble their background and that
reason that so many birds have evolved cryptic markings. Not only

Cornell Laboratorq of Ornitholc9i Handbook of Bird Biologq

3.62 George A. Clark, Jr. Chapter 3 —Form and Function: The External Bird 3.63
"stay put" in it. The pale Piping Plover, for Countershading
example, spends much time on white sandy Many birds are hard to see because
beaches, where it is difficult for even the they are darker on top than below, a pattern
most persistent bird watcher to spot. known as countershading. Eastern King-
Many bird species with precocial birds, Northern Mockingbirds, most gulls,
young—those, such as ducklings, that hatch and many of the smaller plovers, sand-
with feathers, ready to leave the nest and for- pipers, and songbirds are familiar examples
age with their parents—are most cryptically (Fig. 3-55). With the darker back lit by the
colored in the period before they can fly. bright sun overhead and the lighter under-
Then, their best defense against predators is parts in the shade of the bird's own body, the
to be "invisible." Young terns and skimmers bird appears as nearly one color, and until
on beaches, for instance, blend so well into it moves, predators have difficulty seeing it
their background of sand and gravel that they as a three-dimensional object. In addition,
a are in danger of people stepping on them. white underparts may reflect the color of the ground, producing even Figure 3-54. Disruptive Coloration
Birds that we think of as gaudy in pic- more effective camouflage. Countershading is best developed in open- in Killdeer: Note how the black neck
tures or captivity may actually blend into bands of the adult and two chicks break
country birds that are vulnerable to distant predators hunting by sight.
up each bird's outline, making it hard
their natural surroundings. A visitor to the It also is common in birds that spend much time on the water, such as to distinguish against the busy, pebbly
tropics may spend a long time staring at a loons, grebes, ducks, auks, and many pelagic birds. background. Photo courtesy of Mary M.
huge squawking tree before finally glimps- Tremaine/CLO.
ing one of the many large, bright green par- Behaviors that Aid Concealment
rots within. Even birds as brilliantly colored Birds may increase the benefits of cryptic plumage with certain
as Keel-billedToucans and ParadiseTanagers behaviors. Simply holding still is one good way to avoid attracting
virtually disappear against the sun-dappled predators. By freezing into immobility and flattening againstthe beach,
tropical canopy overhead. young terns and gulls eliminate their shadows and look just like bumps
on the sand. The nocturnal potoos, odd Neotropical relatives of night-
Disruptive Coloration hawks, also complement their mottled brown-and-gray plumage with
In addition to resembling their back- behavior. They spend most of the day just sitting, often perched on the
grounds, some birds have disruptive colora- stub of a dead tree limb, with neck stretched up and large eyes closed,
tion. Like the "camouflage" of military gear,
disruptive plumage has patches, streaks, or
other bold patterns of color that break up
the shape of the bird, catching the eye and
distracting the observer from recognizing the
whole bird as one form. For example, the two
bold, black neck bands of the Killdeer com-
bined with its brown back make it virtually
impossible to distinguish against a pebbly
field or beach (Fig. 3-54). Similarly, the dark
or light eyelines found in so many birds are
thought to help disguise the otherwise con-
spicuous eye. Disruptive coloration has the
added advantage of providing camouflage
on a variety of backgrounds. Downy young
Figure 3-53. Cryptic Coloration of the Willow Ptarmigan: a: In winter,
the white plumage of both males and females disappears against the shorebirds in the arctic tundra have varie-
snow-covered tundra. Photo by Dan Stosits/CLO. b: In spring and fall, gated plumages that break up their outline so
as the male molts, his patchy brown-and-white plumage matches the much that predators (and humans, as well)
patchy snow conditions of the tundra. Photo by Johnny Johnson/Bruce
have trouble seeing them in a range of dif- Figure 3-55. Countershading in BlackTumstones: The shadow cast on the light-colored underparts of a standing Black Tu mstone
Coleman Ltd. c: In summer, the female's mottled brown feathers make helps to offset the contrast between the dark upper and light lower portions, making the bird appear flatter aga inst the background,
her nearly impossible to see as she incubates her clutch. Photo courtesy
ferent vegetation types (see Fig. 8-125). and more difficult to see. This effect would not work if the bird were light above and dark below, as demonstrated by the upside
of Al Camel I/CLO. down individual, which is much easier to spot in its dark, rocky habitat. This pattern of dark above and light below is known as
countershading, and is found in many species of birds.

Cornell Laboratorq of Ornithology Handbook of Bird Biologq

3.64 George A. Clark, Jr. Chapter 3— Form and Function: The External Bird 3.65
looking for all the world like an extension of the stub (Fig. 3 56). Many
-

owls, such as Long-eared Owls and screech-owls, adopt similar "stick

postures."The freezing strategy also works for many predators, such as
herons prospecting for fish or frogs along a shoreline. In some cases,
however, movement enhances concealment. American Bitterns blend
their streaked pattern with reeds by standing with their bills pointed
skyward. If wind blows the reeds, the bird, too, may sway slightly from
side to side (see Fig. 2-1 7).

Conspicuous Markings and Predation Northern Flicker

Many cryptically colored birds have conspicuous markings that

Dark-eyed Junco
become obvious only when the bird flies off. The white outer tail feath-
ers of juncos, meadowlarks, and Hooded Warblers; the black-and-
white flight feathers of Willets; the white "windows" in the primary
wing feathers of nighthawks; the bright orange-and-white rump patch
of Killdeer; and the white rump of Northern Flickers are examples
(Fig. 3 57). When such markings are suddenly revealed they may
-

startle an approaching predator, leading it to hesitate or to strike in the

wrong place and miss its target. Because many of these conspicuous
markings disappear when the bird lands, suddenly hiding the bird's
position, they also may confuse predators that had focused primarily
on the bold markings during pursuit.
Figure 3-56. Bird or Stick? The Common
The evidence that this deflective coloration serves an antipreda-
Potoo of Central and South America, a Figure 3 57. Deflective Coloration in
relative of North American nighthawks, tor function is scant, however. Birds sometimes reveal these hidden -

Birds: Many otherwise cryptically col-

spends most of its day motionless, often markings even without flight. A junco or Hooded Warbler hopping ored birds have conspicuous markings
perched at the end of a snag. Photo by J. on the ground, for instance, sometimes spreads and contracts its tail that become visible only when the bird
V. RemsenNIREO. feathers slightly, flashing its white markings prominently. The display flies or spreads its wings or tail. Such
of hidden conspicuous markings may actually function more in social markings, termed deflective coloration,
include the white outer tail feathers of
interactions between members of the same species than in interactions
Dark-eyed Juncos, the white rump of
between species, but more research is needed to evaluate the various Northern Flickers, and the black-and-
possibilities. white patches in the flight feathers of
Prominent markings in other animals, such as insects and frogs, Willets. Although researchers have
long assumed these markings evolved
may warn predators that the individual is distasteful. However, no ex-
as antipredator defenses—the birds
ample of a conspicuous, distasteful bird has yet been found. Moreover, evidence for this hypothesis exists. When Burtt (1 984) painted the nor- revealing them suddenly to startle or
the few known poisonous birds, such as certain members of the genus mal ly dark upper beaks of Willow Flycatchers white, the birds foraged confuse approaching predators, there
Pitohuifrom New Guinea, show no obvious warning coloration .These in the shade more often than those with the normal beak color. When is little evidence for this. Alternatively,
they may function in social interactions
poisonous birds are reddish brown—no more striking in appearance the birds with whitened upper beaks did forage in the sun, they had between conspecifics. Drawings by
than the nonpoisonous species of the same genus in other parts of lower foraging success. In addition, Burtt (1986) noted that species of Charles L. Ripper.
New Guinea. North American wood warblers with dark upper beaks forage in sun-
light significantly more often than those with light upper beaks.
Reduction of Glare for Foraging
Birds foraging in bright sunlight may experience glare as light The Role of Color and Pattern in Social Behavior
is reflected into their eyes from light-colored areas around the eyes, Birds, like humans, may use color and pattern to distinguish
lores, and upper beak. The glare may interfere with their vision, re- among species, sexes, ages, or individuals. The more that research-
ducing their foraging efficiency. Dark colors near the eye may reduce ers study coloration, however, the more they realize its importance
such glare, as in the face mask of the Common Yellowthroat, the dark in male-male (or female-female) competition for mates, and in mate
eye stripe of the Cedar Waxwing, and the dark head and upper beak choice. Many ways that coloration functions in interactions between
of many flycatchers, including the wood-pewees and phoebes. Some individuals are discussed below.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

3.66 George A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.67

Species Recognition Sex Recognition

A bird must recognize other members of its species (termed con- To a bird looking for a mate, knowing the sex of another indi-
specifics) to find a mate. Matings between species (hybridizations) vidual is key, but sex recognition also is critical in
often are evolutionary dead ends, either because no young are pro- numerous other social interactions, including /rtiqN
44"

duced or because the hybrid offspring do not survive or reproduce as birds defending territories or mates. In species
well as offspring from two parents of the same species. Hybridization in which the sexes differ dramatically in appearance,
sometimes occurs when conspecific mates are hard to find. For ex- such as Northern Cardinals, American Kestrels, and
Female
ample, hybrids between the Blue-winged Warbler and Golden-winged Red-winged Blackbirds, males and females
Warbler, known as Brewster's and Lawrence's warblers, are selected as are easy to distinguish. Dif-
mates primarily when pure blue-winged or golden-winged individuals ferences between sexes
are not available (Ficken and Ficken 1968). Hybrid pairing between are more subtle in other
a Blue Jay and a Florida Scrub-Jay occurred when the scrub-jay was species. In many woodpeckers,
the last female of its species remaining in the coastal scrubs of north- for example, the amount of red on the head
reveals the sex. In the Downy, Hairy, and Ladder- Male
eastern Florida.
Hybrids occur frequently in captivity, where the choice of po- backed woodpeckers, only males have red on the
tential mates is limited. This is especially common among ducks. For back of the head. In others, such as the Red-bellied,
example, the Wood Duck of North America and the Mandarin Duck Pileated, and Acorn woodpeckers, males have more red Figure 3-58. Northern Flicker Male and
on the head. Birds undoubtedly use the same plumage cues Female: Northern Flickers may use the
of Asia do not hybridize in nature, partly because they never meet.
black malar (whisker) stripe, found only
They have hybridized in captivity, however, when their mate choices that we do. In Northern Flickers, for example, only males have the
on the male, to determine the sex of a
were restricted. black malar (whisker) stripe (Fig. 3-58). One researcher (who probably bird. When a researcher painted malar
Because individuals that mate with their own species usually also drew mustaches on posters) painted malar stripes on females, and stripes on females, their mates chased
their mates chased them away (Noble, 1936)! When students work- them away! (Noble 1936)
produce more young, this tendency is strongly favored by natural se-
lection. As a result, birds have evolved many different mechanisms to ing with a flock of California Quail dyed the plumage of the females
ensure that they mate with the correct species. Appearance, vocal iza- to resemble that of the males, the males treated their former mates as
tions, courtship displays (see Ch. 6, Courtship Displays), anatomical males. In species with similar-looking sexes, males and females seem
and physiological differences (size, sperm-egg incompatibility), and to recognize each other by behavior.
other behaviors probably all play a role. Note that birds do not require different plumages to recognize
Although researchers have long assumed that color and pattern the opposite sex. About half of all songbirds, for example, have similar
both function in species recognition, devising experiments that clearly plumages in both sexes. In these species, males and females recognize
distinguish their importance is difficult. Therefore, little supporting each other by behavior. This fact reminds us that sexual differences in
data existfor this idea. Moreover, when obvious species-specific mark- plumage may arise for a variety of reasons besides mate selection; rea-
ings, such as the red epaulettes of the male Red-winged Blackbird, are sons that relate to the different roles played by each sex—in courtship,
experimentally covered up, the sexes do continue to establish pairs nest attendance, and territorial defense, for example.
(Searcy and Yasukawa 1983); these experimentally altered males are
Individual Recognition
recognized as conspecifics by the other males. Interestingly, the al-
To us, one Black-capped Chickadee or Yellow Warbler looks
tered males were less able to defend their territories. Clearly, species
much like the next. Occasionally we might recognize a bird with a
recognition involves a variety of cues acting together, behavior plays
distinctive color abnormality or a missing feather, and with much work
a key role, and species-specific color patterns also influence how
we can learn to recognize individuals of some species, such as Downy
conspecifics treat one another.
or Pileated woodpeckers, by differences in the patterns on the backs
Age Recognition of their heads. Among wintering Tundra Swans in western England,
As discussed earlier, many different birds (gulls, American Red- researchers can distinguish hundreds of individuals, mostly by varia-
starts, Red-winged Blackbirds, and others) have distinctive subadult tions in their bill markings. But individual recognition in most species
plumages before they become sexually mature. We know that birds remains a mystery to us—unless, of course, we have colorbanded or
recognize age differences because, given a choice, they usually se- tagged birds for personal identification. Many birds, however, clearly
lect mates in definitive plumage. But we do not know for certain if recognize each other, especially their mates. How? Birds probably
they choose mates on the basis of plumage or some other indicator identify familiar individuals the same way we recognize other people,
of age. Subadult plumages clearly serve other functions besides mate by subtle differences in color, head and body shape, facial features,
selection. posture, and voice. And some are very good at this—a Northern Pintail
can recognize its mate 300 yards away!

Cornell Laboratorti of Ornitholo8q Handbook of Bird Biologq

3.68 George A. Clark, Jr. Chapter 3 — Form and Function: The External Bird 3.69
Several studies have demonstrated that birds use color and pattern of territory quality. A second way that sexual selection can operate is
to recognize individuals. When Ruddy Turnstones—shorebirds with by directly increasing an individual's attractiveness to the opposite sex.
highly variable plumage—were shown models that mimicked their Female House Finches choose mates with the brightest red coloration,
neighbors or strangers, they reacted aggressively only to the strangers and female Great Snipes (an Old World species) choose males at least
(Whitfield 1 986), strong evidence that they could distinguish them partly by the amount of white on their tails. We assume, therefore, that
by appearance alone. In addition, several colonially nesting species, these features—bright red House Finch feathers, and white in Great
including Ring-billed Gulls, can pick their own young from a "crowd" Snipe tails—have evolved through sexual selection.
of young by their facial markings. A trait may be attractive to members of the opposite sex for a num-
ber of reasons, most of which are discussed in Chapter 6. However,
Flock Attraction directly related to plumage color is the suggestion by Hamilton and
Individuals of gregarious species such as gulls, gannets, swans, Zuk (1982) that birds in good health, or with fewer ectoparasites, may
egrets, vultures, crows, or blackbirds often locate other individuals or be better able to sport brightly colored feathers than are less healthy
feeding flocks by sight. Most of these species are black, white, or black- birds. Indeed, bright colors actually might have evolved as an honest
and-white—conspicuous colors that show up well from a distance and indicator of health. Therefore, in choosing their mates, males and fe-
may aid flocking (Savalli 1995). males should select the more brightly colored individuals. A number
of studies have supported the relationship between health and bright
Sexual Selection
colors. For example, in House Finches, males with brighter feathers
Throughout this section we have discussed how birds may use
are apparently in better nutritional condition (Hill and Montgomerie
differences in appearance to avoid mating with other species and to
1994) and the colorful combs of chickens and wattles of turkeys fade
recognize each other in various ways. But the more we learn about
in brightness when the birds become sick (Stephen T. Emlen, personal
birds, the more evidence we find that successfully competing for a
communication).
mate within the species may be one of the most important functions
Why don't birds "cheat" and produce colors or markings that
of distinctive colors and patterns (Butcher and Rohwer 1989; Savalli
advertise a higher quality than the bird actually is? In most cases, pro-
1995).
ducing the attractive colors bears a cost, which only birds of high qual-
Well over a century ago, Charles Darwin recognized that cer-
ity can afford. For example, House Sparrows with large bibs may be
tain inherited traits, such as the gaudy plumes of a peacock or the red
challenged by others with large bibs, and if they don't have the fighting
epaulettes of a Red-winged Blackbird, do not necessarily promote
ability they claim, they may be badly beaten in a fight. And unhealthy
individual survival. Instead, these features improve a bird's chance of
or otherwise poor-quality individuals may be unable to spare the en-
acquiring a mate, and therefore spread in a population because more
ergy needed to produce and maintain brightly colored plumage.
young are produced that bear the advantageous traits. Darwin gave this
Sexual selection is most apparent when it produces extreme
process its own name, sexual selection, although it is,
and colorful plumages, which usually occurs in species in which a
in fact, a special type of natural selection.
few males mate with many different females, as in peacocks and the
Sexual selection can operate in two
gaudy, bright-orange South American Cock-of-the Rock. But it also
related but distinct ways. First, it can pro-
can operate in species with the most common type of mating system-
mote traits that increase a bird's ability to
monogamy—in which birds appear to form a pair bond with only a
compete with other members of its sex, thus
single mate. As researchers look more closely at these species, even
gaining favor with or access to mates. As an
sampl ing the DNA of young and adults to determine the paternity of the
example, consider the black bib of the male
young, they are finding that males and females of many species thought
House Sparrow, thought to have evolved this
to be monogamous commonly copulate with individuals in addition to
way (Fig. 3-59). Researchers have demonstrated
their own mates. In some cases, birds may use plumage coloration as
that male House Sparrows with larger bibs are more
a quick way to assess the quality of their potential consorts. Sexual se-
Figure 3-59. Male and Female House dominant, hold better quality territories, and chase and copulate with
Sparrow: The black bib of the male
lection can even operate in species in which a single male and female
females other than their mates more often than males with smaller bibs.
House Sparrow, thought to have evolved truly do pair, as birds with more "attractive" plumages may acquire a
The black bib, by itself, does not bring these advantages, but serves as
through sexual selection, appears to act better-quality mate or may be chosen earlier in the breeding season.
as an indicator of male quality. Males an accurate way for a male to visually signal his quality to other males,
Sexual selection is discussed in greater depth in Chapter 6.
with larger black bibs are more dom- without fighting. Presumably, males that can avoid the risk of injury
inant, hold better quality territories, associated with fighting have an evolutionary advantage over those
and copulate with females other than We have now scrutinized the "outsides" of birds from beak to
who must fight. Similarly, the red epaulettes of Red-winged Blackbirds
their mates more often than do males foot. This close look has revealed how exquisitely natural selection
with smaller bibs. Drawing by Charles
probably evolved because they give males an advantage in male-male
has fine-tuned birds to meet the demands of their physical and social
L. Ripper. competition for territories, and females choose their mates on the basis
environments, from the way that barbu les interlock on a hummingbird

Cornell Laboratorq of Ornithologg Handbook of Bird Biolo9q

 V"-

3.70 George A. Clark, Jr.

feather and sparrows sputter about during dust baths, to the "snow-
shoes" of a Ruffed Grouse in winter and the cryptic brown streaking
on an American Bittern. We do not know the significance of every
structure or color pattern we've considered, and some may remain a
mystery forever. But the more we find out about each pattern, the bet-
ter we understand how evolution works and why birds behave as they
do. These are just some of the reasons why birds are such a rich and
important group to study and enjoy endlessly.

What's Inside:
Anatormi and Phtisiologq

Howard E. Evans and]. B. Heiser

Much of the thrill we experience watching birds is in see-

ing them fly, listening to their songs, discovering them at
their nest, or simply watching them go about their daily
rounds caring for their plumage and feeding. Rarely do
we consider just how the bird's body actually accomplishes these won-
ders. Exactly what are the various parts and pieces that go together to
make a bird—and how do they perform, in concert with one another,
to produce the marvelous lives that give us so much pleasure?
That is the subject of this chapter—the anatomy and physiology of
birds. The subject is so vast that we can barely scratch its surface. The
topic is somewhat simplified because much of the form and function of
birds is very much like that of our own, thanks to a shared four-legged
terrestrial ancestor. However, birds do have senses and capabilities that
we can only imagine, so different are they from ours.
Most of the distinctive features of avian anatomy and physiology
are adaptations to flight: not only are birds light in weight, but the de-
mands of flight make birds some of the highest energy users for their
size in the animal kingdom. This energy powers flight; heats a small,
easily cooled body; and supports the highly active life birds live even
when not flying. While exploring the anatomy and physiology of a
group of organisms, one often finds that the study of one specialized
characteristic leads to another and then to another. This is especially

Cornell Laboratorq of Ornithologq

 4.2 Howard E. Evans andJ. B. Heiser

true with birds, however, so intimately are their adaptations intercon-

r Chapter 4 —What's Inside: Anatomq and Phqsiologg

cussed are: the skeletal system; muscular system (excluding the skin
4.3

nected; flight affects everything about them. muscles that move the feathers); nervous system including the sense
Throughout this chapter we will take a functional approach, organs; endocrine system; circulatory system; respiratory system; di-
concentrating in each section on anatomical structures with similar gestive system; and urogenital system. The skin and structures that are
functions; these have been grouped together into functional systems. produced by the skin such as feathers, color pigments, scales, claws,
As in all living things, these systems are ultimately composed of beak, wattles, and comb make up the integumentary system, which
cells, the basic units of life. Cells with related and often very similar was considered in Chapter 3. This chapter concludes with a look at
characteristics are aggregated to form tissues. Tissues, often of quite bird metabolism.
distinctive character and function, combine to form discrete organs. At the end of the chapter is a table summarizing the major ana-
A group of organs whose various functions are coordinated to ac- tomical differences between birds and mammals, arranged by organ
complish one or more of the basic functions of life is recognized as system. You may wish to refer to the table from time to time as a quick
an organ system. For example, cardiac muscle cells together form the review of each system.
smooth muscle tissue of the heart, which, together with heart valves
and the inner and outer covering of the heart, form most of the heart
organ. The heart, blood vessels, and the blood together constitute the The Skeletal Sijstern
circulatory system (Fig. 4-1). ■ The skeletal system, composed of bone and cartilage as well as
In this chapter we discuss the important features that are "inside" associated joints, tendons, and ligaments, supports and protects the
a bird, considering the internal organ systems one by one to understand soft structures of the body; provides for the attachment of muscles that
4 the component parts. Interaction and integration of these systems are move the skeleton; and serves as a storehouse for calcium, phosphorus,
of vital importance and are repeatedly pointed out. The function of and other elements. You might think that adult bones, once formed,
each system (its physiology) is then investigated with special attention were "dead" structures and always remained the same, similar to the
to flight, reproduction, and metabolism (energy use). The systems dis- steel girders of a building. But this is an entirely false perspective. Bones
are very much alive: they are sheathed and riddled with living cells.
Cell Tissue Organ Organ System
Bones are constantly changing in shape and composition in response
to physical stress such as that produced by exercise, or by variations
Cardiac Muscle Cells Smooth Muscle Tissue in the vitamins and minerals in the diet, or in the body's demands for
of Heart
HEART the minerals that bones contain. Certain bones of birds also contain
(Heart Valves and cavities filled with red marrow, the primary blood-forming tissue in
Surrounding Membranes)
the adult.
Bone is a tissue composed of living cells in a matrix (the sub-
Connective Tissue Cells Connective Tissue
(Outer Layer of stance between cells in which they are embedded) called osteoid.
Blood Vessels) The matrix contains microscopic fluid spaces and has a blood supply
BLOOD CIRCULATORY that constantly deposits or moves the mineral components, primarily
Smooth Muscle Cells ...pi. Smooth Muscle Tissue
VESSELS SYSTEM
(Middle Layer of hydroxyapatite—a calcium phosphate mineral—from one place to
Large Blood Vessels) another. The calcium residing in one bone in the morning may well
be in another by afternoon, or in an eggshell the next day, should the
Epithelial Cells Epithelium
(Inner Lining of bird be laying a clutch.
Blood Vessels) Bones have distinctive shapes, and are constantly being remod-
eled as they grow. Bones act mechanically as levers for the action of
Red Blood Cells
muscles, and the continued use of a muscle can result in the formation
Blood
of a bump or process on the bone where the muscle attaches. This oc-
White Blood Cells
curs because when a muscle contracts and pulls on a bone it activates
deposition of calcium within the matrix of the bone, especially at the
Figure 4-1. Functional Organization of the Vertebrate Body: Cells are the basic units of living things. Cells with similar charac-
teristics group together to form tissues, and different types of tissues combine to form organs. A group of organs whose function is site of muscle attachment, which may alter the shape or size of the
coordinated to carry out one or more basic life processes is considered an organ system. As an example, consider the components bone. These features are so characteristic that they can serve as land-
of the organ system called the circulatory system, pictured here. Some of the basic units are connective tissue cells, smooth muscle marks for the identification of a particular bone.
cells, and epithelial cells. These cell types aggregate with their own kind to form, respectively, connective tissue, smooth muscle
When a bird is forming an egg prior to egg laying, calcium is taken
tissue, and epithelium. Together, these three tissue types make up the organs known as blood vessels. Another circulatory organ,
the heart, is composed of smooth muscle tissue as well as heart valves and membranes. (The latter two components are really not from the bones, transported by the blood, and deposited as shell on the
tissues or organs, but organ parts.) The heart, blood vessels, and blood (a liquid tissue composed of white and red blood cells) egg in the uterus. If too little calcium is deposited on the egg, the shell
together make up the circulatory system. will be thin and might break when the bird sits on it during incubation.

Cornell Laboratorg of Ornithologq Handbook of Bird Biologq

 4.4 Howard E. Evans andJ. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.5
But if too much calcium is taken from the bones during eggshell for- as in woodpeckers. (How the woodpecker protects its brain from the
mation, the bones may become fracture-prone. Much of the delicate violent impacts of its hammering is still an open question.)
balancing act that makes possible both successful reproduction and Lightness comes from cavities or spaces that develop within
the continued existence of the parent bird is controlled by the endo- almost all bones as a bird grows. These spaces connect to the respi-
crine system (see later in this chapter) and its regulation of calcium ratory system and thus contain air. We call such bones pneumatic
metabolism, especially through the dynamics of living bones. (noo–MAT–ik) and speak of the skeletal system as being pneumatized.
Two general features were acquired by the skeleton of birds dur- Because they are filled with air spaces and not bone and marrow, bird
ing the evolution of flight. One is rigidity and the other is lightness bones are lighter in weight than similar-sized bones of other vertebrate
(Fig. 4-2). groups. For example (Fig. 4-3), a male Mallard and a male mink may
Rigidity of the skeleton is the result of various fusions of neigh- both weigh about two and one-half pounds (just over one kilogram)
boring bones, particularly parts of the vertebral column. Consequently, and be nearly the same lengths (not counting the tails), but they appear
birds (unlike most other vertebrates) are notoriously stiff-backed. As quite different in "size"—the duck has a much greater volume. The
compensation they have long and highly moveable necks. Their body bird's lower density is due in part to the bird's hollow bones. Actually
rigidity strengthens the skeleton for the stressful actions of flying and the skeletons of the two animals are very similar in weight (about 2.25
landing as well as running and jumping. Likewise, fusion of the skull ounces [60 to 65 grams] when clean and dry). But almost every bone
bones allows the use of the beak as a lever or as a "hammer and chisel" of the bird is larger in some or all dimensions, with more surface area
for muscle attachment.
Reduced and Fused Weight Reduction
Finger Bones Aided by Lightweight The air spaces in skull bones arise from nasal passageways, where-
Bones of Skull as those in the vertebrae, sternum, ribs, pelvis, humerus, and femur are
and Toothless Beak connected to either the air sacs or the lungs directly (see Fig. 4-82b).
Modified Joints The largest and most efficient flying birds, such as the albatrosses and
Hollow Long Bones Allow Folding or
1Locking of
frigatebirds, have interconnected air spaces passing from the humerus
Continuous Fused
with Air Sacs ... Wings to the tips of the digits across all of the joint spaces. In contrast, a pen-
Wrist Bones
and Strengthened guin, a flightless bird that swims with its short but powerful wings and
by Internal Struts can dive to considerable depths, has solid bones that lack pneumatic
spaces; thus the skeleton is relatively heavy and functions as ballast
(weight) for diving. Loons (which make long, deep dives) also have less
pneumatization than most nondivers. The degree of pneumatization
does not always indicate the flying or diving ability of a bird, however.
Uncinate Processes The air sacs of the skull are actually fewer and smaller in birds such as
on Ribs Strengthen Coracoid Strong Pectoral Bones
Rib Cage Prevent Collapse of
Clavicle Chest Cavity
Reduced Tail (Wishbone) During Wingbeats

r- -
N Large Keel on Sternum for
Attachment of Flight Muscles
Fused
Pelvic
Girdle Figure 4-2. The Avian Skeleton and its Adaptations for Flight: Most of the dis-
tinctive features of a typical bird skeleton, such as the Rock Dove (pigeon) skel-
eton shown here, are adaptations for flight. Weight is reduced by hollow bones, a
lightweight skull, a toothless beak, and a reduced number of bones in the tail and
hand regions. Rigidity is achieved through the fusion of many bones, including
the pelvic region, the hand, and portions of the vertebral column. In addition,
modified joints allow the wings to lock open, providing rigidity at certain times Figure 4-3. Mallard and Mink: A male
during flight. Strength is added by struts inside the hollow bones; backward-pro- Mallard and a male mink both weigh
jecting, laterally-flattened, and ossified caudal projections (uncinate processes) about 2.5 pounds (just over 1 kg), and
Rock Dove on each rib that overlap the adjacent rib; and large, strong pectoral girdle bones, 1'Zi/P7)".-ZffETer(k.:71rEIZYLETEZflff/
. have about the same body length. The
0#
which support the chest cavity—particularly during flapping flight. Finally, the Mallard Mallard, however, has a much larger
large but lightweight keel on the sternum adds a stable attachment point for the volume and thus a lower body density,
heavy flight muscles. Drawing by Charles L. Ripper. Inset photo of Rock Dove in due in part to its lightweight, air-filled
flight by Marie Read. ' ••••••\\\\• \\\, , ,%,,\ • bones.

Cornell Laboratort of Ornithologq Handbook of Bird Biolo5q

4.6 Howard E. Evans andi. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiologq 4.7
swifts that fly fast, perhaps to allow the head to be smaller and more
compact as an aid to streamlining. Other fast-flying birds, such as Phalanges
shorebirds, also have reduced pneumatization. Extensive skull pneu- Cranium
matization is also decreased in some birds that dive from the air into
water, such as terns and kingfishers, and in woodpeckers that "ham-
mer" wood with their bills and need very strong skulls. Metacarpus
Another distinctive and uniquely important tissue of the skeletal
Carpus
system is cartilage, the same tissue found in human joints. Cartilage,
like bone, is a tissue with living cells embedded in a nonmineralized Ulna
matrix, capable of growth or resorption as well as transformation into Radius

bone. In the growing bird embryo, the initial skeleton entirely of car-
ti lage ossifies (becomes bone) very rapidly around the time of hatching
and continues ossifying at a slower rate throughout life. A similar se- Uncinate Process
quence occurs in other vertebrates, including humans. Bone also can
be formed directly in tissues without going through a cartilage stage. Pelvic Girdle
Such direct ossification is seen in tendons of the hind-limb muscles in
most birds, and is familiar to aficionados of the turkey drumstick.
Tendons, which connect muscles to bones, and ligaments, which Pygostyle
connect one bone to another across a joint, are soft, pliable, and above
all elastic tissues when they are not ossified. They have few living cells
and a restricted blood supply, which explains why they heal from
injury so slowly.
Coracoid
By convention the skeleton is divided into an axial skeleton and
an appendicular skeleton. The axial skeleton consists of the vertebral lschium
column of the neck, trunk, and tail, and the exquisitely complicated
skull, with its associated hyoid apparatus (the supporting framework
of the tongue). The appendicular skeleton consists of the sternum or Pubis
breastbone, the pectoral girdle with wings, and the pelvic girdle with
legs.
Shown in Figs. 4-4, 4-5, and 4-6 are the articulated skeletons
(that is, the bones are joined together as they would be in life) of a
domestic chicken, a Budgerigar (a type of parakeet), and a Golden
Eagle. You may wish to remove these pages and keep them readily at
hand while reading about both the skeletal and muscular systems. The
chicken has its wings extended as if it were about to take off in flight.
This is the standard position used in mounting or illustrating a bird
for anatomical study. The parakeet has its wings folded in a normal
perching position, and the Golden Eagle has its left wing lowered and
pulled slightly away from the body. Refer to these drawings frequently
as you proceed in your reading; they will orient you to the parts being
discussed. You will note differences between the three species of birds Tarsometatarsus
illustrated. The skeletons of all bird species differ from one another
in ways that are not apparent externally but are often significant to
evolutionary and systematic ornithologists. If you have at hand the
actual skeleton of a bird, or even some isolated bones, so much the
better, for you will be able to see how they appear in three dimensions. Figure 4-4. Skeleton of the Chicken: Viewed from the left side, the chicken skeleton is shown with the left wing raised over the
(Perhaps it would be useful to plan on a whole roast chicken dinner body. Compare with Figures 4-5 and 4-6, in which different bird species in different positions provide additional perspectives
of the articulated skeletal system. Not all skeletal components are equally developed, visible, or labeled in each example. The
before reading further!)
adaptations of these three species for their different lifestyles are evident in their bones. On the chicken, notice the robustness of
the leg and foot bones, and the relatively large pelvic girdle, indications that this is a ground-dwelling species. Paired structures,
such as the wings, legs, and ribs, are only shown for the left side of the bird.

Cornell Laboratorq of Ornitholo8q Handbook of Bird BioloBq

 4.8 Howard E. Evans and J. B. Heiser Chapter 4 —What's Inside: Anatomq and Phqsiologq 4.9

Atlas
Radius

Ulna

Humerus
Ulna

Scapula
4 Uncinate Process
Humerus
Ilium
Pelvic Girdle
N

Pubis
Ischium Carpometacarpus Synsacrum

Ulna
Pygostyle

Sternum
(With Large Keel)
Femur
Pygostyle
Ischium

Tibiotarsus

Figure 4-5. Skeleton of the Budgerigar: The skeleton of this Budgerigar (a species of parakeet) is viewed from the left side, in a Figure 4-6. Skeleton of the Golden Eagle: This skeleton is viewed at an angle: from the rear and slightly to the left side, and from
normal perching position, with the left wing folded against the body. In this view the clavicle and coracoid are hidden by the somewhat above. The feet are not shown. The left wing is lowered and pulled away from the body slightly, to demonstrate the
folded wing, but notice the large keel on the sternum indicating that the bird is a strong flyer. Note, too, the relatively small pelvic great mobility of the pectoral girdle (see Fig.4-16). Notice the eagle's massive wing and leg bones, evidence that it is a powerful
girdle and less-developed leg and foot bones—evidence that this bird spends much of its time perching, rather than walking or flier with equally powerful legs used to capture its prey. The robust skull with its massive hooked beak is yet another adaptation
running on the ground. The differences in skull anatomy between this species and the chicken in Figure 4-4 are conspicuous. for a predatory lifestyle. Reprinted from Manual of Ornithology, by Noble S. Proctor and Patricia Lynch, with permission of the
Drawing from Evans (1996). publisher. Copyright 1993, Yale University Press.

Cornell Laboratoni of Ornitholvi Handbook of Bird Biolojt

4.10 Howard E. Evans and,J. B. Heiser Chapter 4—What's Inside: A natornq and Phqsiolocqq 4.11
Figure 4-7. Age-related Changes in a. Dorsal View Figure 4-8. The Skull of the Budgerigar:
the Ossification and Pneumatization Entire cranium pinkish in color
Dorsal View: The cranium, or brain-
of the Passerine Skull: The cranium of Entirely unpneumatized
case, is composed of several bones that
a newly fledged passerine is composed
Fledglings
(June -July) are so completely fused in the adult bird
of a single layer of cartilage and bone. that the boundaries, or sutures, between
As the young bird ages, a second layer them are no longer visible. Notice the
Peripheral Median Line Cranium -
develops under the first, the two layers large orbits in which the eyes reside. The
Pattern Pattern
being slightly separated by air spaces skeleton of the upper beak consists of
and joined by small columns of ossify- the nasal region containing the nostrils,
ing bone. The development of these lay- and the fused premaxillary bones. The
ers is called skull pneumatization, and upper beak connects to the rest of the
is followed by full ossification, usually skull at the flexible craniofacial hinge
Orbit -
complete by the time the bird is one year (also called the nasal-frontal hinge).
old. Although there is variability among b. Lateral View: This view shows more
species, the process typically follows Large pinkish areas,
clearly the cranium's position relative to
small grayish areas
one of two patterns. In the peripheral the bones of the upper and lower jaws,
- 2 - 4 Months Old
pattern, pneumatization develops from as well as the ear openings, which are
(August - October)
the outer edges of the cranium inward, slightly caudal and ventral to the orbits.
Craniofacial
whereas in the median line pattern, Compare this view to that of the chicken
Nasal Hinge
pneumatization starts along a central in Figure 4-9. Most obvious is the differ-
Region
line and develops on both sides of the ence in shape between the premaxilla
cranium simultaneously. Unpneuma- and dentary bones of the two species.
tized areas of a passerine skull appear The Budgerigar has a strong, hooked
Premaxilla
pinkish in color, whereas pneumatized beak typical of parrots and parakeets,
areas appear grayish or whitish and de- used for cracking hard seeds, whereas
Large grayish areas, Ask
velop small white dots as the bony col- the chicken has a straight, stout beak for
umns ossify. If the head feathers of a bird small pinkish areas
pecking at food on the ground. Drawings
5 - 7 Months Old b. Lateral View
in the hand are parted to expose the skin from Evans (1996).
(November -January)
overlying the skull, the degree of skull Cranium
Orbit

V
coloration may be visible. Experienced
bird banders use skull ossification and Craniofacial Hinge
pneumatization to reliably determine Entire cranium grayish, whitish, or
the age of passerines captured in the fall, pinkish-gray in color, with white dots
a technique known as skulling. Adapted Entirely pneumatized
from Pyle et al. (1987, p.9). Adults

Pneumatized Areas of the Cranium

Axial Skeleton
Skull Ear Opening
The skull is the skeleton of the head. Most skull bones are so com-
pletely fused in adult birds that we cannot distinguish any sutures or
boundary lines between them. The presence of visible sutures (which
can be seen through the skin of a living bird) is an indication that the
Articular
skull in question is that of a very young bird. In newly-fledged pas-
serines, the skull is composed of a single layer of cartilage and bone. The skull (Fig. 4-8) is composed of a braincase or cranium, which
As the bird ages, however, a second layer develops under the first, incorporates the ear or otic region on each side. The median nasal
the two layers being slightly separated by air spaces and joined by region and mouth support respiratory and digestive openings. The
columns of ossifying bone. The development of these layers is called lower jaw or mandible of the bird consists of right and left parts (the
skull pneumatization, and is followed by full ossification of the skull, dentary bones) fused at the tip of the beak. The apical region of the up-
both of which are usually complete by the time the bird is one year old. per jaw is formed by right and left premaxillary bones. This proper use
The degree of skull ossification and pneumatization are often used by is still lacking in much ornithological literature in which the potentially
bird banders to age a live passerine bird in the hand, enabling them to confusing terms "upper and lower mandible" are still in common use
distinguish a bird fledged that year from older individuals (Fig. 4-7). (see Baumel et al. 1 993). Throughout this course we will use "upper

Cornell Laboratorq of Ornithologq Handbook of Bird BioloBq

AL_
4.12 Howard E. Evans and J. B. Heiser Chapter 4 —What's Inside: Anatomq and Phqsiologg 4.13
Figure 4-9. The Avian Jaw and Cranial a. Opening the Jaws beak" and "lower beak" when referring to a. Ventral View of Rock Dove Hyoid Apparatus
Kinesis: Shown here is a lateral view of Craniofacial the intact, living bird.
a chicken skull. The premaxillary bones Hinge Tongue Bone
The lower jaw articulates with the
of the upper jaw articulate with the cra- (Entoglossal)
Premaxilla moveable quadrate bone on each side of
nium at the flexible craniofacial hinge,
allowing the upper jaw to move at the the skull; this articulation allows the mouth
same time as the lower jaw—a process to open widely (Fig. 4-9). Because the quad-
known as cranial kinesis. The bird's low- rate bone can also pivot forward at its ar-
CID
er jaw consists of left and right dentary
ticulation with the skull, it allows the lower
bones, fused at their tip. The lower jaw is
Quadrate Rotates
linked to the upper jaw via the articular Dentary jaw to be protruded while the upper jaw is Hyoid Horns
Forward
bone and the adjacent quadrate bone, raised by extreme extension at the cranio-
which play an essential role in cranial Articular
facial (nasal-frontal) hinge. One set of mus-
b. Lateral View of Budgerigar Hyoid Apparatus
kinesis. a. Opening the Jaws: The pro- Palatine
cles attached to the quadrate, cranium, and
cess of bill opening begins when a set Arch
of muscles acts to drop the lower jaw.
lower jaw opens the bill by simultaneously
As the lower jaw moves downward, the lowering the lower beak and rocking the
articular bone applies pressure on the quadrate forward, forcing the upper beak
quadrate bone, causing the quadrate to b. Closing the Jaws upward. Another set of muscles closes the
rotate such that its lower surface moves Tongue Bone
bill by depressing the premaxillary bones Cartilages
forward. As it moves, the quadrate (Entoglossal) of the
pushes against two sets of bony rods, the and at the same time raising the lower jaw.
Larynx
palatine and the fugal arch, which push This flexibility of the jaw joints, which al-
against the premaxillary bones, raising lows the upper jaw to be raised at the same
the upper jaw while the lower jaw is
ti me thatthe lower jaw is depressed, is called
being depressed. b. Closing the. Jaws:
To close the bill, another set of muscles cranial kinesis. Movement of the bird's up-
depresses the premaxillary bones while per jaw contrasts sharply with the fused im-
it raises the lower beak. Adapted from mobility of our upper jaw in relation to the
King and McLelland (1975, p. 17). rest of our skull, and is associated with the
forceps-I ike functioning of the beak to grasp
food (Fig. 4-10).
No living bird has teeth, although several birds, particularly fish- Figure 4-11. The Hyoid Apparatus: The
,-1D) eaters such as the mergansers, have serrated bills. Teeth (structurally like bones and cartilaginous structures form-
ing the skeleton of the tongue are col-
those of other vertebrates) were present, however, in the most ancient lectively termed the hyoid apparatus.
Jurassic birds of Bavaria, such as Archaeopteryx, and continued to be Muscles attached to this compound
/Ostrich present in Cretaceous birds of North America, such as Hesperornis and structure extend and retract the tongue.
Ichthyornis. These ancient teeth are but one of the many characteristics a. Ventral View of Rock Dove Hyoid
Apparatus: Note the two hyoid horns,
that birds inherited from their ancestors.Through natural selection, birds
each composed of two bones, which
Figure 4-10. Cranial Kinesis in Action: subsequently discarded teeth in favor of the lighter bill. extend backward from the tongue bone
The upper jaw of birds, unlike the upper The large orbit or cavity for the eye is so deep that the eyes almost and continue beneath the skull, curving
jaw of humans, is capable of movement, meet on the midline of the skull. Only a thin, sometimes incomplete, upward around the back of the head in
giving the beak a pincer-like motion some species. Drawing by Charles L.
American Bittern known as cranial kinesis (see Fig. 4-9).
interorbital septum separates them. Aside from the beak, the orbits
Ripper. b. Lateral View of Budgerigar
The degree to which cranial kinesis oc- are the most prominent feature of the bird skull. In Figure 4-8 notice Hyoid Apparatus: The length of the hy-
curs in various species is related to their how the orbits crowd the braincase backward. The ear opening lies oid horns varies considerably among
feeding habits. In the Ostrich, a grazing close to the lower rim of the orbit on each side. In owls, the opening species. In the Budgerigar, the horns are
bird, cranial kinesis is poorly developed: short, indicating that these birds use their
to the ear is at a slightly different level on the right and left sides. This
to feed on grasses and other vegetation tongues to manipulate food within the
this species does not need to open its asymmetry allows for a more accurate pinpointing of the direction of
mouth rather than extending the tongue
beak wide. In contrast, the American a sound source by increasing the disparity in arrival times of a sound to feed. The tongue bone itself may be
Bittern has considerable kinesis, open- at the two ears (see Fig. 4-47). spear-shaped, as in the Rock Dove;
ing its beak wide to seize a frog. In the blunt, as in the Budgerigar; or flexible,
American Woodcock
American Woodcock, movement is as in hummingbirds; the differences
Hyoid Apparatus
greatest at the tip of the beak, allowing reflect the different structures and func-
the bird to grasp earthworms while the
Between the two halves of the lower jaw is the hyoid apparatus,
tions of the tongue. The hyoid apparatus
beak is immersed in soft soil. Drawings a series of articulated bones that support both the tongue and the surrounds and is attached to the larynx.
by Charles L. Ripper. muscles that provide for tongue movement (Fig. 4-11). Adapted from Evans (1996).

Cornell Laboratort of Ornithologq Handbook of Bird Biologq

4.14 Howard E. Evans and J. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiologq 415

The term "apparatus" is a collective name for all the bones and a. Lateral View of Cervical Vertebrae

cartilages that compose thisV-shaped structure. The muscles attached

to the bones of the hyoid extend and retract the tongue. In Figure 4-1 1b Anterior Centrum End
note that each horn of the hyoid is composed of two bones that extend of Next Vertebra
HEAD OF BIRD TAIL OF siRn
backward (caudally) beneath the skull and then curve around the back
Centrum
of the head. The horns are particularly long in woodpeckers and other
birds that can extensively project the tongue (Fig. 4-12). The Eurasian Posterior Centrum End
Cervical Cervical
Green Woodpecker has the longest hyoid horns for its body size, and Vertebra A of One Vertebra
Vertebra B
presumably can extend its tongue the farthest. Short hyoid horns, as
in parrots, indicate that the birds use their tongue to manipulate food
within the mouth rather than extending it to collect food. In birds that
eat worms and grubs, the bone that supports the tongue—called the
tongue bone, or entoglossal—may be spear-shaped, and the integu- b. Ends of Cervical Vertebrae
mentary portion of the tongue may bear spines; in birds that manipu-
late seeds or fruits, the entoglossal is blunt and padded by the tongue
tissue; and in nectar feeders, it is flexible and covered by a brush-like Posterior Centrum End: Anterior Centrum End:
tongue. More will be said about the tongue in the discussion of the Concave Dorsoventrally Concave Laterally
digestive system.

Vertebral Column
The vertebral column, commonly called the "backbone," is not a
single bone but a series of complicated, uniquely articulating or rigidly
fused vertebrae (singular, vertebra) that vary in number among spe- c. Coupling Mechanism Cervical Vertebra A Cervical Vertebra B
cies. As in other vertebrates, the vertebrae are named by region (and

Figure 4-13. Cervical Vertebrae and Flexibility of the Bird Neck: Birds are well known for the flexibility of their necks, facili-
Figure 4-12. The Hyoid Apparatus and
tated by having a large number of interlocking cervical vertebrae that can rotate against one another freely in all directions. The
Tongue Protrusion in the Northern
a. Tongue Retracted two ends of the main body (centrum, see a) of each vertebra are shaped differently. The anterior end of the centrum is concave
Flicker: In woodpeckers, a highly pro-
(saddle-shaped) in a lateral direction, whereas the posterior end of the centrum is concave in a dorso-ventral direction (see b). This
trusible tongue is an essential food-gath-
condition of the centrum ends is termed heterocoelous. (Note that the vertical lines between a and b connect the same points on
ering tool. Many woodpecker species
the centrum end between the two different views.) When the posterior end of Vertebra A contacts the anterior end of Vertebra B
drill holes in dead trees and then probe
(see c) the two vertebrae can rotate around each other in all planes of movement. Such flexibility allows many birds to rotate their
with their tongues for insects. Others,
heads 180 degrees in either direction, an ability particularly well developed in owls (see Fig. 4-45).
such as the Northern Flicker illustrated
here, feed on the ground, using their
Hyoid Horn
tongues to extract ants from subter- Sheathed In
ranean tunnels. Woodpeckers have Muscle then numbered within each region): cervical in the neck; thoracic in
elongated hyoid horns with elaborate
musculature, enabling them to greatly the rib cage; lumbar in the lower back; sacral in the pelvic region; and
extend their tongues—in some species caudal in the tail. Nevertheless, fusions within and between regions
up to four times the length of the bill. in different groups of birds blur these distinctions.
a. Tongue Retracted: The long, slender Nearly all mammals have seven cervical vertebrae, whether they
hyoid horns are sheathed by muscle for
b. Tongue Protruded have short necks as in primates, or long necks as in the giraffe. In
most of their length. Anchored by mus-
cles in the flicker's lower beak, the horns birds the number varies from 1 2 in some cuckoos and passerine birds
run separately on either side around the (or even as few as 11 in the Old World hornbills, in which the first 2
Muscle
back of the head, outside the skull, then vertebrae are fused and counted as a single unit) to as many as 25 in
Sheath
together enter the right nostril (see dor-
Contracts, some swans. Most birds have 14 or 15. The relatively large number of
sal view), attaching to the skeleton of Squeezing
the upper beak. b. Tongue Protruded: freely articulating cervical vertebrae allows a marked suppleness of
Hyoid Horn
When the muscles of the sheath con- Forward the neck and turning ability of the head. The flexibility of the neck, in
tract, the hyoid horns are squeezed into a sense, compensates for the rigidity of the back. Most birds—not just
tight contact with the skull and pushed owls—can turn their heads 180 degrees in either direction, thanks
forward, protruding the flicker's tongue
in large part to the saddle-shaped, interlocking ends of the vertebrae
from its mouth. Adapted from drawings
by Charles L. Ripper. (Fig. 4-13). This avian condition of heterocoelous centrum ends is

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

4.16 Howard E. Evans and J . B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.17
unique among living vertebrates, and immediately identifies isolated b. Cervical Vertebra of the Chicken, Lateral View
bird vertebrae.
The first cervical vertebra, termed the atlas, is small and articu-
Spinous
lates with a prominent protrusion, the occipital condyle, on the base Process
of the skull (Fig. 4-1 4a). The atlas is named for the divinity from Greek
mythology who supported the sky, in allusion to the vertebra's support
of the skull. Uniquely, the atlas has a hole or notch on the ventral sur-
ANTERIOR POSTERIOR
face of its central opening (the vertebral canal) into which the peg-like
dens of the second cervical vertebra, the axis, fits. The dens, which
embryologically began as part of the atlas, is attached to the skull by
a ligament. Thus, as in all terrestrial vertebrates, the first two cervical
Centrum
vertebrae, the atlas and axis, are highly modified for the articulation of Rib
the skull with the rest of the vertebral column. The remaining cervical Remnant
vertebrae have either short, fused rib remnants (Fig. 4-14b) or may

c. Thoracic Vertebrae and Rib Attachment

a. Atlas and Axis of Rock Dove
Fused 2nd-5th Thoracic Vertebrae (Notarium)

Natural
1st Thoracic Fused Spinous Processes 6th Thoracic
Placement
Vertebra \ Vertebra
of Atlas
and Axis

ANTERIOR POSTERIOR

c1. The First through Sixth Thoracic Vertebrae of the Chicken

Occipital Condyle of Skull
Facets for Rib
Attachment
Dens of Axis
Fused Spinous DORSAL
Processes

Spinous
Process\
Axis

Figure 4-14. Types of Vertebrae: a. Atlas and Axis of Rock shown in cl, the lateral view of the first through sixth thoracic
Dove: The cervical vertebrae, forming the neck, vary in number vertebrae from the chicken, several thoracic vertebrae are typi-
ANTERIOR
among bird species. The two cervical vertebrae closest to the cally fused together, adding rigidity to the vertebral column. The
head are small and specialized to connect the skull with the rest spinous processes or spines, ridges of bone projecting from the Vertebral
of the vertebral column. The large drawing shows the skull of dorsal surface of all vertebrae, are particularly well developed Articular
a Rock Dove with these two vertebrae separated, to show their in the thoracic vertebrae and are fused into a strong, vertical Surface
articulating surfaces; the inset shows their natural placement. ridge of bone to which the large back muscles attach. On their for Next
The first cervical vertebra, the atlas, supports the head by articu- lateral surfaces, thoracic vertebrae have prominent facets for Vertebra
lating with a prominent peg, the occipital condyle, on the base the attachment of true ribs, which, unlike those found on the Uncinate Process
of the skull. The atlas has a notch or hole on the ventral surface of cervical vertebrae, connect with the sternum. Placement of the
its posterior end, which receives the peg-1 ike dens of the second ribs is shown in c2, the lateral view of three thoracic vertebrae, VENTRAL
cervical vertebra, the axis. These connections permit the bird's and in c3, the anterior view of a single thoracic vertebra from
head to rotate freely. b. Cervical Vertebra of Chicken, Lateral a Rock Dove. Note that only the upper segment of each rib
View: The remaining cervical vertebrae typically have short, (termed the vertebral rib) is shown. All drawings adapted from
fused rib remnants or small, moveable ribs projecting laterally. Ede (1964, pp. 30 and 31), except for the lower two in c, which
c. Thoracic Vertebrae and Rib Attachment: Thoracic vertebrae are adapted from Proctor and Lynch (1993, p. 131). c2. Lateral View of Three Thoracic Vertebrae of c3. Anterior View of Thoracic Vertebra of
make up the thorax or chest region of the vertebral column. As the Rock Dove with Ribs Attached the Rock Dove with Rib Attached

Cornell Laboratorq of Omithologq Handbook of Bird Biologq

4.18 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatomq and Phtisiologg 4.19

bear small, moveable ribs. In either case there is an opening between Figure 4-15. The Thoracic Cage: This
Spinous Process cranial view shows one "segment" of
the vertebra and the base of each of the forked ribs. When cervical the thoracic cage of the Budgerigar, at
Vertebral Canal
vertebrae bear moveable ribs, they are difficultto distinguish from tho- Thoracic (Location of the level of the first thoracic vertebra. The
racic vertebrae, and the term "cervicodorsal" vertebrae may be used. Vertebra Spinal Cord) thoracic cage consists of the ribs con-
If the rib articulates with the sternum, either directly or by a ligament, nected to the thoracic vertebrae above
and to the sternum (breastbone) below.
it is considered to be a thoracic vertebra. Location of It forms a flexible but strong protective
Thoracic vertebrae (from the thorax or chest region) can be dis- Heart, Liver, enclosure for the bird's heart, liver, lungs,
tinguished from other vertebrae by their facets for rib articulation (Fig. Lungs, and
and thoracic air sacs. Each rib consists of
Thoracic Air Sacs
4-14c).They also are characterized by wel I-developed spines (spi nous two hinged sections, the upper vertebral
rib and the lower sternal rib. The hinge
processes) on their dorsal surfaces for the attachment of deep back
Uncinate allows the thorax to expand and contract
muscles. Most birds have between four and six thoracic vertebrae; Process during breathing. From each vertebral
the Rock Dove has five. Some of the thoracic vertebrae may become rib, an uncinate process projects back-
fused with one another to form a "notari um" for added rigidity of the ward, overlapping the rib behind it and
backbone, a benefit in flying and landing. thereby strengthening the thoracic cage.
Notice the large surface area created by
In Figures 4-6 and 4-20 note the synsacrum, another unique fea-
the keel (carina) of the sternum, which
ture of the bird's vertebral column. It consists of a fusion of a variable is the site of attachment of the powerful
Sternal
number of thoracic vertebrae with all of the lumbar, all of the sacral, Rib flight muscles. The spinal cord is located
and the first few caudal vertebrae. This rigid segment is in turn fused on in the vertebral canal, a "tube" formed
by the openings of successive vertebrae.
either side with the ilium bones of the pelvis. The number of vertebrae
Adapted from Evans (1996).
involved in the bird's synsacrum varies among species from 10 to 23.
The tail of a bird consists of from four to nine free caudal vertebrae
and a terminal bone called the pygostyle, formed by several fused ver- Keel (Carina)
of Sternum
tebrae (see Figs. 4-4 to 4-6). The pygostyle is the shape of a plowshare
and provides attachment for the flight feathers of the tail. On top of the
pygostyle rests the oil gland.
The ribs, together with the thoracic vertebrae above and the
sternum below, form a bony "thoracic cage" (rib cage) enclosing the
heart, liver, and lungs, as well as the thoracic air sacs (Fig. 4-15). Each
thoracic rib has a dorsal and a ventral part with a hinge between them.
The upper or vertebral rib articulates with a thoracic vertebra; the
lower segment or sternal rib articulates with the sternum. This hinged
arrangement allows the thorax to be expanded and compressed for Pectoral Girdle
breathing, and thus act as a bellows. The sternum moves downward The pectoral girdle (from the Latin pectus, meaning breast) is
and forward for expansion during inspiration, then upward and back- formed by three bones on each side of the body (Fig. 4-16): the clavicle
ward for compression during expiration. The pattern of inhalation and (collar bone), the coracoid, and the scapula (shoulder blade). In nearly
exhalation while flying may be quite different. During flight, pectoral all birds the right and left clavicles are fused with a small interclavicle
muscles spread the furcula and thus participate in breathing (see Fig. bone to form a singleV-shaped bone, the furcula, popularly known as
5-5). Projecting caudally from the vertebral segment of each rib is an the "wishbone." In most birds the ventral end of the furcu la is attached
uncinate process that overlaps the rib behind it and helps to strengthen to the sternum by a ligament, but in some birds, such as pelicans, this
the rib cage (see Fig. 4-5). ("Process," in the anatomical sense, means connection ossifies and thus strengthens the support of the shoulder
a projection or extension from a bone; uncinus is Latin for "hook.") joint, probably an advantage in diving for food. The parakeet has only
small remnants of the clavicle on each side, and some parrots have lost
the clavicle completely. Although the clavicle provides extra strength,
Appendicular Skeleton it may also limit shoulder rotation, used in balance. Because parrots
The appendicular skeleton consists of the bones of the wings and often climb tree trunks and branches, maintaining their balance is
hind limbs, together with their supporting pectoral and pelvic girdles, apparently more important than the extra strength that a clavicle pro-
and the sternum, which articulates with the pectoral girdle as well as vides.
with the axial skeleton. The coracoids are the stoutest and strongest bones of the pectoral
girdle. They function as a powerful brace holding the shoulder joint,
and thus the wing, away from the body while the pectoral muscles are

Cornell Laboratorq of Ornitholoati Handbook of Bird Biolojt

 Ilv

4.20 Howard E. Evans and j. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiologq 4.21

Figure 4-16. The Avian Pectoral Girdle: pulling oppositely on the wing during flight. The broad base of each
Scapula
The pectoral girdle consists of three bones (Attaches to Rest of Skeleton coracoid bone fits into a groove on the cranial end of the sternum. At
on each side of the body: the clavicle, the by Muscles Only) its other end, the coracoid meets the scapula at the shoulder joint to
scapula, and the coracoid. In most birds,
form a shallow depression, the glenoid fossa, with which the base of
as in the Rock Dove pictured here, the
clavicles are fused to form the V-shaped the wing articulates. The upper end of the coracoid bone articulates
Foramen Triosseum
furcula or "wishbone." The scapula and not only with the scapula, but also with the clavicle, forming an open-
coracoid meet to form a cup-shaped ing at the three-way joint through which the tendon of a powerful
depression, the glenoid fossa, which
flight muscle passes. This supracoracoid (meaning "to go above the
receives the rounded end of the hu- Glenoid Fossa
merus, forming a ball-and-socket joint
coracoid") muscle raises the wing, and the opening, called the fora-
(Attachment for Humerus)
that enables the humerus to rotate freely men triosseum or supracoracoid foramen, serves as part of a pulley
around the shoulder joint. The upper end
— Coracoid
system allowing the downward force of the contracting supracoracoid
Furcula
of the coracoid articulates with the clav- muscle to be redirected to an upward pull on the dorsal surface of the
(Fused
icle as well as with the scapula, and at
Clavicles) wing (see Fig. 5-6).
this three-way joint is an opening termed
the foramen triosseum (also known as
the triosseal canal or supracoracoid Bones of the Wing
foramen). Through this opening passes Evolution has modified bird forelimbs (Fig. 4-17) by reducing
the tendon of the supracoracoideus, a the number and length of the bones that correspond to those of our
powerful flight muscle that raises the
palm (metacarpals) and our fingers (digits—made up of phalanges).
wing (see Fig. 5-6). The lower drawing Keel (Carina)
shows the position of the pectoral girdle of Sternum
The wrist has been reduced to two carpals, the radiale and ulnare, by
(shaded areas) within the skeleton of a formation of a fused carpometacarpus in which several of the wrist
Golden Eagle, seen in posteriolateral bones have been fused with some of the palm bones. All flying birds
view, with the left wing lowered. (The
furcula is not visible.) This view illus-
trates that the only bone-to-bone con- Digit 1
Bird (Alular Digit)
nection between the pectoral girdle (and Carpals (2)
hence the wing) and the axial skeleton Digit 3
is the junction between the base of each (Minor Digit)
coracoid and the sternum. Further con-
nections are provided by muscles that Digit 2
(Major Digit)
hold the scapula in place against the rib
cage. This arrangement creates a "free- Right Scapula
floating" pectoral girdle, allowing the
Carpometacarpus
extreme mobility so essential to flight. Left Coracoid Right Humerus
Main drawing reprinted from Manual of Metacarpals (5)
Ornithology, by Noble S. Proctor and Left Scapula
1 4rOltar:N Scapula
Patrick J. Lynch, with permission of the
Left Humerus Thumb
publisher. Copyright 1993, Yale Univer-
sity Press. Lower drawing adapted from
Proctor and Lynch (1993, p. 139). cel.OOP° ?Aril
oa
004 007000171r
Human 3 ..40t° .1,5* Carpals (8)
4 0"t°

Phalanges

Figure 4-17. The Bones of Human and Bird Forelimb: The forelimb of a flying bird and a human are compared to show the cor-
respondence between the individual bones. Natural selection has modified the bird's forelimb from that of its reptilian ancestor
Location of the Pectoral Girdle
in several ways. One example is the reduction in the number and length of the bones that correspond to the human palm (meta-
in the Skeleton of a Golden Eagle
carpals) and the human fingers (digits, composed of phalanges). Furthermore, the single fused carpometacarpus in birds replaces
some of the bones of the human wrist (carpals) and palm (metacarpals). The three digits in birds are thought by some researchers
to correspond to the human thumb and first two fingers, but embryological evidence indicates that they correspond to the second,
third, and fourth human digits, so their origin is still in debate. Digit 1 in birds (termed the alular digit) carries the alula, and digits
2 and 3 (the major and minor digits, respectively), along with the carpometacarpus, carry the primary wing feathers. Secondary
feathers are attached along the ulna, the thicker of the two lower arm bones. From The Cambridge Encyclopedia of Ornithology,
edited by Michael Brooke and Tom Birkhead, 1991. Copyright Cambridge University Press, reprinted with permission.

Cornell Laboratori of OrnitholoBq Handbook of Bird Biologq

4.22 Howard E. Evans andJ. B. Heiser Chapter 4—What's Inside: Anatomy and Physiology 4.23
Figure 4-18. Wing Spurs: Spurs are Figure 4-19. The Sternum in a Flying
bony outgrowths that may occur at Versus a Flightless Bird: In flying birds,
various sites on the skeleton. Wing spurs the sternum has a midventral keel, or
are outgrowths of the carpometacarpus, carina—a ridge of bone that projects
found in various birds such as cassowar- Ratite: Emu
out from the sternum and to which the
ies, plovers, sheathbills, screamers, and pectoral flight muscles attach. The size
jacanas. a. Northern Screamer: This of the keel is closely related to the size
goose-like, South American bird has of the pectoral muscles and thus reflects
paired spurs on each wing, used in ag- the bird's flying ability. Birds with a keel,
gressive displays and in fights with other // 1' such as the Rock Dove (inset), are termed
Northern Screamers, during which they 1;
1;('' '111i
! carinates. In flightless birds, such as the
can inflict considerable damage. Draw- Emu shown here, the sternum is small
ing by Charles L. Ripper. b. Wattled and shaped like a very shallow bowl.
Jacana: The yellow wing spurs of the r Sternum Lacks It completely lacks a midventral keel,
Wattled Jacana contrast strongly with Keel (Carina) reflecting the reduced wings and poorly
Wing Spurs
its black plumage, especially during the developed pectoral muscles associated
raised-wing display shown here, which with the bird's flightlessness. Birds lack-
occurs during alarm or aggression. ing a keel are termed ratites. Note that
a. Northern Screamer
Photo by Marie Read. in both drawings, corresponding parts
of the sternum (that is, those not includ-
ing the keel) are stippled. Emu reprinted
have the same arrangement and number of wing from Manual of Ornithology, by Noble
S. Proctor and Patrick J. Lynch, with
bones. The fingers are invariably three in num-
permission of the publisher. Copyright
ber with their individual bone segments (pha- 1993, Yale University Press. Inset draw-
langes; singular, phalanx) embedded and con- ing by Charles L. Ripper.
cealed in a continuous skin covering. Which Carinate: Rock Dove
digits are represented is still a matter of debate. Sternum with
Well-developed Keel
Some researchers say they correspond to our
first, second, and third digits. Embryological ev-
idence, however, indicates that they correspond
to our second, third, and fourth digits. The avian
scientific nomenclature committee, a group of a fact strongly indicating that their ancestors could fly (see Ch. 5,
researchers who decide current correct usage, Loss of Flight). In penguins, the bones are simply shortened, flattened,
has decided to call the digits: the alular digit broadened, and generally strengthened into paddle-like flippers suit-
(with one phalanx or two), major digit (with two able for "flight" under water. Among the ratites (see Fig. 5-48) the wing
phalanges), and minor digit (with one phalanx). bones have degenerated in both size and strength, especially in the
The terminal phalanges (especially of the alular kiwis of New Zealand, whose wings are mere stubs hidden beneath
digit) in a variety of birds—swans, ducks, cranes, the feathers.
rails, owls, passerines, and others—may bear
Sternum
a claw. During their first weeks, young South
The sternum or breastbone of all flying birds has a midventral
American Hoatzins have temporary claws on
keel or carina to which the pectoral breast muscles attach (Fig. 4 19). -

one or more of their wing digits. These claws

A general term for birds with a keel is carinates. The relative size of
b. Wattled Jacana allow them to climb back into the nest, from
the keel is directly correlated with the development of the pectoral is
which they jump at times of danger (see Fig. 3-41).
muscle, which provides power for the downward wing stroke, pro-
One should not confuse wing claws with wing spurs (Fig. 4 18). -

pelling the bird upward and forward in flight. Therefore one can judge,
Claws are associated with digits, whereas spurs can be located any-
by looking at a bird's sternum, the relative development of its pectoral
where on the skeleton. Some birds have both. Wing spurs are bony
muscles and consequently its flying ability. A hummingbird has the
outgrowths from the carpometacarpus, but they are not digits. Birds
largest keel of any bird relative to its body size, and is truly the "king"
with wing spurs include cassowaries, screamers (An h imidae), plovers,
of the carinates. Its flying ability is no surprise. The sternum of large
jacanas, and Antarctica's sheathbills. They are used in aggressive dis-
flightless birds such as the Ostrich, Emu, rhea, and cassowary, as well
play and fighting, especially with other members of the species.
as some others, is flat and plate- or raft-like. Such birds that lack a keel
Flightless birds have reduced wing bones. Modern flightless birds
are often collectively spoken of as ratites (from the Latin for raft or
show the same basic arrangement of the wing skeleton as flying birds,
flat-bottomed boat), but this term may lack taxonomic or evolutionary

Cornell Laboratory of Ornithology Handbook of Bird Biologq

4.24 Howard E. Evans and J. B. Heiser
, Chapter 4 —What's Inside: A natomq and Phqsiolo9ti 4.25

Rock Dove

Location of the Pelvic Girdle and Synsacrum

in the Skeleton of a Golden Eagle

Head of
Femur

Pygostyle

Bird

Free Caudal
Vertebrae

Knee — Patella

Fibula
lschium Pubis

Figure 4-20. The Avian Pelvic Girdle: significance, because it is unclear whether these birds are closely re-
The pelvic girdle, shown above in dor-
lated. The lack of a keel on the sternum of Archaeopteryx prompts some Tibiotarsus Tibia
solateral view, consists of three bones on
each side of the body: the ilium (plural:
paleontologists to assume that this ancestral bird glided from elevated
ilia), the ischium, and the pubis. The il- perches, and was incapable of flapping flight.
ium forms the cranial and lateral part of
the girdle, and is completely fused with Pelvic Girdle
the ischium, which forms the caudal and The pelvic girdle or pelvis (from the Latin for "basin") is formed by
lateral part. The ilium has a cup-shaped Proximal End of Tarsometatarsus
three bones on each side of the body: the ilium, ischium (ISK—ee—um),
depression for the attachment of the
femur (upper leg bone). The long, thin and pubis (Fig. 4-20). The right and left ilia are fused to the series of
pubis runs backward along the outer- fused vertebrae of that region, the synsacrum, to form a rigid support
most edge of the ischium. In the pelvic for each half of the pelvis. In all birds except rheas, the pelvis is open 2nd Phalanx
region, the vertebrae are fused into the 3rd Phalanx
below, because the right and left ischia and pubes do not meet. In fe- with Claw, Tarsals (7)
rigid synsacrum, consisting of a few 1st Phalanx
thoracic vertebrae, all the lumbar and
male birds this open pelvis facilitates the laying of eggs that are large Attached Metatarsals
Tarsometatarsus
sacral vertebrae, and the first few caudal relative to the size of the parent. (5)
vertebrae. The ilia are fused with the syn-
sacrum on either side of the bird's body, Bones of the Hind Limb Digits
1 1
forming a strong but lightweight struc- The hind limb, like the forelimb, is composed of a series of bones 2
(Hallux) 3
ture for the attachment of the muscles of
articulated end to end (Fig. 4-21). The femur or thighbone is relatively
the legs, tail, and abdomen, and provid-
ing protection for the abdominal organs. short in all birds, and is usually less than half the length of the next bone
The right drawing shows the location of farther down the leg (the tibiotarsus) in large wading birds. The small
Figure 4-21. The Bones of the Human and Bird (Left) Hind misidentified as the knee, giving the mistaken impression that a
the pelvic girdle and synsacrum within head of the femur fits deeply into the hip joint's socket or acetabulum. Limb: The legs of a bird and human are compared to demon- bird's knees point backward! The actual knee is often partly hid-
the skeleton of a Golden Eagle, in dorso- At the lower end of the femur, the patella or kneecap (an ossification in strate the correspondence between the individual bones. The den by feathers. All birds lack an outermost fifth toe. The most
lateral view. As a demonstration of how
a tendon) glides in a deep groove and adds stability to the knee joint. upper leg of the bird resembles that of the human in basic struc- common arrangement of the four avian toes (digits) is shown
the form of the pelvis is influenced by
ture, although the lengths of the bones differ. For instance, the here, with one toe facing backward and three facing forward.
function, compare the size of the pel- When the knee is bent, the patella raises the tendon away from the
femur, or thighbone, is relatively short in birds, and the fibula The rearward-facing toe, termed the hallux, corresponds to the
vic girdle of the ground-dwelling Emu knee joint. This increases the tendon's angle of pull on the lower leg, is much reduced. The tibiotarsus, consisting of the tibia fused human big toe (digit 1). As in the fingers, the toes of birds are
(Fig. 4-19) with that of a flying bird such making the pulling muscle's action more effective. to the first few ankle (tarsal) bones, may be very long in some composed of bones called phalanges. Each toe has one more
as the Budgerigar (Fig. 4-5). The Emu's
The tibiotarsus (drumstick bone) is usually the bird's longest leg wading birds. The bird's lower leg and foot have been greatly phalanx than its position number, with the terminal phalanx
huge pelvic girdle is evidence that legs,
bone. It is composed of the tibia fused at its outer (distal) end with the modified through natural selection. The elongated tarsometa- bearing a claw. The only portions of the terminal phalanges
not wings, are its means of transport.
tarsus is made up of fused metatarsal bones (the sole of the foot visible in this drawing are the claws. From The Cambridge
Rock Dove pelvis by Charles L. Ripper. proximal tarsal (ankle) bones. The splint-1 ike bone articulating with the
in humans) and the distal tarsal bones (forming the human heel). Encyclopedia of Ornithology, edited by Michael Brooke and
Right drawing adapted from Proctor and lateral condyle (a process) at the distal end of the femur is the fibula, The proximal end of the tarsometatarsus most closely approxi- Tim Birkhead. 1991. Copyright Cambridge University Press,
Lynch (1993, p. 139).
whose distal end (nearest the ankle) does not ossify in birds. mates the heel in humans, yet is elevated such that it may be reprinted with permission.

Cornell Laboratorc of Ornithologg Handbook of Bird Biolo9ii

4.26 Howard E. Evans and J . B. Heiser Chapter 4 —What's Inside: Anatomq and Phifsiolosq 4.27
The tarsometatarsus represents the fusion of the second, third, Figure 4-23. How Muscles Act to
Move Body Parts: Skeletal muscles,
and fourth metatarsals (which form the bones of the foot's sole in hu-
mans) with the distal tarsal bones. Thus separate tarsal (ankle) bones do
Bone A 4 Bone A through their attachments to bones, are
responsible for moving the body parts.
not exist in birds, and the joint of the ankle is known as an intratarsal Muscles, however, can only pull—they
Origin O • Origin
joint. cannot push—so skeletal muscles are ar-
Leg spurs have developed as weapons of offense or defense in Extensor ranged in pairs, one opposing the pulling
1)))111) action of the other, to produce smooth
male chickens and other pheasantlike birds (Fig. 4-22). They grow Flexor
Extensor Flexor movements of the bones. Each muscle
from a spur papilla of the skin that stimulates bone development on the usually bridges one or more joints be-
lower caudal surface of the tarsometatarsus. Peafowl use their spurs tween bones, moving the joint when it
Insertion contracts. Each muscle has two points of
quite aggressively, as do game cocks.
attachment to the skeleton, its origin and
All birds lack the outermost or fifth toe (see Fig. 4-21).The number
its insertion. The origin is defined as the
of bones or phalanges in the four remaining toes is nearly constant, Insertion
end of the muscle whose point of attach-
each toe having one more phalanx than its ordinal (position) number. Bone B ment moves the least during the muscle's
Thus toe number one (corresponding to the innermost, "big toe" of contraction. Muscles are termed flexors
Figure 4-22. Leg Spur of a Chicken: humans), also known as the hallux, has two phalanges, toe number Bone B or extensors depending on the actions
Males of certain birds, notably chickens, they exert on the body parts. This figure
two has three, and so on. A number of birds with widely different habits
peafowl, and other pheasant relatives, shows the actions of two hypothetical
have only three toes, the hallux having been lost evolutionarily. These a. Flexor Contracts Pulling b. Extensor Contracts Pulling bones and muscles. a. Flexor Contracts:
develop bony outgrowths of the lower
Bone B Toward BoneA Bone B Away from BoneA
tarsometatarsus known as leg spurs, include such flightless running birds as rheas, Emus, and cassowaries; Bone B is pulled toward BoneA (a move-
which are used as weapons during ag- shorebirds such as the Lesser Golden Plover and Sanded ing; and two ment termed flexion) when the flexor
gressive interactions with rival males muscle contracts, the flexor becoming
tree-climbing birds, the Black-backed and Three-toed woodpeckers.
of the same species. From Lucas and shorter and thicker while the extensor
Stettenheim (1972).
In addition, some birds such as the diving petrels and the auks, murres, muscle relaxes. b. Extensor Contracts:
other and perform the opposite action on their portion of the body
and puffins—all notable for their ability to swim underwater—also Bone B is pulled away from Bone A (a
(Fig. 4-23). When muscles contract they produce both movement movement termed extension) when
have lost the hallux. The Ostrich is the sole bird with only two toes, as
and heat—actually more heat than work! In effect, muscles are the the extensor muscle contracts. At the
both the outermost and the innermost toes have been lost.
furnaces of the body, and the heat they produce is distributed by the same time, the flexor muscle relaxes,
blood moving through the circulatory system. Shivering—uncoordi- becoming longer and thinner. Drawing
by Charles L. Ripper.
nated muscle fiber contraction—is a way to produce heat without
The Muscular &1st-ern directed movement by muscle contraction.To keep the heat generated
■ There are three general types of muscles—skeletal, smooth, and by exercise or shivering from escaping the body, birds may fluff their
cardiac—distinguished by their function, shape, and microscopic feathers, trapping a layer of insulating air.
structure. Each skeletal muscle consists of several hundred to several thou-
sand muscle fibers bound together by connective tissue called fascia.
Skeletal Muscle These bundles of fibers have two sites of attachment to the skeleton
(and occasionally to other structures); one is called the origin, the other,
Skeletal muscles move the bones and constitute what we call the
the insertion. Usually a muscle bridges one or more joints, producing
"meat" of an animal, whether it be red as in steak, white as in chicken
movement at the joint when it contracts. By convention, the end of the
breast, or any intermediate color. Because skeletal muscle action is
muscle whose point of attachment moves least during contraction is
under conscious control, skeletal muscles are often called voluntary
designated as the origin. The connecting fascia may be in the form of a
muscles.
tendon (which in bird limbs may ossify) or in the form of shiny, broad
Skeletal muscle is a tissue composed of contractile cells (cells that
sheets called aponeuroses. Every muscle is innervated (supplied with
can contract) with nuclei near the cell surface. Skeletal muscle cells
nerves) and kept alive by these nerves. If the nerve to a muscle is cut,
have characteristic alternating dark and light striations (stripes) at right
the muscle will eventually shrivel and atrophy (die) unless new nerve
angles to the length of the cell, which are visible under a microscope
fibers grow into it, a process that usually takes several weeks.
(after the cells are put through a standard laboratory procedure that
Skeletal muscles are often given names that indicate their func-
stains them using dyes that make different substances turn different
tion, location, shape, or derivation. Most anatomical terms were first
colors).
created to describe human anatomy, then uncritically applied to birds
The long, cylindrical cells are bound together as muscle fibers
at a later date. Thus, many inappropriate names for bird muscles have
that can shorten when stimulated by a nerve impulse. Once a muscle
had to be changed to more properly reflect their evolutionary origin
fiber contracts it must be forcibly stretched to regain its "resting" length;
and avian function (see Baumel et al. [19931—the Handbook of Avian
in other words, muscles cannot "push," they can only "pull." Thus,
Anatomy—listed with references).
muscles are generally arranged in opposing pairs; one to stretch the

Cornell Laboratorg of Ornithologg Handbook of Bird Biologg

4.28 Howard E. Evans and J. B. Heiser Chapter 4 — What's Inside: Anatomq and Phtisiolos 4.29
Skeletal muscles that move the wings and limbs (Figs. 4-24 Figure 4-24. Selected Muscles of the
and 4-25) act antagonistically, so that when one contracts, the other Avian Wing: In this drawing, only some
of the muscles are labeled. As is the
relaxes in a continuous fashion, producing smooth rather than jerky Extensor Metacarpi
Biceps Brachii convention in anatomical texts, the
movement. (Handy examples are the muscles of our upper arm. When Radialis Latin names, which reflect a muscle's
(Flexes Forearm)
we raise a cup to our lips, we bend (flex or close) the elbow joint by (Extends Hand)
function and points of attachment, are
contracting the biceps muscle that crosses the inner or flexor surface used. The biceps brachii originates from
of the elbow. In the process, the antagonistic triceps muscle—which Tendons Attaching the shoulder region and inserts on the
Muscles to Hand upper surface of the radius and ulna
crosses the outer or extensor surface of the elbow joint—gradually
near the elbow, and flexes the forearm.
relaxes, allowing the arm's extension to be continuous and smooth. Its antagonist (the muscle that opposes
The reverse is true as well. When we lower the cup and open the elbow C*"/ its action), the triceps brachii, also
joint, the triceps muscle contracts, while the biceps relaxes.) originates from the shoulder region, but
inserts on the under surface of the ulna
The large breast muscles of birds, the pectoralis and supracora-
Flexor Digitorum Triceps Brachii near the elbow, and extends the fore-
coideus, are good examples of antagonistic muscles (see Fig. 5-6). Al- Superficialis (Extends Forearm) arm. The extensor metacarpi radialis
though they lie in similar positions on the keel of the sternum, they have (Flexes Hand) originates above the elbow, inserts on
different actions. This is because the tendon of the supracoracoideus the carpometacarpus by a long tendon,
Pectoralis
passes through the foramen triosseum ("foramen" means "hole"), an and extends the hand. Its antagonist,
the flexor digitorum superficialis, orig-
opening at the shoulder insertion, forming a pulley system that redi-
inates below the elbow, inserts on the
rects the force of the supracoracoideus. The pectoral is attaches to the carpometacarpus, and flexes the hand.
ventral surface of the humerus and draws it and the wing downward. Drawing by Charles L. Ripper.
The tendon of the supracoracoideus passes through the foramen trios-
seum and inserts on the dorsal surface of the humerus so it can raise
(elevate) the wing. Thus the two primary opposing muscles for flight,
the pectoral is for the downstroke and the supracoracoideus for the
upstroke, both originate on the sternum, one on top of the other. lliotibialis Extensor
Even in the chicken and turkey, not known for their flying prow- (Lifts Thigh,
ess, the pectoral muscles account for about one-fifth of the bird's Extends Leg)

weight. Because of the pulley function of the foramen triosseum, the

large flight-powering muscle mass can be carried entirely below the
Figure 4-25. Selected Muscles of the
supporting wings during flight—a considerably more stable weight
Avian Leg: Shown here are some of the
configuration than if the wing elevator muscle were situated on the Sem itendinosus Flexor bird's leg muscles and their arrangements
back, above the wings. Because it takes the most force to get lift (and (Pulls Thigh Backward) for moving the legs and feet. a. Muscles
thrust) from the wing's downstroke, the pectoral is muscle is the larg- and Tendons in Natural Position: The il-
iotibialis extensor, originating from the
est muscle in flying birds. It is placed superficially, thus its bulging
Peroneus Longus Gastrocnemius pelvic girdle, inserts at the knee where
during contraction is not hampered by overlying muscle. For more (Flexes Tarsus and Toes) (Extends Tarsometatarsus it lifts the thigh away from the midline of
information on the flight muscles of birds, see Ch. 5, Functions of the and Flexes Toes) the body and extends the leg. The semi-
Flight Muscles. tendinosus flexor, also arising from the
Refer to Figure 4-26 for more information on the major skeletal pelvic girdle, inserts on the distal end of
the femur and pulls the thigh backward.
muscles of birds.
The peroneus longus originates at the
proximal end of the tibiotarsus, and the
gastrocnemius, from the distal end of the
Smooth Muscle femur. These and other muscles coming
Smooth muscle, also known as involuntary muscle because it from the vicinity of the knee insert by
is not controlled consciously, is composed of spindle-shaped cells long tendons on the tarsometatarsus and
phalanges, moving the tarsus and toes. b.
with a centrally located nucleus and no evident pattern of striations
Tendons Drawn Away from the Skeleton
along the cell. Smooth muscles are found in the walls of hollow organs to Show Their Insertions: The extremities
such as the stomach and blood vessels larger than capillaries. Smooth of the hind limb, like those of the wing,
muscle cells are especially characteristic of the vessels of the arterial are controlled by these tendons, like the
strings of a puppet, from muscles located
system, but also are found in the venous system. Smooth muscles
a. Muscles and Tendons b. Tendons Drawn Away closer to the bird's center of gravity.
are innervated by a separate, non-voluntary (autonomic) portion of
in Natural Position from the Skeleton Drawing by Charles L. Ripper.
the nervous system and also are under direct chemical control from to Show Their Insertions

Cornell Laboratorq of Ornitholos Handbook of Bird Biolos

4.30 Howard E. Evans and,J. B. Heiser
11, Chapter 4—What's Inside: Anatomq and Phqsiologq 4.31

substances circulating in the blood. Smooth muscle is also found in

the respiratory and urogenital systems, in addition to the digestive and
circulatory systems already mentioned—all systems and organs that
Semispinalis are concerned with vital life processes and over which the bird has little
or no control. Smooth muscle occurs in the skin for the movement of
feathers in birds, and for the movement of hair in humans—sometimes
Extensors of causing "goose flesh." Smooth muscle is also essential in the eye for
the Digits changing focus.

Longus Col li
Cardiac Muscle
Multifidis
Cervicis Cardiac muscle is a special type of smooth muscle that forms the
bulk of the heart. The muscle fibers are arranged in a fused network
lliotibialis and have cross-striations but centrally located nuclei.
Levator
Cardiac muscle has an innate rhythmicity—the ability to contract
Caudae
Serratus without being stimulated by nerves. Actually, the heart of an embryo
I Anterior begins to beat rhythmically before any nerves have grown to reach it.
I The nerves that do reach the heart are part of the autonomic nervous
system (see later in this chapter), but they do not start the contractions
Depressor Pectoralis of the heart. Instead, they regulate and modify the rate of the beat.
Caudae
■

Obliquus Abdom in us
The Nervous Suistem
Externus
■ The nervous system is responsible for all the bird sees, hears, smells,
Gastrocnemius tastes, feels, thinks, and does. Thus the nervous system transmits sen-
sory stimuli, evokes appropriate motor responses, and regulates all
Peroneus
Longus internal body functions. The structural parts of the nervous system are
similar in all vertebrates, but they differ in their degree of complexity.
Mammals have the most complex brains of all vertebrates, whereas the
avian brain has traditionally been considered less complex. Calling
someone a "bird brain" is generally not intended to be complimentary!
However, rather than being less complex overall, the bird's brain is
differently organized than that of a mammal. In other words, the brain
of birds is composed of the same basic "components" as that of mam-
mals—due to inheritance of the basic structure from our common
ancestor—but the avian brain is "wired" differently.
To appreciate how any animal perceives the outside world, we
Figure 4-26. Selected Muscles of the Rock Dove: This drawing of the abdomen, such as the obliquus abdominus externus, lie must consider its simple sensory nerve endings and complex sense
shows many of the superficial muscles of the rightside in lateral in sheets at right angles to each other, providing strength and organs, which are constantly gathering and transmitting information
view. Notice the complex network of small muscles along the protecting the underlying viscera. The pelvis and synsacrum about internal and external conditions. Birds have some sensory
neck, the multifidis cervicis, each surrounding and controlling provide a strong base for the attachment of the thigh muscles,
a cervical vertebra and thus contributing to the neck's flexibility. such as the iliotibialis. They also firmly anchor the tail muscles,
capabilities for species recognition and orientation, especially in
Long muscles, the semispinalis and the longus coin, move the such as the levator and depressor caudae, permitting the tail to migration and homing, which we do not yet fully understand (see Ch.
neck up and back, and down and forward, respectively. In function as a powerful rudder and brake during flight. Notice 5, Orientation and Navigation). These include the bird's ability to see
flying birds, such as this Rock Dove, the pectoralis and the that the large muscle masses are located primarily ventrally, ultraviolet light, and the probability that they can hear infrasound and
underlying supracoracoideus muscles, which provide the below the wings and near the bird's center of gravity, providing
ultrasound.
power for flapping the wings, make up between 20 and 30 a stable arrangement for flight. The muscles controlling wing
percent of the body weight, and their importance can clearly and leg movement also are concentrated near the center of the The central nervous system consists of the brain and spinal cord.
be seen here. The muscles of the thorax, for instance the ser- body, moving the limbs via a system of long tendons. Reprinted The peripheral nervous system consists of bundles of nerve cell fibers,
ratus anterior and others obscured by the uplifted wing in this from Manual of Ornithology, by Noble S. Proctor and Patrick]. called nerves, and collections of nerve cell bodies clustered in aggre-
drawing, support the rib cage, provide the power for breathing, Lynch, with permission of the publisher. Copyright 1993, Yale
gations called ganglia. The cranial and spinal nerves serve various, very
and help to attach the pectoral girdle to the body. The muscles University Press.
specific parts of the body. The autonomic nervous system consists of

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 V
4.32 Howard E. Evans andJ. B. Heiser Chapter 4 —What's Inside: A natomq and Phqsiolos 4.33
Figure 4-27. Neuron Structure: The scopic in diameter, may be several feet in length. A wrapping of cells
neuron or nerve cell is the basic com- containing fatty material called myelin surrounds many axons. These
ponent of the nervous system. The two
myelin sheaths function, in part, like the insulation around household
fundamental types of neurons, sensory
and motor, differ in their functions, but wiring. Because the fatty coats appear pale or white, nerves stand out
have the same basic structure. Each visually from most other tissues.
consists of a cell body, many rootlet- The deposition of myelin (myelination) in the nerve sheath is im-
like extensions called dendrites, and a Cell Body
Dendrites portant in the functioning of the nerve fibers. In humans, myelination
very long, cable-like extension called
the axon, which is surrounded along its
begins in the embryo, generally in the more primitive nerve paths,
Axon
entire length by a fatty, insulating layer reaching the more advanced paths after birth. For example, myelina-
called the myelin sheath. Motor neurons tion of the most important motor pathway—the nerves that govern
carry nerve impulses away from the cen- walking—begins after birth and proceeds most rapidly between the
tral nervous system to the muscles and
Cell Body — Axon ages of 12 and 1 6 months. The human infant begins walking when
organs, resulting in muscle movement
or organ activity. Sensory neurons carry myelination of that motor pathway develops to a certain point, and
Myelin Myelin
nerve impulses to the central nervous Sheath not before; so a child cannot be taught or forced to walk until his
— Sheath
system from muscles, sensory organs, nerves and muscles are capable. We assume the process is similar in
and receptors scattered throughout the
birds. The parent bird never "teaches" the nestling to fly. The young
body. Drawing by Charles L. Ripper. Nerve Impulse
Nerve Impulse bird flaps its wings, stretches its legs, stands in the nest, and flies only
from Spinal Cord
and Brain
to Spinal Cord when the nerves and muscles have developed to a certain point. After
and Brain
myelination of the nerves governing flight is complete, nothing, except
confinement or injury, will keep the bird from flying.

Sensory and Motor Neurons

Two types of neurons are distinguished, not on the basis of struc-
tural differences, buton the function and direction of the impulses they
carry (see Fig. 4 2 7).
-

Muscle A sensory neuron conveys impulses to the spinal cord and

brain. These impulses are interpreted as sensations, which may be
Motor Neuron Sensory Neuron conscious—such as visual images of food items, sounds of a pred-
ator, or pain from an injured wing—or they may be subconscious
impulses from muscles, tendons, and joints, informing control centers
those nerves that regulate the smooth muscle of the viscera, glands,
of the position of the limbs and muscles. This gives the bird a "body-
and blood vessels. One cannot tell the difference between cranial,
parts-position sense," and allows it to stand on one leg or fly without
spinal, and autonomic nerves by any means other than their origin,
visual cues. These latter impulses are called proprioceptive, meaning
destination, and function. Physically, all nerves look alike.
"muscle sense" or "tendon sense." Position sense is very important for
proper functioning of skeletal muscles. Because of the proprioceptive
The Neuron neurons, you can move your arms and legs with your eyes closed and
The basic unit of the nervous system is the neuron or nerve cell still know their exact position. Imagine how important these neurons
(Fig. 4-27). What we call a nerve is a collection of specialized portions and the knowledge they provide must be to a bird flying at night, or to
of many nerve cells, surrounded and bound together by connective species that live deep in caves.
tissue (cells that give support and protection), and large enough to be Motor neurons convey impulses from the brain and spinal cord
seen by the naked eye.The simplest neurons have a cell body with long, to stimulate a muscle to contract or permit it to relax, or to cause a
rootlet-like extensions (called dendrites) at one end, and a cable-like gland to secrete. For example, upon seeing a banana split, most of us
extension (called the axon) issuing from the other end. Bioelectric feel a sensation of delight resulting from sensory neurons sending an
impulses (nerve impulses) travel along neurons, from one end to the image message to the brain. The brain will likely send a command by
other. A bioelectric impulse consists of a wave of change in electrical motor neurons to the salivary glands, making our mouth water even
charge sweeping along the surface of the neuron due to ion move- before the first bite.
ment across the cell membrane. Transmission of an impulse from one The motor nerves stimulating skeletal muscles are called volun-
neuron to another takes place across a small gap, or synapse, usually tary motor nerves because they are under conscious control. They are
from the axon of one neuron to one of the dendrites of another. The of vital importance to the well-being of the muscle. If a motor nerve to
cell body of a neuron is microscopic in size, yet its axon, also micro- a skeletal muscle is cut or dies of polio virus, the muscle is paralyzed

Cornell Laboratorg of Ornitholos Handbook of Bird Biolos

 T
4.34 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiologq 4.35
and no longer can be moved voluntarily. With the passage of time, Figure 4-29: A Complex Reflex: A
such denervated muscle wastes away, and its fibers degenerate unless nerve impulse from the skin is carried
by a sensory neuron into the spinal cord.
they are kept alive by regrowth of nerve or artificial electrical stimu-
Through synapses with interneurons
lation. Destruction of nerves within the brain and spinal cord is usually within the spinal cord, the impulse may
permanent; overall, little or no regeneration occurs, although some be transmitted from one side of the body
clusters of neurons deep in the brain show some small regeneration to the other, up and down the cord, or
potential. If an axon outside the brain and spinal cord is severed, to and from the brain. Interpretive input
from the central nervous system, for
however, it will regenerate. The growth is slow, about 0.04 inches (one
instance in the form of experience and
millimeter) per day in humans. The length of time between the loss memory, may modify the reflex action.
of innervation and the re-establishment of nerve contact determines Drawing by Charles L. Ripper.
Spinal Cord
whether the muscle will function again. A wild bird is so dependent
on flight that it will die from an accidentally denervated wing before
any significant regeneration of nerves can occur.
The existence of sensory and motor neurons provides a basis for
the simplest kinds of behavioral actions, called reflexes (Fig. 4-28),
Motor
which may be either automatic or learned. Sensory neurons carry im- Neuron
pulses from all parts of the body to the central nervous system. There, Interneurons

neural activity is transferred by synapse to a motor neuron that stimu-

lates instant action (the reflex) in the muscle or gland it governs. One
example is the speed with which we withdraw our hand from a hot
stove; the arm muscles automatically contract to withdraw the hand
before our brain tells us the stove is hot. Identical automatic reflexes
protect the bird from injury; "learned" reflexes provide greater scope
Sensory Neuron
for other, more complex activities. For example, flying is difficult for
a young bird just out of the nest; it has trouble taking off and landing
properly. Gradually, with continued practice, the many muscular con-
neurons involved in reflexes connect in the spinal cord with additional
Spinal Cord neurons that carry sensations up to the brain. They also synapse with
Figure 4-28: A Simple Reflex: A nerve still other neurons that bring impulses directly from the brain. Brain
impulse from the skin is carried by a sen-
input often modifies a reflex action. For example, when a professional
sory neuron to the spinal cord. There it
chef grabs a hot pan, he may not release it instantly in a reflex action
is transmitted across a synapse between
the sensory dendrites and the dendrites as most people would. Instead, his brain may tell him to hold on even
Sensory Neuron
of a motor neuron, through which it trav- though it is hot, because it is important to the success of his job.
els to a muscle where it stimulates in- "Wiring diagrams" of the nervous system from its inputs to its
stant, automatic action. An example of a
outputs thus become exceedingly complex, even at these relatively
simple reflex is the unconscious way we
pull our hand away from a hot surface; Synapse simple reflex levels of neural integration and behavior. Imagine what
our arm muscles contract automatically occurs in the nervous system of a Clark's Nutcracker as it recalls the
Skin Motor Neuron
to withdraw our hand before our brain location of a pine nut stashed months earlier, and then flies directly to
tells us the surface is hot. Drawing by
the site and retrieves it! (See Figs. 6-12 and 6-13.)
Charles L. Ripper.

tractions necessary for flight are coordinated. Then the bird can turn Central Nervous Si.jstem
its attention to other things—to catching food, watching for predators, The central nervous system (CNS) consists of the brain and the
and even to "navigating," a complex process that we sti ll do not fully spinal cord. Both are composed of millions of neurons receiving sen-
understand. sory information, relaying it to many other CNS centers, and sending
Reflexes are usually much more complex than we have described, out motor impulses. Within the CNS, clusters of nerve cell bodies
because the motor and sensory neurons involved have interneurons (equivalent to the ganglia of the peripheral nervous system [PNS]) are
within the spinal cord interposed between them (Fig. 4-29). Inter- called nuclei, and bundles of axons and their myelin sheaths (equiv-
neurons allow for transfers up and down the cord to other regions, as alent to PNS nerves) are called tracts (Fig. 4-30). The many adjacent
well as between the left and right sides of the body. Furthermore, the tracts within the CNS are known as "white matter" because of the color

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 IF

4.36 Howard E. Evans and J . B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiologq 4.37

Figure 4-30. Organization of the

Vertebrate Nervous System: The brain CENTRAL NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM
and spinal cord together are termed (Brain and Spinal Cord) (All Other Nervous System Structures)
the central nervous system (CNS). The
peripheral nervous system (PNS) con- a. Location of the Brain Within the Skull
sists of all other nervous system struc- Neuron Axons form Tracts Rock Dove
Neuron Axons form Nerves
tures—the cranial and spinal nerves Tracts collectively form White Matter
and their associated ganglia. Within the
CNS, the axons (fibers) of neurons are
gathered into tracts, whereas clusters of Neuron Cell Bodies form Nuclei
Neuron Cell Bodies form Ganglia
neuron cell bodies are termed nuclei. Nuclei collectively form Gray Matter
The collective name for CNS tracts is
"white matter," from the white color of
the axons' myelin sheaths. The collective
name for CNS nuclei is "gray matter,"
from the darker color of cell bodies.
of the myelin sheaths. Areas without myelin, where nerve cell bodies
Within the PNS, the terminology is
different. Neuronal axons are gathered
are concentrated, are darker and called "gray matter." In addition, mil-
into nerves, bundles surrounded by a lions of non-neural cells (neuroglia) form a supporting and protective
protective layer of connective tissue that felt-like bed for the neurons. Surrounding the brain and spinal cord b. Structure of the Brain Cerebral Hemisphere
are often large enough to be visible to the are vascularized membranes called meninges. They consist of an outer
naked eye. Neuron cell bodies are col-
fibrous dura and inner arachnoid and pia layers, tightly applied to the
lected into rounded aggregations called
ganglia (singular, ganglion). surface of the brain and cord (see Fig. 4 33). This complex of non-
- Rock Dove
neural tissues provide sustenance and waste removal for the cells of
the brain and spinal cord—vital functions because no blood vessels
penetrate these organs to perform those duties. At the same time the
meninges establish a blood/brain barrier that protects the delicate Olfactory Lobe
CNS from many potentially toxic substances circulating in the body. Olfactory
Medulla Oblongata Nerve
Brain U 14 II Optic Tract (Optic Nerve)
The brain of a bird is short, bulbous, and very large in relation
to the size of the skull (Fig. 4-31). Most of the brain lies caudal to the
XII IX VIII I VI Pituitary Gland
orbits, and it fills the cranial cavity completely.The skull is thin and the Spinal Cord X & XI VI/
neck vertebrae exceptionally flexible, therefore the brain and cervi-
cal spinal cord can be injured easily, as illustrated by the number of I Through XII = Cranial Nerve Endings
birds that die after flying headlong into windows. The main features of
the bird brain are similar to those of the mammal brain: the two large,
smooth cerebral hemispheres of the forebrain; the two large optic
lobes of the midbrain; and a single large, median cerebellum of the
hindbrain, with typical transverse folds. Between the forebrain and
the midbrain is a region that serves as the brain's central switchboard Figure 4-31. Location and External Structure of the Brain: a. lobes. Thus part of what the right eye sees goes to the left side of
for all incoming and outgoing nerve impulses. The ventral portion, the Location of the Brain Within the Skull: The bird's brain is posi- the brain, and vice versa. The pituitary gland is attached to the
hypothalamus (which contains the pituitary gland), plays a major role tioned toward the rear of the skull, behind the large eye sockets. ventral side of the brain by a stalk, which is not visible here. On
The orientation of the brain in the sku I I varies considerably, but in the dorsal surface of the hindbrain is the large, deeply folded
in the hormonal control of body processes (the endocrine system).
many species it is oriented nearly vertically, as in the Rock Dove cerebellum, which controls muscular coordination, and has
The forebrain, specifically the forwardmost portion known as shown here, in contrast to the classic mammalian orientation in important roles in balance, posture, and proprioception (the
the telencephalon, primitively associated with the sense of smell (ol- which the brain lies horizontally. b. Structure of the Brain: The sense of the position and activity of the limbs). Ventral to the
faction), is narrow rostrally and wide caudally where it overlaps and Rock Dove brain is shown here in lateral view. Dominating the cerebellum is the medulla oblongata, where the nuclei of most
forebrain are the large, smooth cerebral hemispheres, which of the cranial nerves are located, and from which these nerves
partially hides the more caudally positioned optic lobes.The forebrain
coordinate and control complex behaviors. At the anterior end extend out to the head, neck, and thorax. The cranial nerves
of modern birds consists of two smooth cerebral hemispheres, pointed of the hemispheres are the small olfactory lobes, concerned are numbered I through XII; only their ends are illustrated. The
attheir rostral ends where the olfactory nerves from the nasal cavity en- with the sense of smell. The midbrain is dominated by the large, medulla oblongata (also called the brain stem) extends caudally
ter. The cerebral hemispheres are coordinating and control centers for paired optic lobes, which receive the optic tracts from the eyes. to become the spinal cord. Modified from Manual of Ornithol-
most of the bird's complex behaviors, including memories and learn- Upon exiting the eyes, the optic tracts partially cross each other ogy, by Noble S. Proctor and Patrick J. Lynch, with permission
within the optic chiasma (not visible) before entering the optic of the publisher. Copyright 1993, Yale University Press.
ing. Of all birds, the largest olfactory area is that of kiwis—primitive,

Cornell Lahoratorti of Ornitholvi Handbook of Bird Biologq

4.38 Howard E. Evans and3. B. Heiser Chapter 4 — What's Inside: Anatomt and Phiisiologq 4.39
Lateral View, Right Side flightless birds of New Zealand. They are the only birds that have their Figure 4-33. The Spinal Cord in Re-
lation to the Vertebrae: The spinal cord
nostri Is at the tip of the beak rather than nearer the base of the beak.Th is Dorsal Root Fused Thoracic Vertebrae
lies within the protective confines of
position facilitates efficient olfaction, as they feed by probing into the (Contains Sensory Neurons)
the vertebral canal, a bony tube formed
forest leaf I itter.The tubenosed seabirds and some New World vultures Ventral Root by the interconnecting vertebrae. This
also have special nasal passages and/or relatively large olfactory areas (Contains Motor Neurons) drawing shows the section ofspinal cord
and excellent senses of smell. Most birds, however, appear to have few within part of the thoracic region of the
vertebral column. Surrounding the spi-
Fish olfactory talents, depending much more on vision.
nal cord are the meninges, vascularized
The bird's midbrain or mesencephalon is the region where visual Spinal Cord
Dura membranes that nourish the nervous
inputs are regulated and sent to other parts of the brain for integration Arachnoid tissue. They consist of a fibrous outer
Gray Pia layer, the dura, and two inner layers, the
into a response to what has been seen. It consists primarily of two Matter
White arachnoid and pia. The spinal cord itself
greatly enlarged optic lobes, which receive the optic tracts from the
Matter can be seen in cross section, showing the
eyes. These connections between the eyes and the brain are called white matter made up of nerve axons,
Amphibian tracts rather than nerves, because they (and the sensitive layers of the and the gray matter, made up of nerve
Spinal
eyes) are outgrowths and modified extensions of the brain rather than Nerves cell bodies. At regular intervals along its
bundles of peripheral sensory axons. Exiting the eyes, the tracts cross length, the spinal cord gives off bundles
Sympathetic Ganglion of sensory and motor neurons that exit
each other before entering the brain. Thus, what the right eye sees goes
from the cord in pairs between the ver-
to the left side of the brain and vice versa, as in humans. The large optic tebrae; these are termed the dorsal and
lobes of birds are relatively much larger than their corresponding part ventral nerve roots, respectively. These
in mammals (Fig. 4-32). On the other hand, the auditory (hearing) bundles occur symmetrically on both
Reptile
the left and right sides of the spinal cord.
and vestibular (balance) components of the avian midbrain are not as
The members of each dorsal-ventral pair
conspicuous as they are in mammals. At its caudal end, the mesen-
involved in flying and walking. Because of this independent spinal of roots immediately combine to form
cephalon is joined to the cerebellum. a single spinal nerve, which innervates
cord function, when a bird is decapitated, its legs and wings continue
The cerebellum is attached to the dorsal side of the brain stem to function for a brief period (the proverbial "running around like a
nearby muscles or organs. Associated
(medulla oblongata) by two pairs of stout neural tracts.The cerebellum with the spinal nerves is a chain of sym-
chicken with its head cut off"). pathetic ganglia running parallel to the
controls posture and the movements of the legs and wings; it thus reg-
Along its course, the spinal cord gives off spinal nerves between spinal cord on each side. These ganglia
ulates the highly complex muscular actions necessary for flight. The contain the cell bodies of sympathetic
the vertebrae. Each spinal nerve has separate sensory and motor seg-
Bird bird's cerebellum is large relative to other portions of the brain, when neurons, part of the autonomic nervous
ments that exit from the cord, but they are combined into one spinal
compared to mammals, doubtless because of the demands of flight. system (see Fig. 4-35). Adapted from
nerve outside the vertebral canal. At both the level of the wings and Proctor and Lynch (1993, p. 247).
Much of the medulla oblongata is hidden from dorsal view by the large
the hind limbs, the spinal nerves are large and join each other to form
cerebellum. The medulla extends caudally through the foramen mag-
complex web- or net-like structures, called plexuses, outside the ver-
num, the large opening atthe rear of the skull, where the medulla bends
tebral canal (Fig. 4-34). The brachial plexus of the wing is associated
sharply and narrows to become the spinal cord. Important nerves have
with a cervical enlargement of the spinal cord within the vertebral
their nuclei (recall that these are aggregations of cell bodies) within the
Mammal canal. The lumbosacral plexus of the hind limb likewise corresponds
medulla, and extend from it out to the head, neck, and thorax.
to a lumbosacral enlargement of the spinal cord. Whether one of these
It Cerebral Hemisphere spinal cord swellings is the same size or larger than the other depends
Spinal Cord
Cerebellum
on a bird's main type of locomotion. In a bird that relies on walking,
The spinal cord passes through the neck and trunk in the pro-
such as a kiwi, the number and size of the nerves going to and from
Optic Lobe tective, but in some regions highly flexible, vertebral canal formed by
the legs is certain to be large, as are the lumbosacral enlargements of
(barely visible in mammal) the vertebral arches of successive vertebrae (Fig. 4-33; also see Fig.
the spinal cord. In a bird that seldom walks, such as an albatross, the
4-15). Essentially, the spinal cord is a cable of neurons conducting
II Olfactory Bulb cervical enlargement of the spinal cord and the nerves going to the
impulses to and from the brain. Independently of the brain, however,
wings are larger.
reflexes within the cord control many of the bird's muscular functions
A feature unique to birds is an opening—the rhomboid sinus—on
the dorsal midline of the lumbosacral enlargement, which contains
Figure 4-32. Comparison of Bird and Other Vertebrate Brains: Shown here are the brains of a bony fish, an amphibian, a reptile, a a gelatinous mass of supporting neuroglial cells. The mass is rich in
bird, and a mammal, in lateral view, with the parts of the brain shaded identically in each. Differences in the proportions of various
brain parts reflect the varying abilities, needs, and habits of the different vertebrate groups. For example, the optic lobes of birds
the nutritive sugar glycogen, and thus is known as the glycogen body.
are relatively much larger than those of mammals, whose optic lobes are obscured by the large, complex cerebral hemispheres. The function of this structure is still unknown. Perhaps it is an energy
This shows the importance of sight to birds. The bird's cerebellum is also relatively large compared to that of mammals, reflecting reserve that sustains the reflex activity necessary for roosting or other
the importance of balance during flight. Note the relative differences in the sizes of the olfactory lobes: while small in birds, they chronic leg posturing, such as during long flights.
are well-developed in fish, reptiles, and mammals, evidence that these latter three have a sense of smell superior to that of birds.
Adapted from Pough, Janis, and Heiser (1999, p. 102).

Cornell Laboratorg of Ornitholos Handbook of Bird Biolos

4.40 Howard E. Evans and J. B. Heiser Chapter 4 —What's Inside: Anatomq and Phqsiologq 4.41
II. Optic Nerve
Figure 4-34. The Spinal Cord Showing
Nerve Plexuses: At two locations along This large "nerve" of vision is actually a sensory tractfrom the gan-
the spinal cord, spinal nerves exiting glion cells of the eye's retina, rather than a standard nerve. The optic,
the cord are particularly large and nevertheless, is by tradition enumerated as one of the cranial "nerves."
joined into complex web- or net-like
All visual sensations from the millions of closely packed visual cells in
structures called plexuses. The bra-
chial plexus is found at the level of the the retina of a bird are transmitted to the brain over these robust cables.
wings, and is associated with a swell- Each optic tract enters via its own optic foramen into the skull. It then
ing of the spinal cord called the cer- crosses to the opposite side of the brain at the optic chiasma and enters
vical enlargement. The lumbosacral the brain. The optic tracts are larger than any other cranial "nerve." As
plexus, at the level of the hind limbs,
would be expected, the optic nerve is particularly large in visual preda-
is associated with a lumbosacral en- Cervical Enlargement
largement. Which of these spinal cord Brachial Plexus tors such as hawks, and small in many nocturnal birds.
swellings is larger depends on the
style of locomotion of the particular III. Oculomotor Nerve
species. The Rock Dove, shown here, This motor nerve moves the eye by controlling contractions of
relies on both flight and walking, and
some of the muscles that run from the bony orbit to the surface of the
the two plexuses are similar in size. In
a flying bird that seldom walks, such
eyeball. It also supplies the eyelid muscles and the tear gland of the nic-
as an albatross, the nerves going to the titating membrane. The nerve originates in the midbrain and branches
wings are larger and more numerous to its target structures after exiting the skull.
than those going to the legs, and thus
the cervical enlargement also is larger. IV.Trochlear Nerve
The rhomboid sinus is an opening in Lumbosacral
Lumbosacral Plexus This small motor nerve controls just one eye muscle not inner-
the lumbosacral enlargement contain-
ing a mass of neuroglial cells rich in Enlargement vated by the oculomotor nerve. It originates on the dorsal surface of
the sugar glycogen, known as the gly- the brain stem, and exits through its own foramen in the skull.
cogen body. Its function is unknown.
Drawing by Charles L. Ripper. Rhomboid Sinus V. Trigemi nal Nerve
Containing Glycogen Body
This second largest cranial nerve has both sensory and motor
components. It divides into ophthalmic, maxillary, and mandibular
nerves after exiting from the brain, thus its name, which means "triplet."
The ophthalmic nerve is sensory from the nasal cavity (for nonolfactory
nasal sensations), eyeball (for nonvisual eye sensations), upper eyel id,
forehead, and upper beak. It is very important to ducks and geese,
in which it innervates the specialized bill tip organ: a concentration
of touch or mechanoreceptors with which the bird seeks submerged
aquatic vegetation by feel.The maxillary nerve is sensory from the skin
Peripheral Nervous St/stem
of the face, upper jaw, upper eyelid, and conjunctiva (eye covering
The peripheral nervous system consists of cranial nerves that
tissue). The mandibular nerve is sensory from the lower beak and cor-
leave the brain and exit from the skull, spinal nerves that leave the
ner of the mouth, and motor to the muscles of lower beak movement,
spinal cord and exit from the vertebral canal, and the ganglia associ-
which correspond to the chewing muscles of mammals.
ated with them.
VI. Abducent Nerve
Cranial Nerves
This motor nerve stimulates the one remaining muscle of the
Cranial nerves (see Fig. 4-31) occur as twelve sets of bilaterally
eyeball and the two skeletal muscles that pull the nictitating membrane
paired nerves that vary in function: some are sensory, others motor,
across the eyeball.
and some a mixture of both.They are named according to function and
numbered according to the order in which they exit from the brain, VII. Facial Nerve
from rostra! to caudal. This motor nerve stimulates the muscles for protruding the tongue
(muscles attached to or associated with the hyoid skeleton), the de-
I. Olfactory Nerve
pressor muscle that lowers the lower beak, the constrictors of the neck,
The olfactory nerve carries the "sensations of smell" from the lin-
and the muscle that tenses the col umel la ear bone (see Fig. 4-48). It
ing of the nasal cavity to the olfactory bulb of the brain. As mentioned
also may carry some taste fibers from the tongue.
previously, olfaction appears to be poor in most birds.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

4.42 Howard E. Evans and J. B. Heiser Chapter 4 — What's Inside: Anatomq and Phipiologq 4.43
VIII. Vestibu locochlear Nerve organs. Thei r numbers vary directly with the number of vertebrae in the
Formerly called the auditory, acoustic, or statoacoustic nerve, vertebral column, which is generally related to the size of the bird. For
this is the sensory nerve for balance and hearing, as the Latin name example, the Rock Dove has 39 pairs of spinal nerves; the Ostrich has
implies. It is composed of two parts: the vestibular part for balance, 51. Spinal nerves differ in size according to their particular function.
and the cochlear part for hearing. The vestibular part innervates the The large spinal nerves governing the muscles of the wings and legs
region of the inner ear that detects the direction of gravity as well as fuse and branch repeatedly to form networks or plexuses. Although we
accelerations in three-dimensional space. The cochlear part contains mention the spinal nerves here, in conjunction with the central nervous
axons coming from a distinctly different region of the inner ear re- system, they are actually part of the peripheral nervous system.
sponsible for the sensation of sound (see Fig. 4-50). No part of this -----
nerve ever leaves the skull. Subdividing the nervous system into two parts—the central and
peripheral—makes it easier to organize the material for study. But it is
Glossopharyngeal Nerve
XCII. important to understand that neither the central nervous system nor the
This sensory and motor nerve innervates the tongue, pharynx, peripheral nervous system can function by itself. Both are simply parts
esophagus, and throat. It also carries fibers from a specialized ganglion of one elaborately integrated system that also includes the autonomic
on their way to certain blood vessels, and motor fibers to the salivary nervous system.
glands of the tongue.

X.Vagus Nerve Autonomic Nervous Si1stem

This is the major visceral sensory and motor nerve to the ab- The autonomic nervous system is not a series of discrete and dis-
dominal organs. It arises from the medulla by a series of segments in tinct structures as are the other systems considered here. Rather, it is a
close association with the glossopharyngeal and accessory nerves, concept designed to facilitate understanding of the visceral nerve net-
with which it exchanges fibers. After leaving the skull, the vagus sends work and its physiological responses that operate without conscious
fibers to the pharynx and larynx before passing down the neck on control. The system, which controls the "guts" as opposed to the "meat"
the surface of the jugular vein. Within the thorax it branches to the of the bird, is much more complicated than we describe. To most
heart and lungs before sending branches to the gizzard, liver, and of the "rules" we present here, there are some exceptions. Even the
intestine. most basic premise that the system is without conscious control is not
totally true. We know, for instance, that some people can voluntarily
XI. Accessory Nerve alter their heart rate and blood pressure, and control gastric secretion.
This nerve is of visceral motor function and is distributed in the
Nevertheless, the concept of an autonomic nervous system is helpful
head region with the vagus to innervate the constrictor muscles of
to understanding how birds work. When first described, the autonomic
the neck. It exits from the skull with the vagus. Because of its exit site
nervous system was thought to be exclusively a motor system to the
and function it is included in the "cranial" nerves, but it has a very
smooth muscle of various structures. But we now know that some of
circuitous origin within the upper neck that is thought to reflect an
the nerves involved carry sensory fibers as well.
ancient evolutionary "capture" of a spinal nerve for "cranial nerve
Each motor component of the autonomic nervous system is a two-
functions." neuron chain, with a synapse between the neurons (Fig. 4-35). Th is con-
trasts with the voluntary motor nerves (such as those of reflexes discussed
XII. Hypoglossal Nerve
above), whose single cell bodies lie within the CNS. From the cell bodies
The hypoglossal nerve joins with cranial nerves IX and X to form a
of these voluntary motor nerves, axons run directly to the target muscle
combined trunk that controls movement of the tongue, larynx, tracheal
without any other peripheral neuron interposed. Thus the autonomic
muscles, and syringeal (of the syrinx) muscles. The tongue in most
system, while potentially a bit slower than a simple voluntary reflex, is
birds is much less muscular and mobile than that of mammals, and
capable of a great deal of subtle modification outside the CNS.
thus requires less hypoglossal control. Parrots, however, have highly
As in mammals, the bird's autonomic nervous system can be di-
manipulative tongues, and thus the brain stem nuclei for this portion
vided into two segments based on their regions of origin from the cen-
of a parrot's hypoglossal nerve are large in size. The syrinx is unique to
tral nervous system as well as on their functions. The two divisions are
birds, and in those that have complex song, the hypoglossal branch that
the parasympathetic system, with nerves originating in the cranial and
supplies it is of major importance (see Syrinx, later in this chapter).
sacral regions, and the sympathetic system, with nerves originating in
Spinal Nerves the thoracic and lumbar regions.
Spinal nerves are paired in all cases—one on each side of, and The parasympathetic system has its origin in cranial nerves III, VII,
attached to, the spinal cord. They are sensory and motor to a very IX, and X as well as from three sacral spinal nerves. These nerves act
specific (and usually closely adjacent) region of skin, muscles, and on smooth muscle to promote feeding, egg laying, and other "peace-

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

4.44 Howard E. Evans and J. B. Heiser Chapter 4 —What's Inside: Anatomq and Phqsiologq 4.45

Figure 4-35. The Autonomic Nervous ful" activity. Parasympathetic nerve stimulation quiets the bird. Some
System: This complex branch of the parasympathetic nerves carry impulses that reduce the heart rate; others
nervous system controls the automatic
Cerebral Hemisphere promote gastric secretion and peristalsis, thereby facilitating digestion.
functions of the body's internal organs,
acting primarily unconsciously. It con-
In the parasympathetic system, the cell body of the first neuron
sists of two subsystems, each of which lies within the brain or spinal cord. Its axon must then pass into the
Cerebellum
innervates the same organs, but with op- organ being innervated before it meets the cell body of the second
posing effects. The sympathetic system Optic Lobe neuron. Firing of the second neuron causes contraction of the smooth
Eye
functions under conditions of stress—for
muscle in the wall of the organ.Thus a vagal neuron affecting the stom-
example, speeding up a bird's heartbeat
and breathing rate by means of the Lacrimal Gland
ach, for example, is a very long neuron, indeed, leaving the brain and
neurotransmitter epinephrine (adren- reaching all the way to the wall of the stomach, where it synapses with
aline), to prepare for "fight or flight." the second neuron of the pair. In the sacral region the distance that the
The parasympathetic system calms the Salivary Gland
first neuron has to reach is much shorter, because the target organs are
bird, promoting feeding, digestion, and Vagus Nerve
other relaxed activities. All autonomic
Spinal Cord closer to the nerve origins in the spinal cord.
,..-- -------- 1 The sympathetic system consists of nerves that leave the spinal
pathways consist of two neurons in
series, but the organization of these
two neurons differs between the sym-
(' ---' P-v0- 1
,
cord from the thoracic and lumbar levels. Sometimes called the "fight
or flight" system, it functions in emergencies. Its neurons speed up the
/I %
pathetic and parasympathetic systems.
Lun g , \•
i heart rate, increase the blood pressure, provide deeper breathing, and
Sympathetic neurons (solid lines) arise ,
.

from the thoracic and lumbar regions of Sympathetic allow for greater muscular contraction. The sympathetic system also
—Heart
the spinal cord. The cell bodies of the Ganglion dilates the pupil of the eye to produce that look of being "wide-eyed
firstsympathetic neurons have migrated Chain
with fright." When the sympathetic system is activated, digestion slows
outside the spinal cord, gathering into a
or stops, and the bird may vomit or defecate to better prepare its body
sympathetic ganglion near the ventral
surface of each vertebra (see Fig. 4-33).
for fight or flight. Numerous seabirds, frightened at the nest, defecate
A chain of these ganglia runs the length or disgorge the contents of their crops or stomachs, sometimes most
of the spinal cord. The axons of the first effectively in the direction of the intruder! (See Ch. 6, Sidebar 3, Fig.
sympathetic neurons run from the sym- D.) Vultures do the same from the air.
pathetic ganglion to another ganglion
In the sympathetic system, the cell bodies of the first neurons
(open circles) closer to the organ being
innervated, where they synapse with the have migrated outside the spinal cord, where they form visible nod-
cell bodies of the second sympathetic Stomach u les close to the ventral surface of the vertebrae. These nodules (called
neurons, whose axons provide the final sympathetic ganglia) appear as a chain, because their axons may travel
link to the target organ. Parasympathetic
up or down, parallel to the vertebral column but just outside it, before
neurons (dashed lines) originate in the
vagus and other cranial nerves, and passing to their target organs by running along the surface of blood
in the sacral region of the spinal cord. vessels. The cell bodies of the second axons in a sympathetic chain are
Cell bodies of the first parasympathetic Intestine ln , grouped in visible masses, also called ganglia, on blood vessels very
neurons reside within the brain or spi- close to the organs being innervated. As an example, a large cranial
nal cord, and their axons run all the way
cervical ganglion is located on each side of the head/neck junction
to the target organ, sometimes a great
distance, synapsing with the second where axons from the first neurons (coming from the thorax) synapse
parasympathetic neurons (not shown), with the second neurons, which innervate arterioles of the head, caus-
located in or near the target organ. ing their constriction, and therefore an increase in blood pressure.
CIO 3( 1

The Senses
Vision
Sympathetic Neurons Sight is very important to birds, which are thoughtto have the best
Parasympathetic Neurons vision among vertebrates. To provide wide views and bright images,
eyes must be large. Indeed, a bird's eyes are so large that sometimes
Ganglion of Sympathetic Ganglion Chain
(Contains Cell Bodies of First Sympathetic Neurons) their weight may equal, or even exceed, the weight of the brain. The
O Ganglion Containing Cell Bodies of Second
largest eyes of any land animal are those of the Ostrich (Fig. 4-36),
Sympathetic Neurons nearly two inches (50 mm) in diameter! Some birds havethe mostacute

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

4.46 Howard E. Evans andJ. B. Heiser Chapter 4—What's Inside: Anatomq and PINsiologq 4.47

Figure 4-36. The Large Eyes of an Os- third eyelid, which secretes into the space
trich: Among vertebrates, birds have between the third eyelid and the cornea.
the best vision, reflected by the fact
Tears from both glands drain into lacrimal
that birds' eyes are large, sometimes
equaling or exceeding the weight of the
canals in the corner of the eye near the beak
brain. The eyes of the Ostrich, nearly two and nostrils to enter the nasal cavity.
inches (50 mm) in diameter, are the larg- The eyeball (Fig. 4-38) has a tough
est of any land animal alive today. Photo outer layer of connective tissue, the sclera,
by H. Cruickshank/VIREO.
which is stiffened by a ring of bony sclera!
ossicles (Fig. 4-39) near the front of the
eye. Scleral ossicles are present in the eye-
balls of all birds, lizards, turtles, and fishes.
The anterior surface of the opaque white
sclera is specialized as the transparent cor-
nea, which allows light into the eye. The
layer deep to the sclera and cornea is the
vascular choroid, which forms the iris (Lat-
in for "rainbow"), the colored part we see
when we look at an eye (see Fig. 3-34c).
The iris, which contains smooth muscle fibers, encircles the opening Figure 4-37. Great Horned Owl Show-
or pupil (see Fig. 4-40), regulating its size and thus the amount of light ing Nictitating Membrane: The nicti-
tating membrane, or third eyelid, lies
entering the eye.
between the bird's regular eyelids and
(sharpest or best resolving) vision in the animal kingdom. The Golden Within the eyeball, the largest cavity, the vitreous chamber, is the surface of the eye. It moves across the
Eagle exceeds the visual acuity of humans by two or three times and filled with a clear, jelly-like material, the vitreous body, which "in- eye at rightanglestothe eyelids, cleaning
is capable of spotting movements of small prey such as rabbits from flates" the eye and maintains its shape. Projecting into the vitreous and lubricating the eye's outersurface. In
more than a mile away! body from the site where the optic nerve exits the eyeball is a non-sen- this photo it is visible halfway across the
eye of an immature Great Horned Owl.
Unfortunately, the desire to know how our vision (or any of our sory, vascular structure of the choroid called the pecten. The pecten
Photo by Lang Elliott/CLO.
other senses) compares with that of birds is fraught with obstacles. is believed to nourish the retina and to control the pH (acidity) of the
First of all, there are approximately 10,000 different species of living vitreous body. The pecten takes many forms, but it is present in all birds
birds worldwide, and no blanket statement can encompass the visual and known elsewhere only from some reptiles.
abilities of them all. Second, we cannot experience the perceptions of The lens, a crystalline-like structure composed of regularly ori-
other organisms. We must use indirect means—comparative anatomy, ented layers of collagen fibers, is the primary modifier of focus. It is
physiology, and behavior—to compare a bird's capabilities to our own. spherical to ovoid in shape, depending on the species, and is unusually
This is a tricky business, but worth the try. Just how do avian eyes stack soft and pliable in comparison with that of other vertebrates. The lens
up to our own? Let's begin by examining eye structures. is especially soft and pliable in many diving birds, allowing it to be
squeezed and stretched to a variety of shapes, so it can achieve the best
The Structure of the Eye possible vision under a variety of circumstances. The lens is held in
In addition to the familiar upper and lower eyelids, birds have place between the vitreous chamber and the iris by ciliary processes.
a nictitating membrane or third eyelid. It moves sideways across the Only in birds do these processes attach directly to the lens. Ciliary
eye, at right angles to the regular eyel ids, cleaning the eye's surface and muscles attach to the processes, moving them when they contract.
keeping it moist (Fig. 4-37; see also Fig. 1-4). In some aquatic birds, The lens-distorting power of these muscles makes possible the vari-
such as loons, cormorants, diving ducks, and alcids, the nictitating able-focusing powers of the lens. A small chamber in front of the lens
membrane has a special window-like area in the center. These birds is partially divided in two by the iris: a narrow posterior chamber be-
presumably "wear" their nictitating membranes as swim goggles to tween the lens and iris; and a larger anterior chamber between the iris
improve their underwater vision. Dippers, such as the American Dip- and the cornea. Both chambers are filled with aqueous fluid, a cel l-free
per, have an opaque, white third eyelid which, curiously, can be of no fluid similar to blood plasma (see Blood, later in this chapter), which
use in searching for prey underwater. is constantly produced from the blood and secreted into the posterior
On each side of the eye are two tear glands, which moisten the chamber. The aqueous fluid from the posterior chamber passes through
eye and nourish the cornea. One is the lacrimal gland, which lies in the pupil into the anterior chamber, nourishing and removing wastes
the lower part of the orbit and has many ducts that enter the space as it flows. It then drains into sinus spaces and veins at the base of the
between the lower lid and the cornea. The other is the gland of the iris to re-enter the blood.

Cornell Laboratorq of Ornithologq Handbook of Bird Bioiogq

4.48 Howard E. Evans andJ. B. Heiser Chapter 4 —What's Inside: Anatomy and Physiology 4.49
a. Entire Eye The innermost layer of the eyeball is the pigmented ret- a. Cross-Sectional Views of Eagle and Owl Eyes
ina, which consists of the light-sensitive cells, the rods and
Filled with ANTERIOR POSTERIOR
> Lens
cones. A bird sees an object when light from that object is
Aqueous Fluid Eagle
Anterior refracted as it passes through the cornea, lens, and fluid-filled
Cornea
Chamber chambers, focusing an image on the retina. There, the rods
Posterior Iris
and cones absorb some of the light's energy, are stimulated,
Chamber
and transmit the resulting signals to the brain via nerve im-
Ciliary Process
pulses. Acuity (resolving power) depends on close packing
Ciliary Muscle
Sclera) Ossicle
of the bright-light-sensitive cone cells. The packing of cones
7
Sclera)
in some regions of the retina of raptors may be as much as Ossicle

650 mil lion cells per square inch (one million per square mi I-
Sclera
limeter)! This is five times the packing in the human retina. Owl
In addition to being responsible for acuity, cone cells
Choroid
encode information about the spectrum of colors contained
Retina
Vitreous Chamber in the light focused on the retina. Birds have four to five dis-
Filled with tinctive light-sensitive cone pigments plus specialized oil
Vitreous Body droplets in some cones that may function as filters, altering
color sensitivity in the same manner as yellow, pink, or some
Central Fovea
b. Enlargement of Retina other color of sunglasses. Humans have but three light-sen- Sclera)
Pecten
sitive cone pigments, and nothing comparable to the avian Ossicle
Optic Tract (Optic Nerve)
oil droplets. The rods of birds are very sensitive to l ight en-
ergy, but are not capable of differentiating much in the way
of color information. Because they are good at detecting low
light levels, rods are more important than cones in owls and
b. Owl Skull
other nocturnal birds. We humans essentially lose our color
vision from dusk to dawn, seeing little color differentiation
even under bright moonlight, because the light is too dim to
stimulate our cones.
Each rod or cone cell has synapses with a complex of
nerve axons, many of which pass to the brain. As in all ver-
tebrates, the nerves from the sensory cells lie between the
rods and cones and the pupil, blocking some of the light that
would otherwise reach the sensitive cells. This appears to be
an inefficient way to construct a light-sensitive organ, as the
sensory cell layer actually interferes with vision. Th is arrange-
Figure 4-38. The Internal Structure of the Eye: The eye is posi- the vitreous body, and is thought to nourish the retina and con- ment, however, results from the evolutionary history of the vertebrate Figure 4-39. Sclera! Ossicles: The eye's
tioned with the anterior surface up in both of these cross-sec- trol the acidity of the vitreous body. In front of the lens is a small
eye—evolution generally works by modifying existing structures, not outermost layer, the sclera, is stiffened
tional views. a. Entire Eye: The eye consists of three main layers, chamber filled with aqueous fluid and divided into the anterior
the sclera, choroid, and retina, which specialize to form various chamber and the posterior chamber. The aqueous fluid, a cell- by creating new ones that are perfect for the job at hand. Where the by bony rings called sclera! ossicles. a.
Cross-Sectional Views of Eagle and Owl
other structures. The tough, whitish outer layer of connective free fluid similar to blood plasma, provides nourishment and nerve layer is thinnest, vision is best. The axons of the neurons leading Eyes: Here, sections through the eye of
tissue is the sclera. Toward the anterior end of the eye, the sclera removes wastes. b. Enlargement of Retina: The retina is made from the rods and cones pass over the surface of the retina and join to an eagle and an owl show how the large
is stiffened by a bony ring of sclera! ossicles, and across the an- up of light-sensitive cells, the rods and cones, which contain
form the optic nerve. This nerve leaves the eyeball by penetrating the ossicles give each eye its distinctive
terior surface of the eye, it is modified to become the transparent the visual pigments. Cones are responsible for visual acuity and
the sensing of color information. Rods are relatively insensitive retina, choroid, and sclera and thus forms a "blind spot" in the midst tubular shape. Drawing by Charles L.
cornea. The middle layer is the choroid, pigmented and richly Ripper. b. Owl Skull: The large scleral
supplied with blood vessels. It forms the iris, the colored part of to color, but they detect low levels of light and thus are more of the retina, where no rods or cones are present to capture light fall-
ossicles (dark areas) are particularly
the eye surrounding the pupil (see Fig. 4-40). The choroid also important than cones in nocturnal birds. Neurons synapsing ing on that spot. conspicuous in owls. Drawing from
forms the ciliary processes, which attach to the lens and are with the rods and cones form the optic tract (also called the In contrast, most birds, like most mammals, have in the central part Bird Study by Andrew J. Berger (John
moved by the ciliary muscles, thus altering the shape of the crys- optic nerve), which forms a blind spot (where images cannot be
of their retinas an area, the central fovea, where the cones are most con- Wiley & Sons).
talline lens to focus images. The innermost layer is the retina, detected) on the retina as it exits. The point in the retina where
consisting of light- sensitive cells (see b). The large central cavity the cones are concentrated and vision is sharpest is known centrated and the neural layer thinned for the sharpest vision. Hawks
within the eyeball, the vitreous chamber, is filled with a clear, as the central fovea. Main drawing adapted from Proctor and and other fast-flying diurnal predators have, in addition, another such
jelly-like material, the vitreous body, giving the eyeball rigidity. Lynch (1993, p. 251). Inset by Christi Sobel. area, the temporal fovea, in the posterior quadrant of the retina.
The pecten, found in all birds and a few reptiles, projects into

Cornell Laboratory of Ornitholos Handbook of Bird Biolo8t1

4.50 Howard E. Evans andJ. B. Heiser Chapter 4 —What's Inside: Anatomq and PhqsioloBq 4.51
Figure 4-40. Accommodation—The ducks, owls, hummingbirds, and a number of passerines. Nocturnal Figure 4-41. Monocular Versus Bin-
Mechanics of Focusing: To sharply fo- species such as owls probably have little, if any, color vision. In ad- ocular Vision: The placement of the
cus images from varying distances on the Pupil Pupil eyes on a bird's head affects the size and
Ciliary Ciliary dition, many birds apparently can see certain types of ultraviolet light,
retina, the eye changes the curvature of Process Process degree of overlap of the left and right vi-
which is discussed in greater detail later in this chapter. sual fields, which determines the extent
the lens by contracting and relaxing the
ciliary muscles, which move the ciliary Many birds—indeed, many other vertebrates—see the world of binocular vision and thus depth per-
processes, which change the shape of Cornea very differently than we humans do, not because of differences in the ception. The circles shown here are the
the lens. These focusing adjustments are internal anatomy of the eye, but because of the placement of the eyes visual fields of an American Woodcock
referred to as accommodation. a. Dis- Ciliary Ciliary (left) and an Eastern Screech-Owl (right),
Muscles Muscles in the head (Fig. 4-41). Many animals have primarily monocular vi-
tant Vision: To focus distant objects the at the horizontal plane corresponding to
lens flattens; at the same time, the pupil
sion. This occurs when the eyes are situated on the sides of the head the line between points A and B marked
becomes wider, allowing more light into such that an object in the external environment can be seen only by on each bird. The woodcock's eyes are
the eye. b. Close Vision: Forclose objects one eye or the other but not by both eyes at the same time. In contrast, set on the sides of its head, giving ita field
a. Distant Vision: b. Close Vision:
the lens becomes more rounded and the of view slightly greater than 180 degrees
Pupil Wider; Lens Flatter Pupil Narrower; Lens More Curved when the eyes are located toward the front of the head, objects are
pupil narrows. Drawings by Charles L. for each eye, but only a small area of
seen with both eyes simultaneously, resulting in binocular vision. The overlap to the front and the rear. Because
Ripper.
differences between the two are rather like the difference between go- binocular vision occurs only where the
How Birds See ing to a regular movie versus putting on those red and blue glasses and fields of view overlap, the woodcock has
How does a bird use the structural features of its eye to see? What watching a 3-D movie. Why, then, isn't all vision binocular like ours? primarily monocular vision. Although its
information can help us judge how well birds see? Let's begin by exam- binocular vision is limited, this species
As with many biological alternatives, trade-offs are involved. has complete monocu lar coverage of the
ining the process of focusing. Monocular vision can be advantageous because it results in a hemisphere above and behind the head,
To al low the retina to obtain sharp images at varying distances, the wide field of view, sometimes as much as 340 degrees, which allows an adaptation for spotting a predator ap-
eye changes the curvature of the lens (Fig. 4-40). Th is is accomplished an animal to see both in front and in back at the same time. In contrast, proaching from any direction. The owl,
by the action of the ciliary muscles, which move the ciliary processes, in contrast, has eyes located toward the
animals with binocular vision, including humans, have a much nar-
front of the head. The field of view for
which exert pressure on the lens. The lens flattens to focus on objects rower field of view because the visual fields from each eye overlap each eye is therefore smaller than the
far away, and becomes more rounded for objects close at hand. The extensively. Owls, with their binocular vision, can only see through a woodcock's, but the area where the vi-
curvature of the cornea changes as well. These focusing adjustments field of view of up to 70 degrees. sual fields overlap in front is far greater,
are termed accommodation. At the same time, the amount of light allowing considerable binocular vision.
entering the eye is regulated by changing the size of the pupil—open- This is crucial to the owl for the suc-
cessful capture of prey; it is gained at a
ing it for more light and closing it when there is too much light. This
cost, however, as it leaves a blind area
is achieved through the action of muscles in the iris, which open and behind the owl's head.
close the pupil just as the diaphragm in a camera controls the size of
the aperture. The next time you have the opportunity to examine a
bird closely (try a parrot, with its large, easily observed eyes), watch
the rapid change in its pupil diameter. The pupils first narrow to better
see you in the foreground and then widen to keep track of conditions
farther away. If you watch a friend doing the same visual task, the much
slower response of the human pupil lary action will become evident.
Many birds show a remarkable range and speed of accommod-
ation, keeping objects in focus at rapidly changing distances. A stoop- Eastern Screech-Owl
ing falcon, for example, can keep prey in focus until it is in its talons. A
warbler flying swiftly through a forest sees well enough ahead to avoid
the trunks and branches of trees in its path. Some birds, on the other
hand, are nearsighted (myopic). For example, penguins are notably
myopic on land because the structure of their eyes is better suited to A B A
seeing objects, such as food, in the water. (Water's refraction of light
is so similar to that of the eye tissues themselves that, when a bird
is submerged, accommodation requires large, spherical, inflexible
lenses and corneas.)
Based on the presence and complexity of the cone cells, most
Edge of Right Visual Field
diurnal bird species are believed to have very good color vision. Ex- Area of Binocular Vision
Edge of Left Visual Field
perimental results confirm this assumption, as color vision has been Area of Monocular Vision
demonstrated in a diverse set of birds including penguins, pigeons, Blind Area Behind Head

Cornell Laboratorq of Ornitholo8q Handbook of Bird Biolo9q

 V

4.52 Howard E. Evans andJ. B. Heiser Chapter 4— What's Inside: Anatomist and Phqsiologq 4.53
Figure 4-42.A Common Snipe: A female The eyes of the Amer- bird strong cues about the three-dimensional positions of objects in its
Common Snipe is viewed from behind ican Woodcock and the field of view: during these head movements, objects closer to the bird
as it incubates on its nest. The snipe's
Common Snipe (Fig. 4 42)- appear to move across the visual field faster than those at a distance.
eyes are set so far back on its head that
its visual fields overlap more behind are so far back on the head We experience a similar visual effect when watching the countryside
the head than in front. This produces a that these birds can see bet- fly by out the side window of an automobile or train.
greater area of binocular vision to the ter behind than in front.This Birds that have both central and temporal foveae in each eye (usu-
rear than to the front, providing better
may be a protective feature ally predators), tend to have forward-directed eyes for good binocular
protection against predators. Photo by
Marie Read.
for watching overhead for vision (Fig. 4 44). Because images from each side of their field of view
-

enemies while probing in (the regions they are passing through) tend to fall on the central fovea,
the mud with its long bill. it provides acute monocular views of these areas. Images from the
In fact, many animals that front, the part of the world they are about to enter, tend to fall on the
are frequently the targets of temporal fovea, providing acute binocular vision for that area. Thus
predators have monocular these predators see well on both sides while also seeing ahead—an
vision. Another bird with obvious advantage when pursuing prey. These multiple foveae also
Figure 4-43. American Bittern: The monocular vision, the
bittern s eyes are set low on the sides of
'
American Bittern, has eyes Binocular
its head. Thus, with the head held hori-
zontally, it can search the water below
set so low on the sides of Field
I

for food while also seeing ahead. When the head that it can look
alarmed, the bittern stretches its head for food below and see
and neck high and points its bill directly ahead at the same time.
upward, as pictured here, blending in
When alarmed and in a
with the surrounding grasses (see Fig.
2-17). Even in this defensive posture the defensive posture, the bittern stretches its head and neck high and
position of its eyes permits good vision points the bill straight up. In this position it has good vision directly
in front as well as of the sky overhead. forward as well as upward into the sky (Fig. 4 43).
- Monocular Field Monocular Field
Photo by Tom Vezo.
Binocular vision also has an important advantage, however: it
enables a bird to have good depth perception and thus to
determine distances better. Depth perception results from
Visual Field of
forward-facing eyes because each eye gets a slightly dif- Left Eye Visual Field of
ferent view of an object; the closer the object, the more Right Eye
different the two views. The difference allows the brain
to distinguish distance. Many predators, such as hawks,
eagles, and owls, have binocular vision because it aids
them in capturing prey.
A number of birds with restricted binocularity but
wide monocularity obtain the benefits of depth perception
by head actions. American Robins, peering at prospective
food, cock their heads at different angles before picking
it up. They are making sure of its identity and capture by ..%

determining its form and its precise three-dimensional

position. The head-bobbing and teetering movements of
some plovers and sandpipers may have the same function. Dots Represent Relative Density of Cones
Watch a Rock Dove or a chicken as it walks, alternately (Darker Areas are Where Vision is MostAcute)
jerking the head back and forth with pauses in between
movements. In doing this, the bird is getting a series of
different views for determining spatial relationships of Figure 4-44. Visual Fields and Multiple Foveae of a Hawk: Foveae are areas of the retina where the cones are densely packed,
objects in its surroundings. When the bird's head moves providing especially sharp vision. Although most birds have only one central fovea in each eye, many hawks and other avian
predators have two foveae, central and temporal, in each eye. These birds also tend to have forward-facing eyes that allow good
backward relative to its moving body but with little move-
binocular vision. Visual information from the left or right side falls on the central fovea of the corresponding eye, giving sharp
ment relative to the visual scene, acuity is greatest. When monocular views of these areas, whereas information from in front of the bird falls on the temporal fovea, giving a sharp binocular
the head moves rapidly forward, differences in the ap- view of the area ahead. Thus these birds enjoy three well-focused views simultaneously—two side views and one forward—a
parent movement of objects in the visual field give the great advantage for locating and pursuing prey. Drawing by Charles L. Ripper.

Cornell Laboratorg of Omitholcm Handbook of Bird Biologq

4.54 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiologq 4.55
create incredible complexity for instantaneous neural processing and sound vibrations to the inner ear from an eardrum, which stretches
analysis! Some shorebirds whose normal habitat is flat, open, and rel- across the external opening of the middle ear. These structures are dis-
atively featureless, have a foveal stripe that runs horizontally across the cussed in more detail below. Mammals carried the process even further
retina. It probably is specialized for detecting conditions, particularly by adding two more bones on each side, creating a chain of three bones
movement, along the horizon. (malleus, incus, and stapes), and a sound-collecting auricle or external
The eyes of most birds move very little in their sockets. Because of ear—the flap we see when we look at a mammal. Do not, however,
the eyeball's large size, there simply is not much room in the compact, confuse the "ears" of birds such as the Great Horned Owl and Long-
streamlined head for eye muscles. The four rectus and two oblique eared Owl with the birds' true ears (Fig. 4-46).The "ears" of these owls
muscles that move the eyeball in all vertebrates, from fish to humans, are merely tufts of feathers growing from the top of the head, and have
are present but much reduced in size. Birds compensate for the lack no relation to the true ears or to hearing. They are thought to be used
of eye movement by having very mobile necks (Fig. 4-45). Owl eyes in species recognition.
are immovably fixed in the skull, and they have only temporal foveae,
which are used for forward binocular vision. For views to the sides,
they turn their heads, sometimes halfway around.
--- Figure 4-46. Location of Great Horned
So, do birds see better than humans? As should now be evident, Owl Ear Openings: The owl's facial disk
merely deciding what we mean by "better" is a problem. Do we mean of feathers is shown parted to reveal the
large ear opening hidden beneath. Al-
Figure 4-45. A Burrowing Owl Look-
better acuity or better focus? Better light sensitivity or better color d if-
though the tufts of feathers growing from
ing at the World Upside Down: Unlike ferentiation?To each of these individual components the answer seems the top of the head of the Great Horned
humans, birds can move their eyes very to be "Some birds, yes, and some birds, no. Under some conditions Owl, the Long-eared Owl, and other
little in their sockets. Owls have espe- some birds, yes, but under other conditions the same birds, no." That species are often referred to as "ears,"
cially immovable eyes, but like other they have no relation to true ears or hear-
is a part of the magic of birds. No matter how hard we try, their variety
birds they compensate by having very ing. Drawing by Charles L. Ripper.
flexible necks (see Fig. 4-13). Owls reg- thwarts any attempt to generalize. The best we may ever be able to do
Ear
ularly turn their heads halfway around to is conclude that some birds "see better" than we do and that vision is Opening
get a better view behind them, or even the predominant sense of birds as a group.
view the world upside down, as this
bird has chosen to do. Photo by Bryan
S. Munn. The Ear and Hearing
Sound is also an important characteristic of the Nevertheless, many birds do have fleshy or feathery specializa-
environment, and its detection allows a bird to be- tions (often modified auricular feathers [see Fig 1-51 or ear coverts)
come aware of predator and prey, to flee impending around their external ear openings. Like the external ears of mammals,
danger or approach potential mates, and to adver- these help to concentrate sound waves and enhance the bird's ability
tise or warn. The challenge of hearing is to convert to determine the direction from which a sound originated. Because
pressure waves in the air (see Fig. 7-4) into neural sound travels at a fixed speed through air of a given temperature and
impulses that can be interpreted by the brain. All humidity, a sound originating at one point will arrive at other points
animals do this by first changing the varyingpressure at times that depend on their distance from the origin. Even small
waves that make up sounds into vibrations, which differences in distances from the sound's origin, such as the distance
are then altered further to become nerve impulses. between a bird's ears, can create a detectable difference between
Animals with the best hearing can distinguish the arrival times of the sound at the two ears. The greater the difference
direction of origin, and the complexity of frequency in arrival times, the more precisely the position of the sound's origin
variations as well. can be determined. Also, because a sound weakens as it travels, it
A bird's sense of hearing is keen and very im- will be louder in the ear closest to the sound source. Thus, additional
portant for survival and reproduction. The ear had its directional cues may be gleaned from differences in a sound's volume
evolutionary origin in fishes as membranous, fluid- (loudness) between the two ears.
filled chambers called the inner ear, which func- Some species of owls that are strictly nocturnal and consequently
tion in maintaining balance and sensing vibrations. depend heavily on hearing while foraging have their right and left ex-
For hearing in air, amphibians, reptiles, and birds all ternal ear canals at slightly different levels on the head (Fig. 4-47).
evolved additions to the fluid-filled chambers. These This improves the owls' abilities to determine the three-dimensional
included an air-filled middle ear chamber with a position of a sound source. Some owls can pull a fold of skin located
small bone, the columella or stapes, which transmits in front of the ear over the external ear canal to close it off, protecting

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

4.56 Howard E. Evans andJ. B. Heiser Chapter 4 —What's Inside: Anatomq and Philsiologg 4.57

Figure 4-47. Asymmetrical Placement Boreal Owl Skull Anterior View tached to the interior surface of the eardrum. The area internal to the
of the External Ear Canals of a Boreal eardrum, which includes the columel la, is termed the middle ear; it is a
Owl: Many species of owls have consid- Right External
small, air-filled cavity, bounded by bone and open to the throat via the
erable asymmetry in the placement of Ear Canal
auditory (Eustachian) tube. In birds, the auditory tubes join and enter
the external ear openings, although the
Left External the caudal roof of the mouth through a common opening. Perhaps
structures of the middle and inner ears
Ear Canal
are located symmetrically. The anterior you have experienced pressure on your eardrums when climbing a
view shows that the right external canal mountain or being pressurized in an airplane. You may have relieved
is located higher than the left. The dorsal
the pressure by either blowing your nose, yawning, or swallowing. For
view shows further asymmetry, revealing
that the right ear canal is located more a bird constantly changing its altitude in flight, the need to equalize
posteriorly than the left. Asymmetrical the pressure in the middle ear with that of the external ear must be
ear openings help owls to localize the Boreal Owl Skull Dorsal View almost constant. The auditory tubes permit this equalization, allowing
sources of sounds in three-dimensional air taken in the mouth (and thus at the same pressure as ambient air
space with great accuracy, a feat they
achieve by detecting tiny differences be-
and the air in the external ear canal) to move in or out of the middle
tween the arrival times of a given sound ear until equal background pressure is established on both sides of the
at each ear. Owls have the most sensitive eardrum.
acoustic systems of all birds, enabling The columella extends across the middle ear cavity to contact
some species, such as the Barn Owl, to
a soft, pliable spot, the vestibular window (formerly called oval win-
capture their prey in complete darkness.
From Norberg (1978). dow), on the bony inner ear (Fig. 4-49). Unlike the external and
middle ear, which are filled with air, the inner ear is filled with fluid. Its
entire structure is that of two fluid-filled systems, called labyrinths, one
within the other. The inner "sac" is called the membranous labyrinth,
and is filled with a fluid called endolymph. A bony labyrinth, filled with
a fluid called perilymph, encases the membranous labyrinth; thus the
delicate membranous labyrinth floats in the perilymph and is well pro-
sensitive ears from loud sounds; alternatively, the fold can be erected tected. This protection is essential because the sensory cells for each
to enhance the detection of sounds coming from behind. part of the inner ear (termed hair cells) are located on the inner surface
of the membranous labyri nth.These sensory cells send messages to the
Structure and Function of the Ear brain via the eighth (vestibulocochlear) cranial nerve.
Let's now examine the three parts of the avian ear—the external The inner ear has three major regions: (1) the bony cochlea,
ear, the middle ear, and the inner ear—i n more detail (Fig. 4-48). The enclosing the membranous cochlear duct, (2) the bony semicircular
external ear canal leads to the tympanic membrane or eardrum. The canals, surrounding membranous semicircular ducts, and (3) the bony
eardrum, stretched taut over the ear canal, vibrates when struck by the vestibule, which encases two chambers called the utriculus and sac-
pressure waves of a sound. The eardrum's movement is then transferred culus—part of the membranous labyrinth.The first region is concerned
Figure 4-48. Location and Structure of to a piston-like movement of the slender columella bone, which is at- with hearing, and the second and third are concerned with the sense
Rock Dove Ear: The avian ear consists of of balance or equilibrium.
three parts: the external ear, the middle The cochlea of birds is an elongated structure containing three
ear, and the inner ear, all embedded in fluid-filled canals (Fig. 4-50). (In mammals the cochlea is curled like a
bone. As in humans and many other an-
snail's shell, thus giving rise to the name, which means "snail" in Latin.)
imals, the external ear canal (notshown)
leads from outside the body to the tym- The upper and lower canals (called vestibular and tympanic canals,
panic membrane or eardrum. Attached respectively), connected at one end, are part of the bony labyrinth
to the inner surface of the eardrum is a and therefore contain perilymph. Between them is the cochlear duct,
slender bone, the columella, which ex-
part of the membranous labyrinth, filled with endolymph. The lower
tends across the small, air-filled chamber
of the middle ear. At a soft, pliable spot
membrane of the cochlear duct is called the basilar papilla, and lying
known as the vestibular window, the close above it is the tectorial membrane; all along the basilar papilla
columella contacts the bony, fluid-filled are sensory hair cells.
inner ear (see Fig. 4-49), where the Recall that sound waves in the air vibrate the eardrum, which
organs of hearing and balance reside. Columella
Tympanic Membrane transfers its motion to the thin, toothpick-like columella.The columel la
(Middle Ear
Reprinted from Manual of Ornithology, (Eardrum)
Bone) moves the vestibular window and sends pressure waves through the
by Noble S. Proctor and Patrick]. Lynch,
with permission of the publisher. Copy- perilymph of the cochlea and endolymph of the cochlear duct. The
right 1993, Yale University Press. basilar papilla is set into motion by these pressure waves, moving

Cornell Laboratort of Ornithologq Handbook of Bird Biologq

4.58 Howard E. Evans andJ. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiolos 4.59
the hair cells against the tectorial membrane, and triggering a nerve
a. Labyrinths of the Inner Ear
impulse in the affected hair cells. Different frequencies of sound
Bony Labyrinth Perilymph
cause different portions of the basilar papilla to vibrate—the high-
Endolymph est frequencies causing greater movement in the proximal end of the
membrane (near the vestibular and cochlear windows). The brain de-
termines pitch by registering which region of hair cells are stimulated
Membranous (Fig. 4 51 a), and is thought to determine tone (the quality of a sound)
-

Labyrinth Semicircular b. Internal Structure by the distribution of hair cells stimulated. The volume (loudness) of
Canals of the Ampulla a sound is determined by the amount of pressure of the sound wave.
DYNAMIC EQUILIBRIUM Loud sounds cause more vigorous vibrations of the eardrum and thus of
c. Internal Structure of the the fluid in the cochlea, and the resulting increased stimulation of hair
Utriculus and Sacculus
cells is interpreted by the brain as a loud noise (Fig. 4 51 b). At the end
-

STATIC EQUILIBRIUM of the bony labyrinth farthest from the vestibular window is a second
.4-Vestibule soft spot, the cochlear window (formerly called the round window),
Containing which abuts the dead space of the middle ear (see Fig. 4-50). The co-
Utriculus
Statoconia chlear window acts both as a pressure-release valve and as a damper
(Dense, Calcareous Crystals) and Sacculus Figure 4-50. Internal Structure and
for the waves in the cochlea. Each wave is dissipated as it expends its Hearing Mechanism of the Cochlea: The
remaining energy distending the cochlear window membrane into cochlea of birds is an elongated struc-
Columella ture containing three fluid-filled canals.
the middle ear, preparing the inner ear to receive new pressure waves
Two of them, the vestibular canal and
from new sounds. the tympanic canal, connected to each
Vestibular The delicate structures of the inner ear are protected from very other at the tip of the cochlea, are part of
Window Cochlear
loud sounds by the action of a small muscle that enters the middle ear the bony labyrinth, and therefore con-
Window
tain perilymph. The endolymph-filled
cavity from the outside and attaches to the columella. When a loud
canal between them (the cochlear duct,
part of the membranous labyrinth) con-
Cochlea sists of a membrane, the basilar papilla,
along which lie numerous sensory hair
Plane of Section
Through Cochlea cells overlaid by another membrane,
the tectorial membrane. The hair cells
are short at the base of the cochlea, be-
coming longer toward its tip. The flex-
ible vestibular window, at which the
Figure 4-49. Structure and Functions of the Inner Ear: The on the gelatinous material and displacing it, such that it bends Sound Pressure Waves columella of the middle ear contacts
bony, fluid-filled inner ear has three major parts: the semicir- the hairs of the hair cells, stimulating them to send impulses from Tympanum Cause the cochlea, lies at the base (proximal
Columella to Vibrate end) of the vestibular canal. Nearby, at
cular canals and the vestibule, both of which control balance to the brain by means of their associated nerve fibers. For any
(equilibrium), and the cochlea, whose role is in hearing. The given movement, each of the ampullae and thus its hair cells the base of the tympanic canal, is the co-
columella of the middle ear contacts the surface of the bony is stimulated to a different degree, depending on the degree to Position of Cochlear chlear window. Sounds are perceived in
labyrinth (see [al below) at the vestibular window (formerly which each plane of space is involved in the movement. For Window the following way: Sound waves through
called the oval window), a pliable region marking the base of example, just moving the head horizontally would stimulate air vibrate the eardrum, and this motion
the cochlea. A second soft spot, the cochlear window (formerly only the hair cells in the ampulla oriented in the horizontal is transferred to the columella, which in
0 Vestibulocochlear
called the round window), is located nearby. The cochlea and plane of space. The brain combines information from each of C
turn vibrates against the vestibular win-
Nerve
the mechanism of hearing are described in Figure 4-50. The the three ampullae to interpret the bird's motion in space, a type Vestibular dow (dashed arrows), sending sound
Window 0
three semicircular canals are arranged approximately at right of balance known as dynamic equilibrium. c. Internal Struc- pressure waves (solid arrows) through
angles to one another, each lying in a different plane of space. ture of the Utriculus and Sacculus: The vestibule contains two Hair Cells 0 the perilymph of the cochlea and the
a. Labyrinths of the Inner Ear: This inset shows a cross-section organs, the utriculus and the sacculus, which perceive static endolymph of the cochlear duct. Dif-
Vestibular Canal 0
through one of the semicircular canals, and is representative of equilibrium (the position of the head with respect to gravity). 0 ferent frequencies of waves cause dif-
Filled with Perilymph 0
the general internal structure of the inner ear: two fluid-filled These two chambers each contain hair cells and dense crystals ferent portions of the basilar papilla to
0
systems, termed labyrinths, one inside the other. Innermost is called statoconia, both embedded in a gelatinous material that Cochlear Duct 0 Tympanic Canal move, moving certain hair cells against
the membranous labyrinth, filled with endolymph, which floats is surrounded by endolymph. As the bird changes the position Filled with Endolymph Filled with Perilymph the tectorial membrane and bending
in the perilymph inside the bony labyrinth, the outermost layer of its head, the statoconia move around and sink in the direction CO them, triggering nerve impulses. The
CO
of the inner ear. b. Internal Structure of the Ampulla: The base of gravity. This causes the gelatinous material to sag, bending Tectorial - Basilar Papilla impulses are transmitted through the
0 vestibulocochlear (auditory) nerve to
of each semicircular canal contains a chamber, the ampulla, and stimulating certain hair cells. The stimulated hair cells Membrane
which contains sensory hair cells embedded in gelatinous consequently send nervous impulses to the brain, allowing it the brain, where they are interpreted
material. Endolymph surrounds the gelatinous material, filling
the rest of the ampulla. As the bird changes speed or direction,
to determine which direction is down from which particular set
of hair cells is stimulated. Drawings by Christi Sobel.
ti. Sound Pressure
Wave
as sound. The flexible cochlear window
acts as a damper in the system, stretching
Through Fluid
thus moving the head, the endolymph lags behind, pressing to allow the sound waves to dissipate.

Cornell Laboratory] of Ornithologq Handbook or Bird Biolom

4.60 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiolosti 4.61
Figure 4-51. How Pitch and Volume a. Pitch hair cells embedded in a gelatinous material, surrounded by endo-
(Loudness) are Perceived: a. Pitch: lymph. When the bird changes its speed or direction (accelerates),
Sounds of different pitches (frequen- 24,000 Hz
Basilar Papilla the endolymph in the canals lags behind (because of inertia), pressing
cies) are distinguished by the cochlea
because sound pressure waves of a given on the gelatinous material, which consequently applies greater pres- Figure 4-52. Hearing Thresholds of
High Frequency Songbirds Versus Nonsongbirds: This
frequency travelling through the fluid of TIP Sound sure on the hair cells of whichever planes of space are involved in the
the cochlear duct cause a specific region BASE graph shows the hearing thresholds
(Distal)
acceleration (see Fig. 4-49b). Stimulation of the hair cells causes the
(Proximal) (defined as the lowest intensity, or vol-
along the basilar papilla to vibrate more
vestibular nerve to send impulses to the brain. The brain determines ume, at which sounds of a given pitch,
strongly than other regions, moving its
attached hair cells against the tectorial
how the bird moved by combining the relative amounts of stimulation or frequency, can be perceived) of nine
membrane and thereby triggering nerve 4,000 Hz it receives from each of the three ampullae. species of songbirds (dark circles) and
seven species of nonsongbirds (white
impulses. The differential stimulation of The vestibule contains two chambers, the utriculus and the sac-
hair cells is interpreted by the brain as circles). The y-axis is volume in decibels
culus. Each contains hair cells and dense crystals of calcium carbonate (dB), and the x-axis presents frequency
sound of a certain pitch. The frequency
called statoconia, both embedded in a gelatinous material (see Fig. on a logarithmic scale in kiloHertz
sensitivity of the basilar papilla changes
along a gradient, the membrane being 4-49c). The gelatinous material is suspended in the endolymph. The (kHz). Songbirds are able to perceive
bird's brain determines which direction is down by registering which high frequency sounds at lower vol-
most sensitive to high frequencies at 500 Hz
umes than nonsongbirds. For instance,
the proximal end and becoming more sensory cells are stimulated by the gravity-induced settling of these a 10 kHz sound is first heard by song-
sensitive to low frequencies toward the
Low Frequency dense crystals. birds at a volume of about 70 dB, but the
distal end. b. Volume: Volume (loudness)
Sound same frequency sound must be louder,
is a function of the amplitude (height)
of the sound wave. The greater the am-
Hearing Ability nearly 90 dB, for a nonsongbird to hear
We assume that an animal hears, at the very least, the sounds that it. Conversely, nonsongbirds are able to
plitude of a sound, the more vigorous
perceive low-frequency sounds at lower
the vibrations of the fluid in the cochlea, it and other individuals of the same species produce. We also assume
volumes than songbirds. For example,
and thus the greater the displacement that it hears the relevant sounds of prey and predator. Humans in their nonsongbirds first perceive a 0.2 kHz
(bending) of the hair cells along the basi-
b. Volume (Loudness) prime can usually hear sounds between 16 and 20,000 vibrations, or sound at 40 dB, but the sound must be
lar papilla. Stronger stimulation of the
cycles per second (Hertz). The tested hearing range in a series of birds over 50 dB before a songbird can hear it.
hair cells results in more nerve impulses,
Songbirds tested were canary, American
which the brain interprets as sound of a varied from a low of 40 Hertz in the Budgerigar to a high of 29,000
Crow, European Starling, House Finch,
higher volume. Basilar Papilla Hertz in the Chaffinch, a common European bird (see Fig. 7-5). In gen- Blue Jay, Brown-headed Cowbird, Red-
eral, most birds have the greatest sensitivity to sounds in the frequency winged Blackbird, Field Sparrow, and
High Volume
Sound range of 1,000 to 5,000 Hertz—approximately the top two octaves on bullfinch. Nonsongbirds tested were
BASE TIP
a piano. Their ability to detect these sounds appears similar to that of Barn Owl, Great Horned Owl, Rock
(Proximal) (Distal)
Dove, Budgerigar, Mallard, turkey, and
humans within this range of frequencies.
American Kestrel. For more about bird
Each species, however, appears to have its own distinct range sound and its measurement, see Chapter
of frequencies to which it is sensitive. Passerines perceive high-fre- 7. Adapted from Gill (1995, p. 194).
quency sounds better than most non-
passerines, but nonpasseri nes perceive
Low Volume low-frequency sounds better than 100 -
Sound • Songbirds (9 Species)
passerines (Fig. 4-52). As discussed O Nonsongbirds (7 Species)
later in the chapter, some bird species
80 -
are apparently able to perceive ultra- EQ-
-0
noise is received, this muscle contracts, restricting transmission of the sound, although whether they actually •
full force of the eardrum's vibration to the inner ear, thereby protecting "hear" it with their ears or detect it in 60

it. some other way is unknown. In addi-

In all vertebrates, the inner ear functions in balance as well as tion, some differences occur between
40
in hearing, but the sense of balance is especially important to birds young and adult birds of the same
because of the three-dimensional acrobatics of flight. Balance has species. Downy young of the chicken
respond primarily to the low-pitched 0 20
two components: dynamic, the perception of motion; and static, the (r)
perception of gravity. The semicircular canals and ducts function in clucks of the hen, whereas the hen is
dynamic balance, and the vestibule, in static balance. especially sensitive to the high-pitched 0
The narrow, ring-like semicircular canals and their enclosed ducts peeps of the chicks. Compared to hu-
are arranged at approximately right angles to each other, so that one is mans, Great Horned Owls hear low
1 1 I I 1
1 1 I 1

located in each of the three planes of space (see Fig. 4 49). The base of
-
frequency sounds very well, and Barn 0.2 0.5 1 2 5 10
each semicircular duct (called the ampulla) is widened and contains Owls hear high-frequency sounds Pitch (Frequency) in kHz

Cornell Laboratorg of Ornithologq Handbook of Bird Biologq

4.62 Howard E. Evans andJ. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.63
well. In total darkness, many owls (and probably other nocturnal birds)
locate prey with surprising accuracy by sound alone.
Experiments show that certain birds use echolocation to avoid
obstacles while flying in the dark, just like bats do. This process is
well-developed in the Oi !bird ofTrinidad and northern South America,
which nests and roosts in caves (Fig. 4 53). While flying, the Oilbird
-

utters a continuous series of very short, click-like sounds that bounce

back from the cave walls, informing the bird of its position in relation
to reflecting objects. The response of a flying bird to these sounds is
much more rapid than the response of humans to sounds. The Ed-
ible-nest Swiftlet, one of several swifts of Southeast Asia whose nests
are used for bird's-nest soup, also uses echolocation in flying to and
from its nest, which may be as far as 400 yards (366 meters) inside the
entrance to its cave.

Olfaction
In all animals, the sense of smell involves the fitting of an airborne
(or waterborne) molecule into a highly specifically shaped notch on
the surface of an olfactory sensory cell. Much like a lock-and-key sys-
tem, only the right "key" will turn on a particular sensory cell, which
then fires a neural signal recognized as a specific odor in the brain.
As a group, birds have a poor sense of smell. Laboratory tests
indicate that birds may generally be only one-third to two-thirds as
sensitive to testodors as some fishes and mammals, including humans.
The bird's rather weak olfactory sense has been inferred from the rela-
tively small size of the olfactory lobes in most birds' brains. The bird's
nasal cavities are discussed later in relation to the respiratory system,
but note here that they are relatively small. The lining or surface tissue
(epithelium) of each nasal cavity, the olfactory epithelium, contains
the sensory endings of the olfactory nerves but occupies a very limited
area. (The olfactory nerves carry impulses directly to the olfactory
lobes in the brain.) Experimental evidence indicates, however, that a
variety of birds withouten larged olfactory areas may nevertheless have
rather keen olfactory abilities.
Most birds with large olfactory lobes and sensitive olfaction are
ground-dwelling species, aerially hunting vultures, or marine birds
(Fig. 4 54). The ground dwellers include such birds as kiwis and pos-
-

sibly snipes. The kiwis, the only birds whose nostrils are near the tip of
the bill, find earthworms and other prey living underground by smell-
ing them. Their olfactory lobes are about 10 times the size of those of
other birds (Fig. 4 55). Whether the aerially hunting vultures locate
-

dead animals primarily by smell or by sight has long been debated.

Evidence from neuroanatomy, especially olfactory lobe size, indicates
that the Turkey Vulture and the King Vulture of the American tropics
both depend primarily on olfaction to locate their prey. These scav-
engers live in forested areas where carrion is usually hidden by the leafy
canopy. Other American vultures, such as the Black Vulture, depend
Figure 4-53. Oilbirds in Cave: The nocturnal Oilbird of Trinidad and northern South America uses echolocation to navigate
primarily on sight, but may follow other species to the carcasses they
through deep caves where it nests and roosts colonially. A flying Oilbird produces a series of short clicks, which bounce to and
find by smell. In the Old World vultures, a distinctly different group of from the cave walls, informing the bird of the presence of stalactites and other obstacles.

Cornell Laboratory of Ornithologq Handbook of Bird Biologq

4.64 Howard E. Evans andJ. B. Heiser Chapter 4 —What's Inside: Anatomq and Phqsiologq 4.65
sight. Because petrels forage by night as well as by day, these olfactory
cues could be critical for locating food. In experiments, artificial slicks
of dimethyl sulfide were more attractive to the small, zooplankton-eat-
ing petrels than to the large albatrosses that feed on squids and fishes
in the same regions (Sidebar 1: The Amazing World of Avian ESP).

Taste
Taste and smell are related; both are types of chemical reception.
In humans, both senses determine the flavor of foods. The taste bud, a
simple structure usually embedded in the epithelium of the oral cavity Figure 4-56. Location of Taste Buds in
and the tongue, is the receptor for taste sensations in all vertebrates. Human and Mallard: Birds' sense of taste
seems to be poorly developed, as sug-
Although the sense of taste in birds has been studied very little, it is
gested by the few taste buds present in
a. Bonin Petrel b. King Vulture c. Great Spotted Kiwi thought to be poorly developed. Birds have few taste buds when com- the oral cavity of most species. An adult
pared to mammals. They number as few as 24 in the chicken, 27 to human (left) has over 10,000 taste buds,
Figure 4-54. Birds with Sensitive Olfaction: Most birds do not appear to have a good sense of smell, but there are a few excep-
59 in the Rock Dove, 62 in the Japanese Quail, and about 300 to 400 located in circular vallate papillae at
tions. a. Bonin Petrel: Tubenosed marine birds, especially the shearwaters, fulmars, and petrels—such as the Bonin Petrel shown
in various parrots. By contrast, an adult human—a species not noted the back of the tongue and in fungiform
here—are attracted to specific marine odors, helping them to locate the plankton on which they feed. Photo courtesy of Chandler
papillae around the sides and tip of the
S. Robbins/CLO. b. King Vulture: Evidence suggests that at least some aerially hunting vultures of the New World, such as the for its good sense of taste—has over 1 0,000 taste buds! Among birds,
tongue. In contrast, the Mallard has only
King Vulture shown here and the Turkey Vulture (see Fig. 5-32), locate the carrion on which they feed by its smell. Old World however, gustatory ability seems not to be correlated closely with the about 400 taste buds, none of which are
Vultures, however, seem to locate their food by sight. Photo by Steven Holt/VIREO. c. Great Spotted Kiwi: The nocturnal kiwis,
number of taste buds. Birds have few of their taste buds on their tongue located on the tongue. The schematic
such as the Great Spotted Kiwi shown here, use their highly developed sense of smell to locate their underground prey, primarily
and none near the tongue's tip. Most of a bird's taste buds are on the view of a Mallard's oral cavity (right),
earthworms. They probe the ground with their long bill, which has nostrils located at the tip. Photo by B. ChudleighNIREO.
with tongue removed and bill held open
roof of the mouth or deep in the oral cavity (Fig. 4-56). Furthermore,
wider than possible in life, shows the
(Continued on p. 4.69) location of the taste buds. They are scat-
tered mostly in the palate (roof of the
mouth), with a few in the floor of the
mouth.
Figure 4-55. Range of Olfactory Lobe
Sizes: Lateral views of the cerebral
hemispheres of various birds illustrate Olfactory About 50 Taste Buds
the variability in the size of the olfactory — Lobe
lobe (shown in black) at the anterior end Kiwi Emu Duck Snipe
of the brain. Birds with large olfactory
lobes, and by implication, a well-de-
veloped sense of smell, are typically
About 40 Taste Buds
ground-dwelling species, such as snipe,
kiwi, and Emus, as well ascertain ducks.
90 to 140 Taste Buds
The kiwi (see Fig. 4-54c), whose olfac-
tory lobes are the largest, with respect to Kestrel Parrot Flycatcher Magpie 100 to 150 Taste Buds
its brain size, of any bird, relies entirely
on olfaction to locate the earthworms
and other underground prey on which birds that evolved primarily on open savannas and treeless steppes, all Tongue Removed
it feeds. Kestrel, parrot, and flycatcher (Position Shown
species appear to depend entirely on vision to find their food. by Dashed Line)
olfactory lobes are very small, and the
lobes are barely visible in the magpie,
Evidence suggests that many of the tubenosed seabirds, espe-
indicating that these species rely on vi- cially petrels, shearwaters, and fulmars, are able to smell and home Vallate Papillae
Containing Taste Buds
sion rather than smell to find food. From in on specific odors such as the smell of plankton. In these birds, the 30 to 70 Taste Buds
Marshall (1961). olfactory lobes are more than one-quarter the size of the brain hemi- (Under Tongue)

spheres. The attraction of several types of petrels to dimethyl sulfide

Fungiform Papillae
is particularly interesting. Dimethyl sulfide is an aromatic substance Containing Taste Buds
released by phytoplankton (microscopic, drifting marine algae) when
zooplankton (tiny, drifting animals such as copepod crustaceans) are
feeding upon them (Nevitt 1999). The occasional dense patches of
grazing zooplankton—which are the feeding targets of small petrels Human Mallard
About 10,000 Taste Buds, About 400 Taste Buds,
such as the Wilson's Storm-Petrel—are very difficult to distinguish by Mostly on Tongue None on Tongue

Cornell Laboratorq of Ornithologg Handbook of Bird Biologq

4.66 Howard E. Evans and J. B. Heiser Chapter 4 —What's Inside: Anatornq and Phqsiologq 4.67

Sidebar 1: THE AMAZING WORLD OF AVIAN ESP

J. B. Heiser

Although there is little in the litera- a long rubber tube. He struck off sound in a natural environment, but distances—demonstrating, for at ecules (including DNA) absorb UV guides" to locate sources of food.
ture about the ability of birds to com- "through the whole of the Zoologi- quite the opposite is true of infra- least this one substance, a sensitivity wavelengths, but in the process the It has long been recognized that
municate with their long-deceased cal Gardens" poking his whistle on sound. Weather phenomena such much greater than that of humans. electromagnetic energy can disrupt many insect-pollinated flowers
ancestors or to see into the future, the end of his walking stick "as near as thunder, wind blowing over and Under certain conditions, hom- thestructureof the molecule—reason have UV patterns that encourage
there is an amazing, and ever-grow- as is safe to the ears of animals" (as through topographic features, earth- ing pigeons have been shown to use enough to have the otherwise trans- pollination by guiding insects to the
ing literature on the ESP capabilities quoted in Nowicki and Marler 1988). quakes, and ocean waves are all olfaction in orientation (see Ch. 5, parent structures at the front of the part of the flower where the nectar
of birds. The concept of ESP (ex- By observing the reactions of animals sources of infrasound. Infrasounds Navigational Maps), depending, it human eye absorb UV before it can (as well as the pollen) is located.
trasensory perception) is based on to sounds of a higher frequency than travel long distances through air with seems, on how and where they were do damage to retinal pigments. Why, Future research may show that bird-
the sensory capacities of humans; humans could hear, Galton was little attenuation (weakening), re- housed and raised; but it remains un- then, should many invertebrates (es- pollinated flowers have similar UV
whatever is beyond the detection of readily able to demonstrate ultra- maining loud enough to be detected likely that odors play an essential role pecially insects), fish, amphibians, foraging guides. Because many of
the human senses is, by definition, sonic sensitivity in a range of zoo by the kind of sensitivity demonstrat- in bird navigation (Waldvogel 1983; reptiles, and a few mammals, as the fruits that birds feast upon reflect
"extra sensory." For a long time, our inhabitants, especially members of ed by pigeons, even after propagat- Able 1996). Unfortunately, we cur- well as most birds, take the risk of strongly in the UV, but the leaves sur-
anthropocentric perspective slowed the cat family. Historically, animal ing hundreds or even thousands of rently know little more about avian UV damage by having eyes sensitive rounding them do not, the fruits stand
Western science from even consid- ESP researchers often have had to miles from their sources. Although olfactory ESP. to it? Birds apparently benefit from out brightly—possibly strengthening
ering that the sensory experience of wait for appropriate technologies detectable, infrasounds are difficult being sensitive to UV light in three the ripe fruit's signal that "I'm ripe—
other organisms might be different, to be invented and applied before to use in extracting directional infor- major ways: (1) foraging, (2) species so come have a meal and disperse my
let alone that it might be broader and they could observe phenomena that mation because their wavelengths
Extrasensorq Vision recognition and sexual selection, seeds." In addition, many insects that
4
more encompassing, than our own. might be quite common among ani- are measured in yards to tens of Much more is known about the and (3) orientation and navigation. hide from their bird predators in the
In the 1820s the observation that mals, but had never before been ac- yards—longer by far than the dis- extraordinary visual sensitivities of leaves match the leaf's reflectivity in
younger people could hear high- cessible to the human senses. tance between the two ears of any but birds. In addition to their high visual Foraging both the human visible spectrum and
frequency insect song that older ears Unlike Galton's zoo mammals, the biggest of animals. Although the acuity, birds see in a much broader Urea, the main nitrogenous com- the UV, attaining good camouflage.
could not detect led to questioning most birds seem not to be very idea that animals use Doppler effects spectrum of "colors" than do humans. ponentof mammalian urine, strongly Some, however, reflect strongly in
whether there might not be sounds of sensitive to ultrasound (very high (analogous to detecting the change Humans are unable (and perhaps reflects and fluoresces (re-emits ra- the UV. Could they be giving off an
such high frequency that no human sounds ranging from about 15 to in pitch between the whistle of an unusual in this inability) to perceive diation) in the ultraviolet. Voles and aposematic (warning) signal?
ear could hear them. But it was not 20 kiloHertz up to 200 kiloHertz); approaching versus receding train) to ultraviolet (UV) light (wavelengths other small rodents heavily mark
until 1879 that Sir John Lubbock ex- only small songbirds make and extract directional information from of 3,000 to 4,000 Angstroms [300 to their above-ground trails (termed Species Recognition and Sexual
perimentally proved that ants could hear sounds just above our hearing infrasounds has been proposed, if 400 nanometers]). In contrast, UV "runways") with urine and feces so Selection
see light in the ultraviolet range but range—to a maximum of 29 kilo- and how any animal can get direc- vision appears to be a general abil- that other individuals will be able to Many species of birds have
were blind to red light. Lubbock Hertz. Even those few birds known tional information from infrasound ity of most birds (Bennett and Cuthi I I recognize these trails (by their odor). plumage and fleshy ornaments that
thought, but could not provide to echolocate appear to use many remains problematic. A few animals 1994). In fact, birds appear to be In the wild, Eurasian Kestrels have reflect strongly in the UV. Iridescent
proof, that ants also make and hear frequencies audible to human ears. emit infrasounds as communication: more sensitive to UV than to light in shown a preference for areas where feathers, brilliant to the human eye,
ultrasonic sounds. He did, however, The South American Oilbird, when some of the great whales—such as the part of the electromagnetic spec- abandoned runways were freshly reflect strongly in the UV, but there
put his finger directly on the essence flying inside its roosting caves, blue and fin whales—both species of trum visible to humans (4,000 to treated with vole urine and feces are also feathers that reflect very
of animal ESP: "the universe is prob- produces harsh clicks very audible living elephants, and, among birds, 7,000 Angstroms [400 to 700 nano- compared to similar areas where little in the human visible spectrum
ably full of music which we cannot to humans. The Southeast Asian the Eurasian Capercaillie, a giant meters]): the peak sensitivity for the runways were untreated. In the (and thus look black to us) but reflect
perceive...If any apparatus could be Edible-nest Swiftlets make a sound European grouse. vision of the majority of birds that laboratory, kestrels spent more time very strongly in the UV and thus
devised by which [these sensations much like running one's thumb up have been tested is between 3,600 hovering and inspecting urine-treat- must appear riotously colored to the
could] be brought within the range and down the teeth of a comb as they and 3,800 Angstroms (360 and 380 ed runways illuminated under UV admiring bird. The Asian whistling-
of our [senses], it is probable that the navigate deep in dark caves. Extrasensorq Olfaction nanometers). Birds can also distin- light than similarly treated runways thrushes are blue, purple, violet,
result would be most interesting." On the other hand, some birds Although humans have a much guish between wavelengths within illuminated by white light (Vitala and brown birds that have a very
(Pye and Langbauer 1997). have been shown to be sensitive to better overall sense of smell than do the UV portion of the spectrum, per- et al. 1995). It seems that foraging different pattern and appearance
infrasound (very low sounds rang- birds, it is clear from experiments ceiving "color" differences where we kestrels can judge the probable pro- when seen in the ultraviolet (see Fig.
ing down from about 20 Hertz to done with certain wild birds that in see no illumination at all. Birds ap- ductivity of a potential hunting area 3-51) (Andersson 1996). Male and
Extrasensorq Hearing 0.1 Hertz or less). Pigeons have some cases avian sensory percep- parently achieve UV vision through by its ultraviolet "color" caused by female BlueTits (Eurasian relatives of
This "most interesting" world was cochlear neurons sensitive to sound tion, even in the area of olfaction, having UV-transparent corneas and rodent urine! chickadees) appear nearly identical
entered by Sir Francis Galton when in frequencies below 20 Hertz and is beyond ours. As discussed in the lenses (ours absorb UV and are thus No less exotic is the fact that some to the human eye, but in UV their
1883 he mounted, on the end of his demonstrate behaviorally that they chapter text, Wilson's Storm-Petrels, opaque to it) and by having special flowers and fruits have colors or pat- crown patch, which is displayed in
walking stick, a directional, tunable,
• cone cells with visual pigments that terns that are visible only to animals
can detect infrasounds as low as 0.05 one of the smallest of the tubenosed courtship, differs between the sexes
and high-pitched whistle that he Hertz! (Schermuly and KI inke 1990). seabirds, can detect and home in on absorb maximally in the violet or ul- that can see in the ultraviolet—and in the purity of its UV/blue color (An-
could blow from a distance through Typically there is little ambient ultra- dimethyl sulfide slicks from great traviolet range. Many organic mol- birds may use these "UV foraging dersson et al. 1998). Blue Tits tend to

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4.68 Howard E. Evans andi. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.69
display in early morning "woodland two-year-old males than in one-year- from the patterns of polarized light birds do not chew their food; they may manipulate it in their bill or
shade" that is rich in UV light. old males (Andersson and Amund- in the sky. Another consequence of tear off pieces, but then they "bolt it whole" without much processing
Until recently, studies of species sen 1997). Sunblock (which absorbs wavelength-dependent scattering is or time to taste it.
recognition and sexual selection very strongly in the UV) applied to that around dawn and dusk a high
Birds do quickly learn to avoid distasteful substances. Wildlife
have assumed that avian color vi- the throats of males nearly ruined proportion of the light available is of
biologists at Cornell have found that a common flavoring used for
sion is like our own. All these now their sex lives! Females in 13 of 16 short wavelengths, making UV vision
grape soda and gum—methyl anthranilate, which naturally occurs
seem to be potentially invalidated, trials associated most with males particularly adaptive for animals ac-
as studies that incorporate the abil- whose UV reflectance had not been tive at these times. Is this how the in orange blossoms and Concord grapes—is very distasteful to birds.
ity of birds to see UV often produce eliminated. Sunblock-treated males early bird gets the worm? The Environmental Protection Agency has approved the use of this
unexpected results. For example, had greater difficulty attracting mates --- compound at golf courses, airports, and landfills to discourage geese
when given a choice, Zebra Finches and thus had a significantly later start Finally, there are senses of birds and gulls.
preferred a partner viewed through to egg laying in their nests compared that are more than just extensions
UV-transparent Plexiglas over a to the nests of control males. UV-re- of the senses with which we are so
partner viewed through UV-opaque duced males had lower success in familiar. They are senses for which
Skin Senses
material (Bennett et al. 1996). Hunt copulating with females other than we personally know no counter- Birds have many different types of tactile nerve endings in the
et al. (1997) found that even artificial their mates, and they lost paternity in part. An important example is the skin, tongue, palate, muscles, joints, feather follicles, and viscera.
adornment with highly UV-reflective their own nests, as well, when their well-documented magnetic sense of The precise function of any one of these sensory endings is debatable.
leg bands gave male Zebra Finches a mates copulated on the sly more fre- birds. A magnetic compass has been Some sensory organs respond to touch and vibration, others to heat or
leg up over their less spiffily attired quently with non-UV-reduced males demonstrated in at least 18 species of chemical sensations. Birds' skin sensations originate in many kinds of
competitors. In other experiments, (Johnsen et al. 1998). Clearly, for a migrating birds held in the laboratory
nerves: in nerve endings wrapped in connective tissue; in dendritic
female starlings ranked males dif- male Bluethroat, losing your UV-re- and exposed to artificial magnetic
(highly branching) nerve endings; in free simple nerve endings; and
ferently when UV light was present flectance is a serious problem! fields (Wiltschko and Wiltschko
than when it was absent. When UV in a host of variations with different physiological responses under
1996). But what are the perception
was available, they preferred males Orientation and Navigation mechanisms used by these birds? laboratory conditions. These nerve endings usually have been given
with the most UV reflectance, but The physical properties of UV Current research is focused on tiny names (such as Grandry corpuscles, Herbst corpuscles, Paccinian
when UV was absent, they ranked light make radiation in this range of particles of magnetite (an iron-con- corpuscles, Ruffini endings, and Merkels complex) based on name
males in a way that was not based wavelengths potentially important taining, magnetic mineral) that is of the discoverer.
on their plumage reflectance in the for orientation and navigation. Sun- found in the heads of many birds, and The bill tip organ of ducks and shorebirds is an aggregation of
human visible spectrum (Bennett et I ightpassing through the atmosphere on the possibi I ity that photoreceptive sensory cells best developed in snipe, sandpipers, ducks, and geese
al. 1997). is scattered by the molecules it strikes pigments in the eye might provide the (Fig. 4-57). The organ appears to be especially sensitive to rates and
Experiments with the Bluethroat, and is simultaneously polarized (see sensor—but just how the magnetite
changes in rates of vibration stimuli, but its function is unknown.
a Eurasian thrush, have clearly dem- Ch. 5, Sidebar 3: Polarized Light). and other senses interact to calibrate
onstrated the importance of UV- UV light is scattered more and po-
The beaks of parrots have a unique collection of tactile-sensitive
or set the magnetic compass is not
reflectant plumage in reproductive larized to a higher degree than light cell clusters associated with the shelling and manipulation of seeds
known. The pineal gland is also un-
success. of the longer wavelengths of the hu- der consideration as a structure ac- and other objects. The brush-turkeys (megapodes) of Australia, New
The male Bluethroat actively man visible spectrum (Bennett and tively responsible for magnetic field Guinea, and the Indo-Malaysian Archipelago incubate their eggs in
displays his bright throat pattern Cuthill 1994). Thus, being able to detection (Azanza and Del Moral unusual ways: in decaying vegetation, in a sun-warmed earth mound,
during courtship—a colorful, blue see in the ultraviolet should make 1994), but little is clearly understood or sometimes in an ash mound heated by volcanic steam! The male,
signal even to our eyes, but the it easier for birds to gain significant about birds' magnetic ESP. ■ who usually takes sole responsibility for incubation, apparently senses
throat reflects most strongly in the information about the position of the the temperature of the egg site with receptors in his tongue or palate.
UV. This UV reflection is greater in sun, and thus compass directions,
Males that incubate in rotting vegetation and volcanic ash then un-
cover or add cover to the mound, as needed, to maintain the optimal
Suggested Reading incubation temperature (see Fig. 6-36).
Withgott, Jay. 2000. Taking a bird's-eye view ... in the UV. BioScience 50(10):854-859.

The Endocrine Stistent

■ In addition to the fast-acting nervous system, vertebrates have a
much slower coordinating system called the endocrine system. These
two systems interact to produce appropriate responses at a subcon-
scious level. The endocrine system consists of widely separated endo-
crine glands, which secrete specific complex molecules directly into
the blood (Fig. 4-58). These endocrine secretions, called hormones,
are carried by the blood to all parts of the body, where they stimulate

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4.70 Howard E. Evans andJ. B. Heiser Chapter 4—What's Inside: Anatomq and Pliqsiologq 4.71

or regulate the activities of other glands or organs. Both the nervous all of which are fully understood. Most experimental studies of avian
and the endocrine systems are concerned with initiating and regulating endocrinology have involved the Japanese Quail or the chicken, both
bodily activities, and the actions of these two systems are very closely of which have relatively short life spans. Studies are needed of wild
integrated. A bird's anatomical development and its specific behaviors, species, from a variety of short-lived passerines to species with longer
like those of a human, are the result of the interplay between the life spans.
nervous and endocrine systems. In humans the cerebral cortex of the Seabirds have life spans of 20 to 50 years and mature at a late age.
brain can sometimes modify the basic drives that result from the inter- Little is known about their reproductive hormones during their long
action of hormones and physiological processes. Such brain control fertile years, which may include 20 or more annual cl utches.The Com-
appears to be less common in other vertebrates, including birds, which mon Tern, for example, may have its first clutch at three to four years
in part accounts for the stereotyped behavior characteristic of age, but normally reaches full breeding performance only after five
Location of the Bill Tip Organ
in the Upper Bill of the of birds. The details of the dynamics and interactions of years when plasma sex hormones reach adult levels. Some terns have
Domestic Goose hormones are among the most complex phenomena in
the biological sciences. Here, we consider only the
most important endocrine glands and some of their
Pituitary Gland
principal functions.
Although the endocrine system of the bird and
mammal are similar, several differences exist, not
Thymus
Gland
t.
Ultimobranchial Glands
Bill Nail
Bone (Horny Plate at Tip of Bill)
Thyroid and
Adrenal Glands Parathyroid
Glands

Connective Gonads CROP

Cutaway Enlargement of the Tissue
Shaded Area Shown Above
Pancreas
HEAR ,7
Mechanoreceptor Cells
Inside Papilla LIVER

Horny Tubule DU
Enclosing
Connective
Tissue Papilla
Cloaca' Bursa Rock Dove
)

Tactile Cones Protrude Through Pores Figure 4-58. Major Endocrine Glands: The endocrine glands secreting digestive juices into the small intestine, but also has
Formed by Open Ends of Horny Tubules Palate hormone-secreting endocrine tissue. The functions of all the
play an essential role in controlling and coordinating body
(Roof of Mouth) processes by secreting hormones. Transported by the blood- above glands and their associated hormones are detailed in the
stream to target areas throughout the body, hormones regulate text and in Fig. 4-59. Three endocrine glands shown here are
Figure 4-57. The Bill Tip Organ of the Domestic Goose: A bill pore is the open end of a horny tubule through which protrudes the activities of other glands and organs. Shown here are some not described in the text. The pineal gland, located in the dorsal
of the most important endocrine glands of the Rock Dove. The midbrain, secretes the hormone melatonin and plays a role in
tip organ is found in both the upper and lower bill of geese, a peg-like structure, the tactile cone, made of keratin. This flex-
pituitary gland is located on the ventral side of the brain, where regulating daily activity cycles, termed circadian rhythms. The
ducks, and shorebirds; it is thought to sense tactile stimuli dur- ible cap of keratin is attached to a long, slender connective
ing feeding. In ducks and geese it is located within the bill nail, tissue papilla, originating deep within the dermal tissue of the it is connected by a stalk to the hypothalamus. At the base of thymus gland, in the upper neck, and the cloaca! bursa (previ-
the neck are the thyroid and parathyroid glands, and nearby ously known as the bursa of Fabricius) are thought to stimulate
the hooked structure at the tip of the bill. Externally it appears bill, which fills the horny tubule. The papilla contains numer-
are the ultimobranchial glands. The adrenal glands are inter- tissues of the immune system, and may be important only in
as double, or sometimes triple, rows of microscopic pores ar- ous mechanoreceptor cells of two distinct types—G randry and
spersed between the lobes of the cranial end of each kidney. The young birds. Reprinted (with slight adaptations) from Manual
ranged around the inner surface of the tip of the bill. The cut- Herbst corpuscles—with their associated nerve fibers, which
away view shows the internal structure of the bill tip organ. Note become activated when the tactile cone receives stimulation. gonads (either testes or ovary) secrete hormones in addition to of Ornithology, by Noble S. Proctor and Patrick J. Lynch, with
Drawing by Christi Sobel, after Gottschaldt and Lausmann producing sperm or eggs. The pancreas, in the uppermost loop permission of the publisher. Copyright 1993, Yale University
that only the upper bill is shown, and it is slightly rotated away
from the viewer. Microscopic examination reveals that each (1974). of the small intestine, carries out nonendocrine functions by Press.

Cornell Laboratorq of Ornitholos Handbook of Bird Biologq

4.72 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatomy and Physiology 4.73

then remained paired for up to seven successive years. After age 12, affect seasonal breeders by stimulating the growth of the gonads (ovary
breeding appears to decline, but some terns continue to lay eggs and and testes). To do this the endocrine system must obtain "messages"
raise young until ages 17 to 21 or even older. What hormonal dynamics from the nervous system and transfer them to other endocrine glands
account for the stability of these breeding cycles over so many years? such as the thyroid, adrenals, and gonads. It accomplishes this infor-
What accounts for the changes? The basic survey of avian endocri- mation transfer via the anterior lobe of the pituitary gland.
nology presented here will begin to answer these questions. As you This anterior lobe has no nerves carrying stimuli to or away from
read this section, refer to Figure 4-59, a schematic of the endocrine it, therefore it cannot interact through the "neural" language of cel-
system's major glands and hormones and their primary functions. lular electrical activity. Within the hypothalamus, however, are spe-
cial neurosecretory neurons. These are similar to normal nerve cells,
Figure 4-59. Major Glands of the En- except that they secrete neurohormones into blood vessels leading
docrine System and their Functions: An Pituitarti Gland directly to the pituitary's anterior lobe—allowing it to respond to a
overview of the most important endo- The pituitary gland consists of an anterior and a posterior lobe, "neurosecretory" language. In a sense, the neurosecretory cells are
crine glands (shown as shaded ovals),
connected by a stalk to the hypothalamus—a ventral region of the translators from neural to hormonal messages. Depending upon the
the hormones they secrete (printed in
red), and their effects on target organs. brain. The endocrine system can respond to factors in the external en- chemical messages that it receives, the anterior pituitary may secrete
See text for details. vironment, such as day length, temperature, and rainfall, which may any of several hormones into the blood.These hormones perform such
functions as stimulating development of the gonads and reproductive
system, altering the color of the bill and plumage, and initiating the
development of incubation patches. The anterior lobe of the pituitary
also plays a role in stimulating or inhibiting certain sexual behaviors,
Growth Hormone , Pituitary 411PP"• Egg Laying
• Devlopment
Mesotocin ...■ such as courtship displays.
of Young Birds
AnteriorPosterior
Lobe I Lobe
Some hormones secreted by the anterior lobe act directly on
Arginine Vasotocin
Prolactin other organs, and some act only on other endocrine glands, which
• Stimulates Kidney Tubules to
Resorb Water—Conserves
Thyroid-Stimulating Water
then secrete additional hormones that act directly on still other organs
• Formation of Brood Patch
• Increased Appetite in Some Hormone and cells. Because it initiates these chains of interaction, the anterior
Migratory Birds
Adrenocorticotrophic Triiodothyronine pituitary has been called "the master gland." Examples of anterior
Hormone (ACTH)
Gonadotrophic • Annual Increase pituitary hormones that act directly are: prolactin, which stimulates
in Gonad Size
Hormone the formation of brood patches in some species and may stimulate the
Epinephrine • Production of
(Adrenaline) Eggs and Sperm
Thyroxin appetite in some migratory birds; and growth hormone, which acts
Adrenal • Growth and on many different tissues and organs and is vital in the rapid transfor-
Glands GONADS Pigmentation of
• Fight or Flight Response
Medulla Cortex Feathers mation of a hatch I ing into a fledgling.
• Molt
Cells Cells We have noted that the gonads, thyroids, and adrenals are largely
Norepinephrine under the control of the anterior pituitary's stimulatory hormones. In
(Noradrenaline)
Testosterone Estrogens
Parathyroids contrast, the posterior lobe of the pituitary does not fabricate hor-
Estrogens Progesterone mones, but rather is a storage place for hormones secreted by neu-
Steroids
Testosterone
(e.g., Corticosterone) rosecretory cells of the hypothalamus. These hormones can then be
Parathormone
released by the posterior lobe when it receives the proper signals. One
estosterone
• Stress principal hormone released by the posterior lobe is arginine vasotocin,
Reactions Estrogens • Calcium
Resorption a water-conserving (antidiuretic) hormone. It stimulates resorption of
Progesterone
from Bones
water by the kidney tubules and thus helps to conserve water and
change body fluid volume. Another important posterior lobe release
Ultimobranchial
Insulin is mesotocin, the avian equivalent of mammalian oxytocin, which
Sex and Sex-stimulating Hormones from the Pituitary, induces labor. In birds, an egg advances into the vagina under the in-
Adrenal Cortex, and Gonads All Interact to Carry Out Calcitonin
Lowers Blood Sugar
Various Functions, such as:
fluence of hormones probably secreted by the most recently ruptured
Concentration
Glucagon • Development of Gonads and Reproductive System ovarian follicle. Mesotocin then acts on the muscles of the shell gland
• Changes in Bill and Plumage Color
• Elaboration and Maintenance of Incubation Patch • Lowers Blood to cause egg expulsion (laying). Mesotocin injections in birds result
Somatostatin a
\111. Increases Blood Sugar • Activation and Inhibition of Sexual Behaviors such as Calcium
in blood vessel "relaxation" to a larger diameter (vasodilation), and a
Concentration Courtship Displays Concentration
• Development and Maintenance of Certain Structures
consequential decrease in blood pressure. The roles of both argi nine
such as Combs and Spurs
vasotocin and mesotocin in blood pressure regulation of birds need
• In Chickens: Stimulates Secretion of
Glucagon, Insulin, and Avian further study.
Pancreatic Polypeptide

Cornell Laboratory of Ornithology Handbook of Bird Biology

4.74 Howard E. Evans and j. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiolo5N 4.75
As in mammals, the avian adrenal medulla cells contain epineph-
Thiiroid Glands
rine (adrenaline), and norepinephrine (noradrenaline). Although the
The thyroid glands consist of two pink or red superficial nodules
natural functions of these hormones are less understood in birds than
atthe base of the neck. They secrete thyroxin and triiodothyronine in re-
in mammals, in some birds they affect blood pressure, carbohydrate
sponse to anterior pituitary secretion of thyroid-stimulating hormone.
metabolism, and perhaps fat metabolism. These effects are related
The thyroid hormones are essential to the annual re-enlargement of the
to "fight or flight" responses—how the body responds to urgent or
gonads and production of eggs and sperm. Besides its important role
dangerous situations. The cortex tissue secretes a multitude of steroid
in the normal functioning of the gonads, thyroxin is necessary for the
hormones vital to survival. Among them are corticosteroids (princi-
normal growth and pigmentation of feathers, and is somehow related
pally corticosterone) associated with "stress" reactions through regu-
to molting. Experiments suggest a possible relationship between thy-
lation of carbohydrate and electrolyte (ion) metabolism. The adrenal
roxin and migration; injections of thyroxin have induced "migratory
cortical tissue also secretes androgens (male sex hormones), such as
restlessness" (see Fig. 5-56) in some passerines.
testosterone, as well as estrogens and progesterone (female sex hor-
mones). Note that the adrenal glands in both sexes secrete both male
Parathgroid and Ultirnobranchial Glands and female sex hormones, and that the effects of these hormones are
One or two small parathyroid glands may be located on each similar to those produced by the gonads themselves. The adrenal sex
thyroid gland as in the Budgerigar, or just caudal to the thyroid glands hormones, however, may not be as important in the biology of birds
as in the chicken. The parathyroid glands secrete parathormone, a as they are in mammals.
protein that causes calcium resorption from the bones.
The amount of calcium in the yolk and shell of a chicken egg is
Gonads
about 0.07 oz (2 grams), butthe total amount of calcium stored in a lay-
The gonads (testes and ovary) produce sperm and eggs, but they
i ng hen is about 0.7 oz (20 grams), enough for about 10 eggs. A modern
also are important as endocrine glands. The testes secrete the male sex
laying hen, however, lays about270 to 300 eggs in a year; thus calcium
hormone, an androgen called testosterone, and in some birds, they also
metabolism in a laying hen must be intense. Not surprisingly, a large
secrete some female estrogen hormones.The ovaries secrete estrogens,
number of hormones play a role in fine-tuning the level of calcium in
such as estradiol, as well as progesterone; they also secrete some male
the yolk, shell, bone, and blood of the hen. The interactions among
hormones. An intimate interrelationship thus exists among the sex or
parathyroid hormones and estrogen, androgen, and vitamin D (which
sex-stimulating hormones from the pituitary, the cortical interrenal
is converted in the kidney and liver to a hormone that regulates calcium
tissue, and the gonads. These secretions influence the activity of the
metabolism) are complex and not well understood. Not surprisingly,
other endocrine glands. In birds, they also have a profound influence
they are of intense interest to the egg industry.
on the development and maintenance of anatomical structures such as
The ultimobranchial glands are two small, light-colored bodies
combs and spurs, and on behavior patterns. In many birds, especially
located near the parathyroid glands, usually on an artery. They secrete
migratory species, the gonads vary tremendously in size and secretory
a protein hormone, calcitonin, which lowers the blood calcium con-
activity on an annual cycle. During the breeding season, for example,
centration, as it does in mammals. In birds, however, calcitonin has no
the testes of small passerines may grow to several hundred times their
known physiological role in bone calcium turnover.
nonbreeding volume and weight! They regress again for most of the
year, a cycle that probably saves energy during flight.
Adrenal Glands
The adrenal glands are small yellow or orange bodies located at
Pancreas
the cranial end of each kidney. In mammals, the glands have an inner
The pancreas, located in the uppermost loop of the small intestine,
medulla and a surrounding cortex, but in birds the cells characteristic
secretes digestive juices into the small intestine, and it also contains
of the medulla (chromaffin cells) are intermixed with the cortical tis-
endocrine tissue that produces hormones regulating carbohydrate
sue, and both are scattered in pockets among the multiple lobes at
metabolism and blood sugar levels. The hormones secreted include:
the cranial end of the kidneys. Because of this distinction from the
insulin, which decreases blood sugar concentrations; gl ucagon, which
mammalian condition, the avian adrenal tissue (and sometimes the
increases blood sugar concentrations; and somatostatin, or growth-
gland) is called "interrenal." The interrenal tissue produces secretions
inhibiting hormone. In chickens, at least, this latter hormone stimulates
that control a variety of physiological processes associated with both
the secretion of glucagon, insulin, and avian pancreatic polypeptide,
circulation and digestion, and it also produces sex hormones likethose
a substance of unknown function. Glucagon is apparently more im-
produced by the gonads.
portant than insulin in regulating carbohydrate metabolism in birds,
whereas in mammals, insulin is the more important hormone. The

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

4.76 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiologq 4.77
significance of these hormones may vary considerably among gra- and vessels that carry blood away from the heart (arteries) and return
nivorous (seed-eating), herbivorous (foliage-eating), and carnivorous it to the heart (veins). The two systems of vessels are connected by an
birds, but little comparative research has been done. enormous, fine network of tiny blood vessels, the capillaries, the site
Without forming separate glands, the walls of the stomach and of dynamic chemical activity.
those of the first part of the small intestine, the duodenum, also se- The lymphatic system, an outgrowth from the veins, gathers tissue
crete hormones. These stimulate, respectively, the secretion of other fluid that has leaked from the capillaries and returns it to the general
stomach cells and the smooth muscle in the wall of the gall bladder body circulation. The lymphatic system also releases antibodies and
(if present). filters out degenerating cells and foreign substances.

The Circulatort1 Stistem The Heart

The heart provides the force that propels blood into the arteries,
■ The circulatory or blood vascular system is a transport system that but venous and lymphatic return of the circulatory fluids is passive,
carries oxygen and nutrients to the cells of the body and removes the dependent in part on general body movement.
waste products of metabolism. It also regulates body temperature by The bird's heart (Fig. 4-60a) has two relatively thin-walled
distributing the heat produced by muscles and the gut, and carries receiving chambers called atria (singular, atrium). The right atrium
antibodies that protect against infection and hormones produced by receives blood from the head and body via the caval veins. The left
the endocrine glands.The circulatory system consists of a pump (heart) atrium receives blood from the lungs via the pulmonary veins. The
two other chambers, the large ventricles, are the thick-walled pump-
Figure 4-60. Internal Structure and a. Longitudinal Section Aorta and its Branches Carry ing chambers.
Function of the Heart: The muscular Oxygenated Blood to Body
heart provides the force that moves PULMONARY CIRCULATION
blood throughout the body. a. Longi-
Pulmonary Arteries
tudinal Section: The heart consists of
two thin-walled receiving chambers, Deoxygenated Deoxygenated Capillary Bed
Caval Vein
the atria, and two thick-walled pumping Blood From ..., .;:=.1•■ Blood to Lungs of Lungs
chambers, the ventricles. Between each Body
Oxygenated Blood
atrium and its associated ventricle are From Lungs
atrioventricular valves, which prevent •
• Pulmonary Vein Pulmonary Arteries Pulmonary Veins
the backflow of blood. Deoxygenated Right Atrium
blood (dashed arrows) from the body Left Atrium
enters the right atrium of the heart, and
from there moves into the right ventricle. Right x Left Atrioventricular
Contraction of the right ventricle pushes Atrioventricular Valve
this blood into the pulmonary trunk, Valve
X
which branches into the right and left
pulmonary arteries, which carry the
deoxygenated blood into the lungs. In Right Ventricle
the lungs the blood picks up oxygen and Caval Veins __
loses its carbon dioxide. The newly ox- Left Ventricle
ygenated blood (solid arrows) re-enters
the heart through the pulmonary veins,
Figure 4-61. Schematic of Pulmonary
passing into the left atrium and from
and Systemic Circulation: The heart is
there into the left ventricle. The highly
functionally divided so that the pulmo-
muscular left ventricle then pumps the
b. Cross-Section View at Line X nary circulation, carrying blood to and
blood into the aorta, whose branches
from the lungs, is separated from the
distribute it throughout the body. b. RightAtrioventricular
Left Ventricle systemic circulation, carrying blood to
Cross-Section through Points X-X in Valve
, Avv.1 and from the rest of the body. This system
a: This view shows the dramatic dif-
ensures that oxygenated blood (colored)
ference in thickness between the mus-
RightVentricle and deoxygenated blood (white) do not
cular wall of the left ventricle, which Highly Muscular Wall
mix. The oxygen 'content of arterial
must provide adequate force to pump of Left Ventricle
blood thus remains high, an essential
blood throughout the body, and that of Less Muscular Wall
feature for the optimal function of an
the right ventricle, which pumps blood of Right Ventricle
animal with a high metabolic rate, such
only to the lungs. Adapted from Brooke
Capillary Bed as a bird. Adapted from Keeton (1980,
and Birkhead (1991, p. 32).
of Body Tissues p. 282).

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

4.78 Howard E. Evans and J. B. Heiser Chapter 4—What's Inside: Anatomtl and PhNsiolo9N 4.79

Partitions divide the heart so that the pulmonary circulation of all mammals the right atrioventricular valve is composed of three flaps,
the lungs is separated from the systemic circulation of the body (Fig. or pocket-I i ke cusps, whereas the left valve has two. In birds, however,
4-61). Functionally, the right atrium and right ventricle are referred to this arrangement is reversed. These equally functional anatomical dif-
as the right heart (filled with deoxygenated blood). The left atrium and ferences illustrate that evolution, too, has discovered that "there is
left ventricle are the left heart (filled with oxygenated blood). more than one way to skin a cat"!
Venous blood flows into the right atrium and is pumped from there Semilunar valves, with three cusps each, are located at the be-
to the right ventricle. Contraction of the right ventricle forces the blood ginning of the pulmonary trunk and the aorta, preventing backflow of
into the pulmonary trunk, a large artery that branches to the right and blood into the ventricles as the ventricles relax after each beat.
left lungs as the right and left pulmonary arteries. In the lungs, the blood
loses its carbon dioxide and picks up oxygen. Right and left pulmonary Blood Supply to the Heart Tissue
veins conduct this oxygen-rich blood to the left atrium, from which it Even though all blood in the body passes through the heart, only a
is pumped to the left ventricle. Contraction of the left ventricle pumps tiny amount nourishes the heart muscle itself from inside the pumping
the blood into the aorta, whose branches distribute it to all other parts chambers. Instead, heart tissue is supplied by the coronary arteries,
Figure 4-62. Heart ValvesandtheirRole
of the body. Because the left ventricle must pump blood throughoutthe usually two in number, which arise from the first part of the aorta (Fig.
in Blood Circulation: Atrioventricular
valves are located between each atrium body, its muscular wall is much thicker than that of the right ventricle, 4-63). From there they pass over the surface of the heart, where they
and its corresponding ventricle, keeping
which pumps blood only to the lungs (Fig. 4-60b). send branches into the muscle to nourish its life-long toil. Blockage
blood flowing in one direction by pre- of a coronary artery starves the heart muscle of oxygen and can lead
venting backflow. Thin arrows indicate
Heart Valves to heart failure. Coronary veins carry blood and wastes from the heart
the movement of blood. a. Blood Flows
into Left and Right Atria: This actually Atrioventricular valves occur, as the name suggests, between muscle back to the right atrium.
occurs as the ventricles contract, as in each atrium and its corresponding ventricle. They open when the
c, but is shown here as a separate step ventricle relaxes, permitting blood to flow into the ventricle, and Conducting System of the Heart
for simplicity. b. Ventricles Relax: With
close when the ventricle contracts, keeping the blood flowing in one Cardiac muscle has an innate rhythm that causes it to beat before
the relaxation of the ventricles, both any nerves have grown to it. Two nodes and bundles of conducting
atrioventricular valves open (short ar- direction by preventing backf low into the atrium (Fig. 4-62). In nearly
nerve fibers govern this innate rhythm. One node, in the wall of the
rows), allowing blood to flow from each
atrium into its ventricle. c. Ventricles right atrium, initiates the heartbeat and therefore is referred to as the
Aorta
Contract: When the ventricles contract, "pacemaker." It stimulates contraction of the right atrium which, in
both atrioventricular valves close (short turn, stimulates a second node in the bottom of the septum between
arrows), preventing back flow of blood
the atria. From the second node, a bundle of fibers leads into the sep-
from the ventricles into the atria. Instead,
the blood from the right ventricle flows
Pulmonary tum between the ventricles and causes contraction of the ventricular
Trunk Left Atrium
into the pulmonary trunk and then to the muscle.
lungs, while blood from the left ventricle Aorta
Right Atrium
flows into the aorta, which carries the Atrioventricular Valves
Figure 4-63. Exterior of Chicken Heart
blood to the rest of the body. Drawings Right Ventricle Right Coronary Artery Left CoronaryArtery
Showing the Coronary Arteries: The
by Charles L. Ripper. Left Ventricle
heart receives little nourishment from
the blood being continuously pumped
through its chambers. Instead, it has its
own blood supply, transported through
the right and left coronary arteries,
which branch from the aorta soon af-
ter it exits the heart. The fine branches
Pulmonary Trunk
of the coronary arteries carry oxygen
and nutrients across the surface of the
heart and deep into the cardiac muscle.
Coronary veins (not shown) remove the
waste products of metabolism from the
heart muscle, entering the heart's right
atrium. Adapted from King and McLel-
land (1981, Vol. 2, p.244).
a. Blood Flows into Left and RightAtria b. Ventricles Relax c. Ventricles Contract
• Atrioventricular Valves Open, • Atrioventricular Valves Close,
Ventral View Superficial Branches of the CoronaryArtery
Allowing Blood to Flow from Atria Preventing Back flow of Blood
into Ventricles into Atria
_ = Superficial Branches on the Dorsal Side of the Heart
• Blood Flows into Pulmonary Trunk
and Aorta
s Deeply Embedded Branches of the Coronary Artery

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4.80 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiologq 4.81
The pacemaker role of the node in the wall of the right atrium has
been demonstrated by completely separating the right atrium from the
Blood Vessels
Blood vessels (Fig. 4-65) are named in relation to their course
rest of the heart. In this condition, the right atrium continues to beat
away from or toward the heart, regardless of whether the blood they
at the same rate as before; the remainder of the heart will continue to
carry is oxygenated. Arteries carry blood away from the heart, and
beat but at a slower rate. Even isolated pieces of heart will beat inde-
veins carry blood to the heart. Thus the pulmonary artery carries deox-
pendently for some time.
ygenated blood to the lung to be oxygenated, whereas the pulmonary
Although the heart requires no nerve input to begin beating, later
vein carries oxygenated blood to the heart for distribution to the body.
in development the autonomic nerves begin to regulate the rate of the
In the rest of the body, the arteries carry oxygen-rich blood and the
beat. Stimuli received from parasympathetic fibers of the vagus nerve
veins, oxygen-poor blood. Arteries and arterioles (small branches of
inhibit or decrease the heart rate, whereas stimuli received from sym-
the arteries) have muscle cells in their walls and are capable of con-
pathetic fibers accelerate the rate in stress or emergency situations.
stricting, causing a rise in blood pressure.
Location of the Heart
Capillaries
The bird's heart lies on the midline of the thoracic (chest) cav- Figure 4-65. Blood Vessels: a. Arrange-
The smallest vessels, the capillaries (Fig. 4-65b), are extremely ment of Blood Vessels: Blood vessels
ity, below the lungs (Fig. 4-64). In mammals, the thoracic cavity is
tiny; some are so small in diameter that only a single red blood cell are classified as arteries or veins based
separated from the abdominal cavity by a muscular diaphragm that
can pass through at one time. Capillaries are also thin-walled and on whether the blood they transport is
functions to fill the lungs during inspiration. Birds, however, lack a traveling to or from the heart, irrespec-
lack a muscular coat, thus they remain rather constant in diameter.
diaphragm, inhaling in an entirely different way, and have only a thin, tive of the oxygen content of the blood.
Capillaries connect the arterial and venous systems as a network of Arteries transport blood away from the
membranous partition that divides the body cavity into a cranial (tho-
anastomosi ng vessels deeply penetrating almost every body tissue ex- heart, and veins transport blood toward
racic) and caudal (abdominal) compartment. The lungs lie around the
cept in the central nervous system and the outer layer of the skin (the the heart. Arteries divide into branches
heart in the cranial compartment just under the vertebral column. The termed arterioles. Upon reaching target
heart itself is surrounded by a thin membrane, the pericardium, the a. Arrangement of Blood Vessels organs or tissues, arterioles divide into
inner lining of which secretes pericardial fluid that reduces the friction still smaller branches and eventually
of the beating heart against the adjacent tissues. into the smallest blood vessels, the cap-
illaries. Capillaries form a network, or
capillary bed, throughout each body tis-
sue except in the central nervous system
and the outer layer of the skin. Capillary
beds are the interface through which
Vein —
Budgerigar oxygen and nutrients pass into, and
wastes pass out of, the tissue cells (see
Fig. 4-69). Blood from the capillaries
drains into tiny venules, which carry it
Crop through a series of increasingly larger
venules and veins, and eventually enters
Figure 4-64. Position of the Heart: In the heart. b. Structure of Blood Vessels:
this ventral view, the sternum and the Arteries are thick-walled, consisting of
abdominal wall have been removed, Cut Surface of a fibrous outer layer of connective tis-
and the cut surfaces of the pectoralis Pectoralis It I Venule Arteriole sue, a thick middle layer of elastic tissue
muscles and the ribs can be seen. The Muscle and smooth muscle, and a thin lining
Heart
heart is located on the midline of the
thoracic (chest) compartment of the
body cavity. In mammals, a muscular
Lung
Cut Surface I I /9A II Liver
termed endothelium. The elasticity
of arteries allows them to expand as
each heartbeat fills them with blood.
diaphragm separates the thoracic
compartment from the abdominal com-
of Ribs
I /1II Gizzard Capillary
Veins may be larger in diameter than
their corresponding arteries, but they
partment, but the diaphragm is absent in Small
Intestine
11 Body
b. Structure of Blood Vessels
are thinner-walled and flabbier, with
birds, replaced by a thin membranous Cavity a less muscular middle layer than that
partition (not visible in this diagram). of arteries. The venous side of the circu-
Muscle
The heart itself is surrounded by the Endothelium Muscle latory system is low-pressure, because
Connective Endothelium Endothelium
pericardium, a membranous covering Connective less force from the pumping action of the
Tissue\,
too thin to be visible here. The lungs lie Tissue heart is available to keep blood flowing
around the heart in the thoracic cavity. in one direction, so veins have valves
Caudal to the heart, in the abdominal that prevent backflow. Capillaries, the
cavity, are the liver, the intestinal tract, smallest blood vessels, are microscopic
and the remaining abdominal organs. Cutaway View Cutaway View Cutaway View in diameter, with walls consisting of a
Drawing from Evans (1996). of Artery of Capillary of Vein single layer of endothelium.

Cornell Laboratorq of Ornithologq Handbook of Bird Bio1o,9ti

4.82 Howard E. Evans andJ. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiolos 4.83
epidermis). Blood from the arteries to the head, body, and viscera is The aorta, the largest artery in the body, leaves the left ventricle
depleted of oxygen while passing through the capillaries. It is in the and, as the right aortic arch, curves to the right as it passes over the
capillary beds that the metabolically active cells of the surrounding heart and toward the backbone. As it approaches the vertebral column,
tissues consume incoming oxygen from the blood and release wastes the aorta curves again and passes toward the tai I as the descending aor-
such as carbon dioxide and ammonia into the blood. ta. All vertebrate animals have a descending aorta. Birds are unique,
however, in having only a right aortic arch. Reptiles have both a right
Arterial System and left aortic arch; mammals have only a left aortic arch—again a
Arteries (Fig. 4-66) conduct blood away from the heart and are reflection of randomness in evolution. Although no fossil evidence
thicker-walled than veins. The larger arteries have elastic fibers within exists, it is believed that having both right and left aortic arches is the
their walls, allowing the arteries to expand when the heart pumps ancestral condition for all terrestrial vertebrates. The loss of an arch of
blood into them, and to shorten or narrow between heartbeats (Fig.
4-65b). The large arteries branch into distributing arteries whose walls
lack elastic tissue.

Right Cranial Vena Cava

Right Innominate Artery
Leftiugular Vein (From Head and Neck)
Right Subclavian Artery (To Wing)
Left Carotid Artery (To Head and Neck) Right Brachial Vein Left Subclavian Vein (From Wing)
Right Brachial Artery
Left Subclavian Artery (To Wing)

Left Cranial Vena Cava

1) Left Pectoral Vein
j\ (From Pectoral Region)
I
*`\ Branches of Pulmonary Veins
Branches of the Pulmonary Arteries
(In Lungs)

Id '0
- To Liver, Pancreas,
Spleen, and Stomach
is! lit Gastric Vein
(From Stomach)
Aortic Arch Hepatic Veins (From Liver)-
To Small Intestine
Hepatic Portal Vein
Descending Aorta (From Digestive Tract to Liver) 4 0/i /(//

Right Renal Artery (To Kidney) WI

Caudal Vena Cava

Right Femoral Artery (To Leg) Right Femoral Vein (From Leg)
I
Inferior Mesenteric Artery
Renal Portal Vein
(To Intestine and Cloaca)
(From Caudal Mesenteric Vein to Kidney)

Internal Iliac Artery

(To Tail Region and Brood Patch)

Caudal Artery (To Tail)

Right Internal Iliac Vein
(from Tail Region) , 1 Caudal Mesenteric Vein
I (From Intestine to Renal Portal
Veins)

Caudal Vein
(From Tail)

Figure 4-66. Arterial System of the Rock Dove: The body's here) have two, and some have no carotids at all, blood being Figure 4-67. Venous System of the Rock Dove: Venous blood before exiting through the hepatic veins and then flowing into
largest artery, the aorta, leaves the left ventricle of the heart and carried to the neck by other arteries. Arteries branching from the from the wings, head, neck, and pectoral region drains into the the caudal vena cava and to the heart. In the renal portal system,
curves sharply to the right as the aortic arch, continuing toward descending aorta supply blood to the legs, kidneys, intestinal subclavian, jugular, and pectoral veins (only the left of which blood from the lower portion of the small intestine drains into
the tail as the descending aorta. From the aortic arch arise the tract, tail, and other caudal regions of the body. Where these are labeled here). These three vessels converge on each side the caudal mesenteric vein, and is transported to the paired
right and left innominate arteries, which almost immediately arteries are paired, only one side is labeled in this diagram. See to form the left and right cranial vena cavae (or caval veins), renal portal veins that form a venous ring (not labeled) con-
give rise to the paired subclavian arteries to the wing and the text for further details. Reprinted from Manual of Ornithology, entering the right atrium of the heart. Blood from the legs, tail, necting the various lobes of the two kidneys. The blood leaves
paired carotid arteries, which supply the neck and head. Ca- by Noble S. Proctor and Patrick]. Lynch, with permission of the kidneys, and caudal regions of the body drains into the caudal the kidneys through renal efferent veins (not labeled) and is
rotid arteries vary greatly from species to species. Some have publisher. Copyright 1993, Yale University Press. vena cava, which is mostly obscured by the heart in this di- carried to the heart by the caudal vena cava. Portal systems are
a single large carotid on one side or the other, some (as shown agram. Venous blood from the digestive tract passes through described in more detail in Figure 4-68. Reprinted from Manual
one of two portal systems within the venous circulation. The of Ornithology, by Noble S. Proctor and Patrick J. Lynch, with
hepatic portal vein transports blood from the upper part of permission of the publisher. Copyright 1993, Yale University
the small intestine to the liver, where it undergoes processing Press.

Cornell Laboratorq of Omithologq Handbook of Bird Biologq

4.84 Howard E. Evans and J. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.85
one side and the strengthening and enlargement of a single conduit Figure 4-68. Portal Systems: As this
occurred in the evolution of increasingly active and environmentally schematic of the hepatic and renal portal
independent forms. The ancestors of birds evolved one way, and mam- systems shows, portal veins connect two
capillary beds with one another, rather
mals, another, without functional significance.
than connecting one capillary bed with
A short distance beyond its origin in the left ventricle, the aortic the heart as do most veins. Portal systems
arch gives rise to large right and left innominate arteries. These soon allow a second organ to process blood
Heart
branch into the subclavian artery to the wing and the carotid artery to before returning the blood to the general
the neck and head. Presumably because the length of the avian neck circulation via the heart. In the hepatic
portal system, nutrient-rich blood from
varies so greatly in proportion to the size of the body (for instance, in the
the capillary network supplying the mi-
American Woodcock versus the Great Blue Heron), the carotid arteries Hepatic Vein
croscopic folds of the lining of the small
of birds exhibit many different patterns. Instead of two equal carotids, intestine (see Fig. 4-103) is carried to
tTDKI1() the capillary network of the liver by
one on each side of the neck, some birds have a large carotid artery on oelOtO, the hepatic portal vein. At the liver, the
one side and a small one on the other. Some have a single carotid artery; Caudal Vena Cava LIVER F Hepatic
digestive products originally absorbed
and some lack carotid arteries altogether, the blood being carried to the
AU44 from the small intestine undergo further
neck by other arteries, usually within canals of the vertebrae. chemical processing. Blood from the
Branches of the descending aorta carry blood to the rest of the liver's capillary bed leaves by way of the
hepatic vein, returning to the heart via
body. A series of paired arteries passes ventrally around the body wall
the caudal vena cava. In the renal portal
between the ribs to supply the breast and abdominal walls.Three large, I NTESTINE
system, found in birds and reptiles but
single arteries supply: (1) the liver, pancreas, spleen, and stomach, (2)
the different parts of the small intestine, and (3) parts of the large and
Vi/ c
Z, ovA9.. AI
"IP not in mammals, blood from the cap-
illary bed surrounding the lower small
Caudal
small intestine and the cloaca. As it continues toward the tail, the aorta intestine is collected into the caudal
Mesenteric
Renal Efferent / aPcb Vein mesenteric vein, which joins the renal
gives off other paired branches to the kidneys, legs, and organs of the
Vein 1 KIDNEY( portal vein, through which the blood is
pelvic region. Eventually, the aorta becomes the lone artery supplying 09We aft conveyed into the capillary bed of each
the tail. l Cel kidney. From here the blood is recollect-
As the arteries branch and re-branch they become smaller and ed into renal efferent veins and returned
Renal Portal Vein
to the heart via the caudal vena cava.
smaller, becoming arterioles, and finally capillaries. On the return
The function of the renal portal system in
side the capillaries drain into the tiniest venules and then these enter birds is unclear. Note that this schematic
veins. Venous blood from the digestive tract flows through vessels that shows the aorta descending on the bird's
terminate in the hepatic portal vein to the liver (Fig. 4-68). Portal veins left, but in life it actually descends on the
Venous System connect two capillary beds rather than connecting a capillary bed and right, as shown in Fig. 4-66.
Veins (Fig. 4-67) return the blood to the heart. Veins are larger the heart, as most veins do. The portal veins permit a second organ
and thinner-walled than arteries, their size depending on the amount (in this case, the liver) to process blood chemistry before returning
of blood they carry. Tiny venules receive the blood from even smaller the blood to the general circulation via the heart and lungs. Thus, the
capillaries and conduct it into a series of increasingly larger veins until simple products of digestion that entered the blood through the cap-
it reaches the right atrium of the heart (see Fig. 4 65). Correctly then,
- illaries of the small intestine are borne directly to the liver, where the
anatomists speak of the tributaries of the veins but the branches of blood passes through the second capillary network. The blood leaves
the arteries. With a few exceptions, veins run along with arteries and the capillary network of the liver in two large hepatic veins, which
have the same names as the corresponding arteries. One exception is empty into the caudal vena cava just before it enters the right atrium
the jugular vein, which returns blood from the head and neck to the of the heart.
heart. The venous system of the kidneys of birds, like reptiles but unlike
Veins possess valves that prevent blood from flowing backward mammals, has a functional renal portal system (see Fig. 4 68). This -

in this low-pressure side of the circulatory system. Contraction of the system collects venous blood from the lower portion of the digestive
general body muscles is also important in keeping the venous blood tract via a caudal mesenteric vein, and conveys it to the venous ring
flowing. within the kidney. Here some of the blood is passed through a capillary
Venous blood from the wings, head, and neck drains into subcla- bed in the kidney before being recollected by renal efferent veins and
vian, jugular, and pectoral trunk veins. These veins converge on each conveyed to the heart via the caudal vena cava. In the kidney, venous
side to form the right and left cranial vena cavae, which connect to blood mixes with arterial blood. The function of this peculiar circu-
the right atrium of the heart. Venous blood from the legs, tail, kidneys, latory pattern of birds is unknown. Whatever the function, though,
and caudal part of the body wall drains into a single, short caudal vena valves present in the veins enable a bird to bypass flow through its renal
cava, which also empties into the right atrium. portal system altogether.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

4.86 Howard E. Evans and J. B. Heiser Chapter 4—What's Inside: Anatomy and Physiology 4.87

a. Capillary Bed
Blood Body (Tissue) Cell Tissue Space

Blood transports oxygen, nutrients, and hormones to body cells,

and carries carbon dioxide, water, and other wastes (especially ni-
trogenous [nitrogen-containing] wastes), as well as secretions, away
from cells. All body cells use oxygen in the "burning" or oxidation
(breakdown) of digested food, a chemical reaction that releases en-
ergy and two waste products, water and carbon dioxide. In the lungs,
Lymph Capillary
the blood releases the carbon dioxide and absorbs oxygen. The bird's
kidney eliminates excess water and nitrogenous wastes.
Blood Capillary
Blood is composed of a watery fluid, the plasma, containing
certain proteins found only in the plasma, as well as inorganic salts
and sugars. Blood cells and blood platelets float in the plasma. Blood
has nutritive, excretory, regulative, protective, and respiratory func-
b. Metabolic Exchange
tions. The plasma carries: the products of digestion—amino acids, Blood Capillary
glucose, glycerol, and fatty acids; the nitrogenous waste products of
metabolism—ammonium, urea, uric acid, and creatinine; hormones; From
To Venule
antibodies to combat infection; and some carbon dioxide. Arteriole

Some of the fluid portion of the blood, along with nutrients, is

forced by the blood pressure through the walls of the capillaries (Fig.
4-69). It enters the minute spaces between the body cells, where it is
called tissue fluid. Most of the body cells receive oxygen and nutrients
from the tissue fluid and dump the waste products of metabolism into
it.Tissue fluid and its dissolved waste materials diffuse back, either into
the venous end of the capillary network, or into lymphatic capillaries
(see Lymphatic System, later in this chapter), which eventually enter
the venous system. Lymph Capillary
Body (Tissue) Cell
The plasma proteins, including albumins, globulins, and fi-
brinogen, are too large to diffuse through the membranes in the capil-
lary walls and thus remain in the blood vessels.The presence of plasma
Direction of Blood Flow Nutrients and Oxygen Diffuse from Tissue
proteins in the blood makes it more dense than the tissue fluid outside Fluid into Body Cells
the circulatory system. This density difference induces water to flow
01.14 Plasma Flows from Blood Capillary into Tis- Metabolic Wastes and Carbon Dioxide
from the tissue fluids into the capillaries by a process termed osmosis, sue Spaces, Becoming Tissue Fluid Diffuse from Body Cells into Tissue Fluid
the tendency of water from a less concentrated or "thinner" liquid to
flow through a semipermeable membrane toward a more concen- Plasma Protein c:\. Tissue Fluid Flows into Blood Capillary,
Becoming Plasma, and into Lymph Capillary,
trated or "thicker" liquid. The "reconstituted" blood then flows into Becoming Lymph
the venous system.
Two general types of cellular elements (cal led blood cells or cor-
Figure 4-69. Capillaries and Metabolic Exchange: The circu- nutrients and oxygen, is forced by blood pressure through the
puscles) are present in the blood—the red blood cells and the white latory system transports blood to nourish and cleanse the tis- cell membranes of the walls of the capillary, which are only one
blood cells (Fig. 4-70). The red blood cells of birds have a nucleus, sues of the body. The actual exchange of materials between the cell thick. Blood cells and plasma proteins are too large to pass
unlike those of mammals. Hemoglobin, an iron-containing respiratory blood and body cells (also cal led tissue cells) occurs at the blood through the cell membranes, so they remain in the blood cap-
capillary networks supplying every region of the body. Here, illary. The plasma enters the minute, fluid-filled spaces (much
pigment in the red blood cells, carries large amounts of oxygen and
nutrients and oxygen from the blood enter the body cells, and exaggerated in size here) between the body cells, and is now
gives the blood its red color. When a vertebrate is in a situation with a wastes and carbon dioxide from the body cells enter the blood. called tissue fluid. Oxygen and nutrients diffuseout of the tissue
high concentration of carbon monoxide in the air, carbon monoxide a. Capillary Bed: This viewshows a network of fine blood capil- fluid into the body cells. Carbon dioxide and metabolic waste
poisoning can occur because hemoglobin has a special affinity for laries in close association with body cells. Note the presence products diffuse out of the body cells and into the tissue fluid.
carbon monoxide. Carbon monoxide binds to hemoglobin, forming of a similar network of lymph capillaries, intertwined with the Tissue fluid then diffuses back into the circulatory system, either
blood capillaries. b. Metabolic Exchange: An enlargement of a into the venous end of the blood capillary or into a capillary
such a stable compound that the hemoglobin can no longer carry ox-
single blood capillary, with surrounding body cells and a lymph of the lymphatic system, which leads to progressively larger
ygen to supply the body. Because the brain is especially sensitive to a capillary, all bathed in tissue fluid, illustrates the process of met- lymph vessels and eventually enters the venous system (see
lack of oxygen, unconsciousness precedes death in carbon monoxide abolic exchange. At the arterial end of the blood capillary bed, Fig. 4-71). Once it enters a lymph capillary, the tissue fluid is
asphyxiation. By taking a canary into the mine with them, coal miners blood plasma, the fluid portion of the blood, with its dissolved termed "lymph." Drawings by Christi Sobel.

Cornell Laboratory of Ornithology Handbook of Bird Biology

4.88 Howard E. Evans andi. B. Heiser Chapter 4—What's Inside: Anatomy and Physiology 4.89

Figure 4-70. Blood Cells of Bird and Bird Nucleus Lymphatic channels in the intestinal wall carry most products
Mammal: Blood cells are of two general of fat digestion to the venous system by way of the intestinal lymph
types whose functions differ. Red blood
trunk and a thoracic duct (Fig. 4-71). The products of the digestion of
cells (erythrocytes) are flattened, ellip-
tical cells that play an essential part in proteins and carbohydrates, however, are carried by the hepatic portal
cellular respiration. They contain he- vein directly to the liver. Although the process is found in (at least) all
moglobin, an iron-containing pigment, White birds and mammals, exactly why digested fats are initially bypassed
which carries oxygen and gives blood its Blood Cell
around the liver, but other digested foods are not, is unclear.
characteristic red color. The red blood
cells of birds have nuclei, unlike those Thrombocyte
Pressure from body movement and contracting muscles moves
Mammal the lymph through the lymph vessels. Like veins, lymph vessels contain
of mammals, and therefore tend to be
larger than their mammalian counter- one-way valves that give a heart-bound direction to the otherwise pas-
parts. White blood cells (leukocytes, sive lymph flow. Birds, like reptiles, have pulsating lymph hearts in the
sometimes spelled leucocytes), which Figure 4-71. Part of the Chicken Lym-
White pelvic region of the embryo that pump the lymph fluid. In the majority phatic System: This diagram is a sche-
are similar in birds and mammals, are
Blood Cell Platelets of bird species, most of these lymph hearts disappear after hatching, but matic of one small part of the lymphatic
nucleated cells of several types whose
shape, size, and internal structure differ. some persist in Ostriches, ducks, and some passerines. In ducks and system, with lymph vessels shown in
White blood cells function to fight infec- color. The lymphatic system's primary
took advantage of this process, which occurs more rapidly in a small geese, erection of the male copulatory organ is caused by lymphatic
tions. In mammals, small cell fragments function is to return to the blood the tis-
bird than in human-sized animals. pressure, not blood pressure, as is typical in mammals. sue fluid that has leaked from blood cap-
known as platelets function in blood
clotting. Birds lack platelets; instead There are several types of white blood cells. Al I contain a nucleus, Lymph from Thoracic Duct
illaries into the spaces between the body
their blood clotting is carried out, at which varies in size and shape in the different blood cells; none contain Enters Venous System cells. This fluid enters lymph capillaries,
least in part, by thrombocytes, nucle- Through Cranial Vena Cava becoming lymph. Lymph capillaries lead
hemoglobi n. Wh ite blood cells can make their way through the walls of
ated cells that resemble red blood cells to progressively larger lymphatic ves-
the capillaries and move about in the space between the cells. Certain sels that lie along the surface of organs
but have a more dense and complex
internal structure. types are important in combating infections because of their ability to and blood vessels, eventually entering
engulf bacteria or other foreign substances. Pus, the yellowish fluid
seen in infections, is a mixture of bacteria, dead white blood cells,
Right Thoracic \
Lymph Duct
\ Liver
the venous system. This diagram shows
part of the lymphatic system that has an
additional function, transporting the
and fluid. Thrombocytes (see Fig. 4-70), highly specialized blood products of fat digestion from the small
cells, are important in the life-saving process of blood clotting in birds. Duodenum intestine to the cranial vena cava, by-
Aorta
Thrombocytes are nucleated, unlike their mammalian counterparts, passing the liver. Lymph capillaries pick
the blood platelets. up the products of fat digestion at the
small intestine, sending them through
Despite the similarity of its cellular components, bird blood is
larger lymphatic vessels that run along
distinctly different from that of mammals in the proportions of its var- Intestinal the surface of blood vessels in the intes-
Lymph Small Intestine
ious chemical constituents. For example, avian blood plasma has a tinal wall. Eventually, they join the in-
Trunk
higher sugar and fat content than that of most mammals. Not surpris- testinal lymph trunk, which in turn joins
one of the two paired thoracic lymph
ingly, because it is the main nitrogenous waste product of birds (see
ducts (only the right one is shown here)
Urogenital System, later in this chapter), uric acid also is present at that travel along the surface of the aorta
higher concentrations. and eventually enter the venous system
through the cranial vena cava just be-
fore it enters the heart. The products of
Lymphatic Stistem. Gizzard Lymph protein and carbohydrate digestion are
Vessels carried from the small intestine directly
Recall that the primary function of the lymphatic system is to re-
to the liver, via the blood in the hepatic
turn to the blood the cell-free tissue fluid that has leaked from the blood Cloaca Cecum
portal vein. Why the different digested
capillaries, but that it also releases antibodies, and filters out foreign substances are treated differently is not
substances and old or damaged cells. Some of the tissue fluid returns to known. Adapted from King and McLel-
the circulatory system by way of the blood capillaries, but some enters The Respiratorti St1stem land (1981, Vol. Z p. 346)

lymphatic capillaries, becoming lymph (see Fig. 4-69). The lymphatic ■ We have seen that the blood transports oxygen to the cells of the
capillaries lead to progressively larger lymphatic vessels, which eventu- body and carries away carbon dioxide. Recall, also, that the cells use
ally enter the venous system at one or more sites near the heart. Within oxygen in the oxidation of digested food, which releases energy, water,
the tissues, and on the surface of organs, are also lymphatic capillaries and carbon dioxide. The respiratory system provides for the transfer of
that drain into larger lymph vessels or lymph nodes and eventually enter oxygen to the blood and the expulsion of carbon dioxide and water
the great veins leading to the heart. Among birds, only ducks are similar from the blood. This gas exchange occurs in the lungs.
to mammals in having a significant number of lymph nodes thatfunction The respiratory system consists of external nostrils; nasal cavities
to filter lymph on its way back to the venous system. and their associated conchae; openings of the nasal cavities into the

Cornell Laboratory of Ornithology Handbook of Bird Biology

4.90 Howard E. Evans and J. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiologq 4.91
mouth or throat; air sinuses beneath the orbit; and the pharynx, lar- a. Structure of the Nasal and Oral Cavities of the Budgerigar Figure 4-73. Nasal and Oral Cavities
ynx, trachea, syrinx, bronchi, lungs, air sacs, and pneumatic bones. of the Budgerigar: a. The structure of
the nasal and oral cavities, showing
Recall that birds lack the muscular diaphragm of mammals, relying
Nasal Cavity the position of the pharynx (throat). b.
instead on expansion of the rib cage to draw in air during inspiration. The respiratory and digestive pathways
Nevertheless, most components of the avian respiratory system also cross in the pharynx. Air in the respi-
are found in mammals, but avian "plumbing" and airflow patterns are Choana ratory pathway (solid arrows) enters
dramatically different, and are unique among living organisms. The through the roof of the mouth at the
Esophagus
choana and exits through the larynx en
special characteristics of the avian respiratory system are no doubt of
route to the lungs. Food in the digestive
great importance in birds' perfection of flight physiology. A pathway (broken arrows) enters through
the mouth, crosses the respiratory path-
Glottis way in the pharynx, and exits through
Nostrils and Nasal Cavities Pharynx Larynx the esophagus en route to the digestive
In most birds the nostrils open into the nasal cavities at the base tract. Adapted from Evans (1996).
b. Pathways Through the Nasal and Oral Cavities of the Budgerigar
of the bill, but several specializations occur. In albatrosses and their
relatives, which are known to have a good sense of smell, the nostrils
are at the end of hard, horny tubes. These tubes, which appear to func-
tion somehow in olfaction, may provide additional benefits during salt
excretion (see Figs. 3-34a and b). In nighthawks and their relatives, Lateral View of the Larynx of the
which have no known olfactory talents, the nostrils are located at the American Crow
end of soft, flexible tubes. Nostrils are closed over in adult gannets, ANTERIOR
frigatebirds, cormorants, and an h ingas; and are apparently variable in Location of
the Glottis
the Red-footed Booby, with some adults having small, slit-like open- (Not Visible
ings and some having none. in this View)
A nasal septum usually separates the right nasal cavity from the Respiratory Pathway
Arytenoid
left (Fig. 4-72). If the septum has an opening or is absent, the condi- ----). Digestive Pathway Cartilages
tion is called perforate. If the septum has no opening, it is imperforate.
Imperforate septa appear to offer the best arrangement to allow for traps dust, and blood vessels in the membrane warm the inhaled air. Laryngeal
The two nasal cavities lead back, opening through the palate (roof of (Cricoid)
directional location of olfactory sources, since odors entering one Cartilage
Figure 4-72. Structure of the Nasal nostril cannot mix with those entering the other. Perforate septa, how- the mouth) by a single slit—the choana—which is protected between
Cavity: This sagittal section of the up- folds of palatal tissue.
ever, may allow greater sensitivity in detecting an odor. Extending from
per beak gives an internal view of the
left nasal cavity, showing two scroll-like the lateral wall of each nasal cavity are very thin, scroll-like conchae,
conchae—the median concha and the which are covered with a mucus-secreting membrane in which the Tracheal
Pharynx Rings
anterior concha—extending from its endings of neurons of the olfactory nerves are embedded. The mucus
outer wall. The conchae are covered The pharynx (throat) begins at the back of the tongue and serves as
with a mucus-secreting membrane that a crossroads for the digestive and respiratory systems (Fig. 4-73). The
traps dust, and are embedded with blood Cross-Section at Line X, Caudal View pathways for food and air cross each other in the pharynx, because the POSTERIOR
vessels that warm the inhaled air, as well
nasal cavities enter the roofof the mouth, but the larynx—the next step
as olfactory nerve endings, which sense Figure 4-74. The Larynx: The larynx is
odors. A septum separating the left and
Nasal Cavity in the passage of air towards the lungs—lies ventral to the esophagus.
Sagittal Section located beneath the floor of the pharynx,
right nasal cavities is visible only in the Septum
The auditory tube from the middle ear cavities enters the pharynx on and is surrounded by and attached to the
cross-sectional view (taken through the Nasal Median Concha the midline of the palate, and allows air pressure to be balanced on hyoid apparatus (see Fig. 4-11). The la-
nasal cavity at line X.) The septum shown Cavity ryngeal skeleton consists of several car-
both sides of the tympanic membrane.
here completely separates the two nasal tilages, the most prominent of which are
cavities, and is thus termed imperforate Median Concha the paired arytenoid cartilages and the
(see text). The two nasal cavities open
into the mouth through the palate via a
Choana Larynx large, trough-shaped laryngeal (cricoid)
cartilages, which lie just below the ary-
single slit termed the choana. Because The larynx of birds is not the "voice box" as it is in mammals; thus tenoids. The arytenoids stiffen and hold
the choana runs in an anterior-posterior Upper Beak it is a simpler structure and does not contain vocal cords. It consists the shape of the fleshy folds surrounding
direction, and this sagittal section is tak- of two major cartilages called the laryngeal (cricoid) cartilages (Fig. the slit-like glottis (not visible in this lat-
en slightly to the left of the midline, the eral view), whose muscles regulate the
4-74). Its primary function is to act as a valve, regulating the flow of
choana is in front of tissue and not easy passage of air into the respiratory system.
to see in the sagittal section; it is visible, Anterior Concha air into the trachea, rather than producing sound. The opening to the
The cricoids form the floor and sides of
however, in the cross-section. Drawing larynx is the slit-like glottis caudal to the tongue, formed by two half- the larynx. Adapted from King and
Position of
by Charles L. Ripper. circle-shaped cartilages covered with mucous membrane. McLelland (1981, Vol. 4, p. 72).
Choana

Cornell Laboratorq of Ornitholos Handbook of Bird Biolo8q

4.92 Howard E. Evans andJ. B. Heiser Chapter 4 —What's Inside: Anatomt1 and Phtisiologq 4.93

Figure 4-75. Coiled Trachea Within the Figure 4-77. The Syrinx of a Songbird:
Sternum of a Whooping Crane: The tra- The sound-producing organ of birds, the
Scapula
chea, or windpipe, is a tube supported Lateral View syrinx, is located at the point where the
by cartilaginous rings, which conveys air Tracheal Rings trachea divides to form the two bronchi.
from the larynx to the lungs. In most birds a. External View: The syrinx, shown here
•
it follows a straight route, but in some it • Syringeal with its musculature removed, is formed
Semilunar • Muscles by an expansion of either the tracheal
is elongated and looped. In the Whoop-
Membrane
ing Crane illustrated here, as well as
in some swans, its extensive loops lie
coiled within the keel (carina) of the To Larynx 4--
• Pessulus
cartilaginous rings, the bronchial car-
tilaginous half-rings, or, more com-
monly, some combination of the two. b.
sternum. Elongated tracheae are thought Bronchial Internal View: The syrinx here is shown
to aid vocalization, as well as high-al- Rings actively engaged in producing sound.
titude, long-distance flight—warming Tympaniform Flexible tympaniform membranes
Membranes --- stretch between the cartilaginous rings,
the inhaled air and allowing more air to
Lateral Labia permitting the syrinx to change shape
be stored within the respiratory system.
Drawing by Charles L. Ripper. Medial Labia as a result of the actions of one or more
pairs of syringeal muscles, thereby al-
Keel of Sternum a. External View, b. Internal View, tering the sounds it can produce. The
Muscles Removed In the Sound-producing Position medial and lateral labia are particularly
important sound-producing membranes
(see Sidebar 2: Bird Song: From Oboe
and Trombone to Orator and Soprano).
Trachea SifinX
The semilunar membrane and the carti-
The trachea (see Fig. 4-74), or windpipe, is a tube that conducts The syrinx is the bird's sound-producing organ (Fig. 4-77; and laginous pessulus occur only in the syr-
air from the larynx to the lungs. A series of cartilaginous rings holds the see Fig. 7 34). It is formed by modifications of either the tracheal rings
- inx of songbirds, probably contributing
or the bronchial half-rings, or a combination of both. Thus a bird can to the advanced singing abilities of these
trachea open for the passage of air. The rings can telescope into each
birds. Drawings by Charles L. Ripper.
other to shorten the trachea, or can pull apart, exposing soft connective have a tracheal syrinx, a tracheobronchial syrinx (the most common),
tissue between the rings, to lengthen it. In most birds the trachea fol- or two separate bronchial syrinxes. Internal and external tympaniform
lows a straight course from the glottis to the lung bronchi. In some membranes stretch between the cartilages, allowing the shape of the
species, however, it is greatly elongated and looped within the neck or syrinx to change and altering the sounds it can produce. Additional
even farther afield. For example, in some chachalacas (Cracidae) and structures are found within the syrinx of songbirds, the large group of
the painted snipes (Rostratulidae), the loops lie between the skin and birds with the most complex vocalizations: a median cartilage called
underlying muscles; in some ibises, loops lie within the thorax; in the the pessulus at the bifurcation of the bronchi, and a semilunar mem-
Plumed Guineafowl, they lie within the furcula or "wishbone"! Per- brane extending from the pessulus into the cavity of the syrinx. Pre-
haps most bizarre, in the Tru mpeter Swan, Tundra Swan, and Whoop- sumably, these additional structures account, at least in part, for the
ing Crane, the trachea enters the keel of the stern urn (Fig. 4-75). Within singing capabilities of these birds. Some birds are able to control the
the keel it passes caudally before returning toward its point of entry, two branches of their syrinx so well that they actually can sing duets
Tracheal exiting the keel and making another bend to enter the thorax. Some of with themselves (see Ch. 7, Control of Song, and Fig. 7-35).
Bulla these looping tracheae are thought to be adaptations for vocalizations; One or more pairs of syringeal muscles act on the cartilages of the
others may be adaptations to high altitude, long-distance flight—func- syrinx and change its shape, thus tensing or relaxing the tympaniform
tioning to warm the inhaled air and increase the total volume of air that membranes. Air forced past the membranes vibrates them, creating
can be stored within the respiratory system. sound waves. The changes in the tension of the membranes and in the
Other specializations of the trachea include regional expansions diameter of the constricted passage in the syrinx, brought about by the
along its length that modify the birds' vocalizations. One or two di- syringeal muscles, result in different types of sounds. Also important
lations occur between the larynx and the bronchi in South American in sound modulation is whether one or both bronchial passages are
Bronchi screamers—odd, gooselike birds whose calls, among the loudest given constricted by muscle action and to what degree the right and left bron-
by any bird, sound something like a creaky but lively series of groans chial constrictions differ. An increase in the tension of the tympaniform
Figure 4-76. Tracheal Bulla of a Duck: on an old sheep horn. Tracheal expansions also occur in the males of membranes increases their frequency of vibration, and thus raises the
Males of many duck species have a
most species of ducks, many of which also have an expanded tracheal pitch of the sound; an increase in the diameter of the passageway
tracheal bulla—an expanded sac—on
one side of the lower end of the trachea. bul la (sac) on one side at the lower end of the trachea (Fig. 4-76). increases the sound's volume (loudness). (Sidebar 2: Bird Song: From
These tracheal bullae and various other Within the thorax, a short distance before it enters the lungs, the Oboe and Trombone to Orator and Soprano)
tracheal dilations found in other types of trachea of all birds has an expansion, the syrinx, and then divides to
birds are thought to modify the sounds
form two bronchi (singular, bronchus). Incomplete rings of cartilage
produced by the syrinx. Drawing by
Charles L. Ripper. support the walls of each bronchus and continue into the lungs. (Continued on p. 4.98)

Cornell Laboratoni of Omithologq Handbook of Bird Biologq

4.94 Howard E. Evans and ,J . B. Heiser Chapter 4 — What's Inside: Anatomq and Pluisiologg 4.95

Sidebar 2: BIRD SONG: FROM OBOE AND TROMBONE Suboscine numerous species with surprising
results. Brown Thrashers and Gray
TO ORATOR AND SOPRANO Catbirds frequently generate dif-
Trachea ferent sounds simultaneously, re-
J. B. Heiser sulting in true two-voice song. At
MI other times, they may switch one side
complex oscine syrinx that provides MI
We do not know for how many mil- ing, and is thus oxygen-depleted. But or the other off, with various results.
lennia humans have enjoyed the the mini-breaths do seem to perform for much of the variety and beauty
Sometimes they favor the left side,
beauty and musicality of the songs the important function of replacing of bird song. Listen at a woodside Mll
M II and sometimes each side of the syr-
of birds. No less a scientific figure about as much air as was vented in garden almost anywhere in eastern
inx contributes about equally to the
than Charles Darwin felt that birds producing the preceding note(s), North America in spring, and you M III
total production of song. Even when
"On the whole...appear to be the thus permitting the singer to emit will be treated to a great diversity
the contributions are equal, they are
most aesthetic of animals, excepting longer songs. When note repetition of passerine songs. Quite striking,
Bronchus not identical. In all such two-voice
of course man, and they have nearly rates exceed about 30 per second however, is the contrast between the
cases studied, the left syrinx pro-
the same taste for the beautiful as (what we perceive as fast trills), all aesthetic nature of the songs of the
duces lower-frequency notes than
we have." (The Descent of Man and the species of songbirds studied so Northern Cardinal, Song Sparrow, the right in any given series of notes.
Eastern Phoebe Eastern Phoebe
Selection in Relation to Sex, 1874, p. far shift from taking minibreaths and Brown Thrasher (all oscines) The left side can produce notes in the
Left Ventrilateral View Left Dorsolateral View
697). The comparison of bird song to between notes to taking breaks be- and the simple, monotonous, and range of the right and vice versa, but
musical instruments (and vice versa) tween trills; during these "inter-trill" not very musical quality of the East- Oscine they seem always to divide the task of
must have begun with the first whis- breaks a more substantial inhalation ern Phoebe's song. The phoebe, al- singing as do the left and right hands
tles and flutes of Paleolithic humans. takes place. Apparently there is a though a passerine, is a "suboscine;" of a keyboard musician. Northern
It may not be by chance alone that threshold at this repetition rate above its family and several others world- M2
Cardinal songs have sounds that con-
one of the oldest surviving musical which the neuromuscular apparatus wide seem to have split off the main sist of continuous sweeps between
instruments was made of bird bone: of breathing can notfu nction for even passerine lineage early in passerine 3,000 and 4,000 Hertz. Surprisingly,
a flute from France estimated to be the shortest minibreath. evolution (see Fig, 7-22). The ances- the lower-toned part of the sweep
tors of the phoebe became isolated M 3a
10,000 to 15,000 years old! A part of our lack of understanding M 3a is performed by the left side of the
M 3b
In spite of our long love of bird of how birds sing is due to the unique on the South American continent awn M syrinx and, without any detectable
song, understanding how birds sing nature of the avian vocal apparatus, when it was far from any other ma- auditory break, the upper tones are
.1; M 4a
has eluded science right up to the the syrinx. Among living animals, jor land mass and radiated into the M1 seamlessly added by the right side!
M 4b
present day. How, for instance, are the syrinx is as unique to birds as are tyran n id flycatchers we know today. M 4b Some canaries sing about 90 percent
M 4c
birds with a loud, long, complex, and feathers and could just as accurately In spite of the diversity of species M 4c of their song elements on the left side
rapid song able to sustain the airflow be used as a defining feature of birds. that evolved, these flycatchers all re- M 3b of their syrinx, but at the same time
needed to perform such extended Nevertheless, so much variation ex- tained a relatively simple syrinx (Fig. the nerves and muscles of the right
songs without apparently pausing ists between the syrinxes of various A, Eastern Phoebe). From the same side are just as active as if they were
fora breath? Winter Wrens may con- bird groups thatthe structure has long simple syrinx, the oscines, evolving the source of the sound. Only the
tinuously vocalize for as long as 41 been used in constructing evolution- elsewhere, developed, among other muscles that block airflow stay still.
seconds, and Grasshopper Warblers ary hypotheses. The structure of some innovations, a complex syrinx with American Crow American Crow It is not entirely clear why this should
(an Old World temperate zone spe- syrinxes is very complex, especially more than three pairs of intrinsic LeftVentrilateral View Left Dorsolateral View
be the case. With all the variety in
cies) for 60, and perhaps as much as those of the "true" songbirds (Order muscles, allowing for a much greater syringeal structure and function, in
117, seconds. Estimates of the air Passeriformes, Suborder Passeri; also variety of fine control (Fig. A, Amer- Figure A. Musculature of the Syrinx in Suboscine Versus Oscine Passerines: The
addition to the difficulty of studying
available in their respiratory systems known as the "oscines" from the Lat- ican Crow). By the time North and syrinxes of an Eastern Phoebe (a suboscine) and an American Crow (an oscine) are
the syrinx in a living, singing bird, it is
compared in both ventrilateral and dorsolateral views. The muscles are labeled MI
suggest that many birds should run in for "singing bird") (see Fig. 7-22). South America were united by the clear that no single functional model
through MIII in the phoebe and M1 through M4 in the crow. The phoebe's muscle MI
out of breath before completing their Although oscines are so numerous formation of Central America, the is likely to apply to all species; pro-
is considered equivalent to the crow's Ml, and MII is the same as M2. All the other
feats of song. Careful measurements that they make up 48 percent of liv- oscines had populated North Amer- posing to explain "the function" of
muscles are unique, however, derived from different developmental origins in each
of tracheal airflow in certain species ing birds, the syrinxes of all oscines ica. Thus the Central American land species. Notice the greater complexity of the musculature of the oscine (crow) syrinx, "the syrinx" is a fool's task.
have shown that they take "mini- are nearly identical in their complex bridge allowed the two long-isolated evidence of the superior singing ability of these birds. Adapted from Ames (1971, The uniqueness of the syrinx as
breaths" of 15 to 50 milliseconds in structure. These consummate singers I ineages, the oscines and suboscines, Plates 5, 6, and 21). a sound-producing organ and the
duration between notes or closely are almost all small, and the syrinx is to come together, enriching the avi- musicality of the sounds that birds
spaced groups of notes (Suthers and so deep in their respiratory tract (at fauna of both continents. The sound The majority of birds have a syrinx membranes that vibrate to produce produce has long led people to pro-
Goller 1997). These minibreaths the lower end of the trachea), that of the phoebe presumably has many that contains elements of the right sound (Fig. B). The possibility thus pose analogies between bird song
are so short, and therefore so shal- direct studies of its activity during qualities in common with the songs and left bronchi and thus have right arises that these birds could produce and musical instruments. Perhaps
low, that they probably do little to song production have been all but of early passerines. The songs of true and left paired structures. In oscines, two harmonically unrelated tones at the earliest scientifically based
replenish oxygen—indeed, most of impossible. songbirds developed independently, and some other birds, these paired the same time; in essence, duetting proposals were those of the French.
the inhaled air is probably the same Simple observations, however, their evolution made possible in part structures include, at the cranial end with themselves. This "two voice" In 1753 a paper presented to the
air that was just exhaled during sing- will convince anyone that it is the by complex syringeal anatomy. of each bronchus, a distinct set of the phenomenon has been studied in French Royal Academy claimed that

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496 Howard E. Evans and J. B. Heiser Chapter 4 — What's Inside: Anatomq and Philsiologg 4.97
produced by the syrinx are "cleaned nonlinear output; in other words, the 1988). It is now recognized that, in
a. Quiet Breathing b. Sound Production
up" or filtered acoustically by the acoustic flow and sound produced humans, direct interactions between
vocal tract, leaving pure tones to be by it suddenly are not simply pro- the vocal cords and the vocal tract are
emitted. This "acoustic filter model" portional to the driving air pressure. important in determining the quality
4 for the production of pure tones is, The resulting jumps in the frequency of the singing voice. A trained so-
Trachea in fact, more like the production of of a vocalization are equivalent to prano apparently is able to produce
speech by the human voice than the the human voice "breaking" (as her purest tones by changing the
Bronchial Cartilage #3 operation of a musical instrument. in adolescent males) or, in people shape of her mouth, the position of
Twists, Pushing In our speech the mouth, tongue, with some illness or disorder of the her tongue, and the length and shape
Semilunar Lateral Labia Into
Tracheal Cartilage #1 — Air Stream and lips are crucial in modifying vocal cords, having a roughness or of her vocal tract, which changes the
Membrane
Bronchial Cartilage #1 the sounds produced by the vocal "gravelly" quality. These charac- resonantfrequencies within her head
Bronchial Cartilage #2-
14 %my cords, often by suppressing certain teristic jumps are not only produced and chest; these resonances directly
frequencies and augmenting others. by Zebra Finches during natural affect the way the vocal cords vi-
Bronchial Cartilage #3 — Thus bird song has recently come to song, but also by an isolated Zebra brate, and thus affect the quality of
be likened to human speech rather Finch vocal tract when air is passed the sound actually produced by the
Bronchial Cartilage #4 Lateral
Labia than to musical instruments, whose through it. Such nonlinear behavior vocal cords. The fact that birds, too,
• Bronchus post-vibration effects are much more must therefore be an intrinsic char- are now known to affect the syrinx's
Moves
Upward
limited than those of the human, and acteristic of the syrinx. Just how the output by controlling the action of
Medial
Into apparently the avian, vocal tract. elastic and oscillatory structure of the the upper vocal tract, leads to spec-
Tympaniform
Bronchus Trachea During the production of the vo- syrinx functions to change the type ulation that something very similar
Membrane
calizations of most animals, when of response it gives to different driv- to a soprano's controlled singing is
the air pressure in the lungs—which ing pressures—causing frequency going on in birds. Perhaps the clear
Figure B. The Oscine Syrinx and Sound Production: Shown here are schematic, longitudinal sections through the syrinx of an drives the vibrating membranes— jumps—is not understood. But, and undeniably beautiful sound of
American Crow. a. Quiet Breathing: This illustrates the syrinx during quiet breathing, showing the internal structures in relation doubles, the acoustic flow (airflow the exact functioning of the syrinx a pure, sung tone is produced in the
to one another in the resting position. b. Sound Production: This illustrates the syrinx during sound production by one or both over the membranes) also doubles is currently a hot topic among re- same way, no matter whether by a
sides. Muscles stretch the two bronchi upward into the trachea (large solid arrows), and twist the third bronchial cartilages. The (that is, the system behaves linearly), searchers. bird or a human!
latter push the lateral labia into the path of air flowing out of the respiratory system and into close proximity with the medial resulting in a predictable shift in the Another relatively recent dis- Probably no analogy will ever
labia, which have also been forced into the airway by the movement of the bronchi (medium solid arrows). Sound is produced
frequency of the sound produced. covery leads to a further and final explain a significant portion of how
as air rushes between the lateral and medial labia (dashed arrows), causing these soft tissues to vibrate. Adapted from Goller and
Experiments with Zebra Finches, analogy that attempts to explain how birds produce their most compli-
however, have demonstrated that, at bird song is produced: Researchers cated songs. The syrinx has proved
least in these birds, no such simple have found that during a vocaliza- to be not only anatomically unique,
relationship exists (Fee et al. 1998; tion, parts of the upper vocal tract but to be marvelously complex in its
the syrinx acts like the double reed of characteristic sound qualities by need vibrate to produce natural
Gol ler 1998). As air pressure on a Ze- may directly affect the vibrating function and in the scope of its vocal
an oboe. In the early 1800s Georges which we can identify the instru- vocalizations. The actions of the re-
Cuvier, famed French anatomist ment. The avian vocal tract has mainder of the vocal tract have been
bra Finch syrinx is slowly increased syrinx, changing its frequency from ability as well. ■
or decreased, at certain pressures what it would emit withoutthis phys-
and paleontologist, reckoned that these same components: abdominal much debated, but as a result of a
the system spontaneously jumps to a ical feedback (Nowicki and Marler
the French horn (naturally!) and the muscles force air from the air sacs number of innovative experimental
trombone were more accurate com- and lungs through the syrinx with its techniques—including recording
parisons. Subsequently all manner of several membranous tissues, some of birds singing in atmospheres com-
reed and brass instruments and even which presumably vibrate, produc-- posed of gasses of lesser and greater
organ pipes have been promoted as ing sound. The remaining structures density than air—the contributions
the best model for how birds sing. in the vocal tract (the trachea, glot- of the vocal tract are now generally
None of these analogies has proven tis, pharynx, tongue, mouth cavity, agreed to be significant. The width
close enough to the truth to last for and beak) subsequently modify the of the opening of the beak in White-
long, but they have some elements in syrinx's sounds. Although many throated Sparrows and Swamp Spar-
common that may throw light on the membranes of the syrinx have been rows, for example, controls which
mystery of how birds produce their hypothesized to be the ones that vi- frequencies produced by the syrinx
melodious song. brate to produce sounds, it appears are muted and which are emitted
In all of these musical instruments, from tiny fiber- optic endoscopy in at full volume (Gaunt and Nowicki
air rushing through a tube past some the four oscine species studied so 1997).
flexible structure in its path sets that far that only the soft tissues known Significantly, pure, whistle-like
flexible structure vibrating, produc- as the lateral and medial labia (lips) tones are apparently not produced in
ing sound. The features of the tube (see Fig. B) or thin tissues known as their pure form by the syrinx. Instead,
then modify the original sound in a the lateral tynnpaniform membranes sounds with several simultaneousfre-
multitude of ways that result in the (in the Rock Dove and Cockatiel) quencies (a tone and its harmonics)

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4.98 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatomq and Phiisiologq 4.99
exchange in the lungs. Exchange occurs with this air on exhalation, Figure 4-79. Partial Cast of the Lungs of
Lungs and Air Tubes the Chicken: This three-dimensional cast
as it passes out of the air sacs, back into the lungs, and through the
The two surprisingly small lungs lie just below (ventral to) the was formed by injecting the lungs with a
parabronchi.
vertebral column and the ribs. As each bronchus enters the lung, it thick liquid called Wood's Metal, which
The unique internal anatomy of the avian lung is most easily un- subsequently hardened. The lung tissue
loses the half-rings of cartilage and continues as the primary bron-
derstood by examining the accompanying figures. The bird's lung is a was then chemically stripped away, leav-
chus or mesobronchus through the lung (Fig. 4-78). The mesobronchi
mass of interconnecting air tubes, the parabronchi, too small to be seen ing a solid impression of a portion of the
gradually decrease in diameter, branching into secondary bronchi. lungs' internal structure. At the top,
with the naked eye (Fig. 4-79). Each air tube has openings in its thick
Some of these, called recurrent bronchi, connect to the air sacs. Other paired bronchi with regularly spaced
wall that allow air to pass into small interconnecting spaces that weave
secondary bronchi branch to form parabronchi, the major respiratory cartilaginous rings are visible. The thick,
together like a labyrinth through the surrounding blood capillary bed short tubes are secondary bronchi, and
units of the lung. The longest mesobronchi end at the entrance to the (Fig. 4-80). These openings also allow air to pass back from the spaces the longer, narrow tubes are the massed
abdominal air sac. Much inhaled air passes directly through the lungs interconnecting parabronchi, the major
into the air tubes. The capillary bed surrounding the spaces is supplied
via the mesobronchi to the air sacs without being involved in gas respiratory units of the lungs. Drawing
by the pulmonary artery and drained by the pulmonary vein. As blood
courtesy of Howard E. Evans.
flows through the capillaries (generally at right angles to, or in the
opposite direction of, the flow of air—permitting the formation
Parabronchus of a countercurrent exchange system), oxygen in the air spaces
(Longitudinal Section)
Lung dissolves into the blood, and carbon dioxide from the blood
(Shown in Longitudinal section) Parabronchi Secondary
moves into the air to eventually be exhaled (Fig. 4-81).
Bronchus
Clavicular Air Sac This arrangement of lung tissues is very different from
that of mammals, in which respiratory exchange takes
place in dead-end pockets (alveoli) at the termination Secondary
Bronchi
of bronchioles. Birds, however, have no bronchioles
or dead-end alveoli. Because the minute air spaces all
interconnect in birds, rather than ending blindly, birds
Trachea
A .r Capillaries can achieve a continuous flow of air across the surface
of the capillary bed and thus a continuous, highly effi- Pa rabronchi
cient oxygen extraction.

Air Flow Through

Parabronchus (Air Tube)

Abdominal
Air Sac

Keel of Sternum
(Shown in Longitudinal section) Recurrent
Bronchus
PulmonaryVenule
Thoracic Air Sacs

Pulmonary Arteriole

Mesobronchus

Figure 4-78. The Avian Respiratory System: In this functional diagram, the components of the respiratory system are viewed from
Air Spaces Blood Capillaries
the bird's left side. The lung and its internal structures are shown in sagittal section. For paired structures, only one member of the
pair is visible. The trachea divides into two bronchi (singular bronchus), one of which enters each lung, losing its cartilaginous (Blood Vessels Removed)
half-rings and continuing through the lung as the primary bronchus or mesobronchus. The mesobronchi branch into narrower
secondary bronchi, some of which divide into many fine branches termed parabronchi, which are the lung's major respiratory Figure 4-80. Structure of Parabronchus: This cutaway view shows the internal structure of a single parabronchus (air tube).
units—the sites of gas exchange. The inset shows several highly magnified parabronchi sectioned longitudinally. Other second- Air flows continuously through the parabronchus, moving through openings in its walls into a network of air spaces, sometimes
ary bronchi, termed recurrent bronchi, connect to the air sacs outside the lung. Shown here in external view are the clavicular, referred to as air capillaries. Each of these spaces is surrounded by a network of blood capillaries, and it is between these two
thoracic (two on each side), and abdominal air sacs. For clarity, these sacs have been simplified and drawn much smaller than in structures that oxygen and carbon dioxide are exchanged. For simplicity, the blood capillaries have been removed from the left
a live bird; in their natural state, air sacs completely surround the abdominal organs and overlap each other extensively, forming a side of this drawing, and on the right side, the air spaces are mostly obscured by the blood capillaries. Pulmonary arterioles sup-
complex system with connections to air spaces within the bones (see Fig 4-82). Reprinted from Manual of Ornithology, by Noble ply the system with deoxygenated blood, and pulmonary venules transport the oxygenated blood away. Adapted from Brooke
S. Proctor and Patrick]. Lynch, with permission of the publisher. Copyright 1993, Yale University Press. and Birkhead (1991, p. 31).

Cornell Laboratorq of Ornithologg Handbook of Bird Biolo9i

4.100 Howard E. Evans and J. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.101
Figure 4-81. Gas Exchange in Para- a. Lateral View Figure 4-82. Air Sacs: a. Lateral View:
bronchus: This schematic shows gas
exchange between a single air space
I
Air AIRFLOW ∎311; • . • • • • • • •°• •
• .
This view shows the location of the
major air passageways and air sacs of
and adjacent blood capillary in close Space .
R.
. 0 .•,• , °
. • • • •0 • :2. - . the Budgerigar. A system of thin-walled,
proximity within a parabronchus. transparent air sacs extends from the
Cervical Air Sac
Blood flows in the opposite direction to Blood mesobronchus and the lung to different
CO, ' •
■
, '
that of air, establishing a countercurrent Capillary -4111( BLOOD FLOW regions of the body. A single, medial cla-
Trachea Lung
system. Oxygen in the air space diffuses • vicular air sac lies around the trachea. A
into the blood, while carbon dioxide in cervical air sac extends from each lung.
the blood diffuses into the air space, Two thoracic air sacs--anterior (cranial)
Clavicular Air Sac
eventually to be exhaled. • Secondary Bronchi and posterior (caudal)—are fixed in po-
Air Sacs sition on each side. One abdominal air
Thin-walled air sacs (four paired and one median) extend from sac is also located on each side, but its
Anterior (Cranial) position may shift during the day to al-
the mesobronchus or the lung itself to different regions of the body (Fig. Thoracic Air Sac low the bird to maintain a streamlined
4-82). A cervical sac is usually located on each side in the neck region Abdominal shape even after a large meal or before
or sometimes a series of cervical sacs are found along the neck, as in Air Sac
laying an egg. No gas exchange occurs
geese. A large median clavicular sac between the clavicles surrounds Posterior (Caudal) in the air sacs themselves; instead, they
Thoracic Air Sac act as bellows to bring air into the bird
the bifurcation of the trachea. The clavicular air sac has extensions on
and store it until it can pass through the
each side that lie in the shoulder joint region and connect through a gas exchange spaces of the parabronchi
hole in the humerus, the pneumatic foramen, to the pneumatic space during expiration, maintaining a con-
within the wing bones. The clavicular sac also has several connec- tinuous flow of air through the para-
tions with the pneumatic spaces of the sternum. Two thoracic air sacs bronchi. Contractions of the abdominal
muscles and movements of the sternum
are fixed in position on each side, but the pair of abdominal air sacs,
inflate and deflate the air sacs. b. Ventral
which may have connections into the bones of the pelvis and femur, b. Ventral View View: This view of the left side of the
To Coracoid
can shift their position within the abdominal cavity—at different times air sac system illustrates the many con-
To Cervical Vertebrae nections of the lung and air sacs with
of the day they may occupy different areas between the organs. This
the air spaces within the bones. The
adaptation allows a bird to maintain a streamlined shape for flight even Trachea
To Humerus continuation of the air sacs inside many
after a large meal or before laying an egg. bones lightens the bones for fl ight and al-
The air sacs, so thin-walled that they resemble soap bubbles, have Clavicular Cervical Air Sac lows more air to be stored for continuous
no blood vessels and play no direct part in the exchange of oxygen and Air Sac gas exchange in the lungs, but leaves the
To Cervical Vertebrae bird more vulnerable to traumatic injury.
carbon dioxide. Instead, they serve as bellows to bring air into the bird
A bone fracture in a bird is more likely
and store it until expiration. During expiration, this stored air passes
to result in death due to internal bleed-
through the recurrent bronchi into the parabronchi of the lungs to Right
ing or blood clots than is a similar injury
Mesobronchus
interact with the respiratory surfaces. Thus birds get fully oxygenated in other types of vertebrates. Drawings
air into the lungs on both inspiration andexpi ration, and consequently To Thoracic Vertebrae from Evans (1996).
To Central Portion of Sternum and Ribs
have the most efficient respiratory system of any vertebrate.
Left Mesobronchus

Breathing and Gas Exchange To Ventral End of Ribs

and Lateral Parts L T6 Ilium
In review, the process of breathing and gas exchange occurs as of Sternum , ()r
-

follows (Fig. 4-83): With each inspiration, air passes freely through
the interconnecting parabronchi and recurrent bronchi, filling the gas Secondary Bronchi
exchange spaces in the lungs, as well as the posterior air sacs, with
oxygenated air. With each expiration, air returns from the posterior air To lschium
sacs and passes through the parabronchi, replacing the now oxygen- Anterior --"4" and Pubis

depleted air in the gas exchange spaces (which is eventually exhaled) Thoracic
Air Sac
with oxygen-rich air. On the next inspiration, this air (now oxygen-de-
pleted, too) is moved to the anterior air sacs as the next batch of oxygen- Posterior
rich air is brought into the posterior air sacs and gas exchange spaces. Thoracic
Air Sac
As a result there is little residual, oxygen-poor air in the lungs of birds
after exhalation, in contrastto those of mammals. In addition, the bird's
Abdominal
arrangement permits oxygen and carbon dioxide to be exchanged Air Sac

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

4.102 Howard E. Evans and j. B. Heiser Chapter 4—What's Inside: Anatomq and Ph1siologq 4.103
Figure 4-83. The Mechanics of Breathing in the Bird: a. Inspiration 1 Parabronchi during both inspiration and expiration. Also in contrast to mammals,
This schematic illustrates the one-way passage of a sin- Secondary Of Lung
Bronchus Secondary two inspiratory and expiratory cycles are required for a given volume
gle, inhaled volume of air (shown in black) through the
Bronchus of air to traverse the complex avian respiratory system. Such a mech-
bird's respiratory system. The precise pathways taken
by air varies greatly among species, and the pattern Posterior anism, obviously more efficient in birds than in mammals—which only
shown here is greatly simplified. In addition, prob- Air Sacs exchange oxygen and carbon dioxide on inspiration—is undoubtedly
ably no bird maintains discrete parcels of air within
Anterior C
Air Sacs related to the higher rate of metabolism in birds, which is needed to
its respiratory system: in actuality, some lag and mix- C
ing occurs within the air passageways. Note that in
support flight (see Metabolism, later in this chapter for more on this
contrast to mammals, two inspiratory and expiratory subject). The efficiency of air flushing through the entire respiratory sys-
cycles are required for a given volume of air to move tem explains the rapid spread of respiratory illness in domestic birds.
through its complete path. a. Inspiration 1: During The intimate connection of the respiratory system with the skeleton
the first inspiration, a volume of air enters through Aerodynamic Mesobronchus
Valve also explains why traumatic injury to a bird so often results in death
the bronchus and into the mesobronchus. At the
junction of the mesobronchus and the first secondary due to hemorrhage and blood clots.
bronchus, air is prevented from immediately flowing
b. Expiration 1
anteriorly by the presence of an aerodynamic valve.
This valve is not a physical structure, but a vortex-like
movement of air that prevents backflow by forcing the
The Digestive Stistern
incoming air along the mesobronchus and into the ■ The digestive system begins with the beak and tongue, which are
posterior air sacs (consisting of the posterior thoracic used for manipulating foods. It continues with an oral cavity (mouth)
and the abdominal airsacs), which expand to accom-
and pharynx (throat) for swallowing, and an alimentary canal for the
modate it. b. Expiration 1: With the first expiration,
the posterior air sacs contract, pushing the air into sec- passage, digestion, and absorption of food. It ends in the vent, the
ondary (recurrent) bronchi connecting to the lung. An external opening of the canal from the cloaca, the common single
aerodynamic valve here prevents the backflow of air openi ng for both the alimentary canal and the urogenital system. Along
Aerodynamic
into the mesobronchus. Within the lung the air passes Valve the way, enzymes, hydrochloric acid, and associated gland secretions
through the parabronchi, gas exchange occurring as it
moves. c. Inspiration 2: With the second inspiration, convert food items into simpler compounds for absorption, storage,
c. Inspiration 2
the air moves out of the parabronchi (further gas ex- or elimination.
change occurring as it moves), through secondary The alimentary canal includes the esophagus and crop, the two-
bronchi, and into the anterior air sacs (consisting of
part stomach, the long small intestine, the ceca, and the short large
the cervical, clavicular, and anterior thoracic airsacs).
(Simultaneously, a new volume of air (not shown], is
intestine, which, true to its name, is greater in diameter than the small
brought into the posterior air sacs.) d. Expiration 2: intestine. The salivary glands, liver, and pancreas are digestive glands
Finally, with the second expiration, the anterior air that develop in the embryo from its digestive tube and subsequently
sacs contract, forcing the air into secondary bronchi retain their connection by direct tubular ducts. The secretions from
and out through the bronchus to be exhaled. (Simul-
these glands enter the digestive tract through their respective ducts,
taneously, the newer volume ofair [not shown] moves
from the posterior air sacs into the parabronchi.) Note and aid in digestion.
that at any given time, two volumes of air are mov-
ing through the avian respiratory system. The bird's
respiratory system differs from the two-way system of d. Expiration 2 Oral Cavitq
mammals, in which gaseous exchange takes place in
dead-end pockets (alveoli). Mammalian airflow to the Bill
alveoli is oscillatory: air moves in and out through a
Because their forelimbs are highly specialized for flight, birds
common set of air tubes (the bronchioles), with gas ex-
change occurring only during inspiration. Birds have
must obtain food with their bill, or, in the case of birds of prey, with
no bronchioles or dead-end alveoli. Instead, the one- their feet. Many marvelous variations in the shape and structure of the
way airflow system allows birds to achieve a nearly bill can be seen. In fact, a great deal about a bird's diet can be inferred
continuous flow of air through the gas exchange sites, by examining its bill and tongue, because these structures, and the
with the extraction of oxygen occurring during both
muscles that operate them, are usually adapted to handle the specific
inspiration (as air leaves the parabronchi) and expira-
tion (as air enters the parabronchi). Adapted from Gill food the bird favors.
(1995, p. 121). The bills of most hummingbirds are a good example, because
much variety exists in just this single group of birds (Fig. 4-84). Some
hummingbird bills are straight, slender, and rounded in cross sec-
tion for probing deep into the corolla of flowers for nectar. However,
some tropical hummingbirds have very differently shaped bills, from
extremely long to extremely short, from sharply recurved (curved

Cornell Laboratorq of OrnitholoBq Handbook of Bird Biologq

4.104 Howard E. Evans and j. B. Heiser Chapter 4 —What's Inside: Anatomq and Phiisiologq 4.105

Figure 4-84. Hummingbirds and their Figure 4-85. The Diversity of Bird Bills:
Principal Food Flowers: Nectar-feeding a. Oystercatcher The size, shape, and structure of a bird's
birds, such as the New World humming- bill is closely related to its diet, as shown
birds and the Old World sunbirds, obtain by these examples. a. Oystercatcher:
food by probing their thin beaks into the The oystercatcher's bill is flattened from
nectar chambers of flowers. Shown here Centropogon talamancensis Magnificent Hummingbird side to side (see ventral view), giving it
are four species of hummingbirds from a chisel-like shape with which to pry
the highlands of Costa Rica, each with its or hammer open the shells of oysters,
preferred flower. Notice how the shape mussels, and other bivalve (two-shelled)
and length of each bird's beak matches mollusks. b. Grackle: In the roof of the
VENTRAL VIEW
the length and curvature of its principal grackle's bill is a sharp ridge, or keel,
Centropogon valerii Green Violet-ear
food flower, which in turn depends on sticking down into the mouth, against
the bird for pollination. The remarkable which the bird can crack open large
correspondence between these flowers seeds. c. Wrybill: The bill of the Wrybill,
and birds is an example of coevolution b. Grackle Keel a type of plover from New Zealand,
(two or more species evolving with, and curves to the right side (see dorsal view),
in response to, each other). The flowers allowing it to probe for food under rocks
benefit by having a precise shape that Macleania glabra Fiery-throated Hummingbird too heavy for it to overturn. Drawings by
allows just one or a few principal pol- Charles L. Ripper.
linators to reach their nectar, because
their pollen is then more likely to be
transferred to another flower of the
same species. And, the birds benefit
Salvia iodochroa Volcano Hummingbird
because fewer species are competing kr"
for the nectar of their principal flowers.
Coevolution of this sort is most prevalent
c. Wrybill
in tropical areas, where species diversity
upward) to abruptly downcurved. No doubt such bills give their own-
is high and a flower's pollen is therefore
less likely to reach another member of
ers an advantage in obtaining nectar from certain kinds of flowers
the same species just by chance. After unreachable by other birds.
Wolf et al. (1976). Other interesting bills (Fig. 4 85) include those of oystercatchers,
-

which are narrow from side to side, functioning as chisels when the
birds open oysters, mussels, and other bivalve mollusks. Grackle bills
have a sharp keel in the roof of the upper beak; it sticks down into the DORSAL VIEW
mouth, and enables them to cut through the hard shells of big seeds.
The bill of theWrybi I I, a plover from New Zealand, bends to the right in
every individual, presumably for prying out food from under pebbles.
Researchers have no explanation for the consistency of the bend.
The bills of most fish-eating birds—loons, grebes, tropicbirds,
gannets, anhingas, herons, bitterns, terns, and kingfishers—are gen-
erally straight and pointed, with sharp edges acting as pincers for grasp- the two parts of its beak together as its head and neck bend down and
ing, or sometimes spearing, their prey (Fig. 4 86). Bil ls of mergansers
- underneath the body. The bird then draws the head forward and moves
have a further "improvement"—saw-like edges for gripping slippery on with the fish in its bill. The evolution of this peculiar feeding be-
fish. Pelicans, with hooked upper beaks, big mouths, and distensible havior involved changes in the bill, head, and neck. The most obvious
throat pouches, can engulf large fish or great numbers of small ones. is the lengthening and narrowing of the lower beak to a blade-like
A puffin, when returning to its young from the sea, may carry as many structure that cuts through the water with little friction. The extension
as a dozen small fish at a time in its parrotlike bill. The bird manages of the whole lower jaw and the ability to open the lower beak very wide
to wedge each one, as soon as it is caught, between ridges in the roof permit the bird to reach far down while skimming, giving it a better
of the upper beak in a very organized manner. Miraculously, it holds chance of contacting fish.At the same time, the skimmer has the ability
each fish firmly in place while it opens its bill to catch another and to open the shorter, upper beak wider than can its relatives, gulls and
another! terns. This helps to keep the upper beak out of the water where it will
The Black Skimmer, another fish-eating bird, has a bill in which not interfere with the fishing. The lower beak has some diagonal ridges
the lower beak is much longer than the upper beak (Fig. 4 87). With
- with a rich supply of nerve endings, sensitive to the touch of prey. These
an open bill, the bird skims the surface of the water so that the lower sensory endings enable skimmers to detect contact with prey, and also
beak cleaves the water (Fig. 4 88). On striking a fish, the bird snaps
- allow the birds to feed by night (by touch) as well as by day.

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4.106 Howard L. Evans and J. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologg 4.107

Figure 4-87. Bill of the Black Skimmer:

A fish-eating species related to gulls
and terns, the Black Skimmer has a
LATERAL VIEW remarkable bill whose lower portion is
substantially longer than the upper, as
seen in the lateral view. The ventral view
reveals the thin, knife-like lower beak for
slicing through the water. Drawing by
Charles L. Ripper.
VENTRAL VIEW

b. Atlantic Puffin

c. Great Blue Heron

Figure 4-86. Bills of Fish-eating Birds:

a. Merganser: The serrated edges of a
merganser's bill function to grip slippery
fish, giving this bird its nickname, "saw-
bill." Drawing by Charles L. Ripper. b.
Atlantic Puffin: Ridges with backward-
facing spines in the palate of the puffin's
upper beak help to secure each fish as it
is captured, allowing this bird to bring
a billful of fish to feed its young. Photo
courtesy of S. Bahrt/CLO. c. Great Blue
Heron: The Great Blue Heron has the
characteristic bill of a fish-eating bird—
long, straight, and pointed, for pincer-
like grasping. This immature bird has just Figure 4-88. Foraging Technique of the Black Skimmer: This foraging sequence is drawn from a series of movie frames. With its
captured a fish. Photo by Marie Read. d. bill open, the skimmer flies low over the surface of the water, its lower beak slicing through it (see also Ch. 1, Sidebar 2, Fig. B).
Brown Pelicans: Two Brown Pelicans vie Upon contacting a fish, the bird snaps the upper and lower beak together while bending its head and neck down and underneath
fora fish in the waters off the Galapagos its body. The skimmer then draws its head forward and continues flying with the fish in its bill. Several adaptations of the bill,
Islands of Ecuador. The side view of the head, and neck perm it this unique feeding technique. The lower beak has become narrow and blade-like (see ventral view in Fig.
open bill of the closer pelican shows 4-87.) to reduce friction as it moves through the water. The highly extensible lower jaw opens very widely to allow the lower beak
the large, distensible throat pouch. The to penetrate the water's surface in flight, while the upper beak can also open widely to avoid contact with the water. And finally,
second pelican has thrust its bill through the lower beak has numerous sensory nerve endings to allow the bird to detect prey. In addition to these anatomical adaptations,
the open bill of the first to try to snatch the skimmer flies in a distinctive way during feeding, with its wings held high to avoid accidental contact with the water. Movie
the fish. Photo by Tui De Roy. d. Brown Pelicans frames from Publications of Nuttall Ornithological Club Number 3.

Cornell Laboratorq of OrnitholoA Handbook of Bird Biologq

4.108 Howard E. Evans and J. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.109
Flamingos have a "bent" bill with filtering structures for obtaining
their food—tiny organisms—from water and mud (Fig. 4 89). Holding
-

a. Greater Flamingo the bill upside down, the birds draw a current of water into the mouth
by a pumping action of both the throat and the exceedingly thick, pis-
ton-like tongue. They then force the water out, filtering food particles
between the many thin, almost hair-like plates fringing the inner edges
of the upper and lower beaks. Flamingos can feed only in this highly
specialized manner and thus require a very specific set of ecological
conditions—food-rich, shallow water—to survive.
Birds that catch insects on the wing have variously shaped bills,
reflecting the particular methods they use (Fig. 4 90). Swifts, swallows,
-

and nightjars such as nighthawks have short, broad bills with wide
FORWARD gapes for engulfing insects as they overtake them in the air. On the
MOVEMENT other hand, tyrannid flycatchers such as kingbirds have strong, flat bills
Pumping Action of Throat
with hooks for snapping up individual insects, which they locate very
precisely by vision. If you listen as you watch a kingbird, phoebe, or
pewee sally forth from its perch after a passing insect, you will actually
Water Water
Forced Out hear its jaws close on the prey with a sharp snap. Except for swifts, all
Organic Material on Surface of Mud
- - birds that catch insects on the wing have bristles at the margins of the

/;;inTV/11110/1/ lityggy
gape (see Ch. 3, Types of Feathers, and Fig. 3-14a).
,i , Suction Many orioles and oropendolas (tropical members of the blackbird
;//,;11 ,„

family) depend on the strength of the gape as they thrust their closed
bills into fruit and then open them against the resistance of the skin and
b. Lesser Flamingos pulp. Starlings and meadowlarks use their bills the same way when
they probe in the soil for insects.
The size and shape of seed-eaters' bills are an almost legendary
reflection of the type of seeds they preferentially select. The Darwin's
finches species complex of the Galapagos Islands is the classic ex-
ample (see Fig. 1 4 7). In years after El Nino events bring extra rain,
–

there is an abundance of seeds on the islands. The bills of finches show

more variation after such years than after years of more meager seed
production, when there is presumably stiffer competition for finch sur-
vival. Apparently the wide variability in beak structure, which occurs
in every new generation of finches, undergoes fierce natural selection
during the early life of each generation when seeds are scarce, but
survives in rich years.
Figure 4-90. Beaks of Aerial Insec-
tivores: The beaks of birds that catch
.1.2F571.•

insects in flight reflect the capture tech-

niques used. The beaks of swifts (left),
swallows, and nighthawks are short,
broad, and open widely, allowing these
birds to engulf insects as they swoop
through the air (see also Fig. 6-30a).
Figure 4-89. Specialized Bill and Foraging Technique of Flamingos: a. Greater Flamingo: The flamingo feeds by filtering tiny
Tyrannid flycatchers (right) have strong,
organisms from shallow water and mud with its specialized bill. In contrast to most birds, the flamingo's lower beak is large and
flat beaks with hooked tips. They scan for
trough-like, whereas the upper beak is thinner and lid-like, and the entire beak is bent strongly downward. While feeding, the bird
flying insects from a perch, then fly out
holds its beak upside down, swinging it from side to side through the water. Pumping action of the throat and rapid piston-like
and snatch the prey in midair. All birds
movements of the thick tongue suck a current of water into the mouth, forcing it out past numerous fine, hair-like plates, which
that catch insects on the wing, with the
fringe the inner edges of both the upper and lower beak and strain out food particles. The Greater Flamingo feeds on small crus-
exception of swifts, have rictal bristles at
taceans, mollusks, and aquatic insects. Its smaller relative, the Lesser Flamingo (b), has an even finer food-straining mechanism,
the base of their beaks. These are visible
allowing it to feed on microscopic algae. Greater Flamingo by Robert P Allen from National Audubon Society Research Report
Swift Tyrannid in the tyrannid flycatcher. Drawings by
Number 5. Lesser Flamingos by Robert Gillmor.
Flycatcher Charles L. Ripper.

Cornell Laboratorq of OrnitholoBq Handbook of Bird Biolos

4.110 Howard E. Evans andJ. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.111

Figure 4-91. The Diversity of Bird Tongue

Tongues: The tongues of birds vary The tongue, like the bill, suits the bird's feeding habits. Birds use
widely in shape, length, and structure the tongue, depending on its size and structure, in one or more of the
depending on the feeding habits of their
following ways: securing food, manipulating food, swallowing food,
owners. Shown here (not to scale) are
a few of the more elaborate examples. and detecting the texture or taste of food. (As discussed in Taste, birds
Woodpecker tongues are very long and seem to have a poorly refined sense of taste.)The tongue may serve as a
equipped with backward-projecting probe, a brush, a sieve, a capillary tube, or a rasp. In shape, the tongue
barbs at the tip, which help to pry insects
may be rectangular, cylindrical, lance-like, flat, cupped, grooved,
or their larvae from crevices or holes that
the woodpecker excavates. Sapsuckers, spoon-shaped, or forked. It may be horny, spiny, fleshy, feathery, or
unlike their woodpecker relatives, have brush-tipped.The tongue is very small and virtually useless in pelicans,
moderately short tongues with forward- gannets, ibises, spoonbills, storks, and some kingfishers.
facing hairs, which they use to draw sap The long, slender tongues of woodpeckers and hummingbirds
out from the drillings they make in trees.
Yellow-bellied protrude for some distance. In these birds, the horns of the hyoid ap-
The tongue of the Bananaquit is forked
Sapsucker paratus of the skeleton curve up and over the skull, in some cases
and has fine, brush-like hairs, which it
uses to absorb nectar and fruit juices. reaching as far forward as the level of the nostrils (see Fig.
This small, common, Neotropical bird 4-12). These slender, flexible skeletal elements act as
is familiar to tourists in the West Indies
White-headed
sliding anchors for the tongue when it is greatly pro- /IA q 111
for its other feeding habits—visiting
feeders and hotel tables, busily search- Woodpecker truded. In addition to being very long, the tongues z iii,
1111p,,,\\i/y) ■
.0.

ing for food scraps. The long, rectangu- of some woodpeckers have backward-projecting
lar-shaped tongue of the Cinnamon Teal barbs at the tips (Fig. 4-91). These help the bird
(a dabbling duck, like the well-known to snag insects and insect larvae when it projects
Mallard) has many hair-like structures
the tongue into a bark crevice or excavation it has
along its outer borders, which it uses
to strain food from the water. Drawings made itself. The tongues of sapsuckers, however,
Bananaquit Cinnamon Teal
after Gill (1995), except sapsucker, by are shorter than those of most other woodpeckers
Charles L. Ripper. and have forward-projecting, hair-like structures.
These form a "brush," which helps absorb and draw
out tree sap from seeping wounds that the bird pre- ,//
viously has made in the trunk and branches. 4
The forked tongues of hummingbirds (Fig. (4)
4-92), besides being long, tend to be folded at the , o,\.
edges, forming little troughs for bringing nectar from the
flowers to the mouth.

II Salivary Glands and Saliva

Salivary glands secrete saliva, the primary function of which is to
moisten food in the mouth. The presence and development of salivary
22, glands in birds is more or less correlated with the kinds of food they
Figure 4-93. The Edible-nest Swiftlet at
eat. Species eating seeds, plants, and insects have well-developed
its Nest: Many swifts and swiftlets have
salivary glands. For example, chickens have several elongate salivary salivary glands that secrete an adhesive
glands beneath the tongue. Birds that normally obtain their food from substance used to attach nesting material
the water have little need to moisten it, however. Anhingas have no to vertical surfaces. The remarkable nest
salivary glands, and the same is probably true for related birds. of the Edible-nest Swiftlet of Indonesia
and Malaysia is constructed entirely of
The Chimney Swift, the European Swift, and certain swiftlets of
saliva. The whitish, bracket-shaped nest
Figure 4-92. Hummingbird Tongues: Hummingbirds have long, the Western Pacific and the Orient have salivary glands that secrete an is placed high on the vertical wall of a
forked tongues whose outer edges become progressively more
adhesive substance used in nest building. Chimney Swifts use the fluid cave, and is surprisingly strong in spite of
curled inward from the tip to the base of the tongue. The cross
to attach nesting materials to vertical surfaces. The swiftlets must pro- its translucent appearance. Nests of this
sections taken at three different regions along the tongue illustrate
species, harvested by skilled, traditional
how the curled edges form a hollow trough or channel through duce copious saliva, for some species—most notably the Edible-nest
gatherers after the birds have finished
which the bird sucks nectar from flowers. The photo shows a hov- Swiftlet (Fig. 4-93)—bu ild their nests entirely of saliva! It is the nests nesting, are in great demand as they
ering female Black-chinned Hummingbird in Arizona extending of these swiftlets, harvested from the high walls of caves, that are used form the main ingredient of the Asian
its long tongue to gather nectar from a cactus flower. Drawing by
in "bird's-nest soup." The nests of species that incorporate the fewest delicacy "bird's-nest soup."
Charles L. Ripper. Photo by Tom Vezo.

Cornell Laboratoni of Ornithologq Handbook of Bird Biolo8q

4.112 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatomtj and Phtisiologq 4.113
non-saliva materials in their nests sell for the equivalent of $400 per
pound ($880 per kilogram)!
A limentary Canal
Throughout the discussion of the various parts of the alimentary
Woodpeckers have a pair of salivary glands that secrete a sticky
canal, you may wish to refer to Figure 4 95. -
fluid onto the tongue. When the bird runs its tongue far into an ant bur-
row, the ants stick to it. A pair of salivary glands in the Gray Jay provides
Esophagus
secretions that make a bolus of food sticky enough to hold together
The esophagus, a relatively straight and thin muscular tube, has
and adhere to any surface where the bird attempts to store it, such as
no digestive glands, but mucus-secreting glands in its walls moisten the
under bark or in crevices between branches.
food, easing passage. In many species, the esophagus can be greatly
expanded to temporarily hold large quantities of food (Fig. 4 96a). -
Pharynx
Gulls, for example, can hold very large fish in their esophagus while
We briefly discussed the pharynx, or throat, in connection with
one end is being digested in the stomach.
the respiratory system, describing it as a crossroads for the passage
Among widely different kinds of birds there are outpocketings of
of food and air (Fig. 4 94; see also Fig. 4 73). The folds of the palate
- -

the esophagus that play various roles. Some outpocketings are sacs,
on the roof of the pharynx surround the openings of the nasal cavities
as in the Emu, grouse, pigeon, and American Bittern, that serve as
and the auditory tube. In the floor of the pharynx, the laryngeal folds
resonators for sound signals in courtship displays. Grouse such as the
border the glottis, the entrance to the trachea. Caudal to the glottis is
Greater and Lesser prairie-chickens (Fig. 4 97) have sacs that, when
-
the entrance to the esophagus.
inflated with air, are used to produce audible "booming" signals. Whi le

Figure 4-94. Structures in the Oral Budgerigar Oral Cavity Figure 4-95. The Alimentary Canal: In
Cavity: In this illustration, the upper and this functional view, the components of
lower beak of a Budgerigar have been the alimentary canal (digestive tract, or
spread apart widely, in a way never seen Tip of Upper Bill gut) of a Rock Dove are shown removed
in nature, presenting a frontal view of from the body and spread apart to illus-
Esophagus
each surface, which allows the structures trate their relationships to each other. The
to be seen more easily. On either side of liver has been moved to the side from its
the entrance to the esophagus (the tube usual medial position, and the length of
carrying food to the stomach)are the up- the bile duct has been exaggerated. The
Crop
per and lower surfaces of the pharynx, various organs are discussed at length in
or throat. The roof (upper surface) of the Choana (Opening of Folds of Palate the text and are shown in greater detail
v
pharynx is termed the palate. Folds in the Nasal Cavities) Bile Duct in the following figures. For a view of
Opening of Auditory
palate surround the opening of the nasal (Eustachian) Tube o'ior u the alimentary canal in a natural position
Proventriculus
cavities, the choana (see Fig. 4-72), within a bird's body cavity, see Figure
through which can be seen the opening „?.
- Stomach 4-64. Drawing by Charles L. Ripper.
of the auditory (eustachian) tube, which Roof of Pharynx
connects the middle ear with the throat, Gizzard
allowing the equalization of pressure
in the middle ear with that outside the Liver
body. In the floor (lower surface) of the
pharynx, laryngeal folds surround the Pancreas
Entrance to Esophagus
glottis, the entrance to the respiratory
system. A salivary duct, which secretes
Floor of Pharynx
saliva into the mouth, can be see anterior
Small
to the glottis in this species; the numbers Intestine
and locations of such ducts vary consid- Duodenum
erably among species. Notice the short,
rounded, muscular tongue, which the Laryngeal Folds
Budgerigar uses to manipulate food;
compare this to the other avian tongues Glottis
in Figs. 4-91 and 4-92. Adapted from Salivary Duct
Evans (1996).
Ceca
— Large Intestine

Cloaca

Tip of Lower Bill Vent

Cornell Laboratorq of Ornithologq Handbook of Bird Biolopi

4.114 Howard E. Evans and,J. 13. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.115
Figure 4-96. The Esophagus: The inflated, the sacs protrude dramatically. Being covered with bright
esophagus is a relatively straight, thin, yellow or orange skin, they also provide visual signals that enhance
muscular tube, lacking digestive glands, the total display.
which conveys food between the mouth
Other esophageal outpocketings are simple dilations for carrying
and the stomach. A number of different
esophageal adaptations for storing food seeds, as in Common Redpolls and other finches. About 15 families
are found among birds. a. Cormorant: of birds (including the fowl or gallinaceous birds, pigeons and doves,
In many birds, such as cormorants, the and some passerines), most of which eat dry seeds or fruit containing
esophagus can be temporarily enlarged
seeds, have a permanent dilation of the lower esophagus called the
to hold food. Note that part of the Esophagus
cormorant's esophagus has been omit-
crop (Fig. 4 96b) for the storage of food. A thin layer of muscle over
-

ted to shorten the drawing. b. Chicken: the surface of the crop squeezes the crop to empty its contents back
Gallinaceous birds such as the chicken, to the esophagus for passage to the stomach. The crop of the South
as well as pigeons, doves, and some American Hoatzin (Fig. 4 98; see also Fig. 3-41) is thick-walled, mus-
-

passerines, store food in a permanent

cular, and exceptionally large. Hoatzins feed on the thick leaves of
dilation of the lower esophagus known Part of Esophagus
as the crop. Crops are generally found Omitted arums, tropical plants related to the popular houseplants often called
in species that eat dry seeds or fruit "Arrowheads," and the crop actually grinds the food and initiates the
containing seeds. Drawings by Charles first stages of digestion through bacterial fermentation—a rather odor-
L. Ripper.
iferous process. Consequently, the birds are locally known in several
regions as "stinking turkeys"!
Some of the most interesting esophageal specializations have
evolved in birds whose adult diet is indigestible or inaccessible to
Stomach their offspring. Only a small portion of living birds subsists directly on
plant material, a feeding specialization that departs from the common,
ancestral avian diet of animal tissue. Most plant-feeding specialists
initially feed their young on animal matter, usually soft invertebrates
such as insects and spiders, further indicating that plant eating prob-
a. Cormorant b. Chicken

Esophagus

Reduced Proventriculus and Gizzard

Figure 4-97. Greater Prairie-Chicken
with Booming Sacs Expanded: The
Enlarged Crop
esophagus of some birds has out-pocket-
Small Intestine
ings that act as resonators for the sounds
produced during courtship displays.
Grouse, such as the Greater Prairie-
Chicken pictured here, have esophageal
sacs that inflate with air and are used to
create deep "booming" sounds. These
sacs are often highly colored, being
yellow or orange in prairie-chickens
and purple in Rocky Mountain popu-
lations of Blue Grouse. Other species
with esophageal sacs used in sound
Figure 4-98. The Digestive Tract of The Hoatzin: The crop of the South American Hoatzin is thick-walled, muscular, and excep-
production include Emus, bitterns,
tionally large. Hoatzins are unusual birds because they eat mostly leaves, which contain much cellulose and woody materials
and pigeons. Photo courtesy of Mary
that are difficult to digest. The Hoatzin's enlarged crop starts the long digestive process by grinding the food and beginning its
Tremaine/CLO.
chemical breakdown through bacterial fermentation. Adapted from Proctor and Lynch (1993, p. 184).

Cornell Laboraton4 of OrnitholoN Handbook of Bird Biolom

4.116 Howard E. Evans and J. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.117
ably evolved from insect eating. The
American Goldfinch, however, feeds
almost entirely on seeds as an adult,
and also feeds its young exclusively
on a finely chopped mass of seeds that
seems to be partly digested (Fig. 4 99a).
-

o4111 .1 11 11111 uui I '

The food mass, however, is thought to manofill ' . 11111110qviifiliii„ „
be regurgitated from the non-digestive
crop. The greater availability of seeds
later in the plant growing season may Figure 4-100. Male Emperor Penguins
Incubating their Eggs: Huddled to-
explain why goldfinches are such late •

gether for warmth as snow blows and

nesters, not starting nest building until wind howls during the gloomy Antarctic
mid to late summer. winter, nesting male Emperor Penguins
More specialized yet is a habit in await the end of their two-month incu-
bation vigil. Soon the single, large egg
pigeons and doves, highly specialized
that each holds on top of his feet, warmed
a. American Goldfinch seed- or fruit-feeders as adults. Instead and hidden by a muff of belly skin, will
........ ...

of feeding their squabs on insects as hatch. Immediately after laying the egg,
.............

most seed-eating birds do, pigeons and early in the Antarctic winter, the female
returned to the sea, leaving her mate to
doves slough fluid-filled cells from the
incubate entirely alone, with no pos-
crop lining to produce "pigeon's milk" sibility of obtaining food. Before the
(Fig. 4 99b). Pituitary prolactin stimu-
-
female returns with food, the chick may
lates the crop milk production of both hatch, getting its first few meals in the
sexes during the last 10 days to one Mr" form of a curd-like esophageal secretion
provided by the male.
week of incubation. Crop milk alone
is fed to hatchlings for the first four or
five days, but thereafter is mixed with
increasing amounts of seeds through
the fledging of the young. Pigeon's
crop milk is a lipid-rich material of a
"cheesy" consistency, high in vitamins
A and B and with a greater protein and
A final case of a specialized esophageal secretion that has
fat content than human or cow's milk!
b. Mourning Dove evolved in birds whose adult diet is indigestible or inaccessible to
The crop also may come to the
their offspring is that of the flamingo. As previously discussed, the adult
Figure 4-99. Raising Young Birds on a Diet of Plants: Birds whose adult diet is aid of the male Emperor Penguin, who
flamingo's diet (bacteria, algae, aquatic insect larvae and pupae, tiny
composed mostly of plant material, which their newly hatched offspring may somehow survives two months in the
find indigestible or otherwise inaccessible, have developed special strategies shrimps, and so on) is captured exclusively by the complex filtering
dead of the Antarctic winter incubating
for feeding their young. Many seed-eaters simply feed their young insects and bill and tongue apparatus. For the two months that it takes hatchlings
his single, large egg on the tops of his
other small invertebrates, increasing the proportion of seeds or fruit as the to develop the special filter-feeding apparatus of the adults, young
digestive capabilities of the young birds improve. Other species enlist the aid feet (Fig. 4 100)! In the dark and storms
-

flamingos consume only an esophageal "milk." The secretion is not

of their crops. a. American Goldfinch: The American Goldfinch feeds almost of midwinter he may find himself with a
produced from a crop, but from glands along the esophagus and up-
entirely on seeds as an adult, but also feeds its young exclusively on seeds. hatchling before his mate has found her
Here a female feeds its nestlings a mass of regurgitated seeds, partly broken per stomach of the parents. Even richer in fat than pigeon crop milk,
way across as much as 185 miles (300
down and mixed with sticky fluid. Although the finely chopped mass is thought it contains an abundance of red and white blood cells, and is red in
to be regurgitated from the crop, it appears to be partly digested—providing
kilometers) of ice to bring food to the
color. Flamingo milk has a liquid consistency—probably the only
a puzzle for researchers. b. Mourning Dove: Pigeons and doves, which eat chick and parental-duty relief to him. In
form of nutrition compatible with the developing filtering apparatus.
seeds and fruit as adults, have specialized crops that produce "crop milk" or this crisis the male can produce a rich
"pigeon's milk," which they feed to their young. Crop milk consists of a highly A thicker secretion, such as that of pigeon's milk, would no doubt clog
esophagus and crop milk for a few days
nutritious slurry of fluid-filled cells that slough from the lining of the crop. In the chick's growing straining bristles. In addition, flamingo chicks are
until his mate arrives. She then takes
this photo, an adult Mourning Dove is regurgitating crop milk to a second reared on shadeless islands in high-saline lakes, and thus may require
nestling, mostly hidden by the large nestling in front. As the young doves over, ready to regurgitate the fish and
squid she caught at sea, a diet on which considerable water in their diet.
grow, their diet will include an increasing proportion of seeds and other plant
material. Photos courtesy of Mike Hopiak/CLO. These cases of upper digestive tract secretions demonstrate con-
the chick will dine thereafter.
vergent evolution in providing the essential energy and especially the

Cornell Laboratorq of Ornithologq Handbook of Bird BioloBq

4.118 Howard E. Evans andJ. B. Heiser Chapter 4— What's Inside: Anatomq and Pligsiologq 4.119
Figure 4-1 01 . Stomachs of Grain-eating From The latter, a fish-eater with a long, thin neck, has a diverticulum (out-
Versus Meat-eating Birds: In most birds, Esophagus
pocketing) of the proventriculus and an enlarged area in the pyloric
the stomach has two parts. The upper
part, the proventriculus, is elongate
part of the stomach. These probably store fish near the center of mass,
From
and has glands that secrete enzymes Esophagus without disrupting neck streamlining, as the food awaits room in the
that begin the digestion of proteins. The lower gut for digestion.
lower part, the gizzard, is rounded and The gizzard or ventriculus has thick, muscular walls and a lining
Proventriculus —
has thick, muscular walls, often with
Pylorus
of leathery or sandpaper-like material called gastric cuticle or koilin.
hard internal ridges; it functions to grind
food. Seed-eating birds, such as the tur- Koi I i n is a combination of carbohydrate and protein secreted by glands
key, often eat grit or small stones with in the wall of the gizzard. When the gizzard is cut open, this lining can
their food to aid the gizzard in grinding, be peeled from the wall (as is done in the supermarket before sale).
but the power for grinding comes from Gizzard —
1 °00.1; Shedding and resecretion of the lining is probably a more or less reg-
the strong gizzard muscles. In the sec- Proventriculus —
0.g0 Pylorus ular natural occurrence that maintains the efficiency of food mashing
tions through stomachs shown here, 00 o ,

compare the far more muscular gizzard by restoring the toughness of the lining when it becomes worn.
Small
of the turkey to that of the meat-eating
Hawk
Seed-eating birds with well-developed gizzards, such as the
Intestine
hawk. The digestion of seeds requires (Meat-Eater) chicken, quail, turkey, and many ducks and swans, eat mineral grit
much more mechanical grinding than
or small stones along with their food to aid the gizzard in grinding.
the digestion of the proteins in meat. The Muscular Wall
less muscular gizzards of birds that eat The power for grinding comes from the inner circular muscles of the
meat or fish mold indigestible material, Gizzard Lining gizzard, which are enlarged compared to those in the stomachs of
such as bones, fur, feathers, and the outer gizzardless vertebrates; the outer longitudinal muscles have been lost.
skeletons of insects, into compact balls,
The enlarged muscular walls, with their hard internal ridges, contract
known as pellets, which are then ejected
through the mouth (see Fig. 4-102). The in alternating directions, grinding the food with the aid of ingested grit.
pylorus, a muscular sphincter (a circular The gizzard, made more efficient by grit, thus performs part of the work
band of muscle), regulates the passage of Turkey done by the teeth in mammals. If you hold a live chicken that has eaten
food from the stomach into the small in- (Grain-Eater) recently against your ear, you can hear the grinding process inside the
testine. Drawings by Charles L. Ripper.
gizzard. The Ostrich, holder of so many avian big-size records, has
been recorded to ingest stones up to one inch (2.5 cm) in diameter.
protein needed for hatchling growth in the absence of animal food. Unfortunately, some man-made objects are the ideal size for
They have allowed certain species to reproduce successfully in the face large birds to select as gizzard digestive aids. For example, lead shot
of competition and extreme environmental conditions. As such they from the guns of bird hunters kills enormous numbers of birds that are
parallel, in many ways, the adaptations of mammals for providing the never hit by gunfire. Stray pellets strewn in the environment have been
earliest possible nutrition for their offspring. accumulating for a hundred years or more, for they do not "rust," and
thus deteriorate very slowly. When birds ingest the pellets as grit, they
Stomach are pulverized by the grinding action of the gizzard and lead toxins
Nearly all birds have a two-part stomach (Fig. 4-101). The first are absorbed into the bloodstream from the stomach and intestines. A
portion, the proventriculus, is elongate and has gastric glands whose slow death from liver and kidney damage and digestive tract paralysis
secretions begin the breakdown of proteins in the food. The second ensues. In the English Midlands more than half of the dead Mute Swans
part of the stomach is a rather spherical, muscular gizzard that func- tested had died from poisoning following ingestion of lead weights
tions to grind the food. The stomach ends in a muscular constriction, lost by anglers!
the pylorus. Fruit-eating pigeons, such as the large, bulky Imperial-Pigeons
The proventriculus secretes mucus, hydrochloric acid, and an (genus Ducula)of Southeast Asia, have raised bumps like blunt fingers
inactive precursor to pepsin, an enzyme that digests protein. The on the inner surface of the gizzard. These interdigitate during contrac-
pepsin, activated by the acid in the proventriculus, begins breaking tions and thus act as a toothed "polishing wheel" that functions to peel
down proteins. In a few birds, for example petrels, cormorants, herons, fruit and remove the flesh from enormous pits such as those of nutmeg;
gulls, terns, some hawks, and some woodpeckers, the proventriculus the pits are then voided. Several fish-eating birds, including anhingas,
is expandable and can hold food temporarily. This is an adaptation for do not have enlarged muscles of the gizzard for grinding and thus the
feeding the young back at a distant nest or for delayed digestion by proventriculus and the lower region of the stomach appear similar in
the individual. Several birds have enlargements in the pyloric region structure.
between the stomach and the duodenum, the first part of the small In some carnivorous birds, indigestible or slowly digesting
intestine, probably for storing food. A distinct chamber forms in the bones, teeth, feathers, fur, and insect parts are formed into a pellet
Ostrich, some herons (of the genus Ardea), cormorants, and anhingas. in the gizzard that the bird can readily regurgitate after digesting the

Cornell Laboratorg of Omithologq Handbook of Bird Biolom

4.120 Howard E. Evans and,J. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiologq 4.121
Figure 4-102. Pellets of a Barn Owl: In Most of the products of digestion are absorbed by the lining of
various carnivorous birds, the parts of the intestinal wall and pass into the bloodstream. The products of fat
their prey that are indigestible or difficult
metabolism, however, are absorbed primarily into the channels of the
to digest, such as bones, teeth, feathers,
fur, and the outer skeletons of insects, are lymphatic system, which eventually dump them into the bloodstream
compressed into a pellet in the gizzard, for distribution to the body cells. The inner surface of the small intes-
and expelled by regurgitation after the tine has longitudinal folds and minute, finger-like projections in some
bird has digested the flesh. Birds that birds—hawks and other carnivores—and flattened, leaf-I ike structures
produce pellets include meat-eaters
in others—flamingos and many herbivores. Both greatly increase the
such as owls, hawks, and shrikes; fish-
eaters such as kingfishers and grebes; surface area for absorption, but why there are differences that seem to
and insect-eaters such as thrushes, parallel the birds' primary food types is unknown.
nightjars, and bee-eaters. Owl and
hawk pellets may be found beneath nest
trees or roost sites. This photo shows two Aorta
pellets from a Barn Owl. The pellet on
the left has been pulled apart to show its a
Liver
contents. Visible within the fur are limb
bones, jawbones, and part of the verte-
flesh (Fig. 4-102). This habit is characteristic of owls, hawks, grouse, Hepatoenteric Ducts Proventriculus
bral column of a small rodent. Photo
(Bile Ducts)
courtesy of Virginia Cutler/CLO. nightjars, swifts, kingfishers, shrikes, and some thrushes. A pellet from
one screech-owl contained a whole tarsal bone of an American Gold- Spleen
Villi
finch, complete with a numbered metal identification band! For the
first month after hatching, young kingfishers digest the entire fishes
brought to them by their parents, including scales and bones. With Jejunum Gizzard

the development of flight feathers and full size, however, the demand
for calcium and related minerals becomes less and the young king-
fishers start producing pellets of fish bones and scales. By the time
they actually start flying, the bones and scales of their prey are cast up Epithelial Cells
in such good condition that the species of the catch of the day can be With Many
Ileum Microvilli
identified! Rectum of Large Intestine
Grebes, which are primarily fish-eaters, cast pellets consisting Vitelline
Diverticulum
of mostly indigestible plant food and their own feathers. Apparently, Pancreas
the strong acid in the grebe's stomach dissolves most of the fish bones.
Some ornithologists believe that the feathers (and perhaps the plant
matter) the grebe eats act as retainers, keeping the bones in the stom-
ach long enough for them to digest. Also, the indigestible matter may
encapsulate sharp spines and bone edges, preventing damage to the
stomach while the bones are dissolved, and preventing damage to
the esophagus during pellet regurgitation, if any sharp pieces were to Figure 4-103. The Small Intestine: a. Location within Digestive termed hepatoenteric ducts. The small intestine is named for
remain. Tract: In this functional view of the Budgerigar digestive tract, its narrow diameter, not its length, which varies greatly among
The contents of the proventricu I us enter the gizzard very close to the small intestine has been spread out so that its parts may be species, depending on their diet. Birds that feed on foliage or
seen more easily. The small intestine begins at the pylorus at the grain have longer small intestines than those that feed on fruit
the pylorus with its muscular sphincter, which marks the beginning of
lower end of the stomach, and is the longest section of the di- or meat, reflecting the difficulty of digesting the cellulose in
the small intestine. This allows the more liquid portion of the digesting gestive tract; the site where the final processes of digestion take plant material. The end of the ileum marks the beginning of the
food to bypass the grinding chamber of the gizzard. place. Its successive regions, the duodenum, the jejunum, and large intestine. b. Cross Section through Small Intestine: Visible
the ileum, look similar externally, but their glandular structure here are numerous folds, known as villi (singular villus), which
Small Intestine and food-processing functions differ. At the junction between greatly enlarge the small intestine's surface area for absorbing
The small intestine is the longest part of the digestive tract (Fig. the jejunum and ileum there is often a tiny vitellinediverticulum, nutrients. c. Cross Section through a Single callus: Visible in
a remnant of the embryo's yolk sac. Secretions into the small this highly magnified view are the epithelial cells that form the
4-103). This is where the final processes of digestion take place, re-
intestine from the pancreas and liver carry out digestion. Bile, inner lining of each villus. Each cell is edged with microscopic
ducing proteins to amino acids, carbohydrates to simple sugars, and important in fat digestion, is produced by the liver but stored cylindrical processes, termed microvi I I i, that further increase the
fats to glycerol and fatty acids.The small intestine includes regions, the in the gall bladder. Several small bile ducts carry bile from the surface area inside the small intestine for absorption. Drawing
duodenum, jejunum, and ileum, that do not look any different from gall bladder into the small intestine. Some birds, including the a from Evans (1996). Insets from A Dictionary of Birds, by Bruce
Budgerigar pictured here, lack a gall bladder; in these birds the Campbell and Elizabeth Lack. 1985. Reprinted with permission
each other externally, but whose walls have characteristically distinct
ducts that transport bile from the liver to the small intestine are of the British Ornithologists' Union.
cells and functions.

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4.122 Howard E. Evans and& B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiolos 4.123
Secretions from small glands in the wall of the intestine, as well of tissue, which is a remnant of the yolk sac of the embryo. The ileum
as from the pancreas, carry out digestion. Bile, secreted by the liver, becomes the large intestine at the point where the ceca attach.
neutralizes the acid passing into the intestine from the stomach and
also emulsifies the fats (divides them into tiny particles that can be Colic Ceca
more easily digested). The colic ceca (also spelled caeca; singular, cecum or caecum)
The small intestine is named because of its diameter, not its are a pair of pouches extending from the junction between the small
length. Its length varies, in general, with the diet and size of the bird. and large intestines (Fig. 4-104). They function in digestion by hold-
Birds that eat grass and other foliage or grain have a small intestine ing material long enough for bacterial action to further break it down.
that is relatively longer than that of fruit-and meat-eating birds because They then release the material into the large intestine for absorption of
cellulose, a main structural component of plant matter that is generally whatever nutrients have been made available by the bacteria. Herons
absent from fruits, makes extracting nutrients from leaves and seeds a and bitterns have a single cecum rather than a pair, and ceca are absent
difficult process. In the grazing Ostrich, for example, the small intestine entirely in some species of woodpeckers, swifts, kingfishers, doves,
Small
is 46 feet (14 m) long! Fish-eating birds also tend to have a long small cuckoos, and parrots. They also are absent or merely buds in anhingas Intestine
intestine, presumably because fish prey are usually swallowed whole and some hummingbirds.
and require much work to digest efficiently. On the other hand, two pairs of ceca have been reported in the
Among plant-eating birds, the Blue Grouse and Spruce Grouse snake-eating Secretary Bird of the African savannahs. The Ostrich and
feed largely on conifer needles—a low-grade food. The small intes- gallinaceous birds, especially the turkey, have very large ceca that of-
tines of these grouse are about 28 percent longer than those of similar ten harbor intestinal coccidia, protozoans more commonly associated
gallinaceous birds that feed on a higher grade, more nutrient-rich, with parasitic disease. In some species there are outpocketings that
food. Even in the same species, intestinal length may differ among enhance the potential fermentation space of the ceca; these are found
populations when food habits differ.The race of California Quail living in the Ostrich, rheas, kiwis, loons, screamers, bustards (at least of the
along the humid coast of northern California eats considerably more genus Otis), and sand grouse (at least of the genus Pterocles).
green food than the race inhabiting the arid interior of the state, where Gall inaceous birds that browse on grass or other foliage have
seeds and other richer foods are favored. The greens-eating race has longer ceca than their relatives that eat seeds. For example, Grouse,
a small intestine that is 11 percent longer than that of the seed-eating which browse, have ceca as much as 136 percent longer than the ceca
race, reflecting the fact that leaves have a higher ratio of cellulose to of seed-eating quail. Possibly the bacteria in the ceca break down the
Colic
digestible nutrients than do seeds. cellulose in the tough fibers of the grass. In the two races of California Ceca
The small intestine is proportionately shorter in birds than in mam- Quail mentioned previously in connection with intestinal length, the
race eating more green food has ceca about 19 percent longer than Large
mals, and the speed with which food passes through the alimentary Intestine
canal, from mouth to vent, is correspondingly faster. A shrike or a the race eating mostly seeds.
magpie can completely digest a mouse in aboutthree hours; a chicken
Large Intestine
digests grain in about two and one-half hours. Adult and nestling birds
In most birds, the large intestine is a short, straighttube extending
fed berries will pass the seeds within 12 to 30 minutes of first ingesting
from the colic ceca to the cloaca. The large intestine functions to hold Figure 4-104. Colic Ceca of the Grouse:
the berry! In contrast, a small mammal such as a mouse usually takes
intestinal contents while water (and perhaps nutrients made available Illustrated here is the location of the
24 hours or more to pass food completely through its digestive system
by the bacteria in the ceca) is being reabsorbed; the indigestible ma- paired colic ceca at the junction of the
(Milo Richmond, personal communication). small and large intestines. The ceca aid
terial then passes to the cloaca.
The U-shaped duodenum is the first loop of the small intestine. digestion by holding partly digested
The pylorus, a circular band of muscle, marks the end of the stom- material while bacterial action further
Cloaca breaks it down. The ceca then release the
ach and the beginning of the duodenum. It serves as a closed gate to
The cloaca receives feces from the large intestine, urine from the material into the large intestine, where
the small intestine, its muscles only loosening to let food pass when kidneys, and eggs or sperm from the gonads (Fig. 4-105). Because the any nutrients made available by the bac-
stomach digestion is complete. Most of the pancreas lies within the intestine ends in the cloaca there is no anus but rather a common vent teria are absorbed. The size and number
duodenal loop, and into this loop enter the ducts from the pancreas of ceca vary among species. In the
that opens from the cloaca to the exterior of the body. The cloaca! bursa
and several bile ducts from the liver and gall bladder (when one is grouse, shown here, they are relatively
is a lymphoid organ that opens into the roof of the cloaca in young birds large and elongated. In the Rock Dove
present). Many birds lack a gall bladder to collect the bile produced and atrophies in later life. The bursa has no known digestive function. (see Fig. 4 95) they are short and leaf-
-

by their livers. like. In parrots such as the Budgerigar

First described by Hieronymus Fabricius in the 17th century (and thus
The long jejunum and the short ileum are the divisions of the long called the bursa of Fabricius), an understanding of its function (see Fig. 4-103), and various other spe-
remainder of the small intestine. Both are looped and coiled and lack cies, ceca are absent entirely, whereas
has become significant to modern medical research. The structure is in some species two pairs are present.
external distinguishing characteristics. At the junction of the jejunum important in the immune response because it produces B cells, special Drawing by Charles L. Ripper.
and ileum there is often a vitelline diverticulum, a small, blind pouch
white blood cells that populate the lymphatic tissues and are a key

Cornell Laboratorq of Ornitholo5q Handbook of Bird Biologq

4.124 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatoniq and Phiisiologq 4.125
Figure 4-105. The Cloaca: In contrast Rock Dove Cloaca, Sagittal Section from hazards in the environment; thus the sex drive has evolved to be a
to mammals, which have separate ex-
strong and basic instinct. Natural selection operates through individual
its from the body for the digestive and
urogenital systems, birds have a com-
Large Intestine reproductive superiority, however slight, over time producing repro-
mon final chamber, the cloaca, which ductive adaptations that may be exceedingly complex in species that
Cloacal Bursa
is diagrammed here for the Rock Dove (Bursa of Fabricius) continue to survive. These adaptations provide bird enthusiasts with
in sagittal section. The cloaca receives some of our most exciting and memorable observations.
feces from the large intestine, urine from Opening of Ureter Unlike other systems in the bird's body, the reproductive system
the kidneys through the paired openings (from Kidney)
of the ureter (only one is shown here), is active only part of the year in many species. This is especially true for
Opening of Oviduct
and eggs or sperm through the paired birds living in environments that change with the seasons. Following
or Deferent Duct
openings of the oviduct or deferent the breeding season, these birds' reproductive organs and ducts (espe-
duct, respectively (only one is shown).
cially the testes, ovary, and oviduct) regress. They remain small until
The cloaca! bursa (previously known as
the bursa of Fabricius) is a lymphatic or-
just before the next season, when they enlarge again. This cycle un-
gan opening into the roof of the cloaca, doubtedly relates to the "cost" of excess baggage in flying animals.
Circular Muscle
present only in young birds, which func- Controlling Vent
tions in immunity (see text for details).
The cloaca opens to the exterior through Urinary System
the muscular vent, through which both The urinary system, sometimes called the excretory system,
Vent
the waste materials of digestion and
consists of paired kidneys and their excretory ducts, the ureters (Fig.
the products of reproduction—eggs or
sperm—pass. Drawing by Charles L. Epidermis
4-106). The kidneys are irregularly shaped structures, with three inter-
Ripper. connecting lobes in most birds. Sometimes the left and right kidneys
to understanding AIDS development in humans. There are strains of connect caudally to form a horseshoe-shaped kidney. The kidneys lie
"bursa-less" chickens, bred for research, that are unable to fight infec- deep in depressions on the ventral face of the pelvis and the synsacral
tions because they have no B cells. vertebrae and have obvious blood vessels crossing their ventral sur-
face. A tube from each kidney, the ureter, conducts the thick, white
Liver slurry of uric acid to the cloaca. Here it either mixes with the feces, or
The liver, the largest internal organ of the body, has two lobes. In surrounds it as in the Budgerigar, to form a "bull's-eye" dropping. The
most birds, the right lobe is larger than the left. From each lobe several only birds with a urinary bladder are the South American rheas. This
bile ducts lead directly into the duodenum. Many birds have a gall may seem surprising, considering that urinary bladders are a regular
bladder, a reservoir for the storage and concentration of bile secreted feature of vertebrate anatomy. Why should this be? And why is the urine
by the liver. Depending upon the species, the gall bladder may be of birds so different from that of mammals?
oval, sac-like, or long and tubular. However, many birds have no gall In all vertebrates, the liver converts the toxic nitrogenous wastes
bladder, including the Ostrich, the Hoatzin, parrots, cuckoos, hum- of protein metabolism into less toxic and more efficiently excreted
mingbirds, many pigeons, and some woodpeckers and passerines, as forms. In birds this liver-synthesized substance is uric acid, not the
well as at least the Peregrine Falcon among raptors. Besides producing urea created by mammals and some other vertebrates (Fig. 4-107).
bile, which emulsifies fats for better digestion, the liver has many other Uric acid is a more complex molecule than urea and thus probably
functions such as storing sugars and fats, forming uric acid, and re- takes more energy to synthesize, but it has two advantages over other
moving foreign substances from the blood. Accordingly, the liver is excretory compounds. First, it is very concentrated, containing more
richly supplied by the circulatory system. of the potentially toxic nitrogenous wastes per molecule than does
urea—thus ridding the body of more wastes per excreted molecule.
Second, it is not nearly so soluble in water as is urea. Thus to excrete
The Urogenital Stistem nitrogenous wastes, a bird does the following: The kidneys reabsorb
■ The urogenital system includes the urinary system and the repro- most of the water and then excrete a fluid containing a solution of uric
ductive system. The two systems are considered together because of acid that is very near to the concentration at which precipitation of the
their intimate developmental and anatomical relationships. The uri- uric acid would begin to occur. When this solution reaches the cloaca,
nary system develops first and is vital in removing toxic nitrogenous only a small amount of water needs to be withdrawn (an energy-in-
wastes from the circulation. Some of its ducts are also used in the adult tensive process) through the walls of the cloaca to cause the uric acid
bird for reproductive functions. to precipitate to a semisolid, white, pasty mass. The water remaining
The survival of any species depends upon the reproductive suc- in the cloaca (which the precipitate has left behind) is therefore free of
cess of its individuals. If its genes are to survive, an individual bird's re- nitrogenous waste and can be reabsorbed by the body relatively eas-
productive rate must be great enough to offset all the losses of offspring ily, and the precipitated uric acid is then excreted. Mammals, on the

Cornell Laboratorq of Ornitholos Handbook of Bird BioloBq

4.126 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatomq and Phqsiologq 4.127
other hand, must take a solution of urea in water and expend a great
deal of cellular energy withdrawing water from it to concentrate it.The
urea never precipitates, so in urinating, mammals lose more water per
amount of nitrogen waste excreted than do birds. Thus, compared to Converts Toxic
mammals, birds conserve both water and energy during excretion. Nitrogenous Wastes into
BIRD MAMMAL
Because uric acid is a compact, low-volume mass, the cloaca
is all the storage space most birds require for nitrogenous wastes,
explaining why few species have a urinary bladder. The compact
URIC ACID
• Complex molecule
V T(Via
Circulatory
System)
'N41/4, UREA
• Simple molecule
Figure 4-106. Urogenital Sys- nature of bird urine is yet another weight-reduction adaptation for • H ighly concentrated: • Less concentrated:
tems of the Male and Female: flight—birds could not afford to carry the extra weight of the water contains more toxic contains less toxic
The urogenital system consists nitrogen per molecule nitrogen per molecule
that would be required to hold a solution of urea. The great difference
of the urinary and reproductive than urea than uric acid
systems, which share develop- • Low solubility in water Resorbs Water • High solubility in water
mental and anatomical links. Resulting in
The urinary system, like most
Male Urogenital System
other body systems, is active
year round. In contrast, the INACTIVE ACTIVE
Near-saturated Concentrated
reproductive system of many Testes
Solution of Uric Acid (But Not Near-saturated)
birds is active for only part of the Solution of Urea
year; the reproductive organs, or
gonads, and their ducts shrink
411 IMP
after breeding, enlarging again
Kidney
just before the next breeding
season. This figure shows both Removes More Water Stores and Releases
the inactive and active states Resulting in
of the urogenital systems of
male and female Rock Doves. Ureter
The urinary system consists of
Deferent Duct
paired, three-lobed kidneys (Vas Deferens)
with their ducts, the ureters,
which transport uric acid, the Intestine Semi-solid, White Pasty Mass Liquid Solution of Urea (Urine)
waste product of excretion, to of Uric Acid • Conserves less water
Semen
the cloaca. The urinary bladder, Storage • Conserves more water than than bird during excretion
which stores urine in mammals, Receptacle mammal during excretion • Bladder present: weight reduction
is absent in most birds. The male • Bladder absent (except in the less important than for bird
gonads, the paired testes, lie at Cloaca flightless rheas): this reduces
the cranial end of the kidneys. weight, an adaptation for flight
Sperm produced in each testis
is conveyed as semen through Female Urogenital System
the deferent duct (vas deferens), INACTIVE ACTIVE
the lower portion of which is
Left Ovary
enlarged to form a temporary between bird and mammal urine is a clue to how long the two groups Figure 4-107. The Formation of Uric
storage receptacle. During of vertebrates have been evolving separately, and to how differently Acid Versus Urea: This schematic com-
copulation, semen from the stor- Left Ovary pares the formation of uric acid in birds
evolution has proceeded in each.
age receptacle exits the body Kidney with the formation of urea in mammals.
through the cloaca. The female See text for details.
gonad, the ovary, produces ova Infundibulum of
(eggs) at periodic intervals in a Oviduct Genital System.
process known as ovulation. In
most birds, only the left ovary is Ureter Male Genitals (see Fig. 4-106)
functional. The ova pass through The male gonads, testes (singular, testis), produce the sperma-
Left Oviduct Left
a funnel-shaped infundibulum Oviduct tozoa (also called sperm cells or sperm), each of which consists of a
and into the oviduct, exiting
the body at the cloaca. Figure Intestine single cell composed of a DNA-containing head and a propulsive tail.
4-1 11 details an ovum's journey Birds have two types of sperm cells (Fig. 4 108): a short, simple type
-

and the steps that transform it Rudimentary Right Oviduct — in nonpasserines, and a longer, spiral-shaped cell in passerines. The
into the familiar, hard-shelled, testes themselves are oval or elliptical and lie within the body cavity
bird's egg. Drawings by Charles
Cloaca at the cranial end of each kidney. One, usually the left, is larger than
L. Ripper.

Cornell Laboratorg of Ornithologq Handbook of Bird Biologii

4.128 Howard E. Evans and 3. B. Heiser Chapter 4 — W hat's Inside: Anatomq and Phqsiolo,9q 4.129
Figure 4-108. Passerine and Nonpas- Passerine Spermatozoon Figure 4-109. The Cloaca! Protuberance
serine Spermatozoa: The sperm cell, (European Greenfinch) of a Breeding Male Song Sparrow: In
or spermatozoon, consists of a head male passerines, the cloacal region
containing the genetic material DNA, becomes swollen during the breeding
and a long, mobile tail which, during season, reaching its peak size when the
insemination, propels the sperm along bird is in full reproductive condition.
the female reproductive tract. This highly This cloaca! protuberance is visible in
magnified view shows the two types of a hand-held bird with the vent feathers
avian sperm. In non passerines, such as parted; its presence is used by banders to
the chicken, sperm are simple in struc- determine the sex of breeding birds. The
ture. In passerines, such as the European protuberance is caused by the seasonal
Greenfinch, the head and much of the enlargement of structures in the terminal
Tail
tail of the sperm has an elaborate, helical regions of each deferent duct. These
structure, and the entire cell is much lon- structures are the seminal glomus, an
ger than that of a nonpasserine. Drawing Non-passerine Spermatozoon elaborately coiled region that develops
(Chicken) only in passerines and contains densely
by Christi Sobel.
packed active sperm, and an adjacent
spindle-shaped receptacle, present in all
birds, that opens into the cloaca through
a flap of tissue called a papilla (see also
Fig. 4-110). During copulation the
cloaca is everted, and the papillae may
actually enter the female's oviduct. The
presence of the cloacal protuberance
Ve 3.
.

VSt\11 in passerines suggests that maturation

Tail eak\ of their sperm may be temperature
sensitive: the protuberance may help
to keep sperm slightly cooler than the
the other. With the approach of the breeding season, the anterior lobe body's core temperature, much as the
Cloacal
scrotum does in mammals. Why this
of the pituitary secretes gonad-stimulating hormones that start the Protuberance
should be necessary only in passerines
growth of the testes, which increase in size from several hundred to remains unclear.
nearly a thousand times! Sperm produced within the testes move by
the deferent ducts (vasa deferentia) to the cloaca. The deferent duct
is so convoluted that it appears to have striations across it. A cloaca!
protuberance at the caudal end of the deferent duct is common in pas-
serines. It may enlarge so much in the breeding season that it causes an
obvious protrusion of the cloacal region (when seen from the exterior),
a positive indication that a bird is a male in breeding condition (Fig.
4-109). I n most birds, this protuberance is caused by a swelling at the Dorsal View
end of each deferent duct, which opens as a papilla into the cloaca. Figure 4-110. The Cloaca! Phallus of
The cloaca is everted during copulation, and the papillae may slightly a Male Domestic Duck: In this view
Openings Papillae of
enter the female's oviduct. In all ratities and waterfowl, there is a bet- the dorsal half of the cloaca has been
of Ureter Deferent Ducts removed, to show its ventral floor,
ter-developed copulatory organ, the cloaca! phallus (Fig. 4-110).
whereas the spiral-shaped, ridged clo-
This structure, often called a penis, is not the same as that of a mam- aca! phallus, shown in the erect position,
mal because it lacks an internal urethra—so sperm must travel on its is intact. This copulatory organ, present
surface. Also, it erects by lymphatic pressure rather than by the blood only in waterfowl, and ratites, is erected
by means of lymphatic pressure. Note
vascular network responsible for mammalian erection. Presumably
the locations of the papillae of the def-
Viagra would not help an aging Leda's swan. erent ducts, through which sperm are
Cloacal
Phallus transported from the deferent ducts into
Female Genitals (see Fig. 4 106)
-
the cloaca. During copulation, sperm
Large
The female gonad (ovary) ovulates eggs (also called ova; singular, Intestine
travel a long the outer surface of the phal-
ovum) at periodic intervals during the breeding season. As in mam- Cloaca lus. Adapted from King and McLel land
(1981, Vol. 2, p. 76).
mals and other vertebrates, all of the eggs that a bird will ovulate in its
lifetime are thought to be present in the ovary at birth. Most species of
birds have only one functional ovary, usually the left, but in a few spe-

Cornell Laboratorq of Ornithologq Handbook of Bird Biolojq

A.
4.130 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatoin and Phqsiologii 4.131
des, both right and left functional ovaries may be present in over half Figure 4-111. Stages of Egg Formation
of the individuals. These species include the Eurasian Great Crested in the Oviduct: This diagram shows the
female reproductive tract in cutaway
Grebe, Turkey Vulture, Northern Fulmar, kiwis, and a number of birds
view for most of its length. The ovary re-
of prey. leases a mature ovum at daily intervals
The word "egg" has two meanings: it may refer to the ovum, during the breeding season until a com-
which is the female reproductive cell (the female equ ivalent of a sperm plete clutch of eggs has been laid. What
we recognize as the "yolk" of a chicken's
cell), or it may refer to the hard-shelled entity with its white albumen
egg is in fact the ovum, a single cell. As
and yellow yolk. The yolk, a single cell, is the true ovum. Tremendous Ovary the ovum leaves the ovary, the funnel-
in size compared with other cells of the body, it stores highly concen- shaped infundibulum at the cranial end
trated food materials to support the developing embryo until hatching of the oviduct (the tube that transports
Mature Ovum the developing egg to the cloaca) moves
time. The single yolk of a chicken egg is 32 percent of the volume of (Next to be
up to the ovum, opens, and "swallows"
the total hard-shelled egg. The yolk of the much-larger Ostrich egg is Ovulated) Infundibulum
it. Fertilization takes place in the in-
an even greater percentage of the total egg volume. In contrast, the ova of Oviduct
fundibulum, before the ovum has any
(Fertilization
of mammals are very small and barely visible to the naked eye, having Takes Place covering of albumen or membranes. The
almost no nutritive yolk and thus no concentrated food store. Here) fertilized ovum passes along the oviduct
to the region called the magnum, where
In most birds, the ovary releases an ovum at daily intervals during
glands secrete the first layer of albumen
the breeding season until a complete set (clutch) of eggs is laid (Fig. (the familiar "white" of an egg) around
4-111). The oviduct, a tube that transports the egg from the ovary to Magnum (Ovum it, a process that takes about three hours.
the cloaca, is suspended from the dorsal body wall by a curtain-like Receives First Layer of A short, non-glandular region divides
Albumen Here) the magnum from the isthmus. During
membrane. When the ovary releases an egg, the flattened, funnel-
the hour or so the ovum spends in the
shaped opening of the oviduct—called the infundibulum—moves isthmus, egg and shell membranes are
up to the ovary and opens, "swallowing" the egg much like a snake deposited around the ovum, and more
swallows a rat. Thus, an egg being ovulated never crosses a gap to the albumen is added. Next the ovum
infundibulum, as it does in mammals. In rare instances the ovum is passes into the shell gland, whose many
papillae secrete still more albumen and
not swallowed by the infundibulum, but is trapped in the body cavity
the hard, calcium-rich, outershel I. Shell
among the viscera. This condition is a disorder called internal laying pigmentation also takes place here, the
and the ovum must be resorbed by the surrounding tissues. patterns reflecting the speed of the egg's
The oviduct is so convoluted that judging its length is difficult. passage and the fact that it rotates as it
Isthmus moves through the shell gland. Rapid
Following the infundibulum is a glandular region or magnum that
(Egg and Shell movement leads to streaked pigmen-
secretes the first of the albumen or "white" of the egg, followed by the Membranes, tation, whereas slow movement leads to
isthmus, which secretes more fluid albumen and the egg membrane. and More •mosoo,'
a more spotted eggshell. The hard, outer
Albumen
A line of division can be seen between the magnum and the isthmus. Added Here)
shell takes about 20 hours to complete,
Gland-free Line of
The oviduct's next portion is the well-vascularized shell gland, which after which the egg passes through the
Division Between
Magnum and Isthmus lower end of the oviduct, termed the
secretes additional fluid albumen and a calcium-rich shell with or
vagina, and into the cloaca, from which
without pigments—whatever is characteristic of the species. (The shell it exits the body. From ovulation to lay-
gland has many internal papillae and is sometimes called the "uterus," ing, the process of egg production takes
but it has no nutritive function as does the mammalian uterus, because about 24 hours.
birds do not bear live young.) Following the shell gland is a short sec- Shell Gland
Large
tion of oviduct called the vagina, which opens into the left side of the (Albumen, Shell, and
Intestine
Pigments Added Here)
cloaca.
Contractions of smooth muscle in the wall of the oviduct move
the ovum along its length, where the different glandular areas of its
wall add their contributions in succession. An ovum released from the
ovary of a chicken requires about 24 hours to become a hard-shelled Papillae
egg ready for laying. For 18 to 20 hours of this time, the egg rests in the
Vestigial Vagina
shell gland. Before being laid, most eggs are rotated 180 degrees in the Right
vagina so the blunt end exits first. Oviduct Cloaca
Why are there no live-bearing birds?This question has been asked
many times, and although several explanations have been given, none

Cornell Laboratorj of Ornithologg Handbook of Bird BioloBq

4.132 Howard E. Evans and J. B. Heiser Chapter 4 — What's Inside: Anatomy and Physiology 4.133
Figure 4-112. Copulation in Common Copulation and Fertilization
Terns: A mated pair of Common Terns The transfer of male spermatozoa into the
copulates near their nest site on a Long female's cloaca is so brief a contact—sometimes
Island, New York beach. Copulation in
referred to as a "cloacal kiss"—that although it
birds is brief, and consists of the com-
ing together of the two birds' cloacas, could be called copulation, the more general term
termed the "cloacal kiss," during which insemination seems preferable (Fig. 4 112). In the
-

sperm are transferred from the male's process, the male and female cloacas are everted
cloaca into the cloaca of the female.
as they are pressed together. This allows the pa-
Photo by Tom Vezo.
pi I lae embedded in the male protuberance to con-
tact the lining of the female's cloaca, or even to
enter the opening of the left oviduct. As previously
mentioned, in waterfowl and ratites a cloacal phal-
lus, erected by lymphatic pressure, accomplishes a
more intimate union that could properly be called
copulation.
The number of sperm ejaculated at one time varies with the spe- Figure 4-113. Griffon Vulture: Some
cies (or the breed in domestic forms) and age of the bird, the time since species of birds are able to store sperm
and thereby fertilize an entire clutch of
the last ejaculation, and the time of year. Counts made in the rooster
are completely satisfactory. In spite of their great diversity, birds are eggs from a single insemination. In con-
yielded densities of 250,000 to 10,200,000 spermatozoa per cubic trast, birds that lay only a single egg per
the only jawed vertebrate class in which all members lay eggs. The millimeter, with an average of 3,200,000. Total volumes of ejaculated season, such as the Griffon Vulture of
reason usually cited is that flying with the "excess baggage" of a grow- rooster semen (from stud roosters) contain about 3 billion sperm! The Europe and Africa, may copulate many
ing embryo and fetus would be disadvantageous. This is true for most Rock Dove has about 200 million sperm per ejaculate. Male humans times over an extended period before
birds, but for flightless birds it would not be a problem. Yet none are laying. This may be more important for
produce about 500 million sperm in one ejaculation.
strengthening the pair bond than for in-
live-bearing. Furthermore, bats seem to manage very successfully, for Sperm live longer in bird oviducts than in those of mammals, suring fertilization of the egg. Photo by
there are nearly 1,000 species, and all bear live young and can fly. with the possible exception of reproductively specialized mammals C. H. GreenewalVVIREO.
Another reason cited for the absence of live-bearing birds is such as armadillos and bats. Following insemination, female birds can
the high body temperature of the parent bird (104 to 105.8° F [40 to store sperm in "sperm nests" or crypts in the wall of the oviduct at the
41°Q), along with the apparent sensitivity of all terrestrial vertebrate junction of the vagina and shell gland, or in the region of the infun-
embryos to high temperatures. If birds were to bear live young, once dibulum. Sperm are released from these crypts following the passage
the birth process began and the young were disconnected from the of an egg, and make their way to the infundibulum, where they may
parental blood supply, they would have to be born very quickly be- fertilize subsequent eggs. A female domestic turkey may lay as many as
cause the lack of sufficient oxygen and the parental high temperature 15 fertile eggs fol lowing a single insemination, even up to 30 days after
could prove lethal. Furthermore, an embryo retained in the oviduct insemination, and 83 percent of the eggs may be fertile. In contrast,
during gestation might not be viable even with a parental oxygen birds that lay a single egg each season, for example the Griffon Vulture
supply. Experimental evidence from chickens appears to confirm this of Europe and Africa (Fig. 4 113), may copulate frequently for a month
-

possibility. Incubation at temperatures above 104°F results in embryo before layi ng.The extended period of copulation may be necessary for
death, or organ malformation leading to death after hatching. The strengthening the pair bond, rather than for fertilizing the eggs.
chicken, however, is not a good example of normal bird reproductive Sperm deposited in the female cloaca enter the left oviduct and
physiology or of adaptability to environmental stress because it has make their way to its upper end. Fertilization takes place in the region
been selectively bred to meet human requirements, sometimes at the of the infundibulum as the ovum is being engulfed, before the ovum
expense of traits that would help it to survive in the wild. Consider, has any covering of albumen or membranes. The nucleus of the sperm
instead, birds that bury their eggs in decaying vegetation or volcanic, cell and the nucleus of the ovum unite to form a single cell, the fer-
steam-heated earth mounds, as do the Australasian megapodes (see tilized egg or zygote. Cell division proceeds as the egg passes down
Fig. 6-36). One wonders what range of temperatures and levels of ox- the oviduct, and slows or stops after the egg is laid. Growth does not
ygen are successfully endured by megapode eggs. In ground-nesting resume until the egg is warmed by the incubating bird.
birds, bearing live young would reduce the time in the nest—a real
advantage in reducing nest predation. And it would, no doubt, be much Sex Determination
appreciated by male Emperor Penguins (see Fig. 4-100). Nevertheless, How the sex of a bird is determined at conception is an interesting
egg laying is the rule in living birds. phenomenon.To understand it, though, one first must understand how
the genetic blueprints of plants and animals are stored, sorted, and

Cornell Laboratory of Ornithology Handbook of Bird Biology

4.134 Howard E. Evans and J. B. Heiser Chapter 4 — What's Inside: Anatomy and Physiology 4.135
Figure 4-114. Chromosomes of Body a. Body Cells b. Gametes The only cells in a complex organism that do not have their
Cells and Gametes: DNA, the genetic (Some chromosomes in each gamete chromosomes in pairs are the gametes or sex cells (eggs and sperm).
material of nearly all living things, en- originally came from the parent's
codes building instructions for all the
Instead, during their production, eggs and sperm receive only one
Paired mother, and some came from the
body's structures and processes. The parent's father, in a random member of each pair of chromosomes. Interestingly, some of the chro-
Chromosomes
DNA of an organism is divided up into assortment.) mosomes in a single gamete of an individual will be like those of the
paired structures called chromosomes, individual's mother; the others, in a seemingly random fashion, will be
which are further divided into genes.
Unpaired Chromosomes like those originally inherited from the individual's father. Furthermore,
Each gene contains the instructions
for making a particular kind of build- each different gamete produced by an individual will have a different
ing block, or information about how mix of the chromosomes from the individual's two parents. Each sperm
or how fast the building block is to be cell of a male, for example, will contain a different mix of the chromo-
produced. a. Body Cells: In the body somes that male inherited from his two parents. It is this mixing, along
cells, all chromosomes except the Sperm or Eggs
with mutations and a few other types of genetic information sorting,
two sex chromosomes are found in
pairs whose members appear similar. that produces the individual variation in offspring on which natural
Every body cell within a given organ- selection operates to produce evolution.
ism contains the same species-specific Somewhat in contrast to most human concepts of a good in-
number of chromosomes. The chicken, Any Body Cell
formation storage and retrieval system, the information on any one
for example, has 39 pairs. For simplicity, of a Female Bird
only four chromosome pairs are shown chromosome is not all closely related in "subject matter." Indeed, a
in this diagram. One member of each chromosome resembles a filing cabinet whose file folders, instead of
chromosome pair was inherited from being arranged in drawers labeled "upper leg," "lower leg," and "foot,"
the individual's mother, and the other
have a seemingly random arrangement: a cluster of files having to do
was inherited from its father. Although
each member of a chromosome pair
with claw design and construction next to another cluster relating to
contains the same sequence of genes, liver cells, followed, perhaps, by some tongue muscle instructions. Any
the specific traits indicated may differ. attempt to label such a drawer, much less characterize the entire filing
For example, although both might con- cabinet (chromosome), is doomed to failure! To claim that the genetic
tain a gene directing the pigmentation of
filing system is chaotic and random, however, would be incorrect.
the tail feathers of a pigeon, the colors or
patterns indicated by each might differ. In a chromosome pair, both chromosomes—whether from father or
The sex chromosomes of the individual mother—contain the same files in much the same order, even though
shown here are different from each the individual genes may differ (reflecting differences in inheritance
other, indicating that it is a female (see * If this individual were a male, from mother versus father).
Fig. 4-115). b. Gametes: The chromo- the second sex chromosome
somes of the gametes, or sex cells (eggs would also be a Z. There is an exception to this general picture of chromosomes
or sperm), are not in pairs. This occurs in birds, mammals, and some other vertebrates, however, and that is
because during its production, each egg found with the positioning of many, perhaps most, genes dealing with
or sperm cell receives only one copy passed from one generation to the next. The genetic material DNA
sex. The sex genes are concentrated on a single pair of chromosomes.
of each chromosome from its parent. encodes each detail of the blueprints necessary for building proteins,
Unlike all other pairs of chromosomes, this pair can be structurally so
Furthermore, each egg or sperm cell including the instructions that result in the anatomical, physiological,
produced by an individual is different, different, one from the other, that they can easily be told apart in the
and behavioral differences between the sexes. It is the way that DNA
because it contains a different subset of proper sort of microscopic preparation. In mammals, one of these sex
its parent's chromosomes: some origi- instructions are "filed" and "stored," however, that becomes important
chromosomes always resembles the letter X in a microscopic prepa-
nally came from its parent's mother, and in understanding sex determination in birds.
ration, but the second member of the pair may be another X or a "Y
some came from its parent's father. Each subset of DNA instructions for making a particular kind of
chromosome." The second chromosome type is designated Y in refer-
building block of an organism is called a gene. For each building block,
ence to the next letter in the alphabet, not because it is shaped like the
other genes code for the conditions under which it is to be produced,
letterY. Similarly in birds, all individuals have one sex chromosome of
and for the rate of its production. In complex organisms, the millions
a consistent shape and size that has been named the Z chromosome (in
of genes are "stored" within the cell in structures called chromosomes
keeping with the end-of-the-alphabet mammalian sex chromosome
(Fig. 4 114). Each species has a characteristic number of chromo-
-
designations, not because of its shape). In parallel with mammals, the
somes, and each body cell within an organism has that same number
second sex chromosome may be the same (another Z) or of a different
of chromosomes. The chromosomes can be individually recognized by
structure, termed the W chromosome.
shape and size, and are found in pairs of similar structure. One mem-
When the eggs and sperm are produced, individuals with a pair of
ber of each pair of chromosomes was inherited from the organism's
similar chromosomes (XX in mammals, ZZ in birds) will produce gam-
mother, and the other member, with instructions for all the same mate-
etes that all contain the same type of chromosome (X in mammals, Z
rials and processes, was inherited from the father.

Cornell Laboratory of Ornithology Handbook of Bird Biologg

4.136 Howard E. Evans and J B. Heiser Chapter 4 —What's Inside: Anatomq and Phqsiologq 4.137
in birds) (Fig. 4-1 1 5). These individuals are thus called homogametic. Sex determination in many other animals is a more complex sit-
In contrast, in individuals with two different sex chromosomes (XY in uation. Most fishes, amphibians, and reptiles, for example, do not have
mammals, ZW in birds), half of the gametes will be of one type, and recognizable, differentiated sex chromosomes. The genes encoding
half will be of the other type. Individuals that produce two different sexual characteristics may be widely dispersed across the entire set
types of gametes are termed heterogametic. When egg and sperm unite of chromosomes. What sex an individual becomes, and thus whether
during fertilization, the embryo receives either two similar or two dif- it produces eggs or sperm at maturity, may be determined in some of
ferent sex chromosomes, one from each parent. This difference is what these species by such seemingly strange factors as the temperature at
determines the sex of the individual bird or mammal. which embryological development takes place (turtles, crocodiles)
It is here that the similarities in bird and mammal sex deter- or the behavior of other animals in an individual's social group (some
mination abruptly end, for the process is exactly opposite in these fishes). In some species of fish and lizards, individuals may be func-
two lineages of animals. In mammals, heterogametic individuals (XY) tionally hermaphroditic—producing both eggs and sperm—either at
develop into males and homogametic ones (XX), into females. In birds, different periods in the life of the individual or even at the same time
heterogametic individuals (ZW) become females and homogametic in its life!
ones (ZZ) develop into males. This bird-mammal difference seems to
bear no functional significance, but rather reflects the randomness of Hormones and Secondary Sex Characters
evolution. It does mean, however, that it is the male's sperm in mam- As discussed in the section on the endocrine system, sex hor-
mals, but the female's egg in birds that seals the sexual fate of the mones are produced by three sources: the anterior lobe of the pituitary
embryo. gland, the adrenal glands, and, the primary source, the gonads. All
sex hormones interact, influencing the development of anatomical
structures, physiological processes, and the behaviors essential for
MAMMALS BIRDS
successful reproduction. The male sex hormone, an androgen called
e\:\ c et\c' e‘c' toe testosterone, is secreted mostly by cells within the testes, but also by
oe\ sAo
ode ,Aekelcg the ovaries (and adrenal glands). The female sex hormones, estrogens,
\OA axe' ,,xe` • are secreted mainly by the ovary, but the testes of birds of some spe-
cies also secrete some estrogens, as do the adrenal glands. As you read
Sex Chromosomes of Individuals
through this section, refer to Figure 4-116.
Seasonal changes in the reproductive organs are controlled by
Egg\ Sperm light and other environmental factors, which regulate the activity of the
pituitary gland. The pituitary, in turn, governs the secretions from the
Gametes adrenal glands and the gonads. Hormones from the anterior pituitary
activate the growth of the ova in the ovary. Some of the ova mature;
most degenerate. Those that develop will produce estrogens that, when
secreted into the blood, stimulate the development and preparation
of the oviduct to receive the ova. Similarly, under the influence of hor-
Possible Offspring mones from the anterior pituitary, the testes begin their cyclic change,
culminating in the production of spermatozoa and the production and
Female Male Male Female
release of testosterone.
Offspring Offspring Offspring Offspring
The secondary sex characters are the features, besides the sex
Figure 4-115. Sex Chromosomes and Sex Determination in
organs, that distinguish the sexes. Depending on the species of bird,
whereas heterogametic (XY) ones become males. In birds the
Birds Versus Mammals: The sex chromosome "pairs," con- opposite is true: homogametic individuals (ZZ) are males, and these features occur in the plumage, combs, wattles, color of bill,
taining genes determining the gender of an individual, may heterogametic ones (ZW) are females. During gamete pro- presence or absence of spurs, size of body, vocalizations, breeding
be dissimilar in appearance, unlike all other chromosome duction, male birds can produce sperm with only one type of behavior, and so on. Hormones control the secondary sex characters,
pairs. In mammals, the larger member of the pair is termed chromosome (Z), whereas half the eggs a female bird produces
particularly those that change with the seasons.
the X chromosome, after the letter it resembles, whereas the contain a Z and half contain a W chromosome. In birds, there-
smaller is called the Y chromosome. In birds, the larger sex fore, it is the type of sex chromosome in the female's egg that The gonadal hormones, testosterone and estrogens, besides act-
chromosome is termed Z, and the smaller is termed W (refer to determines the gender of the offspring at conception, in contrast ing as stimulants for the development of the reproductive system, cause
Fig. 4-114). At conception, the two sex chromosomes an indi- to the situation in mammals, in which the sperm determines the some or all of the following: (1) the appearance of bright plumage in
vidual receives (one from each of its parents) may be the same, sex of the offspring. Note that in any pairing between a male
males (and occasionally in females such as phalaropes) just prior to
producing a homogametic individual, or different, producing and female bird, approximately half the female's eggs will carry
a heterogametic individual. Mammals and birds differ in how the W chromosome, and half will carry the Z chromosome.
the breeding season; (2) changes in the color of the bill (for example,
these differences are translated into an individual's gender. In Therefore, on average, half of the offspring will be female and in the breeding season, the brown bill of the European Starling changes
mammals, homogametic (XX) individuals develop into females, to bright yellow); (3) an increase in singing; (4) aggressive behavior

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

4.138 Howard E. Evans andJ. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.139
toward other birds, particularly of the same sex and species, and the es- appear, a secretion from the adrenal gland has stimulated incubation
tabl ishment of territory; (5) courtship displays leading to pair formation behavior and activated the production of "pigeon's milk" in the crop
and copulation; (6) nest-building behavior; and (7) in most species, the of birds such as pigeons and doves.
development of an incubation or brood patch. The embryo, developing in the egg, requires constant heat.
Late in the reproductive cycle, the anterior pituitary releases a Because feathers are poor conductors of heat, most incubating birds
hormone that inhibits further secretion of the other gonadal hormones, develop one or more incubation or brood patches on the breast that
retarding the activity of the ovary and the testes. The reduction of these are without feathers (see Fig. 8-89). Heavily suffused with blood ves-
hormones reduces the behaviors initiated by them. By the time the eggs sels, these patches permit direct contact between the warm skin and
the eggs. Hormones control development of the incubation patch.
Figure 4-116. Major Glands and Before the female lays her first egg, her patch begins to develop as fol-
Hormones Involved in the Avian Seasonal Changes lows: it loses its feathers, the outer layers of the skin thicken, the blood
Breeding Cycle: A schematic of the • Day Length
glands involved in reproduction, the • Light Intensity vessels in the region increase in number and some enlarge, and the
hormones they produce, and their • Air Temperature spaces between the cells under the skin fill with tissue flu id and remain
effects, as detailed in the text. • Amount of Rainfall
full during the incubation period. Most male birds that incubate also
• Food Availability
• Behavior of Mate develop an incubation patch.
• Behavior of Other Birds The experimental use of hormones on castrated birds (having the
testes, and thus the source of testosterone, removed) has yielded some

f
Hypo alamus
• Production
of Pigeon's
Milk
strange results. Female hormones injected into castrated male ducks
stop the development of a male-type syrinx and cloaca! phallus. This
indicates that the female hormones are responsible for sexual dimor-
I phism in the syrinx and cloaca, for without them, male characters
Anterior • Incubation
Pituitary Behavior develop even in castrates. In contrast, the injection of testosterone
into both male and female House Sparrows turns brown bills to black,
which is the male breeding condition; injections of estrogens have no
effect on the color of the bill. The same is true of European Starlings:
testosterone turns brown bills to a bright yellow (the color in breed-
ing adults), but estrogen has no effect on bill color. Thus, while major
secondary sex characters appear estrogen-controlled, the seasonal
• Increases in Size • Increases in Size reproductive characters seem to respond to testosterone.
• Activates Growth and Release of Ova • Activates Production of Sperm Gonadal hormones also affect behavior. Female canaries in-
• Activates Production and Release of • Activates Production and Release of
Estrogens Testosterone jected with testosterone develop a male-type song, exhibit male-like
courtship behavior, and become dominant over normal females. Th us
ESTROGENS testosterone dominates estrogen under these conditions. Surprisingly
TESTOSTERONE
(and some
Testosterone)
(and Estrogens it is estrogens that have profound effects on the songbird brain.
in some species)
F. Nottebohm and other researchers have shown that major differences
exist between brain structures in adult male and female birds of various
species. In male brains an enzyme converts androgens to estrogen.
For some reason, estrogen, rather than androgens, probably controls
• Prepares to the development of the brain areas involved in song acquisition, per-
Receive Ova ception, and production. The brain has at least two neural pathways
Develop Seasonal
Breeding Characteristics that contribute to song learning and song production (see Fig. 7 36). -

• Sexual Plumages
One, a motor pathway, controls the muscles of the syrinx for song
• Bill Color Changes
• Brood Patch Development production; the other neural pathway is required for song learning.
In birds, which sexes sing, how much they sing, and when they
Initiate Breeding Behaviors sing varies greatly by species. In most birds, only males sing, but in a
• Increased Singing few species, both sexes sing. Some birds sing year round while others
• Increased Aggression and Territoriality
sing only for a short breeding season. In the future, we can expect to
• Increased Courtship Behaviors
• Copulation and Fertilization hear much more about hormone action in the brain and the neuro-
• Nest Building biology of bird song, an active and exciting field of research at the
present time.

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4.140 Howard E. Evans and J. B. Heiser Chapter 4—What's Inside: A natomq and Phqsiologq 4.141
Factors Bringing Birds into Breeding Condition Figure 4-117. Kea: A large parrot from
Many external factors may stimulate the pituitary to signal the the mountainous regions of New Zea-
land, the Kea begins sperm production
other glands involved in reproduction, thus beginning the breeding
as the days begin to shorten, in prepa-
cycle. They include the amount of light each day, the intensity of light, ration for its nesting season during the
the temperature, the amount of rainfall, the availability of food, and the southern hemisphere winter. Photo by
actions of other birds, including the behavior of the mate. In this list, T J. UlrichNIREO.
the most universally dependable factor is day length and its increase
or decrease as the seasons change (at least, in the higher latitudes). The
effect of the changing day length on the pituitary gland in birds is an
example of photoperiodism (any type of response to day length).

Photoperiodism
In most birds of the temperate zone, an increase in day length
causes development of the gonads and stimulates migratory behavior.
An artificial increase in day length will force some species to come into
breeding condition in the dead of winter. Light, therefore, must play
a role in regulating the onset of breeding in birds of middle and high
latitudes. In some species, an increase in the day length starts devel-
opment of the gonads; in others, exposure to a day length that is at least
as long as some period seems to be more important, still longer days in transequatorial migrants. However, the birds must become insen-
having no greater effect. Presumably, the retina of the eye sends neural sitive or reverse their sensitivity as they reach their destinations.
impulses to the brain that eventually stimulate the hypothalamus.Thus
stimulated, the hypothalamus secretes hormones that in turn stimulate Air Temperature
the pituitary. Much remains to be learned about this process. Every bird species is physiologically adapted to a specific tem-
In experiments, White-crowned Sparrows and Dark-eyed Juncos perature range; any drastic change may affect the beginning of the
respond with a normal increase in gonad size between December breeding season. In many birds an unusually cold spell in the early
and May only if the longest artificial day exceeds 10 hours. Under stages of the breeding cycle may delay nesting.This is true for the Great
photoperiods of nine hours, their gonads develop, but at a much Tit, Blue Tit, Eurasian Blackbird, Pied Flycatcher, European Robin,
slower rate. Just as most avian physiologists were becoming satisfied Chaffinch, and many others. In domestic turkeys and European Star-
with the assumption that day length triggered the reproductive cycle, lings, lower temperatures reduce the production of sperm as well as
however, an experiment showed that light cues are not necessary for the number of eggs laid. Freezing temperatures can cause frostbite of
some birds. The testes of domestic ducks that were kept in total dark- delicate tissues, which may stop all egg production. Thus farmers may
ness for 20 months developed, regressed, and developed again—all remove the comb or wattles of barnyard birds to prevent such signals
without light. from interrupting the harvest.
Natural observations also indicate that increasing day length is Temperature changes affect different species in different ways.
not the single cue for initiating reproduction. The European Robin, for The Emperor Penguin lays its one egg in the middle of the Antarctic
example, begins producing sperm about the first week of January in winter when the air temperature is about minus 30° F (minus 34.4°C).
the foggy midwinter of the English Midlands, when the day length has Thus by hatchingtime the temperature has become higher (5°F; minus
increased by only a few minutes. In New Zealand, the large mountain 15° C) for the chick. Possibly, in such species a decreasing day length
parrot called a Kea (Fig. 4-117), and in Australia, the Emu and the Su- provides the stimulus for gonadal development.
perb Lyrebird, all begin producing sperm as the days begin to shorten.
All three of these species nest in winter. Rainfall
Migration is closely connected with the reproductive system in In arid regions, where rain occurs sporadically between periods
most birds. However, little is understood regarding the role of day of droughtthat lastfor months or years, either the rain itself, or the green
length in birds that migrate across the equator from one hemisphere vegetation resulting from the rain, triggers the breeding cycle. Abert's
into the other. How can we account for development of the gonads in Towhees in Arizona may begin to nest 10 to 14 days after heavy rains in
the Bobolink, which nests in the Northern Hemisphere, migrates to the March or April. Sometimes they nest again following a second period
Southern Hemisphere for the winter, and begins its northward flight of rain that occurs in July. The beginning of egg-laying by California
when the days there are getting shorter rather than longer? Perhaps a Quail varies from year to year by about three weeks, depending on the
summation of the periods of daylight determines the gonadal response temperature and amount of rainfall.

Cornell Laboratorq of Ornitholom Handbook of Bird Biologq

4.142 Howard E. Evans and . B. Heiser Chapter 4—What's Inside: Anaton9 and Pinisiolo94 4.143
Figure 4-118. Rufous Hornero at its Figure 4-119. Male Red Crossbill: No-
Nest: Rainfall may trigger breeding in madic Red Crossbills may breed during
certain species by providing food, nest- any month of the year, initiating nesting
ing material, or cover. The Rufous Horn- when their wanderings take them into
ero of Argentina, shown here, does not areas where bumper crops of their
breed until adequate rainfall provides a principal foods—pine and other conifer
supply of mud with which it can build seeds—are available. The crossed tips of
its huge oven-like nest. This individual's their beaks allow them to efficiently pry
nest is only partially complete; the fin- the conifer seeds from deep within open
ished structure will have a domed roof or closed cones. Food, rather than light,
of mud, and will dry rock-hard in the is thought to act as both the proximate
sun. (See also Fig. 8-34d.) Photo by T. J. and ultimate factors triggering this spe-
Ulrich/VIREO. cies' breeding cycle—because it feeds
its young on a regurgitated paste made
primarily from seeds. Photo courtesy of
Brian Henry/CLO.

Old World warblers (Family Sylviinae) dwelling in the grasslands

of Zimbabwe and Malawi of Africa do not breed until after the seasonal
after each breeding period, regardless of the length of light periods in
rains—they depend upon rain for the growth of nesting material and the laboratory.
cover. The Rufous Hornero in Argentina does not breed until sufficient
rain has produced the mud with which it builds huge, oven-like nests Food
(Fig. 4 118).
-
A bird must time its breeding so that the hatching of young co-
Rainfall is all-important in extreme desert regions because the incides with the best environmental conditions for their survival. In
short period of vegetative growth—possibly little more than a month— the Arctic, for example, Pomarine and Long-tailed jaegers and the
must provide nesting material as well as food for the young birds. Birds Snowy Owl depend heavily on small rodents, particularly the brown
in the desert regions of Australia are often nomadic, moving about in and collared lemmings, for food. When lemming populations are low,
search of food and water. They nest in any month of the year and, if the these birds may lay unusually small clutches of eggs, or they may not
rains finally come, may nest twice in six months. nest at all.
Getting wet from rain, or perhaps even hearing rain, may be a suf- The Red Crossbi I I (Fig. 4 119) restricts its diet to conifer seeds,
-

ficient stimulus to initiate the breeding cycle of some Australian birds. particularly those of pine. Its nomadic tendencies and the fact that it
They begin to breed right when the rains begin, before the rain has may nest during any month of the year suggest that food, rather than
had a chance to increase the supply of food and nesting material, or to light, acts as both the proximate and ultimate factors in initiating the
change the general appearance of the environment. The Zebra Finch, breeding cycle. Artificial light in the laboratory will cause some, but
Black-faced Woodswal low, Budgerigar, and Australian Tree Swallow not complete, gonadal development. In the wild, Red Crossbills nest
are some of the birds that begin nesting at the first drop of rain. only when the conifers produce a good seed crop, feeding their young
Thus, due to the unpredictability of rain in arid environments, a paste of regurgitated seeds, possibly mixed with saliva and some
natural selection has favored the evolution of a reproductive system insect matter. They are indifferent to the cold and their young seem to
that can spring into action quickly. The reproductive system of birds thrive with little or no insect food, a rare phenomenon among most
adapted to such environments can maintain itself without the usual small bird species, regardless of the parents' diet.
nonbreeding period common in temperate zone birds. In experi-
ments, the Baya Weaver of Asia maintained sexual readiness with a Social Interactions
continuous production of sperm for 15 months without any regression Sometimes light stimulation must be reinforced by other external
of the testes. In contrast, the gonads of the Dark-eyed Junco regress stimuli before it will trigger the breeding cycle. An important external

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4.144 Howard E. Evans andJ. B. Heiser Chapter 4 —What's Inside: Anatomq and Phqsiologq 4.145

stimulus for some species is the presence or absence of other indi- Figure 4-120. Bird Versus Mammal Me-
viduals of their own species. A captive female Rock Dove lays eggs Compared to mammals, BIRDS, as a group, have: tabolism: In general, birds have a higher
basal metabolic rate, body temperature,
readily in the presence of a male and less readily when only another heart rate, blood pressure, and blood
female is present. If isolated from all others of her kind, she will not • HIGHER BASAL METABOLIC RATE sugar concentration than mammals, and
lay at all—unless she has a mirror in her cage. Such social contact is a more efficient respiratory system. But,
very important in triggering breeding in colonial-nesting birds such as these differences do not necessarily hold
• HIGHER BODYTEMPERATURE when particular birds are compared to
gulls, boobies, and many other marine birds.
particular mammals, or when birds and
The male House Sparrow must be present before the female will • FASTER HEART RATE mammals ofa similar size are compared.
lay an egg. European Starlings, normally found in flocks during the For example, the respiratory rate ofa bird
nonbreeding season, break up into pairs for breeding. If confined in • FASTER (MORE EFFICIENT) RESPIRATORY SYSTEM
is actually lower than the respiratory rate
of a mammal of the same size. See text
flocks during the breeding season, female starlings do not lay eggs.
for details.
Elaborate courtship behaviors by the male stimulate ovulation in • HIGHER BLOOD PRESSURE
a wide variety of birds, for example the Satin Bowerbird in Australia,
and the Chaffinches and robins in Europe.Vocalizations are important • HIGHER BLOOD SUGAR CONCENTRATION
for development of the gonads in parakeets, and egg laying is enhanced
when three or more birds are present.
In other words, it is the amount of energy needed to maintain minimal
In humid equatorial regions, where day length fluctuates very
body functions. The basal metabolic rate is, naturally, lower than any
little and a mild climate persists throughout the year, birds have a
of several active metabolic rates that an animal can have.
tendency to prolong the breeding season. Estrildid finches such as
As a group, birds have a higher basal metabolic rate than mam-
the Zebra Finch from Australia breed freely and can raise four or five
mals—a higher body temperature, faster heart rate, and faster respi-
broods a year in rain forest regions. Some seabird colonies also are ac-
ratory rate (Fig. 4-120). The amount of food that a bird must eat de-
tive throughout the year. Sooty Terns of Ascension Island breed about
pends partly on the caloric value of its food, partly on the size of the
every 9.6 months; Audubon's Shearwaters of the Galapagos Islands
bird, and very much on the level of activity in which it engages and
breed about every 9 months.
on the temperature of the environment. Because the higher metabolic
rate of birds requires more food calories per unit of time, a bird's blood
sugar concentration is much higher than that of mammals.
Metabolism The size of a bird has important effects on its heat production and
• The term metabolism, in biology, includes all of the chemical chang- loss. The smaller the bird, the larger its body surface area in relation to
es that take place in the cells and tissues of the body—the use of basic its volume. The amount of heat produced by an animal is proportional
food materials to produce protoplasm, living material. Metabolism to its volume, because the volume is composed largely of the heat-
also includes the conversion of complex substances to simpler ones producing muscle. The amount of heat lost, however, is proportional
to produce energy for breaking down the basic foods, for contracting to the amount of surface area, because most heat loss occurs across
the skeletal muscles, and for producing heat. the body surface.
The production of new living material is necessary for an animal's The concept is easy to understand if you consider two cubes
growth. It continues throughout life to allow for the repair of cells and (Fig. 4-121). The first, 1 x 1 x 1 inches, has a surface area of 6 square
tissues, and to permit the continuous turnover of material in the cells. inches (6 sides x 1 square inch per side) and a volume (length x width
Sugars, other carbohydrates, and fats in the diet provide the energy x height) of 1 cubic inch; the surface-to-volume ratio is 6:1 .The second
for this dynamic flux. Enzymes are proteins that act as catalysts in the cube, 2 x 2 x 2 inches, has a surface area of 24 square inches and a
chemical changes that build up and break down the constituents of volume of 8 cubic inches; thus the surface-to-volume ratio is only 3:1.
protoplasm. Metabolism, then, includes all of the dynamic chemical, Therefore, a small bird must produce more heat in relation to its body
physiological activities of cells and tissues. Here, we deal only with the size than a large bird, just to offset the high rate of heat loss from the
major physiological processes: the maintenance of body temperature, surface of the body.
heart rate, and respiratory rate under different environmental condi- To determine metabolic rate, researchers may directly measure
tions; water and salt regulation; and aging. heat calories produced, but more often they measure the amount of
The contraction of skeletal muscles produces both work, in the oxygen that an animal consumes. Th is indirect method works because
form of force applied to the shortening muscle, and heat. Heat is mea- in order to produce heat, oxygen must be consumed—and this occurs
sured in calories; one calorie is the amount of heat required to raise during the continual process of food digestion. Recall thatto digest thei r
one gram of water one degree Centigrade. The basal metabolism of an food, animals combine carbohydrates, fats, and proteins with oxygen,
animal is the number of calories that it uses when completely at rest. breaking down the food into smaller nutrients that can be absorbed

Cornell Laboratorq of Omithologq Handbook of Bird Biologq

4.146 Howard E. Evans andJ. B. Heiser Chapter 4 — What's Inside: Anatonm and Plitisiolosti 4.147
Figure 4-121. Size and Surface-to-
Volume Ratio in Birds: The size of a
bird influences its heat production
and loss, and therefore has important
implications for its metabolic rate. The
amount of heat an animal produces is
proportional to its volume, because
heat-producing muscle makes up
Black-capped Chickadee Wild Turkey
much of that volume. The amount of
, 2"
heat lost, however, is proportional to
an animal's surface area. Small birds,
such as the Black-capped Chickadee,
have a greater amount of surface area
per unit volume (known as the surface-
to-volume ratio) than do large birds,
such as the Wild Turkey. This concept
is illustrated here using two cubes of
different sizes, for simplicity. The cube
with 1-inch sides, representing a small a. Allen's Hummingbird b. Anna's Hummingbird
bird, has a volume (length x width x
height) of 1 cubic inch, and a surface about 104.2° F (40.1° C). Thus there do appear to be evolutionary dif- Figure 4-122. The Metabolic Cost of
area (length x width x number of sides) Hovering Flight: A hovering Allen's
of 6 square inches. The cube with 2-
ferences in the body temperature set point that large groups of related
Hummingbird (a) consumes about 85
Small Bird Large Bird birds share. The maintenance of body temperature within a normal
inch sides, representing a large bird, cubic centimeters (cc) of oxygen per
has a volume of 8 cubic inches, and a range depends on the amount of heat the bird produces, the means gram of body weight per hour, whereas
surface area of 24 square inches. The Surface Area = 6 Sides x (1" x 1"/ Side) Surface Area = 6 Sides x (2" x 2"/ Side)
= 6 Square Inches = 24 Square Inches
it has of conserving its heat in cold weather, and the way it gets rid of the slightly larger Anna's Hummingbird
surface-to-volume ratio of the smaller (b) requires only about 68 cc for the
excess heat in hot weather. The body temperature of nocturnal birds,
cube is 6:1, whereas that of the larger same activity. Hovering is an energy-
Volume = 1"x 1" x 1"= 1 Cubic Inch Volume = 2" x 2" x 2" = 8 Cubic Inches such as kiwis, owls, and nighthawks, is higher at night, when they are
cube is 3:1. A small bird, with its high intensive activity, producing a nearly
surface-to-volume ratio, will lose more most active. The temperature of the kiwi, generally considered to be a sixfold increase in the amount of energy
heat in relation to its body size than will Surface-to-Volume Ratio = 6 : 1 Surface-to-Volume Ratio = 24 : 8 primitive bird, fluctuates more than that of the others. used, compared to that of a resting bird.
a large bird, so the small bird must have = 3:1
Although nearly all adult birds maintain the body temperature The basal (resting) metabolic rates of
a higher metabolic rate to compensate these birds range from 10.7 to 16.0 cc
under varying conditions, most newly hatched young cannot. This is
more readily, and producing heat as a by-product. The amount of heat of oxygen consumed per gram of body
true for both the nearly naked American Robin nestling and the downy
produced is proportional to the amount of oxygen consumed; thus it weight per hour. Photos courtesy of Pa-
Killdeer chick, although the Killdeer chick has some control in air tricia Meacham/CLO.
is possible to use oxygen consumption alone to measure metabolism.
temperatures between 74 and 104° F (23 and 40° C). The temperature
For example, when resting, Anna's Hummingbirds and Allen's Hum-
control of both nestlings increases rapidly during the first 10 days, and
mingbirds (Fig. 4 122) use from 10.7 to 16.0 cubic centimeters (cc) of
-
control by the Killdeer chick equals that of the adult by 27 days.
oxygen per gram of body weight per hour (their basal metabolic rate).
The primary need of newly hatched nestlings that are helpless,
In hovering flight, Allen's requires 85 cc of oxygen per gram per hour;
almost naked, and asleep most of the time is protection from the el-
the slightly larger Anna's requires only 68 cc. Thus basal metabolism
ements. In cold weather, the adult broods (covers) them, providing
is increased nearly sixfold by the activity of flying.
heat from its own body. In hot weather, the adult shades them from the
burning sun and sometimes tilts its wings to deflect the slightest breeze
Bock' Temperature onto them (Fig. 4 123).
-

Birds and mammals are "warm-blooded." This means that they An adult broods the chicks or nestlings only until they have an
usually maintain their body temperatures within a certain narrow and efficient temperature-regulating system of their own. To gain this, the
high range, even when the air temperature changes to far below or young must grow feathers, increase in size (thus decreasing the body
considerably above the set body temperature. "Cold-blooded" an- surface area in relation to volume), increase neural and glandular
imals, such as fish, amphibians, and reptiles, do not maintain a con- controls, and develop air sacs for efficient oxygen delivery to the
stant body temperature in a variable thermal environment. Instead, body cells. In most passerines these changes all take place in about
their body temperatures fluctuate with the surrounding temperature, one week. Nestling Field Sparrows and Chipping Sparrows become
explaining why they are least active on very warm or very cold days. warm-blooded within about six or seven days.
Body temperatures in birds range from 99.8 to 112.3° F (37.7 to Most birds conserve heat efficiently. Their thick covering of feath-
44.6° C). The average resting temperature of 311 passerine species has ers leaves very little bare skin from which heat may escape. Marine
been measured at 105.1° F (40.6° C) and of 90 shorebird species, at birds, such as penguins and petrels, also have considerable fat under

Cornell Laboratorg of Ornithologg Handbook of Bird Biologq

4.148 Howard E. Evans andJ. B. Heiser Chapter 4 —What's Inside: Anatomt and Phitsiolom 4.149
the skin that helps conserve heat, but al I birds depend primarily on their
feathers for insulation. The thick down under the contour feathers of
the Common Eider constitutes just about the finest insulating ma-
terial known (Fig. 4 124a). On cold, wintry days, birds
-

commonly "fluff up" their feathers as one fluffs up

a down pillow, increasing the air spaces (Fig.
4 124b). The more air spaces, the better
-

the insulation. Frequently during

cold weather, birds perch on
one leg, drawing the other
up under the breast for
warmth. Sometimes birds
tuck their bills into the feathers
^ -
of the shoulder for the same reason
(Fig. 4 124c). Some birds roost together
-

Figure 4-123. American Robin Shading overnight to conserve heat (see Ch. 6, Sidebar 4, Fig. H). The legs and a. Common Eider Nest
its Nestlings: Unlike adult birds, most feet of some birds, such as Herring Gulls, are quite insensitive to cold
nestlings have little ability to thermo-
because a countercurrent exchange of heat takes place between ar-
regulate. This is particularly true for
altricial young, which hatch with un- teries and veins before blood enters the foot.
feathered bodies and closed eyes. Par-
ent birds, even in species whose young Countercurrent Heat-Exchange Systems
b. Northern Cardinal
are down-covered at hatching, regularly Countercurrent exchange systems are found in many different
use their bodies to protect their young regions of animals' bodies and are one of the most important ways Figure 4-124. Conserving Heat: Birds use a range of
from temperature extremes. In cold methods to conserve heat. a. Common Eider Nest: A
in which organisms conserve energy or other vital resources such as
weather, adults may brood their young, layer of down from the female's breast I i nes the nest of a
covering them with their fluffed-up belly water or ions. Thus, taking time to understand the basics of how a
Common Eider, lending a thick insulating layer to warm
feathers. In hot weather, adults provide countercurrent exchange works not only helps to understand many the developing eggs. Photo courtesy of Ma ryTremaine/
shade from the sun, sometimes spread- phenomena in physiology, but heightens appreciation of the problem- CLO. b. Northern Cardinal: A male Northern Cardinal
ing their wings to increase the shadow
solving nature of evolutionary adaptation. fluffs up its plumage, increasing the number of insulat-
area or to enhance ventilation, as this ing air spaces among the feathers for protection against
American Robin is doing. Drawing by The problem fora gull standing on ice or swimming in frigid water
the cold of a New York winter. Photo by Marie Read.
Charles L. Ripper. is one of conserving vital body heat while supplying its legs and feet c. Juvenile Black-Crowned Night Heron: A juvenile
with oxygen and essential nutrients. Fortunately for the gull, its legs Black-crowned Night Heron tucks one foot up close
and feet are composed primarily of bone, tendon, and scaly skin—all to its belly and buries its bill in the feathers of its breast
tissues that have low metabolic requirements for oxygen and nutrients. and shoulder to keep warm on a chilly New Mexico
morning. Photo by Marie Read.
The active movements that they undergo are caused by the contraction
of muscles high up on the leg and within the contour of the body, which
are transmitted passively to the foot by tendons. Nevertheless, after
hours of swimming in the cold, a great deal of body heat could be lost
from the trickle of warm blood that must perfuse the legs and feet to
supply their minimal needs. Completely shutting off the circulation to
the limbs is not an option, because the bird has absolute requirements
fora small amount of oxygen, for the removal of accumulating wastes,
and for some warming of the extremities—which may be necessary to
prevent tissue damage due to freezing.
The anatomical basis for the solution to this dilemma, as with all
countercurrent exchanges, is in structural specializations of the blood
vessels (Fig. 4 125). In the normal blood supply, arteries become
-

progressively smaller as they branch toward the tissue to be supplied.

Eventually the blood flows into a capillary bed in the midst of the target
tissue. From the capillary bed the blood recollects into veins of ever-
i ncreasing size, making its way back to the heart. In contrast, a second c. Black-crowned Night Heron

Cornell Laboratorq of Ornithologg Handbook of Bird Biologq

4.150 Howard E. Evans and J. B. Heiser Chapter 4—What's Inside: Anatomq and Phi1siologq 4.151
circulatory pattern develops in a countercurrent system. The second b
system is always characterized by the breakup of the arterial supply Direction of Blood Flow
vessels into a network or mesh of small vessels before the target tissue
is reached, and a splitting of the venous return vessels into a similar felt
terc u
network aftertheveins have collected the blood from tissue capillaries. Location of Sphincter Muscles coon en t)( (a
These arterial and venous networks intertwine, forming the actual That Divert Arterial Blood into Neat
Heat Exchanger
"heatexchanger," a distinct structure not embedded among the cells of
any nonvascular tissue, and often at some distance from the tissue ac-
tually to be nourished and cleansed by the blood they transport. In the a
case of leg and foot countercurrent heat exchangers, the intertwined Artery Vein
Cranial-tibial Vein
vessel networks are stretched out along the upper leg in the region of
the lower tibiotarsus bone. In this heat exchanger, the vessels within
the network are somewhat larger in diameter and thicker-walled than Cranial-tibial
Artery
capillaries, and as in all countercurrent exchangers, they are closely Numerous
Intertwined
packed together. Vessels of the
Countercurrent
The characteristics of the blood entering the two ends of the Heat Exchanger
elongate exchanger are very different. Especially distinctive is the (Tibiotarsal Rete) From Body
(Warm)
high temperature (near core body temperature) of the arterial blood
arriving from above the exchanger and the low temperature (possibly
Arterial
Blood
4. Venous
Blood
Flow Ir Flow
near that of the external environment), of blood returning upward from
95°F 9I.4°F
the tips of the toes. Obviously, heat will flow from the closely packed, (35°C) (33°C)
Metatarsal Metatarsal
small-diameter (and thus large-surface-area-per-volume) arteries to Artery Vein 86°F 80.6°F
(30°C) (27°C)
warm the blood in the veins. As it gives up heat energy to the veins, the
68°F 64.4°F
arterial blood is cooled; thus an exchange of thermal energy occurs (20°C) (18°C)
from arterial to venous blood. 50°F 48.2°F
(10°C) (9°C)
Note that heat exchange would occur even if blood in the inter-
twined arteries and veins flowed in the same direction. If this were the
situation, however, the blood temperature would quickly come into cm, c7) c)k-/ From Foot
(Cold)
equilibrium about midway between the arterial and venous tempera-
tures of blood entering the exchanger. The exchange potential of the
actual system is of much higher efficiency, however, because the blood
Figure 4-125. Countercurrent Heat-Exchange System in the nial-tibial artery and cranial-tibial vein. The tiny vessels rejoin
flow along the length of the vascular network is always in the opposite Leg of a Gull: Certain birds, such as gulls and waterfowl, have to form the metatarsal artery and the metatarsal vein, respec-
direction in the arteries compared to the veins (that is, countercurrent). specialized circulatory patterns to reduce the heat lost through tively. b. Temperature Gradient: An example of the temperature
Because heat energy always will dissipate from an area of higher tem- their feet when standing on ice or swimming in cold water. gradient of the skin of the leg and foot of a gull standing on ice.
perature to an area of lower temperature, chilled arterial blood nearing In a normal circulatory pattern, arteries become progressively The countercurrent heat exchanger allows the bird to keep its
smaller as they approach the tissue being suppl ied. There, blood body significantly warmer than its feet. c. The Mechanism of
the end of its flow through the exchanger on its way to the foot is still
passes through a capillary bed in the target tissue, and returns Heat Exchange: Arterial blood arriving from above the heat
slightly warmer than the coldest venous blood arriving from the foot, to the heart through a series of increasingly larger veins. In a exchanger is the same high temperature as the core of the body,
so the little remaining heat energy can flow from the arterial blood to countercurrent system, the arteries divide into a network or whereas venous blood arriving from the foot is nearly as cold
the venous blood (see Fig. 4-125c). Likewise, at the upper end of the mesh of smal I vessels before the target tissue is reached, and the as the surrounding air. Because of the close proximity of the
veins divide and intertwine with the arterial network after the finely divided blood vessels, heat flows from the arteries into
exchanger, where venous blood is very much warmed, it still can be
capillary bed in the target tissue, along the pathway back to the the veins along the length of the heat exchanger, ensuring that
warmed further because it is flowing close to arterial blood at body heart. This mesh of intermingling arterioles and venules, which the venous blood will be warmed before returning to the rest
core temperature, the highest in the entire exchanger. The elongate is not embedded among the cells of any target tissue, forms the of the body. The key to the warming power of the system is that
countercurrent nature of the exchanger assures near complete ther- actual "heat exchanger." In gulls (main drawing) and waterfowl, the blood flows in opposite directions ("countercurrent flow")
mal exchange: the arterial blood can be nearly as cold as the foot by a countercurrent heat exchanger is located in the upper leg in in the two vessels: note that even toward the proximal end (top)
the region of the lower tibiotarsus, and is technically termed of the heat exchanger, where the venous blood is fairly well
the time it exits the exchanger, and the venous blood can be nearly
the "tibiotarsal rete." Sphincter muscles located in the artery warmed, it continues to receive heat from the arterial blood
as warm as the core body temperature, instead of each being at some just below the heat exchanger close to divert blood through the because it passes near the warmest arterial blood at this point.
temperature in between. exchanger when external temperatures are sufficiently cold (see The numbers illustrate a possible temperature gradient for the
Although the diameter and wall thickness of the vessels in this Fig. 4-126). a. Vessels of the Heat Exchanger: A close-up view blood in each vessel, and are after Campbell (1990). Drawings
of the heat exchanger shows the numerous, closely intertwined by Christi Sobel.
type of heat exchanger in the limbs are small and allow heat to flow
arterial and venous vessels, formed by the breakup of the cra-
efficiently from arterial to venous blood, the diameter is too large,

Cornell Laboratortj of Ornithologq Handbook of Bird Bioloyi

4.152 Howard E. Evans and J. B. Heiser Chapter 4 — What's Inside: Anatomq and PINsiologii 4.153
and the walls too thick, to allow oxygen, nutrients, ions, or wastes to body, which cools the blood flowing just beneath the skin. Some birds
diffuse efficiently—so these things are not "exchanged." Diffusion of open their mouths and pant. In this way, the bird increases the area of
chemicals requires a very great blood vessel surface area compared the body exposed to the air and the amou nt of air moving across the ex-
to the volume flowing through the vessel, which occurs only with very posed skin, enhancing the loss of heat. The evaporation of water vapor
thin-walled, small-diameter vessels. Thus the limb does not suffer de- from the lungs and air sacs also takes away heat. Pelicans, cormorants,
privation of oxygen or nutrients. herons, owls, and nighthawks have an even more efficient cooling
In addition, both the countercurrent exchanger and the normal method, called gular fluttering (Fig. 4 127). They open their mouths
-

arterial system supplying the lower limb are regulated by sphincter wide and vibrate the thin, expansive gular membranes of the throat.
muscles in the artery walls. As a result, blood can either be passed The movement increases the blood supply in the throat and exposes an
through the exchanger to maximize heat conservation or, in times even larger featherless area to moving air, thus accelerating heat loss.
of overheating, can entirely bypass the exchanger, flowing instead The blood also loses heat as it flows through any featherless areas on
through the standard circulatory circuit to the feet to cool the body, the head, body, or legs. Young pelicans, in addition to gular fluttering,
using the feet as radiators (Fig. 4 126).
- may stand in shallow water during the hottest part of the day, the blood
Other types of countercurrent exchangers, with functions other passing through their enormous webbed feet, cooling as it flows.
Figure 4-126. How Blood is Diverted than heat transfer (as in the salt-excreting glands, in the nitrogen-ex-
into the Heat Exchanger: Blood is creting kidneys, and in the parabronchi of the lungs [see Fig. 4-811), Torpor
diverted into the heat exchanger in a
have different characteristics appropriate to their function. The di- In 1946, a California ornithologist found a Common Poorwi II in
bird's leg (see Fig. 4-125) by sphincter
muscles located just beyond the junc- ameter and wall thickness of the vessels may be different, non-blood a rock crevice during the winter (Fig. 4 128). When he picked it up he
-

tion between the artery supplying the vessels may compose the network (as in the kidneys and lungs), and could detect no heartbeat or respiration, yet the bird was not dead.The
lower leg and the artery supplying the so forth. But in all cases, the basic principle of efficiency of exchange bird was torpid (hibernating). Its cloaca! temperature was between 64
heat exchanger. In warm weather, when
through intimate countercurrent flow is the same. and 67° F (17.7 and 19.4° C), whereas a Common Poorwi I l's normal
conservation of heat is unnecessary,
the sphincter muscles relax, allowing
temperature is 106° F (41.1° C). Over an 88-day period, during which
arterial blood from the body to bypass Cooling the air temperature was around 42° F (5.6°C), the ornithologist handled
the heat exchanger and proceed to the Getting rid of excess heat is a problem because birds, unlike the bird at two-week intervals, replacing it in the crevice each time. It
lower leg, where the heat is lost. In mammals, do not have sweat glands. The primary way that animals remained motionless during this entire period, and its cloacal
cold weather, the sphincter muscles
cool themselves is through evaporation of water from the surface of the temperature continued to be near 64° F. The weight of the
contract, forcing arterial blood from
the body through the heat exchanger, bird remained about the same. After 12 weeks the bird
thereby conserving heat. awakened and flew off, just as environmental tempera-
tures began to rise and insects began to appear. When
a bird or mammal goes into a profound state of sleep,
Warm Weather Cold Weather

Artery Vein Artery Vein

a. Cormorant
Heat Heat
Exchanger Figure 4-127. Avian Cooling Methods:
Exchanger
Birds use a variety of methods to cool
Sphincter Muscles Sphincter Muscles
Relaxed: Blood Contracted: Blood Flows themselves in hot weather. a. Cormorant
Bypasses Through Gular Fluttering: A cormorant performs
Heat Exchanger Heat Exchanger ♦ Direction of gular fluttering holding its bill open and
Heat Transfer vibrating the thin gular membranes of its
throat, in order to dissipate heat. Draw-
ing by Charles L. Ripper. b. Eastern King-
bird Cooling Off: Unable to abandon her
duties at the nest on a hot summer day,
an incubating female Eastern Kingbird
reacts to heat stress in several ways: by
panting, by raising her body out of the
nest, and by elevating her wings slightly,
thereby exposing her legs and wings to
b. Eastern Kingbird any breeze. Photo by Marie Read.

Cornell Laboratorq of Ornithologui Handbook of Bird Bioloqq

4.154 Howard E. Evans and,J. B. Heiser Chapter 4—What's Inside: Anatornq and Phtisiologq 4.155
Figure 4-128. Common Poorwill: Cer-
tain birds, such as swifts, hummingbirds,
24
and nighthawks and their relatives—in-
cluding the Common Poorwill shown c 21
here—are known to sometimes enter . EL 18
a state of torpor at night or during cold E
zc 15
weather. A torpid bird's temperature
o 1 ":) 12
drops and its metabolic processes and U
9
reactivity slow profoundly, allowing it to
conserve energy when food is not avail- 6
able. Photo courtesy of Don and Esther O 3
Phillips/CLO.
0
12:00 2:00 4:00 6:00 8:00 10:00 12:00 2:00 4:00 6:00 8:00 10 00
Day Night Day

about 70 beats per minute; of hummingbirds, about 615 beats per Figure 4-129. Fluctuations in the
minute—the fastest in the bird world. In most birds, the heart beat is Metabolic Rate of a Male Anna's Hum-
mingbird: The metabolic rate, measured
considerably faster than in mammals of comparable size.
as oxygen consumption (cc per gram
The rate of circulation of the blood and the general metabolic rate of body weight per hour), of a single,
increase during flight to meet the oxygen and nutrient demands of an captive Anna's Hummingbird varies
allowing its body temperature to drop with a consequent slowdown active body. Because the flapping flight of falcons requires more energy throughout a 24-hour period. During
of all metabolic and stimulus-reaction processes, it is said to be in a the daytime, the bird alternately rests on
than the soaring flight of vultures and hawks, falcons have a faster heart
a perch and hovers briefly to feed, and
state of torpor. rate and relatively larger hearts than the soaring raptors. In contrast, its metabolic rate is relatively steady. At
Poorwi I Is, as determined from later tests, become torpid in tem- in the Great Black-backed Gull, the Mallard, and possibly other birds, around 6:00 P.M. there is a pre-roosting
peratures between 35.6 and 66° F (2 and 18.9° C), and in that state the volume of blood pumped per heart beat increases during flight, peak of feeding activity, after which the
use only 0.35 ounces (10 grams) of stored fat in 100 days. We now metabolic rate declines precipitously,
instead of the number of beats per minute increasing. This, of course,
indicating a period of torpor that lasts
know that several species of swifts and hummingbirds, and the Lesser also increases the blood pressure. through the night. Around 4:00 A.M.
Nighthawk, may also regularly enter a torpid state. At night, in a torpid, The heart rate also varies between individuals of a species, de- metabolic rate again rises as the bird be-
predator-vulnerable metabolic condition, the body temperatures of pending on the individual bird's activity and body temperature, and the comes active. By going into torpor, the
both Anna's and Al len's hummingbirds decrease, and both species use surrounding air temperature. A three-day-old House Wren, essentially hummingbird, with its energy-intensive
less than 3 cc of oxygen per gram of body weight per hour, a two-thirds foraging strategy, conserves energy
cold-blooded at that age, has a heart rate of 121 beats per minute at 70°
when food resources are temporarily
or more reduction below their basal metabolic rates (10.7 to 16.0 cc F (21.1° C), 320 beats at 90° F (32.2° C), and 411 beats per minute at unavailable. Adapted from Welty and
oxygen) (Fig. 4 129). By going into torpor, a bird conserves energy
-
100° F (37.8°C). Many small birds, when active, double or even triple Baptista (1988, p. 132); originally from
when food resources are unavailable. It is not a strategy without risks, the heart rate of their resting state. Pearson (1953).
however. A coyote finding the above-mentioned poorwi I I would not
have replaced it in its rocky crevice! SPECIES Resting Heart Rate (Beats/Minute)
Mouse 700
Heart Size and Heart Rate Hummingbird 615
Birds' hearts are larger than those of most mammals of compa- Shrew 600
rable size. In most birds, the greater the body weight, the smaller the American Robin 570
Table 4-1. Resting Heart Rates of
heart in proportion to the weight. In the Ostrich and Sandhi I I Crane, Black-capped Chickadee 520 Selected Birds and Mammals: A com-
the heart is less than one percent of the body weight; in hummingbirds, White (Laboratory) Rat 350 parison of the heart rates of various
the heart may be as much as 2.75 percent of the body weight. A rela- American Crow 342 birds shows that as body size decreases
the resting heart rate tends to increase.
tively larger heart is necessary for smaller birds, which are generally Duck 240
At opposite extremes are the Ostrich at
more active and have a far more rapid metabolism, in part owing Rock Dove 200 60 to 70 beats per minute and the hum-
to their greater rate of heat loss. In some species, males have larger Mourning Dove 165 mingbird at 615 beats per minute. A sim-
hearts than females. Heart weight is greater in relation to body weight Rabbit 150 ilar relationship between body size and
Turkey Vulture 132 heart rate holds for most mammals. The
among species that inhabit higher elevations (with lower temperatures
heart rate of a bird is often higher than
and oxygen concentrations) and higher latitudes (lower temperatures) Dog 100 that of a mammal of comparable size,
compared to their lowland or more equatorial kin. Domestic Turkey 93 however. For example, compare the
Similarly, the heart rate increases with a decrease in body size Human 70 duck heart rate of 240 beats per minute
(Table 4 1). The resting heart rate of the Ostrich and cassowaries is
-
Ostrich 60-70 to that of the similar-sized rabbit at 150
beats per minute.
Elephant 25
Cornell Laboratory of Ornithologq Handbook of Bird Biolo,sii
4156 Howard E. Evans andJ. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologq 4.157
Blood pressure, like heart rate, also tends to be higher in birds
than in mammals.The mean arterial pressure in humans is equal to that
of a column of mercury 100 millimeters high. The mean blood pres-
sure of the Rock Dove is 135 mm; the American Robin, 118 mm; and
the European Starling, 180 mm. Extreme fright in birds may increase
the blood pressure so much that the aorta or atria rupture, resulting
in death.

Respiratorq Rate
Birds need a great deal of oxygen and food to sustain their high met-
abolic rate. Although the oxygen requirements of most birds are higher
than for most mammals, the respiratory (breathing) rates of birds are
slower than for mammals of comparable weight. This results primarily
from the more efficient avian respiratory system. The breathing rate of
domestic turkeys and chickens at rest is 16 to 38 breaths per minute,
about the same as in humans. In smaller birds, however, the rate varies
from 45 breaths per minute in the Northern Cardinal to over 80 in the
HouseWren.The respiratory rates of sleeping Black-capped Chickadees
vary from 65 per minute with the air temperature at 50° F (10°C), to 95
per minute with the air temperature at 89° F (31.7° C). In contrast, nest-
ling European Swifts, when in a torpid state during bad weather, may
have a respiratory rate as low as eight breaths per minute.
Oxygen requirements and respiratory rate increase in flight. The
respiratory rate of the House Sparrow increases from 50 breaths per
minute when at rest to 212 when in flight. This increased respiratory
rate accompanies an increased rate of heat production from muscular
activity, but also an increased rate of heat loss—because much more
air is passing more rapidly into and out of the lungs and air sacs, where
Both measures are indications of just how dramatically loons can re- Figure 4-130. Common Loon Forages
heat from the body warms the air and eventually is lost to the atmo- Underwater: Special respiratory chal-
duce their short-term need for oxygen (Fig. 4 130).
-

sphere upon exhalation. lenges face birds that dive underwater

Because the lungs are very close to the flexible rib cage, which to find their food. They must balance re-
deforms with each wingbeat (see Fig. 5-5), it seems as though a bird Water and Salt Regulation ducing their buoyancy, which requires
exhaling upon diving, with maintaining
must breathe in and out with each wi ngbeat.Th is does occur in pigeons: The correct proportions of salts and water must be maintained an oxygen supply for their metabolic
they inhale on each upstroke and exhale on each downstroke.Th is is not within the cells, in the spaces between the cells, and in the blood. If needs while underwater. The Com-
true, however, for all birds. In flight experiments, some birds with bills there are too many salts, the body retains water in an attempt to dilute mon Loon is able to reduce its oxygen
encased in rubber balloons demonstrated that breathing during flight requirements dramatically, allowing
the salt concentration; too few salts, and dehydration occurs. If the
it to remain underwater for as long as
is irregular and that they may inhale on either the upstroke or down- wrong proportions of different salts exist, cell membrane function be- 15 minutes, and to dive as deep as 180
stroke. In other experiments, a flying Western Gull had an average of comes impaired. The correct balance is critical to the survival of the feet below the surface. Photo by Tomas
242 wingbeats and 81 breaths per minute; a flying Lesser Scaup had an cells and therefore of the animal itself. The system that regulates salt Cajacob/Minnesota Zoo.
average of 645 wingbeats and 140 breaths per minute, and a Red-tailed balance, however, is exceptionally complicated. Nevertheless, we
Hawk beat its wings 13 times without taking a breath. must mention one particularly interesting feature of birds with respect
Birds that dive have special respiratory problems. Because they to salt balance.
must reduce buoyancy, it seems logical that they exhale upon diving, Birds have a challenge in conserving water; they must make up
reducing the air in the lungs and air sacs and thus their buoyancy. for water lost as vapor from the lungs and air sacs. This conservation
Deprived of respiratory gas, the heart and oxygen consumption rates becomes especially critical as respiration rate increases. The skin,
slow. Penguins, in simulated underwater conditions, reduce thei r con- feathers, and scales all help in preventing the loss of body fluids from
sumption of oxygen by 2 0 or 25 percent. Common Loons are known to the general body surface. The greatest conservers of water within a
survive underwater for at least 15 minutes, and have been underwater bird, however, are the kidneys, which resorb most of the water from
long enough to tangle themselves in fish nets more than 180 feet deep. the urine before it passes from them.

Cornell Laboratorq of Ornitholo9q Handbook of Bird Biolom

4.158 Howard E. Evans and J. B. Heiser Chapter 4—What's Inside: Anatomq and Phqsiologg 4.159
Figure 4-131. Location of the Salt Table 4-2. Maximum Life Span of Selected Wild Birds: This list
Glands in Marine Birds: Seabirds that Life Span and Senescence presents the maximum known age (in years and months) of a se-
drink only salt water have special salt-ex- When compared to mammals, and consider- lection of North American birds, determined from banding data
creting glands to remove excess salt from ing their body weight, birds are generally long-lived from the Bird Banding Laboratory at the PatuxentWildlife Research
their bodies. These paired salt glands Center in Laurel, Maryland. The maximum age is calculated as the
(Table 4 2). The Japanese Quail has one of the short-
-

(colored areas) are located on top of the difference between the age of the bird at banding and either the
head, each in a shallow depression in est life spans, at 2 to 5 years. Apparently many birds
date of its subsequent live recapture or the date of the recovery of
the skull above or adjacent to the eye, have evolved mechanisms to protect against rapid its band, if the bird died. As of this writing, further longevity infor-
or in some species within the orbit of aging. Parrots have certainly found the "fountain of mation is available from the following Internet web site <www.
the eye. Like the kidneys, they remove pwrc.usgs.gov/bbl/homepage/longvrec.htm >
youth." As a group they have the longest absolute
salt from the bloodstream and concen-
trate it. The salty fluid produced by the
life spans of any bird, African Grey Parrots living to Maximum Age
salt glands flows through ducts into the 60 or 70 years, and macaws of the genus Ara living Species (Years-Months)
nasal cavity, and then through the nostrils to as much as 90 years! These ages are more than Greater Roadrunner 3-09
or mouth to the outside. In gulls, the salt four times as old as would be predicted from their Blackpoll Warbler 4-03
solution emerges from the nostrils and Golden-crowned Kinglet 5-04
body mass, compared to a mammal. The compara-
drips from the tip of the bill, whereas in Carolina Wren
tive longevity of birds is surprising, because they 6-02
cormorants, it flows along the roof of the
Yellow-bellied Sapsucker 6-09
mouth to the tip of the bill. The pelican Petrel have high body temperatures, high blood glucose
has grooves along the upper surface of
Western Kingbird 6-11
levels, and high metabolic rates. All of these condi-
its bill that channel the fluid to the bill Roseate Spoonbill 7-09
tions tend to limit the mammalian life span. Western Tanager
tip, preventing it from entering the bird's The avian process of excess salt elimination was once puzzling. 7-11
pouch and being re-ingested. Each of
Senescence (aging) occurs as a result of sev- Eastern Bluebird 8-00
The kidneys and sweat glands provide this function in mammals, but eral factors that are not well understood, but it must
these birds simply shakes the salty liquid Barn Swallow 8-01
off of its bill tip. In petrels, however, the birds have no sweat glands, and the kidneys eliminate only a portion be related to the breakdown of cellular protective Burrowing Owl 8-08
fluid is forcibly ejected ("sneezed") out of the salts. In seabirds that drink only salt water, the kidneys secrete mechanisms. These mechanisms include cells be- Ruby-throated Hummingbird 9-01
of the bird's tubular nostrils. Drawing by urine that is only half as salty as the seawater they have been drinking. ing able to maintain and repair their external and Common Yellowthroat 11-06
Eric Mose, from Schmidt-Nielsen (1959).
Where does the rest of the salt go? internal membranes, and to successfully divide in a Sanderling 12-01
Used with permission.
Scientists have long known that birds eliminate excess salts controlled (nonmalignant) manner. Birds may prove Black-capped Chickadee 12-05
through salt glands located either in a skull surface depression above Loggerhead Shrike 12-06
very interesting in aging research.
the eye, or within the orbit (Fig. 4 131). The excess salts, dissolved in
-
Wild Turkey 12-06
clear fluid, flow from the glands through ducts into the nasal cavities. Common Loon 12-11
House Sparrow 13-04
By way of the nostrils or mouth, the salty fluid then flows to the tip of Major Anatomical American Kestrel 13-07
the bill in droplets that the bird shakes off. This excretion can be seen
Purple Martin 13-09
most readily in seabirds. Several land birds, such as the Australian
Budgerigar, have large salt glands that allow them to drink from brine
Differences between Red Knot 13-11
American Crow 14-07
pools in their native habitats without accumulating salts in their bod-
ies (Fig. 4 132).
-
Birds and Mammals Northern Cardinal
Hairy Woodpecker
15-09
15-10
Figure 4-132. Budgerigars at a Water-
■ The table on the following pages contrasts some Blue Jay 17-06
hole: The gregarious, nomadic Budgeri- of the structures seen in present-day birds and mam- Whooping Crane 18-10
gar exploits any avai lable water source in mals to illustrate how they differ. Explanations of the American Woodcock 20-11
its arid native habitat—the deserts of the differences cited can be found in the discussions of American Coot 22-04
Australian interior—even drinking from Bald Eagle 22-09
each organ system in the text or in the figures.
brine pools. It is one of several land birds Great Blue Heron 23-03
with large salt glands that prevent salt
Trumpeter Swan 23-10
build-up in its body. Here, a huge flock
Red-tailed Hawk 25-09
of Budgerigars descends on a waterhole.
Photo by Andrew Henley/Biofotos.
Mallard 26-04
American White Pelican 26-05
Ring-billed Gull 27-03
Great Horned Owl 27-07
Canada Goose 28-05
Leach's Storm-Petrel 31-01
Mourning Dove 31-04
Atlantic Puffin 31-11
Arctic Tern 34-00
Laysan Albatross 42-05

Cornell Laboratori of Ornitholo8q Handbook of Bird Biolo8ti

4.160 Howard E. Evans and J. B, Heiser Chapter 4 — What's Inside: Anatornq and Nuisioloaq 4.161

BIRDS MAMMALS BIRDS MAMMALS

Skeleton Ear
• light, air-filled (pneumatic) bones • heavy, marrow-filled bones • no external ear • large external ear
• skull has cranio-facial hinge: moveable upper jaw • no cranio-facial hinge: non-moveable upper jaw • tympanic membrane convex (curved outward) • tympanic membrane concave (curved inward)
• single occipital condyle for skull • double occipital condyles • single auditory ossicle: columella (stapes) • three auditory ossicles: malleus,incus, and
stapes
• few sutures visible on skull • distinct skull sutures
• inner ear surrounded by pneumatic bone • inner ear surrounded by dense bone
• jaw articulation is quadrate to articular bone • jaw articulation is dentary to temporal bone, the
quadrate having become the incus and the • short cochlea • long, coiled cochlea
articular having become the malleus of the
middle ear
• vertebral regions are variously fused • vertebrae are distinct
Eye
• shape of eyeball flat to tubular • eyeball spherical
• sternum large and keeled • sternum small and segmental
• bony ossicles in sclera • no sclerotic bones
• forelimb with three digits • forelimb usually with five digits
• ciliary processes attach to lens • ciliary processes not attached to lens
• fusions of limb bones as: a carpometacarpus, • separate carpus, metacarpus, tibia, tarsus, and
tibiotarsus, and tarsometatarsus metatarsus • ciliary muscle contraction forces • ciliary muscle contraction relaxes the lens,
lens to become round by squeezing it allowing it to become round by elastic
• pelvic symphysis absent • pelvic symphysis present
rebound
• "wishbone" (fused clavicles and interclavicle) • clavicles, if present, not fused as "wishbone"
• both lens and cornea change shape to focus • only lens changes shape
present
object
• coracoid bone acts as a strong brace of the • coracoid bone absent
• pecten present in vitreous chamber • no pecten present
shoulder
• formula for the number of phalanges in digits • formula for the number of phalanges in digits
1 to 4 of pelvic limb is 2-3-4-5 1 to 5 is 2-3-3-3-3 Circulatory System
• functional ankle joint is intratarsal • functional ankle joint is intertarsal • aorta derived from right 4th arch • aorta derived from left 4th arch
• pubis directed caudally • pubis directed cranially • right and left precavae present • usually only right precava present
• nucleated red blood cells • nonnucleated red blood cells

Muscles • few, if any, lymph nodes • many lymph nodes

• breast musculature massive • breast musculature small • lymph "hearts" in tail region • no lymph "hearts"
• limb tendons often ossified • limb tendons rarely ossified • lymphatic erection of phallus • arterio-venous erection of penis
• dorsal vertebral muscles reduced and of little • dorsal vertebral musculature of great function • two portal systems (renal and hepatic) • only hepatic portal system
in function locomotion

Respiratory System
Nervous System • epiglottis absent • epiglottis present
• cerebral cortex thin; corpus striatum large • cerebral cortex thick (serves as major • vocal cords absent • vocal cords usually present
(serves as major integrative region) integrative region); corpus striatum
• thyroid cartilage absent • thyroid cartilage present
relatively small
• tracheal rings complete • tracheal "rings" open dorsally
• corpus callosum (a major connection between • corpus callosum present
the two hemispheres of the brain) lacking • syrinx present • no syrinx
• cerebrum smooth • cerebrum has folds and grooves • small, compact lung • large, spongy lung
• mesencephalic optic lobes are largest • telencephalic optic lobes are largest • lung not expansible • lung greatly expansible
• small olfactory lobes • large olfactory lobes • anastomosing parabronchi • dead-end alveoli
• few taste buds • many taste buds • air sacs present • air sacs lacking
• glycogen body in spinal cord • no glycogen body • no diaphragm • strong diaphragm

(Continued on p. 4.162)

Cornell Laboratorq of Ornithologq Handbook of Bird Biolooq

4.162 Howard E. Evans and J. B. Heiser

BIRDS MAMMALS

Digestive Stistern
• teeth lacking • teeth usually present
• crop usually present • crop absent
• stomach in two parts: glandular and grinding • stomach usually single, never a grinding portion
• colic ceca usually paired or absent • cecum usually single or absent
• cloaca always present • cloaca rarely present

Urogenital Stjstevn
• kidney recessed in skeleton
• bladder absent
• all egg-laying
• kidney not recessed in skeleton
• bladder present
• only monotremes lay eggs
Birds on the Move:
• functional ovary only on left side • functional ovary on both sides
• left oviduct functional
• mammary glands absent
• testes always internal
• both oviducts functional
• mammary glands present
• testes usually external
Flight and Migration
• cloacal phallus in some • external penis except in monotremes
• female heterogametic (ZW) • male heterogametic (XY)
• embryo derives nutrition from yolk • nutrition from placenta except in monotremes
Kenneth P Able

SugBested Readin8s Ten miles off the southern coast of New Zealand, I was
Darling, Lois and Louis. 1962. Bird. Boston: Houghton Mifflin Co. huddled in the lee of a ship's cabin, my arm wrapped
around a railing to prevent being thrown overboard or
Evans, H. E. 1996. Anatomy of the Budgerigar and other birds. In Diseases of
swept away by the waves crashing over the stern of the
Cage and Aviary Birds.W. J. Rosskopf and R.W.Woerpel, editors. Baltimore:
Williams & Wilkins, Inc. boat. On th's, my roughest sea voyage, with the ship plunging up and
down the waves, I had trouble holding the binoculars steady: the view
King, A. S. and J. McLel land. 1984. Birds: TheirStructure and Function, Second
Edition. London: Bailliere Tindall. oscillated between blank walls of water and the sky. The conditions
were not conducive to bird watching.
King, A. S. and J. McLel land. 1979-1989. Form and Function in Birds. Four
Volumes. London: Academic Press. But birds there were. Hundreds of them. Shearwaters and al-
batrosses for the most part—this world, so alien and difficult for me,
Leahy, C. 1982. The Birdwatcher's Companion. New York: Bramercy Books
was their everyday habitat. Into the gale they flew, effortlessly angling
(Random House Value Publishing, Inc.).
upward, then swooping down among the swells. So perfectly were
Pough, F. H., C. M. Janis, and J. B. Heiser. 1999. Vertebrate Life, Fifth Edition.
they adapted that they made it look easy (Fig. 5 1). Shipbound and
-
Upper Saddle River, New Jersey: Prentice Hall.
nauseated, I envied them. Like many before, I wished that I could
Proctor, N. S. and P. J. Lynch. 1993 Manual of Ornithology. New Haven , CT:
briefly do what they were doing, feel the world as they felt it, and sense
Yale University Press. 340 pages.
in my muscles the kind of exquisite control of movement they must
Van Tyne, J. and A. J. Berger. 1971. Fundamentals of Ornithology. New York:
experience. Impossible, of course, and so, like those of generations
Dover Publications, Inc.
before, I simply looked with awe and enjoyed vicariously the splendor
Waldvogel, J. A. 1990. The bird's eye view. American Scientist 78(4):342-
of their flight.
353.
The power of flight is the quintessential characteristic of birds,
Welty, J. C. and L. Baptista. 1988. The Life of Birds, Fourth Edition. Orlando,
the central adaptation around which many of the most interesting as-
FL: Saunders College Publishing. 581 pages.
pects of avian anatomy, physiology, and behavior have been molded.

Cornell Laboratory of Ornithology

5.2 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.3

Figure 5-2. Fossil Pterodactylus: Shown

here is a fossil of one type of pterosaur
(ancient flying reptile), the sparrow-sized
Pterodactylus. The wings of pterosaurs,
somewhat I ike those of bats, consisted of
a membrane of skin that stretched from
the front limbs to the sides of the body,
and possibly to the hind limbs as well.
Pterosaurs lived in the Mesozoic era
and, like birds, had hollow, long bones;
in contrast to flying birds, their sternum
had no keel. Note here the long bones
of the wings, as well as the flexible neck
and long jaws. Photo by GeoScience
Features Picture Library.

Figure 5-1. LaysanAlbatross: With grace The birds I was watching from the ship spend most of their lives on
and elegance, an albatross glides low the wing. Not only do they fly magnificently in difficult conditions,
over the water on long, narrow wings.
they travel vast distances, some of them literally circumnavigating
The Laysan Albatross, pictured here, Figures-3. GlidingAnimals: Shown here
ranges throughout the northern Pacific the globe. These two characteristics—the power of flight and their in-
area few animals that can glide, at least
Ocean, breeding mostly on coral atolls credible migrations—are the main reasons why birds have fascinated briefly, through the air. Many use gliding
in the Hawaiian Islands. Photo by P La people down through the ages. to escape more earth-bound predators,
TourretteNIREO. Flying Fish
Although some species of birds have lost the ability to fly during as well as to simply change locations. By
the course of evolution, all modern lineages of birds arose from flying expelling a stream of water forward, fly-
ing squid (0 m mastrep h es i ecebrosa)
ancestors. In the 450 million years since life first emerged on land, project themselves backward with such
powered flight has evolved in only two phyla, the arthropods (insects, speed that they often shoot three to four
crustaceans, and their relatives) and the chordates (vertebrates, tuni- yards out of the water, sometimes even
cates, and lancelets). Insects, birds, bats, and the extinct pterosaurs onto the decks of passing ships.
The more tropical flying fish
(featherless, flying reptiles) (Fig. 5 2) all have made flight their major
-

(species pictured: Exocoetus

means of moving about. Parachuting and gliding—more limited types vol itans) undulate their tails
of flight—are found in most vertebrate classes (for example, flying from side to side, first picking up
fishes, parachuting frogs, gliding agamid lizards, flying squirrels, fly- Flying Dragon speed underwater, then on the surface.
Then, spreading their large pectoral fins,
ing lemurs, and marsupial sugar gliders), and in a mollusc (the flying
they glide through the air up to 1 00 yards,
squid) (Fig. 5-3). sometimes skimming off the surface for
Flying Squirrel
up to 400 yards. The flying dragons (ge-
nus Draco), forest dwellers of Southeast
The Flight Stindrome Asia and the East Indies, can glide for
30 or more yards from the treetops by
■ Occupying the fluid medium of air and using powered flight for extending a skin flap between the limbs.
mobility have required birds to evolve a suite of extraordinary adap- Similarly, many small, arboreal mam-
mals, such as the North American flying
tations, which sets birds apart as the most distinctively different class
squirrels (genus Glaucomys), glide great
of living vertebrates. These adaptations also constrain their form such distances between trees. The flying frogs
that birds, as a group, resemble one another more than do members • 11' (pictured here, genus Rhacophorus) ex-
tit
of most other vertebrate classes. The most notable of these adapta- tend membranes between their toes to
tions are briefly described here. Please refer to Figure 5 4 as you read
-
glide from treetops, even executing turns
Flying Squid while airborne.
through adaptations 1 to 7 below.

Cornell Laboratorq of Orndholo9q Handbook of Bird Biologq

5.4 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.5
Figure 5-4. Avian Adaptations for 1 A Strong, Light Skeleton: The skeleton of a flying bird must be both 2. Reduced Body Weight: Weight reduction is the theme throughout
Flight: Most of the distinctive features light, to enable the animal to fly, and extremely strong, to withstand the avian body. The reptilian teeth have been replaced by a light-
of a typical bird skeleton are adapta-
the stresses placed upon it. As any engineer knows, this combination weight beak. The small, internal gonads shrink to almost nothing in
tions for flight, as demonstrated by this
Rock Dove (pigeon) skeleton. Weight is of characteristics is difficult to reconcile. Compared with the bones the nonbreeding season.
decreased by the hollow bones, light of terrestrial vertebrates, bird bones contain much more air. Portions 3. A Rigid Skeleton: Skeletal rigidity is achieved by the fusion of many
skull, toothless beak, and reduced num- of the hollow long bones of the wings are continuous with the air
berof bones in the tail and hand regions.
bones—those of the hand and fingers, most of the wrist bones, and
sacs (part of the bird's respiratory system) and strengthened by series elements in the pectoral and pelvic girdles. Bony uncinate processes
Rigidity is achieved through the fusion
of many bones, especially those in the
of diagonal internal struts. Both the air sacs and struts are obvious extend back from the upper part of each rib, overlapping adjacent
pelvic and hand regions, and in por- adaptations for flight, and have disappeared in large flightless birds ribs to reinforce the rib cage.
tions of the vertebral column. Drawing such as Ostriches and Emus.
by Charles L. Ripper. 4. An Enlarged, Keeled Sternum: The avian sternum (breastbone)
is greatly enlarged and has a large keel to which the major flight
muscles are attached. In poor fliers, the keel and associated flight
muscles are smaller, and the sternum of flightless birds lacks a keel
Reduced and Fused Weight Reduction altogether (see Fig. 4-19).
Finger Bones Aided by Lightweight
5. Strong Bones in the Pectoral Girdle Prevent Collapse of Chest
Bones of Skull
and Toothless Beak Cavity During Flight: The coracoids and the furcula (wishbone),
formed from a fusion of the clavicles (collar bones), are supporting
Modified Joints
Allow Folding or elements that resist the huge pressures on the chest cavity created
Locking by the beating of the wings. High-speed x-ray movies of European
Hollow Long Bones
Fused 1 of Wings Starlings flying in a wind tunnel (Jenkins et al. 1988) show that the
Continuous with Air Sacs
t Bones furcula bends outward to each side during the downstroke of the
and Strengthened
by Internal Struts wings and recoils like a spring during the upstroke. The sternum
moves upward on the downstroke, and downward on the upstroke
(Fig. 5 5). This furcular "spring" and sternal "pump" may facilitate
-

the movement of air between the lungs and air sacs independent of
breathing. This system is particularly important because birds, un-
like mammals, have no muscular diaphragm to drive their breathing
apparatus.
Uncinate Processes
on Ribs Strengthen Strong Pectoral Bones
Coracoid Downstroke
Rib Cage Prevent Collapse of
Clavicle Chest Cavity
(Wishbone) During Wingbeats
Reduced Tail
Coracoid

Humerus

Fused Z Large Keel on Sternum for

Pelvic Attachment of Flight Muscles
Girdle
Furcula
(Wishbone)
Furcula
(Wishbone)

Figure 5-5. "Pump and Spring" Mechanism of Furcula and Sternum: Shown is a cross-sectional view of the pectoral girdle, look-
ing head-on toward the tail. Arrows indicate bone movement. During the downstroke, the furcula bends outward to each side
Rock Dove and the sternum moves upward; during the upstroke, the furcula recoils inward like a spring, and the sternum moves downward.
The action of this furcular "spring" and sternal "pump" probably helps to move air between the lungs and air sacs during flapping
flight, supplementing the normal breathing mechanisms.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 I
5.6 Kenneth P. Able Chapter 5— Birds on the Move: Flight and Migration 5.7
a. Downstroke b. Upstroke like perfection in the air, natural selection doesn't produce perfection.
It selects what works best from among the existing variations.
Scapula
Scapula
Tendon of the Foramen Foramen
Supracoracoideus Triosseum
Humerus
Triosseum Functions of the Flight Muscles
Humerus
Coracoid ■ Both of the major flight muscles, the pectoral is and the supracora-
Coracoid coideus, have their origin on the sternum and their insertion on the
Tendon of the
Sternum Supracoracoideus Sternum humerus of the wi ng. The traditional view of the action of these muscles
during flight was that the pectoral is pulled the wing down on each
downstroke, and the supracoracoideus lifted the wing back up during
each recovery stroke.
Supracoracoideus
Pectoralis Supracoracoideus New studies have shown, however, that the process is consid-
Muscle Pectoralis
Muscle Muscle
Muscle erably more complicated. Some of these studies use a technique (elec-
tromyography or EMG) in which fine wires are implanted in a muscle,
Figure 5-6. Pulley System for Tendon of Supracoracoideus Muscle: Shown is a cross-sectional view of the large flight muscles
recording the electrical activity associated with muscle contraction.
and pectoral girdle. a. Downstroke: The pectoralis muscle contracts (as indicated by black Vs), lowering the humerus and thus These analyses have revealed that the pectoral is is divided into two
the wing. b. Upstroke: The supracoracoideus muscle is attached to the dorsal surface of the humerus by a tendon. As a result of portions which have rather different functions. The larger portion
its dorsal attachment, when this muscle contracts (black Vs), it raises the humerus and thus the wing. The tendon reaches the top serves as the primary depressor of the humerus, but also slows down
of the humerus by passing through a hole formed by the junction of the coracoid, scapula, and humerus. This hole, termed the
the wing at the end of the upstroke and pulls the wing forward. The
foramen "triosseum" because it is formed by three bones, creates a pulley system that allows the supracoracoideus muscle to
remain below the wing and yet function to elevate it. As discussed in Skeletal Muscles, Ch. 4, this weight configuration is much smaller portion also acts as a depressor, but unlike the larger portion,
more stable for a flying bird than what would result if the supracoracoideus muscle were located on the back above the wings. is positioned to pull the wing backward. The supracoracoideus slows
down the wing at the end of the downstroke, and accelerates it at the
beginning of the upstroke.
6. Modified Joints in Wing Allow Folding or Locking: The bird wing Different species have varied flight requirements that are reflected
contains the same bones found in the human forearm, but they are by numerous adaptive differences in flight muscles. For example, in
greatly modified. In addition to much fusion of individual bones, birds such as hummingbirds, which use the upstroke as well as the
which imparts strength to the limb, the joints are modified to permit downstroke to generate power, the supracoracoideus is quite large.
each wing to fold neatly when the bird is at rest, or to lock rigidly to Another example of adaptive difference is that the fibers of bird flight
resist the forces acting upon it during flight. muscles are of several types. The most obvious are the red fibers, which
we know as "dark meat," and the white fibers, which constitute "white
7. Large, Powerful Flight Muscles: A bird's major flight muscles are the
meat." Red fibers get their color from their massive capillary beds
pectoralis and supracoracoideus (Fig. 5-6). The larger pectoral is is
containing blood and myoglobin, a substance within muscle cells that
proportionately the most massive paired muscle in any four-limbed
carries oxygen, the energy source for most cells. Using this oxygen (in
animal. It accounts for as much as 15 to 25 percent of a flying bird's
a process called aerobic respiration), red fibers oxidize fats and sugars
total body mass. These large muscles and a host of smaller ones not
to power sustained flight. The pectoral muscles of most long-distance
only provide the power to fly, but permit exquisite control over all
fliers are composed largely or entirely of red fibers, explaining why
aspects of wing movement.
ducks, for example, have so much dark meat. White fibers are of larger
diameter than red fibers, have fewer capillaries associated with each
For ease of discussion, each of these adaptations has been treated muscle fiber, and contain I ittle myoglobi n. Wh ite fibers derive their en-
as a more or less independent entity. Actually, they are intimately ergy from anaerobic ("without oxygen") respiration, and because this
related parts of a package that we may call the flight syndrome. Even process releases a byproduct called lactic acid—the same substance
though natural selection works through details—a small change in that builds up in the leg muscles of long-distance runners—these fi-
the mass of the pectoral is muscle, say, or in the length of a feather—it bers fatigue quickly. They are ideal for quick bursts of action, but not
is the individual as a whole that natural selection works against or sustained exercise. For example, the large amount of white fibers in
favors. In other words, it is how well the bird flies under natural condi- the breast muscles of turkeys enables them to burst into flight from the
tions—which House Finch escapes from the Cooper's Hawk and which ground and climb rapidly to clear trees. However, a turkey cannot fly
doesn't—that determines which characteristics natural selection sus- very far. I once watched a turkey try to fly across about a quarter mile
tains. In this way, natural selection has sculpted most birds into exqui- (0.4 km) of open water. It ran out of gas, plopped into the water about
site flying machines. Note, however, that although birds surely look 20 yards (18 m) from shore, and swam the rest of the way to land.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

5.8 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.9

How Do Birds Fig? lowing takes a simplified look at flight, concentrating on the basic
physical forces that act upon a bird (or bat, or butterfly, or airplane)
• Since the beginnings of recorded history, members of our essentially moving through the air.
earthbound species have been fascinated by the ability to fly. The first
attempts at human-powered flight took place in machines designed
Forces Acting on a Bird in Flight
to replicate the flapping action of bird wings. These ornithopters de-
Most of us have watched some very large bird, such as a Great
pended on humans flapping their arms to lift the crude wings (Fig.
Blue Heron, in fl ight.The next time you see one, pay careful attention to
5 7). Of course, they didn't get off the ground because wing flapping
-

exactly what the bird does. I recently saw a Great Blue Heron perched Figure 5-8. Great Blue Heron Flight
is much more complex than a simple up-and-down movement. In ad-
in the top of a large white pine on the edge of a woods. As I watched, the Sequence: As a heron takes off it bends
dition, human breast muscles are not proportionally as strong as the
heron leapt into flight, bending its legs and thrusting upward with them its legs to a crouch, then jumps up into
breast muscles of birds, and the human body is too heavy and lacks the air as it opens its huge wings and
as it began to beat its gigantic wings (Fig. 5 8). Through this effort it rose
-
essential streamlining for flight. Physicists have calculated that a 150- begins flapping. After a few wingbeats,
slightly, but once fully airborne it lost altitude for a few wingbeats until it reaches level flight with legs extended
pound (68kg) human would require a breastbone projecting 6 feet (1.8
it finally achieved stable, level flight, its neck drawn into an S and its straight back and neck drawn into an S.
m) forward to support ample flight muscles!
legs and feet extended straight back. The bird was headed for a nearby As it prepares to land, it glides to the de-
Mythological stories relating the unfortunate consequences of sired altitude or location, then extends
pond to hunt, so it flapped steadily, maintaining its altitude for some
Icarus's attempts to fly are familiar to everyone. But some progress has the neck and lowers the legs, bringing
distance. As it approached the pond, it set its wings and began to glide,
been made: hang gliding and parasai I ing bear witness to the power of its body into a more vertical position.
gradually losing altitude, approaching the ground at a rate that would The wings now flap more front-to-back
modern, computer-aided engineering coupled with space-age mate-
bring it precisely to the shore. I n the last seconds of flight, it extended than up-and-down, thus "catching" the
rials. But we still have to jump off high places, or be dropped from
its neck, dropped its legs, adopted a more vertical body alignment, and onrushing air and slowing the bird so
or towed behind airplanes, to get off the ground. Even with modern that it lands gently on its outstretched
again began to flap. The wings, previously oriented to slice through
technology, we have reached only the stage of the gigantic pterosaurs legs. Lower left photo courtesy of Lee
the air like knives, now were brought up to beat against the onrushing Kuhn/CLO. All other photos by Marie
and earliest birds, which could apparently glide but perhaps not initi-
air to brake the bird's forward and downward speed and avert a crash Read.
ate powered flight from the ground. Compare these simple feats with
those of Ruffed Grouse or even Wild Turkeys, which can burst upward
from the ground at a very steep angle, and accelerate over the treetops
faster than we can aim our binoculars at them.
Although gliding is an important component of bird flight, in most
species the flight process is much more complex—so complicated,
in fact, that researchers still do not completely understand it. The fol-

Figure 5-7. Man with Ornithopter: The

first attempts at human-powered flight
were in machines termed ornithopters
(literally, "bird wings," from the Greek
roots) that mimicked the flapping mo-
tion of birds. Humans, however, lack
certain critical adaptations for flight,
so these machines never made it off the
ground. Drawing courtesy of Daniel

Cornell Laboratorq of Ornithologq Handbook of Bird BioIoBq

5.10 Kenneth P. Able Chapter 5 —Birds on the Move: Flight and Migration 5.11
landing. Ultimately the bird was moving too slowly to remain airborne, Figure 5-10. Airfoil inAirstream: Shown
here is an airfoil in a stream of air. As the
and it landed gently on its outstretched feet.
airfoil moves through the air, it splits the
This was an everyday observation of a feat that herons and other oncoming airstream. Note that the air
birds perform thousands of times during their lives. Flying is, after all, layers below the airfoil remain roughly
as natural to birds as walking is to humans. But such a simple flight parallel to each other, while the air lay-
can raise a host of interesting questions. Once in flight, why does the ers above the airfoil are pushed upward
and crowded together. Note also that the
heron initially drop in altitude? Why doesn't it continue to drop? When
forces are the same whether the airfoil
it begins to glide it again loses altitude. Why, and what controls its rate moves through stationary air, or the air
of descent? How does it manage to stop and alight more or less grace- moves past a stationary airfoil. This air-
fully? No one yet understands all the minute steps that control even this foil is approximately the same shape as
a bird's wing (viewed in cross section),
simple flight and descent, but one can begin to grasp the fundamentals
and behaves similarly.
by understanding the basic forces that act upon a bird in flight: gravity,
lift, drag, and thrust.

Gravity
time that the air is physically split into two airstreams, each airstream
The first and most familiar force is gravity, the attractive force
acts as a separate physical system, and they behave differently from one
between masses of matter. For our purposes, gravity is the force tend-
another because of the shape of the wing. This difference in airstream
ing to draw objects toward the center of the Earth. For an object to
behavior makes flight possible. Because flight is the quintessential
stay aloft, it must overcome the pull of gravity, a tricky endeavor in
characteristic that rules almost every aspect of bird evolution, form,
the insubstantial, fluid medium of the atmosphere. Balloonists defeat
and ultimately behavior, it is worth looking at in some detail. The fol-
gravity by filling their balloons with enough light, warm air—or lighter-
lowing explanation is adapted in part from the account in Ruppell's
than-air gas—to compensate for the weight of balloon and occupant;
Bird Flight (1975), cited in the Suggested Readings. For simplicity,
rockets burn fuel to create sufficient power to overcome the pull of
this discussion will be limited to gliding flight, in which a bird moves
gravity by brute force.
forward through the air without flapping.
Birds use a completely different strategy: they remain airborne
Figure 5 10 shows how the layers of air move around a wing as it
-
by manipulating the motion of air past their wings. The key term here
passes through an airstream. You get a picture like this when you put an
is "motion," and it is in this respect that the wing differs from other
airfoil in a wind tunnel and trace the motion of the air with streams of
means of overcoming gravity. A person standing on the ground need
smoke. Note that the layers of air below the wing remain parallel, but
not move to keep from sinking; a balloon will float in a completely still
those passing over the top of the wing are crowded together. The crowd-
atmosphere; a rocket doesn't even require an atmosphere. For a bird's
ing above the wing occurs because oncoming air is pushed up and over
wing to overcome the pull of gravity, however, the air must be flowing
the convex surface of the airfoil, butthe air already above the wing resists
over and under it, and it doesn't matter whether this flow results from
this additional input of air by pushing back. Thus the air forced over the
the wing moving through the air or, on a windy day, from the air mov-
wing is "constricted" to an area near the upper wing surface.
ing past the wing.
Constriction of the airflow increases its speed. You demonstrate
Gravity so pervasively controls every aspect of the physical world
this every time you have a birthday: if you try to blow out candles with
that we tend not to explicitly consider its influence. But a moment's
your mouth wide open, you can't generate much of a puff; if you purse
reflection shows that gravity—or, rather, the need to overcome it—is
your lips and constrict the airstream, it speeds up and you get them all.
the single most crucial influence on a bird's form. Most obviously,
The same principle is at work when you make your garden hose spray
gravity is the force that determines weight, and the need to reduce
farther by narrowing the nozzle or putting your finger partially over
weight dominates the structure of every part of the bird's body, from

411111111 ■0•••,..., the lightweight beak to the hollow feathers and bones.
the end to squirt your brother.
Because of the constriction, the air flows more quickly over the
top of the wing than under the bottom. How does this produce lift? To
Lift
Being light in weight, however, is only part of a bird's challenge. answer this, you must understand two properties of moving air and the
To fly, a bird must be able to counteract the force of gravity. The force way these properties are related.
Figure 5 9. Airfoil: A typical airfoil,
-

such as the wing of a bird or airplane, is that serves this need, called lift, is provided by the special shape of a The first property is static pressure: the force, produced by ran-
convex (rounded) on top and concave bird's wing. This shape, known as an airfoil, is curved such that it is dom motion of molecules, thatair exerts uniformly in all directions. For
(curved inward) below. This shape cre- example, when you squeeze a balloon, you feel the static pressure from
convex on top, concave below, and tapers at the rear edge (Fig. 5 9). -

ates lift as the airfoil moves through the

When it moves through the air, the airfoil cleaves the air into two sep- the air inside. The atmosphere outside the balloon also has static pres-
air. (To learn how an airfoil creates lift,
see text and Fig. 5 1 1 .)
-
arate airstreams, one on the top and one on the bottom. During the sure. The second property, dynamic pressure, is the pressure of move-

Cornell Laboratorq of Ornithologg Handbook of Bird Biologq

5.12 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.13
Figure 5-11. HowanAirfoil Creates Lift: ment. You feel dynamic pressure when wind blows against your face;
a. Airfoil in Still Air
Horizontal lines represent airstream;
the harder the wind blows, the more dynamic pressure you feel.
lengths of arrows indicate relative
In a given system of airflow, a law of physics termed Bernoulli's

I
magnitudes of the forces they represent. Static
a. Airfoil in Still Air: Because of the Pressure law governs the relationship between static and dynamic pressure. It
random motion of air molecules, static states that these two types of pressure must always add up to a constant.
pressure is equal above and below the That is, when one increases, the other necessarily decreases; when one
airfoil. b. Symmetrical "Non-airfoil"
decreases, the other must increase. A full explanation of Bernoulli's law
in Moving Air: Moving air creates dy-
namic pressure, the force you feel when is beyond the scope of this course. But it's important to know that this
the wind blows against your face. The relationship between static and dynamic pressure is a consequence
Static
symmetrical shape in this airstream con- of the law of conservation of energy: the total energy in a given system
Pressure
stricts the air equally above and below,
remains constant regardless of changes within the system.
so the air speed is increased the same
amount above and below Therefore, the
Consider once more the air flowing over the top of a bird's wing.
Static Pressure Equal Above and Below Because it is constricted, it flows more quickly, and because it flows
dynamic pressure (and static pressure)
No Lift
above and below are the same, and no more quickly, its dynamic pressure increases.Therefore, in accordance
lift is created. c. Airfoil in Moving Air: with Bernoulli's law, its static pressure decreases. So the static pressure
Dynamic pressure and static pressure b. Symmetrical "Non-airfoil" in Moving Air
of the air flowing over the top of the wing decreases. But the airflow
offset each other: if one increases, the
other must decrease. An airfoil constricts ♦ Dynamic Pressure belowthe wing is not constricted, so the dynamic and static pressures
only the air flowing above it, increasing there remain the same. Thus, the static pressure above the wing is
the speed and thus the dynamic pressure lower than the static pressure below the wing, creating an upward (if
Static
above the airfoil. Because the dynamic
Pressure the wing is horizontal) force known as lift. If the pressure difference
pressure increases, static pressure must
decrease (Bernoulli's law). Below the
provides enough lift to compensate for the bird's weight, the bird re-
airfoil, the air is not constricted and thus mains airborne (Fig. 5-11).
air speed, dynamic pressure, and static "Lift" always operates perpendicular to the flow of air over the
pressure are unaffected. The result is wing. It doesn't always "I ift" the bird vertically off the ground, however,
higher static pressure below the airfoil, Airflow so the term is not really appropriate. If a bird dives straight down with
creating an upward force known as lift,
which keeps a flying bird aloft. its wings spread, for instance, "lift" will deflect its descent horizontally
in the direction of the top of the wing. In a bird flying upside-down,
as some kites and hawks do briefly while diving or during courtship
Static
Pressure displays, "lift" produces downward movement! Lift operates relative
to airflow, not relative to the ground—a concept that may be difficult
♦ Dynamic Pressure
for terrestrial creatures such as ourselves to appreciate (Fig. 5-12).
Static Pressure Equal Above and Below A bird can vary the amount of lift that its wings generate by chang-
No Lift
ing the angle between the wing and the oncoming airstream, an angle
known as the angle of attack. Lowering the front edge of the wing
c. Airfoil in Moving Air
below the horizontal so that airflow strikes the upper wing surface, for
1M=1 1■1 =IM •111011. Dynamic Pressure instance, generates a net downward force. Elevating the wing's front
edge increases lift, up to a poi nt.Too great an angle of attack, however,
separates the airflow from the upper surface of the wing and causes
Static turbulence—a disorderly flow of air, quite different from the smooth
Pressure (laminar) flow seen at lower attack angles (see Turbulence, later in this
chapter). When this occurs, the requirements for lift are no longer met,
and the bird stalls (Fig. 5-13a, b, and c).
Airflow
For lift to keep a bird airborne, air must flow over its wings at
a certain rate. At some slower speed (which depends on the bird's
LIFT weight, wing shape, and other factors), the bird will stall and fall ver-
Static Pressure
tically. This happens when the lift generated is no longer greater than

♦ Dynamic Pressure the bird's weight (gravity). Birds may deliberately stall as part of their
landing procedure, but sometimes birds need to fly slowly—or with
Static Pressure Greater Below the wings at a steep angle of attack—without stalling or landing. Some
Lift Generated

Cornell Laboratory of Ornithology Handbook of Bird Biology

5.14 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.15
a. Angle of Attack 0° LIFT Figure 5-13. The Effect of the Angle of
Attack on Turbulence in a Gliding Bird:
III T Horizontal and curved lines represent
a the airstream; dotted lines represent
the angle of attack (the angle between

Airflow
0111111111111 Very Little
the airstream and the horizontal axis of
the airfoil); lengths of arrows indicate
Turbulence
relative magnitudes of the forces they
(Lift not reduced)
represent.

V a. Airfoil Parallel to Airstream: When

GRAVITY the angle of attack is zero, some lift and
Direction of Motion of Bird very little turbulence are produced.

b. Shallow Angle of Attack LIFT

b. Shallow Angle ofAttack: As the angle
of attack is increased slightly (by tilting
the front edge of the wing upward), more
GRAVITY
lift is created because the airstream is
more constricted above the wing. More
turbulence (shown by curved lines be-
hind the airfoil) is also created.
Some Turbulence
b LIFT Airflow
(Lift reduced some-
Angle of c. Steep Angle of Attack: When the front
what by turbulence,
Attack edge of the wing is tilted steeply upward,
but has net increase
the smooth flow of air over the airfoil
due to increased
(termed laminar flow) is disrupted, and
angle of attack)
the airstream separates from the airfoil
GRAVITY
in swirls of turbulence. Gains in lift from
increased air constriction above are can-
celled out by turbulence, resulting in a
c. Steep Angle of Attack
LIFT net decrease in lift, and consequently,
Bird stalling.
Motion of
Direction of d. SteepAngle ofAttack withAlula Pres-
GRAVITY
ent on Wing: When the alula (a group of
Airflow three small feathers; see Figs. 1-8 and
5-14) is extended, it forms a slot just
Angle of above the wing that forces air above the
Attack Severe Turbulence wing to flow quickly and close to the
(Lift reduced top of the wing (in other words, restoring
dramatically) laminar flow). This decreases turbulence
GRAVITY and therefore increases lift. Birds that
need to fly slowly or at steep angles of
attack without stalling (as in hovering or
d. Steep Angle of Attack LIFT landing) often employ the alula.
DRAG with Alula Present •
Direction of Motion of Bird
A lula
Laminar Flow Over Top
of Wing Restored
Airflow byAlula
GRAVITY LIFT
Angle of Turbulence
Figure 5-12. Gliding Bird in Airstream: The force of lift always operates perpendicular (at right angles) to the flow of air over the Attack Reduced byAlula
airfoil—in this case, the bird's wing. Gravity, however, always pulls straight down. a. Bird in Level Flight: The only time that lift • (Allows steep angle
operates straight up is when a bird is flying level. Note that a gliding bird cannot fly level for long, as gravity will bring it to earth. of attack, gener-
b. Bird in Angled Flight: When a bird angles toward the ground, lift still operates perpendicular to the airfoil. The upward portion ating greater lift,
GRAVITY
of the lift force keeps the bird aloft, and the small forward component of the force propels the bird forward. c. Bird Gliding Upside without much re-
Down: In this hypothetical example, "lift" actually operates to pull the bird toward the ground. Some birds may be briefly oriented duction of lift due
upside down during aerial courtship or prey-capture maneuvers, but these generally involve flapping flight to keep the bird aloft. to turbulence)

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

5.16 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.17
birds address this problem by creating a slot above the front of the wing Figure 5-14. Hovering American Kes-
(Fig. 5-14). This slot, formed by the alula (see Fig. 1-8), forces the air trel with Alulae Spread: The kestrel has
a particularly large alula (small feathers
above the wing to flow quickly and down across the top wing surface
projecting above the bend in the wing),
(laminar flow), preserving the lift that would otherwise be lost as the which allows it to hover with a steep
airstream separated from the top of the wing (Fig. 5-13d). angle of attack at very slow speeds. Kes-
Because even the most efficient airfoil is useless in still air, a bird trels typically hunt for prey by hovering
over fields and grassy areas, and are of-
must somehow start a flow of air over its wings to become airborne.
ten noted by motorists, who see them
Our heron did this by launching itself from a high perch. If the wind hovering over roadsides. Illustration by
is strong enough, a bird standing on an exposed bluff can generate Evan W. Barbour.
enough lift to get off the ground just by extending its wings and fac-
ing into the wind, as gulls and albatrosses sometimes do. In the right
circumstances, these passive means of achieving lift can be quite ef-
fective.

Drag
The force that slows down a gliding bird, or any moving bird,
eventually to the point at which it can no longer maintain the lift nec-
essary to overcome gravity, is called drag. Essentially, drag is friction
between air and a moving body. For instance, when you put your arm Figure 5-15. Scaup in Flapping Flight:
If so, try this: Stand up and hold your arms straight out from your sides, In the first frame, the downstroke is
out your car window you feel drag; the faster you drive your car, the
palms down. These are your wings; the palms are the undersides and just beginning, with the primaries
more drag you feel, because drag increases with increased air speed.
the backs of your hands are the tops of the wings. Holding your arms overlapped and curved upward from
The size, shape, and surface area of the object also influence drag. pressure against the air. As the wings
out, run around the room. (If you like, you can chirp, coo, peep, or
Hold your hand out the window palm down and it slices through the continue downward, the primaries
squawk, too.) As you run, the airstreams moving over and under your
air; turn it so the palm faces the onrushing air and it blows backward. act as propellers by pulling the wings
airfoil-hands create lift. forward and the whole bird with them.
Drag operates in opposition to the motion of the body; in other
Now stand still, arms still outto your sides, and turn your hands so Meanwhile, the secondaries provide
words, it has a slowing effect (see Fig. 5-12). If you're driving due east, most of the lift. In the second frame, the
the thumbs point down and the palms back. Holding your hands in this
the drag force on your car is directed due west. If you are a bird flying downstroke is completed, with the wings
position, start to flap your wings vertically, with a stroke down toward
straight up, the drag force is straight down. If you parachute straight reaching forward and downward to the
the ground. Now you will note thatthe airstreams, as they move up and maximum extent. In the third frame, the
down from a plane, the drag force is straight up.
around your hand-wing, are passing over and under your "tilted" wing upstroke is underway, with the primaries
Recall the example of a heron taking flight. If the bird merely
such that the "lift" operates, not vertically, away from the ground, but separated and drawn toward the body.
leapt from the tree and extended its wings but did not flap them, its During this recovery stroke, the prima-
horizontally, to pull you forward. This is the source of thrust.
wings would be somewhat analogous to a parachute. By extending ries may push backward slightly against
In what portion of a wingbeat does a bird generate thrust? A bird's
its wings, it increases friction with air and generates an upward drag the air to propel the bird forward while
wingbeats are not just up and down. In typical powered flight the the secondaries provide lift. In the fourth
force that slows its fall. Over time, it would descend passively to the
wing is pulled down and forward as it approaches the bottom of the frame, the upstroke nears completion as
ground like a parachutist. the primaries begin reaching far back-
downstroke, and backward and upward on the upstroke (Fig. 5-15).
ward and upward. In the final frame, the
In all birds except hummingbirds, thrust is produced primarily on the
Thrust upstroke is completed and the wings are
downstroke. A common misconception is that birds achieve thrust about to undertake another downstroke.
So far this chapter has discussed only gliding flight. A gliding bird
through pushing back against the air, much as a rower pushes a boat Drawing by Robert Gilimor.
counteracts gravity with lift, but drag eventually brings the bird to the
ground. The heron I was watching that day did not glide down to the
ground, however, but sustained level flight for some distance. To do
this, it must be able to overcome drag, and it does so by producing
another force, thrust, the final force to be discussed here.
Thrust propels a bird forward through the air. It is created only
in flapping flight, not when a bird is simply gliding. Flapping the
wings also creates lift, and allows a bird to start a flow of air over its
wings, which is required to begin flight without a high perch or strong
winds. Th
Like lift, thrust is also derived from the airfoil shape moving
through an airstream. Are you reading this in the privacy of your home? Downstroke Upstroke

Cornell Laboratorg of Ornithologt1 Handbook of Bird Biologii

 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.19
LIFT Figure 5-17. Twisting of Primary Feath-
ers During Flapping Flight: Because the
primary feathers have a narrower vane
on the edge that leads in flight (outer
vane) than on the trailing edge (inner
vane), they tend to twist somewhat
like venetian blinds as the wing moves
through the air during flapping flight.
a. Downstroke: As the wing moves down
and forward, air pressure pushes each
broad inner vane up against the outer
vane of the feather over it, creating an
Cross Sections of unbroken surface (like closed venetian
blinds). b. Upstroke: As the wing moves
Feathers at Green Line
upward and back, air pressure from
above pushes each broad inner vane
down, twisting the primaries open. On
GRAVITY a. Downstroke b. Upstroke the upstroke, air is able to pass through
the primaries, thus reducing drag.
Direction of Motion of Bird

Figure 5-16. Bird in Flapping Flight: forward by pressing the oars back against the water. Indeed, the term for So, the bird's wing generates lift and provides thrust. However,
By flapping its wings, a bird creates a the flight feathers of the wings, the "remiges," is based on Latin terms different parts of the wing make different contributions to these two
force called thrust, which propels it for-
that mean, roughly, "that which rows." What actually happens may forces. Thrust is produced mainly by the movement of the primary
ward. Thrust is opposed by drag, which
always operates in a direction opposite look analogous to rowing, but is actually quite different, and is based feathers attached to the manus (the outer, "hand" portion) of the wing.
to the bird's motion. As a bird is moved on "forward lift." The wing motion that produces thrust is complicated In contrast, the proximal portion of the wing, with the secondary feath-
forward by thrust, airflow over the wings and difficult to grasp intuitively, and will be discussed later, in Sidebar ers attached, provides most of the lift.
creates lift, which keeps the bird aloft. Study Figure 5 17 and note the positions of the primary feathers
1: Flapping Flight. -

To fly on the level at a steady speed, a

How much thrust does a bird need to stay aloft? Consider a sled. during flapping flight. The individual primaries are shaped such that
bird must create enough thrust to exactly
compensate for drag, and enough lift to To push the sled over snow you must apply sufficient force to overcome each behaves as an individual airfoil, each generating some lift, as does Figure 5-18. Carolina Chickadee Dur-
the wing as a whole. In addition, their asymmetrical shape and direc- ing Upstroke: During the upstroke, air
exactly oppose gravity. friction (drag). The more force you apply, the more quickly you accel-
pressure on the broader inner vanes
erate and the faster you go; decrease the force and friction eventually tional flexibility cause them to twist such that on the downstroke, the
causes the primaries to twist open, re-
drags the sled to a stop. air pressure pushes the broader trailing edge (the inner vane) of each sulting in less resistance to the air. Photo
A similar process occurs when a bird is flying. Like a sled, a bird primary up against the outer vane of the feather over it. This produces by C. H. Greenewalt/VIREO.
experiences drag only when it is moving. However, a sled that is not an unbroken surface, much
being pushed hard enough to overcome friction merely slows down like closed venetian blinds,
and ultimately stops. A bird producing insufficient thrust to overcome moving through the air. On
its own drag also slows down, but it also loses lift, and eventually the upstroke, air pressure
descends. twists the primaries, open-
Therefore, to fly horizontally at steady speed, thrust must com- ing them, like the slats on
pletely compensate for drag (Fig. 5 16). When thrust equals drag, the
-
opened venetian blinds, so
bird flies at a steady speed. When the bird's thrust exceeds drag it flies that air may pass through
faster, which produces more lift and causes the bird to ascend. If the (Fig. 5 1 8). This arrangement
-

bird's thrust falls below the drag, the bird slows, produces less lift, and of the primaries generates a
descends. downstroke having about ten
Except during take-off, when a bird may use its legs to gener- times as much air resistance
ate momentum, thrust is produced by the action of the wings. The as the upstroke.
Great Blue Heron I observed used its legs and wings to generate thrust, You can demonstrate
overcome gravity, and launch itself into the air. For a second or two, this twisting action of the pri-
it actually climbed before descending and then leveling off. Could it maries by lightly holdingtwo
have continued to climb? Certainly, but at great energetic cost, and in primary feathers (of some-
this case there was no need. what similar size, the larger
the better) parallel to each

Cornell Laboratorq of Ornitholo9q Handbook of Bird Biologi

5.20 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.21

Figure 5-19. Demonstration of Feather

VIEW FROM ABOVE Function of the Tail
Twisting: To roughly imitate the twisting When we think about fly-
of the primary feathers during a wing- ing birds we naturally focus on
beat, hold two large primaries of similar
the wings, but the tail also plays
size parallel to each other between your
index and middle finger, as illustrated. a role in flight. This role may be
Your fingers should be parallel to the limited—most birds can fly with-
ground, and the feathers perpendicular out their tails, and males of spe-
to the ground. Face the leading edges to-
cies such as birds-of-paradise
ward your finger tips, and al low the lead-
ing edge vane of one to partially overtop
(see Fig. 3-10), with extremely
the trailing edge vane of the next, as in long tails, can probably fly bet-
a bird's wing. a. Upstroke: Move your ter without them. The tail's main
hand straight upward quickly, and notice function in flight seems to be to
how the feathers twist to create a slot
act as a rudder to help the bird
between them. b. Downstroke: Move
your hand straight downward quickly, steer (Fig. 5 20). Accipiters such
-

and the feathers twist and overlap, clos- as the Cooper's Hawk apparently
ing the slot. Photo courtesy of Marie evolved long tails because they
a. Upstroke b. Downstroke
Read/CLO.
Hand Moves Upward Hand Moves Downward help the birds maneuver as they
(Toward Viewer) (Away From Viewer) chase their avian prey through
Feathers Twist and Separate Feathers Flatten and Overlap dense vegetation. Birds with
particularly short tails, such as
other between your index and middle fingers (Fig. 5 19). Hold them
- loons, grebes, auks, and many
Figure 5-20. Bald Eagle Using the Tail so the barbs overlap loosely as they would on a bird, with the feathers ducks, can fly quickly (because
to Steer: A Bald Eagle steers to its left, its a short tail reduces weight and drag), but have a reduced ability to
at right angles to your fingers, and your fingers parallel to the ground. Figure 5-21. Red-tailed Hawk UsingTail
tail acting as a rudder to aid in turning. It
Then, quickly move your hand straight up and notice that the feathers make sharp turns. Some of these birds instead use their webbed feet to To Land: During landing, many birds,
also tilts and turns the body and lowers
such as this western morph Red-tailed
one wing in the chosen direction. Photo twistto open a gap between them. Now quickly move your hand down; steer and brake. The tail is also used during take-off and landing (see
Hawk, lower and spread the tail. The ad-
by Tom Vezo. the feathers twist to close tightly next section), and by perched birds to stabilize themselves in a wind. ditional area of the tail acts somewhat
together. Note that on a bird, the In pigeons, research using EMG has revealed that the tail muscles are like a third wing, providing extra lift and
feathers stay attached at the base, active with each wingbeat, and the patterns of activity change with thus allowing the bird to keep flying at
so the barbs closer to the feather the varying demands of take-off, slow flapping, landing, and other ac- a very slow speed without stalling, until
just the right moment for a controlled
tip twist more than those closer to tions. In a walking pigeon, on the other hand, most of the tail muscles
landing. Photo courtesy of Rick Kline/
the base. In your demonstration, are inactive. CLO.
however, the entire feather twists
in your fingers.
As mentioned earlier, a bird's
Landing
Controlled landing is in many ways more difficult than taking
wing moves down and forward on
off or maintaining flight, because the bird must stop its forward mo-
the downstroke and backward and
mentum and coordinate its movements to bring about a stall at pre-
upward on the upstroke, but this
cisely the altitude and speed that will allow the extended legs to make
description is greatly simplified.
contact gently and avoid a crash.
Lift and thrust on different parts of
During landing, the tail is typically lowered and spread, much
the wing are constantly changing
like a jet that extends and lowers the flaps on the trailing edge of its
during wing strokes, and the many
wings. Some birds spread their rectrices wide on both sides to form a
muscles in the wing (50 or more)
kind of rear wing, as seen in high-speed photographs of birds taking
integrate these complex dynamics
off or landing (Fig. 5 21). This "tail wing" provides extra lift to prevent
-
(Sidebar 1: Flapping Flight).
stalling until the last seconds, permitting the bird to remain airborne at
slower speeds that are more amenable to a controlled landing. The ac-
tion of the tai I also helps to suck air downward over the wing, reducing
turbulence and again increasing lift to permit slower flight.

(Continued on page 5.26)

Cornell Laboratory of Ornithology Handbook of Bird Biology

5.22 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.23
How do these motions contrib-
Sidebar 1: FLAPPING FLIGHT ute to flight? As discussed earlier in MOST OF LIFT Forces On Inner Wing
edited &I Sandi Podulka this chapter, a bird maintains level
flight by developing a force (thrust)
that counteracts the drag operating
Flapping flight is remarkable for its ers attach, simply moves down; ing the downstroke so that the lead-
against forward movement. The
automatic, unlearned performance. whereas the outer wing, where the ing edge of the outer wing is tipped
flapping of the wings, especially the
A young bird on its maiden flight uses primaries attach, moves both down downward relative to the body axis,
outer wings, produces this thrust. The DRAG
a form of locomotion so complex that and forward. This movement occurs while the inner section of the wing Flow of Air Direction of
inner wings primarily generate lift.
it defies precise analysis in physical because the flapping wing extends at remains roughly parallel to the body Across Movement of Bird
It is easiest to consider the forces Inner Wing
and aerodynamic terms. The nest- the wrist joint between the primary axis. The upstroke is both upward
operating on the inner wing (sec-
lings of some species develop in and secondary feathers. In addition, and backward, returning the wing to
ondary feathers) and outer wing GRAVITY
confined spaces, such as burrows in the wing twists at the wrist joint dur- its original position.
(primary feathers) separately (Fig.
the ground or cavities in tree trunks, Figure C. The Inner Wing During Flapping Flight: Shown here is a cross section
B). Most of the lift, and also most of
where they cannot spread their wings through the inner wing (see Fig. B). During flapping flight, the inner wing acts much
the drag, results from the forces act-
and practice flapping before they like the wing of a gliding bird: because it is relatively stationary, not moving up and
Paths Described by Wing ing on the inner wing and body of a
leave the nest. Despite this seem- down as much as the outer wing, most of the airflow comes from the front-a result
Tip and Wrist During a flying bird (Fig. C). The inner wing
ing handicap, many of them can fly of the bird's forward motion. Because the inner wing meets the airstream head-on,
Single Wingbeat acts much as if the bird were gliding:
considerable distances on their first instead of being tipped forward like the outer wing, air flowing over the airfoil gen-
since it does not move up and down erates lift nearly straight up during level flight.
flights. Diving petrels may fly as far
Path of much during flapping, most of the
as six miles (10 km) the first time out Wing Tip effective airflow over the inner wing
of their burrows! On the other hand, on comes from straight ahead, due to the
young birds reared in open nests fre- Upstroke movement of air over the airfoil pro- the outer wing is both upward and
motion of the whole bird through the
quently flap their wings vigorously duces lift nearly straight up. forward, because, as you will recall,
Path of air. Unlike the outer wing, the inner
in the wind for several days before Wrist on On the outer wing, however, the lift always operates perpendicular to
wing is not tipped forward, so the
flying—especially large birds such Upstroke situation is very different (Fig. Da). the flow of air over an airfoil. This re-
as albatrosses, storks, vultures, and There, the airflow is mostly upward sulting lift force, directed at an angle
eagles. Such flapping may help to Path of
W on
and slightly backward with respect to with respect to the bird's body, can
develop muscles, but it is unlikely the body axis of the bird. The upward be divided into two components:
Downstroke
that these birds are learning to fly; flow results from the rapid movement one force directed forward, along
however, a bird's flying abilities do of the outer wing downward, and the the body axis of the bird, and an-
improve with practice for a period "44),
.4.
111
- 41•■ backward flow results both from the other force directed straight upward.
after it leaves the nest. forward motion of the wing during a The forward-directed component

41f
Flapping flight involves so many downstroke and the forward motion is called thrust; the upward com-
variables that understanding exactly of the bird. Even though the wing is ponent is an additional source of
how it works is difficult. A beating tipped forward, the rapid downward lift, and adds to the upward lift force
wing is flexible and yields to air ,1) Inner Wing
flap produces such a large upward generated by the inner wing.
pressure, unlike the fixed wing of an Path of airflow that the effective angle of at- An essential ingredient in the
airplane. As a wing moves through —Wing Tip on
tack is very steep. The wing would production of lift and thrust is that
its cycle of motion, its shape, cam- Downstroke
stall if that were all that happened, the wings move at a high speed with
ber, angle with respect to the body, and no thrust would be generated. respect to the air. For thrust, this is
and the position of the individual Outer Wing
What actually happens, however, provided by the high rate at which
feathers all change remarkably. This is that the force of air from below birds flap their wings. Most of the
is a formidable list of variables, and causes the primary feathers to twist thrust is generated as the wings move
thus it is no wonder that flapping such that the leading edge rotates rapidly downward and forward on
flight has not yet fully yielded to forward and down (recall that the the downstroke, but in some cases
explanation in aerodynamic terms. Figure A. Paths Described by Wing Tip and Wrist During Wingbeat: Colored curves Figure B. Wing Cross Sections: Cross sec- primaries are asymmetric, with a thrust is generated on the upstroke
Nevertheless, the general properties show path of wrist (joint between outer and inner wing) and black curves show path tions through the wing at two locations wider vein on the trailing edge than as well (see below). Lift, however,
of a flapping wing can be described of wing tip for one complete wingbeat. The paths do not show the forward motion of are indicated:the inner wing, the portion
on the leading edge). In this orien- is mainly provided by the airflow
and analyzed. the bird. Dots are wing positions at evenly spaced points in time, and thus indicate of the wing from the wrist to the shoul-
tation, each primary feather acts like created by the forward motion of
Consider, first, the flapping cycle the relative speed of the wing: the farther apart, the faster that portion of the wing is der, where the secondary feathers attach;
a small, individual airfoil. The twist- the bird, which results from thrust.
moving. Straight lines connecting inner and outer dots, like wheel spokes, link the and the outer wing, from the wrist to the
of a small bird (Fig. A; also see Fig. ing brings each primary feather more Throughout the flapping cycle, the
two parts of the wing at the same point in time. Note that because of twisting at the wing tip, where the primary feathers at-
5 1 5 ). On the downstroke, the inner
-
in line with the airflow, reducing the secondaries act much as if the bird
wrist, the wrist and wing tip take very different paths through the air, and the wing tip tach. Note that both wing sections are the
section of the wing (from shoulder angle of attack, and preventing stall- were gliding, providing some lift at
covers much more area than the wrist. The exact path of the wing varies a great deal shape of an airfoil. Adapted from Burton
to wrist), where the secondary feath- between species. Adapted from Burton (1990, p. 40). (1990, p. 32). ing (Fig. Db). The resulting force on all times because air continues to

Cornell Laboratory of Ornithology Handbook of Bird Biology

5.24 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.25
flow from front to back over the in-
a. Downstroke of Outer Wing if Primaries Did Not Twist
ner part of the wing as long as the bird
is moving forward.
Bird Wing A flying bird increases its speed
by increasing the depth of its wing-
Direction of
beats, but the frequency of wingbeats
Movement of Bird
remains nearly constant at all speeds
Angle of during level flight. During take-off,
Flow of Air Attack however, some birds increase the
Across speed of their wingbeats briefly, to
Outer Wing Angle of Attack Large Bird Stalls
give them a bit of extra lift until they
reach level flight. Large birds have
slower wingbeatfrequencies than do
small birds, and strong fliers usually
b. Forces on Each Primary Feather of Outer Wing During Downstroke have slower beatfrequencies than do
weak fliers. II
Single Primary Downstroke Upstroke
Not all birds perform flapping
Feather Before ----- --------------
flight in exactly the same way. Of Figure E. One Complete Wingbeat of a Rock Dove Taking Flight: When taking flight, birds need extra force (thrust), which they
Twisting
particular interest are differences be- get from the upstroke. Illustrated here is a sequence of wing positions as a Rock Dove takes flight. The figure "eight" below each
Direction of
tween small and large birds. In both, picture shows the path of the wing tips during a complete wingbeat; the dark arrow indicates the portion of that cycle illustrated
Resulting Movement of Bird
the thrust produced on the down- in the frame above. During the downstroke, the wings sweep forward and down, the bases of the primaries flattening against
Force each other to form a large, unbroken surface (see also Figs. 5-17and 5-19). On the upstroke, the wings bend at the wrist and the
stroke causes an increase in speed.
Additional Lift primaries twist open as the wings move up and back. During this backward sweep (fourth and fifth frame), the upper surfaces of
In small birds, the upstroke is mainly
Component the twisted primaries push against the air and generate some thrust. At the end of the upstroke, the outer wing twists and flicks
passive: the heavier body of the
upward (last frame), generating some extra lift. Adapted from Burton (1990, p. 62).
Primary Feather Has bird falls slightly with respect to the
Thrust Component
Twisted to Reduce Angle lighter, more drag-vulnerable, wings;
of Attack to Near Zero thus the wings rise slightly with re-
(responsible for the downstroke) flukes up and down. These broad ever, instead recruiting several other
spect to the body, contributing to the
to the supracoradoideus is a good flukes function essentially as airfoils, muscles of the shoulder region. The
upstroke. Thus, little or no thrust is
indication of a bird's reliance on a generating thrust to propel them- other highly successful aerial ani-
produced and the bird slows down
Flow of Air Across Each Primary Feather powered upstroke; such ratios vary selves forward on both the upstroke mals, the insects, use a huge range
during the upstroke. In larger birds
from 3:1 to 20:1. and downstroke. Humpback whales of lift-based techniques and a variety
Figure D. Forces and Airflow on Outer Wing During Downstroke: Because the outer with slower wingbeats, the duration
We tend to think only of birds have remarkably long pectoral fins of wing movements in their mastery
wing moves down and forward rapidly on the downstroke, and this movement is much of the upstroke is too long to spend in
when considering movement that that may be used to produce lift, di- of the air.
faster than the forward movement of the bird, the airflow over the outer wing is mostly a state of deceleration. A similar sit-
involves creating lift, but this type of recting the animals either upward or In summary, note that the only
up and somewhat to the rear of the bird. a. Outer Wing if Primaries Did Not Twist: uation exists when any bird takes off:
Shown here is a cross section through the outer wing (see Fig. B). Note that the leading locomotion is not restricted to birds. downward in the water. difference between the model of
to get going, it needs thrust on both
edge of the wing is tipped slightly down and forward, unlike the inner wing shown in Many fish, mammals, and insects use Birds share the air with another flapping flight discussed here and a
the downstroke and the upstroke.
Fig. C. If the primary feathers did not twist during the downstroke, the upward flow of lift-based mechanisms in their loco- group of vertebrates, the bats; with simple analysis of a wing being held
Thrust on the upstroke is produced
air would produce a very large angle of attack (shown in color). Try turning the page motory repertoire. Although we often roughly 900 species, bats are among rigid, as in gliding, is that with flap-
clockwise to orient the airflow horizontally, as in previous figures in this chapter, to
by bending the wings slightly at the
think that fish swim by beating their the most successful mammals. Bats ping flight you need to visualize the
more easily visualize the large angle of attack of the wing. Large angles of attack cre- wrists and elbow and by rotating the
tails from side to side, many fishes, have highly modified wing mem- complex twists and turns carried out
ate turbulence and can cause the bird to stall. b. Primary Feather ShowingTwisting: humerus upward and backward (an
such as the surfperches (familiar branes spanning their digits and by a bird's wing during the down-
The airfoil in this diagram represents a cross section through a single primary feather action powered by the supracoracoi-
sport fish along the Pacific coast of extending to the shoulders and legs stroke and upstroke. These twists and
during the downstroke, not an entire wing section, as in the previous drawings. The deus muscle). This movement causes
North America), flap their long pec- or ankles.The mechanics of bat flight turns form a complicated motion that
asymmetry of the vanes causes each primary feather to twist (in actuality, just the tip the upper surfaces of the twisted pri-
of the primary feather twists) as the wing moves through the air on the downstroke, toral fins much like birds flap their are similar to those of bird flight: the is difficult to analyze, but they are
maries to push against the air and to
such that the leading edge rotates forward and down (dashed lines show position wings to achieve forward movement. wing tip describes a figure-eight pat- essential in generating the forces that
of feather before twisting). In its new position, each feather acts like an individual
provide thrust (Fig. E). In this type of
flight the wing tip describes a rough
If you watch one swim, you will no- tern, and most of the lift and thrust allow a bird to fly. ■
airfoil, meeting the flow of air head-on, reducing the angle of attack to near zero, and tice that it holds the tail still while is generated during the downstroke.
preventing stalling. Moving through the air in this position, the primaries generate a figure eight through the air. As speed Portions of this sidebar were reprinted
the pectoral fins beat steadily up and Like birds, bats have highly devel- from Vertebrate Life, 4th Edition, by F.
lift force (arrow labeled "resulting force") perpendicular to the direction of airflow. increases the figure-eight pattern
down, producing forward thrust via oped pectoral is muscles (accounting Harvey Pough, John B. Heiser, and Wil-
This force, because it has magnitude and direction, can be thought of as a vector. is reduced. In species that rely on liam N. McFarland, 1996, pp. 528-531.
a lift-based technique. In addition to for up to 10 percent of their total body
Refer to Fig. 5-62, for information on vectors and their addition. This resulting force a powered upstroke for fast, steep 01985. Reprinted by permission of Pren-
fish, some of the largest mammals on mass), but also use a few additional tice-Hall, Inc., Upper Saddle River, NJ.
vector can be divided into two components: (1) a horizontal force directed forward, takeoffs, for hovering, or for fast
earth, the whales (and many of their muscles on the downstroke. Bats do Other portions of the sidebar were writ-
called thrust, which propels the bird forward through the air, and (2) a vertical force aerial pursuit, the supracoracoideus ten by Sandy and Bill Podulka, in consul-
directed upward, which, together with the lift generated by the inner wings, keeps relatives), use lift-based strategies to not have a supracoracoideus muscle tation with ProfessorJohn Hermanson of
muscle is relatively large. In fact, the
the moving bird aloft. generate thrust by undulating their to facilitate the upstroke, how- Cornell University.
ratio of the weight of the pectoralis

Cornell Laboratorg of Ornithologq Handbook of Bird Biologq

5.26 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.27
Bluebird Figure 5-24. Arctic Tern Hovering:
Hovering is an energetically expensive
type of flight, but it is the only way for a
foraging Arctic Tern to get an aerial view
as it hunts for fish. Neither the open
water nor the flat, treeless Arctic Tundra
where it lives offer good vantage points
for searching for prey. The Arctic Tern
alternates slow, low-level flight over the
water with periods of hovering, similar to
the hunting style of theAmerican Kestrel
and Northern Harrier—which also hunt
in open areas with few good perches.
Photo by Tom Vezo.

Hovering has been carried to its ultimate in the hummingbirds—

the only group of birds that can hover for any substantial length of time
in still air, beating their wings up to 80 times per second. Using subtle
adjustments of the wings that become visible only with high-speed
Figure 5-22. Bluebird and Scaup Landing: When descending to a perch, the ground, or water, a bird slows down by braking
photography (first carried out by Greenewalt [1960]), hummingbirds
against the onrushing air—it positions the body upright (increasing the angle of attack to slow forward momentum); spreads the
tail to resist the air; and "back-strokes" with horizontal wingbeats. Meanwhile the bird brings its feet forward, ready for impact. can fly forward, backward, or hover in one place with apparent ease.
Drawings by Robert Gillmor.
Lift
Birds often reduce their momentum by landing facing into the
wind, increasing the angle of attack of the wings, and beating the
wings horizontally against the direction of airflow (Fig. 5 22). Many -

birds swoop upward when landing, using gravity to counter their mo-
mentum (Fig. 5 23). Species with webbed feet, as well as Old World
-

Vultures with their unwebbed feet, often extend and spread their feet
as an air brake when landing. Wing Wing
Figure 5-23. Downy Woodpecker Motion Motion
Landing: Many birds, including the
Downy Woodpecker shown here, Hoverin9
have a flight pattern termed bounding Many species of birds with a variety of wing shapes hover at least
in which they alternate flapping (dur-
occasionally. Hovering is an energetically expensive mode of flight
ing which they rise slightly) with glides
on closed wings (during which they achieved by beating the wings more or less horizontally. Forward thrust
descend slightly). To land, they swoop must be balanced by wind speed, and gravity exactly compensated for
upward to contact a tree trunk, using
Figure 5-25. Belted Kingfisher Hov-
by I ift (Figs. 5 24, 5 25).
- -
ering: When hesitating in midair for
gravity to counter their momentum.
one reason or another, most birds, such
Drawing by Robert Gillmor.
as this Belted Kingfisher, hover by posi-
tioning the body more or less vertically
and simply flapping the wings forward
and backward horizontally to provide
lift but not thrust. Hovering uses a great
deal of energy because to stay aloft the
bird must flap hard enough to generate
Gravity an upward force equal to its own weight.
Drawing by Robert Gillmor.

Cornell Laboratort1 of Ornithologg Handbook of Bird Biologtj

5.28 Kenneth P. Able Chapter 5 —Birds on the Move: Flight and Migration 5.29
Figure 5-26. Hummingbird Hovering: Because of the unique structure of the hummingbird's humerus and its
When hovering with the body mo- Overhead View Side View articulation with the pectoral girdle, its shoulder can rotate, allowing
tionless, as when taking nectar from a
the wing to push air in almost any direction, depending on the angle
flower, a hummingbird moves its wings
in a unique pattern that, unlike the wing (Fig. 5 26).
-

motion of other hovering birds, gener- The small, pelagic storm-petrels use a unique form of hovering to
ates lift on both the forward and back- search the ocean for tiny organisms. Storm-petrels hover low over the
ward stroke. This is possible because the
water with their feettreading ("pattering") on and just below the surface,
hummingbird wing differs from that of
other birds; the arm bones are reduced
looking very much as if they were "walking on water" (Fig. 5 27). This
-

such that the hand (outer wing) makes up unique behavior probably earned them their name, in reference to St.
most of the wing area, and the elbow and Peter's attempt to "walk on water." Storm-petrels search the surface of
wrist joints are locked to form a nearly the open sea for prey by letting the wind blow them along. Then, when
rigid, unbending wing that moves from
they need to look more closely, they hover or fly very slowly while fac-
the specialized shoulder joint. Pictured,
from top to bottom, is the sequence of ing into the wind, pattering their feet.The storm-petrel's flight is typically
wing positions involved in one complete called "hovering," but it is really more like soaring into the wind. Instead
wingbeat. Note that on the backward of expending much energy, as in other forms of hovering, the storm-
stroke, the wing does not fold. Instead,
petrel actually uses the wind's energy to stay aloft. In addition, unlike
it rotates such that the lower surface
faces up. Adapted from Burton (1990,
most types of hovering, the wings remain relatively still, held out over
the back in aV. (The wings do flip over and back, but how they generate
lift in this way is beyond the scope of this course.)
Storm-petrels soaring in this fashion would be blown backward
with the wind and would lose lift as the speed of the airflow relative
to their wings dropped to zero, if they did not do something to hold
themselves back. By dangling their feet in the water, storm-petrels
create drag that helps to "anchor" them in place against the wind, like
someone holding the string of a kite (Withers 1979). If the feet were
motionless in the water, the birds would still be pushed backward by
the wind, but much more slowly than if their feet were not in the wa-
ter. By pattering their feet, storm-petrels can hold themselves steady,

Figure 5-27. Wilson's Storm-Petrel

"Walking on Water": A Wilson's Storm-
Petrel hovers low over the ocean with
its feet treading the water, searching for
small marine animal prey. Looking much
like large butterflies, storm-petrels hold
their wings over their backs in a V and
actually "soar" into the wind, dangling
KEY
Path of Wing During their legs in the water to create enough
Upper Surface Full Stroke drag to hold them in place against the
wind. Wilson's Storm-Petrels are pos-
IIII Lower Surface Cross-section Through
Outer Wing sibly the most numerous seabirds in
(Where Primaries Attach) the world. Photo by Doug Allan/Oxford
Scientific Films.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

5.30 Kenneth P. Able Chapter 5 -Birds on the Move: Flight and Migration 5.31
or perhaps even push themselves slowly
forward, against the force of the wind.
Wing Loading
The storm-petrels' particularly I ight wing An important factor influencing how a bird flies is its wing load-
loading allows them to generate suffi- ing, the ratio of body weight to wing area, or how much "load" each
cient lift to stay above the water's surface unit area of wing must carry. The wing loadings of birds vary tremen-
in winds that are light enough to allow dously between species. The Leach's Storm-Petrel spends much of its
their foot-dragging technique to work. life in flight over the sea, has very large wings for its weight, and has a
low wing loading of 0.0015 lb/in 2 (0.1 g/cm 2). Larger birds with rela-
Complex Control of Flight tively smaller wings (loons, auks, albatrosses) may have wing loadings
of up to 0.03 lb/in 2 (2.1 g/cm 2 ) or more. The American Crow has an
Watch a Barn Swallow coursing
average sort of wing loading at 0.0058 lb/in 2 (0.41 g/cm 2). In contrast,
over a hay field as it chases flying insects,
the wing loading of a Boeing 747 aircraft is much heavier, at 0.805
and you witness an unceasing array of
I b/i n2 (56 g/cm2).
swirling, swooping flight maneuvers of
In general, smaller birds have lighter wing loadings than larger
consummate grace. To describe such a
birds, but flight style is also a factor. For example, large soaring birds,
performance in terms of gravity, drag,
such as eagles and vultures, have lighter wing loadings than other
lift, thrust, and a little use of the tail, is
similar-sized birds (Table 5-1).
like explaining the boundless flexibility
of the human hand and arm by saying "It
all results from the contraction and relax- Table 5-1. Wing Loadings of Various Birds: Presented here are the wing loadings (how much "load" each unit area of wing must
ation of the muscles." True enough, but carry) for a variety of bird species, arranged from lightest to heaviest body weight. Note that, in general, larger birds carry a heavier
that doesn't really explain how it works. wing loading, but flight style and other aspects of a bird's lifestyle play a role as well. Weights are presented in ounces (oz) and
Therefore, one must imagine the pounds (lb), and areas in square inches (in 2). Metric conversions for each are given in grams (g) and square centimeters (cm 2).
Adapted from Welty and Baptista (1988, p. 473). Originally from Poole (1938).
forces that control flight not as separate
elements that the bird controls using a SPECIES WEIGHT WING AREA WING LOADING
few static techniques at all times-as a pi- oz (g) in2 (cm 2) lb/ in2 (g/ cm 2)
lot controls a plane-but as a constantly
changing melange of forces which the Ruby-throated Hummingbird 0.11 (3.0) 1.92 (12.4) 0.0033 (0.24)
Figure 5-28. Rufous Hummingbird at bird manipulates with almost infinite flexibility. House Wren 0.39 (11.0) 7.50 (48.4) 0.0033 (0.23)
Columbine: Birds carry out all sorts of
Within rather wide limits, birds can vary their wing area, wing Black-capped Chickadee 0.44 (12.5) 11.78 (76.0) 0.0023 (0.16)
aerial maneuvers with such elegance
that, to us, their flight appears effortless. camber (the arch of the wing's airfoil), and angle of attack. They can Barn Swallow 0.60 (17.0) 18.37 (118.5) 0.0020 (0.14)
To the contrary, flight is precisely con- glide; they can flap their wings slowly or quickly; they can flap continu-
Chimney Swift 0.61 (17.3) 16.12 (104.0) 0.0024 (0.17)
trolled by strong muscles acting in ously, like a duck; or in spurts, producing the bounding flight of wood-
complex ways, much like ballet. Photo Song Sparrow 0.78 (22.0) 13.41 (86.5) 0.0036 (0.25)
peckers and various finches, and the flap-glide flight of ravens, hawks,
courtesy of Donald Waite/CLO. Leach's Storm-Petrel 0.93 (26.5) 38.92 (251.0) 0.0015 (0.11)
and other large birds. They can spread the al u lar or primary feathers at
will, or tilt their wings backward. Birds can spread their tail feathers, Purple Martin 1.52 (43.0) 28.76 (185.5) 0.0033 (0.23)
arc them up and down, and tilt them to either side. Birds also can move Red-winged Blackbird 2.47 (70.0) 37.98 (245.0) 0.0041 (0.29)
each wing independently of the other, allowing them to twist and turn European Starling 2.96 (84.0) 29.50 (190.3) 0.0063 (0.44)
in the air, sometimes quite abruptly. Birds can alter the proportions of Mourning Dove 4.59 (130.0) 55.35 (357.0) 0.0052 (0.36)
I ift and thrust in the course of a single stroke of the wi ng, and many birds Pied-billed Grebe 12.12 (343.5) 45.12 (291.0) 0.0168 (1.18)
are capable of producing lift on the upstroke as well as the downstroke. Barn Owl 17.81 (505.0) 260.93 (1683.0) 0.0043 (0.30)
Gravity is the antagonist of lift, but birds constantly use gravity to gain American Crow 19.47 (552.0) 208.37 (1344.0) 0.0058 (0.41)
momentum or to counteract it when landing; drag opposes thrust, but
Herring Gull 29.98 (850.0) 311.01 (2006.0) 0.0060 (0.42)
birds use drag to maneuver and stop.
Peregrine Falcon 43.12 (1222.5) 208.06 (1342.0) 0.0130 (0.91)
Like ballet, flight appears effortless and free, but only because
the muscles are strong and the movements involved are precisely con- Mallard 49.66 (1408.0) 159.54 (1029.0) 0.0195 (1.37)
trolled. Indeed, the fine control of the complexities of flight, involving Great Blue Heron 67.20 (1905.0) 687.75 (4436.0) 0.0061 (0.43)
muscular control over not only the wings and tail but also individual Common Loon 85.54 (2425.0) 210.54 (1358.0) 0.0254 (1.79)
feathers, is so fluid and so complicated that it is still not well under- Golden Eagle 164.52 (4664.0) 1010.85 (6520.0) 0.0102 (0.72)
stood (Fig. 5-28). Canada Goose 199.72 (5662.0) 437.21 (2820.0) 0.0286 (2.01)
Mute Swan 409.24 (11602.0) 1055.50 (6808.0) 0.0242 (1.70)
Cornell Laboratorq of Ornithologq Handbook of Bird Biologt
5.32 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.33
Wing loading imposes the ultimate limit on the size of flying an- Because higher wing loadings make flight more difficult, larger
imals. One might think there would be an optimum wing loading, so birds must compensate in various ways. Most solve the problem by
that larger birds would simply have proportionally larger wings. As the increasing speed. Birds with low wing loadings, such as grouse, quail,
size of birds increases, however, their volume (which determines their or dabbling ducks, can leap into the air and start flying. But birds with
weight) increases faster than their surface area. To maintain the same higher wing loadings must speed alongthe ground to become airborne,
wing loading as small birds, then, large birds would require wings that and must maintain higher speeds to stay aloft. Albatrosses get a running
were proportionally much larger with respect to the rest of the body start or launch themselves from high ground; diving ducks and loons
(Fig. 5 29). For example, for a bird the size of a swan to have a wing
- paddle across the water (Fig. 5 30). Alcids (auks and puffins), which
-

loading as light as that of a small passerine, its wings would require have very high wing loadings so that they can dive under water, often
more than ten times the surface area that swan wings actually have. hold their webbed feet, toes spread, on either side of their tails while
Such immense wings would be impossibleto power or to control.Thus, flying. This apparently increases the available lift-generating surface.
larger birds tend to have large wing loadings. Considerations of wing loading and power requirements sug-
gest that the maximum weight for a flying bird is near 26 lb ( 1 1 . 8 kg).

Figure 5-29. Wing Loading in Relation Volume is assumed to roughly determine weight:
to Body Size: For a large bird to have
the same wing loading (the ratio of body L= length W = width D= depth
weight to wing area) as a small bird, the
wings must be much larger with respect
to the body. This is true because as the BIRD A
overall size of a bird increases, the vol- Wing Surface Area = LxW = z ,yor
ume (which is directly related to weight) Volume (Weight) = LxWxD = y
increases faster than the wing area. Be- Wing Loading = y /z
'444104,
cause large birds are generally unable to
power the huge wings they would need Several living species from different lineages are near this size: the Figure 5-30. Scaup Taking Flight: Birds
to have the same wing loading as a typ- with high wing loadings, such as this
Kori Bustard, American White Pelican, Trumpeter Swan, and Andean
ical small bird, large birds tend to have scaup, other diving ducks, loons, swans,
heavier wing loadings. BIRD B Condor. The largest known flying bird was the Pleistocene condor, geese, and alcids, must reach high
Wing Surface Area 2L x 2W = 4z Teratornis incredibilis, which is estimated to have weighed about 44 ground speeds before they can generate
Volume (-Weight) 2Lx2Wx2D = 8y lb (20 kg) and to have had a wingspan of 16 feet (4.9 m). Presumably sufficient lift to become airborne. They
Wing Loading 8y/4z = 2y/z it flew almost entirely by soaring; how it got airborne remains unclear. do this by running and flapping across
the water's surface during takeoff. Some
For a person of average weight to take off under his or her own wing
If the overall size of the bird doubles, the wing surface heavy birds are unable to take flight
power, he or she would need about 30 square feet (2.8 square meters) from land or from small bodies of water.
area increases by a factor of 4, and the volume increases
by a factor of 8. Thus the bird's wing loading is twice as of wing area; each wing would weigh about250 lbs (113.5 kg)—much Drawing by Robert Gillmor.
great as that of Bird A. more than a human could hold out horizontally!

Turbulence
Although birds are beautifully streamlined, certain aspects of
their movement through air still generate turbulence. In particular,
BIRD C
turbulence may be created when smooth airflow is disrupted by very
Wing Surface Area = 8z
Volume (Weight) = 8y
high angles of attack, or by friction with surfaces such as a bird's wing
Wing Loading = 8y/8z = y , z feathers. Because turbulence, in turn, increases such friction, it is an
important source of drag, and can create unwanted stalling, requiring
a bird to use excessive amounts of energy.
As in Bird B, the overall size of this bird's body has doubled (over Bird A) such that
the volume is approximately 8 times that of Bird A, and is equal to that of Bird B. Turbulence is often formed at the trailing edge of the wing as the
But here the wing surface area is increased even further, so that the wing loading air closest to the top surface of the wing is slowed by friction with the
is equal to that of Bird A. Note that fora bird's overall size to increase without an
feathers. As mentioned previously (see Fig. 5-13), the airflow may
increase in wing loading, the wings must become much larger in proportion to the
rest of the body. separate from the top of the wing as turbulence in the form of swirls of
To simplify the math here, it is assumed that the large wings do not contribute signif- air that move forward from the trailing edge of the wing. This type of
icantly to the weight. If the increased weight of the wings were taken into account, turbulence is greatest at slow air speeds and at high angles of attack
their surface area would have to be even larger to keep wing loading constant from
with heavy loads.
Bird A to Bird C.

Cornell Laboratorq of OrnitholoBq Handbook of Bird Biologq

5.34 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.35

Another type of turbulence, called tip vortex, is created at the tip Like other types of turbulence, tip vortex creates drag that inter-
of the wing. It consists of currents of air spiraling off the wing tip be- feres with lift, and this drag is greatest at slow air speeds. The drag can
hind the bird (Fig. 5-31). (A bird flying close behind another can take be offset in several ways. One method is to elongate the wings (holding
advantage of the lift created by the rising portion of these spirals; see width constant), which increases the surface area between the tips that
Flocking and Flying in Formation, later in this chapter). Recall that the creates lift and is not affected by drag. Elongation improves the ratio
static air pressure below a moving wing is higher than that above, due of lift to drag (termed the lift-to-drag ratio, an important aerodynamic
to the airfoil shape and Bernoulli's law. Because air tends to flow in a property) and thus compensates for the drag induced at the tip. The
direction that decreases pressure differences, air from the high-pres- effect is most pronounced in long, narrow wings, because the leading
sure area below the wing flows toward the low-pressure area above edge of the wing produces most of the lift. Long wings also decrease
the wing. This airflow, combined with air flowing from front to back drag because they keep the areas of turbulence at opposite wing tips
across the top of the wing, creates the spirals of tip vortex. These ed- farther apart. Because gliding birds use high lift-to-drag ratios to stay
dies sometimes may be seen as trails of white behind the wing tips of aloft, one would expect them to have relatively long, thin wings—and
large airplanes as they take off or land, and are particularly visible on most, such as storks and albatrosses, do. Some albatrosses glide so well
rainy days. These rings of air circulate in a counterclockwise direction that they can cover 50 to 60 feet (15 to 18 m) while losing only 3 feet
on the left side of the bird or aircraft and clockwise on the right, when (1 m) of altitude (Kress 1988).
viewed from the front. Another way to reduce the drag created by tip vortex is to have
In a flapping bird, the rings of tip vortex are generated as the wings narrow, pointed wing tips. The smaller the wing tip area, the less the
move up and down—a motion accompanied, as you will recall, by pressure difference below and above the tip, so the lower the amount
twisting and turning of the outer wings. The exact orientation of the of turbulence, and therefore drag. In contrast, broad, rounded wing
vortex ring will depend on the angle of the wing stroke. The size of the tips create the most tip vortex.
vortex ring and its velocity of circulation will depend on both the angle A final way to decrease tip vortex is to have wing tips with a high Figure 5-32. Soaring Turkey Vulture:
degree of slotting. Slots are gaps between the feathers of the wing tips, Large soaring birds, such as this Turkey
of attack relative to the airflow and the degree of camber of the wing.
Vulture, usually counter the lift-reducing
These latter two variables affect ti p vortex because they determine how created when a bird having narrow-tipped primaries spreads them
effects of tip vortex by having wings with
much pressure difference is created as the air flows across the upper during flight. Common in large soaring birds such as eagles, vultures, a high degree of slotting. Slots are gaps
and lower wing surfaces. condors, and certain hawks, slotting makes the wings look as though between the feathers of the wing tips
they were tipped by widespread fingers (Fig. 5-32). Slotting reduces that make the wings look as though they
were tipped by widespread fingers; they
tip vortex by turning each primary feather into an individual, narrow,
are created by having primary feathers
pointed "wing tip." It also increases lift, because each separated pri- with narrow tips and by spreading the
mary feather acts as an individual airfoil (even without a flapping mo- primary feathers during soaring. Photo
tion), generating its own lift. Slotting thus allows a bird with a broad, by Marie Read.
rounded wing tip to increase its I ift-to-
drag ratio.
As the understanding of tip vor-
tices and their effect on bird flight has
improved, researchers have been bet-
ter able to assess the energetic costs of
flight and to explain why such a diver-
sity of flight styles exists. For example,
the bounding flight of woodpeckers, in
which the birds alternate flapping with
gliding on closed wings, may be an ad-
aptation that decreases the effect of tip
Figure 5-31.11pVortex on a Flying Snow vortices: closing the wings temporarily
Goose: As a bird flies, swirls of turbulent gets rid of the vortices, and thus al lows a
air cal led tip vortex spiral off the wing tip glidingphasewith lessturbulence. In the
behind the bird, and trail downward. In a future, advances in the understanding of
flock, a bird flying at an angle close be-
vortices will undoubtedly provide even
hind another bird (as in the V formations
of Snow and Canada geese) can use the greater insight into the mechanics and
rising portion of the spirals to gain some energetics of bird flight.
"free" lift.

Cornell Laboratorq or Ornithologq Handbook of Bird Biologq

5.36 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.37

Variations in Wing Shape and Flight Stgle pect-ratio (Fig. 5-34). Although these categories are arbitrary and
falsely group many flight styles, they can help to simplify the extraor-
Spend some time watching birds fly, and you quickly will notice
dinarily wide array of wing shapes found in nature.
the variations: big birds fly differently than little birds, fast birds fly
differently than slow ones. Those with short, stubby wings fly differ-
Elliptical Wings
ently than those with long wings. From the buzzy flight of the tiniest
Most birds that live in forests, woodlands, or shrubby areas where
hummingbird to the sedate movements of giants such as condors and
they must maneuver around and through dense vegetation have el-
albatrosses, birds fill the air with a diversity of flight styles.
liptical wings. Most songbirds, crows, grouse, and quail fall into this
Flying requires a tremendous amount of energy, and birds are
category, even though they are not closely related. Exact wing shapes
under intense selection pressure to reduce energy demands any way
among this group vary a good deal, but in general, elliptical wings are
they can. One important factor is wing shape. For typical flapping
short and broad—that is, they have a low aspect ratio. The aspect ratio
flight, the most aerodynamically efficient wings are large, long, and
is the ratio of the length to the width of a wing. Long, narrow wings
relatively narrow. But such wings also have costs: they are harder to
have a high aspect ratio; and short, broad wings have a low aspect
control and maneuver, they may interfere with takeoff, and they do not
ratio. The turbulence created by the broad tips of elliptical wings is
necessarily allow the most rapid flight. Other wing shapes, although
offset somewhat by a high degree of slotting of the primary feathers,
less energy-efficient while flapping, perform some of these tasks better.
which increases lift.
Birds also can reduce the energy demands of flightthrough gliding and
Birds with elliptical wings have traded the aerodynamic advan-
Figure 5-33. Types of Flight: The flight soaring, the latter of which is best performed with a wing shape not
tages of a longer wing for the maneuverability of a shorter wing. The
styles of birds are as varied as their food well suited for flapping flight.
breadth of their wings creates less lift for their size, but helps to reduce
habits and plumage colorations, but All types of flight—both gliding and flapping—require lift, and
they can be grouped into a few basic wing loading and thus further increases maneuverability. This wing
flapping flight also requires thrust. Around that basic theme, however,
categories. Note that a given species or shape also produces a relatively slow flight.
individual bird may use different types of
the flight styles of birds are as varied as the habitats they occupy and
flight under different circumstances. the lifestyles they lead. Indeed, each lifestyle requires different skills
and different flight styles. So, the wing shape of each species Figure 5-34. Major Wing Types: The
tremendous diversity of bird wings have
is a result of evolutionary compromises that allow the bird
been classified by ornithologists into
FLIGHT TYPES to meet the total array of life challenges—not just those four major types based on both shape
challenges posed by efficient flapping flight. You may and flight performance. Although these
want to refer to Fig. 5-33 during the following dis- categories are imposed by humans onto
cussion of flight styles and wing shapes. a characteristic that actually varies
through a continuum, they are helpful
Bird wings have been classified into four
POWERED NON-POWERED in making sense of the overwhelming va-
(No Flapping or Thrust Involved ) general types based on shape and aero- riety of bird wings. See text for detailed
(Flapping)
• Bird Provides Thrust • Bird Does NOT Provide Thrust dynamic performance: elliptical, high- descriptions of each wing type and the
• Most Often Used by Birds speed, slotted high-lift, and high-as- flight styles that make use of it.
With Elliptical or
High-Speed Wings

GLIDING SOARING
(Losing Altitude) (Gliding With No Loss In Altitude— High-Speed Wing
• Used by Birds With Either Horizontal or Rising Flight)
Any Wing Shape

STATIC SOARING
(Bird Propelled Upward by Moving Air)
• Used by Birds With
DYNAMIC SOARING
(Bird Uses Wind Speed Gradients
and Its Own Momentum)
1....,
Swift 41w ■ 4111111114.
1. 111) Falcon
Slotted High-Lift Wings • Used by Birds with High-Aspect-
Ratio Wings
Duck

'41111111111 Sandpiper
THERMAL SOARING SLOPE SOARING
(On Rising Thermals) (On Rising Air Along a Slope) Tern

Cornell Labomtorq of Ornithologg Handbook of Bird Biolooi

5.38 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.39
The importance of habitat in selecting for elliptical wings can be swim under water, may also need high-speed wings
seen by comparing closely related birds of different habitats. Forest to remain airborne.
hawks and owls, such as the Cooper's Hawk, Sharp-shinned Hawk,
and Barred Owl, have short, rounded wings, whereas their open-coun- Slotted High-lift Wings
try counterparts, Northern Harriers and Short-eared Owls, have long, Another group of birds has evolved a type of
narrow wings (Fig. 5-35). flight called static soaring. They take advantage of the
energy in rising air masses to obtain lift with little or
High-speed Wings no energy expenditure on their part. The most familiar
The high-speed wing is the tapered, pointed, often swept-back examples are eagles, vultures, storks, and some owls
wing characteristic of falcons, swifts, swallows, terns, ducks, and many and hawks, such as Broad-winged Hawks and Red-
shorebirds. The primaries have no slotting, and the wings have a high tailed Hawks. These birds seek air masses rising fast
aspect ratio (Fig. 5-36). Flying with this type of wing is energetically enough to propel them upward, and remain in them
expensive because the birds must flap constantly to move fast enough long enough to rise to great heights, often by soaring
to generate sufficient lift. in a series of tight spirals. They then use their height
Birds with this wing shape generally feed on the wing or migrate to glide effortlessly for a long time, either to cover a
very long distances, situations in which high speed and control are territory, to migrate, or to search for food.
crucial. But, they have traded efficient lift generation for these ben- Soaring of this sort requires a slotted high-lift
efits. Birds that need a high wing loading, such as those that dive or wing. As the name implies, such a wing tends to be
broad with a deep camber and to have very prominent
Forest Raptors
slotting (see Fig. 5-32).The aspect ratio is moderate—
es
between that of elliptical wings and high-aspect-ratio
l;e wings. The broad wings help to catch rising air, some-
what like a kite, and help to reduce wing loading.
They also allow slow flight speed, which enables the
birds to turn in tight spirals. The slotting produces additional lift (while Figure 5- 36. High-speed Wings of a
reducing tip vortex), increasing a soaring bird's ability to fly slowly. Forster's Tern: The wings of this winter
(basic) plumage Forster's Tern are typi-
The extra lift also allows these birds to carry heavy prey. Many soar-
cal of birds with "high-speed wings;"
ers can fold or spread their primaries and tail feathers, changing their they are tapered, pointed, swept-back,
wingspread and tail shape to increase maneuverability. long and narrow, and not slotted. Like
other bi rds with this wing shape, Forster's
Static Soaring Terns must flap constantly to move fast
111 111 Static soaring takes several different forms. Perhaps the most fa- enough to generate sufficient lift to stay
'J11110111,1 : Barred Owl aloft. Photo by Marie Read.
miliar is thermal soaring. Thermals are columns of rising warm air
that result from differential heating of land surfaces by the sun. Dark
Cooper's Hawk surfaces such as plowed fields or asphalt parking lots heat up faster
than adjacent forests or water bodies, and the south-facing slopes of
hills heat up faster than those that face north. It is over these warmer
Open-country Raptors
areas that thermals form and "kettles" (large aggregations of rising,
spiraling, birds—usually hawks) assemble (Fig. 5-37). Broad-winged
Hawks are famous for their kettles containing hundreds of birds during
Figure 5 -35. Wing Shapes of Forest migration (see Ch. 6, Sidebar 4, Fig. Fa). Thermals are most common
versus Open-country Raptors: The Coo- - - - •
in warmer parts of the world and in the interior of continents, where
per's Hawk and Barred Owl, both forest
birds, have short, rounded ("elliptical") te' I ft lateral winds are less likely to break up the pattern of air movement.
Thermal soaring is used by species as diverse as Old and New World
wings that allow them to maneuver eas- oit.604
ily among the trees. Open-country rap- - —
vultures, diurnal raptors, cranes, storks, pelicans, and swifts. In many
tors, such as the Northern Harrier and of these species, notably the vultures, hawks, and eagles, thermal
Short-eared Owl, have longer, narrower soaring is used to search for food. Many of these species are near the
wings, trading in the maneuverability
maximum weight for flying birds and must cover large areas to find
of short wings for several aerodynamic
Short-eared Owl food. Thus, the subsidy they derive from the energy of the atmosphere
advantages, such as reducing wing tip
Northern Harrier
turbulence and increasing lift. is crucial to their way of life.

Cornell Laboratorq of Ornitholos Handbook of Bird BioloA

5.40 Kenneth P. Able Chapter 5 —Birds on the Move: Flight and Migration 5.41
KEY
Movement of Air
Movement of Birds

Warm
Air

Forest Open Land Forest

(Plowed Field, Asphalt Parking Lot,
or Rock-strewn Plain . . .)

T
t
1

Thermal soaring also can be used to move cross-country (Fig. Figure 5-38. Moving Cross-Country
5 38).The bird climbs in a thermal (propelled upward by the rising air-
-
with Thermals: In a process similar to that
described in Figure 5-37, thermals may
stream), often reaching a height of 6,000 feet (1,830 m) or more, then
develop in temperate areas over south-
glides out in the chosen direction, losing altitude as it goes. When it lo- facing slopes. During the spring and fall,
Figure 5-37. Development of alhermal: Thermals, rising columns or bubbles of warm air, are created by sunlight. They frequently
develop over isolated patches of ground that heat up more quickly than their surroundings; these are often large, dark surfaces
cates another thermal (possibly by the presence of other soaring birds), when the sun's rays strike these slopes,
such as plowed fields or asphalt parking lots. The late-morning sunlight strikes these areas, causing them to radiate heat, warm- the bird repeats the process. This strategy is used by migrating hawks, they may be warmed more than north-
facing slopes, which remain in shadow.
ing the air just over them and forming a warm mass of air surrounded above and to the sides by cool air (top drawing). Note that vultures, storks, and cranes. Energetically, it is very efficient. Some
adjacent forested areas, although they may be dark as well, do not radiate heat as fast, partly because the high moisture content Because of this differential heating, series
estimates indicate that the total rate of energy expenditure is about of thermals may develop along south-
and complex structure of the forest causes it to retain its heat. As the warm air mass heats up further, the air expands and, because
one-thirtieth that required to fly the same distance under power. facing ridges. By entering one thermal,
it is lighter than the surrounding cool air, rises like the bubbles that form on the bottom of a heated tea kettle (middle drawing).
Cool air moves in below the rising bubble; soon it, too, is warmed and forms another rising bubble. Within each bubble the air Turkey Vultures and Black Vultures, although both static soarers rising in it, and gliding out to the next
circulates upward in the center and downward on the outside, producing a revolving ring of warm air somewhat like a smoke possessing slotted high-lift wings, have different wing shapes that are thermal, birds may use these thermals
ring (bottom drawing). to move cross-country. Migrating hawks,
correlated with their differences in behavior and distribution. Turkey
Soaring birds use thermals to gain altitude with little input of their own energy. They enter the thermal and circle upward on vultures, storks, and cranes may cover
Vultures have much longer wings and consequently a lighter wing great distances in this manner, using very
the rising central column of air. When the speed of the rising air currents is sufficient to offset a bird's weight, it can glide in the
circle with little or no flapping, gaining altitude as the bubble continues to rise.
loading. Thus• they can take advantage of weaker thermals, and can little of their own energy.

Cornell Laboratory or Ornithology Handbook of Bird Biology

5.42 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.43

live in more northerly areas, where thermals are not as strong or as

common. Turkey Vultures are also active in the earlier and colder part
of the day, whereas B lack Vultures must wait for stronger thermals to
develop before taking flight (Fig. 5 39).
-

In slope soaring, a bird derives lift from the rising air deflected
upward when wind strikes a hill or ridge. This kind of soaring is com-
mon along seacoasts, where gulls, terns, fulmars, and gannets may
soar for hours above the tops of windward sea cliffs (Figs. 5 40, 5 41).
- -

In strong winds, birds may remain motionless relative to the ground

for long periods. Even birds with high wing loading, such as alcids or
cormorants, can slope soar when the wind is strong enough. Ravens
and crows often slope soar, and the small American Kestrel frequently
uses updrafts from road cuts to hang in the air while it watches for
prey. This phenomenon also produces the concentration of migrating
i •k\
hawks along mountain ridges, especially those that parallel the basic
migration direction. Hawk Mountain, a high, slender part of the north-
south Kittatinny Ridge in Pennsylvania, is one of the many excellent
'
\ \ MEE= •

places in eastern North America to view autumn hawk migration. The a. Onshore Wind b. Offshore Wind

flow of hawks is particularly strong on clear, windy days following the Figure 5-40. Slope Soaring: Birds frequently fly
passage of a cold front (see Fig. 5-64). along cliffs by simply gl iding and rising on the up-
drafts created by (a) oncoming winds striking the
High Aspect Ratio Wings
- - perpendicular surfaces and deflecting upward,
B irds that spend most of their lives soaring possess what is called or by (b) winds from the opposite direction spill-
ing over the cliffs and eddying upward. Gulls are
a high aspect ratio wing. Like the high-speed wing, it is narrow and
- -

notorious for riding updrafts along sea cliffs or

unslotted; however, the proximal area of the wing that generates lift updrafts caused by ships. Although slope soaring
is greatly elongated. This wing is highly efficient at producing lift at may occur along any windy ridge, it is most com-
mon along seacoasts, where winds are steady
and strong. Drawing by Charles L. Ripper.

Turkey Vulture

Black Vulture

Turkey Vulture Range

Figure 5-39. Turkey Vulture versus Turkey Vulture and

Black Vulture Ranges and Wing Shapes: Black Vulture Range
Although both birds soar on slotted
high-lift wings, Turkey Vultures have
much longer wings than Black Vultures,
resulting in a lighter wing loading. They Figure 5-41. Northern Gannets Slope Soaring:
are thus less dependent on thermals, al- Northern Gannets hang in the air over a seaside
lowing them to live in more northerly cliff in Scotland, held aloft by updrafts created as
areas where thermals are not as strong wind striking the cliff face deflects upward. Photo
or as common. by B. GadsbyNIREO.

Cornell Laboratory of Ornithology Handbook of Bird Biology

5.44 Kenneth P. Able Chapter 5 —Birds on the Move: Flight and Migration 5.45

Some Flight Facts and Figures

Air Speed
Much information about matters such as the fastest or highestflying
bird is based on anecdotal observations, many of which took place only
once.The numbers garnered are often suspect because of the means used
cu
cu to measure them. Based on reliable data from tracking and Doppler radar
a..

x
(r) (Fig. 5 43), most small songbirds fly at air speeds of between 20 and 30
-

mph (32 and 48 km/h). Air speed

is a bird's speed relative to the air it
is moving through; air speed does
not include increases of speed
caused by being carried along by
the wind, so it may or may not re-
flect a bird's speed relative to the
ground. Waterfowl and shorebirds
can fly at higher sustained speeds
Figure 5-42. Dynamic Soaring: Alba- relatively high flight speeds, but maneuverability and ease of takeoff
trosses and other seabirds with high-as-
of 55 to 70 mph (89 to 113 km/h);
are sacrificed as a result of the length. Such wings are found in a few
pect-ratio wings use the wind gradient a Red-breasted Merganser pursued
seabirds that are highly specialized for soaring over the ocean, such
over the ocean to travel long distances by a plane was clocked at 80 mph
without spending much of their own as albatrosses, shearwaters, petrels, and to a lesser extent, gulls (see
(129 km/h). House Sparrows are
energy. Over the southern oceans near Fig. 5-1).
among the slowest species timed,
40 degrees latitude, winds are strong and
steady, but air moving over the surface Dynamic Soaring at 15 to 18 mph (24 to 29 km/h).
of the ocean is slowed by friction with The high-aspect-ratio wing allows a special type of soaring called The Peregrine Falcon has a repu-
the water, with the air layers closest tation for great speed, although
dynamic soaring, which is usually associated with albatrosses. Dy-
to the water being affected the most.
namic soaring is possible only in regions where winds are strong and measurements appear to be few.
The result is a vertical gradient in wind
speed (arrow length represents relative constant, such as the so-called "roaring forties"—the belt of water in Peregrines apparently cruise at 40
wind speed). In dynamic soaring, a bird the southern oceans around 40° latitude. Because air moving over the to 62 mph (64 to 100 km/h) and are reported to be capable of reaching Figure 5-43. Radio-tracking a Gray-
glides down the wind gradient at an 175 mph (282 km/h) in a dive. Dive speed is limited, because if a per- cheeked Thrush: One technique used to
surface of the ocean is slowed by friction, winds are slowest close to
angle, then turns and abruptly rises into follow a bird in migration, gaining infor-
the water's surface, and progressively increase with height up to about egrine reached too high a speed during an "attack dive," it might break
the wind, using its momentum to gain mation on route and speed, is radio-tag-
height quickly. It then turns and glides 50 feet (15 meters). apart on impact. In straight, powered flight, the fastest bird is reported to ging: attaching a tiny radio transmitter
downwind again, crossing the ocean in An albatross at the top of the gradient glides downwind at an be the Spine-tailed Swift of India at up to 217 mph (349 km/h). to a bird's back and tracking the bird
large zig-zags or loops, with little effort. from an airplane equipped with a radio
angle, increasing its ground speed (Fig. 5 42). As it nears the water's
-

See text for details. Adapted from Burton Wingbeat Frequency to receive impulses from the transmit-
surface it turns back the way it came and glides upward into the wind, ter. A Gray-cheekedThrush radio-tagged
(1990, p. 106). The wingbeat frequencies of most songbirds are in the range of 10
using its momentum to rise, much as a car coasting down a hill can in the spring at Champaign, Illinois and
to 25 beats per second during the flapping portion of their undulating
coast part-way up the next hill without using any gasoline. As it rises, tracked by air from the moment it started
flight. A male Ruby-throated Hummingbird has been recorded at 70 north in the early evening, is fancifully
the bird encounters progressively faster winds, which increase its lift
beats per second and a chickadee at 27 beats per second. Larger birds pictured here as it passes over Chicago
(recall that greater wind speeds produce more lift on an airfoil). Glid-
generally have substantially slower wingbeat frequencies. Large vul- and heads east and then north into the
ing into the wind decreases the albatross's speed, however, so it does darkness over Lake Michigan. Drawing
tures, for example, may flap their wings only once per second.
not cover as much ground as it did on its glide with the wind. When courtesy of Guy Coheleach. Originally
it reaches the top of the wind speed gradient, it no longer can use the from Graber (1965).

energy of the wind to rise, so it turns forward and glides downwind Flocking and Flying in Formation
once again.Thus, an albatross flies over the ocean in a series of vertical Some bird species are characteristically encountered in flocks,
zig-zags or loops. In the roaring forties, albatrosses circumnavigate which form in many different circumstances (see Ch. 6, Sidebar 4:
the globe using the westerlies to cover vast distances while expending Living in Groups). For example, large numbers of crows assemble
remarkably little energy. When not dynamic soaring, an albatross may in communal nighttime roosts during winter. Shorebirds and gulls
slope soar on the air currents along the windward face of a wave, until typically rest and feed in groups, and in winter many songbirds—es-
it encounters an upward gust of wind sufficient to initiate dynamic pecially those that inhabit open country, such as Horned Larks and
soaring. longspurs—move about in flocks.

Cornell Laboratort1 of Ornithology Handbook of Bird Biology

5.46 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.47
Figure 5-44. V-shaped Flock of Snow
Geese: A bird flying close behind an- Area of Low
other bird, at an angle, may gain some Pressure
Movement of Air
extra lift from the rising portion of swirl-
ing air currents trailing behind the wing Relative to Vehicles
tips of the bird ahead (termed tip vortex, Second Vehicle is
see Fig. 5-31). By flying in V formations, Pulled Forward
birds appear to be able to reap this en-
ergetic advantage, but evidence so far
comes only from theoretical models.
Photo by Tom Vezo.

Figure 5-46. Drafting: A moving vehicle, such as the truck pictured here, continuously displaces air by moving forward, creating
an area of low pressure behind itself. Air moving back over the top of the truck swirls down into the low pressure area, and air
from below swirls up toward the area, creating a current of air that pulls the second vehicle forward, if it is close enough. A bird
flying close behind another in a single-line formation may be pulled forward in a similar manner, reducing the amount of energy
that it must expend to produce thrust through flapping flight. Drawing by Christi Sobel.

Some species move in flocks during migration. These include

most waterfowl, cranes, cormorants, pelicans, the Common Night- that many are made up of a single species (for example, Eastern King-
hawk, and Broad-winged and Swainson's hawks. Whether flock mem- birds, Blue Grosbeaks, or Orchard Orioles). It is hard to imagine how
bers pool their navigational expertise in determining which way to fly is they could sort themselves out in this way unless they already were
not known. For some, such as geese and cranes, the flocks may include together in a loose aggregation. Why they form flocks at daybreak is not
family groups of older, experienced birds and youngsters on their first clear, but the selective advantage of flocking for most birds is certainly
migration. Migrating in family groups provides an opportunity for the protection it affords against predation.
first-time migrants to learn the migration route and important feed- Many species fly in various kinds of formations. Most fam i I iar are
ing and resting places along the way. Family groups of Tundra Swans, the V-shaped formations used by many geese and cranes (Fig. 5 44) -

for instance, migrate together until their arrival back on the breeding and the single-file formations of Brown Pelicans and cormorants. Al-
grounds the following year. though not all specialists agree, flying in such formations probably
Most songbirds that migrate at night do not move in flocks, at confers an energetic advantage to all except the flock leader. In V for-
Figure 5-45. Single-line Flock of
least not in tight, well-integrated ones. They may move in loose as- mations, for example, followers probably take advantage of the rising
Double-crested Cormorants: Each bird
flying closely behind another bird in a
semblages, however, as is suggested by observations of night migrants portion of swirling air currents trailing behind the wing tips of the bird
single-line formation may save energy that are forced to continue to migrate into daytime because they find ahead (termed tip vortex, see Fig. 5-31). Theoretical models suggest
in the same way that a car saves energy themselves over water at dawn—as happens regularly to spring mi- that geese may save nearly 20 percent of their flight energy by flying
by closely following a truck on the high- grants crossing the Gulf of Mexico. As observed on radar, the loosely in V formation (Berthold 1993), but no one knows whether this energy
way—a technique termed "drafting."
dispersed migrants flying in darkness ascend and form into flocks at savings is actually achieved, and what other factors may be involved,
See text and Fig. 5-46 for more infor-
mation. Photo by Tom Vezo. dawn. An observer watching these flocks arrive at the coast will find The point (lead) bird in such a formation does not receive much en-
ergetic benefit and changes frequently during flight. Researchers do
not know, however, if the leaders actually change to save energy. In
single-file formations, too, each bird that flies directly behind another
bird may derive energetic benefits (Fig. 5 45). -

Flying straight behind a flockmate is similar to a driving technique

known as "drafting," often employed by race car drivers by following
each other closely, or by cars closely following a truck on the highway
(Fig. 5 46). In each case, the vehicle in front continually displaces
-

air by moving forward, creating a low pressure area behind itself. Air
moving back over the top of the first vehicle swirls down toward the
low pressure area, and air from below swirls up, creating an air cur-
rent that pulls the second vehicle forward. In this same way, a bird that
flies closely behind another is pulled forward, reducing the amount of
energy that it must expend to fly.
One of the most impressive flocking maneuvers is the synchro-
nized wheeling and zigzagging flight of dense flocks of shorebirds or

Cornell Laborator.1 of Ornithologq Handbook of Bird Biolo8q

5.48 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.49

Elephantbird

Figure 5-47. Shorebird Flock Maneu- starlings in the presence of a flying hawk, especially an accipiter or to move around. Therefore, the power of flight may disappear when, Figure 5-48. Sample Ratites: One of the
vering in Air: The seemingly impossible, for many generations, a bird population finds itself in a situation in best-known groups of flightless birds is
falcon (Fig. 5 47). In fact, a wheeling flock of starlings often is a hint
-

split-second twists and turns of a dense the ratites. Most, like the Ostrich, are
that a hawk is flying nearby. How such groups manage to move as one which the ability to fly provides no strong advantage. In all flightless
flock of birds is one of the most awe- large, diurnal birds of open country, too
organism without individuals colliding into each other remains one of birds, the keel on the sternum and the mass of the flight muscles are heavy to fly, which rely on their long,
inspiring sights in nature. Recent stud-
ies with high-speed photography have the most intriguing aspects of bird flight. both reduced—thereby saving the energy of maintaining and moving powerful legs to outrun predators. The
revealed that any bird can initiate a Recent studies using high-speed photography have revealed around with these costly structures (see Fig. 4-19). three species of kiwi are atypical rat-
flock maneuver, and that once begun, Flightlessness has evolved in many lineages of birds. Best known, ites. Duck-sized and nocturnal, they
some of the mechanisms that permit such precision (Potts 1984). First, roam the forests of New Zealand using
it spreads rapidly much like a "wave" perhaps, are the penguins and ratites (the Ostrich of Africa, rheas of
from fans at a sporting event: birds do
there is no consistent flock leader. Birds change position frequently, their highly developed sense of smell to
and any individual can initiate a flock maneuver, which then spreads South America, the Emu of Australia, cassowaries of New Guinea and search the ground for earthworms and
not wait for their near neighbors to re-
act, but watch the movements of more through the rest of the flock in a wave. Some rules are followed, how- Australia, the kiwis and recently extinct moas of New Zealand, and the other small arthropods. The elephant-
distant birds so they can anticipate the extinct 970-lb (440-kg) elephantbirds of Madagascar) (Fig. 5 48). birds, a group of huge (970-Ib; 440-kg),
ever. For example, flock members always seem to follow the lead of -

appropriate time to change direction. extinct, flightless birds that once lived
individuals that bank toward the center of the flock. Such arbitrary Penguins apparently evolved flightlessness very early in their his-
Shown here, a winter flock of nearly on the island of Madagascar, are among
rules probably help prevent indecision and allow a flock to respond tory. Many diving birds (for example, loons, auks, and some diving the largest birds ever known. Their egg,
4,000 Dunlin (with a few Western Sand-
pipers), fills the air at Stone Harbor, New rapidly during attacks by birds of prey. Once one of these wave ma- ducks) have legs positioned far to the rear of the body, and the wings measuring up to 1.3 by 9.5 inches (33 by
Jersey. Photo by Kevin T Karlson. neuvers has begun, it travels through the flock very rapidly—in fact, are used for swimming as well as flying. But penguins carry these 24 cm) is considered the largest single
tendencies to an extreme, and literally use their flipperlike wings to cell in the animal kingdom. Drawings
at a speed much greater than should be possible based on the birds' of Ostrich and kiwi by Charles L. Ripper.
individual reaction times. Propagation time from neighbor to neighbor fly under water. In the Northern Hemisphere, the extinct Great Auk,
Elephantbird redrawn from Pough et al.
is about 15 milliseconds, nearly three times faster than would occur the only known flightless member of its family (Alcidae), closely re- (1996, p. 543).
if birds were simply following the action of adjacent flock members. sembled the penguins.
Such rapid reaction apparently is possible because birds pay attention Because flying and swimming are very different modes of travel,
to more distant individuals in the flock, allowing them to anticipate requiring different body adaptations, a bird that has evolved to do
an approaching change in direction in much the same way that fans just one or the other will generally do it better than a bird that does
coordinate "waves" at sporting events. both (Fig. 5 49). The Antarctic land mass and the plethora of nearby
-

islands may have provided low, safe nesting places for penguins, thus
reducing their need to fly, and allowing them to evolve into swimming
Loss of Flight specialists. In contrast, many Arctic islands are steep-sided, with fewer
Although flight gives birds a tremendous advantage in exploiting good nest sites for flightless northern swimmers. Perhaps competition
habitats and avoiding predators, it is an energetically expensive way

Cornell Laboratoni of Ornithologq Handbook of Bird Biologq

5.50 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.51
Flightless species occur in many other groups. These include
flightless grebes on Lake Atitlan (now apparently extinct) and Lake Titi-
caca in the Andes, the Flightless Cormorant of the Galapagos, ducks in
southern South America and New Zealand, pigeons on several islands
in the South Pacific and Indian Oceans (including the extinct Dodo),
a flightless parrot in New Zealand, and flightless rails on many islands
AVAP • ' throughout the world. Only a few flightless passerines are known. The
most famous is the tiny Stephens Island Wren (family Acanthisittidae),
Ok"
which lived on an island in Cook Strait between the North and South
\ Islands of New Zealand. It is known only from a few specimens brought
4‘1110,11;:4 RtV‘
Emperor Penguin in by the lighthouse keeper's cat, which subsequently killed all the rest
Pigeon Guillemot
of the species.
The fossil record reveals an amazing array of flightless birds, from
the gigantic predatory Diatrymas (see Fig. 22 in Evolution of Birds
and Avian Flight), Phorusrhacids, and the bizarre, ducklike, Hawaiian
Moa-nalos to a three-foot-tall owl that hunted ground sloths and other
mammals in the West Indies.
Flightlessness has evolved most frequently on islands where
bird populations found themselves in environments free of predators.
When humans arrived on these islands, bringing with them dogs, cats,
rats, and other predators, many flightless birds were quickly driven to
extinction, and many that remain today are severely threatened.
The anatomy and brain structure of all flightless birds shows con-
clusively that they evolved from flying ancestors, and some groups
seem more prone to the evolution of flightlessness than others. The
rails, for example, include many flightless and nearly flightless forms,
and in all of them, the sternum does not finish its growth until the bird
Figure 5-49. Penguin versusAlcidAdap- for these limited nest sites resulted in only the largest of the alcids,
tations for Swimming: Penguins are the is nearly fully grown. This pattern of development may predispose
the now-extinct Great Auk, being able to use the low sites and conse-
supreme underwater swimmers of the rails to lose the power of flight through an evolutionary phenomenon
quently give up flying. The fact that this species restricted its nesting
bird world. Their feet, positioned at the known as neoteny, the retention of juvenile traits into adulthood. One
far end of the body, are in the best pos- to a couple of low islands in the North Atlantic Ocean undoubtedly
could thus speculate that flightlessness in rails may have evolved as
sible location to serve as steering rud- hastened its demise.
ders for their streamlined, torpedo-like
the sternum eventually stopped growing before it had reached full size
Most of the flightless ratites are large birds too heavy to fly. Many
bodies. Their rigid wings (flippers) lack in some species.
live in open country where they rely on long, powerful legs to outrun
typical flight feathers, allowing them to
use the entire wing to "fly" underwater.
predators. Cassowaries have massive legs and a long, sharp claw on
each foot.They defend themselves by jumping off the ground: by kicking
By tilting the leading edge of the wing up
on the upstroke and down on the down- forward powerfully, they can disembowel dog-sized mammals. Kiwis
Migration
stroke, penguins can produce thrust on also have thick, powerful legs, but they live in forests and are nocturnal. ■ Animals that live in strongly seasonal environments where they can
both strokes, the wing literally acting
They evolved in New Zealand in the absence of terrestrial predators and meet their life requirements during only part of the year face a serious
as an underwater "airfoil" (hydrofoil).
Alcids (auks), such as the Pigeon Guil- apparently relied on the cover of darkness, cryptic plumage, and spend- problem. Many species of mammals, reptiles, amphibians, insects, and
lemot pictured here, still retain the ing the day in burrows to avoid a now-extinct, huge eagle. other invertebrates have solved this problem by entering an inactive, dor-
ability to fly and thus have not become Flightlessness, then, appears to have been able to evolve in ratites mant state known as torpor or hibernation. A very few birds, including
completely specialized for swimming.
because the birds could avoid predators by their large size, or because some hummingbirds, swifts, and especially nightjars, are also known
Their feet, like those of penguins, are
used for steering, but are not set as far
they originated on an island that had no terrestrial predators. Further- to enter a torpid state of lowered body temperature and metabolism.
back on the body. Pigeon Guillemots, more, none of the ratites had a need to fly into trees, as they obtained The Common Poorwi II may remain torpid for weeks or months (see Fig.
unlike other alcids, also use their feet for their food on the ground, either by grazing on grasses, or by probing 4-128). Highly mobile animals have another option: they can leave the
propulsion. The wings of auks are short the soil for earthworms (kiwi). In fact, in all ratites except the kiwis, inhospitable area entirely. Endowed with strong powers of flight, most
with short inner secondary feathers, and
predator avoidance by their Eocene ancestors apparently depended birds deal with fluctuating environments by migrating.
are kept partly folded at the elbow when
underwater, forming a smaller, broader on increased body size and strength of legs and feet at the expense of When ornithologists speak of migration, they usually mean sea-
"paddle" than that used in flight. their wings. sonal migration, such as movement between breeding and overwin-

Cornell Laboratorq of Ornitholo9q Handbook of Bird Biolosil

5.52 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.53

Figure 5-50. Arctic Tern Fall Migration tering areas. An extreme case is that of the Arctic Tern. Breeding on Furthermore, migrations are not always in the north-south direction, Figure 5-52. Vertical Migration of the
Route: The Arctic Tern has one of the lon- islands in the far north, it migrates as far south as the waters around and are not always synchronized with spring and fall. Many tropical Blue Grouse: The Blue Grouse, a resi-
gest migration routes known, traveling dent of mountainous regions of western
Antarctica in the winter, a flight that may be as much as 11,000 miles birds such as certain quetzals, hummingbirds, and parrots, migrate
up to 11,000 miles (17,700 km) from its North America, breeds in a wide range
breeding grounds on islands in the far (17,700 km) one way (Fig. 5 50). During the course of a year, an in-
- in response to the seasonal alternation of rainfall and drought, which of open habitats, from various shrub and
north (dark green) to the outlying pack dividual Arctic Tern may cover a distance equivalent to flying around changes the availability of fruits, seeds, insects, and nectar. These grassland communities to open montane
ice waters of Antarctica, where it over- the world. Equally amazing is the Blackpoll Warbler, which weighs migrations are often "vertical"—up and down mountainsides. Blue forests and edges. Birds from every type
winters. Drawing by Robert Gil lmor. of breeding range, however, all seem to
about one ounce (31 grams) before migration, when laden with stored Grouse in western North America also migrate vertically (Fig. 5 52). -

overwinter in coniferous forests, feed-

III Breeding Grounds

fat. In autumn, blackpolls depart from the coast of the northeastern
United States and fly over the waters of the Atlantic Ocean to South
The diversity of migration strategies can best be understood in an
ecological context: the variability and predictability of the resources—
ing mainly on conifer needles. Most
populations of Blue Grouse migrate
America (Fig. 5 51). Unlike the
- food, water, cover, and other necessities—that the bird depends on seasonally, but not in the north-south
tern, they cannot land on water determine what type of migratory behavior is likely to evolve. By con- direction typical of most temperate zone
woe
birds. Instead, they migrate "vertically,"
or feed along the way. They fly sidering the spectrum of bird movement patterns in terms of seasonal
moving up mountainsides in the fall to
nonstop, day and night, for four resource variability and predictability, one can bring order to what reach coniferous forests, and moving
or more days to make this 2,480- might otherwise seem like a collection of disparate behaviors. Refer back down to the breeding grounds in
mile (4,000-km) trip. to Figure 5 53 as you read through the following examples of bird
-
the spring.

movement patterns.

Patterns of Migration
Migration comprises not
only long-distance round trips,
lll lllllllll ip011f„ 00(1111 11A,01111 1 111f,kje
11,114,01(p%
but a broad continuum of sea- 041164 w
Arctic Tern sonal movements, ranging from
sporadic mass movements over Winter Habitat
(Elevation 9,000 to 12,000 Feet
relatively short distances to jour-
(2,745 to 3,660 ml)
neys spanning a hemisphere.

Blackpoll Warbler
Rim l
1 1111, 0 11 1T

' ,101111-11 1 11 77,

• )1'r. . . 1r11114„,i Y
__ ° 1617rf,
'717 7,7 ID.,
'' 7
' it, ',Orr

tAt;srivi
O
Breeding
Vn
Range
"n111,.̀7,
:i07.--- • "*-

Figure 5-51. Blackpoll Warbler Fall Mi-

gration Route: In the fall, postbreeding
family groups of blackpolls gather into
larger and larger flocks, then make their
way from their breeding grounds in the
boreal forests of Canada to the north-
eastern United States. From this staging •

area, they set out over theAtlantic Ocean

to fly nonstop, day and night, for four or
more days to their wintering grounds in
South America, a total distance of 2,480
miles (4,000 km). Reprinted from Ken- Winter
neth P Able, ed.: Gatherings of Angels: Range Summer Habitat
Migrating Birds and Their Ecology. (Elevation 6,000 to 7,000 Feet
Copyright 01999, Cornell University. (1,830 to 2,135 ml)
Used by permission of the publisher,
Cornell University Press.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologt.

5.54 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.55
Migration is costly in terms of both energy and risk (Table 5 2). -
Table 5-2. Survival and Reproductive Success of Residents and Migrants: Estimates of annual adult survival (percent of adult
birds surviving to the next year) and annual reproductive success (number of young fledged per year) are provided for birds that
For example, migrants have annual adult survival rates of about 50
reside year round in the tropics, birds that reside year round in temperate areas, and birds that breed in temperate areas but mi-
percent compared to tropical residents, which have rates on the order grate to the tropics for the winter. Birds in each category appear to have evolved to produce as many young as possible over their
of 80 to 90 percent (Gill 1990). However, tropical species have much lifetimes, but their strategies differ: tropical residents live long, producing few young each year; temperate residents have shorter
lower reproductive success than birds that breed in temperate areas lives, but produce more young each year. Migrants live moderately long, and raise a moderate number of young. Adapted from
Gill (1990, p. 247).
(both migrants and temperate zone residents). Therefore migrants have
apparently traded in higher adult survival rates for higher productivity
in any one year. (Temperate zone residents have even lower annual TROPICAL RESIDENT MIGRANT TEMPERATE RESIDENT
survival rates, in the range of 20 to 50 percent, since they must face
Tropical residents do Temperate residents must
the hardships of winter.) But migration has other disadvantages. Mi- ANNUAL not face the hazards of endure the harsh weather and
grants that do return alive may be weakened from their journey. They ADULT migration or harsh winter Migrants escape winter, but restricted food supply
also must expend energy setting up a new territory each spring—and SURVIVAL weather. many die during migration. • in winter.
temperate residents may acquire the best breeding territories before High (80-90%) Moderate (50%) Low (20-50%)
migrants arrive.
————
In areas where all necessary resources are predictably available
year round, natural selection favors individuals who are resident. Migrants feed their young on
ANNUAL seasonally abundant insects in
Northern Cardinals, Northern Mockingbirds, and most chickadees, REPRO- Tropical residents have the temperate zone, but each Temperate residents can
titmice, and woodpeckers are permanent temperate zone residents; DUCTIVE no seasonally abundant ___ year divert time and energy take advantage of the huge,
they can count on adequate reserves of seeds, berries, and dormant SUCCESS source of food for their from breeding into migrating seasonal flush of insects to
insects to see them through the winter. ■ young.
_
and setting up new territories. feed their young.
When resources in the breeding area differ greatly from season Low Moderate High
Figure 5-53. Relationship between Mi- to season, and when this pattern is highly predictable, as it is for birds
gration Strategies and Food Resources:
nesting at high latitudes that eat insects or nectar, the pattern that
In temperate climates, migration strat-
egies are related to seasonal variation
evolves is obligatory annual migration, in which all individuals mi-
these species with relatively inflexible "migratory programs," which
and predictability of food resources in grate toward the equator for the winter. This type of pattern is seen in
ensurethat virtually all individuals will leave the breeding areas before
the breeding area. Shown here are six many flycatchers, thrushes, vireos, hummingbirds, and wood war-
migration strategies that may be defined food resources reach dangerously low levels.
blers. Selection against individuals that make the mistake of trying
based on resource predictability (Y axis) In environments where the variability is less extreme and less
to stay in the north all year is strong—a flycatcher that decides to try
and variability (X axis). These strategies predictable, birds adopt more flexible behaviors (these are the nomads,
exist on a multidimensional continuum, catching flies in the winter will die rather quickly. Evolution equips
facultative partial migrants, and irruptive migrants of Fig. 5-53, as dis-
as represented by the central arrow clus-
ter, such that not all individuals within a
cussed below). Birds of these persuasions may stop their southward
species or population necessarily con- migrations at any of a number of points, depending on conditions. If
form exactly to the six strategies shown OBLIGATE they can meet all of their needs in a northerly location, they may try to
on the graph. For example, Eastern PARTIAL spend the winter there but be prepared to move on if conditions wors-
Bluebirds may be facultative partial MIGRANT OBLIGATE
en. The Lapland Longspur and many sparrows and water birds seem
migrants in some geographic locations, ANNUAL
HIGH Some Blackcaps to fall into these categories, as do some fruit-eaters such as American
and residents in others. Most species, MIGRANT
(An Old World Warbler)
however, follow the basic behavioral Flycatchers
Robins and Eastern Bluebirds.
Predictability of Food

RESIDENT
patterns shown here. Birds thatare year- A Hummingbirds Migration schedules do not necessarily follow seasonal changes
round residents, for example, occupy Northern Cardinal Wood Warblers in cl i mate.The seeds and buds eaten by various finches such as redpol Is
environments with high resource pre- Downy Woodpecker
dictability and low seasonal variation in
and Pine Grosbeaks fluctuate dramatically in abundance, not only
resources. In other words, resident birds IRRUPTIVE seasonally but also from year to year and region to region. These fluc-
can count on a roughly constant supply
NOMAD MIGRANT tuations may be quite unpredictable. Migration in these species must
of food throughout the year. At the other Pine Siskin be facultative (flexible), directly responding to local food availability.
Budgerigar
end of the continuum, irruptive migrants FACULTATIVE Redpol Is
LOW Crossbills Such movements have been termed irruptive because in some years
contend with low predictability and PARTIAL Pine Grosbeak
high variability in food resources. These MIGRANT Evening Grosbeak large numbers of birds move out of the northern forests and in other
conditions have led irruptive migrants to American Robin
years they stay put. Similar irruptive migrations are well known among
adopt a strategy of sporadic movements the tundra predators of lemmings such as Snowy Owls, Rough-legged
Belted Kingfisher
to areas with plentiful resources when
Hawks, and jaegers.
food supplies in the breeding area sud-
LOW HIGH Between the extremes of predictability and variability lie a range
denly plummet. See text for descriptions
of migration strategies. Seasonal Variability of Food in Breeding Area of intermediate situations that seem to select for a type of behavior

Cornell Laboratorg of Ornitholop4 Handbook of Bird Biolo9ti

5.56 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.57
termed partial migration—some individuals in a population migrate subspecies, Zonotrichia leucophrysgambelii, migrates from Alaska and
while others behave like residents. Partial migration may arise from two theYukon south to the southern plains and into northern Mexico. Farther
different types of control mechanisms. In one type, the difference be- south, the subspecies Z. I. pugetensis breeds from southern British Co-
tween a migrant and a resident individual might be genetically deter- lumbia southward to northern California. It migrates a shorter distance,
mined; these birds are called obligate partial migrants. The individuals overwintering in the lowlands of central and southern California. A third
with genes for migration would always migrate, and the nonmigrant subspecies, Z. I. nuttalli, is a year-round resident in coastal California,
genotypes would always behave as residents. This arrangement most sharing its habitat in winter with migrants from farther north.
likely evolves in environments where resources are always sufficient
to enable some, but not all, individuals to overwinter successfully in
the breeding area, and when the number of individuals who can stay is
The Origin and Evolution of Migration
relatively stable from year to year. This kind of genetic polymorphism Today, a diverse range of birds migrates with the seasons, in-
seems to exist in the European Robin and in southern European popu- cluding some penguins (on foot), loons, storks, hawks, owls, hum-
lations of the sylvi id warbler, the Blackcap (Berthold 1996). mingbirds, parrots, and songbirds. Migration occurs on all continents,
When the number of birds that the environment can support var- wherever the environment changes periodically, whether the change
ies from year to year, we can expect a more flexible strategy to evolve. results from temperature cycles, alternation of rainy and dry seasons, or
In this situation, known as facultative partial migration, the number some other factor. Although the earliest origins of migratory behavior
and identity of the individuals migrating varies from year to year in are probably lost forever, it is reasonable to conclude that migratory
direct response to resource availability. Which birds migrate is not behavior has evolved (and disappeared) repeatedly within the avian
predetermined genetically, although the migrants may be predomi- lineage. It may have appeared almost as soon as birds could fly well
nantly young or socially subordinate members of the population. The enough to travel long distances. Although some current migration pat-
Blue Tit of Europe seems to fit this pattern, and some North American terns in the Northern Hemisphere undoubtedly were shaped by events
chickadees may too, during their occasional flight years. during the Pleistocene, when episodes of glaciation alternated with
It is not clear that any bird species is truly nomadic (constantly warmer periods, large-scale migration surely existed long before the
on the move, showing no tendency to return to previously occupied glacial epochs.
places). Frequently cited examples are species that occupy the arid In the simplestterms, migration beginsto evolve when individuals
interior of Australia, such as the Budgerigar, but researchers need more that move from one area to another produce more offspring than those
information about their movement patterns to determine whether that do not move. When the environment changes, migratory behavior
these birds are true nomads. apparently can develop dramatically in just a few generations. In the
Thus, migration and residence behavior patterns span a con- early 1940s, for instance, House Finches from a sedentary population
tinuum from permanent residency to obligate long-distance migration, in California were released on Long Island, NewYork. The introduction
and many cases may not be easily categorized. Even within one spe- was wildly successful, and House Finches have become one of the
cies, different populations may have very different migration strategies. most abundant birds in urban and suburban areas of the northeastern
As an example, consider the White-crowned Sparrow populations of United States. Because the environmental conditions of the Northeast
coastal western North America (Fig. 5-54). The northernmost breeding change much more with the seasons than do conditions in California,
migration appeared within 20 years after the birds were introduced.
Although some individuals remain year-round residents in the North-
Figure 5-54. White-crowned Sparrow: east, others migrate back and forth to the Gulf States. Therefore, the
Along the western coast of North Amer-
eastern House Finch has become a partial migrant.
ica, different populations of this species
have very different patterns of migra-
Migratory behavior also can be lost rapidly from a population.
tion, ranging from year-round residency It was surely some migrating Dark-eyed Juncos gone astray that col-
to long-distance migration. Photo by onized Guadeloupe Island, some 1 55 miles (250 km) off the coast
Marie Read. of Baja California. The species is now established there as a seden-
tary population. Similarly, if less dramatically, populations of White-
crowned and Savannah sparrows along the coast of California have
lost the migratory habit. Because none of these populations (juncos
or sparrows) has evolved enough differences to be considered a new
species, researchers assume that their isolation is recent, and that the
loss of migratory behavior must have been fairly rapid.
A number of different theories have been proposed for the way in
which seasonal migration evolved, including the following:

Cornell Laboratorq of Ornithologq Handbook of Bird Biologt

5.58 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.59
1. Climatic Changes: As conditions changed slowly, due to glacial toward the temperate zone, lured by the seasonal flush of insect food
advances or retreats or shifting continents, birds migrated to return and greater day length, which allowed them to raise more young an-
to favorable conditions. For example, temperate zone migrants may nually (four to six, on average) than their resident tropical relatives
have evolved when the region's cl i mate was more tropical, thus they (two to three young, on average). As their breeding sites moved to the
leave in winter to live in the warmer conditions to which they are temperate zone, the birds developed migration to return to hospitable
better adapted. habitats during the colder part of the year. Thus, in the Northern Hemi-
sphere, selection favored a long-distance migration north to breed, and
2. Lack of Needed Resources: For example, birds may leave the tem-
then south to overwinter. In the Southern Hemisphere the directions
perate zone in winter to move to warmer areas where more food,
are reversed.
such as fruit, nectar, or insects, is available.
Many aspects of migratory behavior vary from individual to in-
3. Seasonal I nterspecific Dominance Interactions: In certain seasons, dividual, even within the same species. For a behavior or any other
the competition between species (for food, nest sites, or some other trait to evolve under the influence of natural selection, the individuals
resource) is so great that some individuals must leave to find the of a population must exhibit variation in the trait, and the variation
resource elsewhere. must have a genetic basis (Ch. 1, Sidebar 2: The Evolution of an Idea:
4. Seasonal Intraspecific Dominance Interactions: In certain seasons, Darwin's Theory). Although scientists have assumed that variations in
the aggression of dominants toward subordinants causes some migratory behavior are inherited, the details have only recently begun
members of a species to migrate to other areas. to emerge. These details are the result of studies performed on a small
Eurasian warbler, the Blackcap, by Peter Berthold and his colleagues
5. Seasonal Tracking of Fruit or Nectar: Some birds migrate to fol low in Germany. The Blackcap breeds throughout western Europe from
the fruiting or flowering of their key food plants. Scandinavia southward to areas around the Mediterranean Sea (Fig.
5-55). Blackcap populations also exist on the Canary and Cape Verde
As discussed by Rappole (1995; see Suggested Readings), none of islands. Conveniently, this species exhibits a wide range of migratory
these theories satisfactorily explains the seasonal movements of birds, habits, from long-distance obligate migrants in the northern part of the
such as Neotropical migrants, which move both north and south. Mi- breeding range to partially migratory populations around the Medi-
gration is a two-way street, and thus arguments for its existence need terranean, and resident populations on Cape Verde. Blackcaps from
to explain both why birds migrate from an area and why they return. all of these populations breed with one another in captivity, making it
If (as outlined by Theories 1 through 4 above) birds leave for a better possible to study the genetic control of their migratory behavior.
climate, more resources, to avoid competition with other species, or
to avoid aggression from conspecifics, why do they return? Theory 5
above can explain migration in several directions, as birds move back
and forth to areas with the most abundant or preferred fruits or flow-
60° E
ers, but seems to apply mainly to migration within tropical areas, as in
quetzals, hummingbirds, parrots, and others.Tropical species have not
needed to migrate as far as the temperate zone to find an abundance
of fruit or nectar, and species that rely on these foods do not appear to Figure 5-55. Variation in Migratory
have evolved originally in the temperate zone (see below). Habits of Blackcaps: Various popula-
Theories 1 and 2 above, in order to apply to Neotropical migrants, tions of Blackcaps (a species of Old
Blackcap World warbler) differ in their migra-
would have to assume that the birds or their ancestors evolved in the
tory habits. Birds that breed in northern
temperate zone, and then developed migration away from the area to Europe and Asia (light red) are obligate
avoid adverse situations during winter. In contrast, researchers believe annual migrants: all individuals migrate
Azores
that most land birds that migrate to the Neotropics to overwinter, are, to Africa for the winter. Birds in south-
in a sense, returning home. Strong evidence for this tropical origin of Madeira western Europe and on the Canary Is-
lands (medium red) are partial migrants:
migration is that most of "our" vireos, flycatchers, tanagers, warblers,
Canary Islands , some individuals migrate to Africa for
orioles, and swallows have evolved from Neotropical forms. In fact, cS the winter, while others remain within
78 percent of all Nearctic migrant species have close relatives in the the breeding grounds. Because experi-
C‘ C2P
same genus or even populations of conspecifics that reside in the v oVI ments have shown a genetic basis for
Neotropics year round. Cape Verde this difference, these birds may be con-
Islands Obligate Migrant Population sidered obligate partial migrants. Birds
A more acceptable theory for how Neotropical migrants evolved •• breeding in the Azores, on Madeira, and
.••
II Obligate
■
Partial Migrant Population
migration is that through many generations, the tropical ancestors in the Cape Verde Islands (dark red) are
Resident Population
of "our" migrants dispersed away from their tropical breeding sites year-round residents.

Cornell Laboratorq of Ornitholo8q Handbook of Bird Biologg

5.60 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.61
Berthold's cross-breeding experiments have revealed a remark- Figure 5-57. Circular Orientation
able degree of genetic control over a number of facets of migratory Cage: Reseachers often determine the
direction in which a bird orients its
behavior. For example, when members of long-distance migratory
migratory restlessness by placing the
populations were bred with partially migratory birds from the Canary bird in a circular orientation cage for
Islands, the offspring showed intermediate amounts of migratory the night. A typical cage, as shown here,
activity, which was monitored by the amount of hopping and flutter- is screened on top but open to the sky. A
piece of white blotting paper makes up
ing at night (Berthold 1996) (Fig. 5 56). This migratory restlessness
-

the sides of the funnel, and an ink pad,

was first discovered by German scientists, who termed it Zugunruhe, the floor. As the bird hops and flutters
literally "migratory unrest." Because night migrants are inactive and against the sides of the funnel, it leaves
sleep at night except during the migration period, this restlessness inky footprints. The compass orien-
provides a good measure of an individual's desire to migrate. Simi- tation of the footprints indicates which
direction the bird would tend to fly, if it
larly, the direction of orientation can be recorded by using circular
were free to migrate, and the degree to
"orientation cages" and recording the compass direction of the side of which the footprints are concentrated in
the cage the birds hop and flutter against the most (Fig. 5 57). During - one direction indicates the strength of
their first migration, the compass direction of orientation of the hybrid the bird's tendency. Drawing by Robert
Gillmor.
Blackcap offspring also showed high heritability. Blackcaps from the
western part of central Europe migrate southwestward and go around of migratory activity was eliminated from the population. The rapidity
the western end of the Mediterranean and then into Africa. Those from with which the behavior responded to selection indicates strong ge-
eastern Europe fly around the eastern end of the Mediterranean. Hybrids netic control. Th is suggests that in nature, given potent selection by the
between individuals from the two sides of this migratory divide showed environment, many aspects of migratory behavior have the potential
intermediate orientation—to the south—a direction that apparently has to evolve quite rapidly.
been selected against in wild populations (Berthold 1996) (Fig. 5 58). -
The Blackcap provides yet another illuminating case study. Over
Figure 5-56. Degree of Migratory
Partially migratory populations provide particularly good oppor- the last 25 years or so, central European Blackcaps have developed a
Restlessness in Captive Blackcaps: Re- new migratory pattern. Instead of migrating to African winter quarters,
searchers studying nocturnal migrants
tunities to study the genetic control of migration. About 79 percent
of Blackcaps from southern France are migrants. The remainder are some individuals have begun to fly northwest, overwintering in the
have long used the degree of migratory
restlessness (hopping and fluttering in residents. In captivity, one can selectively mate migrant types with mi- British Isles. The success of this evolutionary adventure has apparently
a cage at night) as a measure of a bird's grants and residenttypes with residents. In a sense, such an experiment depended in part on the increase in feeding of wild birds in Britain and
desire to migrate—because these birds Ireland in recent years. The Blackcaps use feeders in winter and this,
simulates, in an extreme way, what might happen if the environment
are typically inactive at night except
suddenly began to strongly favor either the migrant type or the resident coupled with the lower cost of migrating to Britain rather than to central
during the migration period. The captive
breeding experiment with Blackcaps il- type. Only three generations of such selective breeding of migrants Africa, may result in higher overwinter survival. The birds wintering in
lustrated here determined the number were necessary to produce a group of birds that were all migrants Britain may also return earlier to their breeding areas on the continent
of 30-minute periods each night dur-
(again, as measured by the amount of Zugunruhe) (Berthold 1996). In and thus enjoy a reproductive advantage.
ing which birds displayed migratory The key to the evolution of this new migratory pattern lies in the
restlessness (vertical axis). Each point
six generations of selection for residents (nonmigrants), all evidence
existence, before winter bird feeding increased in the British Isles,
plotted is the mean for a 10-day period,
and the vertical line at each point shows of individuals with the genetic trait for migrating in a northwestward
one standard error of the mean (a mea- direction. A minority of birds captured in Germany orient in that di-
sure of the variability in the data). The Southern Germany Population
rection, as do most birds from the British winter population brought
horizontal axis indicates the number
of days after migratory restlessness
began. Because individual birds may
have begun their periods of migratory
✓\L
1./ Li 1
S. Germany X Canary
Obligate Migrants
back to Germany and tested in the fall (Berthold 1996). In earlier times,
this genetic variant would presumably have been selected against in
the population, because conditions did notfavor overwinter survival in

-fr 1
restlessness on different days, the data Islands Hybrids Britain. With the increase in bird feeders, this migration direction be-

i,,,,i1 -'\I
is adjusted seasonally to align all the came a more favorable option, and the genes that code for it increased
periods. When obligate annual migrants
in the population.
from a population in southern Germany
(top line) were bred with partial migrants
from the Canary Islands (bottom line),
4

,
a
I 1
,

....,.L.J.
the resulting offspring (hybrids) showed is 1.... Controlling and Siinchronizing the Annual Gide
,,...ICanary Islands Population.
an intermediate amount of migratory .r........4„. The daily lives of most organisms are regulated by internal bio-
I V Partial Migrants
restlessness (middle line). This demon- ...,,
1 logical clocks, which produce daily cycles of behavioral and phys-
-...,
strates, at least for Blackcaps, a genetic .......,
I I
iological events called circadian rhythms. For example, some plants
basis for their migratory behavior. 0 50 100 150
h

Adapted from Berthold and Querner move their leaves (Fig. 5 59), open and close their flowers, or produce
-
Number of Days After Migratory Restlessness Began

Cornell Laboratorq of Omithologq Handbook of Bird Biologq

5.62 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.63
Figure 5-58. Genetic Control of Orien- condition, molt, and other circannual rhythms in the same sequence
N
tation Direction in Migrant Blackcaps:
as wild birds. In small songbirds, these cycles have persisted for more
In fall, Blackcaps from western central
Europe migrate southwestward, flying
than ten years—longer than the birds would be expected to live in
around the western end of the Medi- nature. In obligate migratory species, then, the primary stimulus that
terranean to reach Africa; those from triggers migratory behavior arises from the bird's internal physiology
eastern central Europe migrate south- rather than from immediate external environmental conditions.
eastward, flying around the eastern
Under constant conditions in captivity, the cycle lengths are not
end of the Mediterranean. When birds
from each of these groups were tested exactly 12 months long, so the birds' rhythms gradually drift out of
in circular orientation cages, their mi- phase with the actual seasons. Under natural conditions, however,
gratory restlessness was oriented in the circadian and circannual rhythms are synchronized, or "entrained,"
same direction as in the wild: birds from
by daily cues, such as cycles of daylight and darkness, and by seasonal
Germany (western Europe) oriented to
the southwest (solid triangles), and birds
cues, such as seasonal variation in the photoperiod (day length).
from Austria (eastern Europe) oriented A bird's specific response to the internal migratory stimulus may be
to the southeast (open triangles). When modified by environmental conditions, which may determine whether a
birds from these two populations were bird begins to migrate on a particular day or how far it will fly. A species
hybridized, their offspring showed ori- • Blackcaps From Western Europe that develops a powerful urge to migrate as the days grow shorter, for
entation in an intermediate direction: to
✓ Blackcaps From Eastern Europe
the south (solid dots). In this diagram the instance, may decide to sittight on a particular day if the wi nd is blowing
• Hybrids
circles each represent a circular orien- in the wrong direction, or to take off if the wind is right.
tation cage (see Fig. 5-57); the inner When birds come into migratory condition, a host of physio-
circle shows results for the parents, and nectar in daily cycles; some crabs are darker in the morning than in logical changes takes place. Their daily patterns of activity and rest
the outer circle, the offspring. Each dot or the afternoon; flying squirrels have daily activity patterns; birds have
triangle represents the average direction change. Night migrants become active during darkness, and the me-
daily cycles of activity and body temperature; and humans show daily tabolism of many species changes such thatthey begin to deposit large
chosen by an individual bird. Each arrow
indicates the average direction for all cycles in body temperature, blood pressure, and sensitivity to drugs, quantities of fat, which serves as fuel for flight. The biological clock,
birds from a particular group. Adapted among other things. All these cycles persisf even when the organisms fine-tuned by changes in photoperiod, controls all these circannual
from Berthold (1993, p. 145). Originally are kept under constant conditions. The physiological mechanism by
from Helbig (1989).
rhythms. They are further mediated through the nervous and endocrine
which biological clocks operate is not well understood. systems, although the hormonal control of migratory behavior is not
Birds and other creatures also have annual cycles, which are well understood.
controlled by a clock with a much longer periodicity. Migration is The life of a migratory bird is played out on an enormous stage,
one component of a suite of integrated events that constitutes the an- and the success of migration as an evolutionary strategy depends on a
nual cycle of a bird. Other important annual events include one or host of variables, including conditions on the breeding and wintering
more molts per year and breeding. These cycles are called circannual grounds and along the path between them. In many ways, both ener-
rhythms because they have a periodicity of about ("circa") one year. getically and in terms of risk, migration is the most demanding event
Examples of nonavian circannual rhythms include yearly cycles of on a bird's annual calendar. To cope with the rigors of migrating long
hibernation and weight loss in golden-mantled ground squirrels, and distances and thereby increase the odds of survival, birds possess an
the shedding and growth of antlers in some deer. elaborate suite of behavioral and physiological adaptations, which are
The existence of these circannual rhythms is revealed by hold- described next.
Figure 5-59. Circadian Rhythm of ing birds captive for very long periods under "constant conditions" in
Leaf Movement in Bean Seedlings: The which they have no hint of the changing seasons. For instance, the light
leaves of some plants, such as these
bean seedlings (Phaseolus coccineus),
may be constantly dim, or the days of constant length. Birds treated in The Pinisiologq of /Migration
move in a daily cycle. During the day this way continue to go through cycles of migratory activity, breeding Flying is strenuous, and even though birds are beautifully suited
the leaves move outward, perpendicu- to their aerial life with such adaptations as extraordinarily efficient
lar to the sun's rays; at night, they drop hemoglobin, a lung and air-sac system that enables maximum oxygen
to a more vertical position. Rhythms
uptake, and hollow bones, a calorie is still a calorie, and it takes a lot
such as these, which persist even when
the plant (or other organism) is placed of them to propel a body through the air for hundreds of miles. Fat
under constant conditions of light, tem- provides most of the needed fuel.
perature, humidity, and other variables, To produce fat, birds change their feeding behavior as the mi-
are called circadian rhythms. In these
gration season approaches. They dramatically increase the amount
constantconditions, however, the cycles
usual ly become slightly longer or shorter
they eat by as much as 25 to 30 percent (a phenomenon termed hy-
than 24 hours because they lack daily perphagia, literally "overeating"). The diet may change, too, especially
environmental cues. Day Night in autumn when insect populations decline and many plants produce

Cornell Laboratorg of Ornithologg Handbook of Bird Biologq

5.64 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.65
fruit. Fruits are relatively easy to digest and high in carbohydrates, a burden, of course, and it can reduce a bird's maximum range on a
which can be easily converted to fat. Many species of migrants, such single flight by as much as one-half.
as thrushes, warblers, and sparrows, and also some shorebirds, ducks, Using information on the energy yields of fat and the typical flight
and gulls, increase the amount of fruit in their diet immediately before speeds of birds, one can construct models to predict how far a bird
and during migration. Laboratory studies have shown that birds can should be able to fly with a given amount of fat. Several types of models
select food items with the highest fat content from an array of choices exist and they do not always agree, but they do yield some approximate
of equal caloric value. Bird metabolism also appears to change before figures. On a single flight without refueling, some shorebirds can go
migration. Production of fat increases, and energy reserves already up to 6,000 miles (9,600 km), many passerines can cover 620 miles
stored as carbohydrate may be converted to fat. The efficiency of food (1,000 km), and even the Ruby-throated Hummingbird can fly across
digestion and absorption also may increase. the Gulf of Mexico (500 miles [800 km]) in spring.This means that birds
Fat is the most energy-rich substance that animals can store in operate on the same order of performance as large aircraft!
their bodies. When oxidized (burned), it yields about twice as much As a migrant flies it depletes its fat stores, which must be replen-
energy per gram as carbohydrate or protein. Migratory fat is deposited ished at stopover locations. The quality of the habitat a migrant finds
all over a bird's body, even within the muscles and internal organs such determines how rapidly it can refuel and be on its way. Daily fat depo-
as the heart and liver. Most, however, is laid down in fat bodies just sition for migrating songbirds is typically 2 to 3 percent of their lean
under the skin; the most conspicuous fat bodies lie over the abdomen body mass, but it may be as high as 10 percent. Depleted fat reserves
and in the depression formed anterior to the breast muscles where the reduce a bird's propensity to initiate migration, and unless the bird
clavicles fuse to form the wishbone. If you part the feathers of a long- finds itself in a place where it can gain a little weight, it is likely to
Figure 5-60. Nonmigratory versus Pre- distance migrant with a full fat load, you can see that the bird is nearly remain grounded until it stores enough fat for the next leg of the jour-
migratory Fat Load: During the weeks encased in a layer of yellowish fat (Fig. 5 60). Bird banders and other
- ney. Ironically, some of the best places for bird watchers to see large
before migrating, birds eat more than
researchers routinely examine birds in this way, rating the amount of numbers of grounded migrating birds may be among the worst from a
usual, and also may eat more fat and
carbohydrates (often as fruits), which fat deposited as an index of the birds' energetic condition and potential bird's point of view. Offshore islands such as the Dry Tortugas in Flor-
are easily converted to fat. Migratory fat to continue migration. ida attract large numbers of exhausted birds, but such sites often lack
is deposited all over the bodies of birds, The amount of fat deposited varies greatly among migratory spe- sufficient food and fresh water. The longer birds remain in such places,
but most is laid down in fat bodies just
cies. Typically, long-distance migrants or those that must cross large the less likely they will be to reach suitable refueling places. Likewise,
under the skin. To determine the physical
condition of migratory birds, researchers
ecological barriers where food is scarce lay down more fat prior to migrants lured to tiny islands of natural vegetation amid large urban
often inspect and "score" the amount of migrating. A typical nonmigratory bird carries 3 to 5 percent of its lean areas might do better by continuing to fly.
fat deposits in the conspicuous interclav- (fat-free) body mass as fat. For passerine migrants, the figure is 60 to A bird in flight generates heat and therefore loses water by evapo-
icular and abdominal regions. When 100 percent. In terms of total body mass (including fat), long-distance ration, so birds can become both overheated and dehydrated on long
present, the clumps of pale yellow fat
migrants often carry 30 to 50 percent as fat when they begin a flight, flights. Nevertheless, field and laboratory studies suggest that fuel, not
in these regions are easily observed
compared to the surrounding pink, vas- short-distance migrants, 10 to 25 percent. Carrying this much fat is the need to avoid dehydration or overheating, is the main factor that
cularized skin. limits migratory flights. The need to avoid heat and water stress may,
however, have been a selective factor that favored night migration in
many species.

No
Dailq Timing of Migration
Subcutaneous
Subcutaneous
Fat Filling
Some birds migrate during daylight. Soaring birds such as hawks,
Fat Visible cranes, and storks—which rely on thermals for lift—must migrate dur-
Interclavicular Region
ing the day, when thermals appear. Swifts and swallows, which feed as
they fly, also migrate by day. Most waterfowl and shorebirds migrate
during either the day or night, depending on weather conditions. Other
Subcutaneous
Fat Filling Lower diurnal migrants include some woodpeckers, kingbirds, crows and
Abdominal Region jays, larks, pipits, bluebirds, American Robins, blackbirds, and car-
dueline finches.
The majority of species and individual passerine birds however,
migrate almost exclusively at night. (When forced to cross large eco-
logical barriers such as the Gulf of Mexico that cannot be passed in
one night, these species of course continue flying in the daytime.) In
addition, many species make low-altitude movements du ri ng the early
NONMIGRATORY CONDITION PREA4IGRATORY CONDITION morning hours. Why so many normally diurnal birds migrate at night
Cornell Laboratory of Ornithologq Handbook of Bird Biology
5.66 Kenneth P. Able Chapter 5-Birds on the Move: Fli8ht and Migration 5.67
has been the subject of speculation for years. As with so many "why" KEY
18,000 -
questions in biology, the hypotheses on this topic are often untestable:
you can make up any story you like and no one can prove you wrong.
The best guesses are (1) that migrating at night allows birds more time
I Typical Migration Altitude

Potential Migration Altitude

during the day for feeding and replenishing fat stores; (2) that the struc-
15,000 - 44-Shorebirds, • Mixed Passerine
ture of the atmosphere at night is more stable (there is less turbulence Puerto Rico ♦ Flocks Over
from convection) and more conducive to flight by slow-flying birds; Puerto Rico

and (3) thatthe generally cooler air at night reduces stress from heat and
Mixed Passerine
dehydration. Of course several different forces could favor nocturnal ♦ Flocks Over Antigua,
migration; natural selection takes whatever advantage it can. 12,000 - Caribbean Sea

Studies using moon-watching (observing the silhouettes of mi-

grants as they pass in front of the moon), radar, and radio-tracking have
shown that most nocturnal migration begins 30 to 45 minutes after
sunset. The number of birds aloft then increases dramatically, reach-
ing a peak before midnight and then decreasing steadily until dawn.
Most night migrants have landed long before daylight. Radar and visual Tundra Swans,
studies show that diurnal migrants begin their flights shortly after dawn; USA
migration peaks around 1 0:00 A.M. and declines thereafter. Of course,
Individual
unusual weather may alter these typical patterns. 6,000 - 4-Swainson's Thrush
Maximum Between
4 Illinois and
The Altitude of Migration Maximum for
Common Cranes, Scoters and
• Manitoba

Not until the advent of surveillance radar during World War II -.1Southern Sweden Ali-Long-tailed
3,000 - IF Ducks Over Land,
could we accurately measure how high migrating birds fly. Although •
Finland •
there are many old claims that birds migrate at fantastic altitudes, most Average for
nocturnal songbird migrants fly at low altitudes over land. At night, 4- Broad-winged Scoters and •
Radio Tower
in the absence of heat from the sun, there is probably no reason to fly
Hawks, Southern
Texas, USA
Long-tailed Ducks
Over Water,
• •
I4-Kills of Nocturnal
Migrant Passerines •
higher in the stronger winds and colder, thinner air, which contains • •t -Finland

less oxygen for respiration. The majority of songbirds usually migrate 0

Soaring Waterfowl Shorebirds Passerines Passerines
below 2,000 feet (610 m), and some 90 percent typically fly below Birds Over Land Over Water
6,500 feet (1,983 m).
Figure 5-61. Migration Altitude of Various Bird Groups: The Nocturnal migrant passerines over land usually fly 2,100
Depending on weather conditions, particularly at the altitudes height at which birds migrate is influenced by the physical to 2,400 feet (700 to 800 m) above ground, but often fly much
at which favorable winds may be found, nocturnal passerine migrants characteristics of the birds themselves, as well as by many en- lower, as demonstrated by the numerous migrants killed by
may fly up to 15,000 feet (4,575 m) or even higher, but this is unusual. vironmental variables, including whether the flight is over land flying into large radio, television, and cellular phone towers.
or water, the topography, and most importantly, the weather Some passerines, however, do fly higher than this over land.
Birds also tend to fly higher when making long crossings over water.
conditions-especially wind speed and wind direction. Con- Forexample, an individual Swainson'sThrush fitted with a radio
Larger, stronger-flying shorebirds sometimes fly much higher. Even sequently variation within groups is high and generalities are transmitter was tracked for seven nights from east-central Illi-
over land it is not unusual to find them at 15,000 to 20,000 feet (4,575 difficult to arrive at. This figure presents, for five bird groupings, nois into Manitoba, Canada, during which its average altitude
to 6,100 m). Daytime land bird migration over land usually occurs at typical altitude ranges (solid lines) and potential ranges (dot- was 1,065 feet (355 m), with a maximum of 6,000 feet (2,000
quite low altitudes, but soaring raptors, waterfowl, and gulls may fly ted lines)-altitudes at which migrants have been occasionally m) (Cochran 1987).
observed, but migration may be more common than observa- Passerines migrating over the water may fly much higher.
at considerable heights (Fig. 5-61).
tions suggest-as well as examples of individual observations Using an extensive radar network, Williams et al. (1977) ob-
Headwinds or cloud cover usually lower flight altitudes. When for each group. The ranges were determined by an exhaustive tained altitude information for a mixed flock of migrating pas-
cloud layers are not too thick, birds may ascend through them and search of the literature, but new information from modern sat- serines (and possibly small shorebirds) during their 1,875-mile
reach the clear skies above. This occurs most often when favorable ellite-tracking techniques may change our understanding of (3, 000-km), nonstop fall flight from North America to the coast
migration altitude in the future. of South America. From the North American coast to Bermuda
winds exist above the clouds, although how the birds know about
Soaring migrants such as hawks, vultures, storks, and cranes, the bulk of migrants flew below 6,000 feet (2,000 m) above
these winds is a mystery. rely on thermal activity and thus tend to migrate below 3,000 sea level. Approaching the island of Antigua, however, the
Most of the really high altitude records of bird flight come from feet (1,000 m), but are sometimes found as high as 4,500 feet birds climbed dramatically, to well above 12,000 feet (4,000
mountainous regions. In the Himalayas, Lammergeiers (large vultures) (1,500 m). Migrating waterfowl may fly as high as 10,500 feet m), gradually descending as they approached South America.
(3,500 m), but often fly as low as 300 to 1,200 feet (100 to 400 Concurrent weather observations from Antigua suggested that
and Yellow-billed Choughs (relatives of crows) have been observed
m) during daylight. Migrating shorebirds typically fly higher the birds increased their altitude to avoid strong winds in the
flying at 24,600 and 26,900 feet (7,503 and 8,205 m), respectively. region. Adapted from Kerlinger and Moore (1989, p. 122).
than most other birds, consistently higher than 3,000 feet (1,000
Bar-headed Geese regularly migrate over the highest Himalayas and m), and sometimes considerably higher.

Cornell Laboratory of Ornithology Handbook of Bird Biology

5.68 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.69
Figure 5-62. Flight Path of a Bird: The have been recorded at least as high as 27,880 feet (8,503 m), and a a. Low Pressure System
flight speed of a bird with respect to the Mallard struck a plane at 21,000 feet (6,405 m) over Nevada. Andean
ground (ground speed) is the sum of
Condors have been documented at 19,800 feet (6,039 m). A large Af-
two other variables: the bird's air speed
(how fast it moves with respect to the rican vulture, the Rueppell's Griffon, collided with an aircraft at 37,000 b. Warm Front
air) and the wind speed (the speed of the feet (11,285 m) over the Ivory Coast!
air pushing on the bird). The direction
a bird is actually pointing its beak as it
flies is called its heading, but any wind Flight Speed and the Progress of Migration
not coming from directly behind or in
The progress of migration is determined by a bird's ground speed,
front of the bird will blow it sideways to
or how fast it moves over the earth's surface. This speed is a function of Direction
Cold
some degree. The direction the bird ac- Warm Air
of Travel Air
tually travels with respect to the groundtwo variables: the forward propulsion of the bird with respect to the air of Low
is called its track. (its air speed), and the action of the wind upon its flight path. The di- Pressure
These speeds and directions are System c. Cold Front
rection in which a bird is pointing its beak and propelling itself through
illustrated here with vectors for a bird
heading due south in a wind blowing
the air is called its heading. Unless the bird is flying in a direct head-
from the west. A vector is a variable wind, direct tailwind, or still air, its actual direction of movement over
with both magnitude (size) and direc- the ground differs from its heading, because the wind blowing from an
tion, and is typically shown as an arrow angle affects its direction. This actual direction of movement over the
whose length represents magnitude and Warm
ground is called its track. For example, a bird heading due south in a Air
whose orientation represents compass Cold Air
direction. Both ground speed and wind wind blowing from the west has a track to the southeast, because the
speed are actually vectors, since they bird is pushed to the east by the wind. Its ground speed will be greater
have magnitude (how fast the bird is go- than its air speed because a component of the west wind pushes it to
ro(11( Cold Front Precipitation
Figure 5-63. Weather Systems: Weather
ing) and direction (which way the bird
the southeast, adding to its speed like a tailwind (Fig. 5-62).
0 conditions have profound effects on the
movements of birds during migration.
is going). To add two vectors, place the Air Circulation
beginning of one at the end of the other,
During migration, most passerines fly at relatively slow air speeds —411\11 Warm Front a. Low Pressure System: The passage
of 20 to 30 mph (32 to 48 km/h). Waterfowl and shorebirds fly consid- of low pressure systems across North
maintaining the orientation of each.
Thus, to add wind speed to air speed, erably faster, at 30 to 50 mph (48 to 80 km/h). By selecting weather
L Low Pressure Area America is particularly important to
migrating birds in this region. These
one could move the wind speed vector conditions that provide tailwinds, birds can achieve ground speeds up large systems, which consist of cold
to the end of the air speed vector (dotted
to two or more times faster than their air speeds. As explained in the refueling conditions at the stopover sites. Waterfowl and shorebirds and warm air masses circulating around
arrow). The end of the wind speed arrow
next section, a tailwind is often critical to the success of a migratory tend to make longer nonstop flights, even when flying over land; ducks a low pressure area (L), are found only
in its new position gives the end point for
in the middle latitudes, and usually
the vector sum. For this example, then, flight. and geese have been observed flying up to 1,865 miles (3,000 km) from travel from west to east. In the Northern
the track of a bird heading south in a west Migrating birds seem very attuned to their air and ground speeds. Canada to their Gulf Coast wintering areas in two days. Hemisphere, winds circulate counter-
wind is to the southeast, and the length of
Radar studies have shown that when flying with a tailwind, birds slight- clockwise around the low pressure area
the ground speed arrow represents how
fast the bird is moving over the ground. ly reduce their flight effort (and therefore their air speed); when flying (in the Southern Hemisphere, they circu-
into a headwind they increase their air speed and work harder. Weather and Migration late clockwise). b. Warm Front: Where
Just as long-term changes in climate may mold the evolution of the warm air mass overtakes cold air, it
The progress of migration on the ground de-
pushes up over the denser cold air, is
bird migration, seasonal and day-to-day changes in weather dramati-
N pends not only on flight speed, but on the duration cooled, and thus forms clouds and often
and frequency of the migratory flights. Evidence cally influence the timing and rate of progress of migration.The number precipitation: this interface between the
suggests that spring migration proceeds more rap- of migrants may vary by up to a thousandfold from night to night. In two air masses is called a warm front.
Wind favorable weather, a staggering number of birds may be in flight, prob- c. Cold Front: Where cold air overtakes
Direction
idly than fall migration, at least for songbirds. This
Wind Speed warm air (at a cold front), the dense,
seems to result from shorter stopovers and perhaps ably hundreds of millions over North America alone. I vividly recall
F cold air tends to wedge under the warm
longer flights; the speed at which individuals fly a September night in northern Georgia when weather radar showed air mass, forcing the warm air up and
does not seem to change from spring to fall. Pre- 200,000 birds crossing a line one mile (1.6 km) long every hour. This cooling it quite abruptly, forming pre-
sumably, the shorter spring migration is a response passage went on for much of the night! cipitation that is often accompanied
Air Ground by strong winds and lightning, and is
to selection pressure—birds that arrive early to es- Many analyses of the relationships between weather and mi-
Speed Speed heavier and of shorter duration than the
tabl ish a breeding territory may have a reproductive gration volume have been conducted, and they consistently show that
precipitation associated with a warm
advantage. temperature and wind direction are the two most important factors. front. Adapted from Lutgens and Tarbuck
Assuming they do not have to cross a large eco- In spring, northbound birds migrate in the warming temperatures and (1998, p.211).

logical barrier, passerines tend to migrate in a series southerly winds that characterize the western sides of high pressure
of relatively short flights of up to 200 miles (320 km) systems. In autumn, migrants favor the falling temperatures and north
Heading (S) Track (SE)
or so, interspersed with one to three days of rest, winds that occur after the passage of a cold front. Figures 5-63 through
S
depending upon weather, the birds' fat loads, and 5-65 illustrate these patterns. Birds avoid migrating in rain, clouds, fog,

Cornell Laboratorti of Ornithologq Handbook of Bird Biologii

5.70 Kenneth P. Able Chapter 5 — Birds on the Move: Fli5ht and Migration 5.71

Figure 5-64. How Birds Use Weather

Systems During Migration: (Circled WARM FRONT
numbers refer to sections of Fig. 5-65;
see that figure for weather conditions 0 Ahead of Warm Front:
High clouds develop slowly,
Front Passes:
Overcast skies.
Behind Warm Front:
at each number.) Low pressure systems Clear skies.
can occur at any time of year. In different becoming lower and thicker Heavier but steady Warm temperatures.
seasons, migrating birds rely on different over 12 to 24 hours. Winds precipitation. Temperature South winds.
sectors of a low pressure system to aid
from the east. Light precipitation rises. Winds change from
them in their travels.
In spring, northbound migrants begins as front nears. east to south.
move in great numbers with the south-
erly winds that accompany a warm Spring Migration: None None In full force
front. Precipitation ahead of the front
often prevents migration, but once the Fall Migration: May be in progress Stops None
front has passed, waves of migrants may
stream by. These warm fronts usually oc- COLD FRONT
cur before the passage of a low pressure
region and after a high pressure system
(winds circulate clockwise around a
0 Ahead of Cold Front:
Rapidly approaching
0 Front Passes:
Heavily overcast skies.
Behind Cold Front:
Skies clear rapidly.
high in the Northern Hemisphere, so low, dense clouds. Severe to heavy Temperature drops.
winds are from the south after their pas-
Gusty winds, from the precipitation of short Winds from the
sage). Spring migration stops when a
cold front, with its north and northwest south to southwest. duration (including northwest.
winds, passes by. possible thunderstorms
In fall, southbound migrants take and hailstorms).
flight after the passage of a cold front,
Cold Front L Low Pressure Area Winds from the west.
when skies clear and northerly winds
provide a favorable tailwind. These cold
Spring Migration: Slowed Stops None
fronts usually occur after a low pressure Warm Front Air Circulation
system and before a high. Migration
Fall Migration: None None In full force
may continue until the winds change to
Movement of Birds
come from the south, as when a warm
front arrives. Figure 5-65. The Effects of Warm and Cold Fronts on Migration: Numbers 1 to 6 refer to the circled numbers on Fig. 5-64. In this
chart, detailed information on precipitation, wind direction, cloud cover, and the progress of spring and fall migration is given
and strong winds, and may even stop their journey if they encounter for the six regions indicated within the low pressure system pictured in Fig. 5-64. Note that there are several locations labeled
deteriorating weather while over land. For example, in the spring, number 1—ahead of a warm front—on Fig. 5-64 because the figure only shows one low pressure system. In reality, series of
low pressure systems move across North America, one following another, and the region "ahead of a warm front" may be right
land birds crossing the Gulf of Mexico from the south usually come to
behind a cold front, or quite far behind a cold front, depending on how closely the second low pressure system follows the first.
earth far inland. If a cold front meets them on the coast, however, they Fall migration, at peak after a cold front, may remain in progress ahead of a warm front until either the winds become unfavor-
descend immediately. At times small birds "flood" the coastal areas of able, or precipitation becomes too heavy.
the Gulf states and at other times there seem to be no birds at all.
Like the weather conditions through which the migrant must sends them on their way is not the weather, but internal changes in
fly, conditions at the destination also are important. In many species, physiology, as discussed earlier.
males tend to migrate earlier in the season than females, and thus arrive Birds whose migration routes take them across large bodies of
on the breeding grounds ahead of their potential mates. As mentioned water or deserts face the ultimate migration challenge. In these cases,
earlier, a male who arrives early gains a considerable premium in terms selecting the right weather conditions for migrating—for example, tail-
of establishing a territory, obtaining a mate, and getting an early start winds—can mean the difference between life and death. In autumn the
on breeding. But birds that arrive early in spring are more likely to B lackpol I Warbler flies nonstop over the western Atlantic Ocean from
encounter bad weather, and for a bird who has just completed a long, the northeastern United States to South America, an amazing feat that
tiring trip, cold, snow, or even heavy rain can be dangerous. may take three to four days and nights (see Fig. 5-51). The birds depart
In the fall, when most birds head toward more favorable climates, North America under the clear skies and north winds that follow the
the risk of arriving early is not so great. Although many water birds passage of a cold front. But favorable conditions at the outset do not
linger in the north until freezing temperatures force their departure, in guarantee an uneventful passage; trouble, such as late-season tropical
most species, natural selection has favored individuals that anticipate storms, may arise when the birds are so far along that turning back is
seasonal change and migrate well before conditions turn bad. Thus, impossible. When this happens, some individuals land on Bermuda
most insectivorous songbirds depart breeding areas in late summer or other islands; others may be displaced off-route to Florida. Untold
when the weather is fine and food is still plentiful. The stimulus that numbers undoubtedly perish.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

5.72 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.73
Clearly, a migrant's life depends upon its ability to correctly as- Along the New England coast in autumn, large numbers of night
sess the weather. To what extent can it do so? Researchers are not sure. migrants may be blown offshore in the northwest winds that follow
Pigeons are extremely sensitive to small changes in barometric pres- strong cold fronts. Many of these birds undoubtedly fall into the sea,
sure; it is possible, though not yet demonstrated, that by monitoring but others land on ships and offshore islands; during the day they
pressure changes, birds can anticipate weather changes long before can be seen flying back toward the mainland. Large numbers of mi-
more immediate signs appear. grants blown off course sometimes may establish populations in new
Even if migrating birds can foretell the weather, they still may be locations; the colonization of Greenland in 1937 by the Fieldfare, a
at risk from bad weather. Many birds are blown off course by wind. In Eurasian thrush, is an often-cited example.
extreme cases, hurricanes and other intense cyclonic storms transport
birds over hundreds or thousands of miles. Numerous instances of sea-
birds such as albatrosses, shearwaters, petrels, frigatebirds, and trop- Migration Routes
icbirds appearing far inland result from violent storms (Fig. 5 66). - Each migratory species has a characteristic general route of travel
between its nesting and winter range, but for most species these mi-
30' 70° gration routes are quite broad. Waterfowl tend to follow narrower
Figure 5-67. Elliptical Migration Route
I
(c-
corridors, which are often determined by the availability of suitable
Prevailing winds from the Northeast of the American Golden-Plover: The
stopover habitat. In fact, biologists once thought that individual wa- American Golden-Plover migrates from
I terfowl populations followed distinct, narrow flyways (the Atlantic
Provinc town its breeding grounds in the high Arc-
flyway, the Mississippi flyway, and others). However, leg band recov- tic tundra to winter on the grasslands
eries showing that individuals from one nesting area could be found of South America, a distance of nearly
8,000 miles (12,800 km) one-way. Most
migrating in several different flyways put that idea to rest. members of this species follow an ellip-
In North America, however, there are some general patterns of tical migration route, heading south over
migration flow. Songbird migration in the eastern half of the continent the Atlantic Ocean in fall and returning
tends to move northeastward in spring, and southwestward in fall. by a different, more westerly, route over
land in spring. These routes take advan-
In a large number of species, the round-trip migration path forms an
tage of the seasonal wind patterns and
ellipse. A classic, extreme example of this elliptical pattern can be are used by a number of other shorebird
seen in the American Golden-Plover, which in spring migrates from species. Drawing by Robert Gillmor.
its wintering grounds in the pampas of South America to the high
Arctic by passing through the interior of North America (Fig.
5 67). In fall, it first flies southeastward to the Canadian
-
45,943 t,z)
v0til‘ri

Maritimes and then over the western Atlantic to South

Sandy Neck Reach America. This route takes advantage of prevailing
seasonal wind patterns and is used by a number of
other shorebird species, such as the Hudsonian God-
wit, Buff-breasted Sandpiper, and the nearly extinct
Eskimo Curlew.
Radar surveillance indicates that nocturnal
migrants move in a dispersed fashion with slight
regard to what lies below. But birds migrating by
day tend to follow topographical features trending
north and south, such as mountain ranges, chains of
lakes, river valleys, and peninsulas extending into
Figure 5-66. Northeaster off New England in Winter: Each fall and winter, seabirds such as alcids, sea ducks, and phalaropes
large bodies of water. As these features narrow, the
(pelagic members of the shorebird family) wander the open ocean. These relatively weak fliers are often at the mercy of wind and
weather. During New England winters, storms called northeasters (or Nor'easters) sweep in from the northeastAtlantic, causing flight lanes narrow correspondingly, causing mi-
spectacular seabird sightings along the coast from Maine to Long Island. Severe northeasters can devastate pelagic bird popu- gratory movements to be concentrated and con-
lations, often pushing birds ashore or even inland in what are known as seabird wrecks, in which many birds die. Seabird wrecks spicuous.
American Golden-Plover
usually occur at capes and along the shores of enclosed bays such as Cape Cod Bay. Northeasters often create excellent birding Hawks migrating in the fall pass in large
conditions along the shores of Cape Cod as seabirds swept from the ocean by strong winds are forced into the mouth of the bay.
numbers along the Great Lakes, where they skirt
Once trapped there, they parallel the coast in a counterclockwise pattern. Bird watchers along the shore have ringside seats as
normally inaccessible pelagic birds pass in review. Northern Gannets may dive for fish mere yards beyond the surf and thousands around or parallel these wide bodies of water
Breeding Range
ofshearwaters, alcids, sea ducks, and phalaropes may fly within binocular range. Reprinted from Manual of Ornithology, by Noble rather than cross them (Fig. 5 68). On days after
-

S. Proctor and Patrick J. Lynch, with permission of the publisher. Copyright 01993, Yale University Press. ME Winter Range
a cold front when westerly winds blow strongly,

Cornell Laboratorq ofOrnithologq Handbook of Bird Biologq

5.74 Kenneth R Able Chapter 5—Birds on the Move: Flight and Migration 5.75

the passage of these daytime predators is impressive in such spots as

Fall Hawk Migration Port Credit and Am herstbu rg (Ontario), Cedar Grove (Wisconsin), and

J QUEBEC
Duluth (Minnesota).
In the spring, large numbers of hawks, northbound through Lower
Michigan, come together at the northern tip of Lower Michigan on the
south side of the Straits of Mackinac. Here, reluctant to fly over the
MINNESOTA ONTARIO water if the weather is rainy and windless, they settle on trees and other
Brockway
Whitefish
Pal
1",11.?Sluit Ste. Mar)
1\1
I perches until the next clear day with a favorable wind, when they spiral
Duluth
UPPER MICHIGAN
up and head north over the Straits.
Straits of Mackinac

Site Fidelity
Coboura
/ V 001°'‘ Individual birds often show amazing loyalty to places they occu-
...:Der•yHill
Port Credit • 1.0
WISCONSIN pied during previous breeding and nonbreeding seasons, and to stop-
Grimsby • Braddock Bay
LOWER
MICHIGAN Port Stanley NEW YORK over points between the two, a phenomenon known as site fidelity.
Cedar Grove
For example, banding studies have shown thatindividual Eastern
Holiday
t.‘C Phoebes are very likely to return to the same breeding site from one
Ne
Beach ,
Lake Erie Metropark
year to the next, even pairing with the same mate. Individual Barn
PENNSYLVANIA
\ ILLINOIS —7— 1-
Swallows, too, remain faithful to previously used colonies, often re-
INDIANA OHIO
turning to the same nests and mates year after year. And the Bobolink,
despite having one of the longest migration routes of any songbird,
Spring Hawk Migration
shows high breeding site fidelity, as individuals regularly return to the
hayfields in which they nested the previous year.
Birds also may demonstrate fidelity to wintering areas; the same
QUEBEC
individual Ovenbirds have been recaptured in successive years from
MINNESOTA ONTARIO the same locality in southern Mexico (Ely et al. 1977), and individual
owe
Whitefish
• Beookway Poi Northern Waterthrushes return to the same areas in Venezuela, Pan-
ain
Sauft Ste Mar fek..
Duluth
196l
tl
ama, Trinidad, Belize, and Jamaica. Individual WoodThrushes inhabit
.... of Mackinac the same nonbreeding territories each year on their wintering areas
Escanaba
in Veracruz, Mexico, and also return fairly consistently to the same
Coboura
Sw on` G'` °
breeding territories in the United States.
C Port Credit
vos erbyHill
WISCONSIN
a
BraddockBay /
Fidelity to stopover sites during migration is particularly common
Grimsby
c,
Port Stapley
among large birds—waterfowl, cranes, and storks—that often migrate
Cedar Grove
NEW YORK
1 LOWER in flocks composed of family groups of older, experienced birds and
MICHIGAN
to youngsters. Sandhill Crane family groups, for example, gather into
Honda
Beach \-6 enormous flocks attraditional stopover sites, with endangered Whoop-
Lake Erie Metropark
ILLINOIS
INDIANA
ing Cranes sometimes joining them. In spring, 80 to 90 percent of the
PENNSYLVANIA mid-continent population of Sandhill Cranes stop in the North Platte
OHIO
and Platte River Valleys of Nebraska. Individual Sandhill Cranes also
Figure 5-68. Spring and Fall Hawk Migration Routes Around Point Mourne State Game Area.
return year after year to the same breeding territories and wintering
the Great Lakes: Migrating hawks are generally reluctant to fly In the spring, northbound hawks moving through Lower grounds. Shorebirds, too, exhibit strong loyalty to traditional staging
over large bodies of water, such as the Great Lakes, and thus Michigan are channeled by Lake Michigan and Lake Huron and areas along their migration routes (Sidebar 2: Showdown at Delaware
tend to follow the shorelines until they find a way around. In come together to cross the water at the Straits of Macki nac. Birds Bay).
fall, southbound birds that reach Lake Superior move either migrating north through Wisconsin and Upper Michigan move
Most songbirds, especially nocturnal migrants, seem to migrate
east or west along the lakeshore, large numbers flying by Hawk along the south shore of Lake Superior, passing in great numbers
Ridge in Duluth, Minnesota (55,000 per season, on average), by such locations as Brockway Mountain on Upper Michigan's alone or in loosely defined aggregations. Whether they show high
or being channeled into Upper Michigan at Sault Sainte Marie. Keweenaw Peninsula, Whitefish Point (14,000 per year), and fidelity to particular migration routes or stopover sites is hard to de-
Farther east, southbound birds are concentrated between Lakes Sault Sainte Marie. Northbound birds that reach Lake Erie or tect, because songbirds are much less likely to be recaptured than
Huron, Ontario, and Erie, passing in abundance by such sites Lake Ontario tend to move northeast along the shorelines, an
waterfowl, cranes, and other large birds.
as Grimsby (14,000 per year) and Holiday Beach (81,000 per average of 30,000 birds per season passing by well-known
year), Ontario, as well as two Michigan sites averaging100,000 spring hawkwatch sites such as Braddock Bay and Derby Hill,
hawks per year that are monitored by the Southeastern Mich- New York. Drawings by Robert Gillmor.
igan Raptor Research—Lake Erie Metropark and the adjacent (Continued on p. 5.79)

Cornell Laboratorq of Ornitliolosq Handbook of Bird Biologq

5.76 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.77

Sidebar 2: SHOWDOWN AT DELAWARE BAY

Paul Kerlinger
For Joan Walsh, a biologist at the
New Jersey Audubon Society's
Cape May Bird Observatory, spring
of 1997 was ominously quiet. By
mid-May, the shores of Delaware
Bay that Walsh frequently visits are
usually packed, not with beachgoers
but with throngs of mating horseshoe
crabs, tens of thousands of migrating
shorebirds, and the biologists, bird-
ers, and simply curious who come to
see them.
For millennia, horseshoe crabs
(these ancient animals are more
closely related to spiders than to true
crabs) have hauled their tanklike
bodies onto the shores of Delaware Figure A. Horseshoe Crabs Mating: A pair of horseshoe crabs, the smaller male at-
Bay by the millions to mate (Fig. A). tached to the female, comes ashore to lay eggs at Reeds Beach on Delaware Bay. The
Some beaches are carpeted black as female digs a nest in the sand six to eight inches (15 to 20 cm) deep and deposits her
Figure C. Shorebirds Refueling at Reeds Beach: In mid-May, hundreds of thousands of migrating shorebirds, most of them Red
eggs. As she crawls away, the male passes over the nest, fertilizing the eggs. If horse-
the paired crabs (the males attach Knots, Ruddy Turnstones, and Sanderlings, stop along the shores of Delaware Bay in New Jersey to feast on horseshoe crab eggs
shoe crab densities on the beach are high enough, laying females will accidentally
themselves to the larger females) before continuing their journey to breeding grounds in the Arctic tundra. Visible with the shorebirds are Laughing Gulls and Her-
dig up the nests of females who laid earlier, littering the beach with eggs that are thus
emerge from the surf. As the female ring Gulls, who also take advantage of the banquet. Photo by Kevin T Karlson.
made available to migrating shorebirds. With lower numbers of horseshoe crabs, the
deposits her eggs in the sand, the eggs remain safely buried in the sand. Photo by Sandy Podulka.
male fertilizes them. Then he may critical to the birds' successful mi- females; the demand is therefore coming from as far away as Massa-
help the female cover the eggs be- gration. high for those same animals that chusetts and South Carolina—were
*•
fore the couple heads back to sea. • -*.t* This crossroads of mating horse- provide spring fare for shorebirds. lining up on the bay shore in May and
The female can lay up to 80,000 shoe crabs (locally called king crabs) Traditionally, the fishermen picked early June (Fig. D). Some scientists,
eggs a season (Fig. B), so the crabs and migrating shorebirds now draws the crabs off the beaches by hand and even casual observers, reported
might repeat this mating act several visitors from around the world. It and at no cost; this harvest was rela- seeing fewer horseshoe crabs, es-
more times before they move into the • • 31 „. ' Er . 0.! was brought to public attention in tively small. But with the burgeoning pecially on the New Jersey side of
• • ',"
deeper waters of the bay and ocean the 1970s by, among others, Cape market for eel and whelk both here the bay. In the late 1980s, biologist
for another year. The eggs hatch in
!...• ••
• /
*a. * • •

* plit
May Bird Observatory director Pete and abroad, a market for the crabs Mark Botton of Fordham University
about a month, and the young, too, IP •• 011*
AP' 4V. • • *re Dunne and shorebird biologist Brian began to develop along the entire estimated that the population of this
41•4114, .10
go to sea. •. % ' Harrington. Birding records from the East Coast, and anyone selling them species in the neighboring Atlantic
Not all horseshoe crab eggs hatch, 41010-
.0 •
• 111*."
1930s through the 1960s make no could get 50 cents per crab. This was between 2.3 and 4.1 million
but few go to waste. Just as the crabs mention of the annual spectacle, pre- price attracted commercial fish- crabs. But Botton and others believe
are laying their eggs, anywhere from sumably because it didn't happen. ermen, whose incomes had suffered that annual harvests since then of
500,000 to 1.5 million shorebirds— Between the 1880s and 1920s, about from stringent regulations and the more than half a million crabs, com-
the majority of them Red Knots, a million horseshoe crabs were har- overharvest of other fish, as well as bined with the slow maturation of
Sanderlings, Ruddy Turnstones, and vested each year for fertilizer and hog those who saw a fast and easy buck. this species (they start reproducing
Semipalmated Sandpipers—stop Figure B. Horseshoe Crab Eggs: Coating the beach like tiny, greenish pebbles, bil- fodder. Although the market waned, Some fishermen converted their at about 10 years old), have led to a
along the bay shores of New Jersey lions of horseshoe crab eggs provide a much-needed meal of fat and protein for the decline.
50 years passed before crab numbers boats to trawlers, which can drag a
and Delaware on their migration hundreds of thousands of migrating shorebirds who stop at Delaware Bay to refuel,
rebounded, shorebirds came back in net across the sea floor and ensnare Fishermen remained uncon-
en route from South America to their breeding grounds in the Arctic tundra. Photo
from South America to the Canadian huge numbers, and the phenomenon tens of thousands of crabs in a single vinced, even when four separate
by Kevin T Karlson.
Arctic (Fig. C). They gorge on the was "rediscovered." day. In the past 10 years, the harvest scientific studies by Botton, Limuli
abundant eggs, which provide the weight in fat within 10 days to two Today, horseshoe crabs are again has grown from a cottage industry to Laboratory (an independent, for-
over the holidays. Some 80 percent
fat and protein to fuel the next 1,500 weeks while feeding furiously at the a valuable commodity, but this time a regional business complete with profit company), the New Jersey
of the North American population of
to 2,000 miles (2,400 to 3,200 km) egg-rich beaches—something like as bait. According to fishermen, eels middlemen. Bureau of Marine Fisheries, and
Red Knots stops over each year on the
of their trek. Red Knots may gain and whelks (locally called conch) By the early 1990s, pickups and the Delaware Division of Wildlife
a 160-pound (73-kilogram) human shores of New Jersey and Delaware;
50 percent or more of their body putting on 80 pounds (36 kilograms) are particularly fond of egg-bearing even large refrigerated trucks—some all reached similar conclusions.
horseshoe crab eggs are therefore

Cornell Laboratory of Ornithologt1 Handbook of Bird Biologq

5.78 Kenneth P. Able Chapter 5— Birds on the Move: Flight and Migration 5.79
force. By May 1997, the issue got
the attention of New Jersey Gover- Orientation and Navigation
nor Christine Todd Whitman, who
issued executive orders temporar- ■ Birds and many other animals have the ability to return to precisely
ily banning all trawling and hand- the same sites they occupied previously, and birds may travel halfway
harvesting. When the New Jersey around the globe to do so. This amazing feat raises an obvious ques-
Marine Fisheries Council failed to tion—how do they do it?—and that question provides the impetus for
adopt new standards, the DEP drew scientists who study bird navigation. Although homing ability has been
up rules based on Whitman's orders. known and exploited in pigeons since the time of the early Greeks,
But in September 1997, the council rigorous studies of the mechanisms of orientation and navigation did
vetoed the DEP rules. In October,
not get under way until well into the 20thcentury.
the council reversed its decision in
To understand orientation and navigation, it is important to corn-
an out-of-court settlement with the
prehend how young, inexperienced birds reach the overwintering area
New Jersey Audubon Society and
the American Littoral Society, and of their species or population on their first migration.The problem is es-
the bans were reinstated. While pecially acute for the many species in which young do not migrate with
fishermen aren't happy with the new experienced birds from whom they might learn how to reach the winter
restrictions, they can take solace in quarters. The solution to this problem began to emerge in the 1950s,
the governor's decision to commit when Dutch ornithologist A. C. Perdeck conducted an extensive study
$80,000 to research the population with banded European Starlings (Perdeck 1958). He captured 11,000
size of the crabs and the migrating starlings during autumn migration on the Dutch coast, banded them,
Figure D. Truckload of Bait: The harvest of horseshoe crabs, used as bait in eel and
shorebirds. The study should help
whelk fishing, increased dramatically in the 1990s, as the market for eel and whelk and transported them by plane to be released in Switzerland. Perdeck
flourished. By the early 1990s, pickup trucks and large refrigerated trucks lined the answer the lingering question: How
advertised his study widely to alert ornithologists, hunters, and others
shores of Delaware Bay, waiting to haul loads of crabs. Photo by Kevin T Karlson. many crabs can be harvested without
to report recoveries of the birds. He had great success, as 354 were
tipping the delicate balance?
Horseshoe crabs, meanwhile, reported. His experiment is diagrammed in Fig. 5 69. -

Relying either on estimates of adult Conservation Foundation, DuPont, The most important finding was that birds captured as adults,
having already bounced back once
crab numbers or on population Mobil Oil, and Atlantic Electric) who had migrated to the winter grounds at least once before, tended
after decades of wholesale harvest,
estimates based on surveys of eggs called for emergency regulations
are likely to recover again. As a to move from their release site in a northwestward direction toward
deposited on bay-shore beaches, all on horseshoe crab fishing, citing not
species, these rugged creatures the correct overwintering area for this population. First time migrants
-
four studies concluded that since only ecological but also medical and
have survived 200 million years of (birds born that year), on the other hand, moved primarily toward the
about 1990, horseshoe crab popu- economic reasons for protecting the
changing climate and habitat. And southwest, in the compass direction their migration along the North
lations have declined by more than crabs. Pharmaceutical companies
according to Bolton, a synthetic
50 percent. Aerial surveys conducted use the crabs' blood to detect bacte- Sea coast would have taken had it not been interrupted by capture.
horseshoe-crab "scent" that is being
by Kathy Clark of the New Jersey rial contamination in pharmaceutical The conclusion from this classic study, now supported by much ad-
developed would reduce the need
Endangered and Nongame Species products and to screen for diseases ditional evidence, is that a young bird on its first migration has some
for the animals as bait.
Program (New Jersey Division of such as gonorrhea and spinal men- innate knowledge of the direction (and the approximate distance) that
The situation for migrating Red
Fish, Game, and Wildlife) show that ingitis. Once captured and bled, the it should fly. It does not, however, seem to know the specific goal of
Knots and other shorebirds is more
fewer Red Knots are using the New animals are returned to the water, its migration. After arriving within its winter range, the young bird ap-
delicate. Good stopover sites are few
Jersey beaches and that more are where their survival rate is about 90
and far between, and no substitute parently locates an appropriate site, to which it imprints (see Ch. 6,
now found on the Delaware side, percent. The "harvest" is thus small in
exists for Delaware Bay. Years could Learned Behavior) over the winter. After this experience, the bird can
where horseshoe crabs are more comparison with that of the bait busi-
pass before horseshoe crab popu- navigate toward this goal even if displaced while en route.
abundant. Whether the decline of ness. The May spectacle of horseshoe
lations are restored and they lay A bird's first migration is controlled by a circannual rhythm, as
horseshoe crabs is already having crabs and shorebirds also helps sup-
eggs in such abundance that peak
an effect on the hemisphere's pop- port a growing ecotourism industry discussed earlier in this chapter. The execution of this so-called mi-
numbers of shorebirds are again
ulation of Red Knots is not known, in southern New Jersey. A study by gratory program has been termed vector navigation and can in theory
lured to New Jersey. Biologist Walsh
but without abundant crab eggs to the Cape May Bird Observatory take a first-time migrant from its natal area to a point within the winter
thinks that real conservation will
feed on, the future of these birds is found that birders and other wildlife range of its population on an appropriate schedule, provided it is not
come only when we see horseshoe
in jeopardy. watchers annually bring millions of waylaid by some researcher or storm. The same phenomenon can be
crabs not as bait but as a national
In January 1995, an unusual and dollars to local businesses.
large coalition of environmental In response to the coalition, the
treasure. ■ demonstrated with birds exhibiting migratory hopping in orientation
cages. The European Garden Warbler, for instance, first migrates
groups and businesses (including New Jersey Department of Environ- Reprinted with permission of Natural
History (May, 1998). Copyright the
southwest from northern Europe toward Spain and Portugal and
the New Jersey Audubon Society, mental Protection (DEP) restricted
National Audubon Society, Ameri- hand-harvesting to two nights per American Museum of Natural History then turns south into Africa. Hand-raised warblers held for the entire
(1998). migration season in Frankfurt, Germany, showed the same change in
can Littoral Society, New Jersey week. But trawling continued full

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

5.80 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.81
Figure 5-69. Perdeck's Displaced covering approximately 250 miles (400 km) per day. To accomplish
Starling Experiment: In the 1950s, A. this, especially from Venice, they must possess some very sophisti-
C. Perdeck captured 11,000 European
Ancestral
Netherlands
cated navigational equipment. In other studies, Laysan Albatrosses
Starlings at The Hague in the Nether- 0
lands (star) during fall migration, banded from Midway Island have been displaced over vast distances in the
them, transported them 380 miles to the Wintering Pacific basin. At least 82 percent returned, from distances of up to
southeast (dashed arrows), and released 4,100 miles (6,600 km), and at speeds of up to 317 miles (510 km) per
them in Switzerland (triangle). During day. The more prosaic Wh ite-crowned Sparrow has performed feats of
the winter, 354 of the birds were recap- o
tured. The distribution of recovery sites
similar magnitude. Several hundred sparrows wintering near San Jose,
for adult birds (open circles)—birds that 0 Adultso California, were captured and flown to Baton Rouge, Louisiana (1,800
had migrated to the wintering area at 0
•• el miles [2,900 km]), and to Laurel, Maryland (2,400 miles [3,860 km]).
least once previously—shows that these • • Thirty-four of these birds were recaptured the following winter on the
• •• I/
birds somehow adjusted for their new lo- •
0 Switzerland same quarter-acre (one-tenth-hectare) plot in California, apparently
cation and flew back toward their ances- • •
tral wintering area, in some cases even • having visited their northern breeding areas in the interim. How might
•
reaching the usual wintering grounds. •
• Itivendes', 0 Ie birds accomplish such homing feats?
However, the distribution of recovery • In theory, a homing animal might employ one or more of the fol-
sites for juveniles (solid circles)—birds
lowing mechanisms: (1) the animal might maintain direct or indirect
on their first migration—shows that they
flew the same direction (southwest)
sensory contact with the home area; that is, it might be able to see, hear,
and distance that they should have if
they were still in the Netherlands. Thus,
first-time migrants appear to have some
innate knowledge of the direction and
distance they should migrate, but not
of the specific goal of that migration.
• Juveniles Recovered
Once birds reach appropriate wintering
o Adults Recovered
grounds, they apparently learn more
specific information about the area that
allows them to navigate toward that
goal in the future. Drawing by Robert
S
Gillmor.
August Through September

direction in their hopping at approximately the right time during the

migration season (Able 1995) (Fig. 5-70). N
S
The European Starling experiment of Perdeck described earlier April Through June
illustrates a fundamental difference in the navigational abilities of ex-
perienced and inexperienced birds. In the simplestterms, it shows that
for a bird to be able to return to (or home to) a specific place, it must
have some direct experience with that place. We do not know precisely
what birds learn about places that enables them subsequently to home
to those spots, but it seems to require at least spending some time mov- S
ing around in the local "target" area. What we do know is that most October Through December Normal Migration Patterns in
(and perhaps all) birds, once experienced with a place, can home to Free-living Garden Warblers
that location from great distances and from places well beyond those
that the birds are familiar with. Figure 5-70. Migratory Orientation in Free Versus Caged Garden Warblers: Garden Warblers breeding in Europe migrate to
Most experimental data come from homing pigeons, but extraor- south-central Africa for the winter. But in fall, their migratory route (solid arrows on map) is not straight to the south. Migrants from
northern Europe first head southwest toward Spain and Portugal and then turn southeast across Africa. In the spring, the migrants
dinary homing feats are known from other species, both migratory and
head more or less straight north (hatched arrow) to their breeding grounds. As demonstrated by experiments with hand-reared
nonmigratory (Papi and Wallraff 1992). The classic examples involve Garden Warblers (three circles), the birds apparently have an innate migratory program, controlled by a circannual rhythm, which
strong-flying seabirds (Fig. 5-71). For example, Manx Shearwaters takes them in the correct direction at the right time of year. When lab-reared birds were tested in circular orientation cages, they
once were flown by plane from nesting islands off the coast of Great oriented in the same direction as the wild migrants in each of the three periods of time tested. The length of each line in the circles
represents the relative amount of nocturnal migratory hopping in a given direction. The solid arrow at the periphery of each circle
Britain to Boston, Massachusetts and Venice, Italy and then released.
gives the average direction for all the data in that circle. Caged birds were held in a constant cycle of 12 hours light and 12 hours
Shearwaters do not fly over land, so they must have taken an overwater dark, with no view of the sky. They were, however, exposed to the Earth's normal magnetic field. Adapted from Gwinner (1986).
route to return to their nest burrows, which they did in 12 to 14 days, Map originally from Gwinner and Wiltschko (1978 and 1980).

Cornell Laboratori of Ornithology Handbook of Bird Biologq

5.82 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.83
tigator, transported pigeons to very distant release
sites under rigorously controlled conditions that
prevented them from perceiving any navigational
information—visual, acoustic, magnetic, olfactory,
St. George I., 0 or inertial—during the trip (Wallraff 1980). The
Pribilof Islands, 0
Alaska Prestwick, a birds were carefully transported in closed, airtight
etre Scotland
eac h Stors in g pays cylinders and provided with bottled air. Light in
2,70mil eiles I day)
(300 r"
the cylinders was turned on and off at random, and
Kent I., New
4/hidby I., kokhovv
Inal
. Brunswick ater loud white noise was played. The cylinders were
Washington Shea rN wales
DaY!_
Mann Mx
3 20-
iles in 2
rs (250 niniesiaar
enclosed in magnetic coils that provided a chang-
o
Boston, 13 H' u ing magnetic field, and were placed on a tilting
Massachusetts
, toss 0, Oasis
n .L3n .‘ _ 1(3a•P ,
turntable hooked to a computer that varied both
va`r00 140,00kes the rotation and tilt at random. Yet when these
3,2 nt31
Midway 1. 0
0
o. pigeons were released at very distant, unfamiliar
Hawaiian 0%, b
Archipelago places, they showed no deficit in their ability to fly
in the homeward direction (once they recovered
a
from some initial nausea). This experiment, more
than any other, demonstrated that homing pigeons
could navigate based only on information they
Figure 5-71. Flight Speeds of Four or smell its goal. A male silkworm moth, for instance, follows the odor gained at the release site.
Birds: Evidence from banding studies gradient of the mating pheromone (an odorous substance) emitted by
(Ruddy Turnstone) and experimentally
How pigeons and other birds use all the
the female and finds her at the end of the trail. During his flight, he is means available to them to solve a homing prob-
displaced seabirds (other three species)
shows that birds have a remarkable abil- in continuous sensory contact with the female via the odor plume. (2) lem remains an interesting question; in the end,
ity to navigate for long distances at rel- The animal might use some random or patterned search strategy until we must conclude that at least some birds possess
atively high speeds. A Ruddy Turnstone it encountered familiar ground. A bird that flew in an ever-increasing a very extensive map that is sufficient to enable them to home from Figure 5-72. Homing Pigeon Fitted with
banded and released in late August at spiral, for example, would eventually encounter territory it had seen completely unfamiliar sites at vast distances from known areas. Orni- Frosted Eye Covers: Experiments with
St. George Island in the Pribilofs of the
Bering Sea was shot four days later in
before. (3) It might perform some sort of inertial navigation, logging thologists call this ability to take the proper course toward a specific homing pigeons often use some type
in its brain all the turns and accelerations of the outward trip and in- of frosted eye covers or frosted contact
the Hawaiian Islands after migrating goal true navigation. lenses that let in light, but prevent birds
2,300 miles (3,700 km), an average of tegrating these to compute the route back home. (4) It might refer to To explain how birds perform such navigation, researchers during from seeing objects more than a few
575 miles (925 km) per day. A Manx a learned, familiar-area "map" (formed in its brain, based on its own
Shearwater transported by plane to
the first half of this century suggested a number of sweeping theories, yards away. Photo courtesy of Steve
experience) to localize its position, relying on familiar landmarks that including astronomical navigation systems based on the sun or on the Johnson.
Boston returned 3,200 miles (5,150 km)
to its nesting burrow on Skokholm, an could be detected by sight, sound, smell, or some other sense. (5) stars, and a map based on both the physical coordinates of the mag-
island off the coast of Wales, in 12 days Finally, it might possess a more extensive map that extends well be- netic field (providing latitude) and the Coriolis force (providing lon-
and about 13 hours, an average of 250 yond areas of fami I iarity, presumably based on extensive gradients that gitude). Each of these approaches, however, has been rejected on the
miles (400 km) per day. A Leach's Storm-
could act as analogs of latitude and longitude. basis of experimental tests employing homing pigeons. Nevertheless,
Petrel returning 2,700 miles (4,340 km)
from Prestwick, Scotland to its nest on
These mechanisms are not mutually exclusive; a bird facing a the magnetic field alone may form the basis for one type of navigational
Kent Island, New Brunswick, in the Bay navigational problem might call on any or all of them. Good evidence map, as discussed later.
of Fundy, averaged about 300 miles (480 indicates that homing pigeons use familiar landmarks when available, Gustav Kramer, a German pioneer in bird migration and orien-
km) per day for nine days; and a Laysan and that they also consult information perceived during the outward
Albatross flew 3,200 miles (5,150 km) tation studies, discovered in 1950 that birds could use the position
journey, such as direction of travel and odors encountered (Papi and of the sun as a compass, as is discussed in more detail in the next
from Whidby Island in Washington State
to its nest on Midway Island near Hawaii Wallraff 1992). Evidence from homing pigeons also shows, however, section. He considered how possessing such a compass might be
in just over 10 days, an average of 317 that neither of these types of information is necessary for homing. incorporated into a homing navigation system. But a compass alone
miles (510 km) per day. The flight of the Schmidt-Koenig and Sch I ichte (1972), in experiments both in Germany is not sufficient to enable homing from an unfamiliar locale. Imagine
Ruddy Turnstone, a shorebird requiring
and at Cornell University, fitted pigeons with frosted contact lenses or yourself dropped off in the middle of an unfamiliar forest and given
land to rest, was undoubtedly nonstop,
whereas the flights of the others, all pe-
eye covers that rendered them unable to see objects more than a few a compass. How would you find your way home? A compass will
lagic seabirds able to rest on the water yards away, but did let in light (Fig. 5 72). These birds appeared to
-
indicate directions, but that is useless information unless you know
and feed on the wing, probably included home just as well as control birds wearing clear lenses, but did not rec- where you are relative to your goal—whether your destination is
stops for resti ng and feeding. Drawing by ognize their home loft when they arrived there and so fluttered down
Robert Gillmor. north, south, east, or west. In short, you need a map. Once you know
to the ground and waited for the researchers to pick them up and carry your position on a map, you can tell which direction you must go
them inside. In another experiment, Hans Wallraff, a German inves- to get home, and for that a compass is useful. This idea is the basis

Cornell Laboratorq of Ornitholo5q Handbook of Bird Biologq

5.84 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.85
of Kramer's map and compass model of homing navigation, which Starling N Window
provides the theoretical basis for nearly all current research on hom- Orients
ing (Kramer 1953). Virtually all data from pigeon homing experiments
are consistent with the notion that true navigation is a two-step pro-
cess involving one mechanism to identify spatial position (a map) and
N NW

Orientation Cage
Opaque Outer Enclosure

another to identify directions (a compass). Let us turn first to what is a Sun's Rays
— — -- — —
known about bird compasses. ) Normal
Direction
(From E)
Compass Mechanisms
Some sort of compass sense is involved in both homing navi-
gation and migratory orientation. Such a sense told Perdeck's young
starlings which direction was southwest. To learn how bird compasses
work, ornithologists have relied primarily on two sources of infor- Mirror
Sun's Rays Deflected 90° Counterclockwise
mation: the initial flight directions of homing pigeons released at sites
(From E to N)
far from home; and the spontaneous, oriented hopping of migratory
birds in several types of circular orientation cages. Researchers now
know that birds possess several different compass capabilities, which
are described here in the order of their discovery.
•

Sun Compass b
Gustav Kramer discovered the sun compass in 1951 by performing
experiments on European Starlings in orientation cages (Kramer 1951).
He used mirrors to shift the apparent position of the sun as viewed by Starling
/
Orients
starlings in their cage, and found that the birds shifted the direction of
SW
their migratory restlessness to match the compass directions indicated
by the altered position of the sun (Fig. 5 73). This demonstrated that
-

in choosing directions, the birds compensated for the changing posi- Starling
/
tion of the sun as the earth rotated on its axis. At the time of Kramer's Orients NE
discovery, little was known about biological clocks in animals, but
researchers soon showed that the sun compass was coupled with the
circadian clock, which provided the means for time compensation
(making allowances for the changes in the sun's position in the sky
over the course of a day).
Working with homing pigeons, another German researcher,
Klaus Schmidt-Koenig, demonstrated how this time-compensated
sun compass operates (Schmidt-Koenig 1960). He placed pigeons in
a closed room for several days with an altered cycle of light and dark,
thereby resetting their circadian clocks. When he released the birds on
a sunny day, they interpreted the position of the sun on the basis of their Sun's Rays Deflected 90° Clockwise (From E to S)
internal clock, which was now out of phase with real time. They thus
inferred thatthe sun's position indicated a compass direction that it did Figure 5-73. Starling Orientation with Respect to the Sun: Gustav Kramer performed numerous experiments, one of which
is shown here, demonstrating that European Starlings use the sun's position to orient themselves. a. A European Starling was
not, and made a predictable error in choosing a homeward direction
placed in a circular orientation cage (inner circle) within an opaque outer enclosure containing six windows through which the
(Fig. 5-74). This experiment has been done many times and reveals a sun's position in the sky could be viewed directly. When the sun was in the east, the starling oriented to the northwest (solid ar-
peculiarity concerning how pigeons (and other animals using a sun row)-135 degrees counterclockwise from the sun—the direction the bird would normally migrate at that time of year (spring).
compass) use the sun. When their clock has been shifted in a certain The dots in the circle diagram to the right are the recorded directions in which the starling fluttered during migratory restlessness;
way, they may mistake a noontime sun for a rising or setting sun. This is the arrow inside the circle is the average direction of the observations. b. When Kramer added to each window an opaque screen
containing a mirror that deflected the sun's rays 90 degrees counterclockwise, so that the sun appeared to be in the north instead
a mistake that humans would not make, because at noon the sun is high
of the east, the starling adjusted its orientation accordingly. It now oriented to the southwest, still 135 degrees counterclockwise
in the sky, whereas at sunrise or sunset it is near the horizon. Animals from the apparent position of the sun. c. When the screens and mirrors were adjusted so that the sun appeared to be in the south
apparently ignore these differences in the sun's elevation; instead, they rather than the east, the starling oriented to the northeast, still 135 degrees counterclockwise from the sun. Adapted from Griffin
(1974, p. 123).

Cornell Laboratorq of Omithologq Handbook of Bird Biologt

5.86 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.87

Figure 5-74. Hypothetical Experiment Clock-shifted Figure 5 75. Star Compass Research in a Planetarium: To
-

Demonstrating How the Time-compen- Flight Path determine how birds use the night sky to orient, professor
sated Sun Compass Works: a. A bird .41(-.
1 Stephen T Emlen of Cornell University tested Indigo Bun-
flying south at 9:00 A.M. might have a 441.
41 la• ilir +
tings in circular orientation cages (funnel-shaped boxes
• .4, •
flight path 45 degrees to the right (from to o seen hereon stepstools) in a small planetarium. He was able
\e, ••
the bird's perspective) of the direction to ee •• 4 5 .•
•
• to expose the birds to normal and manipulated skies, even
the sun (dotted line). b. By 3:00 P.M. the • „..4. changing the pattern of star movement so that the night sky
• . Sun
- .••• •• 90
sun will have moved approximately 90 45° • • 45 appeared to rotate around Betelgeuse instead of the North
:',,. .
„_ f‘y 1i 7 •
degrees in the sky. For the bird to con- _Flight • Star, Polaris. Photo courtesy of Cornell University.
tinue to fly to the south, it must be able to Path •
•••
adjust its orientation with respect to the Y....
sun according to the time of day. In this S s S
case, it now flies 45 degrees to the left of
a. 9:00 A.M. b. 3:00 P.M. C. 3:00 P.M.
the sun. c. If birds are held in captivity in Figure 5 76. How Indigo Buntings Use
Natural
Under Sky Under Natural Sky Under Natural Sky -

a specific, altered cycle of light and dark the Night Sky to Orient: Experiments by
After Biological Clock
fora few days, their internal clock can be
was Set Back Six Stephen T. Emlen at Cornell University
reset to six hours earlier than the actual
Hours in the 1960s demonstrated that Indigo
time: thus the bird "thinks" it is 9:00 A.M. Buntings (in the Northern Hemisphere)
when it is really 3:00 P.M. A bird clock-
determine north by the patterns of stars
shifted in this way, trying to fly south at 3:
surrounding the North Star, Polaris,
00 P.M. (when it should orient 45 degrees consider only its azimuth direction, the compass direction at which a which is always nearly due north in the
to the left of the sun) will actually orient night sky. Although all other stars in the
vertical I ine from the sun to the ground intersects the horizon.
45 degrees to the right of the sun, and night sky appear to rotate around the
head west. The direction it takes is the The sun compass is the compass of first choice in homing pigeons.
North Star, the positions of these stars,
correct direction according to its own, Researchers know this because whenever the sun is visible, releasing relative to each other, do not change. a.
internal, shifted clock. Adapted from clock-shifted pigeons results in the predicted deflection of their flight At 9:00 P.M. on a spring night, captive
Goodenough et al. (1993). Originally
directions relative to control birds whose clocks are running on real Indigo Buntings in a planetarium under
from Palmer (1966). a typical night sky for that time oriented
time. If pigeons preferred a different compass system, clock-shifting
north, as would a spring migrant in the
them would affect their orientation only when they were unable to
wild. b. At 3:00 A.M., with the plane-
use their preferred system. Whether the sun compass plays any role in tarium sky showing the typical night
migrating birds is unclear at present. sky for that time, the caged buntings still
Through a series of experiments in a planetarium (Fig. 5 75), Emlen -
oriented to the north. c. Caged birds still
To be able to use the sun as a compass, pigeons must learn its path.
showed that the star patterns near Polaris (called circumpolar constel- oriented to the north when they were
If, for example, young pigeons are allowed to see the sun only in the
lations: the Big Dipper, Little Dipper, Draco, Cepheus, and Cassiopeia) shown a typical 3:00 A.M. sky at 9:00
morning, they will not be able to use it as a compass in the afternoon. P.M. If they were using the rotational
are then apparently memorized in this context, so that by the time of
How the pigeon knows, for example, that the sun rises in the east and positions of the stars to navigate, they
migration, the birds can select the proper migratory direction even
sets in the west is not completely clear, but some evidence suggests would have assumed the stars were in
under a stationary planetarium sky (Figs. 5 76, 5 77). Although many
- -
the correct position for 9:00 P.M. and
that it may use its magnetic compass (see below) to assign compass
other animals might use a star compass, it has been demonstrated only oriented in the wrong direction. Draw-
directions to the azimuths of the sun's path.
in birds. ing by Adolph E. Brotman, from Emlen
(1975).
Star Compass
.a b
Shortly after Kramer's discovery of the sun compass, another Ger- Cassiopeia
man team, Franz and Eleanor Sauer, took up the study of the mecha- Cepheus Cassiopeia
nisms of orientation that might serve nocturnal migrants. In a series of • .•
•
classic experiments under the dome of a planetarium, they showed that
night migrants use the stars as a compass (Sauer 1957). In keeping with z .-.- • North Star .
much of the thinking of the time, the Sauers believed that birds were
born with a genetically encoded star map in their heads, but extensive •
analysis of the stellar orientation system of the Indigo Bunting by an
American, Stephen Emlen of Cornell University, showed that this was •
not the case (Emlen 1967a and b). Emlen showed that young buntings • • • Big Dipper
Big Dipper
observe the rotation of the night sky that results from the earth's rotation
Direction Direction
around its axis. By learning the center of this axis of celestial rotation of Flight
of Flight
(the North Star, Polaris) they can locate true north. (This is true at any
Bird 9:00 P.M. Bird 3:00 A.M.
time of night, since Polaris does not appear to move much in the sky.)
Sky 9:00 P.M. Sky 3:00 A.M.

Cornell Laboratory of Ornithology Handbook of Bird Biology

5.88 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.89
Figure 5-78. Helmholtz Coil System for
Manipulating the Magnetic Field: By
Helmholtz Coil System: placing two sets (indicated by the solid
Two Pairs of Coils Aligned at Right Angles and open shading) of Helmholtz coils,
to One Another Allow the Horizontal and oriented at right angles to each other,
Vertical Components of the Magnetic Field around a bird in a circular orientation
to be Manipulated Independently cage, researchers can independently
manipulate the horizontal component
(direction to magnetic north and south)
and vertical component (related to dip
angle, see Fig. 5-79) of the magnetic
field experienced by the test bird.
European Robin
Changing the amount of electric cur-
Orientation rent running through the coils creates
Cage magnetic fields of different intensities.
The pioneers of this technique, Friedrich
Merkel and Wolfgang Wiltschko, were
able to change the migratory orientation
of caged European Robins (that were
prevented from using sun, star, and light
cues) in predictable ways, by altering the
direction of the magnetic field.

Power Source
Birds Never Exposed to a Normal Sky Modified Sky
Point Source of Light Rotating Around North Star Rotating Around Betelgeuse

BET. Power Source

• Magnetic Compass
That animals might sense the earth's magnetic field and use it
as a compass is a very old idea. The first empirical demonstration of
magnetic orientation, however, came in the 1960s from the laboratory
of Friedrich Merkel and Wolfgang Wiltschko in Frankfurt, Germany.
Worki ng with the European Robin, they showed that birds in migratory
condition would hop in appropriate migratory directions when tested
• in covered cages in a closed laboratory room to eliminate sun, star, and
• • light cues. Most important, by employing Helmholtz coils surrounding
No Directional Orientation Migratory Orientation Migratory Orientation the cage to change the direction of the magnetic field experienced
Away From North Star (South) Away From Betelgeuse by the birds, they were able to change predictably the orientation of
Zugunruhe in the birds (Wiltschko 1968) (Fig. 5 78). Although these
-

results were initially met with skepticism, rigorous demonstrations of

Figure 5-77. How Indigo Buntings Learn to Use the Night Sky to the south, the appropriate direction for fall migration. (Ar- magnetic orientation are now available from 18 species of migratory
to Orient: Experiments by Stephen T Emlen at Cornell Uni- row indicates the mean direction taken by birds tested.) c. The
birds as well as the homing pigeon.
versity showed that the early visual experience of young Indigo third group never saw the sun and was exposed to a modified
Buntings plays an important role in the development of their night sky every other night for two months; Betelgeuse, a star Many additional experiments by Wolfgang and RoswithaWiltsch-
celestial-orientation abilities. Three groups of nestlings were in Orion, became the new polestar around which all other ko revealed details concerning how the magnetic compass works. In-
captured and hand-reared in the laboratory. a. The first group stars rotated. When these birds were tested in the fall under a terestingly, unlike our compass instruments, the avian magnetic com-
lived in a windowless room with diffused lighting and never normal night sky, they continued to regard Betelgeuse as the pass is not based upon the polarity (the distinction between north and
saw a point source of light. In the fall the birds began to display polestar and oriented their activity away from it. Thus young
intense nocturnal activity. When they were tested in circular
south) of the field. It is as if the bird has a magnetic compass of the sort
buntings initially learn the north-south axis from the rotation of
orientation cages under a stationary night sky in a planetarium, stars; star patterns by themselves are not useful cues to a naive that you might use on a hiking trip, but the compass needle is identical
they did not orient in any particular direction. b. The second bunting. The star patterns take on directional meaning only on both ends. It can detect the north-south axis, but can't tell which of
group never saw the sun and was exposed to a night sky in a after they have become part of the bird's general orientational the two directions is north. To determine north, the bird uses the fact
planetarium every other night for two months. Normal celestial framework, the formation of which is influenced, at least in
rotation (around the North Star) was simulated. When the birds
that magnetic lines of force not only point toward the poles, but dip
part, by observing the rotation of stars. Drawing by Adolph E.
were tested in a planetarium under a normal sky during their Brotman, from Emlen (1975). toward the earth's surface at an angle (Fig. 5 79). Birds can apparently
-

fall migratory period, they oriented away from the North Star, detect that dip angle in some way that we do not yet understand. Our

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

5.90 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.91
Figure 5-80. How European
Figure 5-79. The Magnetic Field of the Magnetic Field Condition
Robins Use the Earth's Magnetic Orientation of
Earth: The earth, with its two different
Field to Determine North: Results European Robin *
magnetic poles, acts like a large mag- Northern Hemisphere:
Magnetic of a series of classic experiments a
net. Arrows indicate the direction of the Lines Dip
North Pole by Wolfgang and Roswitha
magnetic field of the earth. On the right Toward the Earth Normal Magnetic Field: Geologic NE
Lines of Wiltschko in which the orien- Magnetic N = Geologic N
half of the diagram, complete magnetic S (= Magnetic NE)
Magnetic Force tation of European Robins under "North End" of Compass
lines have not been drawn: the arrows (Normal)
different magnetic field conditions Needle Dips Down
intersecting the earth's surface indicate Dip Angle was tested in circular orientation
the direction of the magnetic field at cages. The drawings at left are side
each point, and the length of each ar- views, with geologic north to the
row is proportional to the strength of left and south to the right; a line b
Magnetic Field Direction Geologic SW
the magnetic field at that point on the pointing toward the bottom of Reversed:
VEST EAST (= Magnetic NE)
earth. The magnetic field is stronger at the page would represent a line Magnetic N = Geologic S
(Opposite Normal)
the poles and weaker at the equator. going straight into the earth. Each "North End" of Compass
The dip angle, the angle at which the drawing shows the magnetic field Needle Dips Down
magnetic field lines contact the earth, condition tested, and the average
is 0 degrees at the magnetic equator, response of birds tested. For sim-
and approaches 90 degrees as you ap- plicity, the picture of the bird faces c
proach the magnetic poles. Note that Southern either north or south, although Magnetic Field Direction and Geologic NE
the magnetic field lines point away from Hemisphere: the birds actually oriented either Dip Reversed: (= Magnetic SW)
Magnetic Lines Angle northeast or southwest. The birds Magnetic N = Geologic S
the earth in the Southern Hemisphere N S (Normal)
South Pole Away From were tested in Frankfurt, Germany "South End" of Compass
and toward the earth in the Northern
the Earth in the spring, when they would Needle Dips Down
Hemisphere, paralleling the earth at
normally be migrating to the
the magnetic equator. Note also that the
northeast. a. Normal Magnetic
magnetic poles and equator do not quite
Field: When tested in the normal, d
coincide with the geographic poles and
unmodified magnetic field of Magnetic Field Dip Reversed: Geologic SW
equator. If you had a compass whose Frankfurt, the birds oriented to Magnetic N = Geologic N (= Magnetic SW)
needle was free to dip up and down as the northeast. b. Magnetic Field S "South End" of Compass
N (Opposite Normal)
well as to swing around, it would align Needle Dips Down
human-made compasses work because the needle aligns itself with the Direction Reversed: Only the di-
itself at the same angle as the magnetic rection of the magnetic field lines
field lines, with its north end pointing
earth's magnetic lines of force; the needle on many compasses does not
were modified, such thatmagnetic
down in the north and up in the south. dip up and down because it is held in one plane. If, however, you have north was now toward the earth's
Adapted from Able (1994). Originally a compass whose needle, instead of just spinning around, is also free geologic south pole (the "north- e
from Waterman (1989) and Wiltschko seeking end" of a compass needle Magnetic Field Dip Eliminated: Bird Orients
to dip up and down, then in the Northern Hemisphere the end of the Magnetic N = Geologic N
and Wiltschko (1991). would pointsouth in this situation). Randomly
needle that points north will dip down, and the end that points south • S Neither End of Compass
Although it may appear that the Needle Dips Down
will tip up. The opposite will be true in the Southern Hemisphere. direction in which the magnetic
In some very clever experiments that involved changing the lines dip has also been reversed,
dip angle of the magnetic field lines, the Wiltschkos showed that a from the bird's point of view it
is still the same, as the lines dip KEY
European Robin in the Northern Hemisphere considers the direction toward magnetic north (the north N Geologic North
in which the field lines dip downward to be north (Wiltschko and end of the compass needle would S Geologic South
Wiltschko 1995) (Fig. 5 80). dip down as it pointed toward
-
Compass Needle: Head of Arrow (Needle) Always Points Toward
magnetic north [geologic south]).
The magnetic compass seems to develop spontaneously in young Magnetic North. Needle is Free to Dip Toward North or South
In this situation, the birds reversed
birds. All that is required is that they grow up in a normal magnetic their orientation, and tried to head * Experiment Performed in Northern Hemisphere Spring
field; they need not have experience with the sun or stars. Researchers southwest. c. Magnetic Field Di-
still do not know how birds sense the very weak magnetic field of rection and Dip Reversed: As in (b), the direction of the magnetic field lines were reversed, but in addition, the direction in which they
dip was reversed so that the north end of the compass needle would now angle up as it pointed to magnetic north (geologic south). In
the earth. Current research is focused on tiny particles of magnetite
this case, the birds oriented to the northeast, taking the direction in which the field lines dip, rather than the direction to magnetic north,
(an iron-containing, magnetic mineral) that have been found in the as an indication of geologic north. d. Magnetic Field Dip Reversed: As in (a), the magnetic field direction was left normal, but as in (c),
heads of many birds, as well as in the abdomens of bees and in cer- the direction in which the lines dipped was reversed, such that the north end of the compass would point up as it pointed to magnetic
tain bacteria, both of which can orient to a magnetic field, and on the (and geologic) north. Birds under these conditions oriented to the southwest, again taking the direction in which the lines dipped,
rather than magnetic north, as an indication of which way was geologic north. e. Magnetic Field Dip Eliminated: When the magnetic
possibility that photoreceptive pigments in the eye might provide the field direction was again left normal, but the dip angle was eliminated (magnetic lines of force were parallel to the earth's surface, as
sensor (Walker et al. 1997). The magnetic compass is an important they would be at the equator), the birds did not orient in any particular direction. This series of experiments clearly shows that birds use
component in the orientation equipment of migratory birds, and in the dip angle to determine north or south: if they, instead, used magnetic north and south to determine direction, they would always
fly toward magnetic northeast (thus birds in groups (c) and (d) should have oriented in a direction opposite to the direction they took,
homing pigeons it seems to serve as a back-up compass that is used
and birds in group (e) should have oriented to the northeast); but if the birds used the dip angle to determine north or south, they would
when the sun is not visible. always fly in the direction in which the arrow dips—as was found in every case. Using this type of magnetic-sensing system, one would
expect the birds in group (e) to be unable to orient—as was the case. Note that condition (c) is not found on the earth, and condition (d)
simulates the Southern Hemisphere. Adapted from Able (1994). Originally from Wiltschko and Wiltschko (1972).

Cornell Laboratory of Ornithology Handbook of Bird Biology

5.92 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.93
Sunset Cues past the loft area. This local map, much like a topographic map of a
Most nocturnal migrants initiate flights shortly after sunset. Re- familiar region, may gradually be extended through exploratory flights
cent orientation cage studies have shown that visual cues around the (Fig. 5-81).
time of sunset are very important in the decisions these birds make Think of a pigeon sitting in its home loft. As winds blow from the
about which way to fly. Work in my own laboratory showed that birds east, for example, the pigeon smells the odor of a pine forest. If the
possess yet another compass, this one based on patterns of polarized pigeon is later taken away from home and released in a place where
light in the sky. These patterns are present throughout the day, but the odor of pine is very strong, it might conclude that it had been
Figure 5-81. Odor Gradient Map: Hom-
nocturnal migrants apparently use them most at sunset, when they transported eastward from its loft. Papi's group and Hans Wallraff of ing pigeons living in a loft southwest of
need directional information to begin their flights (Sidebar 3: Polarized Germany have performed many experiments to test this olfactory map a farm and west of a pine forest might
Light). hypothesis. Their evidence that olfactory information is involved in use the odors coming from these sites
One might ask why birds have so many different ways of deter- to develop a map of their home region.
homing by pigeons at distances of 310 miles (500 km) or more from
The map would be based on the direc-
mining compass directions, and given that they have many, how are the loft has led Wallraff to propose that odors might form an extensive tion and intensity of the odors. When
they related to one another?The answer to the first question is only con- gradient map. A gradient odor map is based on small but systematic released at unfamiliar sites within the
jecture. Presumably it is advantageous to have backup systems to cope changes in the intensity or composition of odors over a large area. As home region, the birds might be able
with the problems a bird can face during migration, such as places one moves in a given direction, each particular odor becomes steadily to determine their location with respect
where the magnetic field is severely disturbed, or cloudy weather that to home by sensing the intensities of
stronger or weaker. An animal could even, in theory, extrapolate its
the two odors and comparing them to
obscures visual cues. With regard to how these compass mechanisms map to areas well beyond those with which it is directly familiar. their memory of the odor intensities at
are related to one another, there is a good deal of information, but (Continued on page 5.96) their home loft. For example, at Release
researchers still do not know the whole story. The various compass Site 1, a bird would sense that both the
systems interact in complex ways both during their development in farm and forest odors were stronger and
determine that it was northeast of home.
young birds and in older individuals during migration. There seems to
At Release Site 2, a bird would find the
be a great deal of calibrating of one system by another and there are N farm odor stronger and the forest odor
comparable data from too few species to draw any very firm gener- weaker, thus placing itself northwest of
alizations. The best evidence at the moment suggests that the earth's Release home.
rotation, as indicated by the rotation of the stars at night or changes 0 Site 2
in polarized skylight patterns in the daytime, is important to young „..
birds in the calibration of orientation mechanisms with each other. In
birds on migration, faced with the short-term problem of selecting a Release
migration direction, magnetic cues seem to take precedence over stars, Stron 0 Site 1
and polarized skylight at dusk seems to override both of those stimuli.
Thus, the different compass capabilities are arranged in a hierarchy E
of subordination. Recall that in homing pigeons, in contrast, the sun Farm Odor Pine
compass is the preferred method of orientation. Gradient Forest

Navigational Maps
Experimental evidence very strongly suggests that homing pi- Weak •

geons and other birds possess some sort of navigational map, but
discovering the physical basis of that map has been one of the most Stron

enduring and contentious issues in the study of animal behavior. To

some extent, it remains one today. It is important to bear in mind that, Pine Odor
as with the compasses of birds, there may be more than one map. At Gradient
present, there are two possible hypotheses regarding what may con-
stitute the navigational map, and both are derived almost entirely from
work with homing pigeons.
The first is the surprising idea, put forth by Floriano Papi and col-
leagues from the University of Pisa, that atmospheric odors may form
the physical basis of the map (Papi et al. 1991). The hypothesis is that
pigeons learn an odor map of the vicinity of their loft by associating
airborne odors with the directions from which winds carry the odors
S
Cornell Laboratoni of Ornithologq Handbook of Bird Biolo91,1
5.94 Kenneth P. Able Chapter 5 —Birds on the Move: Flight and Migration 5.95

Sidebar 3: POLARIZED LIGHT Thus the polarized light patterns can

indicate the sun's position even when
Sandt1 Podulka it is hidden behind clouds (although
the patterns themselves can only be
Although humans are able (with tation to create waves, but only the polarized as it is scattered by pass-
seen in areas of clear blue sky). And,
practice) to see some types of po- vertical waves will reach the door- ing through the molecules in the
the motion of the light patterns can
larized light, we generally do not knob. All others have been stopped atmosphere. Humans and certain
reveal the direction to true north.
notice or use it in everyday life—so or absorbed by the box. You have just species of insects, amphibians, fish,
By using Polaroid filters to alter
it remains a bit of a mystery to us. Re- created a polarized light beam: one and birds are all able to detect some
the polarized light patterns seen by
call from Chapter 3 that light is in the that is made up of a reduced number patterns of polarized light in the sky.
birds in orientation cages and by
form of a wave. You can represent this of different orientations of waves, The details of how these polarized
employing depolarizing material to
wave with a simple demonstration in this case, only vertical waves. If light patterns are produced and move
eliminate polarized light, researchers
(Highland 1963). Tie one end of a you, instead, made a horizontal slot, are beyond the scope of this course,
in my laboratory have shown that
rope to a doorknob, and shake the only horizontal waves would pass but a few basic points will be men-
birds can use polarized light in the
other end up and down, creating a through. The cardboard box in these tioned here.
sky as a compass (Able 1989). But,
vertical wave (an action you prob- situations acts like a polarizing lens The atmosphere produces a gra-
exactly how birds extract directional
ably carried out with a garden hose or filter, by selectively transmitting dient of polarization with the most
information from the polarized light
when you were a child) (Fig. A). You
can also shake your hand right and
waves with certain orientations.
Polarizing lenses that transmit
weakly polarized light areas near
the sun and directly opposite the
patterns is not yet understood. ■
left creating a horizontal wave, or only vertical waves are used in sun, and the most strongly polar-
Suggested Reading
between upper right and lower left sunglasses and car windshields to ized areas 90 degrees from the sun
Able, Kenneth. P. 1982. Skylight
creating a wave at an angle. In fact, cut out other waves that may create (Fig. C). This pattern of polarization
polarization patterns at dusk in-
you can shake your hand in any glare from horizontal surfaces such maintains its orientation to the sun as
fluence migratory orientation in
orientation that is perpendicular to as the road. Polarizing lenses are also the sun's position moves in the sky. In
birds. Nature299:550-551.
the line of rope between you and used in microscopes and cameras. addition, the earth's rotation causes
the door, and still create a wave. An In contrast, a depolarizing material the pattern, like the stars, to rotate
ordinary light beam is a random mix- can be used to take a light beam that around Polaris in the Northern Hemi- Figure B. Polarized Light Beam Simulation: If, to your demonstration in Figure A,
ture of all these waves with different has been polarized and vibrate it in sphere. (Although the polarized light you add between you and the door a cardboard box with a deep vertical slot, and
orientations. all directions, creating waves of all patterns are not visible at night and you pass the rope through the slot, you can create a beam of "polarized light." The
Now place a cardboard box with box, like a polarizing filter, allows only light waves with a certain orientation (in this
orientations, to form an unpolarized Polaris is not visible by day, the pat-
case, vertical) to pass through. See sidebar text for details. Adapted from Highland
a deep vertical slot between you and beam. terns still rotate around the location
(1963, p. 42).
the door (Fig. B), and run the rope The atmosphere acts like a weak of Polaris, which does not move in
through it. With this setup you can polarizing filter, and in the clear the sky and is always very close to
Patterns of Polarized Light in Sky with Sun at Different Elevations
still shake your hand in any orien- parts of the sky, light from the sun is north in the Northern Hemisphere.)

DANN.
........=. -
Now t
.....lall
lkit
411
:-A,
41111 .
Itic. 1111y
d r
Ihoe,
war 111110
0, Sun on Horizon Sun at 45° Elevation Sun at Zenith
(Dawn) (Perhaps 9:00 A.M.) (Noon)

Figure C. Patterns of Polarized Light in the Sky: The atmosphere, acting as a weak polarizing filter on sunlight, produces a gra-
dient of polarized light in the sky, which moves with the position of the sun. The most strongly polarized area (darkened region
on each diagram) is a band across the sky 90 degrees from the sun. Areas of the sky with more weakly polarized light (light areas
on each diagram) are close to the sun, and opposite the sun, in the sky. Positions of polarized light bands are shown for the sun
Figure A. Light Wave Simulation: By tying one end of a rope to a doorknob, and shaking the other end in various directions, you (small circle) on the horizon, at 45 degrees (around 9:00 A.m.), and directly overhead. Animals able to perceive these patterns of
can simulate light waves with various orientations: vertical, horizontal, and angled. Unpolarized light is a random mixture of polarization can use them to orient. Adapted from Animal Navigation by T. H. Waterman. Copyright ©1989, Scientific American
light waves with these orientations as well as everything in between. Library. Used with permission by W H. Freeman and Company.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 Kenneth P. Able Chapter 5—Birds on the Move: Flight and Migration 5.97
5.96
Figure 5-82. Manipulating the Olfac- Although hundreds of olfactory experiments have been per- and Andreae 2000; Wallraff 2000). Whether or not pigeons use these Figure 5-83. Flight Paths of Homing
tory Environment of Homing Pigeons: gradients, however, remains unknown. Pigeons in Magnetic Anomalies: Con-
formed and scores of papers published, the olfactory navigation hy- tour lines show the earth's magnetic
To determine whether homing pigeons The other current hypothesis on the nature of the navigational
pothesis remains controversial (Wallraff 1996; Wiltschko 1 996; Able field over a small region; peaks indicate
use olfactory information to form a
map is that birds might possess a magnetic map. Using the earth's
navigational map of their home region, 1996). In general, two types of experiments have been performed. First magnetic anomalies where the strength
loale, Nozzolini, and Papi (1990) con- are those that attempt to eliminate the sense of smell—by plugging magnetic field as a map is much more difficult than using it as a com- of the magnetic field is elevated by up to
ducted the experiment illustrated here. pass. For example, because the earth's magnetic field gets stronger 3,000 nanoTesla (nT)—approximately 1
nostrils, cutting the olfactory nerves (see Ch. 4, Olfaction), applying
The experimental pigeons lived in a loft as you move from the equator toward either pole, an animal might percent above the average. a. Birds Re-
local anesthetics to the olfactory membrane, transporting the pigeons leased in Normal Magnetic Field: Birds
that was exposed to the natural odors use the strength of the field at any given point to estimate latitude.
and breezes of the area; they were also
in sealed containers provided with bottled air, or some combination of released outside a magnetic anomaly
these methods. Experiments of this type have been used to eliminate But to use the magnetic field in this way requires a level of sensitivity near Worcester, Massachusetts gen-
exposed, at times, to the odor of benzal-
dehyde, artificially blown toward them access to environmental odors during transport to release sites (to much higher than that needed to use the field as a compass, because erally flew straight over the anomaly,
from northwest of the loft. Control birds the changes in magnetic field strength are very small even over long heading in the correct direction (ENE)
eliminate outward journey information), at the release sites, or both. toward home. b. Birds Released at
were exposed only to natural odors. distances. There is, however, considerable evidence that pigeons are
Experiments of a second type are designed to manipulate the odor Magnetic Anomaly: When released at
During homing trials, both control and
environment experienced by the pigeons (Fig. 5 82). This approach responsive to magnetic field changes of the order necessary to extract the magnetic anomaly at Iron Mine Hill,
experimental birds were exposed to the -

has been used to attempt to alter the development of the odor map the requisite information. Rhode Island, homing pigeons became
odor of benzaldehyde—both during
disoriented and remained so for some
transportation to the release site and at by birds at the loft using various cage and enclosure designs, fan-pro-
time after leaving the vicinity of the
the site. Birds were taken to a site east a. Birds Released in Normal Magnetic Field
duced winds, and artificial odors; it also has been used to predictably anomaly, but they eventually head for
of the home loft and released singly.
Researchers recorded the compass
change the pigeons' perception of the route of displacement from the N home. Each of the two plots shows the
loft by performing detour experiments of various types and by exposing flight paths of a different set of released
direction each bird was flying when „ Home
birds. These results suggest that magnetic
it vanished on the horizon. The circle pigeons to samples of air from different routes or release sites. How- tve Direction
anomalies affect a pigeon's "map," but
diagram shows vanishing bearings for ever, attempts by other workers to replicate some of the experiments not its compass system. Adapted from
10 experimental and 10 control birds.
have been unsuccessful, and all have been criticized for one reason Baker (1984).
The arrows in the middle of the circle
indicate the average direction taken by or another. The most compelling experiments are those that directly
birds in each group. Control birds head- manipulate the odor environment, but we have little evidence as to
ed west, the correct direction to home; which atmospheric substances might provide the physical basis for an • Homing Pigeon Release Site
their orientation was unaltered by the
olfactory map. Wallraff has recently documented spatially stable and Flight Path of Individual
odor of benzaldehyde. The experimental
birds, however, headed southeast. This directionally distinct gradients in ratios of a number of commonly oc- Homing Pigeons
would be expected if they had inter- curring atmospheric hydrocarbons that are sufficiently reliable to ac-
preted the odor of benzaldehyde at the count for the known precision of pigeon homing navigation (Wallraff
:-.. 2000 -
release site as an indication that the re- Intensity ot . /ezt 3km
lease site was northwest of the loft. When ,
Magnetic Field
Above Normal
experimental birds were not exposed to __---- tnD 0 3
benza ldehyde during a release, they ori- Distance (km)

ented toward home, just like the control r/rt t

fir;
b. Birds Released at Magnetic Anomaly
birds. Adapted from Goodenough et al. 5,11 i:r_ N
(1993). N
Home
Direction r, Directi
y Di
Home
rect i•on

N S

6;) '

11*--/-
Benzaldehyde

NW o Control Birds tta

pce.
TArs •■■

• Experimental Birds

Home .- ",■■ or 2000 2000

Intensity 1km
31.5 miles Intenstty 0 3km
Mafnetir held
MaA,netic Field
(50.2 km) Above Normal Above Normal
m T1 (CT)

Demo, rkei Distance rk,ne

Cornell Laboratorq of Ornithologq Handbook of Bird Biologui

5.98 Kenneth P. Able Chapter 5 — Birds on the Move: Flight and Migration 5.99
Empirical evidence supporting the existence of a magnetic map detail how a migratory bird does what we know it does—return with
comes almost entirely from studies of homing pigeons released at mag- incredible precision to specific spots on the earth after traveling thou-
netic anomalies—places where the earth's magnetic field is disturbed, sands of miles over often unfamiliar terrain.
usually by large deposits of iron near the surface (Fig. 5 83). American
-

researcher Charles Walcott discovered that pigeons released within

a magnetic anomaly tended to fly off in random directions (Walcott Suggested Readings
1 9 9 6 ) . Once outside the anomaly, however, the birds corrected and
headed for home. This effect was found even on sunny days, when Able, Kenneth P. 1993. Orientation cues used by migratory birds: a review of cue-
pigeons use their sun compass, which suggests that the effect of the conflict experiments. Trends in Ecology and Evolution 8(10):367-371.
anomaly is not on the magnetic compass (which they were not using
A technical article that reviews the various bird compasses and their inter-
at that time). In addition, the effect is found only in pigeons released actions.
right atthe anomaly; pigeons required to fly across a magnetic anomaly
on the way home are unaffected. Both of these facts suggest that being Able, Kenneth P. 1995. Orientation and navigation: a perspective on fifty years
released at a magnetic anomaly disrupts only the critical map step of of research. Condor 97:592-604.
Kramer's map-and-compass model. An historical account and perspective on bird orientation research.
Recently, Walcott discovered that pigeons from some lofts are not
disoriented by release at magnetic anomal ies.Th is led to an interesting Able, Kenneth P., editor. 1999. Gatherings ofAngels: Migrating Birds andTheir
new finding: birds that lived in a loft situated in an area with a rather Ecology. Comstock Books, Ithaca, NY. 193 pp.
steep, regular gradient of change in magnetic intensity of the sort likely The world's most knowledgeable migration researchers share their personal
to provide useful navigational information were disoriented when re- and professional experiences regarding some of the most fascinating aspects
leased at the anomaly; those from a loft where the magnetic field had of bird migration.
very little gradient were not affected.
This observation is consistent with the idea that pigeons, and Alerstam, Thomas. 1990. Bird Migration. Oxford: Oxford University Press.
perhaps other birds, possess a flexible navigation system in which the 420 pp.
information they learn to rely on depends in part on the availability General reference covering all aspects of migration; uses primarily European
and reliability of several potential components. Data from experiments examples.
performed in the Wiltschko lab suggest that a similar scenario may
work with the olfactory map (Wiltschko et al. 1 989). Pigeons raised Baker, R. Robin. 1984. Bird Navigation: The Solution of a Mystery? NewYork:
exposed to winds and airflow that would provide good olfactory cues Holmes & Meier. 256 pp.
were strongly affected by anesthetizing their olfactory membranes Somewhat slanted overview of bird orientation and navigation mecha-
prior to release, whereas those that grew up in a sheltered locale were nisms.
unaffected and flew homeward immediately.
In the case of migratory birds, we know that many species exhibit Berthold, Peter, editor. 1991. Orientation in Birds. Basel: Birkhauser. 331 pp.
remarkable fidelity to breeding and overwintering sites, but we know Collection of technical reviews of all aspects of orientation and navigation,
next to nothing about when and how they navigate to these places. We each written by an expert in the field.
do not know, for example, whether most of migration is accomplished
Berthold, Peter. 1993. Bird Migration: A General Survey. Oxford: Oxford
by compass orientation alone, with navigation to the specific goal oc-
University Press. 239 pp.
curring only in the final stages of the journey, or whether the birds are
oriented toward a specific destination throughout their trip. General review of all aspects of bird migration studies.
-----
Despite the many startling discoveries about bird migration dur- Burton, Robert. 1990. Bird Flight: An Illustrated Study of Birds'Aerial Mastery.
New York: Facts on File. 160 pp.
ing the last 50 years, we obviously still have much to learn. Animal
navigation is a very active area of current research, and important new Beautifully illustrated, readable accountof many aspects ofbird flight, from
ecological to mechanical.
findings are being made every year. Just 25 years ago, most workers
in the field were very skeptical about the reality of magnetic orienta-
Burton, Robert. 1992. Bird Migration:An Illustrated Account. NewYork: Facts
tion, and almost no one except the original discoverers believed that
on File. 160 pp.
pigeons used odors in homing navigation. Perhaps the next decade or
so will seethe discovery of new and important pieces of the navigation Beautifully illustrated,. readable account of all aspects of bird migration.

puzzle. What is certain is that we cannot yet explain in step-by-step

Cornell Laboratorq of Ornithologq

L Handbook of Bird Biologq

5100 Kenneth P. Able

Dingle, Hugh. 1996. Migration: The Biology of Life on the Move. Oxford:
Oxford University Press. 474 pp.
A detailed and technical treatise that presents a unified look at migration
r
in all animal groups.

Gauthreaux, SidneyA., Jr. 1982 .The ecology and evolution of avian migration
systems. In Avian Biology, Vol. 6, edited by D. S. Farner, J. R. King, and K.
C. Parkes. New York: Academic Press.
In-depth review of the evolutionary and ecological aspects of bird mi-
gration.

Goslow, G. E., Jr., K. P. Dial, and F. A. Jenkins, Jr. 1990. Bird flight: insights and
complications. BioScience 40:108-115.
Readable account ofsome of the recent discoveries concerning mechanisms
of flight. Evolution of Birds
Gwinner, Eberhard, editor. 1990. Bird Migration: Physiology and Ecophysi-
ology. Berlin: Springer-Verlag. 435 pp.
Collection of technical reviews on all aspects of the physiological control
and energetics of migration, each written by an expert in the field. and Avian Flight
James, Helen F. and Storrs L. Olson. 1983. Flightless birds. Natural History
92:30-40.
Very readable account.
Alan Feduccia
Kerlinger, Paul N. 1989. Flight Strategies of Migrating Hawks. Chicago: Uni-
versity of Chicago Press. 375 pp.
Technical treatise on hawk flight, use of thermals, and strategies of cross-
country flight. Most of the Handbook of Bird Biology focuses on living
birds, but no in-depth discussion of a group of organisms
Kerlinger, Paul N. 1995. How Birds Migrate. PA: Stackpole Books. 228 pp. would be complete without exploring its fossils and evo-
Covers all aspects of how birds migrate, described clearly and concisely. lutionary history. The full story of the origin of birds, how-
ever, remains elusive. As researchers seek more pieces of the puzzle,
Pennycuick, Colin J. 1972. Animal Flight. London: Edward Arnold. 68 pp. they continue to discover new birdlike fossils. These new finds usually
generate lively discussion in the scientific community as well as in the
Short, readable account of the mechanics of animal flight.
news media, often compelling scientists to revise their theories—so
Rappole, John H. 1995. The Ecology of Migrant Birds:A Neotropical Perspec- our view of the origin and evolution of birds is continually evolving.
tive. Washington and London: Smithsonian Institution Press. 269 pp. Because this topic is so complex, and students may vary widely
in their backgrounds and interest in it, this chapter is optional. For stu-
This book covers the topic of migration in the New World. It includes chap-
ters on the habitats of migrant birds, their resource use, their impact and dents taking the Home Study Course in Bird Biology, exam questions
membership in tropical communities, and comparisons with Old World for this chapter are provided to help you review the most important
migration systems. Of particular interest is the book's focus on the evolu- points, but you do not need to submit your answers to Home Study
tion of migration from tropical latitudes. Course staff.
This chapter discusses early birdlike fossils and their similarities
Waterman, Talbot H.1989. Animal Navigation. NewYork: Scientific American with different groups of ancient reptiles; the major theories on the evo-
Library, W. H. Freeman. 243 pp.
lution of birds, bird flight, and feathers; the massive extinction of birds,
Readable, well-illustrated account of homing and navigation in all an- dinosaurs, and most other living things at the end of the Cretaceous
imals.
period; and how the few birds thought to have survived the Cretaceous
extinctions may have given rise to modern birds. Throughout these
discussions, you may wish to refer to the two bird evolution diagrams

Cornell Laboratorq of Ornitlioloaq

E.2 Alan Feduccia Evolution of Birds and Avian Flight E.3

included as Appendices A and B to this chapter, as well as to the Geo-

logical Ti me Scale in Appendix C of Chapter 1.You will note that the first Haarlem Specimen
references to the most i mportantfossi I organisms discussed in this chap- Found in 1855,
ter are printed in color.These indicate organisms whose illustrations and Recognized in 1970

detailed descriptions may be found in Appendix C to this chapter.

Archaeoptergx and Other Urvogels

■ The fossil record allows us to place organisms and their lineages on
the geological time scale, and permits us to see changes in diversity Single Feather
Found in 1860
and morphology through time.The oldest known bird, Archaeopteryx,
London Specimen
was preserved in late Jurassic period limestone, dated at about 150
Found in 1861
million years old. Figure E 1 illustrates all the fossil specimens of Ar-
-
ly
chaeopteryx, as well as a single feather. You will want to refer to it as
you read through this section.
Each of the seven known specimens of Archaeopteryx was re-
covered from the fine-grained Solnhofen limestone, named for the
nearby village of Solnhofen in Bavaria. Although fossils are rare in this
limestone, the meticulous mining of this highly prized stone, espe-
Berlin Specimen
cially for the lithographic printing process, has produced an array of Found in 1876
amazingly well-preserved fossils of a variety of plants, invertebrates, Eichstatt Specimen
fishes, and reptiles. They provide a remarkable window on the past, Found in 1951,
Recognized in 1973
allowing us to form some idea of the late Jurassic habitat and the con-
ditions that led to its wealth of fossils. The diversity and numbers of
fossilized insects in the Solnhofen deposits indicate that they could
not have formed far from land. And, many insects found at Solnhofen,
including mayflies, caddisflies, and most of the dragonflies, could not
have been permanently away from fresh water or brackish coastal wa-
ter, where they deposittheir eggs and undergo developnnent.These and
other observations have led researchers to assume that the Solnhofen
deposits were formed from marine sediments that were deposited in
an arid, tropical climate near the coast. In addition to arthropods,
the fossils include numerous fishes, turtles, ichthyosaurs, plesiosaurs,
lizards, and crocodiles. Of special interest is a fossil of a single, small
theropod dinosaur, Compsognathus.
In 1861, Hermann von Meyer reported that an impression of a sin- Maxberg Specimen
gle feather had been discovered in rock from a quarry near Solnhofen. Found in 1956
Even though this first specimen was merely a feather, the unexpected
discovery caused a sensation, because it clearly showed that birds
Solenhofer Aktien-Verein Specimen
dated from the Mesozoic—the Age of Reptiles. This first fossil feather 5 inches
New Species ofArchaeopteryx
was a secondary wing feather, 2.5 inches (60 mm) long and 0.44 inches 10 cm Solnhofen Specimen A. bavarica
Recognized in 1987 Found in 1992
(11 mm) wide, with the vane on one side of the shaft roughly half as wide
as that on the other side—the same asymmetry as in the flight feathers of
modern birds (Fig. E 2). Within a month of his announcement, Meyer
-

reported the discovery of a complete fossil skeleton from the same de-
posit, but from another quarry. Because this first skeletal specimen of
Archaeopteryx ended up in the British Museum, it is popularly known Figure E-1. Seven Fossils and a Feather of Archaeopteryx: Shown here are the seven fossil skeletons and a solitary feather of
as the "London Specimen." It had a long, reptilian tail exhibiting many Archaeopteryx, including the popular name and the year of discovery or recognition. See text for details on each fossil. From Chat-
vertebrae, but attached to each vertebra was what appeared to be a terjee, Sankar. The Rise of Birds: 225 Million Years of Evolution, p. 84. Copyright 1997. The Johns Hopkins University Press.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

E.4 A Ian Feduccia Evolution of Birds and Avian Flight E.5
pair of short tail feathers. The limestone had captured these subtle Figure E-3. Berlin Specimen ofArchae-
impressions, as well as the startling image of feathered wings. The opteryx: Considered the "Rosetta Stone"
skull exhibited teeth in the upper and lower jaws. Here, clearly, was of avian paleontology, the Berlin spec-
imen of Archaeopteryx was discovered
a mosaic of avian and reptilian characteristics. The Germans use in 1876 in a limestone quarry near the
the general term "urvogels" to refer to early, primitive birds such Bavarian town of Eichstatt. Courtesy of
as these. Humboldt Museum fiir Naturkunde,
From its fossilized bones alone, the creature would have been Berlin.
Corn Crake Archaeopteryx Weka classified as a reptile. But, because the uniquely fine-grained Soln-
hofen limestone was able to preserve the details of such structures
Figure E-2. Comparison of Flight Feath- as feathers, this fossil appeared to be more than "just another reptile."
ers from Archaeopteryx and Modern Meyer gave it the genus name Archaeopteryx, which means "ancient
Birds: Archaeopteryx had primary and
wing" (archaos, ancient; pteryx, wing), and the species designation
secondary feathers with asymmetric
vanes similar to those of modern flying
lithographica, in reference to the lithographic limestone in which it was
birds such as the Corn Crake. Flight- preserved. In 1877, while scientists all over the world were debating
less birds, however, have symmetrical the significance of this Jurassic bird specimen, another discovery was
flight feathers, as in the Weka from New announced from another quarry, near the town of Eichstatt. Known as
Zealand. Because asymmetrical feath-
the "Berlin specimen," this beautifully preserved fossil ended up in the
ers play a key role in the mechanics of
flight, their presence in Archaeopteryx Humboldt Museum in Berlin, and is considered a veritable "Rosetta
suggests that the bird may have been Stone" of avian evolution (Fig. E-3). Its wings are outstretched and
capable of flight. Modified from Feduc- articulated in a natural pose, and attached to the outspread arms and
cia and Tordoff (1979); drawing by Ellen
hands are complete impressions of primary and secondary flight feath-
Paige. Copyright 1979 AAAS.
ers, nearly identical in detail to those of modern birds. The perfectly
preserved skull, with upper and lower teeth, is arched back over the
neck. In addition, each of the three fingers exhibits a sharp, decurved,
terminal claw. The feet were those of a perching bird, with three toes
directed forward, and a hindward, opposable first toe or hal lux. The
long tail shows a pair of tail feathers attached symmetrically to each
vertebra. Th is Berlin specimen is no doubt the most widely known and
illustrated of all fossil animals.
Remarkably, another specimen of Archaeopteryx came to light al-
most a hundred years later. The third specimen, discovered in a quarry
shed, was mainly a torso and was badly articulated; it is known as the In this specimen, a sternum (breast bone) was preserved for the first
"Maxberg specimen." In 1970 still another specimen was recognized. time. The presence of an ossified sternum, even though it was flat and
Now known as the "Teyler" or "Haarlem specimen," it was originally without a keel (a downward-projecting ridge of bone to which the ma-
recovered in 1855 and described in 1857 as a pterosaur (flying reptile), jor flight muscles of modern birds attach), suggests that Archaeopteryx
Pterodactyl us crassipes. But 120 years later it was shown to be an Ar- was capable of powered flight.
chaeopteryx! In 1973, another small specimen of Archaeopteryx was A rival for Archaeopteryx, named Protoavis, was announced
announced; beautifully preserved, it had very faint feather impressions in August of 1 986.Fragmentary bones from two crow-sized crea-
and for some 20 years had been misidentified as the small theropod tures—dating fronn 225-million-year-old (I ate Triassic) rocks ofTexas,
dinosaur Compsognathus. This "Eichstatt specimen" is roughly one- and thus alive at the dawn of the age of dinosaurs—were claimed
third smaller than the London specimen. An additional specimen was to be those of a fully volant (flying) bird. Evidence that these bones
discovered in 1987—the "Solnhofen specimen"—which was about represent an early bird is scant, however, and there is no evidence
10 percent larger than the London specimen. of feathers. For the time being, Protoavis must be considered of un-
In 1992, Peter Wellnhofer discovered a new specimen, this one certain affinities.
smallerthan the London specimen,with longer hind limbs—especially In 1995 another urvogel emerged, this time from the early Creta-
the tibiae. Wellnhofer hypothesized that the strongly curved claws of ceous of China (about 25 million years after Archaeopteryx). Named
the foot were adapted for perching (Fig. E-4). Th is "Solenhofer Aktien- Confuciusornis and represented by several species, the predominant
Verein specimen" (named after the quarry company that owns it) is the being C. sanctus, this urvogel occurred in incredible numbers around
youngest of the Archaeopteryx fossils, and was sufficiently different freshwater lakes. Confuciusomis resembled Archaeopteryx in having
from the others to be named a new species, Archaeopteryx bavarica. three free, clawed fingers and a primitive pelvic region, but the tail was

Cornell Laboratoru of Ornithologq Handbook of Bird Biologj

 E.6 Alan Feduccia Evolution of Birds and Avian Flight E.7
Figure E-4. Form and Function of Claws: a. Scale Drawings of Claws of Archaeopteryx and Modern Birds: Lateral View some type of complex mating system. Temporal
Openings Orbit Antorbital
a. Scale Drawings of Claws of Archae- Other more controversial birds to emerge from the
Fenestra
opteryx and Modern Birds: Lateral same deposits that produced Confuciusomis include two
View: Archaeopteryx had two types of
claws: (1) claws on its toes, and (2) three
feathered, but flightless creatures recently described as Pro-
claws on the first digit of the manus of Long-Eared Eurasian tarchaeopteryx and Caudipteryx.They were proclaimed to
each wing. Comparing the shape of Owl Sparrowhawk \ Alpine Swift be "feathered dinosaurs," evidence that dinosaurs were
I)
each claw type to the shapes of the ancestral to birds. However, an alternative analysis suggests
claws of modern birds with known hab-
that they are secondarily flightless Mesozoic birds resem-
its can provide hints as to the lifestyle
of Archaeopteryx. Shown here are the Archaeopteryx bling kiwis (see Fig. 5-48). If this latter interpretation proves
claws of magpies—perching birds that correct, they have little, if anything, to do with the evolution
forage on the ground, Long-eared Owls
arditt‘\
of birds. Despite their superficial resemblance to small dinosaurs,
and Eurasian Sparrowhawks—preda- Toe 3 \ Manus 1 ) White-backed Lesser Spotted
Woodpecker Woodpecker they show anatomical distinctions associated with the flightless condi- Figure E-5. Diapsid Skull of a Primitive
tory birds that use their feet to grasp
tion in modern birds. Caudipteryx is preserved with a mass of gizzard Archosaur: Diapsid reptiles are those
prey, Alpine Swifts—cliff dwellers,
Inches mm with two openings (fenestrae) on each
and White-backed and Lesser Spotted stones, and must have been able to grind very resistant food. It may
0!.5 b side in the temporal region of the skull,
woodpeckers—both tree climbers. Be- have been an herbivore, unlike the carnivorous theropod dinosaurs posterior to the orbit (eye socket). Diap-
cause the toe claws of Archaeopteryx considered by some to have given rise to birds. sids include basal archosaurs or thec-
appear most similar in shape to those
odonts, as well as snakes and lizards. Il-
of the perching magpies, and the wing
lustrated here is a skull of the thecodont
claws appear most similar to those of the
tree-climbing woodpeckers, researchers
b. Comparison of 30 Bird
Species Showing Claw Arcs The Descent of Birds Euparkeria from early Triassic deposits
of South Africa. Thecodonts are a diverse
believe that Archaeopteryx was proba-
bly a perching bird with strong climbing ■ Charles Darwin andThomas Huxley argued that Archaeopteryx was assemblage of early reptiles, united by
having teeth set in sockets (the term
abilities. Adapted from Feduccia (1996, really a sideline of early avian evolution and noton the direct line lead-
"thecodont" [literally, a "receptacle for
p. 106). Originally from Yalden (1985). ing to modern birds. In fact, the entire issue of flight origins (see next teeth"] indicates this), and an antorbital
b. Claw Arc Comparisons: Claws are 200 section) has been sidetracked by Archaeopteryx, which, despite some fenestra, as well as the two temporal
Mean Value of
very complicated geometrically, but
180 Archaeopteryx Manus Claws popular belief to the contrary, was already a bird in the modern sense, fenestrae found in all diapsids. From
to compare those of different species,
Mean Value of I Romer, A. S. 1966. Vertebrate Paleon-
researchers often consider them as 160 • • with fully developed flight adaptations. Archaeopteryx, therefore, can
Archaeopteryx Toe Claws :
. ; I • tology, 3rd Edition. The University of
simple arcs (see inset), measuring them 140 • • I tell us very little about the initial stages in the evolution of flight, al-
• • • I •
Chicago Press. Copyright 1966 by The
in relative degrees of a circle. The angle though the fossil is important in exploring the relationship between
120 • :• ; • ; • University of Chicago. All rights re-
E (y)—from A to B—is a measure of the de- • . '
1. .1 1 ; I . • birds and reptiles. Recent discoveries in China and elsewhere have served.
grees of arc, and is termed the claw arc. 100
Compared here are claw arcs, in degrees • i climbers shown clearly that early avian evolution was not linear, that there was
80 • : ,
of curvature, for 30 species ()thirds. Each an early split in avian evolution involving the sauriurine and ornithu-
vertical column of data points presents 60 _ . 1 I • • Perchers
I • rine birds (see The Early Fossil Record of Birds, later in this chapter),
a range of values for a single species. 40 . .
and that early avian evolution was more bushlike, with many lineages
Note the almost complete segregation
of the claw arc values of ground dwell-
20
Ground
becoming extinct.
ers, whereas perchers and climbers What, then, were the reptilian ancestors from which Archae-
have some overlap. The mean value for 0 10 20 30 opteryx and other birds evolved? Most of the major groups of Me-
Archaeopteryx toe claws (about 120 Species sozoic reptiles—from lizards to pterosaurs and from crocodiles to
degrees) is indicated by the line in the
reduced to a long, fleshy pygostyle (the tail bone of modern birds, dinosaurs—have, at one time or another, been considered the ances-
center of the perchers, and the mean for
wing claws (about 145 degrees), by the formed by fusion of the last few vertebrae). The flight architecture was tors of birds. After much more than a century of investigation and a
line in the middle of the climbers. These
much more advanced than that of Archaeopteryx, and the beak was fossil record of reptiles that is fairly satisfactory, bird ancestry remains
data, as in (a)above, suggest thatArchae- highly controversial. Two major theories are widely debated today, the
like that of a modern bird. Some of the skull features were more prim-
opteryx was a perching bird with strong
itive than those of Archaeopteryx, however, including the temporal re- pseudosuchian thecodont hypothesis and the dinosaur theory. They
climbing abilities. Inset and drawing (b)
reprinted with permission from Feduccia gion (the sides of the forehead, or temples), which was fully diapsid differ with respect to specific lines of descent, and equally important,
(1993). Copyright 1993 AAAS. (had two openings on each side), like that of early archosaurs (Fig. they differ as to the time when the first bird appeared. By tracing the
E-5). Like Archaeopteryx, Confuciusomis was a perching bird, with genealogy of reptiles, one can see where the two theories diverge. You
a typical perching foot with three anterior toes and a well-developed may want to refer to Appendix A: Bird Evolution Theories and Early
posterior hallux. Now known from literally hundreds of specimens, Diapsid Reptiles as you read through the rest of this section.
Confuciusomis must have been a highly colonial species, and one in All modern reptiles except turtles evolved from diapsid rep-
twenty specimens exhibits long tail plumes resembling those of certain tiles—the same group that also gave rise to birds. Diapsid reptiles first
birds-of-paradise. Scientists consider the long tail plumes evidence of appeared in the late Carboniferous. By late Permian to early Triassic

Cornell Laboratory of Ornithology Handbook of Bird Biology

E.8 Alan Feduccia Evolution of Birds and Avian Flight E.9

Ilium Thecodonts
(Basal Archosaurs)

Crocodiles Dinosaurs Pterosaurs

Ornithischians (bird-hipped) Saurischians (reptile-hipped)

(herbivorous)
Duckbills
Ceratopsians
Sauropods Theropods
Stegosaurs (carnivorous)
(herbivorous)
Ankylosaurs
Diplodocus
Ornithopods
Brach iosaurus
Apatosaurus Carnosaurs Coelurosaurs
Plateosaurus Tyrannosaurus Deinonychus
Ornithischian Pelvis Saurischian Pelvis Camarasaurus Allosaurus Struthiomimus
Coelophysis
Figure E-6. Comparison of Ornithischi- times, some 245 million years ago, two groups of diapsids can be
an and Saurischian Hips: Dinosaurs are distinguished clearly, one containing the snakes and lizards (Lepido-
divided into two main groups, theomith- Figure E-7. Descent of Ruling Reptiles from Thecodonts: Th is diagram shows the general descent of the Mesozoic ruling reptiles
sauromorpha), and the other containing the archosaurs (Archosiuro- from thecodonts. Most scientists accept the descent of pterosaurs and the branching of the dinosaurs shown here, regardless of
ischian or "bird-hipped" dinosaurs and
the saurischian or "reptile-hipped" dino- morpha). The latter includes thecodonts (basal, or early, archosaurs) their specific views on the origin of birds. Representatives of groups printed in color are illustrated in Appendix C.
saurs, based on the orientation of the pel- and their descendants: crocodiles, ornithischian and saurischian di-
vic girdle bones. Compared here are the nosaurs (Fig. E 6), pterosaurs, and the highly derived (evolutionarily
-
that the phylum of the Class of Ayes has its foot in the Dinosaurian
pelvises ofStegosaurus, an ornithischian modified) birds. Most of theTriassic archosaurs are included within the Reptiles—that these, passing through a series of such modifications
(bird-hipped) dinosaur and Allosaurus, as are exhibited in one of their phases by Compsognathus, [have]
Thecodontia, a catchall term for the various early archosaurs, some of
a saurischian (reptile-hipped) dinosaur.
which gave rise to the various groups of derived archosaurs, includ- given rise to [birds]." Most of Huxley's comparisons involved the sim-
Compare these to the pelvic girdle of a
modern bird, illustrated in Fig. 4-20. Al- ing the dinosaurs. The name thecodont refers to the fact that the teeth ilarities between the hind limbs of theropod dinosaurs and chickens
though their pelvic girdles are similarly are set in sockets. Archosaurs also are identified by the presence of an (both ground-dwelling runners), with little attention paid to the earliest
oriented, ornithischian dinosaurs are not known bird, Archaeopteryx.
opening in front of the orbit (eye socket) called an antorbital fenestra
ancestral to modern birds. Drawing from
(see Fig. E-5).The thecodonts were ancestral to all the Mesozoic ruling The argument shifted when Robert Broom, a prominent South
Marsh (1896).
reptiles, including the dinosaurs (Fig. E 7); through one forebear or
-
African paleontologist, first proposed what has become known as the
another, thecodonts gave rise to birds. pseudosuchian thecodont hypothesis for bird evolution. "Pseudo-su-
Proponents of the pseudosuchian thecodont hypothesis of bird chian thecodont" (pseudosuchian meaning literally "false crocodile")
ancestry place the origin of the first bird at this point—the early to was used historically to refer to the basal archosaurs, referred to simply
middle Triassic—suggesting that birds descended directly from thec- as "thecodonts" in this course. In 1913 Broom described from the rich
odonts about 230 million years ago. The dinosaur theory, however, early Triassic deposits of South Africa the pseudosuchian Euparkeria,
postulates the entry of birds into the evolutionary arena much later, which he believed was ancestral not only to birds, but also to the
after thecodonts had given rise to the saurischian dinosaurs, and after dinosaurs. Euparkeria was a small, 230-million-year-old thecodont,
the saurischians had split into distinctive lineages. According to the still quadrupedal (moving on four legs) but tending toward bipedal ity,
dinosaur theory, birds descended directly from the theropods, a later and it appeared to have all the necessary anatomical qualifications for
lineage of carnivorous dinosaurs that evolved from bipedal thecodonts bird anddinosaurian ancestry. No longer was it necessary to deal with
with shortened forelimbs. More specifically, most recent advocates the problem that most dinosaurs seemed too specialized to have been
of the dinosaur theory picture birds evolving directly from a group ancestral to birds. Broom, then, was arguing that birds and theropod
of theropods called dromaeosaurs, typified by the early Cretaceous dinosaurs evolved from a common ancestor (a thecodont), not that
Deinonychus and the late Cretaceous Velociraptor. birds descended from dinosaurs.
Thomas Huxley originated the theory that birds evolved from The publication of Gerhard Heilmann's The Origin of Birds in
dinosaurs. Huxley (1868, p. 74) found the resemblance between the 1926 was a major event in the bird evolution debate. Heilmann con-
small Solnhofen theropod Compsognathus and birds very telling: sidered Broom's Euparkeria the key to bird ancestry, and he argued
"Surely there is nothing very wild or illegitimate in the hypothesis forcefully that birds evolved from thecodonts. He also argued for an

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 E•10 Alan Feduccia Evolution of Birds and Avian Floht E.11
arboreal theory for the origin of bird flight: that fl ight originated among Archaeopteryx had an elliptical wing that was similar in profile to
tree-dwelling avian ancestors. Heilmann's book was engaging and that of woodland birds such as woodcock or quail (see Fig. 5-34). Such
well documented; it had all the earmarks of authority. One of his major wings are designed to produce high lift at low speeds, and to provide
arguments was the lack of a typically birdlike furcula (wishbone—see maneuverability in tight, woodland settings. There can be little ques-
Fig. 4-16) in theropod dinosaurs. We now know, however, that a tion that Archaeopteryx was a flying, most probably arboreal, bird.
number of theropods have a furcula, although it may not be truly ho- The reversed first toe of Archaeopteryx is further evidence that
mologous with that of birds. A furcula is now also known in an early it was not primarily a ground dweller or a dinosaur. Why would a
archosaur, so the evolutionary importance of this structure remains ground-dwelling dinosaur have a hallux? It only would be a hindrance
uncertain. Heilmann's theory of an early thecodontian bird ancestor in running, and no dinosaur is known to have had one. The hallux is a
was repeated in virtually every subsequent textbook and paper on
avian evolution until the early 1970s, when the dinosaur theory of
bird evolution re-emerged.
In 1973, Professor John H. Ostrom of Yale University published
a page-long paper in the British journal Nature, outlining the basis of
his new version of the dinosaurian origin of birds. Ostrom's hypoth-
Cranium Expanded, Skull Bones Fused
esis, simply put, is that birds not only are descended from theropod
dinosaurs as proposed by Huxley, but are close to forms such as the
Hand (Manus)
Cretaceous coelurosaur Deinonychus, in which Ostrom saw many Bones Fused
similarities with the earliest bird, Archaeopteryx. Ostrom's theory
gained considerable momentum during the ensuing years, and now
is widely accepted by vertebrate paleontologists. The major concern
regarding Ostrom's argument is whether the similarities between the-
ropods and Archaeopteryx result from common ancestry or conver- Pelvic Bones Tail Vertebrae
Fused Reduced in Number
gent evolution. Many ornithologists remain skeptical of the dinosaur
and Fused
theory because they see many of the anatomical similarities between
birds and theropods as superficial, because they think the fossi I record
Pygostyle
shows that the timing is wrong for an ancestor/descendent relation-
E ship between birds and dinosaurs, and because they do not support
the idea that avian flight originated in ground-dwelling animals—a Ribcage Strengthened
hypothesis that is often coupled with the dinosaur theory. with Uncinate Processes

For vertebrate paleontologists, Archaeopteryx represents lit-

Domestic Pigeon
tle more than a feathered dinosaur, and many consider it a small,
ground-dwelling predator. However, recent studies show Archaeop-
Enlarged,
teryxto be more birdlike than previously thought (Fig. E 8). It has a
-
Keeled
birdlike quadrate (a bone of the skull), birdlike occiput (skull base), Sternum

birdlike brain, and conical teeth that are devoid of the serrations Archaeopteryx

that characterize theropod teeth. It also has a birdlike foot with a

fully reversed hallux (found in no dinosaur), and highly decurved
claws, which are typical of modern perching birds. On the forelimb
it has decurved, flattened wing claws, similar to those of modern
trunk-foraging birds and climbing mammals (see Fig. E-4). It has
the wings and feathers of modern birds, which have remained
essentially unchanged in 150 million years of bird evolution. Its
feathers are identical in microstructure to those of modern birds, Figure E-8. Comparison ofArchaeopteryx and Pigeon Skeletal Features: The skeleton ofArchaeopteryx appears quite birdlike,
and the primary and secondary flight feathers have asymmetric but modern birds have a number of skeletal features not found in Archaeopteryx. Most of these are thought to be refinements to
vanes—a feature that turns each feather into an individual airfoil improve flying ability. In modern birds (illustrated here by the pigeon), but not in Archaeopteryx: (1) the cranium (braincase) is
expanded and skull bones are fused; (2) the separate hand (manus) and finger bones are fused, forming rigid wing elements; (3)
during flapping flight, and is correlated with flight capability in
the separate pelvic bones (ilium, ischium, and pubis) are fused into a single sturdy pelvic girdle; (4) there is a reduction and fusion
modern birds (see Fig. E-2). In birds that become secondarily flight- of tail vertebrae to form one bone, the pygostyle; (5) the ribs are strengthened by horizontal uncinate processes; and (6) the keel
less, such as the Ostrich or flightless rails, the flight feathers tend to of the sternum is expanded for the attachment of flight muscles. From Evolution of Vertebrates, by E. H. Colbert. Copyright 1955
lose their asymmetry, the vanes becoming more nearly symmetrical. John Wiley & Sons, Inc. Reprinted by permission of Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc.

Cornell Laboratorg of Ornitholcog Handbook of Bird Biohoul

E•2 Alan Feduccia Evolution of Birds and Avian Flight E.13
Figure E-9. Feet of Two Theropods, Ar- There also is the problem of timing.The most superficially birdlike
chaeopteryx, and a Modern Bird: Com- theropods are from the end of the Cretaceous, with forms such as Ve-
pared here are the left feet of two types
Remnant
lociraptor appearing almost at the K–T event (the massive, worldwide
of theropod dinosaurs (ceratosaurs and Remnant
dromaeosaurs), Archaeopteryx, and a Fifth Toe Fifth Toe extinctions at the Cretaceous–Tertiary boundary), some 80 million
modern bird—represented by the chick- years after Archaeopteryx. The entire group of theropods thought to
en, Gallus. Notethatthetheropodshavea have given rise to birds, the dromaeosaurs, is restricted to the Creta-
remnant fifth toe, butArchaeopteryx and ceous, the geological period after the Jurassic of Archaeopteryx. If
modern birds have, at most, four toes. In
many modern birds, such as the chicken,
Archaeopteryx is, indeed, an early bird and not merely an evolutionary
the first toe is reversed and points toward sideline, this raises a "temporal paradox": you can't be your own grand-
3 3
the bird's rear. This reversed toe, called mother!
the hal lux, is an adaptation for grasping Ceratosaurs Dromaeosaurs Archaeopteryx Modern Bird
Finally, consider the problem of the origin of avian flight. A
branches while perching, and is unique
ground-dwelling animal evolving the ability to fly is a near biophysical
to birds. Unlike theropods, whose first
toe is not reversed, Archaeopteryx had a impossibility, yet that is the usual flight-origin theory linked with the
hallux—further evidence of its arboreal dinosaur theory of bird ancestry—because early theropods already ap-
lifestyle. Modified from Chatterjee, San- peared to be specialized for a terrestrial life. In contrast, the evolution
unique avian adaptation for perching in trees, and many ground-dwell-
kar. The Rise of Birds: 225 Million Years
ing birds reduce or eliminate it (Fig. E 9). of flight in a tree-dwelling animal is easily explained, and this scenario
of Evolution, p. 214. Copyright 1997. -

The Johns Hopkins University Press. Birds differ from dinosaurs in many additional ways. Although fits well with the theory that birds evolved from thecodonts—because
both birds and dinosaurs have a hand reduced to three fingers, the or- many thecodonts were small and arboreal. The following section con-
igins of the digits differ (Fig. E 1 0). In theropod dinosaurs, the fingers
-
siders the evolution of bird flight in more depth.
that form the hand are the thumb (digit 1) and the next two, digits 2 -----
and 3; in late Triassic forms, digits 4 and 5 appear as small vestigial Archaeopteryx was well on its way to becoming a true bird, and
structures. In contrast, virtually all embryological evidence indicates could well be descended from some form intermediate between rep-
that the bird hand consists of digits 2, 3, and 4, the middle three fin- tiles and birds that occurred much earlier than the first dinosaurs. As
gers.Theropods have decurved, flattened, serrated teeth, whereas early Columbia University's Walter Bock (1999, p. 568) has noted, until we
birds have simple, peglike, conical teeth, constricted at the base and know more about the actual ancestors of birds, "...it is best to consider
devoid of serrations. The five or so theropod dinosaurs in which the birds as part of the great archosaurian radiation without being more
skin is nicely preserved all show typical thick, tuberculated (nodule- specific, as has been agreed by zoologists for more than a century."
covered) reptilian skin, with no hint of anything remotely resembling
feathers. Simply put, you have to put a round peg in a square hole to
turn a bird into a dinosaur.
Flight Origins
■ When they began to fly, ancestral birds either lifted themselves up
from the ground or glided down from high places; imagining an alter-
native is difficult. In either case, the anatomical changes required for
flight must have evolved in a sequence of very small steps, because
nothing we know about evolution suggests that feathered wings could
have appeared abruptly as an innovation in avian anatomy. Each new
modification of body plan or limbs must have made some contribution
to fitness long before the day when a jumping or gliding creature gave
the first strong beat of its forelimbs and ceased simply falling back to
3
2 2 earth.
Ceratosaurs Dromaeosaurs
To reconstruct the evolution of modern birds, researchers must
2 Modern Bird (Chicken) accountfor the sequence of changes that replaced reptilian scales with
Archaeopteryx
feathers, and, along the way, must answer certain questions: Were the
Figure E-10. Left Manus of Two Theropods, Archaeopteryx, and a Modern Bird: Compared here is the left hand or manus (part reptilian ancestors of birds runners and then jumpers, or parachuters
of the wing) from two types of theropod dinosaurs (ceratosaurs and dromaeosaurs), Archaeopteryx, and a modern bird—rep- and then gliders? Was Archaeopteryx itself at home on the ground or
resented by the chicken, Gallus. Both birds and dinosaurs have fewer fingers in the hand than do mammals. In theropods and
in trees? Could it only glide, or did it already have the ability to sustain
Archaeopteryx, the digits are the thumb (digit 1), and digits 2 and 3. Three digits are also present in the wing bones of modern
birds, butwh ich three is a subject of debate. Embryological evidence suggests that they correspond to digits 2, 3, and 4, but many flight by flapping? What was the original advantage of feathers or their
researchers believe they correspond to ancestral digits 1, 2, and 3 (numbers in parentheses). In either case, there is a reduction epidermal (skin) precursors?
and fusion of the hand bones in modern birds. Modified from Chatterjee, Sankar. The Rise of Birds: 225 Mi II ion Years of Evolution, Consider other vertebrates that have taken to the air. Parachut-
p. 212. Copyright 1997. The Johns Hopkins University Press. ers are known among the frogs, snakes, and geckos; and numerous

Cornell Laboratort of Ornitholo8t1 Handbook of Bird Biolo9q

 r
E.14 Alan Feduccia Evolution of Birds and Avian Flight E.15

Bird Ancestor

•,,
Running Leaping
Landing \
Flying Dragon
Figure E-12. Cursorial Theory of the Evolution of Avian Flight: The cursorial theory, first proposed in 1879 by Samuel Williston,
an expert on fossil reptiles and a dinosaur collector for paleontologist 0. C. Marsh, suggests that ancestors of birds first ran along
the ground and eventually began to jump and leap. Wings (and feathers) developed to extend their ability to leap by aiding in
Flying Squirrel propulsion and balance, leading eventually to flight. This theory is closely linked to the belief that birds descended from small,
ground-dwelling, theropod dinosaurs. Modified from Chatterjee, Sankar. The Rise of Birds: 225 Mil lionYears of Evolution, p. 150.
Copyright 1997. The Johns Hopkins University Press.
Figure E-11. A Sample of Gliding and lizards, both living and fossil, have evolved the ability to glide us-
Parachuting Vertebrates: In addition ing specialized expansions of their rib cage. Powered flight evolved
to birds, other vertebrates—including Marsh proposed, apparently for the first time, an arboreal theory on
among the extinct flying reptiles, the pterosaurs. Among mammals,
fishes, amphibians, reptiles, and mam- the origin of flight. He suggested that small, tree-dwelling, reptil-
mals—have evolved a limited ability to flight now ranges from full-powered flight in bats, to gliding in mar-
ian birds jumping from branch to branch eventually began gliding,
"fly" by gliding or parachuting. Shown supials (sugar gliders), rodents (flying squirrels), and colugos (flying
here are a parachuting frog (genus Rha-
aided by rudimentary feathers on the forelimbs. Intuitively facile,
lemurs; primitive mammals resembling flying squirrels), and modest
cophorus), flying fish (Exocoetus voli- this arboreal theory has been favored by many since then. In fact,
parachuting in primates (Fig. E 11). All of these flying or gliding
-

tans), flying dragon (genus Draco), and the same general theory was proposed by Charles Darwin in 1859
flying squirrel (genus Glaucomys).
vertebrates evolved flight while living in trees, with the possible
to account for the origin of flight in bats.
exception of the pterosaurs, which may have glided out from sea
Nevertheless, the cursorial theory for the origin of avian flight
cliffs. None began to fly from a purely ground-dwelling existence.
continued to have numerous adherents and experienced a revival
Early in their evolution, fliers use the energy provided by gravity;
early in the 1900s. The revival resulted partly from an examination
they climb up and coast down. They do not start their flight with
of modern quadrupedal animals that can rise up to run on their hind
the burst of effort needed to rise directly off the ground. This fact
legs, as do the living lizards called basilisks (Basiliscus) of Central
argues strongly against the theory that birds began flight as runners
America and the frilled lizards (Chlamydosaurus)of Australia. Both
and jumpers, which seems essential to a theory that birds evolved
the basilisks and theAustralian frilled lizard are agile tree climbers,
from theropod dinosaurs.
and basilisks can run across water for short distances to escape pre-
dation (Fig. E 13)! What these lizards illustrate best, though, is the
-

Ground-Up (Cursorial) Theorq extreme behavioral plasticity of animals, and the near impossibility
Since it was first proposed in 1879, many researchers have ad- of ascribing behavioral repertoires to fossil creatures: animals are
vocated a cursorial theory (from the Latin cursus, a rapid running mo- always capable of at least twice the behavior that their anatomy
tion) to explain the origin of flight (Fig. E 12), probably because they
- alone would suggest. In fact, throughout the history of vertebrates,
believed that birds descended from cursorial dinosaurs rather than adaptive behavior has probably evolved before anatomy in the
tree dwellers. As late as 1877, paleontologist and dinosaur hunter invasion of virtually every major new habitat or niche.
0. C. Marsh supported a dinosaurian origin of birds. Then in 1880,

Cornell Laboratory of Ornithology Handbook of Bird Biology

E.16 Alan Feduccia Evolution of Birds and Avian Flight E.17
Figure E-13. Plumed Basilisk Running Ostrom developed his insect-net
CHANGE ADVANTAGE
Across Water: Basilisks (genus Bas- theory considering features of Archae-
i liscus) of Central America can rear up opteryx anatomy as well as dinosaurs
and run on their hind legs in a semi-erect
contemporary with it. He argued that 7. Original Scale Protection
posture. Some paleontologists believe
that an animal much like these lizards "warm-bloodedness" (endothermy)
was the first step in the transition from first evolved among dinosaurs. In this 2. Elongation Solar Reflection
reptile to bird. The hind feet of basilisks scenario, the first feathers served cer-
have long toes lined with flaps of skin that
tain groups of dinosaurs as a thermo- 3. Splits Flexibility; Greater
spread their weight over a larger area,
permitting them to run rapidly over the regulatory pelt. Accordingly, he ar- Size Possible
surface of water for short distances, earn- gued that the coelurosaurs, the small
ing them the nickname "Jesus Christ Liz- theropod dinosaurs that Archaeopteryx
ards." Photo by Joe McDonald.
anatomically resembled, at least super-
4. Fraying and Insulation and
ficially, were warm-blooded animals, Pigmentation Display
and that the first feathers evolved as
insulating material, not as aids to flight
(Fig. E-15). Ostrom also argued that the
head and mouth of Archaeopteryx in- 5. Elongation on
Forelimbs and
1 7- Balance and Flight
dicate that it preyed on relatively small
Imagine the incredible energy that a cursorial creature would Tail
animals, such as insects, lizards, and
have to expend to become airborne, as the cost of running and leaping
small mammals. Running after such
into the air is much greater than that of climbing and then gliding. The 6. Secondary Splits Lighter in Weight;
creatures on its two hind legs, Archae- and Hooklets Flight and Insulation
flailing forelimbs, augmented by the development of feathers, would
opteryx used its forelimbs to catch
add to the thrust and speed of the running biped, but once aloft, where
them. In time, elongation of the fore-
could the would-be flier find the power to stay in flight? The main 7. Diversification of Water Repellency
limb feathers made them more efficient Structures
thrust, provided by the traction of the hind feet on the ground, would
for trapping prey, and they became a Support
have disappeared. Proponents of this theory have suggested flapping
kind of insect net. Display Cleanliness
forearm propellers, but these seem i nsufficient to prevent the bird from
In the 1980s, Jeremy Rayner of the Sound Tactile
crashing promptly back to earth. The cursorial theory simply ignores Production Sensation
University of Bristol calculated that if a
the fact that the animal would be fighting gravity all the time.
0.44-pound (0.2-kg), bipedal, cursorial
In 1976, nearly a hundred years after the first cursorial theory
theropod were to jump while running at speeds of up to 6.6 feet (2 Figure E-15. Hypothetical Steps in the
was advanced, John Ostrom proposed a very different version, which
meters) per second, its speed would drop by 30 to 40 percent, which Evolution of Feathers from Scales: Elon-
has been termed the "insect-net" theory (Fig. E-14). Unlike its prede- gation and splitting of reptilian scales
would present a serious problem in attaining any type of flight (Rayner
cessors, Ostrom's theory was widely accepted, especially by paleon- aided reflection of solar heat and per-
1985). He claimed that the first "flights" of a fluttering proto-flapper mitted larger, flexible scales. Increased
tologists and those advocating a dinosaurian origin of birds, and his
would have been at low speeds, at which the energetic demands of fraying and pigmentation of the larger
view of Archaeopteryx as a nonflying, reptilian "fly swatter" is found
flight are at their most extreme, and the wingbeat cycle in living fli- scales made them more effective in insu-
in many textbooks. lation and displays. Elongation of feath-
ers is at its most complex. Rayner suggested that the fluttering model
ers on the forelimbs and tail improved
fails because it ignores the extreme morphological, physiological,
balance on extended leaps and ultimate-
and behavioral specializations required for flight. He argued that the ly led to flight. Secondary splitting led
strategy of running, jumping, and gliding produces air speeds that to the evolution of branches with inter-
are apparently too slow to favor flying, and that reaching speeds at locking hooklets, and eventually to the
modern feather structure that aids flight
which flapping is mechanically straightforward requires more energy
and insulation. In addition, this versatile
441111114111111 1111411111A 11.111111111"1 - than appears possible. The costs of flight at the low speeds attainable structure is easily modified for special
Bird Ancestor Insect Net - Feathered Wings by runners are so high that demands on the forelimb musculature purposes, including sound production,
become extreme. Given these problems, Rayner hypothesized that a tactile sensation, support, and water re-
Figure E-14. "Insect-Net"Theory of the Evolution of Avian Flight: In 1976, John Ostrom, a paleontologist from Yale University, cursorial runner would be unlikely to get off the ground. pellency. Adapted from Ornithology, by
proposed the "insect-net" theory, a variation on the cursorial theory for the evolution of flight. He envisioned Archaeopteryx Frank B. Gill, Copyright 1990, 1995 by
Furthermore, Walter Bock (1986) has pointed out that no small,
as a small, terrestrial theropod dinosaur using its wings as an insect trap. As the forelimb feathers elongated, they became more W H. Freeman and Company. Used with
four-legged animals about the size of Archaeopteryxthat are primarily permission.
efficient for catching prey. Eventually the swatting motion became flapping flight. Ostrom also suggested that Archaeopteryx
and dinosaurs contemporary with it were warm-blooded (endothermic) and that the first feathers evolved not for flight, but for terrestrial (in other words, not flying-running forms, or secondarily
insulation. Modified from Chatterjee, Sankar. The Rise of Birds: 225 Mill ion Years of Evolution, p. 152. Copyright 1997. The Johns flightless or degenerate flying forms) use their forelimbs for balance
Hopkins University Press. during fast running or during leaping. A biophysically convincing

Cornell Laboratorq of Ornithologq Handbook of Bird Biologu

E.18 Alan Feduccia Evolution of Birds and Avian Flight E•19
model for the cursorial origin of avian flight, which would be a unique The beginning stage involves an ancestral, fairly small, ground-
pattern among flying vertebrates, both living and extinct, has yet to dwelling reptile with either bipedal or quadrupedal locomotion. The
be developed. animal might have been essentially warm-blooded, but able to use
behavioral mechanisms (such as sunbathing or seeking shelter from
heat) to supplement the internal regulation of its body temperature.
Trees-Down (Arboreal) Theorq
A critical point in Bock's arboreal theory is the invasion of the trees,
A theory that contradicts none of the evidence from either Ar-
which he suggests evolved for nesting, hiding, or sleeping in a place
chaeopteryx or other fossil finds is the arboreal hypothesis that was
safe from predation. He views the invasion of trees, which shifted the
first sketched out in 1880 by 0. C. Marsh (Fig. E 16):
-
animal into a cooler microclimate, as the main reason that natural
The power of flight probably originated among small selection favored the evolution of endothermy and of feathers for insu-
arboreal forms of reptilian birds. How this may have com- lation. Once this ancestral bird took to climbing and the arboreal life, it
menced, we have an indication in the flight of Galeo- presumably began leaping from tree to tree—so selection would favor
pithecus (Cynocephalus, the flying "lemur"), the flying any adaptation that would decrease the rate of descent or lessen the
Figure E-16. The Arboreal Theory of the squirrels (Pteromys), the flying lizards (Draco), and the impact. For example, flattening the body and spreading the limbs hor-
Evolution of Avian Flight: The arboreal flying tree frog (Rhacophorus). In the early arboreal birds, izontally would increase body surface area and lessen impact. Also,
theory, first proposed by 0. C. Marsh in
1880, suggests that flight probably orig-
which jumped from branch to branch, even rudimentary increasing the length of feathers would improve parachuting ability.
inated in small, arboreal, reptile-like feathers on the fore limbs would be an advantage as they This ancestral bird could then slowly expand its repertoire to include
birds that may have jumped from branch would tend to lengthen a downward leap or break the force not only parachuting, but gliding, and finally, active, powered flight.
to branch or climbed a tree and glided to of a fall. (1880, p. 189) Using an elegant aerodynamic model, Ulla Norberg has shown
the nexttree. Gliding is an energy-saving
form of locomotion, as it costs an animal Marsh's views were widely accepted, and were tremendously that the transition to active, powered flight from gliding is both me-
less to climb a tree and glide to the next bolstered in 1926 by Gerhard Hei !mann in his The Origin of Birds. Hel- chanically and aerodynamically feasible. Norberg (1990, p. 260)
one, than to climb up and down a tree
lmann reconstructed, in convincing detail, the hypothetical stages of showed that "...for every step along the hypothetical route from glid-
and run to the next. Feathered forelimbs ing, through stages of incipient flapping, to fully powered flight, there
would have allowed the evolution of
evolution from terrestrial to tree-dwelling to flying animals. However,
he paid little attention to the adaptive advantage of each small step would have been an advantage over previous stages in terms of length
gliding and thus increased the horizontal
distance covered by a downward leap. that eventually led to the large-scale change from reptile to bird. More and control of the flight path."
The arboreal theory has been widely ac- recently, Walter Bock has analyzed the arboreal theory and identified
cepted since it was first proposed. Modi-
fied from Chatterjee, Sankar. The Rise of
the adaptive purpose of each intermediate stage, showing that evolu- Earlq Bird Flight
Birds: 225 Million Years of Evolution, p. tion could, indeed, account for the changes occurring at each (Bock
A particularly important factor in the evolution of flight, usually
156. Copyright 1997. TheJohns Hopkins 1985; 1986). Bock's model depicts an evolutionary pathway following
given scant attention, is body size. Rayner pointed out that because of
University Press. a simple, direct route without elaborate intermediate steps.
mechanical considerations, flight must have evolved in relatively smal I
animals, certainly much smaller than the closest known nonfeathered
dinosaur, Deinonychus, which was about 10 feet (3 m) long.
Indeed, small size is absolutely essential for both arboreal life
and the origin of arboreal flight. Sam Tarsitano (1985, p. 321) wrote
"Parachuting requires that the [ancestral bird] be small, lightly built,
and able to extend its limbs to present as much surface area as possible
to the airflow." Specialization for arboreal life required a decrease in
Jumping size, which conferred a favorable ratio of mass to surface area, lessen-
ing the effect of an impact should the animal jump or fal I to the ground.
Take-Off
A smaller-sized animal also can move through the air at a lower rate of
speed on proportionately smaller wings.
An animal that climbs a tree and then glides to the next tree uses
Gliding less energy than it would if it climbed up and down a tree and then
Bird Ancestor
Parachuting ran to the next. Ulla Norberg has suggested that maximization of net
Climbing energy gain during foraging in trees might have augmented selection
pressure for increased gliding performance. Once gliding evolved, an
animal could dramatically increase its foraging efficiency and drasti-
cally reduce its locomotion time during foraging. Parachuting or glid-
ing to escape from enemies also may have been an important aspect of

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

E.20 Alan Feduccia Evolution of Birds and Avian Flight E.21
avian evolution. Norberg (1990, p. 259) has pointed out that "Gliding the Spanish Iberomesornis and Eoalulavis. The latter have a well-
must have been used only for commuting and not for insect catching, developed, modern type of alu la, indicating that they had achieved a
which would require high maneuverability, which did not evolve until fully developed, modern flight apparatus. All opposite birds became
true flight was well established." extinct at the end of the Cretaceous period, along with the dinosaurs.
In conclusion, avian flight most logically originated in the trees, Other Mesozoic birds belonged to the Subclass Ornithurae; some
taking advantage of the energy-saving locomotion provided by high of these go back to the earliest Cretaceous and were contemporary with
places and the power of gravity. It follows, then, that the actual ances- the opposite birds. The Chinese Lianingornis and Chaoyangia are typ-
tors of birds are most likely represented by small, arboreal archosaurs ical. Gansus, known only from a foot, was apparently a shore-dwelling
from theTriassic or early Jurassic. Many thecodonts, although structur- ornithurine. Nevertheless, Gansus illustrates a basically modern type
ally close to dinosaur "grade" in form, were small, had not yet become of avian tarsometatarsus and toe structure.
fully erect and bipedal, and were arboreal, with little reduction in their A better-known group of Cretaceous ornithurine birds includes
forelimbs. These thecodonts could easily have retained or evolved the the famous Hesperornithiformes (including Hesperornis and Bap-
elongation of the forelimbs seen in Archaeopteryx and presumably tornis), foot-propelled, toothed divers that superficially resembled
present in early birds. In contrast, the early theropods already had modern loons through convergent evolution. They were denizens of
attained the erect posture and greatly reduced forelimbs suggestive the great seaways characteristic of the Cretaceous period. Hesper-
of terrestrial, rather than arboreal, locomotion. For early theropods to ornithiformes became extinct at the close of the Cretaceous, along
develop lengthened forelimbs from reduced and somewhat vestigial with their ternlike contemporaries, the Ichthyornithiformes, which
hands would demand a dramatic reversal in evolution. included the well-known Ichthyomis and Apatornis. The early Creta-
The assumption that the numerous anatomical similarities be- ceous Mongolian Ambiortus was a fully volant ornithurine the size of
tween birds and certain dinosaurs are due to common ancestry has a pigeon. It possessed a well-developed sternal keel and other features
been seriously challenged. If the challenges are valid, then late Creta- of the pectoral region typical of modern birds, confirming that true
ceous, birdlike dinosaurs were convergent with, rather than related flying birds existed by about 12 million years after the appearance of
to, birds. Archaeopteryx.
The presence of both opposite birds and archaic ornithurine
birds shortly after Archaeopteryx points to a major dichotomy in the
The Earlq Fossil Record of Birds early evolution of birds. The mosaic nature of the anatomy of Confu-
Throughout this section, you may want to refer to Appendix B: Hy- ciusornis—more primitive than Archaeopteryx in parts of the skull, but
pothesized Relationships Among Ancient and Modern Bird Groups. more advanced in having a horny beak and a well-developed flight
apparatus—shows that, like the early evolution of mammals, the early
■ The primitive birds mentioned previously are placed within the diversification of birds was probably a complicated bush, not a linear
Subclass Sauriurae; most other known birds are placed within the evolutionary pattern. There must have been many extinct lineages
Subclass Ornithurae. The Sauriurae also contains another major that at one time may have been more advanced in some features of
group of archaic birds known as the "opposite birds" or enantior- their anatomy than their ultimately more successful contemporaries.
nithines. The predominant land birds of the Mesozoic, the enan- Archaeopteryx was not the ancestor of modern birds, but a sideline of
tiornithines are thought to be close allies of Archaeopteryx. Now archaic birds that became extinct by the end of the Jurassic, and was
known from Cretaceous deposits throughout the world (Spain, replaced by the opposite birds and ornithurines of the Cretaceous.
China, South America, Europe, Australia, and Madagascar), these
birds had a well-developed flight architecture, but a relatively Palaeognathous Birds
archaic pelvic region and a long, fleshy pygostyle (tail bone). They
The modern avian radiation consists only of ornithurine birds,
are called opposite birds because their three metatarsals (middle foot
and these are divided into two major groups, the Superorders Palae-
bones; see Fig. 1-11) fuse in a direction opposite (from the proximal
ognathae (ratites) and Neognathae (all other forms). The living ratites
to distal end) to that of modern birds. They also have a distinctive
consist of flightless birds such as Ostriches, rheas, Emus, cassowaries,
formation of the foramen triosseum—the opening among the shoul-
and kiwis, as well as their South American, chicken-like relatives, the
der bones through which passes an important tendon associated
fully volant tinamous (Fig. E 17). Although unique among ratites in
-

with the flight muscles. Most opposite birds had teeth on both upper
their ability to fly, tinamous, like other ratites, have a "palaeognathous
and lower jaws that closely resembled those of Archaeopteryx. In-
palate," different from that of other modern birds (Fig. E 18). The rat-
-

deed, the skull of the early Cretaceous forms is very similar to that of
ites once were thought to represent a very ancient group of birds that
Archaeopteryx. Particularly well-described genera from the early
dated well back into the Mesozoic, but no fossils of these birds are
Cretaceous include the Chinese Sinornis and Cathayornis, and
known prior to the beginning of the Tertiary period, 65 million years

Cornell Laboratort of Omithologli Handbook of Bird Biologt

E.22 Alan Feduccia Evolution of Birds and Avian Flight E.23

Premaxilla

Premaxilla

Vomer

Maxilla Choana Vomer (reduced)

Choana
Palatine Palatine
Flexible Joint
Pterygoid Between Palatine Pterygoid
Basipterygoid
and Pterygoid
Process
Quadrate — Quadrate

Northern Cassowary
Basipterygoid
Process
(reduced) Basisphenoid
Basisphenoid
Palaeognathous Palate Neognathous Palate
Emu Swan

Figure E-18. Comparison of Palaeognathous and Neognathous Palates: Modern birds are divided into two major groups, the
palaeognathous birds and the neognathous birds. This division is largely based on the structure of the palate, an area of the skull
more commonly referred to as the roof of the mouth. In neognathous birds, such as the swan pictured here, the vomer and ba-
sipterygoid process are reduced and a flexible joint forms between the pterygoid and palatine bones. In the palaeognathous Emu,
the roof of the mouth is formed by larger, more rigid bones. Modified from Chatterjee, Sankar. The Rise of Birds: 225 Million Years
of Evolution, p. 260. Copyright 1997. The Johns Hopkins University Press.

ago. More recently, researchers have discovered fully volant, tina-

mou-like palaeognathous birds known as I ithornith ids, thoughtto have
been common in North America and Europe during the early Tertiary
(Paleocene and Eocene). These chicken-like birds are thought to be the
ancestral stock that gave rise to large, flightless forms all over the earth:
the I ithorn ith ids may have flown to remote parts of the world and given
rise to various I i neages of flightless birds. Other examples of extinct rat-
ites include huge birds on the islands of Madagascar and New Zealand.
The elephantbirds (Fig. E 19) of Madagascar were contemporaneous
-

with the native peoples of the island, but probably became extinct in
historic times. The same is true in New Zealand, where some dozen
species of large moas evolved and survived until the
Greater Rhea arrival of the Polynesians, who subsequently ex-
tirpated them (Fig. E 20). Elephantbirds and
-

Red-winged Tinamou moas left no fossils earlier than 10 to 20

mil lion years ago, in the Miocene, per-
Figure E-19. Elephantbird: The ele-
haps indicating that the ancestors of phantbirds (Aepyornithidae) are an ex-
these giants did not arrive on these tinct group of ratites. These large, flight-
islands much earlier. Whether or less birds lived on the island of Mada-
gascar, but were exterminated by human
not the elephantbirds and moas
activity. The "giant" of the elephantbirds
are closely related to each oth- was Aepyornis maximus, which stood
er, or to the ratites, is unclear. about 10 feet (3 meters) tal 1 and weighed
Figure E-17. The Living Palaeognathous Birds (Ratites): Although all ratites have a palaeognathous palate (see Fig. 18), they are Another Tertiary group of gi- about 1,000 lbs (450 kg). Fossil elephant-
a diverse assemblage of mostly flightless birds whose evolutionary relationships remain controversial. Species representing the ant birds (some as large as the birds are found primarily in Pleistocene
modern families of ratites are the Northern Cassowary (Casuariidae), Emu (Dromiceidae), Brown Kiwi (Apterygidae), Ostrich and Holocene deposits. Redrawn from
largest elephantbirds), known
(Struthionidae), Greater Rhea (Rheidae), and Red-winged Tinamou (Tinamidae). Drawing by George Miksch Sutton, used with Pough et al. (1996, p. 543).
permission from Alan Feduccia, who was granted use by the late Dr. Dorothy S. Fuller, sister of George Miksch Sutton. as the dromornith ids, existed

Cornell Laboratorq of Ornithologq Handbook of Bird Bioloq

E.24 Alan Feduccia Evolution of Birds and Avian Flight E.25
in Australia, but became extinct during the Ice Age. These birds, origi-
nally grouped with the Palaeognathae, are now thoughtto be members
of the Superorder Neognathae, and to be most closely related to theAn-
seriformes (ducks, geese, and swans) (Murray and Megirian 1998).

Bird Evolution's Big Bang

• Al l existing dinosaurs became extinct 65 million years ago in the
K-T event, along with many of the earth's other animals (Fig. E 21). -

These widespread extinctions are thought to have resulted from a me-

teor or some other major object from space colliding with Earth. Such
a collision would have caused immediate devastation for hundreds of
miles from the site of impact, and would have hurled dust and steam
into the atmosphere, blocking out sunlight and causing a dramatic drop
in temperature for years. By exterminating so many species and entire
groups of organisms, this cataclysmic event dramatically altered the
path along which evolution has progressed ever since.
Over the years, many ornithologists have postulated that most
modern orders of birds originated in the middle Cretaceous and grad-
ually evolved into the modern forms. However, if birds were as severely
affected by the K-T event as were other forms of life, few lineages from
the middle Cretaceous were likely to have survived. The few avian sur-
vivors probably were related to primitive shorebirds, and represented
the wellspring of modern bird evolution. Like their mammalian coun-

Figure E 20. Moa: Moas (Euryapteryx) are huge, extinct ratites that flourished in New Zealand until the arrival of the Polynesians.
-

Shown here is a photograph of a museum exhibit of a moa on South Island, New Zealand, during postglacial times (5,000 years Figure E 21. The K T Event: Artist Michael Ramus' satirical epitome of dinosaur history and extinction. From Glenn L. Jepsen,
- -

ago). Courtesy of Department of Library Services, American Museum of Natural History, Neg. No. 322337. "Terrible lizards revisited,"Princeton Alumni Weekly, Nov. 26,1963. Courtesy of Princeton Alumni Publications, Inc.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 E.26 Alan Feduccia Evolution of Birds and Avian Flight E.27
terparts, birds evolved explosively during the early Tertiary. Within
a very narrow period of time—about 5 to 10 million years—whales Appendix A:
evolved from terrestrial ungulates (hoofed mammals). Perhaps the
modern orders of birds appeared during the same short time period in
BIRD EVOLUTION THEORIES AND EARLY DIA PSID REPTILES
The two primary theories on the origin of birds both postulate that birds arose from diapsid reptiles.
the early Tertiary. Such an explosive evolutionary event for birds can
They differ, however, in the time period and specific group from which birds evolved. The pseudosuchian
be best described as bird evolution's "Big Bang."
thecodont hypothesis suggests that birds evolved approximately 230 million years ago from thecodonts,
Following the extinction of the dinosaurs, among the first birds
whereas the dinosaur theory suggests that birds evolved approximately 150 million years ago from the-
to appear in the Paleocene and Eocene of North America and Europe
ropods. This diagram shows the major groups of diapsid reptiles and their possible relationships to early
were the bizarre Diatrymas large, flightless predators that had enor-
—

birds. Note that the amount of space between one-million-year increments on the time scale is not the
mous heads the size of those of modern horses. Diatryma, which fed
same in the different geologic periods.
on the small mammals of the early Tertiary, is thought to have taken
over the niche left vacant by the extinction of predatory theropod
dinosaurs (Fig. E 22).
-

By the late Paleocene and early Eocene, around 50 million years

ago, all of the major orders of birds were present. Then, by the Oligo-
cene, some 35 million years ago, most of the modern families were
present; and by the Miocene, about 23 million years ago, modern gen-
era began to appear. Passerines, which first evolved in the very late Eo-
cene or early Oligocene, evolved explosively in the Miocene, radiating
into a tremendous range of niches. Many researchers hypothesize that
their great success resulted from their ability to build complex and di-
verse nests. Most species of birds alive today probably evolved during
the Pleistocene, when the waxing and waning of glaciers alternately
isolated and reunited groups of birds, fueling rapid speciation (see Fig.
1-68). The Tertiary was clearly the "Age of Birds and Mammals."

Figure E-22. Diatryma Feeding on Early

Horse: Standing more than 6.5 feet (2
m) tall and weighing about 385 pounds
(175 kg), the giant, predatory Diatryma
of the Paleocene and Eocene apparently
took over the niche left by the extinction
of predatory theropod dinosaurs. These
flightless, terrestrial birds had vestigial
wings and a massive head and beak.
Here, a Diatryma feeds on the carcass
of an early horse, while a carnivorous
mammal (an oxyaenid creodont) looks
on. From Biomechanics of the jaw ap-
paratus of the gigantic Eocene bird Dia-
tryma: implications for diet and mode
of life, by L. M. Witmer and K. D. Rose,
1991. Paleobiology 17:95-120. Reprint-
ed with permission of Paleobiology.
(Open)

Cornell Laboratory of Ornithology Handbook of Bird Biology

 ▪▪
• • • -•
C.) (2) Cr
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U IL) -.. --,---

•
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L.
C r. CU (1.) ...., --..„
— -= C -0 0
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z -0 CY
• smaller theropods

(Late Jurass ic)

CU c.... r:C. 1%, L CU

4 CU ..6 0 C+= MI 0
Coe lurosaurs

>
ro -.0 CU CUCt' ..-,
5 • 0 V) • C
0 'V 45 = •
c
"TS _C - •- Er, cl.) cu •.. 0
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E
Exa mp les:

2 '4) ■...J 1".. V =0 73

et ..-. co r.,
__ ett 0. V
• °- •a) z CU X u
LI_ 0 tpc CU '''''

rz,
E

I
popad
i
AW OZ -'
snoappiao popad a!ssein

013 DIOZOS3W
(Aw)sara4 UO!IIIW i o
pOpaci )ISSPRI
Aw s
popad uepluad

013 DIOZOIlVd
popad
snoaanuociarD
E.28 A Ian Feduccia Evolution ofBirds and Avian Flight E•29

Appendix B:
HYPOTHESIZED RELATIONSHIPS AMONG ANCIENT - AND
MODERN BIRD GROUPS
The relationships among early fossils resembling birds and the groups of birds alive today are poorly
understood. This diagram presents the most widely accepted ideas concerning these relationships, but
our view of the origin of birds continues to evolve as more fossils are discovered. Note that the amount
of space between one-million-year increments on the time scale is not the same in the different geologic
periods, and that time from the Eocene to present is not shown to scale.

(Open)

Cornell Laboratorq of 0 rnithologq Handbook of Bird Biologq

 •
• •

Re lations hips Fa ir ly We ll Established

ro

Time When a Group We nt Extinct

I
CU T E dC
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Foss i lRecordTime Spa n

O

Un known Re lations hips

'ct.t
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(N U (4 (0 C2,-= -0 U CU ..-, ,...
• • • • • • •• • • •

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t% •

SUBCLASSSAURIURA E
metatars a ls fuse fro m

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DIOZON33 DIOZOS31/1/
E.,30 Alan Feduccia Evolution of Birds and Avian Flight E.31

Appendix C:
INDEX TO FOSSIL ORGANISMS
Archaeopteryx: a feathered reptile from 150-million-year-old Jurassic limestone deposits; it possessed a mosaic of
bird and reptile characteristics. Since its discovery in the early 1860s, Archaeop-
teryx has been one of the most important and controversial fossils in paleontology,
raising many questions about the origin of bird flight and the evolution of birds.

Compsognathus: a chicken-sized theropod dinosaur so closely resembling Archaeopteryx that for many years an
Archaeopteryx fossil was misidentified as Compsognathus. Adding to the con-
fusion, fossil remains of Compsognathus were recovered from the same German
Sol n hofen limestone deposits as Archaeopteryx.

Confuciusornis: a pigeon-sized fossil bird from 125-million-year-old Jurassic-Cretaceous boundary deposits in

China. Currently grouped with the enantiornithine birds ("opposite birds"), Con-
fuciusornis is a mosaic of primitive and advanced features. It is the earliest-known
toothless bird and possessed contour feathers, indicating that it might have been
endothermic.

Deinonychus: early Cretaceous (110-mi Ilion-year-old) dromaeosaur discovered by John Ostrom in 1964. The name,
meaning "terrible-claw," was derived from the large, curved claws on the feet,
which were apparently used to rip open prey. Based on Deinonychus and similar
organisms, Ostrom modified Huxley's dinosaur theory for the origin of birds, sug-
gesting that birds descended not from the 150-million-year-old theropod Comp-
sognathus, but from more recent theropods similar to Deinonychus.

Diatryma: a giant, flightless bird that inhabited the Northern Hemisphere during the Paleocene and Eocene epochs.
Diatryma stood over 6.5 feet (2 m) tall and weighed about 385 I bs (175 kg).

Enantiornithine Birds: termed the "opposite" birds, their fossils were first discovered in Argentina, and are now
known from around the world. This group of small to medium-sized birds flour-
ished in the Cretaceous between 70 and 140 million years ago. They are called
"opposite birds" because their metatarsals (the instep bones of humans) fuse to
form part of the tarsometatarsus (see Fig. 1-11) from the proximal end to the distal
end, a direction opposite to that of modern birds. Genera include lberomesomis
(upper left), Enantiornis (upper right), and Sinornis (bottom).

Cornell Laboratorg of Ornithologq Handbook of Bird Biologq

E.32 Alan Feduccia Evolution of Birds and Avian Flight E.33
Euparkeria: a small, Triassic (230-million-year-old) thecodont that was discovered in South Africa by paleontologist Pterosaurs: flying reptiles from the Triassic that radiated and diversified in the Jurassic and Cretaceous. Although
Robert Broom and described in 1913. This quadrupedal dinosaur, which was many pterosaur features, such as hollow bones and a slight keel on the sternum,
tending toward bipedal ism, appeared to be ancestral to both birds and dinosaurs. were convergent with those of birds, their highly developed wings were struc-
Robert Broom argued that birds and dinosaurs arose from a common ancestor turally unique. Each of the large membranous wings was supported by a single,
(the pseudosuchian thecodont hypothesis) based on the characteristics of Eu- greatly elongated, fourth finger and attached to the side of the body and possibly
parkeria. also to the hind limb.

Hesperornis: a genus in the extinct order Hesperornithiformes—a group of toothed seabirds that thrived in the late Saurischian or "Reptile-hipped" Dinosaurs: one of the two major groups of dinosaurs, the saurischian dinosaurs
Cretaceous. Hesperornis was a flightless, foot-propelled swimmer and diver that branch into two evolutionary lines, the herbivorous sauropods and the carnivorous theropods.
superficially resembled modern loons.
Sauropods: the herbivorous group of saurischian dinosaurs. It includes such giants as Plateosaurus (left),
Diplodocus (center), and Camarasaurus (right).

Ichthyornis: a genus in the extinct order Ichthyornithiformes. These toothed, ternlike birds were found in the same
shallow sea deposits as Hesperornis. They were flying birds with a well-developed
keel on their sternum and short backs and tails.
Theropods: the carnivorous group of saurischian dinosaurs. Theropods are further divided into two groups,
the carnosaurs and the coelurosaurs, distinguished by size and other skeletal features.

Carnosaurs: the group of larger theropods, including the familiar Tyrannosaurus (pictured here)
and Allosaurus.
Ichthyosaur: the most specialized marine reptiles of the Mesozoic, reaching their peak diversity in the Jurassic. Their
limbs were modified into paddles and many aspects of their body resembled those
of modern porpoises.

Coelurosaurs: the group of smaller theropods, including a bird mimic Struthiomimus (top)—a
Ornithischian or "Bird-hipped" Dinosaurs: one of the two major groups of dinosaurs. Called ornithischian because dinosaur from the late Cretaceous that is convergent with modern Ostriches (ge-
of the superficial resemblance of their hips to modern bird hips, ornithischian nus Struthio); the chicken-sized Compsognathus (lower left); Coelophysis (lower
dinosaurs were highly specialized herbivores that included the duckbills (Had- center)—a Triassic ceratosaur about 9 feet (3 m) long; and the dromaeosaurs, such
rosaurus, upper left), armored ankylosaurs (Ankylosaurus, upper right), plated as Deinonychus and Velociraptor (lower right).
stegosaurs (Stegosaurus, lower left), and horned ceratopsians (Styracosaurus,
lower right).

Plesiosaur: marine reptiles with their front and hind limbs modified into large paddles used to row the body through
water, much like today's sea lions. They appear in the fossil record from the late
Triassic to the Cretaceous.

Thecodonts: also known as basal archosaurs, thecodonts are a diverse group of reptiles from the early Mesozoic. They
are united by three key characteristics: a diapsid skull, teeth set in sockets (termed
Protoavis: a 225-million-year-old fossil discovered in Texas and described by San kar Chatterjee in 1991. The fossil thecodont teeth), and an antorbital fenestra. Many paleontologists believe they
pre-dates Archaeopteryx by 75 million years and is thought by Chatterjee to be a are the common ancestor from which dinosaurs, crocodiles, pterosaurs, and birds
closer relative to living birds than is Archaeopteryx. Because of the fragmentary evolved—a theory widely promoted by Gerhard Heilmann in the 1920s.The term
nature of the fossil and the lack of evidence for feathers, its position in bird evo- "pseudosuchian thecodont" was used historically to refer to the thecodonts or
lution remains uncertain. basal archosaurs, most notably by Robert Broom in his "pseudosuchian thecodont
hypothesis" for bird origins. Euparkeria, illustrated here, is a thecodont.

Cornell Laboratorq of Ornithologg Handbook of Bird Biologq

E.34 Alan Feduccia

Figure Credits for Appendix C

Confuciusornis, lberomesornis, Sinornis, Enantiornis, Hesperornis, Ichthy-

ornis, Velociraptor, and Archaeopteryxfrom: Chatterjee, San kar. The Rise
of Birds: 225 Million Years of Evolution, pp. 9, 96, 103, 110, 114, and 156.
Copyright 1997. The Johns Hopkins University Press.
Deinonychus, Diatryma, Hadrosaurus, Ankylosaurus, Stegosaurus, Styra-
cosaurus, Plateosaurus, Diplodocus, Camarasaurus, Tyrannosaurus, and
6
Coelophysis from: Pough, F. H., C. M. Janis, and J. B. Heiser. Vertebrate
Life, 5th Edition. Copyright 1999 Prentice-Hall. Reproduced by permission
of Prentice-Hall, Inc.
Euparkeria from: Pough, F. H., J. B. Heiser, and W. N. McFarland. Vertebrate
Life, 4th Edition. Copyright 1996 Prentice-Hall. Reproduced by permission
of Prentice-Hall, Inc.
Plesiosaurs from: Watson, D. M. S. Paleontology and Modern Biology. Copy-
Understanding
right 1951 Yale University Press.
Compsognathus from: Origins of the Higher Groups ofTetrapods: Controversy
and Consensus, edited by Hans-Peter Schultz and Linda Trueb. Copyright
1991 by Cornell University. Used by permission of the publisher, Cornell
University Press.
Bird Behavior
Protoavis from: Chatterjee, Sankar. 1991. Philosophical Transactions of the
Royal Society of London B, Vol. 332, pp. 227-342. Used by permission of
the Royal Society of London and S. Chatterjee.
Struthiomimus from: Russell, D. A. 1972. Ostrich dinosaurs from the late John Alcock
Cretaceous of Western Canada. Canadian Journal of Earth Sciences
9:375-402. Courtesy of Dale Russell.

Millions of people love to identify birds, but few get the

opportunity to study and experience the pleasure of un-
derstanding bird behavior. Everything birds do—from
selecting nest sites and detecting elusive prey to the
squabbles among Black-capped Chickadees at bird feeders and the
migrations of massive flocks of shorebirds into and out of the High
Arctic—raises fascinating and challenging questions. Does a robin
hear the worms it captures, or see them? How can Yellow Warblers
be so naive as to devote themselves to the care and nourishment of
parasitic cowbird fledglings twice their size? Do Clark's Nutcrackers
remember where they stored hundreds of caches of pinyon nuts on
an Arizona mountainside? If so, how do they do it? Why does a male
Greater Prairie-Chicken spend hours stamping around in circles on a
little patch of prairie in the springtime? Why do bands of Mexican Jays
defend communal territories, even though only two members of the
group may get to breed there in a given year? Do gannets and other
seabirds breed in large colonies to protect themselves from predators,
or do these groups assemble for other reasons and actually attract
more predators?
We can ask endless questions of this sort, and behavioral biolo-
gists have begun to explore some of them.Th is chapter focuses on some
hi of the intriguing puzzles of bird behavior and how ornithologists have
tried to solve them.

Cornell Laboratonl of Ornithologq

6.2 John A lcock Chapter 6 — Understanding Bird Behavior 6.3
questions would ask about the long
Questions About Behavior history behind a car's design, which
■ In organizing our thinking about bird behavior, we can start by would help us to understand the
recognizing that all questions about behavior can be placed in just transformation of a horse-drawn
two fundamentally different but complementary categories. Let's illus- carriageto a steam-driven truck, and
trate this point by thinking about the many questions raised by a robin eventually to a modern sedan with
hunting worms, which it does by hopping across a lawn, stopping to an internal combustion engine.
cock its head to one side, and sometimes stabbing its beak downward, Because proximate questions
coming up with a worm that it pulls steadily out of its burrow (Fig. ask how things work in the imme-
6 1). How do robins locate worms? Can they see subtle visual cues
- diate sense, whereas evolutionary
made by worms moving at or near the surface of the ground? Or do questions ask how they got that
they hear worms sliding through way historically, the two kinds of
their underground tunnels? How questions (and their answers) com-
does the organization of the plement each other. To have a com-
robin's nervous system help it to plete picture of any animal's behavior, we must understand its internal Figure 6-2. Common Yellowthroat
stab accurately? Is the robin born operating rules and the forces that led species over time to evolve the Feeding a Brown-headed Cowbird
with the ability to identify worms special proximate mechanisms found in living individuals today. Fledgling: Why does this male Com-
mon Yellowthroat feed a fledgling that
as a delectable food? Are certain To reinforce this point, consider some possible proximate rea-
is so obviously (to us) bigger than itself,
robin genes key in developing sons why a pair of Yellow Warblers or other small songbirds "permit" and thus not its own young? Many pos-
worm-hunting behavior? Do rob- themselves to be exploited by a cowbird fledgling (Fig. 6 2). Maybe
- sible explanations exist, on both the
ins get better at worm hunting as the young cowbird has a certain appearance or makes certain sounds proximate and ultimate levels—and
they grow older, learning from each of these points of view contributes
that stimulate a parental response from the warbler. Or maybe war-
significantly to our understanding of
experience where to hunt, how to bler genes somehow guide the development of parental abilities that bird behavior. Photo courtesy of John
detect a victim, and how to grab it cowbirds exploit. These are proximate possibilities because they deal Gavin/CLO.
so that it doesn't get away? with what goes on inside a Yellow Warbler that might cause it to react
Every one of these questions to nestling cowbirds in a particular way.
Figure 6-1. American Robin Capturing deals with factors within robins, with the design of the birds' phys- On the evolutionary level, we could ask why cowbird "adop-
an Earthworm: A foraging robin hop- iological systems, which enable them to hunt worms in a particular tion" has persisted from generation to generation in Yellow Warblers.
ping across a lawn stops, cocks its head
way. In the jargon of behavioral biology, these questions are labeled Perhaps today's warblers received the hereditary basis for cowbird
to one side, and stabs downward with
its beak, sometimes coming up with a proximate because they are concerned with the immediate, internal adoption from their ancestors. It could be that the behaviors of war-
worm, which it pulls steadily up out of causes of the robin's response to worms. To use an automobile analogy, blers caring for cowbirds are so helpful for warblers rearing their own
its burrow, as shown here. Even an act a proximate question would ask how the car's engine causes the car to offspring that they have been maintained over evolutionary time, even
as simple as this raises many questions move down the highway. With animals, proximate questions require though they sometimes lead to victimization by cowbirds.
about behavior, but they all can be put
investigations into how the internal living "machinery" of the animal Knowing that immediate causes for individual actions and long-
into two major categories—proximate
and ultimate. See text for descriptions operates to give it certain special abilities. term evolutionary causes for species' characteristics both exist keeps
of these categories. Photo by A. Carey/ But let's say that we eventually figured out everything one could us from wasting time in mistaken arguments. Imagine, for example,
VIREO. know about how the robin's genes, developmental processes, and someone contending that a White-throated Sparrow's drive to defend
nervous system all function to help it hunt, kill, and eat worms. Our its territory is caused by high levels of the hormone testosterone in its
curiosity would not be completely satisfied because an entire battery bloodstream. If another person said, "No, no. The sparrow is territorial
of unanswered questions remains, questions about whythe robin pos- because it belongs to a species in which territorial individuals repro-
sessed these genes and not others, why it had its own particular array duced more than nonterritorial ones in the past," the debate would
of visual and acoustical abilities, and why it preferred some foods over be needless. The hormone hypothesis is proximate because it has to
others. For example, why are robins worm-hunting experts and not do with the immediate internal causes of the bird's territoriality; the
seed-eaters? What reproductive advantage does the worm-eati ng robin second hypothesis is evolutionary because it seeks to explain territorial
gain from its behavior? In other words, why has it evolvedto behave like drive as the long-term outcome of historical processes within the spe-
a robin and not like an Eastern Towhee or a cardinal? These questions cies. The two explanations are not mutually exclusive; they both could
require a long-term, evolutionary perspective that examines how the be right, in which case each would contribute to our understanding
history of the robin species has shaped its abilities and attributes. In of the behavior.
the lingo of behavioral biologists, these kinds of questions are labelled Another way to look at this issue is to recognize that evolutionary
evolutionary or ultimate. To return to our car analogy, evolutionary

Cornell Laboratorq orOmithologq Handbook of Bird BioloBq

 6.4 John Alcock Chapter 6— Understanding Bird Behavior 6.5
Willie-wagtails, and many other birds be so competent in so many
PROXIMATE DISCIPLINES ULTIMATE DISCIPLINES aspects of their behavior, yet make simple mistakes of this sort?
A proximate explanation for these "errors" is that the bird's
nervous system is designed to activate specific responses whenever
the bird detects certain simple cues in its environment. For a wagtail
Evolutionary Biology:
attacking a car mirror or a cardinal throwing itself at its reflection in
Behavioral Genetics —pp. Historical Pathways Leading a window, the key cues are apparently visual. Give a territorial male
Internal
to Behavioral Traits wagtail the right set of color cues and he switches into territorial de-
Mechanisms:
Genetic fense mode. Let a jackdaw see a black, dangling, jackdaw-sized object,
Functional Anatomy Developmental 1— Behavioral Ecology: and it activates the "attack the predator" response, even when it is
Hormonal Survival and Reproductive
Neural Value of Behavioral traits familiar with the animal holding the object.
Skeletal Therefore, if we see a pair of Yellow Warblers or some other
Physiology and Psychology Muscular
small passerines feeding a big brood parasite such as a cowbird, one
proximate explanation is that the cowbird provides the special visual
and acoustical cues that "turn on" the feeding response in parental
Developmental Biology: warblers and the like. These cues are examples of releasers, specific
Individual Maturation — ■
objects, physical features, or behaviors that activate (or "release") a
specific response in an individual. They also are present in young Yel-
••••••••
low Warblers, and usually stimulate parent birds to feed large, healthy
young of their own (Fig. 6-4).
This hypothesis, or tentative explanation, is based on the as-
Figure 6-3. Proximate Versus Ultimate explanations about behavior can tell us why a particular proximate sumption that as a Yellow Warbler matures, development of its ner-
Disciplines: The internal mechanisms mechanism, such as a hormonal system or neural network, happened vous system is controlled by an interaction between the bird's genes
underlying behavior (proximate mech- to spread through populations in the past.Th is past history of a species and its environment. (The term "environment" is used here to embrace
anisms) are investigated by different bi-
ological disciplines than those that focus
determines its current internal machinery, and thus in this sense, the everything from the foods the bird eats, which provide the molecular
on the evolutionary basis of behavioral two levels of explanation in biology are linked together. building blocks for its growing nervous system, to the bird's various
traits (ultimate mechanisms). sensory experiences, some of which can influence the development of
certain neural circuits.) Asa result, a Yel low Warbler's nervous system
The Proximate Basis of Bird Behavior has particular components designed to detect key stimuli (for example,
• The fact that proximate and ultimate approaches complement each the begging calls of nestlings) and activate specific responses to those
stimuli (for example, placing food in the mouth of the begging bird).
other is reflected in the different disciplines that explore these two
6 levels of research in behavioral biology (Fig. 6-3). Remember that The "releaser-activated response" hypothesis has been tested for
both approaches are required for a total picture of the causes of any some birds in the following way. If the hypothesis is correct, it follows
behavioral trait. logically that when an experimenter presents the right stimuli, the
To illustrate some interesting proximate puzzles about bird bird will produce the specialized response. For example, Lars von
behavior, consider the many seemingly "unintelligent" things that Haartman (1953) predicted that the begging calls of the European Pied
birds do. In Australia, I was amused on several occasions to see a Wil- Flycatcher were releasers that caused the parents to feed the young. To
lie-wagtail, a small black-and-white bird, assaulting his image in the test his prediction, he placed several hungry nestling flycatchers out
side-view mirror of my van. The bird fluttered in front of the mirror, of sight behind the wall of a nest box that held a pair of parent birds
launching peck after peck at the reflective surface before flying up to and their offspring.The parents fed their own brood until they were full
land on it. He would remain calm for a moment, but if he bent down and had stopped calling. But the hungry hidden youngsters continued
far enough to catch a glimpse of himself, he went off in another par- to beg, and the adults continued to bring food to their silent, gorged
oxysm of senseless rage, even though the mirror did not respond like offspring. Clearly, the acoustical cue provided by begging youngsters
a live rival wagtail. stimulated parental feeding behavior, a conclusion supported by re-
Similarly, Konrad Lorenz (1952) reports in his wonderful book, cent additional work with the European Pied Flycatcher (Ottosson et
King Solomon's Ring (see Suggested Readings), that a band of jack- al. 1997).
daws, members of the crow family, went berserk when they saw him The next question is whether the flycatcher's response to the
carrying a pair of black bathingtrunks in his hand. Although these birds begging calls of nestlings is instinctive. An instinctive (or "innate")
normally seemed to trust him thoroughly, on this occasion the whole behavior is one that is triggered in full form, without any learning, the
flock attacked him, filling the air with alarm cries. How can jackdaws, first time an individual responds to the releaser. A human infant, for

Cornell Laboratorq of Ornithologq Handbook of Bird Biology

6.6
Figure 6-4. Begging Fledgling and Adult
Northern Cardinal: Begging birds,
whether juvenile or adult, provide vi-
John Alcock r Chapter 6— Understanding Bird Behavior

Ethologq, Ornithologq, and Instincts

The study of instincts in birds and other animals was of particular
6.7

sual and acoustic cues that stimulate interest to the early ethologists, a group of European biologists who,
feeding by another individual. These
beginning in the 1930s, developed the scientific study of animal be-
cues are examples of releasers. a. Beg-
ging Fledgling: A Northern Cardinal havior into a flourishing discipline. Unlike American psychologists
fledgling (left), begging to be fed by its interested in animal behavior, who focused primarily on laboratory
parent, crouches open-billed, fluttering studies of domesticated rats and mice, the ethologists emphasized
its wings and calling persistently. Beg- field studies of species ranging from insects to free-ranging birds. Niko
ging postures, releasers for adult feeding
Tinbergen and Konrad Lorenz pioneered the field, and described their
of young, are so similar among birds that
sometimes adults may be stimulated to research in some wonderfully written books for the public (see Sug-
feed young of the "wrong" species (see gested Readings). The importance of their work was eventually recog-
Fig. 8-103). A range of stimuli may trig- nized when they received the Nobel Prize in Medicine in 1973.
ger begging: calls from the parents, sight
Although the study of animal behavior has changed a great
of a parent or other object above the nest,
vibrations of the nest (as when a parent deal since the era of Tinbergen and Lorenz, their tests of the instinct
lands), darkening of the nest hole (in hypothesis are still admirably instructive and useful. For example, Tin-
a. Begging Fledgling
cavity nesters, as when an adult blocks bergen and his co-workers proposed that the gaping behavior of hun-
incoming light by appearing at the nest gry nestling Eurasian Blackbirds was released by very simple stimuli.
entrance), or even air currents (in hum-
Through a series of experiments with eight-day-old birds whose eyes
mingbirds and Chimney Swifts, as from
the motion of adults arriving at the nest). had just opened, Tinbergen established that anyobject that (1) moved,
Photo by Marie Read b. Courtship Feed- (2) had a vaguely bill-shaped projection at least 0.12 inches (3 mm)
ing: An adult female Northern Cardinal wide, and (3) was above the head of the nestling, would elicit the beg-
begs from her mate during courtship.
ging response, even if the object had a most imperfect resemblance to
In many birds the female begs to her
mate using postures and calls similar to a living, three-dimensional adult (Tinbergen 1951) (Fig. 6-5).
those of begging young, stimulating him Likewise, Tinbergen and Lorenz showed that an incubating adult
to feed her. The function of this ritual- Greylag Goose would retrieve almost any round object, even one
ized courtship feeding, which occurs
vastly larger than a Greylag egg, that was placed outside its nest. It did
only during courtship and incubation,
remains a matter of some speculation.
so by extending its neck, placing the bill on the outer side of the "egg,"
Traditionally, researchers have thought and rolling it carefully back into the nest.
courtship feeding in many species
strengthened the pair bond, rather than
provided nutrients to the female—es- b. Courtship Feeding
Moving Above Nestling's Head —4. Begging Figure 6-5. Characteristics of Begging
pecially because some females beg at
Not Moving —4. No Begging go Releaser in Nestling Eurasian Black-
bird feeders or when their bills are full of
birds: Tinbergen and his co-workers

9 f
food. But increasing evidence suggests example, will smile instinctively at another human face (or even at a presented objects of various shapes
that the food may, indeed, improve the releaser as simple as two dark spots drawn on a white circle), and will to nestling Eurasian Blackbirds whose
female's condition (see Fig. 8-100).
grasp tightly with its hand when it feels something touching its palm. eyes had just opened, in an experiment
Furthermore, in some species the male's
To determine whether the flycatcher's response is instinctive, it would k----- to determine which characteristics of
competence in courtship feeding may
the objects were necessary to activate
allow the female to gauge his ability to be helpful to perform von Haartman's experiment on adults nesting the nestling begging response. They
provide food for the young—if he's not for the first time. If inexperienced parents fed their young when they discovered that any object that moved,
good enough, she may reject him as a
heard begging calls, one could claim with some confidence that these had an approximately bill-shaped and
mate! In Common Terns, for example,
vocalizations were an innate releaser of parental feeding behavior in Moving Below bill-sized projection, and was above the
males who bring more food during
Nestling's Head —I, No Begging head of the nestling, would elicit beg-
courtship are better at feeding their this species.
ging (Tinbergen 1951).
young later in the season. If a begging call also prompts instinctive feeding in Yellow
Warblers, the feeding response of adults hosting a cowbird can be
explained in part, at the proximate level, as an innate reaction to the
begging calls of the nestling cowbird, which resemble those of nestling
warblers closely enough to release parental feeding behavior. Later we
will explore the ultimate bases of the intriguing relationship between
cowbirds and their hosts.

Cornell Laboratorq of Ornithologg Handbook of Bird Biologt

 6.8 John AIcock Chapter 6 — Understanding Bird Behavior 6.9
In these and other cases in which the instinct hypothesis was con- many potential food items, but
firmed, the ethologists demonstrated that the animal was responding to after eating a single poisonous
only a fraction of the available stimuli, and that simple cues (releasers) monarch butterfly, and vomiting
seemed to turn on a particular response. The ethologists called this the noxious prey, they learn to
response a fixed action pattern (FAP). FAPs are behaviors that are touch them no more (Brower
played out in complete form even the first time the animal encounters 1969) (Fig. 6-7). Likewise,
and reacts to the releasing stimulus. Baby thrushes do not need to learn fledgling male White-crowned
through experience what objects to beg from. Likewise, right from the Sparrows learn their species'
start, fledgl i ngTu rquoise-browed Motmots do not need to handle coral full song by listening to adult
snakes to learn to avoid this potentially lethal "prey;" motmots have an males. Prevent a young male
innate avoidance response to long, thin objects with the coral snake from hearing his species' song
color pattern (Smith 1975) (Fig. 6-6). and he never will sing a typical
song when he becomes an adult
(see Ch. 7, Vocal Development in
Learned Behavior
Songbirds).
Although many bird behaviors appear to be programmed reac-
Note that to learn anything,
tions to releaser stimuli, many other responses seem to be learned.
a Blue Jay or White-crowned
Learning can be defined as behavior modification resulting from par-
Sparrow must have an innate capacity to develop the circuits where Figure 6-7. Captive Blue lay Learns
ticular experiences. For instance, captive Blue Jays will sample a great to Avoid Poisonous Prey: Captive Blue
the bird stores information from certain experiences, information that it
Jays will sample any likely food item
later uses to modify its behavior.Thus, the distinction between instincts
including the monarch butterfly, which
and learning is not that one depends on genes and the other does not, contains toxic and distasteful substanc-
or that one requires special features within the nervous system and the es. Eating a monarch causes the BlueJay
other does not. Indeed, they both require genetic information, and they to vomit soon after its meal, and from
Hand-reared Turquoise-browed Motmot
both occur because of special elements within the nervous system. But this single negative experience the jay
immediately learns to avoid this but-
instincts (FAPs) depend on neural components that can recognize key
terfly species forever. Photos by Lincoln
releaser stimuli (such as the cues provided by a begging nestling) and P Brower.
turn on an "automatic" response. Learning, on the other hand, depends
on neural units that store information from certain experiences (such
as the nausea associated with eating monarch butterflies), enabling the
animal to modify its behavior on the basis of that stored information
Wooden l'OrroL 9 9 .". A.
4 Will- -1 101 , (Table 6-1).
Models
0 Pecks 89 Pecks 60 Pecks 79 Pecks 90 Pecks
6
(only 15% directed (47% directed at
at patterned end) patterned end)
KEY Table 6-1. Instinctive Versus Learned Behavior
Red and Yellow Rings *
Instinctive Behavior Learned Behavior
Green and Blue Rings
Development of Responds fully the first Requires previous exposure
Red and Yellow Stripes
Response time a relevant stimulus to stimulus before
* This Pattern is Closest to the Coral Snake Pattern
is encountered. responding fully.
Requirement for Requires key releaser Requires stimulus and memory
Coral Snake Response stimulus. of past experience.
(Color Pattern is Red, Yellow, and Black Rings)
Physiology of Ability to recognize Ability to assimilate and
Figure 6-6. Turquoise-browed Motmot with Snake Models: Motmots, spatulate-tailed relatives of kingfishers, inhabit Central and
Response stimulus and respond. store information, and to respond.
South America where snakes make up part of their natural diet. Hand-reared young Turquoise-browed Motmots in a laboratory
setting were presented with thin, wooden models about 3.2 inches (8 cm) long, painted in various colors and patterns. Curious and Human Example Baby grasps when pressure Baby learns to reach out and
exploratory birds, they investigated these potential food items by pecking at them. Yet despite having had no previous experience is applied to palm of hand. grasp an object it wants.
with snakes, the laboratory motmotsspecifical ly avoided the model with red and yellow rings, the one that most closely resembled
a coral snake (which actually has red, yellow, and black rings), giving it no pecks, although they pecked numerous times at all Avian Example Nestlings beg for food when Young birds learn to avoid non-
the other models with different color and pattern combinations. Notice, however, the model with one end ringed red and yellow adults land on edge of nest. palatable prey, such as monarch
and the other plain: the motmots pecked much less frequently at the ringed end. These results suggest that the Turquoise-browed butterflies, through trial and error.
Motmot has an innate avoidance response to objects resembling the poisonous coral snake (Smith, 1975).

Cornell Laboratory of Ornithology Handbook of Bird Biology

 r
6.10 John Alcock Chapter 6— Understanding Bird Behavior 6 11
The simplest type of learning is habitu-
a. Woodpecker Finch
ation, the permanent loss of a response as a
result of repeated stimulation without reward hbJ
or punishment—in other words, learning to
ignore unimportant stimul i. Even young birds
in the nest learn by habituation. If you tap
lightly on the side of a nest when the young
still have their eyes closed, they raise their
heads and open their mouths wide: in their
small world, a light tap means food. If you
repeat the tapping without giving the young
any food, they eventually stop responding;
b. Green Heron
they have become habituated to the stimulus.
Birds that routinely feed along the side of a
road habituate to passing cars by learning not
to fly up each time a car goes by. Habituation
is clearly adaptive because it saves time and
Figure 6-8. Turkey Chicks Habituate energy, and allows an individual to concentrate on more important
to Moving Objects Overhead: a. Young stimuli. After putting on your clothes, you quickly habituate to the feel
turkey chicks crouch in response to all
of their touch. If you were aware of each brush of fabric against your
objects moving overhead, from falling
leaves to large flying birds. b. Older, skin, you would have trouble noticing other, more important stimuli
more experienced chicks soon habituate around you (Fig. 6 8).
-

to falling leaves and cease crouching Another type of learning is trial and error, in which a bird learns
whenever one flutters down. Because c. New Caledonian Crow
to associate its own behaviors with a reward or punishment. Behaviors
large flying birds are rare and may
represent real danger, young turkeys
that result in reward are repeated, and others are abandoned. Just as
never habituate to them and continue captive Blue Jays learn to avoid eating monarch butterflies, the diets
Hooked-twig
to respond by crouching. Drawing by of recent fledglings are influenced by trial-and-error learning. While Tool
Charles L. Ripper. a fledgling still depends on its parents for food, it moves about peck-
ing at small objects—pebbles, leaves, anything that contrasts with the
background (Fig. 6 9). Eventually it finds an insect and eats it. Once
-

the bird has tasted the insect reward, it pecks more carefully, soon
associating a food reward with a certain class of objects. Over time it
learns what to peck, what not to peck, and which items to eat. Birds
learn to visit bird feeders and eat foods they might never see in the wild Stepped-cut Tool Cut From Pandanus sp. Leaf
through trial and error. Hummingbirds learn that the color red usually
provides profuse nectar (since the flowers that have evolved to attract
and reward them as pollinators are most often red), so they readily visit
hummingbird feeders adorned with red. Tool use (Fig. 6 10) probably
-
Figure 6-10. Tool Use in Birds: Using tools was once considered abilities of the New Caledonian Crow are putting even that
results from a type of learning similar to trial and error. an exclusively human trait, but we now know that over 30 spe- notion to rest. Hunt (1996) discovered that these crows, from
cies of birds as well as some chimpanzees use tools. One of the the South Pacific islands of New Caledonia, make and use two
Galapagos finches, the Woodpecker Finch, picks up a cactus distinctly different types of tools (c). One, a hooked-twig tool, is
spine and uses it as a tool for extracting insects and larvae from made by stripping the leaves and usually bark from a living twig,
Figure 6-9. American Robin Fledgling holes in trees (a). Similarly, the Brown-headed Nuthatch of the leaving a small portion of intersecting twig to form a distinct
Pecking at a Leaf: Newly fledged robins eastern United States uses pieces of bark to probe into holes for hook at one end. The other, a stepped-cut tool, is made by biting
develop their diet through trial-and-error food. Some herons, such as the Green Heron (b), have learned a long, jagged piece from the toothed leaves of the Pandanus
learning, pecking at any items that stand to drop insects, leaves, berries, twigs, feathers, or whatever else plant to form a tapered, spined, probe. Both are used to pull
out from the background, such as leaves they can find into the water to lure fish within striking distance insects and worms out of holes in trees and dead wood. The
and pebbles. When they eventually (Higuchi 1987). And the Egyptian Vulture actually picks up crows carry their tools from site to site as they search for food,
find something edible, they associate large stones in its bill and throws them at Ostrich eggs to break and may even stash them in a safe place for a while, returning
the food reward with the item's charac- the shell and get to the tasty insides. later to use them again. Drawing a by Robert Gi Ilmor; drawings
teristics, and overtime refine thei r search More recently, people pointed to the making of standard- in c by Liz Grant/Massey University.
for food to certain types of items. ized tools as a uniquely human skill, but the newly discovered

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 ▪

6.12 John Alcock Chapter 6— Understandin5 Bird Behavior 6.13

Learning plays a role in many different aspects of bird behavior, the birds hid pine seeds taken from a feeder in the room. After letting
from the trial and error that shapes the diet of some species, to the a number of birds cache seeds in about 20 cups, the nutcrackers were
special effect of acoustical experience on singing, and to the effects of ushered out of the room into holding cages elsewhere. Then, between
imprinting, a special form of early learning in which a young animal 11 and 285 days (more than nine months!) later, the nutcrackers were
quickly acquires specific information for certain experiences. For allowed to reenter the room when they were hungry. The 20 or so cups
example, Konrad Lorenz's famous experiments with Greylag Geese in which they had cached food each contained one pine seed; the 300-
demonstrated that recently hatched goslings rapidly learned what to plus cups in which they had not cached food contained only sand. If
follow on the basis of certain experiences in their first few hours of life the birds remembered where they had stored their caches, they should
outside the egg (Lorenz 1970). Usually, of course, goslings see and hear have been able to find the hidden seeds more quickly than if they hunted
their mother; when she moves off the nest, the youngsters fol low, having randomly through the hundreds of sand-filled cups.
imprinted on this moving, calling object. If Lorenz took the place of a
Clark's Nutcracker Food-caching Experiment Figure 6-13. Layout of "Food-caching"
parent goose at that time, however, the youngsters walked after him,
Room: Balda and Kamil (1992) built an
learning through their special experience with Lorenz that he was the A BCD E F G H I J K L M N O experimental room to test the extent of
individual to associate with and follow (Fig. 6 11). 1 o 0 I 0 0 0 O 0 0 0 0 0 0 0
••al
0 long-term spatial memory in the Clark's
•• MK
- .

2
8 ‘ Nutcracker. 330 holes in the plywood
Even more amazing, when the geese in these experiments reached 0 o 0 O 0 0 . 0 0 0 0 0
sexual maturity, the males courted human beings rather than members 3
0
• 0
4
0 O 0 0 0 0, 0 0 0
floor held sand-filled cups. The room
o 0 0 • 0 o contained numerous potential land-
I • • •
of their own species. Here the particular experiences that goslings had marks—rocks, boards, and bricks—
while following a moving companion led to imprinting on a parental
4 o l e 0 0 0 0 0 0 O 0 0 0 0 0 0 0
•y NI IV scattered around the floor, as well as
figure andto sexual imprinting, with early experience determining their 5 o o 'o 6' -0000 0 0 0 0• 0 0 perches, and a feeder filled with pine
-I I
adult mate preferences. 6 0 0 0 0 0 0 0 seeds. Individual nutcrackers were set
o olo, 0 0 0 o o O
loose in the room and permitted to cache
Figure 6-11. Greylag Goose Goslings Another form of specialized learning has been explored by Russell 7 o s o
Imprinted on Konrad Lorenz: Young
birds rapidly learn to follow the first
Balda and Alan Kamil (1992) in their studies of spatial learning(learning
the location of objects in space) by Clark's Nutcrackers (Fig. 6 12). In
8 o o0
o o

o
• O

O
Q
•
0 0 0 0 0 0 0 0

/0 0 0 0 0 0 0 0
4,
0
seeds in the sand-filled cups of their
choice. Each bird was then removed
for lengths of time varying from 11 to
moving object they encounter in their - t
post-hatching experience—an example
of the special form of early learning
nature these birds are unusual in caching supplies of pinyon pine nuts in
holes in the ground, to which they may return months later. Do the birds
9

10 o
o 0

0 •
0

0 0 0 0 0
0 --- O / 0
O
a •
0 0 0 0
o
il
o

O
• o

0
0

0
285 days before being brought back to
the room (now feederless) in which the
known as imprinting. Usually, of course, 1 bird's cached seeds remained. The birds
actually remember where they hid food, or do they just poke around 11 o 0 0 0 .0 0 0 0 0 O 0 0 0 0 0 found seeds with far fewer probings of
this object is the parent bird, but if a hu-
in likely places for seeds that they or some other birds might have put •
dui f
• the cups than expected by chance alone,
man takes its place, the young birds will
imprint upon the human and follow away for a hungry day? Testing these alternatives would be difficult in 12
1111i •
• suggesting that they remembered where
o \o 0 0 0 0 lo 0 0 0
•
0 0 0 0 0 they had hidden their food even after
the field, but laboratory experiments can test whether the birds learn
him or her as they would their parent,
as ethologist Konrad Lorenz discovered precisely where they hid their food caches.
13
o 10 .4 0
•
0 0 0 0 0 0 O 0 0 0 0 0 several months had elapsed. Diagram
in his classic experiments with Greylag 14
• • • courtesy of Russell P Balda.
Balda and Kamil built a "food-caching room" with 330 holes in o 0 0 O 0 0 0 0 O 0 0 0 0
Geese. Photo by Thomas McAvoy/Life • • 0 5
6 Magazine, copyright Time Inc.
the plywood floor scattered among tree limbs, rocks, and other po- 15
o ol 0 O 1 0 0 O oc O 0 0 0 0 0 6
tential landmarks (Fig. 6 13). The holes held sand-filled cups in which
-
16
■ •
0 0 0 0 O 0 0 O 0 0 0 0 0
o
• 04 •
17 0 0 0 0 0 0 O 0 0 0 0 01 0 0 0
• •
18 o 0 0 0 0 • 0
•
O 0 0 % 8- 0_20 0 0
•
19 O 00 . 0 0 0 0 0 0 0 o o \o 0
f 0
20 o 0 0% 0 0 0 o o. 0 o o

21
•
o o o 0 0 0 0 o o O o o o
1 •
22 O o o 0 0 0 0 0 0 o o o o o o
Figure 6-12. Captive Clark's Nutcracker
Caches a Pine Seed in a Sand-filled Cup:
In the wild this species caches pinyon Floor Plan of Experimental Room
nuts and other seeds in holes in the
ground, depending on these stores as a
major source of food in the winter. The KEY
fact that individuals seem to remember Food-caching Site (Sand-filled Cup)
0
the location of their sites has led to
experiments investigating their spatial f Di ♦ Landmarks (Rocks, Boards, Bricks, etc.)
memory capabilities. Photo courtesy of
Russell P Balda. — — — Perch

Cornell Laboratorq of OrnitholoBq Handbook of Bird Bioloo4

6.14 John A Icock Chapter 6 — Understanding Bird Behavior 6.15
motmot avoiding a coral snake) appears fully developed the first time
that the individual reacts to a particular releaser in its environment.
Many people mistakenly believe that instincts are somehow
more "genetic" or "hereditary" than learned behaviors. But whether
instinctive or learned, all of a bird's actions are caused by its nervous
system, which is in turn the developmental product of an extraordi-
narily complex interaction between the individual's genetic informa-
tion and the environment in which development occurs. Food from
the environment helps build the nervous system. Moreover, the envi-
ronment is the source of key experiences stored in the bird's memory.
To learn a song, to have the capacity to imprint on a moving parent, to
Figure 6-14. Captive Common Raven When tested, most of the nutcrackers did indeed find seeds with remember the appearance of rewarding and punishing foods, to learn
Retrieves a Suspended Piece of Meat: far fewer probing inspections of cups than expected by chance alone. anything at all, requires a nervous system with specialized properties.
When Bernd Heinrich (1995) tied a These design features could not develop without genetic input.
For example, "Karl" investigated 69 cups, relocating 15 of those he
chunk of meat to the end of a long string
had used to make caches six months previously; had he been hunting By the same token, an innate response to a releaser depends
and dangled it from a perch in his aviary,
some Common Ravens were able to re- randomly, he would have been expected to find just four of his caches on neural components that "recognize" key stimuli and activate the
trieve the piece of meat in the following in 69 tries. The shorter the interval between caching and recovery, the appropriate response. The neural units in question could not have
way: they reached down and grasped the developed without environmental input. Traditionally, debates have
better the birds usually did, but even when many months had elapsed,
string in their beak, pulled the string up,
the nutcrackers used their long-term spatial memory to relocate their raged among behaviorists and psychologists over dividing behaviors
and then clamped the retrieved section
of stri ng to the perch with their foot, while cache sites remarkably well. into "genetic" ("nature") versus "environn mental" ("nurture"); but
retrieving another section of string. They Finally, we can ask if some birds possess what has been called dividing behavior in this way makes no sense. Furthermore, many be-
repeated this sequence until the meat insight learning, modification of behavior that occurs without pre- havioral actions almost certainly represent a combination of instincts
was within reach of their bill. The fact
vious experience with a particular problem. Although humans can and learning, with animals storing feedback information from innate
that the ravens were able to solve this
complex problem on their first try, with occasionally think up solutions to novel problems (how to build a responses, and learning from experience to modify their original in-
no similar previous experience, suggests certain machine, how to repair a defective device), the possession of stinctive actions. (Sidebar 2: Play)
that they studied the situation and used analogous abilities by any bird is a matter of debate. Perhaps the most
insight to solve the problem, rather than
convincing avian example uncovered to date involves the capacity of
trial and error. Photos courtesy of Bernd
Heinrich.
some, but not all, ravens to reach a chunk of meat suspended at the Ultimate Causes of Bird Behavior
end of a long string that Bernd Heinrich had tied to a perch in their ■ Now let us turn from proximate to ultimate causation in behavior.
aviary (Heinrich 1995) (Fig. 6-1 4). The ravens that appeared to exhibit We can explain a young motmot's reluctance to pick up thin objects
insight "studied" the situation for a time, then reached down, grasped banded red, yellow, and black as an instinctive response to a particular
the string in their beaks, pulled the string up, and clamped it to the releaser. This process is mediated by proximate mechanisms in the
perch with their feet, repeating the sequence until they could reach the bird's body—the genetic information that guided the development of a
meat. Some ravens could perform this task on their first try, convincing nervous system that could detect the releaser and order the avoidance
Heinrich that they used insight to recognize how to get a meal, then reaction. But this proximate explanation does not explain why living
carried out the necessary actions without trial-and-error practice, even motmots evolved their special behavioral abilities. All living things
though they could not have practiced similar behaviors in the wild have an evolutionary history, so knowing how behavior has changed
before they were captured. (Sidebar 1: Bird Brains) over many generations provides an avenue for understanding why
living species behave the way they do.
A Comparison of Instincts and Learning In the case of the motmot, which preys on many small snakes, it
seems likely that in the past those individuals who lacked an innate
In summary, both genes and environment play vital, albeit dif-
ferent, roles in developing nervous systems whose operating rules avoidance response for thin, black-yellow-and-red-banded objects
would have been tempted to pick up coral snakes. Although edible,
may permit learned responses to some stimuli and innate responses
to others. Learned behavior (with the exception of insight learning) coral snakes have extremely dangerous venom. If coral snake at-
differs from innate behavior in that it requires specific experiences tackers died young compared to those who had an innate aversion
to the coral snake pattern, the genes of attackers would have had less
to develop fully. Individuals with the ability to learn do so by storing
information from key experiences and using it to modify their behavior chance of being passed on to offspring than the genes of avoiders. If
accordingly—as when Blue Jays learn to avoid bad-tasting butterflies this process continued generation after generation, eventually only
after eating one. In contrast, an instinctive response (for example, a (Continued on p. 6.22)

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 6.16 John Alcock Chapter 6 — Understanding Bird Behavior 6.17

tasty and green indicates unripe and bitter, and therefore ferent attributes shows that he does not respond rotely to
Sidebar 1: BIRD BRAINS choose the red fruit. The second is the more complicated a particular object and, furthermore, that he understands
Irene Pepperberg ability to choose, from among many sets of acquired how attribute labels themselves are categorized (such as
information, the set appropriate to the current problem; red and blue under "color"). Alex's competence in this
"Bye.You be good. I'm gonna go eat dinner. that is, to recognize conditions under which the selection task is comparable to that of a chimpanzee.
I'll see you tomorrow." I hear these words of green fruit might be wise (for example, when red in- Alex also understands more complicated categorical
most nights as I leave my laboratory. Such dicates spoilage). An organism limited to the first ability questions. Shown a tray of seven different items, he an-
utterances would not be surprising were has learned some important associations, but lacks the swers questions such as "What color is item X?" or "What
they to come from the lips of my students, flexibility that is a hallmark of intelligence. object is shape A?" Moreover, if several items are, say,
but they come from a beak—that of my Initially, tasks to determine whether nonhumans have blue and several are square, but only one has both attri-
research subject, a Grey Parrot (Fig. A). these abilities were based on human intelligence and butes, he can correctly answer questions such as "What
Alex, who is over 20 years old, shares sensory systems, as in the pigeon study described earlier. object is blue and square?" On both types of tasks, Alex
the laboratory with two other Grey Parrots, But such designs may put nonhumans at a disadvantage: is as accurate as dolphins and sea lions.
five-year-old Kyaaro and one-year-old wild pigeons do not peck colored lights for food. To give
Griffin. For several hours each day these a reverse analogy, a bird testing human abilities might Birds Understand Concepts of
birds interact freely with each other and assess how well singing by men attracted mates and kept "Same" and "Different"
their human caretakers, requesting toys, intruders out; with perhaps a few exceptions, the bird "Same" and "different" are not merely forms of cat-
food treats, and tickles. But they spend would conclude that humans were not very competent. egorization (knowing that A "fits with" A and not with
most of their time "in class," as the focus Some researchers, therefore, try to design tasks that not B). To understand these concepts you must understand
of research to examine their intelligence only are based on human criteria but that also are rel- that two nonidentical blue things are related in the same
and communicative abilities. evant to an animal's ecology and physiology. Scientists way as are two nonidentical green things—in terms of
The birds and researchers commu- FigureA. Grey Parrot, Alex, with Irene Pepperberg: Dr. Pepperberg showsAlex now test avian spatial memory, for instance, by allowing color—and also know that the blue things are related to
two items of a similar material (wood) but with different shapes (one is two-
nicate vocally, using English speech. Alex birds to hide and recover seeds in semi-natural settings. each other in a different way than are two nonidentical
cornered (football-shaped], the other, five-cornered). Alex's ability to correctly
in particular understands many labels Although researchers can strive to make tasks more spe- square things. In other words, you must recognize which
answer the question "What's the same?" about the objects suggests that he can
and how to use them in a limited manner. categorize objects in complex ways. Experiments exploring parrots' conceptual cies-relevant, these tasks wi II always have to be evaluated categories of attributes are the same and different, and
When you say "What color is the key?" understanding, numerical competence, and communication skills conclude from the standpoint of human sensory systems and per- more importantly, you must understand how relation-
for example, Alex knows to describe the that birds have more advanced mental capacities than formerly thought. Photo ceptions of intelligence: this obstacle is one that humans ships within pairs are related to relationships between
key in a particular way, even though he courtesy of David Linden. can't surmount. pairs. Such understanding requires complex information
doesn't understand what keys are for. For Another problem in determining the "intelligence" of processing.
him, keys are head-scratchers. He can identify over 50 "match") earned the bird a food reward. Scientists deter- birds is that avian abilities differ across species. Migrating Until my work with Alex, few people believed that
items, including paper, truck, cork, block, chain, gravel, mined how many trials the pigeon needed to learn such birds will probably outperform other species on orientation birds could understand "same" and "different." Natural
cup, chair, chalk, foods, and water; seven basic colors; a task, and how many additional trials it needed to learn tasks, whereas songbirds with large repertoires will prob- behaviors such as song matching and individual recog-
and five different shapes, which he designates as two-, to reverse itself (that is, peck green) if red was no longer ably have better auditory discrimination. Although using nition (see Chapter 7) require sorting into categories of
three-, four-, five-, or six-corner. (Two-corner items look rewarded. In such studies, particularly the reversals, different tasks for different species precludes exact cross- "same" versus "different," but do not demonstrate (to hu-
like minifootbal Is.) Alex also uses and responds correctly pigeons needed many more trials to learn than did species comparisons, such an approach demonstrates the mans) that a bird truly understands what characteristics
6
to "no" and "come here," and effectively uses phrases mammals. Then in the 1970s the aptly named "cognitive range of avian capacities. The following is a small sample are the same or different. Accordingly, researchers must
such as "I want [objectl" and "wan na go [location]." He revolution" proposed that levels and types of intelligence of the diverse experiments on avian intelligence. design special tasks to demonstrate such abilities. On
learns by watching students demonstrate the meaning of in other species formed a continuum with those of hu- these tasks, Alex, like chimpanzees, shows he under-
labels or questions—he sees them rewarded for correct mans, and inspired researchers to study a wider range of Birds Categorize Objects stands "same" and "different" and their absence. He does
responses and scolded for errors. After correctly identi- species and types of learning. Scientists, accustomed to Categorization is how we divide the world into de- not simply state whether objects are identical. Queried
fying or responding to a question about an object, Alex working with primates, adapted their field and laboratory finable bins. Clearly, wild birds must categorize items to "What's same?" or "What's different?" about any two ob-
can play with it; this procedure helps him firmly associate projects for use with various avian species, and data on survive: food/not-food, predator/not-predator, shelter/ jects, even those he has never seen before, he states which
the object with its label. the advanced capacities of birds began to emerge. not-shelter, mate/not-mate, my species/other species. attribute ("color," "material," or "shape") is the same or
Alex's abilities startled the scientific community; tradi- The cognitive revolution, which inaugurated an ex- In the lab, pigeons learn to differentiate slides that show different, or "none" if no attribute is the same or different.
tionally, people assumed that mammals were the smart- traordinary era of study, raised three crucial questions: natural stimuli (trees, people) from slides that do not, Pigeons do not seem able to accomplish similar tasks.
est creatures. Until the 1970s, however, we knew little First, what actually is intelligence? Second, can we judge even when shown slides they haven't seen before.
about avian intelligence. A few experimenters had shown nonhuman capacities using human tasks and definitions? Some bird species may be limited to dividing the Birds Have Advanced Numerical Capacities
that parrots and canaries could learn tasks such as dis- Third, how do we fairly test creatures with different sen- world into "target" and "other" categories, but for my Birds are sensitive to quantity. Eurasian Blackbirds,
tinguishing a three-item set from collections containing sory systems from ours? These questions have not been Grey Parrot, at least, categorization is more complex. His wood-pewees, and cardueline finches, for example, ap-
other quantities, but most researchers concentrated on answered to anyone's complete satisfaction, but ongoing appropriate responses to "What color?," "What shape?," parently respond in different ways depending upon the
pigeons and topics such as "delayed match-to-sample." studies provide some preliminary suggestions. and "What matter?" for a green triangle made of wood, number of times a neighbor repeats certain vocalizations.
In a typical delayed match-to-sample experiment, re- Intelligence probably requires two abilities. The first for example, show he knows that "green," "three-corner," In lab experiments, canaries can select a three-item set
searchers trained a pigeon to peck a red light to start a is simply the ability to use experience to solve current and ','wood" represent instances of different categories; from a variety of sets containing other quantities; choose
trial. After a delay of several seconds, the pigeon had problems. A Cedar Waxwing faced with green and red he is not simply sorting "green" from "not-green." In- the second, third, or fourth object in a group; or eat a
to choose between red and green lights; pecking red (a fruits, for instance, might recall that red indicates ripe and stead, his flexibility in categorizing the same item by dif- specified number of seeds. Pigeons discriminate "more"

Cornell Laboratorg of Ornitholojg Handbook of Bird Bioloti

 6.18 John A (cock Chapter 6 — Understanding Bird Behavior 6.19
versus "less." Shown "n" objects, some birds can pick a have been based on remembering patterns of rewards.
set of "n" other objects from a choice of several numerical Further study is necessary to determine how well birds
Sidebar 2: PLAY
arrays. Grey Parrots, ravens, and jackdaws succeeded understand transitive inference. Sandi,/ Podulka
for quantities up to eight, pigeons for five or six, and
chickens, two or three. Some corvids and parrots also Birds Have Sophisticated Communication Skills
Kittens play. Puppies play. Young young animals to practice and hone few of its components are restricted
learned to "add" items until they achieved the designated Communication provides insights into avian intelli-
otters, foxes, and raccoons play. their skills before mistakes become a exclusively to play. Nevertheless, the
quantity: birds would open boxes containing zero, one, gence. Mockingbirds and Brown Thrashers, for example,
But do young birds truly play? A matter of life and death. context and sequence of actions can
or two seeds until they reached, for example, four if the sing hundreds of different songs, which suggests exten-
kitten pouncing on a ball of yarn Early researchers tended to label provide hints that an animal is play-
boxes were red, or six if the boxes were black. To perform sive learning and memory. Some birds seem sensitive to
is not much different from a young as "play" any behavior that seemed ing. For example, corvids (crows,
this task they also had to understand that colors could the importance of serial order. Common Nightingales
screech-owl pouncing on a wind- to serve no immediate purpose, jackdaws, ravens, and related spe-
represent numbers (for example, "red" meant "four"). can acquire strings of over 60 songs by "chunking" the
blown leaf or a young Peregrine but more recent observations have cies) use rising air currents to help
Alex can vocally label groups of up to six items, and can tutors' strings into packages of 3 to 7 songs; they main-
Falcon pouncing on a pine cone. revealed certain features common them travel, but those that soar to-
do so for novel items, for groups of different items, and tain the serial order of the packages, but not necessarily
Nevertheless, we are comfortable to both mammal and bird play. For gether on air currents, swoop down
for items in no particular pattern. He can also state the of songs within each package. Marsh Wrens apparently
with the notion of mammal play—we example, play is most frequent in to earth, then rise again, over and
number of items in a subset of objects, such as how many learn the order of their own several hundred songs and
know that playful urge—but are not young animals, and often consists of over, are surely playing.
corks in a collection of corks and keys. those of neighbors and may respond to a singing neighbor
so comfortable with the thought that incomplete or rearranged sequences In birds, play is most prevalent in
In all these examples, however, the birds may have de- by producing the neighbor's next song before he does;
birds, too, might play. Yet, clearly, of actions, incomplete movements, species with a well-developed fore-
termined quantity by using a perceptual strategy akin to how they remember such astonishingly long sequences
they do. exaggerated motions, or highly repe- brain, a portion of the brain impor-
pattern recognition, rather than by actually counting: we has inspired much speculation. Studies of certain parrots,
Play in birds, as in mammals, titious actions, often performed out tant in learning; and indeed, species
use such a strategy to determine, without counting, how crows, and chickens suggest that, like vervet monkeys,
enhances learning of motor and sen- of context (Ficken 1977). But even whose development relies heavily on
many spots are on a given domino face; for quantities some birds use different alarm calls to alert their group
sory skills and the social behaviors when we know what kinds of ac- learning tend to play more. For ex-
up to about four, we don't even need a particular pattern to the presence of ground versus aerial predators (for
necessary for survival as an adult. The tivities play entails, the behavior can ample, play is more common in the
to succeed. To eliminate this possibility, we gave Alex a example, raccoons versus hawks). Furthermore, Alex's
trial-and-error nature of play allows be difficult to distinguish because avian orders with altricial species,
task for which humans cannot use perceptual strategies: use of English speech demonstrates striking parallels
quantifying a subset of items distinguished from other between avian and primate capacities.
subsets by two categories. Thus, Alex saw mixed collec-
tions of items such as blue keys, red keys, blue cars, and The Future
red cars, and had to answer, for example, "How many Researchers are just beginning to examine avian
blue key?" He performed about as well as humans for abilities. Current topics include timing capacities (for
subsets up to 6 in collections containing up to 18 objects. example, how does a bird learn to time its movements
Because Alex may be even better than humans at using when evading predators, or to maximize food intake
perceptual strategies, we are currently devising stringent over time?) and visual processing (for example, does a
tests to determine whether he can actually count. flycatcher learn to track the evasive actions of a moth?).
Many questions remain. How does Alex learn to control
6 Birds Understand "Transitive Inference" his vocal tract to produce human speech, and how do he
Animals in hierarchical societies may infer linear and other birds, with brains organized so differently from
relationships among group members (for example, A those of mammals, succeed on tasks requiring complex
dominates B, B dominates me; therefore A dominates mental capacities? Scientists' answers to these questions
me). Animals lacking such "transitive inference" may will force humans to reevaluate their preconceptions
engage in fruitless, possibly dangerous, challenges. Yet about intelligence and notions about the evolution of
before the 1970s, few nonhumans were thought capable mental capacities. At least that is what I reflect upon when
of transitive inference, which seemed to require complex Alex greets me each day with "Hiyo...Come here!" ■
skills, including language. Interestingly, some humans
solve the standard verbal transitive inference task (Jack Suggested Readings
is taller than Jim, Joe is shorter than Jim; who is tallest?) Pearce, J. M. 1987. An Introduction toAnimal Cognition.
by representing the relationships in mental images London: Erlbaum Assoc.
rather than words in their minds. Even without words,
Pepperberg, I. M. 1990. Some cognitive capacities of an
transitive inference requires considerable mental effort:
African Grey Parrot. In P. J. B. Slater, J. S. Rosenblatt, &
one must understand the sentences, remember the items
C. Beer (eds.), Advances in the Study of Behavior 19:
in the sentences, and order the sequences appropriately.
357-409. San Diego: Academic Press.
Although pigeons respond correctly that B is greater
than D after learning A>B>C>D>E, their task may not Premack, D. 1976. Intelligence inApe and Man. Hillsdale,
Figure A. Young Herring Gull Playing With a Skate Egg Case: The most common type of play in birds is object play, in which the
involve mental representation or transitive inference: NJ: Erlbaum Assoc.
bird handles an item, often nonedible, repeatedly tossing it into the air and catching it, or dropping it and catching it in midair.
pigeons were rewarded for learning pairs of elements in Ristau, C. 1991. Cognitive Ethology: The Minds of Other Here a young Herring Gull plays with a skate egg case on the seashore, repeatedly shaking it and tossing it into the air—behavior
the series (for example, A>B), so their responses might Animals. Hillsdale, NJ: Erlbaum Assoc. that may help the young bird develop prey-capture and prey-handling skills.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

6.20 John A (cock Chapter 6 — Understanding Bird Behavior 6.21
ball, pebbles, or snail shells into the
air and caught them. At other times,
it lay on its back and shifted various
playthings between beak and claws
(Thorpe 1966a). Other captives ob-
served by Gwinner (1966) learned to
fall forward from a perch like an ac-
robat, in order to hang upside down
by their feet, wings outstretched, then
let go one foot at a time. While
upside down, sometimes
they carried pieces of food,
or shifted items from beak to
feet. One, while holding onto
a branch with his feet, learned
to propel himself around and
/7, , /,
// , i)
j; around the perch by flapping his
• • •I

wings, like a gymnast on uneven par-

11,
1
allel bars in a sort of "loop-the-loop."
19;17. 444 Gwinner's captive ravens also played
balancing games: carefully walking
out as far as possible to the end of a
tiny branch until it bent downward,
turning them upside down; or trying
to stand on a stick or bone held in
the feet, while balancing it on top of
Figure B. Eiders Play in Tidal Rapids: In August 1934, B. Roberts watched a group of eiders "playing" by a fjord in Iceland. He
and parallel to a perch made from a
described his observation as follows: "At the entrance of the fjord there is a long narrow sand-spit jutting out into the sea, and
thick, round wooden dowel (Fig. C).
when the tide is ebbing a very strong current races past the end of this spit into the open sea beyond. I watched a party of Eiders
"shooting" these rapids, and was amazed to see them land on the outer side of the spit, walk across it, and immediately "shoot" The playful inventiveness of captive
the rapids again. They were plainly doing it for enjoyment, and repeated the performance over and over again, sometimes even corvids demonstrates how well they
running back across the spit, apparently in great haste to experience the sensation once more." Roberts (1934, p. 252). can modify their behavior to suit their
immediate environment—an asset
which are born helpless and rely play with feathers. Behaviors such Captive young White-fronted Parrots greatly enhanced by the extensive
more on learning, than in those that as these undoubtedly help develop engaged in various "play" forms of learning period each young corvid
are primarily precocial and are more the prey-capture and prey-handling allopreening, bill-nibbling, pseudo- experiences. This adaptability may
fully developed at birth (Ortega and skills of predatory birds. Another copulation, bill-gaping, and neck- be one major reason corvids can oc-
Bekoff 1987). These correlations of type of play is loosely termed "lo- stretching (Skeate 1985). Their most cupy such a diversity of habitats.
play behavior with forebrain size and comotor." Common Eiders were frequent "game," however, was play
altricial young, although interesting, observed by Roberts (1934) floating fighting, in which they slowly and Although many possible functions
do not necessarily imply cause and down tidal rapids, then hurrying deliberately bit gently at the toes may be hypothesized for these and
effect. back to the beginning to ride again, and tarsi of their playmate. In real other examples of play, it is tempt- Figure C. Raven Balancing a Stick on a Perch: Corvids, such as crows and ravens,
Although play is more widespread over and over (Fig. B). Four Common fighting, the parrots gape and jab have the most complex play behavior. Here a captive raven stands on a stick, while
ing to suggest that they just might
in mammals, avian examples are nu- Ravens were seen taking turns slid- rapidly and aggressively at the heads balancing that stick upon and parallel to a wooden perch—a raven's version of "log
be "fun." But then, has the feeling of
merous. The most common is "object ing down a snow bank on their tails, of their opponents. Corvids also en- rolling, " perhaps. This is just one of many games played by the captive ravens observed
"fun" evolved because it positively
play" (Fig. A). Hawks, eagles, gulls, feet first (Bradley 1978), and captive gage in extensive social play. Young by Gwinner (1966).
reinforces behaviors that contribute
terns, corvids, and others carry items ravens developed a game in which may develop complicated games to an individual's survival, or is it an
such as twigs, stones, leaves, or dead they repeatedly slid down a smooth similar to "king of the mountain," end in itself? Questions such as these
prey into the air and drop them, only piece of wood in their cage.Thefunc- "follow the leader," or "keep-away," remain unanswered—for humans as
to catch them again in midair. One
Hooded Crow repeated this perfor-
tion of these activities is not known, and one Common Raven was seen well as for birds and other animals. ■
although they may help to improve playing with a dog, the two taking
mance dozens of times, catching his motor skills. turns chasing each other around a
"toy" after it had dropped about 36 Social play, relatively uncommon tree (Thorpe 1966a).
feet (11 meters) (King 1969). Simi- in birds, may help young to develop Of all birds, corvids have the most
larly, cormorants and pelicans play social ties and to learn sexual, ag- complex play behavior. One captive
with fish and stones, and swallows gressive, and submissive behaviors. raven repeatedly tossed a rubber

Cornell Laboratort1 of Ornitholo8q Handbook of Bird Biologq

 r
6.22 John A lcock Chapter 6 — Understanding Bird Behavior 6.23
the genes associated with coral snake avoidance would remain in the Figure 6-15. Variation in Size of Breed-
motmot population, and all the birds in this species would avoid coral ing Territories: Bird species vary widely
in the size of their breeding territories.
snakes. Shown here are two extremes a. Part
The process I just described is one in which evolutionary change of a Dense Nesting Colony of Northern
occurred by Darwinian natural selection. Charles Darwin realized that Gannets: Notice the regular spacing
if individuals within a species had inherited differences that affected between the tightly packed individual
nests—each gannet's breeding territory
their chances of leaving surviving descendants, then those that repro-
is limited to less than a square yard or
duced more would shape the species in their image. The reproductive meter, little more than the area around
failures, on the other hand, would take their hereditary attributes out its nest that it can defend as it incubates.
of the gene pool—all the genes existing in a population at any given Photo by Tom Vezo. b. American Kestrel
Territories: Some birds of prey defend
time.
very large territories. American Kestrel
territories average about 50 acres (20
hectares), whereas those of larger raptors
Territorialiti1, Dominance Hierarchies, and may be up to 1,000 acres (400 hectares).
These territories typically include food
Ritualized Aggression resources as well as a nest site. Inset
Darwinian theory provides a powerful approach to studying the a. Part of a Dense Nesting Colony of Northern Gannets drawing by Sam J. Norris.
evolution of all living things. The theory suggests that the attributes of
species, including their behaviors, have evolved through reproductive
competition, and therefore should help individuals reproduce suc-
cessfully. Thus, the question for the evolutionary biologist is how a
b. American Kestrel Territories
particular behavioral trait helps an individual leave as many surviving
descendants as possible.
Consider the fact that birds are often aggressive toward other
members of their species during the breeding season as they stake
out breeding territories. When a gannet tries to claim a suitable nest
territory in a dense rookery (Fig. 6-15a) on Bonaventure Island, its fel-
low gannets do not assist it in any way. Instead, they regularly assault
the newcomer with their formidable beaks, trying to drive it away. The
newcomer may be sufficiently persistent and aggressive to force his
way into the colony, in which case he has some chance of attracting a
mate and rearing a brood of young.
A gannet's territory is a very small patch of bare ground (less than a
square yard or meter), but many birds have breeding territories that are
substantially larger (Fig. 6-15b), ranging up to 1,000 acres (400 hect-
ares) or so for some larger birds of prey. These territories are essential
for successful reproduction, because they contain superior nest sites,
food resources, or both. Therefore, it is not suprising that regardless of
the size of a territory, its defenders react strongly to intruders. In spring
in Arizona, the male Vermilion Flycatchers in the mesquite bosque
near my home spend hours calling and watching over the territories
they have carved from the open forest. When an intruder approaches dl I1420 (HAMBURG) 1 .21 1422 1.23 OINTERIOR—GEOLI
5865 in SW

a territory holder, the resident immediately chases him to the edge SCALE 1:24000
1 MILE
of his territory, calling vigorously all the while. The two birds weave
1000 1000 2000 3000 4000 5030 6000
NEW RINGGOLD, PA.
7000 FEET
through the mesquite trees in a beautiful aerial ballet with an entirely ‘1 400 7 5-F8-TF-024
1.- PENNSYLVANIA.
5 1 KILOMETER 1 992
serious purpose. )
DMA 5865 111 NW-SERIES V831
CONTOUR INTERVAL 20 FEET
If two contestants for a territory come in contact with one an- NATIONAL GEODETIC VERTICAL DATUM OF 1929
QUADRANGLE LOCATION

other, an all-out fight is possible. Niko Tinbergen's film Signals for

Survival shows territorial Lesser Black-backed Gulls clubbing each American Kestrel Breeding Territory
• American Kestrel Nest Site Approximate Size is 50 acres (20 hectares)
other with their bills and trying to pull feathers from their rivals.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologt

6.24 John Alcock Chapter 6— Understanding Bird Behavior 6.25
Physical aggression, however, is uncommon because most conflicts a. Resting Postures and Threat Displays of Red-winged and Yellow-headed Blackbirds
are resolved without contact between the opponents. The songs of ter-
ritorial White-throated Sparrows, for instance, are sufficient to deter
most other males from invading their domains. When experimenters Red-winged Blackbird Yellow-headed Blackbird

place tape recorders that play white-throat songs in an area, other

white-throats are less likely to enter the site than when the recorder is Normal Resting Normal Resting
turned off (Falls 1988). Even when a bird who has no territory invades Posture Posture
another's territory, the intruder typically flees at once when challenged
by the resident. Moreover, this challenge often takes the form of a rit-
ualized aggressive display, rather than an all-out assault (Fig. 6-16).
The puzzle here is that without a breeding territory, which is a scarce
commodity, most birds have no chance to reproduce. Yet those who
have not acquired a territory appear very reluctant to attempt to take a
site from an established rival. Why would a bird so readily give up its
chance to raise young and pass on its genes?
A similar evolutionary puzzle is that in winter, some flocking
birds with low positions in the pecking order "voluntarily" concede "Bill-Up" "Bill-Up Flight"
food to others, even though their future reproductive success depends Display Display
on getting enough to eat. Thus, aggression without combat is the rule
in the winter mobs of Dark-eyed Juncos and bands of Black-capped
Chickadees gathered about feeders in the northeastern United States.
These flocks are highly stratified in a dominance hierarchy that de-
termines which birds will have their way and which must step aside
(Fig. 6-17). The mere approach of a dominant individual (sometimes
supplemented by a noncontact threat display) generally causes a sub-
ordinate to give up food or a safe perch to its superior. Why do birds
who are low on the totem pole behave this way instead of fighting for "Wings-Up"
Display
their "fair share" (Fig. 6-18)?
One explanation of apparent self-sacrifice was proposed in 1962 "Head Forward"
Display
by V. C. Wynne-Edwards, who argued that territorial behavior and the
formation of dominance hierarchies evolved through group selection,
the differential survival of groups based on variations in group attri-
butes. According to this argument, some birds voluntarily refrain from
breeding or from fighting for limited resources when restraint is advan-
tageous for the species as a whole. Thus, if the population of gannets
became extremely high, some "excess" individuals could assist their
species by not producing young. In this view, too many gannets would
put extra pressure on the fish stocks essential for the long-term survival
of the gannet species. Wynne-Edwards also argued that dominance
hierarchies help species avoid extinction by insuring that when food
Figure 6-16. Threat Displays: Threatening birds tend to adopt stylized attack postures: extending the head forward, spreading the
is in short supply, at least the dominant birds have enough to eat to
tail, raising the wings, or opening the beak. Often these displays make the aggressors appear as large as possible or emphasize their
perpetuate their species. weapons—beaks and wings. Many songbirds, especially thrushes and blackbirds, have a Head-up threat display in which they
Wynne-Edwards' theory of group selection had a certain super- move the head upward and compress the feathers. Another songbird threat display, particularly among finches and warblers, is
ficial plausibility, but George C. Williams soon pointed out a fatal Head Forward, in which, holding its body horizontally, the bird points its head at the opponent, often gaping or raising the wings.
Threats usually cause the opponent to leave without a fight. The illustrations here and on the following two pages portray threat
defect (Williams 1966). Imagine that some gannets really did sacrifice
displays in a range of species. a. Resting Postures and ThreatDisplays of Red-winged and Yellow-headed Blackbirds: Territorial
their breeding chances for the good of their group. If the self-sacrificing male Red-winged Blackbirds respond to intruders with ritualized Bill-up and Head Forward displays. Territorial Yellow-headed
behavior of these birds had a hereditary basis, what would happen Blackbirds employ Bill-up Flight and Wings-up displays. Most intruders flee without fighting with the territorial individuals. Draw-
to their genes and the behavior they controlled? Clearly, the genetic ing by Gene M. Christman. From Orians, G. H. and G. M. Christman. 1968. A comparative study of the behavior of Red-winged,
basis for stepping aside would become progressively more rare as the Tricolored, and Yellow-headed blackbirds. University of California Publications in Zoology, Volume 84.
(Figure continued on next page)
(Continued on p. 6.28)

Cornell Laboratorq of Ornitholom Handbook of Bird Biologj

6.26 John A lcock Chapter 6— Understanding Bird Behavior 6.27
Figure 6-16. (Continued) b. Great Blue
Heron "Forward" Threat Display: Seen e. White-breasted Nuthatch g. Common Redpoll "Head Forward"Threat Display
in a variety of heron species, this display "Wing-Spread"Threat Display
is considered to be a ritualized attack b. Great Blue Heron
sequence. The bird retracts its neck; "Forward"Threat Display
erects the plumes of the head, neck,
and back; and stabs its bill toward the
opponent; sometimes also squawking
and snapping its bill. The display most
often occurs in the vicinity of the nest as
part of territorial defense. From Mock,
D. W. 1976. Pair formation displays
of the Great Blue Heron. Wilson Bul-
letin 88(2):185-376 (p. 206); drawn
from movie frames of a filmed display.
Drawings reprinted with permission r e
Figure 6-16. (Continued) e. White-
of Douglas W. Mock. c. Black-capped
breasted Nuthatch "Wing-Spread"
Chickadee "Bill-Up" Threat Display:
Threat Display: The bird raises its body
The bird tilts back its head until the bill
f. Young Great Horned Owl Threat Display away from its perch, points its bill up-
is vertical; in moments of high intensity,
ward, fully spreads its wings and tail, and
the bird also leans its whole body back
sways slowly from side to side for one or
and points its tail directly downward.
two seconds. This display is often given
d. Hairy Woodpecker "Bill-Wave"
at bird feeders when the nuthatch is
Threat Display: The bird waves its bill
competing with birds of its own or other
from left to right, spreads and flicks its
species. f. Young Great Horned Owl
tail from side to side, and may also flick
Threat Display: The bird fluffs its feath-
its wings and call. The behavior usually
ers and raises its wings, making itself ap-
occurs when two woodpeckers of the
pear larger than it really is. Drawing by
same sex have a territorial conflict.
Charles L. Ripper. g. Common Redpoll
d. Hairy Woodpecker "Head Forward" Threat Display: The
"Bill-Wave"Threat Display redpoll extends its head forward, and in
situations of high intensity may raise its
wings and gape at the opponent. Draw-
ing by William C. Dilger.

c. Black-capped Chickadee
"Bill-Up"Threat Display
LOSERS

RRR YTT GC BGT RRF BRF RC Total Wins %Wins

RRR 11 7 64 96
YTT 6 9 28 85

WINNERS
GC 6 1 11 31
BGT 3 2 8 44
RRF 12 18 40
BRF 9 20
RC 0 0

Figure 6-17. Dominance Relationships in a Winter Flock of Black-capped Chickadees: Shown are the results of 138 interactions
between the seven members of a Black-capped Chickadee winter flock. For each possible pairing, for example, BRF vs. GC,
you can determine the number of times each bird won by locating its "winner" row, and then reading across until it intersects
its opponent's "loser" column. Thus, BRF won over GC 2 times, and GC won over BRF 6 times. GC is therefore above BRF in the
dominance hierarchy, as indicated by its placement in the row and column headings. This flock had a linear dominance hierarchy
with bird RRR at the top as alpha male, followed by YTT, GC, BGT, RRF, BRF, and then RC. Note that in all but 3 of 67 interactions
with other flock members, RRR displaced his companions. In 3 of 11 interactions with bird BGT, however, RRR was the loser:
(Figure continued on next page) BGT is female, and is RRR's mate. Adapted from Hartzler (1970).

Cornell Laboratory of Ornithology Handbook of Bird Biologq

6.28 John A lcock Chapter 6 — Understanding Bird Behavior 6.29
a. Herring Gull "Facing Away" Display self-sacrificers failed to reproduce and pass on the genes for Figure 6-18. (Continued) c. Black-capped Chickadee "General Sleeking"Appeasement Display
"good-of-the-group" behavior. In a population composed of
both self-sacrificing gannets and reproductively selfish gan-
nets, the genetic basis for successful reproduction should
increase, while the genes for species-benefiting self-sacrifice
should decrease and then disappear.
Theorists continue to explore whether some other form of
group selection might contribute to the evolution of species.
For our purposes, however, it is enough to recognize that, un-
like Wynne-Edwards' theory of evolution by group selection,
zny11:. :k Wh
the theory of evolution by Darwinian natural selection is ewrfairiff*****
based on the defensible premise that hereditary traits which d. Canada Goose
advance the survival and reproductive success of individuals "Head-Down" Appeasement Display
will become more and more common. Therefore, if we observe
Wh ite-throated Sparrows that are unable to acquire territories
and are not attempting to reproduce, a Darwinian biologist
might propose that by postponing breeding attempts when

b. Great Blue Heron "Stretch" Display

4
e. American Crow
"Foot Putting"Appeasement
Display

Fig 6-18. (Continued) c. Black-capped

Chickadee "General Sleeking" Ap-
peasement Display: This display
involves flattening all the head and
body feathers and leaning away from a
dominant individual. d. Canada Goose
"Head-Down" Appeasement Display:
The head and neck are drawn in to-
ward the breast and the bill is pointed
downward. This display is given by an
individual who is near a more dominant
goose. e. American Crow "Foot Putting"
Appeasement Display: Subordinate
crows near dominant individuals, es-
pecially when approaching a breeding
Figure 6-18. Appeasement Displays: Birds trying to decrease its bill to the vertical position, with lower neck plumes fully
pair, may put one foot out to the side, as
the aggression of a mate or rival may adopt certain postures that spread. It then gives a long, moaning call that continues as the
if trying to keep from being driven away.
have become ritualized to convey submission. These postures legs are flexed and the head and bill are lowered to their rest-
Yearling crows may even roll over on
are often the opposite of those used in threat displays and tend ing positions. This display is used in a variety of contexts, and f. European Starling
"Submissive Crouch" their backs in submission. f. European
to de-emphasize the bird's weapons or size and to expose vul- in only a couple of them does it seem to have an appeasement
Display Starling "Submissive Crouch" Display:
nerable parts of the body to the opponent. A submissive bird function. Mock (1976) has described these as follows: First,
Many bird species give a Submissive
may point the beak down or away, fold the wings, lower or turn when one mate arrives at the nest to relieve the other of incu-
Crouch display when confronted with a
away the head, point the tail down, or adopt some combina- bation duties, the bird on the nest gives a stretch display, which
threatening individual.
tion of these postures. Many birds use appeasement displays may indicate "I will not attack."And second, during nest build-
in courtship, presumably to reduce the mate's natural aversion ing when the female inserts a stick and then sends her mate
to being so physically close to another individual of the same off to gather another one, she gives this display, presumably to
species. a. Herring Gull "Facing Away" Display: Many gulls appease him and promote cooperation in the task. From Mock,
and other birds have a mate-appeasement display in which D. W 1976. Pair formation displays of the Great Blue Heron.
the members of the pair stand next to each other and turn their Wilson Bulletin 88(2): 185-376 (p. 188); drawn from movie
faces away. Drawing by Charles L. Ripper. b. Great Blue Heron frames of a filmed display. Drawings reprinted with permission
"Stretch" Display:The heron smoothly lifts its head and raises of Douglas W. Mock.
(Figure continued on next page)

Cornell Laboratory of Ornithology Handbook of Bird Biology

6.30 John Alcock Chapter 6— Understanding Bird Behavior 6.31
conditions are unfavorable, these birds actually increase their lifetime
chances of producing surviving offspring. According to this hypothesis,
some white-throats may be weaker than others, and so are unable to
fight successfully for the kind of territory essential to rearing young.
But by skipping a breeding season, a nonbreeding bird can eventually
build up its reserves, and then at some later date win a territory in good
habitat where the demanding investment in a reproductive attempt
has a reasonable chance of paying off in the currency of surviving
offspring.
This Darwinian hypothesis leads to the following testable pre-
dictions: (1) nonbreeding individuals should be young, or in relatively
poor condition, and therefore at a competitive disadvantage in the
struggle to acquire territories, (2) birds that attempt to breed in places
which most other members of their species avoid (probably because
of poor habitat quality) should tend to have fewer surviving offspring
than individuals that secure popular, highly contested territories, and
(3) birds that forego reproduction one year should often attempt to
reproduce in a subsequent breeding season, without regard to overall
population density. These predictions have been found to be true in
studies of many bird species. Male Pied Kingfishers, an African spe-
cies, are much less likely to reproduce successfully in their first adult
year than in their second (Reyer 1984). In the European GreatTit, birds
forced to settle in "leftover" habitat have fewer surviving offspring on
average than those who get into favored areas (Krebs 1971).
The same approach can be applied to acceptance of low status in
dominance hierarchies and the use of ritualized aggression to resolve
conflicts. Chickadees that cannot defeat a stronger flock member in
an all-out fight save their time and energy by not engaging in futile,
costly challenges. Instead, they move aside at once when threatened
by a higher-status bird, deriving what benefits they can from flock
membership (such as safety from predators), and increasing the odds
that they will live long enough to move up the dominance hierarchy,
at which time they, in turn, will be able to displace rivals from food
with just a glance.
Using ritualized signals to settle disputes can advance the re-
productive success of both winners and losers. If birds can judge in
advance of a fight who would win and who would lose, then both save
time and energy and reduce the risk of injury by using threats, rather
than a feather-pulling, beak-stabbing battle, to resolve their dispute.

The Evolution of Ritualized Displays

We briefly examined how agonistic (threat and appeasement) Figure 6-19. Whooping Crane Courtship Display: A displaying pair is shown in two different positions during the spectacular
dance, described by Robert Porter Allen (1947, p. 139) in the following way: "Suddenly one bird (the male?) began bowing his
displays may enhance the survival of birds, but how, in evolutionary
head and flapping his wings. At the same time he leaped stiffly into the air, an amazing bounce on stiffened legs that carried him
terms, do these and other ritualized displays arise? How, for example, nearly three feet off the ground. In the air he threw his head back so that the bill pointed skyward, neck arched over his back.
did natural selection produce an action as bizarre as Whooping Crane Throughout this leap the great wings were constantly flapping, their long black flight feathers in striking contrast to the dazzling
courtship, described by Slinger (1996, p. 73) as "a couple of NBA cen- white of the rest of the plumage. The second bird (the female?) was facing the first individual when he reached the ground after
ters performing the Dance of the Sugar Plum Fairies" (Fig. 6-19)? completing the initial bounce. This second bird ran forward a few steps, pumping her head up and down and flapping her wings.
Then both birds leaped into the air, wings flapping, necks doubled up over their backs, legs thrust downward stiffly. Again they
A close look at displays reveals that some may have arisen from
leaped, bouncing as if on pogo sticks. On the ground they ran towards each other, bowing and spreading their huge wings. Then
intention movements, motions that are either incomplete or that another leap! The climax was almost frantic, both birds leaping two and three times in succession. Quickly it was all over, after
indicate what the "actor" is about to do. For example, an American about four minutes, and an extended period of preening followed."

Cornell Laboratort of Ornithologq Handbook of Bird BioloBq

6.32 John A lcock Chapter 6— Understanding Bird Behavior 6.33
Goldfinch about to attack another goldfinch might a. Mandarin Duck Figure 6-22. Mandarin Duck and Mal-
crouch down and tense its muscles. The better the "ob- lard Courtship Displays: To investigate
how certain displays might have evolved,
server"—the bird being attacked—is at interpreting the behaviorists often compare the actions
crouched, tensed posture to mean "attack," the better of related species. The Head-turning
his chance of escaping unharmed, and thus surviving display of courting male ducks, which
to reproduce more goldfinches with "quick detection" shows off the brightly colored speculum
--- • 1111111111 1 0 of the wing, is a good example. The male
1111
genes. In this way, natural selection would favor observ- ,
■ 1111111111{10 "III
Mandarin Duck (a) merely touches one
"1 4 1 ,01
, ers that could respond to the slightest hint of impending brightly colored feather with his bill, but
IWllIIIIIII
, ......
IIIII ~~~ uuuuwuuuwuumuuw attack. The aggressor, too, benefits by quick, nonviolent the male Mallard (b) actually does dis-
ompniumuno min ......
resolution of the dispute. Because natural selection fa- placement preening as part of a similar
display, suggesting that the Mandarin's
vors aggressors who clearly signal their intent to attack,
brief Head-turning display may have
intention movements may become more exaggerated b. Mallard evolved from displacement preening.
from generation to generation. The evolutionary pro- Drawings by Charles L. Ripper.
Figure 6-20. Common Goldeneye cess by which these and other everyday motions become exaggerated,
"Head-1hrow"Display: In this ritualized repeated, and stereotyped into displays presenting a clear message SI0511
14111 nzilli
courtship display, the male repeatedly is called ritualization. Behaviorists speculate, for example, that the
flicks his head rapidly backward in a
Head-throw courtship display of Common Goldeneyes (Fig. 6 20) may-

smooth arc, pointing his bill upward.

have evolved from motions showing intent to leap out of the water (pre-
sumably to mate), and that the Forward threat display of many herons Occasionally a bird directs an appropriate action at an inappro-
(see Fig. 6-1 6b) evolved from motions indicating intent to attack. priate subject. These redirected activities often appear at times of stress
NikoTinbergen suggested that some displays appear to arise from or conflicting motivations. Falcons, irritated yet afraid to attack humans
behaviors performed at times of conflicting motivations or indecision. who approach their nest, may attack other birds passing by. And, an
Often these acts, termed displacement activities, seem totally inap- Argus Pheasant, perhaps frustrated yet aroused when the object of his
propriate or out of context: a Blue Jay in the middle of a fight may sud- attention did not cooperate, courted a stone water trough. Mammals,
denly stop to wipe its bill vigorously on a branch; sparring European too, may redirect behaviors: a pet dog or cat, just disciplined by its
tits (chickadee relatives) may stop to peck at tree buds; and courting owner, may take a swipe at a fellow pet, rather than its owner. How
ducks and gulls may interrupt their antics to preen (Fig. 6 21). Other
- often have you come home and yelled at a sibling or spouse when
animals, including humans, engage in displacement activities. Think you really wanted to scream at your teacher or boss, but were afraid
of the person who, while his boss is yelling at him, obsessively straight- to? Sometimes redirected behaviors, like displacement behaviors, are
ens up his desk; or the man who, in a heated argument, keeps rolling ritualized into displays. Male Herring Gulls defending their territory
and unrolling his shirtsleeves or running his hand through his hair. often pull deliberately at nearby grasses (Fig. 6 23). In the past, male -
Figure 6-21. Herring Gull Displace-
ment Preening: Displacement activities Behaviorists cannot travel back in time to observe the stages Herring Gulls facing an opponent, unsure whether to attack or flee,
are actions that seem out of context or through which a particular display evolved, nor are behaviors pre- may have pulled at the grass or pecked at the ground, instead
inappropriate, as when a Herring Gull of launching an outright attack. Over time, this behavior may
served in the fossil record. So researchers are limited to comparing
suddenly stops to preen in the midst of
similar behaviors in a range of closely related living species for hints have evolved into a display signaling aggression.
a territorial conflict or courtship. Ethol-
ogists hypothesize that such behaviors on the origin of any particular display. Consider the Head-turning Unfortunately, few things are as simple as they ap-
may occur because of conflicting display of many courting ducks, in which the male touches his bill pear. Behaviorists cannot actually talk to birds, so they
motivations or indecision. Drawing by to part of a wing—often the brightly colored speculum, which may can never know exactly what message is being commu-
Charles L. Ripper. nicated. They can see what the actor and the observer do
have evolved to enhance the effectiveness of the display. In some spe-
cies, such as the gaudy Mandarin Duck of Asia (Fig. 6 22a), the male
-
before and after a display, and can look for behavioral changes that Figure 6-23. Herring Gull Redirected
appear to correlate with the display, but they can only speculate on the Aggression: A male Herring Gull, de-
merely touches one large, bright orange feather. In other species, such
fending its territory from another gull,
as the Mallard (Fig. 6 22b), the male actually preens. Although certain
-
exact meaning. To further complicate matters, birds often have several
tugs forcefully at a clump of grass.
preening motions were originally displacement activities performed different displays for the same apparent message, and the same display This display may have evolved from
when the male wanted to go after the female yet did not quite dare to, may be used in different contexts. redirected aggression: in the past, ter-
they may have evolved to signal a male's courtship i ntent.Th rough time The traditional hypotheses presented above on the origin and ritorial gulls, conflicted as to whether
to attack or flee from an opponent, may
the preening may have become more highly ritualized, to the extent function of displays are appealing, but very difficult to test—so they
have directed their aggression toward an
that, in the Mandarin, the bill merely touches the wing. If we saw only remain unconfirmed. More recently, researchers have suggested that inappropriate recipient—such as grass.
the Mandarin's display, we might consider wing-touching an odd and displays do not simply increase the clarity of a message; rather, they Over time, this may have evolved into a
inexplicable element of courtship, but comparing it to the Mallard's may involve ambiguity, deceit, and bluffing. Perhaps bird displays re- display signalling aggression. Drawing
veal only what is necessary to appear convincing, and sometimes mis- by Charles L. Ripper.
preening gives a clue to its possible origin.

Cornell Laboratort of Ornitholom Handbook of Bird Biologg

6.34 John A 'cock Chapter 6 — Understanding Bird Behavior 6.35
lead, in an attempt to manipulate competitors. Other researchers have
suggested that displays must honestly advertise a bird's true intents and a. "Grunt-Whistle" Display (Male Only)
abilities, or they would not be effective for long. These intriguing ideas
are currently the subject of much debate among behaviorists (Dawkins
and Krebs 1978; Johnstone 1997). If all the researchers met to discuss
their ideas, what types of displays would they use to convince others,
and how would an observer from another world interpret the meaning
Grunt Call
of the gestures and expressions?

Courtship Displays
The formation of a pair bond, whether temporary, seasonal, or b. "Head-Up-Tail-Up" Display (Male Only)

lifelong, involves an exchange of signals between a male and female.

In most songbirds, the males procure territories through squabbles
with other males, and then the females arrive and choose their mates.
At first, each male behaves aggressively to all members of his species,
both males and females, intruding on his territory. If the sexes differ in
color or size, the male may be less aggressive toward the female right
away, but in species with identical sexes, he treats her just as he would Whistle Call
another male—so the first stages of courtship may be difficult to distin-
guish. If, on being chased, the female assumes a submissive posture or
merely refuses to leave, the male gradually becomes less aggressive
and directs his energy toward courtship activities.
Courtship displays are the most complex and intriguing rituals
c. "Down-Up" Display (Male Only)
carried out by most species, perhaps because they serve a number of
crucial functions. First, the displays have evolved to assure that only
members of the same species will copulate—natural selection elim-
inates most individuals that choose a mate of a different species be-
cause hybrid matings usually produce sterile or weak young, or none
at all. Second, the displays communicate the sex, breeding status, and Whistle Call
sexual readiness of the two potential mates. Finally, courtship helps Figure 6-24. Mallard Courtship Displays: Beginning in the fall, before migration, nearly every body of water on which Mallards
to stimulate and synchronize the breeding behavior of the partners. and other ducks congregate becomes a stage upon which groups of males "strut their stuff" to females. The courtship displays and
It is probably for this reason that species such as White-breasted Nut- pair-bonding rituals continue right through migration and on the wintering grounds. Many individuals arrive on their breeding
hatches and Canada Geese, in which mates spend their whole adult grounds in spring already paired, but courtship displays are still very common at this time, both because some individuals are not
yet paired, and because members of established pairs use displays to strengthen the pair bond and as precursors to copulation.
lives together, still carry out courtship rituals before each breeding Although copulation also occurs in the fall and winter, it is probably not effective in fertilization until spring, when the testes are
season. no longer regressed. Once females are no longer fertile and begin incubation, the pair bond dissolves and the males leave to join
Courtship displays take many forms—from the presentation of other males and begin molting.
elaborate plumes in birds-of-paradise (see Fig. 3-10) to the aerial rolls Mallard courtship behavior includes a variety of displays which, because of the species' familiarity and tameness, provide an
excellent opportunity for close observation and study. Some of the displays illustrated are performed by groups of males toward
and loops of some birds of prey—but a few main themes are com-
females, one may be done by either sex, and others take place between members of a pair. Because many other duck species,
mon. Many displays show off the male's assets—his colorful feath- such as Northern Pintail, Gadwall, American Wigeon, American Black Duck, and various teal, have similar displays, learning
ers, his ability to dominate other males, or his parental skills—to his those of the Mallard will provide insight into the behaviors of a number of different species.
prospective partner. Others include some type of ritualized nesting a. "Grunt-Whistle" Display: The Mallard drake (male) lowers his bill into the water, arches his neck, and raises his body
or breeding activities, such as carrying and presenting nest material upright and almost out of the water, while still keeping his bill in the water. When the neck is most arched, the drake tosses an
arc of water droplets into the air with his bill and gives a loud, sharp whistle. As he returns to his normal position he gives a deep
by Eastern Bluebirds and Northern Mockingbirds, and feeding of the grunt. The entire display takes about one second to perform and is typically performed by groups of males.
female by many terns and birds of prey. b. "Head-Up-Tail-Up" Display: With a loud whistle, the Mallard drake quickly draws his head and neck upward and back-
On the following pages are examples of the amazing variety of ward, at the same time curving his rump upward and ruffling his rump feathers, making his body short but tall. His folded wings are
courtship displays used by birds in various stages of mate attraction, also briefly raised, showing off his bright blue wing patch and his curly tail feathers. After about a second he returns to his normal
position, turning his head toward the female to whom the display was directed. This display is typically performed in groups.
pairing, and breeding (Figs. 6 24 through 6 29; see also Figs. 7-56
- -

c. "Down-Up" Display: The Mallard drake tips forward and rapidly dips his bill into the water. He then flips his bill up, cre-
and 7 67).
-
ating a small arc of water droplets, while giving a whistle followed by a nasal call that sounds like rhaebrhaeb. The display lasts
about two seconds and is typically performed in groups.
(Continued on p. 6-42) (Figure continued on next page)

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

6.36 John A lcock Chapter 6 — Understanding Bird Behavior 6.37

d. "Nod-Swimming" Display (Male or Female)

a b

e. "Pumping" (Male and Female)

f. "Inciting" (Female)

Quegeg Call

Figure 6-24. (Continued)

d. "Nod-Swimming" Display: The Mallard swims very rapidly for short distances with its neck outstretched and its head Figure 6-25. Great Blue Heron Advertising Displays: Advertising or mate attraction displays are performed by the Great Blue
flattened down to just graze the surface of the water. This display may be performed by either males or females. When done by Heron at its nesting colony. After selecting a territory—a branch in a tall tree—the male often performs as follows:
females, it is directed toward groups of males who, by their behavior, are expressing an interest in courtship. The female Nod-swims
toward each male, swimming in quick arcs around as many of them as possible. This stimulates the males to give their own court- a. He howls, starting this loud call at a fairly high pitch with the head and neck stretched up.
ship displays. Drakes perform Nod-swimming during bouts of the Head-up-tail-up display and also immediately after mating. b and c. He then lowers the pitch as he lowers his head and body. Toward the end of the call, he increases the pitch
e. "Pumping": The male and female Mallard face each other and begin rhythmically bobbing their heads up and down. quickly.
The head is thrust upward with the bill held horizontally, then jerked downward. While bobbing, the male and female move d. After a bout of howling he may reach out and tug at a twig, or
their heads in opposing directions: while the male is at the highest point, the female is at the lowest. The pumping display may be e. perform Bill Sharpening.
repeated many times, and is usually followed by mating. f. Eventually, after more howling, a female arrives and proceeds to preen.
f. "Inciting": The female Mallard follows closely behind her chosen mate, repeatedly flicking her head back over her g. When she flies off, he follows. Both birds will return and leave the territory repeatedly until the pair bond is formed.
shoulder while giving a distinctive call that sounds like quegegegegegegeg. The display is given when the pair is approached by
a strange male. Drawings by Richard P Grossenheider.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

6.38 John A (cock Chapter 6 — Understanding Bird Behavior 6.39
Figure 6-26. (Continued) b. The Weed
Northern Gannet Great Crested Grebe Ceremony of the Western Grebe: The
sequence of mutual displays shown
here occurs late in the pair-formation
process. The conspicuous behavior
b. The Weed Ceremony of the Western Grebe known as Rushing, in which two or
more Western Grebes run side-by-side
across the water's surface, has often been
described as a courtship display. It may,
however, occur between a male and
female, between two males, or between
a female and two or more males, so it
probably has several different functions,
including mate attraction and male-
male competition, as well as courtship.
When Rushing is performed by a male
and a female, it may be followed by the
Adelie Penguin Eared Grebe display sequence known as the Weed
Ceremony: Surfacing from a post-Rush-
ing dive, the two courting grebes swim
toward each other. They participate in
Neck-stretching—an erect posture with
raised crest during which the bird gives
"Neck-Stretching" a drawn-out trilling call—and/or Bob-
shaking in which the bill and forehead
are dipped into the water, then pulled out
and shaken to and fro, all in a ritualized
way, creating a slight splash. The birds
then begin to Weed-dive, repeatedly
diving from the water's surface to search
"Weed-Diving" for submerged plant material. They ap-
proach each other closely, each holding
its billful of weeds high, then perform
Weed-dancing. Breast to breast, the two
Wandering Albatross Red-necked Grebe grebes rise up vertically, churning the
water strongly with their feet, and bring
their weeds together over their heads,
sometimes spiraling around each other
or slowly moving forward in the process,
"Weed-Dancing"
while still maintaining bodily contact. It
is thought that Weed-dancing is derived
from nest building. After Weed-danc-
ing ends, the birds swim side-by-side,
Weed Ceremony performing mutual Bob-preening—re-
peatedly going through preening mo-
tions—and mutual Arch-clucking in
which each bird displays with its neck
stretched into a high arch and its crest
Figure 6-26. Mutual Displays: Many long-lived birds that mate for life engage in mutual displays—intricate, synchronized dances
spread laterally, while giving clucking
that appear to stimulate and coordinate breeding behavior between the pair and to reaffirm the pair bond. Typically, male birds calls. Adapted from Nuechterlein and
do more of the courting, but in these mutual displayers, males and females share courtship equally. Birds that display mutually
Storer (1982).
include gannets, penguins, grebes, albatrosses, cormorants, boobies, herons, and storks. All are large, monogamous birds with zg.
sexes of similar appearance. Songbirds, though often monogamous with similar sexes, rarely give mutual displays. "Bob-Preening"
a. Mutual Displays of Various Species: Pictured here are Northern Gannet, Great Crested Grebe, Adelie Penguin, Eared
Grebe, Wandering Albatross, and Red-necked Grebe pairs engaged in mutual displays. To get an idea of what may be involved,
consider in more detail the mutual display of the Northern Gannet. Northern Gannets display mutually during pairing, and at any "Arch-Clucking"
time throughout the nesting cycle, especially after a temporary separation. When a gannet returns to its mate on the nest from a
bout of fishing, both birds stand and face each other, stretch their necks high with bills pointed upward, partially open their wings,
and clash their bills together. Then, in a display termed "mutual fencing," they keep their bills in contact while rapidly rolling one
bill around the other from side to side, as if in a mock duel. Drawings by C. G. Pritchard.
(Figure continued on next page)

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

6.40 John A Icock Chapter 6 — Understanding Bird Behavior 6 41

Front View of c

d
-
„.- , A „AA •
ec.

/
PIM •
MIN IV/71W 1/7 ,,,,,,,
pv/////////m,' //4// .. !:•,.”

Front View

Figure 6-27. Precopulatory Displays of the Male Red-winged Blackbird: Immediately before copulation, birds frequently give Figure 6-28. Copulatory and Postcopulatory Displays of the Great Blue Heron: These displays take place on the pair's territory.
displays that are primarily invitation or solicitation performances. Shown are some of the postures of the male Red-winged After greeting calls and precopulatory displays, copulation follows, either (a) on the nest, or (b) on a branch nearby. Th is is followed
Blackbird that precede copulation. a. Perched above or near the female, the male arches his body. b and c. As the intensity of by (c) shaking and preening, and (d) Neck-crossing accompanied by Bill-snapping. Drawings by Richard P Grossenheider.
his excitement increases, he leans forward into a crouching position, spreading his wings slightly. He maintains this posture for
several seconds. d. Just prior to copulating he is deeply crouched, with body feathers ruffled, wings drooped, and tail spread. e.
As he approaches the female he flutters his wings in a ritualized way that shows off his red epaulettes. The female, like females of
other species, assumes a more submissive posture—flexing her legs, holding her body horizontal or somewhat tipped forward,
and elevating her tail (see Figure 7-56). Drawings by Gene M. Christman. From Orians, G. H. and G. M. Christman. 1968. A
comparative study of the behavior of Red-winged, Tricolored, and Yellow-headed blackbirds. University of California Publica-
tions in Zoology, Volume 84.

Cornell Laboratorq or Ornithologq Handbook of Bird Biologui

6.42 John A lcock Chapter 6 — Understanding Bird Behavior 6.43
"Barrel Roll" "Barrel Roll" vors from receiving their fair share of food. Therefore, Yellow Warblers
that host cowbirds definitely leave fewer descendants on average than
those who avoid them.
Nevertheless, as noted above, the warbler's parental drive could
be adaptive because it usuallycauses them to direct food to the largest,
most vigorously begging of their own offspring. Big, active nestlings
and fledglings may be the ones most likely to survive to reproduce and
thus propagate the genes of the parents. Parent warblers that refused to
feed large, healthy offspring might very well avoid feeding cowbirds,
but they also might raise fewer of their own progeny than a less dis-
criminating, more parental member of their species.
Furthermore, Yellow Warblers that abandon parasitized nests al-
together could actually rear fewer offspring on average than those that
stayed with a cowbird-infested nest. (Yel low Warblers and other small
Figure 6-29. Courtship Display of the
Northern Harrier: The dramatic aerial The Use of Darwinian passerines do not have the option of removing a cowbird's egg from
courtship display of the male Northern their nests because their bills are too small and the cowbird's egg too
Harrier has been aptly named "sky-
dancing." With wings flapping rather
Evolutionarq Theorq tough to puncture.) In the north temperate United States and Canada,
the breeding season available to small passerines is short, which lim-
slowly and loosely, the bird climbs ■ The logic of Darwinian evolutionary theory leads to ultimate hy- its their options. If a pair of Yellow Warblers abandons a nest with a
steeply into the air, on average reaching
potheses that focus on a trait's possible reproductive benefit to an
60 feet (18 meters), but sometimes as- cowbird egg in it (as they sometimes do), they lose valuable time and
cending much higher. At the peak of the
individual, not to the species as a whole. The first trick for an evolu-
increase the chance that any fledglings from their second nest will - be
climb he performs a midair "barrel roll" tionary biologist is to identify how an evolved trait might be adaptive
too small or too young to survive the fall migration.
by rolling onto his side, then continuing (that is, better in promoting individual survival and reproductive suc-
to rotate in the same direction to right
We can test the hypothesis that when Yellow Warblers accept
cess than some alternative form of that characteristic). The next trick
himself. Then he immediately launches cowbird eggs, they do so because this option is more adaptive than
is to testthe adaptation ist hypothesis that one thinks might be correct.
into a steep earthward dive, checking the alternatives (nest abandonment or burying the parasite egg under
just above the ground. Depending on Many hypotheses that are fully consistent with Darwinian theory have
a "second-story" new nest [see Fig. 8-144]). This hypothesis predicts
the intensity of the display, this sequence been shown to be incorrect. To pick just one example, in Ravens in
thatYellow Warblers further into the nesting season will be more likely
may be repeated many times to create a Winter (see Suggested Readings) Bernd Heinrich describes how he
series of spectacular deep undulations to acceptthe parasite's eggs than those victimized earlier in the season.
once thought ravens called loudly by dead moose and deer to attract
through the sky, covering a distance of When the season is advanced, it should be better to stick with one's
up to one-half mile (0.75 km). other carrion-eating ravens to the spot. The discoverer would thus not
clutch, even though the nest also has a cowbird egg, because some
be alone when he went down to the carcass, where a predator might
chance of rearing young warblers is better than none. In fact, Yellow
be lurking. According to this argument, the caller gained survival ad-
Warblers are more likely to continue to brood a cowbird egg in the
vantages from its behavior, and those that joined him gained a chance
second half of the clutch initiation period than in the first half of the
for a good meal. Thus, the explanation is a perfectly good Darwinian
season (Sealy 1 995).
possibility. But Heinrich found, using dead goats he placed out in the
We now explore the ultimate basis of a spectrum of bird behav-
Maine woods, that ravens continued to call long after a large group
iors, showing how an adaptationist approach has illuminated puzzles
had gathered and begun to feed safely. He therefore rightly concluded
associated with how birds (1) select food, (2) react to predators, (3)
that the "dilution-of-risk-of-predation" hypothesis could not be the
breed colonially, (4) choose mates and reproduce, and (5) behave
right explanation for calling by ravens. Actually, Heinrich eliminated
parentally, five important determinants of an individual's lifetime re-
a whole spectrum of possible explanations for calling before he found
productive success.
support for the hypothesis that callers were territorial intruders at-
tempting to attract a mob of outsiders to the carcass, the better to
overwhelm the defenses of the territory owners. Testing Darwinian FeedinB Behavior: Whq Do Birds Generallg
ideas is essential.
The really interesting cases for Darwinian biologists to solve
Restrict Their Diets, 18norin8 Some Edible Foods
through hypothesis testing involve traits whose reproductive disad- in Favor of Others?
vantages are clear enough, but whose benefits are not so obvious.
The variety of foraging techniques that birds use is as impressively
Adopting cowbirds, for example, surely handicaps a small passerine
diverse as the range of avian bill sizes and shapes (Fig. 6 30). Ruby-
-

whose average life expectancy is one year. Cowbird nestlings eject

crowned Kinglets hover by pine branches to pluck minute insects from
some or all of the host's nestlings from the nest and prevent most survi- (Continued on p. 6.48)

Cornell Laboratori1 of Ornithologq Handbook of Bird Biologq

6.44 John Alcock Chapter 6 — Understanding Bird Behavior 6.45
Figure 6-30. Foraging Techniques: Birds use an amazing diversity of techniques to procure their food. Some of the most common
methods are shown here and on the following pages.

Barn Swallow a. Aerial Insect Capture: The Barn Swallow pursues insects in flight, Figure 6-30. (Continued) d. Chiseling and Pounding: Most woodpeckers,
capturing them in midair in its mouth, a technique known as sweeping. such as the Pileated Woodpecker shown here, feed by hammering on tree
Birds that sweep for insects generally have huge mouths and small beaks. trunks and limbs. The pounding may disturb insects in the wood enough
Swifts, nighthawks, and many swallows use this feeding style. Hawking is that they come to the surface, and the chiseling creates holes through which
a very different technique for catching aerial insects, performed by many the woodpecker can insert its long, barbed tongue to grab the insects. Sap-
flycatchers, kingbirds, bee-eaters, and sometimes by waxwings and certain suckers also chisel living wood to create sap flows: they return later to these
woodpeckers. A hawking bird sits very still on a high or exposed perch with sites to drink the oozing sap and eat the insects attracted to it. In addition,
a good view until it sees an insect. Then it flies out and snatches the insect oystercatchers pound open the shells of shellfish to reach the flesh inside.
from the air, and returns to the same or a nearby perch to eat its prey.

Pileated
Woodpecker

b. Insect Gleaning: Taking insects and other small

invertebrates, such as spiders or slugs, from the
surface of vegetation or other substrate is known
as gleaning. Like many wood-warblers, the Yel-
low-rumped Warbler, shown here, practices perch
gleaning—capturing prey without flying from its
perch, by searching among the leaves, stems, twigs,
and bark for prey. Red-eyed Vireos, chickadees, tit-
e. Raptorial Predation: The Great Horned Owl
mice, and certain small flycatchers such as Least,
Great Horned Owl captures a rabbit by pouncing upon it from midair
Acadian, and Willow flycatchers practice sally
and pinning it against the ground—a method used
gleaning. With this technique, a bird sits still and
Yellow-rumped Warbler by many other owls and hawks. Falcons, such as
watches the surrounding vegetation until it sees an
the Peregrine Falcon, employ stooping—dropping
insect move. It then flies out to pluck the prey item
through the air at great speed in pursuit of a flying
from the distant surface. Hover gleaning, hovering
bird or insect, stunning and snatching it in midair.
while taking food from vegetation surfaces, is per-
formed by kinglets, phoebes, and Great Crested \
_\

Flycatchers. _riAN
,N\1,4,74-.4tVv_4‘;:i/a4t/

f. Diving: The Hooded Merganser uses surface div-

Hooded Merganser ing to submerge itself from a swimming position
c. Probing: A probing bird plunges its beak into
to pursue aquatic prey, as do other diving ducks,
the substrate to search for prey. Some wading
grebes, cormorants, and loons. Kingfishers, Brown
birds, such as the White Ibis pictured here, and
Pelicans, auks, gannets, and Ospreys plunge dive
many shorebirds, including woodcock and snipe,
into water from the air to capture their prey (see
probe in mud for their prey; the specific type of
Fig. 1-31); Ospreys capture fish with their talons,
motion used may be characteristic enough to help
whereas the others catch their prey in their long,
humans to identify them. Other birds, such as
pointed bills.
Brown Creepers, Black-and-white Warblers, and
nuthatches, probe under tree bark and into crevices ,
•

for their prey.

1111111 r. inn iiiii n •

. rrrnmr nrutlnl

(Figure continued on next page)

Cornell Laboratoni of Ornitholo8q Handbook of Bird Biologq

6.46 John Alcock Chapter 6— Understanding Bird Behavior 6.47
Snowy Egret

Figure 6-30. (Continued) j. Nectar

Hummingbird Feeding: Hummingbirds hover at flow-
ers, plunging in their long bills and us-
ing their long tongues to sip the nectar.
_
-
Other nectar-eaters cling to flowers
to feed. These include the Old World
---araruirroyfalUf
sunbirds, the honeyeaters of the South-
western Pacific region, some Hawaiian
honeycreepers, tropical honeycreepers
and other tanagers, and orioles.
Figure 6-30. (Continued)g. Stalkingand Stabbing: Various herons, such as the Snowy Egret portrayed here, use the stalk and watch
method to find their prey. They slowly walk or wade, or simply stand still and watch for fish or other aquatic prey to come within
reach, then suddenly stab or snatch the creatures from shallow water. Birds such as plovers, robins and other thrushes, and larks
use similar methods on land, taking their prey from the soil's surface. A more active approach involves foot-raking and stamping,
sometimes used by herons and egrets to scare prey hiding in the sediments or in submerged vegetation out into the open. Wing-
flashing is also done by some herons, egrets, and storks such as the Wood Stork—one or both wings are quickly raised or brought k: Water Surface Feeding: The pair
forward as the bird moves along through the water. This behavior may frighten prey out of hiding, or alternatively may provide a of Northern Shovelers shown here is
shady place where unsuspecting prey can try to hide; either way brings the prey within the bird's reach. dabbling—moving the beak rapidly
on the surface of shallow water to pick
Northern Shovelers up small aquatic animals and plant
material. Northern Shovelers and other
h. Sifting: Spoonbills, such as the Ro- dabbling ducks also tip their tails up and
Roseate Spoonbill reach down under the water's surface to
seate Spoonbill, strain small animals
and plant material from mud or water obtain submerged food. Unlike most
by sweeping the partly open bill from dabblers, the Northern Shoveler has a
side to side while wading. Some ducks, specialized beak for straining out food
including Northern Shovelers, sift for (see Fig. 6-30h). Other surface feeders
food as they swim in shallow water. include storm-petrels, who patter across
Sifting birds have bills with specialized the ocean's surface picking up floating
edges that trap small aquatic creatures food (see Figure 5-27). Phalaropes also
as the water drains out of the bill. Fla- pick up food from the ocean's surface,
mingos use a similar technique, but spinning around to create a vortex that
actually pump the water through their brings up food from below the water to
specialized bills (see Figure 4-89). within the bird's reach.

Eastern Towhee I. Searching through Leaf Litter: Many

ground-feeding birds, especially in
i. Pecking and Biting: The Ruffed Grouse forested habitats, search for food by
feeds by pruning—biting off and eating leaf-tossing—throwing aside the leaf
plant buds. Grouse and Wild Turkeys litter. Eastern Towhees keep both feet to-
Ruffed Grouse
also pluck ripe fruits from their stems, gether as they kick back leaves, looking
as do waxwings, robins, and catbirds. for insects and other small invertebrate
Goldfinches peck at plant seedheads to prey. Fox and White-crowned sparrows
remove the seeds, as do grosbeaks feed- also leaf-toss with both feet, whereas
ing on tree seeds. Pheasants, juncos, grouse and turkeys scratch at leaves
sparrows, and blackbirds of various with one foot at a time, and thrashers
species also peck on the ground to pick "thrash" with their bills to achieve the
up fallen seeds. Grazing involves biting same end—a habit that has earned them
off clumps of grass or other vegetation their name.
with the bill, as done by geese.

(Figure continued on next page)

Cornell Laboratorq of Ornithologg Handbook of Bird Biolom

 r
6.48 John A (cock Chapter 6— Understanding Bird Behavior 6.49
Figure 6-30. (Continued) m. Specialists: foraging. Reto Zach (1979) figured out a way to test this proposition, by
A number of species search for food us- accepting the assumption that the unconscious goal of whelk-hunting
ing specialized techniques. Shown here, crows was to maximize their intake of calories during the time they
a Parasitic Jaeger pursues a Forster'sTern,
devoted to searching for this food. If true, then (1 ) large whelks should
intent on stealing the tern's fish—an act
termed piracy. Frigatebirds and various require fewer drops to break than medium or small specimens, and
gulls also make a living this way. An- (2) any improvement in the odds of breaking a whelk from heights
other specialized foraging technique is Forster's Tern greater than five meters should be slight, whereas drops below five
blood-feeding. One subspecies of the meters should yield a markedly lower breakage rate.
Sharp-beaked Ground-Finch, a Gala-
Zach tested these predictions by building a simple apparatus for
pagos finch nicknamed the "Vampire
Parasitic Jaeger
Finch" and confined to one island in the elevating whelks of different sizes to various heights on a small plat-
Galapagos archipelago, eats the blood form; he then pushed the whelks off the platform so that they fell onto
of Red-footed and Masked boobies that a hard surface. He found that as predicted, large whelks were substan-
nest there (see Fig. 1-47). The finches
tially more likely to break open when dropped from any height (Fig.
land on the backs of the boobies and bite
the skin at the base of the flight feathers
6 31). Thus, they required fewer time- and energy-consuming drop
-

in the elbow region, opening a wound flights than medium or small whelks. Also as predicted, the probability
W1 1 1 1 11 11111111 1 1116 111111
and causing blood to ooze from the skin that a large whelk would break open increased sharply up to around
along the shaft of the feather. These same five meters in drop height, after which the additional improvement in
finches also eat insects and cactus blos-
soms. Another special foraging strategy
opening whelks was slight. In other words, crows that dropped their
is that of the honeyguides of Africa. They prey from three or four meters would be forced to try and try again,
"lead" humans and honey-badgers to much more than birds using the five-meter drop height. However,
beehives, keeping just 15 or 20 feet crows that took their prey up to six meters or more would be only mar-
ahead of the followers, giving a special
ginally more likely to break a whelk on any given drop, and therefore
call, and fanning their tails. After either
the person or the honey-badger has they would not be compensated for the greater energetic expense of
the foliage. Fish-hunting gannets plunge dive from great heights into the higher flights.
opened the hive, the honeyguides feast
on the wax of the honeycomb, a unique the ocean. Olive-sided Flycatchers swoop out from an ambush perch
food for a bird. As discussed earlier in to intercept passing flies and other large insects. Northwestern Crows
this chapter, some birds store food tem- break open whelks (a type of mollusc) and clams by flying up and
porarily, mostly in autumn, for use later
dropping them onto a hard surface, such as a breakwater.
when the food becomes scarce or dif-
ficult to obtain. A few birds in northern
The adaptive value of the different foraging methods seems ob-
latitudes—the nuthatches and the Acorn vious in most cases. To get at the calories and nutrients in clam flesh
Woodpecker, for example—place seeds requires one technique, to feast on fish meat requires another. But a
or insects in cracks and crevices in the full exploration of the ultimate causes of different foraging methods
bark of trees. The Clark's Nutcracker
can go considerably further by once again looking for elements of 60- • Small Whelk
(see Figs. 6-12 and 6-13) buries pinyon
nuts in the ground and retrieves them in the behavior that appear costly, disadvantageous, or a handicap to o Medium Whelk
the winter when the food supply is low. reproductive success. o Large Whelk
40
Many other examples of specialized The Northwestern Crow, for example, is very choosy when it
foraging techniques exist, including the <Id co
comes to collecting whelks to drop on rocks in the intertidal zone Northwestern Crow
following: scavenging (see Sidebar 4:
in Washington and British Columbia. The birds bother only with the 20
Living in Groups, Fig. 0), shell-smashing z •
0 •
by dropping (see Fig. 6-31), cooperative larger whelks. Why do they I i mit themselves to a small fraction of the 0 •
0 •
- p er
feeding (see Sidebar 4: Living in Groups, potential prey? Passing over small and medium-sized whelks has clear 0 I I Cr i 8
Fig. E), and skimming (see Fig. 4-88). 2 3 II4 5 6 7 8 9 10 11 12 13 14 15
costs—it takes more time to find a large whelk. Selective birds, one
Height of Drop (m)
might think, would get fewer calories per hour of hunting than birds
that were less fussy about prey size.
Figure 6-31. How Northwestern Crows Feed On Whelks: Northwestern Crows break open whelks and other molluscs to obtain
In addition to firmly preferring larger whelks, the crows consis-
their flesh by carrying them up into the air and dropping them onto a hard surface. This graph shows data from Zach (1979) on the
tently fly up with them for about five meters (1 6.5 feet) before dropping number of times a whelk had to be dropped before it broke, for different drop heights (in meters). Note that for any drop height,
them. Why not three meters, or four? Lower drop flights would save large whelks break more easily (with fewer drops) than medium or smaller ones; also note that the breakage rate increases sharply
time and energy that could be spent finding more prey. with height, but only up to about 5 m (16.5 feet). The crows' behavior seems to match these findings, as they strongly prefer large
whelks over small and medium ones, and typically drop the large whelks from a height of about 5 m (16.5 feet ). The crows thus
On the other hand, if the birds' behavior evolved through natural
maximize their caloric intake through their choices in feeding behavior—an example of optimal foraging. From The Cambridge
selection, then their decisions ought to contribute greatly to repro- Encyclopedia of Ornithology, edited by Michael Brooke and Tim Birkhead, Cambridge University Press, 1991. Reprinted with
ductive success, perhaps by maximizing caloric gain in the time spent permission of Cambridge University Press.

Cornell Laboratoni of Ornithologq Handbook of Bird Biologg

6.50 John Alcock Chapter 6 — Understanding Bird Behavior 6.51
Because small and medium-sized whelks were actually less likely all predators; the vigilance of chickadees on a feeder, always ready to
to open when dropped from five meters, and because large whelks dive for cover should they spot danger; and the alarm calls given by
contained more meat, the crows maximized their net caloric gain Mexican Jays that have detected a snake in a nest tree (Sidebar 3: De-
through their foraging choices. Nevertheless, not every bird is likely to fense Behavior). Even some seemingly trivial actions, such as parent
be an energy-maximizer with respect to every item in its diet. Indeed, birds removing eggshells from exposed nests, may have evolved as an
Northwestern Crows almost certainly make some foraging decisions antipredator response. NikoTinbergen showed long ago that egg- and
based on the n utrientval ue of a food item (as well as its caloric content), chick-eating crows could use opened eggshells, which are conspicu-
the risks required to hunt for it, and other factors. Hypotheses about ously white on the inside, as a visual cue to locate nests with vulnerable
the possible adaptive value of foraging behavior that take these fac- nestlings or unhatched eggs. Breeding adults have something to gain
tors into account will be very different from the energy-maximization by removing this cue to their nest's location.
explanation illustrated above. Given that as a general rule birds sensibly seek to minimize con-
For example, Steven Lima noticed that chickadees often (but not tact with their predators, it is surprising that a great many species occa-
always) leave an exposed bird feeder with a sunflower seed, flying sionally seek out deadly enemies (Fig. 6-32). Eastern Kingbirds badger
some distance back to dense cover to eat the food before returning for Red-tailed Hawks, Northern Mockingbirds swoop over domestic cats,
another seed. Fora bird attempting to maximize the number of calories and wood-warblers assemble noisily around Great Horned Owls. The
eaten per minute of foraging, the sensible approach would be to pre- reproductive costs of these activities to a mobber are not hard to dis-
pare and eat the food bits at the feeder rather than spending time and cern; they include the chance that the mobber will be captured by the
energy flying to and from the food source. But Lima recognized that harassed predator (or by another enemy lurking nearby) as well as the
the reproductive success of foraging chickadees may be influenced by time and energy invested in the activity.
more than their efficiency in acquiring calories. Assuming that prepar- (Continued on p. 6.57)
ing and eating some foods under concealing shelter is safer than eating Figure 6-32. Black-tailed Gnatcatchers
them out in the open, he proposed that chickadees compromise energy Mobbing Elf Owl: Many birds group
together to harrass their predators—div-
intake to improve their survival chances (Lima 1 985).
ing at the predator, flying around it, and
Lima tested this hypothesis by predicting that if he could experi- making lots of noise (which attracts
mentally heighten the chickadees' perception of the risk posed by even more mobbers), but usually keep-
predators, the birds would take a higher proportion of their food to cov- ing just out of the predator's reach. They
er. He arranged for a "predator"—a model of a hawk that "flew" along a invest valuable time and energy in this
behavior in spite of some risk of capture.
wire—to fly over a feeder being visited by a flock of chickadees. As he
Why mobbing occurs has intrigued sci-
predicted, after exposure to the "predator," the birds became substan- entists, who have suggested a variety
tially more likely to take sunflower seeds to cover than they had been of benefits that mobbers may reap (see
before. Thus, chickadees that sensed a predator in their neighborhood Table 6-2). Drawing by Marilyn Hoff
Stewart, courtesy of John Alcock.
modified their foraging behavior, sacrificing short-term energy gain to
improve their long-term survival chances.

Antipredator Behavior:
Whq Do Some Birds Mob Predators?
I still remember vividly an encounter between a Cooper's Hawk
and a pigeon that I witnessed more than 30 years ago.The hawk chased
the pigeon over an open pasture near my home in southeastern Pen n-
sylvan ia.The big, gray hawk relentlessly kept pace as the pigeon zigged
and zagged, forcing the doomed bird lower and lower until it ran out of
room to maneuver. As I watched with racing heart, the Cooper's Hawk
slammed into the pigeon, knocking it into the grassy field, where it lay
incapacitated with the hawk perched on its body.
Most birds run a gauntlet of predators every day of their lives,
and much of their behavior bears the imprint of selection by their en-
emies: the remarkable aerial agility of pigeons and other prey species,
which nevertheless provides no absolute guarantee of escape from

Cornell Laboratorg of Ornithologg Handbook of Bird Biolo94

6.52 John Alcock Chapter 6 — Understanding Bird Behavior 6.53

Sidebar 3: DEFENSE BEHAVIOR Threatening

Confronted at close quarters with potential
Sandi,/ Podulka danger and unable or disinclined to flee, birds
may perform threat displays similar to those
As constant subjects of predation, they direct toward members of their own spe-
all birds have numerous behavioral cies, though usually more exaggerated. These
adaptations to promote their survival. threat displays may include special features to
Birds are ever alert, ready to respond make the performers appear as formidable as
to danger signals. Sharp sounds or possible (see Fig. 6-16).
quick movements invariably trigger
escape behavior, but if the sounds Snake mimicry
-

and movements prove to be harmless When a predator draws near the nest, adults
and are repeated often enough, the of some cavity-nesting birds, such as chicka-
birds become habituated to them and dees, may mimic a snake. From inside the hole
no longer respond. Birds continually the bird hisses, and may even open its mouth
watch their surroundings, including and sway back and forth, sometimes thumping
the sky. Those typically preyed on by its wings against the walls of the hole (Fig. B).
hawks respond with alarm to nearly Squirrels and raccoons may be startled enough
any shape moving overhead that sug- to give up and explore a different hole.
gests an avian predator. FigureA. Piping Plover Chick Defense Behavior: Threatened with danger, some birds,
How birds respond to danger particularly those with cryptic coloration such as young shorebirds, freeze in defense, Giving Distraction Displays
signals depends on their stage of the crouching against the ground to eliminate their shadows—behavior that makes them Birds with nests and young sometimes feign
more difficult to distinguish from the background. Photo by Marie Read.
breeding cycle, as well as the types injury when a human or other predator in-
of predators they must evade. Some trudes upon them. Ground-nesting birds from
threaten and attack predators most Ostriches to songbirds fake injury by fanning,
vigorously when they have eggs or beating, and dragging one or both wings; fluff-
young to defend, fleeing or hiding ing the back and rump feathers; and spread-
from danger at other times. ing the tail—always revealing any bold, at-
Some of the more common re- tention-grabbing colors or patterns (Fig. C).
actions of birds to danger signals a. Killdeer During the act they give "distress" calls, and
are discussed below. One group alternately move with and away from
defense, mobbing, was discussed the intruder. If the intruder follows,
earlier in this chapter and in Ch. 2, the bird suddenly "recovers" just in
Mobbing. time to avoid capture. Birds nesting
in trees feign injury too, fluttering or
Fleeing and Freezing parachuting "helplessly" earthward.
Threatened by a predator such as a Birds that nest on the ground in
hawk, many birds flee to the nearest thick grass or other vegetation may
cover, where they "freeze"—stay mo- sneak off the nest away from the in-
tionless with feathers sleeked, head truder and then scurry along like a
in line with body, one eye cocked in meadow vole, occasionally hopping
the direction of the predator, and legs up into view to attract attention while
flexed for a quick take-off. Birds on continuing to run away.Th is is appro-
the ground crouch to eliminate shad- priately termed "rodent-running."
ows cast by the body. Birds with cryp- As with other defense behaviors,
tic coloration commonly respond to the intensity of distraction displays
danger by freezing in place, a habit varies with the stage in the nesting
that no doubt accompanied the evo- cycle, being greatest from a few days
lution of their concealing coloration b. Black Skimmer before the eggs hatch until the young
(Fig.A). Open-country birds that lack Figure B. Snake Mimicry: An Antipredator Behavior by a Nesting Black-capped Figure C. Distraction Displays: a. Killdeer: Feigning injury by dragging and flapping near independence. If the displaying
cryptic colors, or cover in which to Chickadee: When surprised at its nest hole by a potential predator, such as a squirrel, one wing, a Killdeer gives a broken-wing display accompanied by distress calls, bird is harried for a long time, how-
hide, rely on fast or erratic flight to a Black-capped Chickadee may give a dramatic display that strongly suggests a striking slowly fluttering along to divert the attention of a potential predator away from the ever, the performance gradually
outdistance or outmaneuver their snake. The bird rises up, lifting its head up high, and then lunges forward, bringing its bird's nest on theground. Photo byT.J. UlrichNIREO. b. Black Skimmer: Near its nest, wanes in intensity. Sometimes a spe-
predators. head sharply down while giving a hissing call. At the same time it spreads its wings a Black Skimmer gives a similar distraction display, involving exaggerated spreading cies gives a distraction display to one
forcefully, sometimes hitting them audibly against the nest cavity walls. motions of both wings to suggest injury. Photo by A. and E. MorrisNIREO. kind of intruder, but attacks another

Cornell Laboratorq of Ornitholom Handbook of Bird Biolo8q

6.54 John Alcock Chapter 6 — Understanding Bird Behavior 6.55
kind. A Killdeer, for instance, feigns efits of flocking, see Sidebar apparent. In many cases the
injury vigorously when a human dis- 4: Living in Groups. caller, by drawing attention
covers its nest, yet attacks any cattle to himself, presumably in-
that come near enough to step on the Giving Alarm Calls creases his own risk of being
nest. (Whether humans should be Nearly all birds have one preyed on. This assumption
flattered or insulted by this difference or more calls that they give is extremely difficult to test
in treatment is unclear.) in response to nearby danger, in birds, because attacks are
usually a predator. Jays, do- so rare and the caller is often
Attacking mestic chickens, and many hard to locate and follow.
Birds with nests and young may others even distinguish be- In species such as jays and
attack a predator outright, instead of tween ground and aerial crows that give alarm calls
just threatening it, particularly when predators by giving different from high, exposed perches,
they are safe from physical retaliation calls. Some birds, especially it seems reasonable to as-
themselves. A Red-winged Black- Figure D. Northern Fulmar Projectile Vomiting in Self-defense: Fulmars, together the songbirds, give a low, sume that the caller incurs an
bird, for example, will pursue a large with their marine "tubenose" relatives, feed in the open ocean, their stomachs con-
easy-to-locate chink to warn added risk, but no data on this
verting fat-rich prey into an oily mix of flesh and fluid, which they regurgitate to feed
hawk or crow and savagely strike it of danger on the ground and topic currently exist.
to their young. They also may use this foul-smelling substance to repel a potential
from above as it passes over the home a harder-to-locate, high seet Why, then, should any
predator approaching the nest: adult and young fulmars alike may vomit this stomach
marsh. Nesting Northern Goshawks, oil forcefully at the intruder, projecting the fluid for several feet. or zee when the danger is bird give an alarm call, if do-
Great Horned Owls, and a few of the airborne (see Fig. 7-18 and ing so decreases his chance
other large birds of prey may actually plished at this art: a bird on the nest ficult for the attacker to isolate and Track 18 on CD). Having dif- of survival? Researchers of-
strike humans that intrude near their can spit foul-smelling oil from the capture just one bird. When threat- ferent types of alarm calls al- fer several hypotheses to
nest, as will some colonial seabirds stomach at a predator 2 to 3 feet (0.6 ened, ducks on a pond bunch up lows birds to respond appro- explain this dilemma. First,
such as the powerful skuas. to 0.9 m) away. Even the unhatched on the water, blackbird and starling priately to the type of danger if the caller can save several
Some birds vomit unpleasant young can spit—through small holes flocks pull quickly into a dense ball, at hand—taking flight to es- relatives at only a small risk
substances in self-defense. Vultures, in their pipped eggshells. and shorebirds take flight in a tight cape a cat or fox, and freez- to himself, the tendency to
herons, gulls, and all the tubenoses flock that swerves and dips while ing or diving into thick cover sound the alarm can actually
(albatrosses, petrels, fulmars, storm- Massing trying to elude the pursuer (Fig. E). to avoid a Sharp-shinned Figure F. Florida Scrub-lay GivingAlarm Call: In response be promoted through natural
petrels, and diving petrels) use this Birds with gregarious habits often These dramatic defense maneuvers Hawk or Merlin. The simi- selection, because close rel-
to danger, such as the approach of a predator, most birds
technique to ward off predators (Fig. respond to a predator by massing into inspire awe in anyone lucky enough larity among the alarm calls give alarm calls, both to warn others and to alert the po- atives share a percentage of
D). Fulmars are the most accom- a compact formation, making it dif- to witness them. For more on the ben- of many species is a striking tential attacker to the fact that it has been sighted. Here, genetic traits. In other words,
example of convergent evolu- a Florida Scrub-Jay serving as a sentinel calls to warn its by warning relatives, the
a tion and allows birds to avoid flockmates of impending danger. Florida Scrub-Jays and caller increases his chances
b
some other species have different types of alarm calls for
predators detected by spe- of having at least some of his
aerial versus terrestrial predators. But scrub-jay vocal com-
cies besides their own. Even genetic material passed on
plexity goes even further: call intensity may vary with the
some mammals, notably the urgency of the situation. Photo by Brian Kenney.
to the next generation (see 6
ground squirrels, have calls Fig. 6-48 and Mate Choice:
that follow these patterns. By Why Cooperate in Court-
the same token, deer, foxes, and squir- rick, personal communication). The ship Displays?, later in this chapter).
rels routinely heed the loud warnings most obvious function of alarm calls Any breeding bird warning a mate
of Blue Jays, and alert birders can dis- is to warn others of the approach of or fledglings of impending danger,
cover hawks and owls by tuning in to a predator in time for them to freeze, then, improves the young's chances
avian alarm calls. flee, hide, or aggregate—whatever of survival, an evolutionary benefit.
Florida Scrub-Jays also use dif- it takes to foil an attack. But alarm Nonbreeding birds with long-term
ferent calls for ground and aerial calls also let the predator itself know pair bonds also benefit from warning
predators. A high-pitched, thin it has been sighted. Having lost the a mate, both because they will not
screech warns of a falcon or accipiter, advantage of surprise, the predator have to spend energy finding a new
prompting nearby jays to dive for cov- may decide to abort its attack. If a mate and because experienced pairs
er, whereas a scolding sound incites predator is thwarted each time it often have greater reproductive suc-
off others to mob the terrestrial intruder, stalks a particular prey species or cess than new pairs. Birds that live in
usually a cat or large snake (Fig. F). hunts in a particular area, it may extended family groups or colonies
But in addition, scrub-jays vary the eventually hunt elsewhere or seek should benefit even more, because
Figure E. Massing in a Flock of European Starlings: Flocking birds, such as starlings, blackbirds, and shorebirds, often respond intensity of their alarm calls to convey other types of prey. their alarm calls are likely to warn
to an approaching predator by tightening their flock formation into a compact mass, making it difficult for the attacker to isolate the urgency of the situation, giving Although alarm calls clearly ben- more relatives.
and capture any one individual. a. Typical density of an unthreatened starling flock in flight. b. The starling flock draws together
several rapid screeches when danger efit the listening prey animals, the We would predict, then, that in
into a tight ball when a raptor approaches.
is close by, for example (J. W. Fitzpat- advantages to the caller are not so colonies with related individuals,

Cornell Laboratorq of Ornithologq Handbook of Bird Biologg

6.56 John A lcock Chapter 6— Understanding Bird Behavior 6.57

those with more relatives nearby Table 6-2. Possible Explanations of the Adaptive Value of Mobbing
would give more alarm calls. This
hypothesis has not been tested in 1. The "Predator Move On" Hypothesis: Once the mobbers inform the predator that they are alert
birds, but supporting evidence is to its presence, the predator leaves. The mobbers gain because they don't need to modify their
available for mammals. Belding's
activities to avoid the now-departed enemy, and the predator gains by leaving the area to hunt
Ground Squirrels live in matrilineal
for unsuspecting prey elsewhere.
societies: the females remain in
their natal colony, while the males 2. The Predator Distraction Hypothesis: The mobbers protect their offspring by keeping the pred-
disperse upon reaching adulthood. ator from concentrating on the search for their vulnerable young.
Thus, in any given colony females
are related to each other and to 3. TheAlarm Call Hypothesis:The activities of the mobbers alert others (notably mates and relatives)
many of the young, but males are of the presence of a predator; the alerted birds then can take action to avoid danger.
only related to their own young. In
4. The"Attract a Predator of the Predator" Hypothesis: The mobbers' noisy, conspicuous behavior
these societies, females give more
reveals to larger predators the whereabouts of the smaller predator that is being mobbed.
alarm calls than males and call the
most when close relatives are nearby
(Sherman 1977).
An alternative explanation for the , 4 ,1k4

existence of alarm calls is that the •

The benefits of mobbing are much more difficult to identify.
caller as well as all listeners clearly 64, 444,Y '
Kingbirds cannot seriously injure a hawk by pulling at its tail feathers
benefit if, as mentioned before, a .,..tvn •
any more than aYel low-rumped Warbler can physically harm a Great
predator stops hunting the caller's ss„
e_Aphi4,• • -
Horned Owl. The puzzle of mobbing is sufficiently intriguing to have
species or in his area because it is
discouraged by repeated run-ins
attracted a great many behavioral ecologists, who have developed
Figure G. Sentinel Behavior in American Crows: Some birds that spend all or part of
with an efficient alert system. a large number of alternative hypotheses (Curio 1 978), a sample of
their lives in small, stable groups have sentinel systems in which group members take
Some researchers also suggest that turns watching for predators while their companions forage. American Crows may live which appear in Table 6-2.
alarm cal ling can benefitthe caller if it in extended family groups encompassing individuals from up to several generations, Some of these hypotheses have been tested for certain species.
increases the likelihood that another all of whom help in the nesting attempt. On their breeding territories, American Crow The communal mobbing of foxes, hawks, and large gulls by some of
individual, even an unrelated one, family members take turns acting as sentinels—as pictured here. When crow families
the smaller colonial-nesting gulls, for example, has been explained
will return the favor at a later date—a gather into larger flocks during the winter, the system of coordinated vigilance ap-
pears to break down.
as a form of parental care under the predator-distraction hypothesis.
very difficult prediction to test. When egg or nestling predators show up, nesting Black-headed Gulls
In at least one species, the White-
of northern Europe often respond by flying at them in force and trying
fronted Bee-eater of East African sa- only occasionally, it is in the best in- In some parts of their range,
to strike them with a beak or foot while defecating on them. Although
vannas, females appear to use alarm terests of others to heed the warning American Crows also live in ex-
calls deceitfully (P. H. Wrege and S.
these attacks cannot gravely injure the predators, they may expose
and take cover. tended family groups; some contain
T. Emlen, personal communication). The questions surrounding who as many as 15 birds from up to seven
them to infection. Perhaps for this reason, a fox or Carrion Crow keeps
During breeding, males frequently gives alarm calls and when and why generations. On their breeding ter- an eye on mobbing gulls and tries to avoid contact with them, which
chase and attempt to force copu- they call are exciting to explore, but ritories, American Crows take turns may compromise its ability to search for eggs or nestlings.
lations with females other than their much more research will be nec- acting as sentinels (Fig. G), but when Hans Kruuk (1964) tested this proposition by placing chicken
mates. Chases can be tiring for the essary before answers are found. they gather into larger feeding flocks, eggs on the ground at intervals, beginning outside a large colony of
females, as they are pursued relent- coordinated vigilance appears to Black-headed Gulls and continuing into the nesting area itself. The
lessly both near and away from the Posting Sentinels break down. One or more crows of- idea was to test whether, as expected, eggs outside the colony were
nesting colony. Occasionally, a flee- Some birds that live in small, ten can be seen sitting in trees while more likely to be eaten by egg-hunting predators (notably Carrion
ing female gives the alarm call for stable groups have sentinel systems others forage on the ground, but
Crows and Herring Gulls) than those inside the colony. If mobbing
an aerial predator—causing most in which group members take turns they do not appear to take turns, and
birds, including her pursuers, to dive truly distracts predators, then eggs placed near nesting Black-headed
watching for danger. In Florida Scrub- whether they even serve as "official"
into the bushes, ending the chase. Jays, which live year round in extend- lookouts is not clear (K. J. McGowan,
Gulls should be better protected by the colony's aggressive response
In the open savanna habitat, where ed family groups, all individuals take personal communication). As these to intruders.
bee-eaters may be easy prey for Ga- turns sitting on an exposed perch, larger flocks are less stable, often Kruuk found that "survival" of the experimental eggs was indeed a
bar Goshawks and various harriers, mechanically scanning the sky for changing in composition from day function of their proximity to the colony (Fig. 6-33). Predators foraging
ignoring the aerial alarm call carries raptors (McGowan and Woolfenden to day, the development of a coor- outside the colony were not mobbed by bands of gulls and had little
a high cost. If females "cried wolf" 1989). When the sentinel spots a dinated sentinel system is probably trouble finding and eating Kruuk's donations. But as they approached
frequently, the tactic might become predator, he or she gives the appro- just not possible. ■ the nesting area, egg hunters were increasingly likely to be mobbed,
less effective, but since they do so priate type of alarm call.
and their foraging success declined in proportion to the intensity of

Cornell Laboratorq of Ornitholos Handbook of Bird Biologq

6.58 John Alcock Chapter 6— Understanding Bird Behavior 6.59
in birds. Clearly, birds that breed in colonies must gain some strong
reproductive advantage because, as Richard Alexander (1974) points
out, living closely with others has a great many obvious disadvantages
100
• 100
in terms of survival and reproductive success. Clumping increases the
CU ,n
chances that infectious disease and parasites will spread. For example,
(-) the offspring of Cliff Swallows nesting in large, dense colonies are
>..
more likely to be infested with blood-sucking parasites than the young
2 of swallows nesting in smaller colonies. Moreover, when individuals
< live close together they can interfere with each other in many ways,
Div including sneaking copulations and killing each other's offspring. Un-
50 50
mated males of the colonial-nesting Barn Swallow regularly practice
rti
infanticide, plucking helpless nestlings
- c
ers by the head from unguarded nests and
-o
o "-
throwing them to the ground. (In this way, 40 -
killer males sometimes gain partners who
produce a second brood with them rather
than with their previous companions.) 30-
B C D E
The question becomes, what repro-
Distance from Center of Colony ductive advantages does social living offer
to outweigh its clear disadvantages? Let us
Outside Colony Border Inside Colony
apply this question specifically to seabird
colonies, which provide some spectacular
Figure 6-33. Effectiveness of Black-headed Gulls in Mobbing Carrion Crows: Carrion Crows eat the eggs of Black-headed
examples of aggregated nesting birds (see
Gulls—colonial nesters of Europe who communally mob their predators, including Carrion Crows. Kruuk (1964) indirectly tested
the effectiveness of this mobbing in deterring Carrion Crow predators by placing chicken eggs on the ground at various distances Fig. 6-15a). For further discussion of the
from the center of the colony (see x-axis of graph). He then gathered two types of data: One, the percentage of eggs eaten by any advantages and disadvantages to group I I I 1 1 •
predator at each distance from the colony's center (open triangles, see y-axis of graph, at right side), and two, the probability of living, see Sidebar 4: Living in Groups. 8 12 16 20 24
a Carrion Crow being mobbed intensely (more than 10 attacks per minute) by gulls at various distances from the colony (solid Time of Day (Hours)
Researchers have proposed several
dots, see y-axis of graph, at left side). He found that eggs were less likely to be eaten by predators, and that crows were more likely
to be mobbed, the closer that each was to the center of the nesting colony. This suggests that mobbing by Black-headed Gulls is
hypotheses for colonial breeding, among
effective in deterring the egg-eating crows. Adapted from Kruuk (1964). them the information center hypothesis and the dilution effect hy- Figure 6-34. Synchronous Fledging in
pothesis. The first hypothesis focuses on the possible foraging benefits Thick-billed Murres: This arctic species
nests in huge colonies on cliff ledges.
that birds living together might enjoy. In colonial species, such as gan-
the mobbing. These results support the distraction hypothesis for the The young fledge while still flightless and
nets or Cliff Swallows, unsuccessful hunters might find feedi ng grounds head immediately for the safety of the
evolution of mobbing by nesting Black-headed Gulls.
by following previously successful foragers to good hunting spots. In ocean.Althoughalwaysaccompaniedby
Similarly, William Shields (1984) found that in nesting colonies
contrast, the dilution effect hypothesis emphasizes the possible anti- a parent, they are extremely vulnerable
of Barn Swallows, the birds that mobbed a potential predator (a stuffed to predation during their quick descent
predator benefits of living together in numbers large enough to over-
screech-owl in this case) were far from a random sample of the birds to the sea. Data from Daan and Tinber-
whelm the consumption capacity of local predators. If local predators gen (1979) show that youngThick-billed
in the area. Adult swallows with young in the nest were greatly over-
kill, say, 100 gannets in a breeding season in a given area, then birds Murres (known as Brunnichs' Guillemots
represented in the group that took the initiative in swooping at the
that form a nesting colony of 1,000 members are safer (one chance in in Europe, where the study was carried
stuffed owl. Nonbreeding adults and juvenile birds that happened to
ten of being killed) than if the colony were smaller (for example, 200 out) leave the nesting colony primar-
be hanging around the colony almost never harassed the owl. Thus, in ily during a four-hour period (between
birds, each with one chance in two of becoming a victim).
this case, mobbing occurs because parents try to protect their offspring 8:00 P.M. and midnight—see graph)
Evidence in support of both hypotheses exists for certain species. each day during the fledging period.
by distracting predators.
Thick-billed Murres nest in vast rookeries in the Arctic. Their young The huge numbers of fledgling murres
fledge before they can fly, jumping off their cliff nest sites in an attempt thus overwhelm the local predator pop-
Nest Spacing: to reach the ocean far below. Although a parent accompanies each ulation with potential prey, increasing
the chance of survival for any individual
fledgling on its dangerous descent, gulls are waiting to capture them
WIN Do Some Birds Nest in Large Colonies? murre chick. This synchronous fledging
in midair, and foxes hunt for those that reach the ground and are walk- is consistent with the dilution effect hy-
The fact that Black-headed Gulls and Barn Swallows nest colo- ing to the sea. Most of the young murres leave the colony at about the pothesis (see text) proposed to explain
nially enables individuals to gain protection for their eggs through same time of day during the fledging period (Fig. 6-34). A synchronous colonial breeding. Adapted from Daan
communal mobbing. Perhaps this and other antipredator benefits ac- and Tinbergen (1979).
exit floods the local gulls and foxes with potential prey, improving the
countfor the fact that colonial nesting is a fairly common phenomenon (Continued on p. 6.68)

Cornell Laboratorq of Ornithologq Handbook of Bird Biolopi

6.60 John A Icock Chapter 6 — Understandin8 Bird Behavior 6.61

Sidebar 4: LIVING IN GROUPS

Sandtj Podulka

Some birds live together in per- Mei

manent groups, some group only
during certain seasons, and a few
never group at all. Groups can be
small or large, made up of a single
or mixed species, and may or may
not have a defined social order. The
types of groups are as varied as the
reasons for joining them. Groups
range from winter feeding flocks of
Red-winged Blackbirds, communal
roosts of Turkey Vultures, migrating
flocks of shorebirds or warblers, and
nesting colonies of herons or swal-
lows, to permanent complex soci-
eties of White-fronted Bee-eaters
or jackdaws (Fig. A). But one fact is
true for all: life in a group is always
a compromise. This sidebar explores
some of the reasons that birds live
in groups and some of the trade-offs Lesser Greenlet
'Lan% 9 rt.av
they make to do so. Because colonial Figure A. Group of Eurasian Jackdaws: This species is gregarious year round, nesting Red-eyed Vireo
Tropical Gnatcatcher
nesting is discussed in the text, and colonially as well as forming communal roosts in both the breeding and nonbreeding Shining
Magnolia Warbler
complex societies are covered in seasons. Drawing by Charles L. Ripper. Summer Tanager Honey- NO"
creeper tt
Sidebar 6: Bird Families as Models for Silver-throated Tanager

Understanding Ourselves, only the this time depends almost entirely on each individual bird in a flock more Golden-winged Black-and-white
Warbler Warbler
nonbreeding season is considered the types and numbers of predators time to forage. Shorebirds, for ex-
here. it must escape and on the amount, ample, spend roughly 20% of their Barred Becard

When they are not breeding, most type, and distribution of its food. time scanning for predators when
birds live in groups. Many land birds alone, 5% when in a flock of 5 birds,
that are territorial as pairs in the Groups and Predation and 3% when in a flock of 25. On 6
Figure B. Mixed-Species Flock in the Neotropical Forest Canopy Certain birds, termed Neotropical migrants—including various
breeding season form flocks at other Groups are by nature more con- the African savannas, each Ostrich
warblers, tanagers, thrushes, orioles, and robins—migrate from North America to the tropics of Central and South America, often
times. Some, including warblers, tan- spicuous and easier for predators spends a smaller proportion of its
joining mixed feeding flocks of residents and other migrants during the winter. Foraging together for nectar, fruit, and insects in
agers, thrushes, orioles, and robins, to locate than individual birds, but time scanning for predators when the Neotropical forest canopy may be resident birds such as the Tropical Gnatcatcher, Lesser Greenlet, Shining Honeycreeper,
migrate south and spend the winter group advantages in evading pred- in a group than when alone, yet the Silver-throated Tanager, Barred Becard, and Banana quit, right along with migrants such as the Summer Tanager, Golden-winged
in mixed flocks (Fig. B). Year-round ators may more than compensate percentage of time that at least one Warbler, Red-eyed Vireo, Magnolia Warbler, and Black-and-white Warbler. Migrants may join a mixed feeding flock for various
residents such as chickadees and for their prominence. Group ad- bird is scanning increases with flock reasons: to take advantage of residents' knowledge of good feeding sites, to increase their foraging success as prey are scared up
Song Sparrows form small single- vantages such as mobbing and the size (Bertram 1980). Furthermore, by flockmates, or to obtain the antipredator benefits that come with being in a group.
species flocks and range over larger "dilution effect" are discussed in the because each Ostrich raises its head
areas than their breeding territories, main text. In addition, a group has to scan for predators independently
whereas juncos, American Tree Spar- many eyes and ears that are alert of the others, it is nearly impossible
en masse, and pigeon or blackbird when just one is thrown? Gathering speed into a tight flock of starlings or
rows, White-throated Sparrows, and to danger, allowing earlier preda- for a predator such as a lion to sneak
flocks rapidly gather into tight clus- into a dense group also may be the re- any other prey, sincethe risk of injury
others form flocks and shift south- tor detection. In experiments with up when no bird is looking—the
ters which, as they swoop and turn, sult of each flock member attempting from accidental contact is too great.
ward, the distance depending on the trained goshawks, Kenward (1978) "down times" are unpredictable for
confuse the predator, so that isolating to move toward the middle—a safer Bird flocks, like fish schools,
severity of the winter weather. found that they were less successful groups.
and grabbing one individual is dif- spot because predators generally at- amaze all who watch them. How
During the nonbreeding season, when their prey, Common Wood-Pi- Once an attack is under way,
ficult (see Sidebar 3, Fig. E). You can tack the edge, where their chance of they move so quickly and gracefully
most of a bird's time and energy geons, were in larger flocks—mostly groups, especially aerial flocks, are
simulate the "confusion effect" by separating one bird is greatest. More- as one "being," how they maintain
is devoted to surviving: avoiding because the large flocks spotted the better than lone birds at avoiding
throwing tennis balls at a friend. Is it over, some researchers hypothesize uniform spacing, and why indi-
predators and getting enough food. hawk at greater distances and took capture. When they spot a hawk,
harder or easier for him to catch a ball that a Merlin or Peregrine Falcon viduals never crash into each other
Whether a bird lives in a group at flight. Group vigilance also leaves feeding shorebirds take to the air
when three are thrown at once, or might be reluctant to plunge at high have long mystified scientists, but

Cornell Laboratorq of Ornithologq Handbook of Bird Biolo,qq

6.62 John A (cock Chapter 6 — Understanding Bird Behavior 6.63
frame-by-frame analysis of videos neuver, and the more we learn, the of food nearly always obtains more prey more effectively than a lone drive the fish into shallower water, together (Schenkeveld andYdenberg
is beginning to reveal some of their more impressive they appear; but in a group, as many eyes can search bird could. Groups of predators, for trapping and concentrating them by 1985). Since the gulls cannot hassle
secrets. When birds in the front of many mysteries remain. more effectively for the next ephem- example, are much better than single circling around them or by forming a all the scoters at once, the chance that
the flock curve left or right or swoop eral banquet. predators at catching prey that is itself semicircle against the shore (Fig. E). any one scoter's prey will be stolen is
lower, the birds next to them follow Groups and Feeding Instead of maintaining close in groups: Eleonora's Falcons feeding Cormorants and mergansers may use reduced. Ground-feeding blackbird
suit, and so on through the flock in a Groups offer many advantages groups, some birds whose food is on flocks of autumnal migrants cross- similar tactics. Avocets and Black- flocks in fields may advance in a thick
nearly instantaneous chain reaction to foraging birds, especially if their plentiful yet unpredictable seem to ing the Mediterranean are much necked Stilts often band together, line, stirring up insects for each other
(see Fig. 5-47). It's hard for us to food is found in large patches that spread out and scan for food, usually more successful when they hunt in forming a wedge of birds wading as they proceed. While the ones in
imagine such quick responses, but provide superabundant food for a keeping an eye or ear tuned to their flocks (Walter 1979). Many water through shallow water and gleaning front pause to eat, birds from behind
birds have much faster reaction brief period, but whose location is neighbors. When one vulture finds a birds use social foraging techniques. aquatic insects, crustaceans, and fly up to the front, pause to eat, and
times than we do—as becomes unpredictable at any point in time. dead animal, for example, his neigh- For example, upon discovering a fish molluscs along the way. Wintering in turn are passed. From a distance,
clear when you watch two birds Large schools of fish, aerial insect bors see him and drop in, as do their school, swimming American White Surf Scoters, when harassed by the noisy flock appears to roll across
twist and maneuver in an aggressive swarms, dead animals, and sizable neighbors, and so on, assembling Pelicans may form a line, and by Glaucous-winged Gulls attempting the field in a frenzy.
chase through vegetation. Although trees or orchards at their peak flow- birds from great distances to the feast beating and splashing their wings to steal their catch, adjust the lengths Some birds forage in groups
flock members "follow" whomever ering, fruiting, or seed-setting stages (Fig. D). One observer counted 237 and dipping their bills into the water, of their dives so that they all surface containing many different species.
is in front at any given time, flocks offer far more food than even the vultures at a single horse carcass. On In these "mixed species flocks"
appear to have no set leaders, since most gluttonous gull, tern, swallow, locating a fish school at sea, many the member species usually have
individuals shift positions within vulture, parrot, or blackbird can eat petrels, shearwaters, gulls, and terns different types of prey or different
the group as they turn one way and by itself (Fig. C). Yet these foods are attract other birds by calls or flight methods of foraging, to avoid com-
another, often changing who holds available only for a few hours (fish, behavior. petition. To some, the benefits of
the lead position. We have certainly insects, carcasses) or days (flowers, Many bird groups use special flocking may be primarily predator
just begun exploring how flocks ma- fruits, seeds). A bird seeking this type foraging strategies to exploit their evasion, as discussed earlier. But
others may actually increase the for-
aging success of their flockmates by
scaring up prey for each other as they
move through an area. Shorebirds,
waders, waterfowl, and numerous
small insectivorous birds in both
temperate and tropical forests typi-
r.
cally feed in mixed flocks. Migrants
passing through an area often join
local mixed flocks, gaining some
of the advantages discussed above,
and possibly benefitti ng from the res-
White-backed Vulture
.414 idents' knowledge of good feeding 6
sites and ways to avoid local pred-
ators. One of the best ways to find
migrant warblers in spring or fall is
to listen for the chickadee flocks with
which they often associate.
Although birds may be better able
to find and exploit certain foods in
rAn,,•, •
,Ak",..
Att,, , •
a group, they must share whatever
ttA, • food they can find with other flock
Veh011elii4°44
)\( 41 ",
members. Competition for food may
Lappet-faced Vulture thus be a major factor in determining
Rueppell's Griffon
whether birds group and how large a
group they form. In House Sparrow
Figure D. Vultures Descend on a Carcass in theAfrican Savanna: Vultures often search
for food in very loose groups—the location of their food is hard to predict, so they
flocks, the first bird to discover food
spread out and search—but once found, there is plenty for everyone. The soaring often gives a chirrup call, drawing
Figure C. Cormorant Flock Feeding on a School of Fish: Group foraging may benefit birds whose food is distributed in patches
that are unpredictable in their location at any point in time, but are so large that plenty of food is available for many individuals vultures pay close attention to their neighbors' behavior, though. If one individual in others to dine. In experiments by
once a patch is located. Examples of this type of food resource include fish schools, insect swarms, and enormous fruiting or locates a carcass and drops down upon it, others circling nearby notice and follow, Elgar (1986), House Sparrows given
flowering trees. By grouping together, foraging birds are more likely to find such food patches than if they searched alone—more attracting the attention of still more distant neighbors who immediately fly in to join a slice of bread in crumbled form
eyes and ears are on the lookout. Here, a large flock of cormorants feeds on a school of fish, attracting the attention of terns and the ever-growing crowd of scavengers. Shown are White-backed and Lappet-faced gave the chirrup cal I, but those given
gulls who join in the feeding frenzy. vultures and Rueppell's Griffons descending to feed on a wildebeest carcass. a whole slice kept quiet. Although

Cornell Laboratorq of Ornithologq Handbook of Bird Biolo51,1

6.64 John Alcock Chapter 6 — Understanding Bird Behavior 6.65
actively seek each other's company but superabundant, sources of food populations toward one strategy or
(Fig. F). The concentrations break has led to the development of a more the other. A stable, defensible food
up at the wintering grounds, where gregarious social system. supply leads to territoriality, whereas
hawks once again defend territories. We can think of territoriality unpredictable, indefensible, super-
Vultures are the exception among and grouping as opposite ends of abundant food promotes flocking.
raptors, as they rely on each other a continuum, with the details of Some species change social systems
to quickly locate perishable carrion. food supply and predation pressure as their food availability changes.
This need to quickly locate isolated, evolutionarily driving species or When food becomes patchy, unpre-
dictable, or inadequate, then crows,
jays, magpies, and White Wagtails
44,
A s4
-•• relinquish their territories and join
f V
> 4 A. flocks (Davies 1976; Verbeek 1973).
- I'
.of
A.
-
N 4
. ,. . A AA l t k" 1 4 .4. 1 i
Communal Roosts
A few species spend the night
## ... 4 N 4
*1 /4 4 \/ 1 1 4 in large aggregations termed com-
....,
munal roosts. Some roost in groups
4
"a AO ' I,A A,„„,.,..
k year round, others roost only in the
s," i
", , „

■ •••
4 A
...4 4 v nonbreeding season. Mixed groups
1 A 4I
N, k 4' A 4 4
4 44 , 44 4 -\ •
A
of grackles, blackbirds, cowbirds,
k• , 4.
44 1
4A
t ••• f • and robins roosting along the Mis-
ti 4.
4.1 A
v AA a .. ,1 1 ., A
I sissippi River may contain up to
a
A -• 1/4.
4. A'• 4 VI ‘.• , , 4 15 million birds. Vultures, ravens,
-1 s4 '
A41 ' 4• 44 IN .
r
crows, starlings, herons, egrets, and
44 4' A
A
, .1, 41 . — ' 4 4 41 ibis are all notorious for their large,
noisy roosts (Fig. G).
a. Migrating Broad-winged Hawks There is much speculation on the
functions of communal roosts. Some
species certainly benefit from each
Figure E. Group Foraging in American White Pelicans: Cooperative (or social) foraging enables American White Pelicans to other's warmth: on cold nights, more
effectively exploit their schools of prey. When they locate a school of fish, groups of foraging pelicans may form a line (a), and than 10 Eastern Bluebirds have been
by beating and splashing their wings and dipping their bills in the water in a coordinated way, they drive the fish into shallower found together in one cavity (Fig.
water, trapping and concentrating them. During this process, the pelicans sometimes form a circle around the prey, and at other
H); and Common Bushtits, which
times they form a semicircle against the shore (b). American White Pelicans also may forage singly or in small groups, and many
normally won't let another bird ap-
variations on the cooperative foraging technique exist. Other species of pelicans, as well as cormorants and mergansers, may
proach within two inches, can be
use some degree of cooperative foraging at times. 6
seen roosting shoulder to shoulder.
Chickadees, titmice, Brown Creep-
ers, and Tree Swallows also huddle
the amount of food was the same mud and grasping any snails they can year. Because nectar is generally not in groups in cavities on particularly
each time, a whole slice is not easily feel. One possible interpretation is superabundant in any one spot, most cold nights. Vultures often roost near
shared, so perhaps birds only invite that flocking helps redshank evade hummingbirds defend territories sites where good early morning
a flock to divisible food. Another predators, but that during the day that shift with the seasons. The food thermals develop, allowing them to
drawback to flock foraging is that the the cost of disturbing each other's of woodpeckers and most hawks is start the day with less effort. And, as
presence of many individuals may prey outweighs the predator-related evenly dispersed at low levels, so discussed in the chapter text, there
scare or alert certain types of prey, advantages (Goss-Custard 1976). again, the birds spread out and de- is growing evidence that some com-
decreasing the capture rate for each fend territories. Hawks often appear b. Foraging Red-tailed Hawk
munal roosts and nest colonies serve
bird. During the day, Common Red- Grouping Versus Territoriality to migrate in flocks, as thousands as "information centers." Cliff Swal-
shank feed by sight, either solitarily A very few birds, including hum- pass traditional lookouts such as Figure F. Mass Migration Versus Territoriality in Hawks: a. Huge Kettle of Migrat-
low, Black Vulture, Common Raven,
or in widely spaced groups, seeking ing Broad-winged Hawks: Hawks migrating en masse do not form true flocks—the
mingbirds, woodpeckers, and birds Hawk Mountain, in Pennsylvania, on and a few other communal roosts
groups are actually aggregations that result from each individual bird favoring routes
small shrimp that sit with only their of prey, do not form groups but peak days. But most of these "flocks" appear to function in this way.
with good soaring conditions, such as the thermals along a ridge (see Fig. 5-38),
tails protruding from the surface of remain territorial when not breed- are really concentrations that result Occasionally roosts come into
and also from each bird's tendency to avoid flying over open water. Photo by N. G.
the mud. At the first patter of red- ing. Nectar-producing flowers, the from each individual favoring routes SmithN1REO. b. Foraging Red-tailed Hawk Soars Alone Over its Territory: Whether conflict with human desires, espe-
shank feet, the shrimp duck into the food of hummingbirds, occur in with good soaring conditions (for on their breeding grounds or in their wintering areas, most birds of prey (other than cially when birds gather in urban
mud.At night, redshank feed in flocks small patches, and the sites at peak example, along ridges) and avoid- vultures) rely on an evenly distributed, defensible food supply, so each individual or suburban sites or areas prized for
by sweeping their beaks through the flowering change slowly through the ing open water; the hawks do not holds a separate territory. Photo courtesy of Frank Schleicher/CLO.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

6.66 John A kock Chapter 6 — Understanding Bird Behavior 6.67
agriculture or timber. People may be of sun lit the bird-filled mangrove Birds that gather in conspicuous continually weighs the benefits and
disturbed by the noise, masses of mounds, setting the birds afire, groups often have been persecuted costs of living alone and living in
droppings, killing of vegetation due like Christmas lights red as glowing by humans. Although the extinction groups. In choice of social systems
to the toxic effect of the droppings, embers. of Passenger Pigeons was partly due as in other aspects of behavior, indi-
or even destruction of trees—the The experience would have been to the clearing of their oak-beech for- viduals who adopt the best strategy
extinct Passenger Pigeons roosted perfect, except for the actions of oth- ests for agriculture, the birds' huge or whose behavior is flexible enough
in flocks so thick that sometimes er humans. A boat arrived part-way communal roosts and dense migra- to change as food or predation levels
trees as large as two feet in diameter through the show, and motored close tory flocks and nest colonies made change, leave more of their kind. This
toppled under their weight. to the roost trees, scaring the birds up them easy to kill. People used guns, process of perpetual fine-tuning al-
But roosts also can provide hours into a cloud of red that quickly settled nets, dynamite, and clubs to slaugh- lows generation after generation to
of quiet pleasure for those willing to down again. Then another boat went ter the birds, and burned grass or meet the changing ecological chal-
sit and watch them for a while. Most by, the people clapping their hands sulfur below their roosts to suffocate lenges they face. ■
birds arrive and leave roosts at a to scare the birds and laughing at them by the thousands (Fig. I).
particular light intensity, so you can their success. This was a typical Thankfully, most predators do Suggested Readings
enjoy a stream of birds flying in or evening, our guide told us. Although not have such potent destructive Krebs, J. R. and N. B. Davies. 1993.
out, and can estimate the number of legally protected, the birds were still forces at their command, so the con- Living in Groups. Chapter 6 in: An
birds at the roost. As sites within the frequently killed and served as deli- spicuous nature of groups is rarely as Introduction to Behavioural Ecol-
roost may vary in quality—some are cacies—often by those responsible detrimental as it was for the unlucky ogy. Oxford & Boston: Blackwell
too exposed to the elements, some for their protection. Passenger Pigeons. Natural selection
Figure G. Communal Roost of Turkey Vultures: Certain bird species spend the night Scientific Publications.
are too vulnerable to predators, in large communal roosts—some only during the nonbreeding season, others year
some are targets for droppings from round. Some roosts consist of a single species such as the Turkey Vultures shown here,
above that may soil feathers—you whereas others may contain many different species: herons, egrets, and ibis often
may see aggressive and submissive roost together, as do various blackbirds, grackles, cowbirds, and starlings. Other spe-
displays as individuals sort out who cies that may roost communally at certain times of the year include swallows, crows, -*.,i' 'IV,— -')" .
may perch where. ravens, geese, and cranes. Photo by Joe McDonald -.1■,,
is -:-.N.-
" , -‘14( ..- V-....g- 'led ---",4,--
... .,„„ '1, , -sft 11.- . ,. . . . . `11P-
One evening on the island of ''''''' — N,_ , "ek: ..„4... ti ..lor N"":
-.... -,„..... ir
Trinidad off the coast of Venezuela,
'' •■,- 04 a-
I was lucky enough to visit a Scarlet
Ibis roost in the Caroni Swamp.
The engine noise of even our small
boat seemed a crass intrusion on ''''. 1 ' "Mi.fr "4 —
,, -....„.e-
'
-"Ss. ,,—
v.74'-'41-7V-- te-

the lazy jungle river, so I was re-

lieved when we paused and cut the
engine. Ahead lay open water as
vivid blue as the sky, cluttered with
large, steeply mounded mangrove
islands, rising like tortoises against
the horizon. We waited, watching
the blues and greens darken a bit
as dusk approached, and finally, a
bright red speck appeared in the
sky. As it drew closer I could clearly
see the black wing tips against the
scarlet body, vibrant in the setting
sun. It landed in a nearby mangrove.
Another appeared, and another, and
soon streams of red were coming in
from all directions. As the islands
slowly turned from green to scarlet,
the clamor increased, as if some-
Figure I. Shooting Wild Pigeons In Iowa: Birds that gather in conspicuous groups always have been vulnerable to persecution by
one were gradually turning up the
humans. The Passenger Pigeon, shown here, migrated in dense flocks and roosted in huge aggregations, both of which allowed
volume on a recording of a noisy Figure H. Eastern Bluebirds Roosting Together in Winter: One of the functions of people to slaughter them by the thousands. People shot multitudes of birds from passing flocks, and used many methods to kill
crowd. Then, in a vision etched for- roosting together may be to keep warm at night in winter. This group of 11 Eastern roosting birds en masse. Clearing of oak-beech forests for farming also contributed to the species' extinction. From Leslie's Il-
ever in my mind, the last direct rays Bluebirds (females on the right, males on the left) spent chilly nights together in a lustrated Newspaper, September 21, 1867. Artwork reprinted with permission of the State Historical Society of Wisconsin (item
hollowed-out log. Photo by Michael L. Smith. number WHi(X3)14277).

Cornell Laboratorq of Ornithologq Handbook of Bird BioloBq

6.68 John Alcock Chapter 6 — Understandin8 Bird Behavior 6.69
odds of survival for any one of the departees. These observations are Northern Gannet
consistent with the predictions of the "dilution effect" hypothesis. Huge, Dense
Danielle Clode (1993), however, argues that the clustering of Nesting Colony

nesting birds actually attracts many predators, and thus the "dilution
effect" only slightly reduces this negative consequence of colonial
life. Instead, she favors the "information center" hypothesis, arguing
that the primary benefit to individuals in large seabird colonies lies in
foraging gains.
Clode's position is based on an analysis of three categories of birds
that feed in or near the ocean during the breeding season: (1) offshore
or pelagic feeders, which hunt schooling fish far out to sea and far from
their nests, (2) inshore feeders, which forage close to shore, reasonably Offshore Feeding
near their nesting areas, and (3) shore feeders, such as marine waders, Little Tern
which hunt on shore in the intertidal zone, closest of all to their nests.
Clode points out that the birds that feed farthest from their nests form
the largest and mostdensely aggregated colonies (Fig. 6-35). Birds such
as gannets and mu rres hunt for patchily distributed prey that is unpre-
dictable in space but extremely abundant when located. Under these
circumstances, individuals may well gain by observing their fellow
hunters' successes. Moreover, not only can they locate large schools
of fish well out at sea by living where they can observe others, they
also can join forces with their fellow colony members to dive into the
school together. Mass attack defeats the evasive tactics of schooling fish,
providing more food for all. In contrast, inshore and shore feeders—for
example, the small terns and shorebirds such as sandpipers—pursue
prey that is probably more evenly distributed. If so, communal foraging
produces fewer benefits because there is no prey "hot spot" to locate,
which reduces selection for nesting together.
The fact that pelagic seabirds are highly aggregated, that inshore
feeders nest in smaller colonies, and that waders nest solitarily is con-
sistent with the information center hypothesis. Nevertheless, Clode's
conclusion that information sharing is the primary factor in the evolu-
tion of large nesting colonies of seabirds is currently under investigation
and remains tentative at this time.

Reproductive Behavior: WIN Are There Different Shoreline Feeding

Kinds of Avian Mating Stjstems?

Because of Darwinian natural selection, reproduction is the
central feature of bird life, around which all other aspects of behavior Figure 6-35. The Relationship Between Seabird Nest Colony Size and Distance From Feeding Area: Colonial breeders may de-
rive foraging benefits from living together. The information center hypothesis proposes that individuals living in dense colonies
revolve. One striking aspect of avian reproduction is the extent to
may improve their food-gathering success by following neighbors that are successful foragers to good feeding areas. Evidence
which one male cooperates with one female in the attempt to leave supporting this theory comes from analyses of the breeding habits of various seabirds (Clode 1993). Offshore or pelagic feed-
surviving descendants. Almost all the birds whose behavior we have ers, such as Northern Gannets (top), feed on schooling fish far out to sea, at a great distance from their vast nesting colonies. The
mentioned thus far, fromYel low Warblers to gannets, are monogamous location of such fish schools at any given time is impossible to predict, but once one is located, there is plenty of food for many
species in which one male pairs with one female in a given breeding predators. The information center theory suggests that individual birds may locate the fish schools more easily if they live com-
munally, where they can observe the success of their fellow colony members. In contrast, inshore feeders (middle), such as Little
season. In fact, over 90 percent of all birds fall into this category. This
and other terns, forage closer to shore, reasonably close to their smaller, less-dense breeding colonies. Their prey is less patchily
observation is puzzling; monogamy is exceptionally rare in all other distributed and easier to locate, so an "information center" is less important for their foraging success. Finally, shoreline feeders
groups of animals, for which the standard mating system is polygyny, (bottom), such as the American Oystercatcher and other marine waders, search for their evenly distributed food in the intertidal
in which one male mates with several females in a breeding season. zone, closest of all to their nests, which are located solitarily. Information sharing with other birds would presumably be of no
help to them in locating their prey.

Cornell Laboratory of 0 mitholo8y Handbook of Bird Bioloti

 John A (cock Chapter 6 — Understanding Bird Behavior 6.71
Monogamy in birds is a Darwinian puzzle for the following rea- Figure 6-36. Nest Mound of the Australian Mal-
sons. Males, by definition, produce sperm, the smaller of the two kinds leefowl: a. Male Malleefowl at his Nest Mound.
b. Malleefowl Pair at a Nest Mound: The male, on
of gametes generated within a species. Females, by definition, produce
the left, is scratching material toward the center of
eggs, which are larger and more costly to manufacture.The difference in the nest mound to regulate the temperature. c. In-
the sizes of sperm and eggs is enormous in all birds; whereas sperm are ternal Structure of the Nest Mound: The male digs
microscopic, a single egg constitutes at least 4 percent of the female's a pit and fills it with a mound of leaves, twigs, and
other organic matter. This forms the egg chamber,
body weight in most birds, and may reach 25 percent for certain kiwis
over which a layer of sandy soil is deposited. Fer-
and albatrosses. Females are limited in the number of eggs they can mentation of the organic matter provides the heat
produce, but males have the potential to fertilize a huge number of necessary for incubation. By poking his bill into
eggs. Therefore, a male's reproductive success would seem to be deter- the mound, the male tests the temperature, which
mined primarily by the number of eggs his sperm fertilize, and the more he then adjusts by moving material to and from the
mound. Photos a and b courtesy of John Alcock.
females inseminated, the more eggs his sperm can reach. The logic of Drawing c by Charles L. Ripper.
this argument dictates that males should compete among themselves
for access to multiple partners, with those winning the competition
becoming successful polygynists. a. Male Malleefowl at his Nest Mound
But most birds seem to ignore this adaptive recipe for male
behavior. Instead, male birds typically remain with a single female
during a breeding season, usually assisting her in nest building, incu-
bation, and feeding the young (Sidebar 5: Length of the Pair Bond). b. Malleefowl Pair at a Nest Mound

In the Northern Mockingbird, males take over exclusive care of young

fledglings when their mates start to construct a new nest for a second
clutch of eggs. For some days, males are in total charge of "child care,"
single-handedly feeding and protecting their fledglings against a large
array of mockingbird consumers.
Male megapodes are even more impressive examples of pa-
ternal birds. Males of the Australian Malleefowl, for example, build
a huge nest mound that contains an average of 7,480 pounds (3,400
kg)—nearly 4 tons—of sand, dirt, and decaying vegetation (Fig. 6-36).
Females, about the size of small hen turkeys, lay their eggs at intervals
in the mound. Each time a female visits, the male opens the mound so
she can deposit a single egg deep in the pile; then he closes it up again.
Moreover, after the eggs are well buried, the male regulates the heat
within the "compost heap" by shifting mound material onto or away
from the eggs. The average amount of debris a male moves to prepare
the mound to receive an egg and then cover it up is about 1,870 pounds
c. Internal Structure of
(850 kg), about 500 times the bird's mass, or the human equivalent of the Nest Mound
shoveling about 35.2 tons of dirt (Weathers et al. 1993). Although male
Mal leefowl are remarkable paragons of paternal ity, the parental contri-
butions of males of most other bird species are not to be sneezed at. Egg Chamber

What factor has selected for the spread of monogamy in bird

populations? According to Gordon Orians (1969), the answer is the
male bird's unusually high potential for productive parental care. Un- Undisturbed Soil
like male mammals, which cannot produce milk and so generally do
not feed their young, male birds can do almost everything that a female
can—except lay eggs. As a result, the potential to improve the repro-
ductive success of a partner is unusually high in the typical male bird
compared to a typical male mammal.
If this argument is correct, experimentally removing a helpful male
parent should greatly reduce the production of young by the surviving
(Continued on p. 6.73)

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

6.72 John Alcock Chapter 6 Understanding Bird Behavior
—
6.73
Sidebar 5: LENGTH OF THE PAIR BOND female parent. When the experiment was done
with Snow Buntings (Lyon etal. 1987), there was 8
Sandy Podulka
in fact a sharp decrease in the output of young
(Fig. 6 37), which supports the hypothesis that
-

A few types of birds, such as grouse data from banding studies show that individuals all have been known to
monogamous males are compensated for their
and manakins (see Fig. 6-42), asso- for most species, this is the exception. pair for three consecutive years, and
ciate with the opposite sex only to
inability to be polygynous by helping their part-
Of 200 pairs of Song Sparrows studied Downy Woodpeckers, for four.
copulate. Others stay together for a by Margaret Nice, for instance, only 8 ner to raise more young.
Some species, especially the
few days (Ruby-throated Humming-
4.5
retained their mates the next breeding long-lived ones, mate for life. Geese,
birds), and some split after a pro- season. Between breeding seasons, swans, cranes, petrels, albatrosses,
longed courtship and mating period of course, many birds die, especially
Reproductive Behavior:
oystercatchers, Herring Gulls, some
(ducks), but most birds stay together migrants. But the rate of mate-chang- shearwaters and penguins, ravens, Resource-defense and 2.7
for at least a breeding season. We ing is much higher than the mortal- some crows, many parrots, road-
tend to imagine that birds keep the ity rate. Occasionally birds do keep runners, Wrentits, Tufted Titmice, Female-defense Polqgqnq
same mate from year to year—surely the same mates. Certain American White-breasted Nuthatches, Pygmy Although most birds form monogamous
the same pair of Eastern Phoebes is Robin, Northern Cardinal, Song Nuthatches, Brown Creepers, Cactus pair bonds, a few do not. Understanding ex-
nesting under my eaves again?—but Sparrow, and Northern Mockingbird Wrens, and some House Sparrows
ceptions to the rule is always interesting, so
all retain the same mate from one
we shall explore the unusual cases at some 0
breeding season to the next (Fig. A).
length to show how evolutionary theory can Widowed Control
One Royal Albatross pair was seen (13 Nests) (11 Nests)
together for 15 consecutive years, help to explain the rare mating systems of birds
as well as the most common type. Among the Figure 6-37. Effect of RemovingMale on Snow Bunting Reproductive
and a pair of Mute Swans in England
Success:Snow Buntings are monogamous, with both parents bringing
lasted 8 years before one mate died. small minority of nonmonogamists are those
food to the young. When Lyon et al. (1987) experimentally removed
The "widow" waited three years be- that practice one or another form of polygyny. the male parent from 13 nesting attempts, they found a decrease in
fore re-pairing. Male Red-winged Blackbirds caroling in a cat- the reproductive success of the widowed females compared to that
Birds that keep their mates from tail marsh are familiar polygynous birds. The in 11 control nests. Widowed Snow Buntings raised an average of
year to year may reap some benefits. calling, chasing, and red-epaulette-flashing
2.7 young to fledging age, whereas control females who retained
Since they begin the breeding sea- their partners raised an average of 4.5. This study provides evidence
are part and parcel of the competition among that males who remain and help to rear young in monogamous situ-
son with a mate, they may be able
males for territories that may attract more than ations, instead of leaving to pursue other females, may gain benefits
to secure a better territory or start
nesting sooner—young fledged ear-
one mate (Fig. 6 38). Because female redwings
- in terms of the number of young they raise. These benefits may offset
choose partners by evaluating the quality of the those potentially lost by not being polygynous. Adapted from Lyon
lier in the season have more time to et al. (1987).
gain strength and experience before territories controlled by males, the mating sys-
winter. Also, experienced couples tem of this species has been labelled resource-
presumably have already learned defense polygyny by Stephen Emlen and Lewis
how to cooperate in a breeding ef- Oring (1977).
fort. In Black-legged Kittiwakes, ex- The reproductive benefits of this mating
perienced pairs start breeding earlier, system are clear for the males that achieve
lay more eggs, and raise more young
polygyny. The puzzle is why female redwings
than do new pairs. ■
would bond with a male that had already se-
cured one or more mates, if unmated males
Figure A. Greater Sandhill Crane Pair:
Many long-lived bird species, such as were available (and they almost always are).
these Greater Sandhill Cranes (a sub- Females with polygynist partners must accept
species of Sandhill Cranes), mate for life. less parental assistance for their offspring than
By starting the breeding season already
females that pair with a previously unclaimed
paired (and thus spending less time in
mate attraction and courtship), these
male, who can then provide undiluted care for
species may reap some benefits such as their progeny. However, when the quality of ter-
obtaining a better territory, or beginning ritories varies greatly, as has been documented •
to nest earlier in the season—and young in a number of locations, females that share a Figure 6-38. Displaying Male Red-winged Blackbird: Loud calling
fledged earlier may have a better chance and displaying of prominent scarlet epaulettes is part of the com-
resource-rich territory with other females can
of surviving. Experienced pairs also petition among male Red-winged Blackbirds for control of prime
may benefit by already knowing how to potentially do as well as, or better than, those territories. Females choose mates based on the quality of their ter-
cooperate in a breeding effort. Photo by that pair with a male on a territory that is short ritories—an example of resource-defense polygyny. Photo by Marie
Marie Read. of food or safe nesting sites. Read.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 John A lcock Chapter 6— Understanding Bird Behavior 6.75
Figure 6-39. Montezuma Oropendola
Nest Colony: Females of this Central Reproductive Behavior: Lek Polieinq
American species weave their long, Males of some other polygynous birds defend tiny display sites at
hanging nests in colonies in certain
a traditional mating location termed a lek.The sites do not contain use-
isolated trees. Males gather at these sites
and compete fiercely with each other
ful resources or nesting colonies of females. Displaying males of these
for control of the clumped females—a lek polygynous species may be visited briefly by sexually receptive
mating system known as female-de- females. After mating, the females leave their partners and go to other
fense polygyny—forming a dominance areas to nest and rear the young entirely without male assistance.
hierarchy in which the top-ranking male
Famous examples of lekking birds include the birds-of-paradise,
secures the majority of copulations.
Main Photo: Montezuma Oropendola Ruffs (Fig. 6-40), many of the manakins and bowerbirds (Fig. 6-41),
nest colony in a tree. Photo by R. and both cock-of-the-rock species, certain pheasants (such as the pea-
N. Bowers/VIREO. Inset Lower Left: cock), and many grouse. Males of the Satin Bowerbird, for example,
Close-up view of a male Montezuma
defend small territories on which they build their bowers, two parallel Figure 6-40. Lek of the Ruff: In lek
Oropendola. Inset Lower Right: Close-
up view of the nests showing their pen-
rows of curved twigs painted with saliva and charcoal (see Fig. 6 41 a). - polygyny, many males perform their
dulous shape. Inset photos courtesy of In front of the avenue between the twigs, males scatter a variety of courtship displays at a traditional court-
Michael Webster. generally blue items, especially parrot feathers, which they collect ship ground termed a lek, where each
bird defends only a small display site.
from the forest. Neighboring males drop by from time to time, and if
Females visit the lek only for mating. A
the resident bower builder happens to be absent, they may wreck his well-known example of a lekking spe-
bower and steal his decorations, which they take back to ornament cies is the Ruff, a shorebird that gathers
their own bowers (Borgia 1986). in the breeding season at established
leks in the Eurasian tundra. The male
Females also occasionally visit a series of bowers; at each stop
Ruff in breeding plumage has exagger-
they are treated to elaborate visual and acoustical displays from the ated ear tufts and a collar of prominent
bower owner (male bowerbirds are vocal mimics that incorporate neck feathers, both of which show great
the songs of many other species into their lengthy display routines). individual variability in color and pat-
Despite the displays, females usually go on their way, but sometimes tern. Males display to females by running
excitedly around with fluttering wings
they enter the bower, crouch down, and permit the male to copulate.
and expanded ruffs, and then suddenly
freezing in place, bowing low with their
spectacular ruffs fully erected, wings
outspread and quivering. Shown here
are four males displaying to a single
female. Drawing by Robert Gillmor.

6 A very few birds practice female-defense polygyny, in which

males fight for control of clusters of nesting females, rather than re- ••"9-

source-rich territories. In the Montezuma Oropendolas of Central

America studied by Michael Webster (1994), females form nesting • I. 04 110 .4

colonies in certain trees (Fig. 6-39). Males gather at these sites when
females are fertile and compete for access to them. A male dominance
■ %6 '
l if , f %' •
Pf^om- • • • "
••
Ilip q •1 /
,.4._. ...
) .: l%.
0460000111tN ■ /ANA•1/.44‘ s' 1 11∎•.• •
'414
i,„, %! .ts--
' -
hierarchy results, with alpha, beta, gamma, and still more subordinate .% Vj
I,
...i•C-'-•-•-=:.--
- . 11'
.„.:... ,..„..„_. l.
Vi VAN
• •••.‘ thAi
\ \ 11/.01 ‘ \411 ‘`,\
' 0)7 *W101.\\ ,, ' t.,„„,„.,,
individuals perching in and around the nesting tree. The top male at- . \.\\1/4/''!, .‘„,•,,
tacks rivals that approach receptive females and physically prevents
•' A
them from mating. As a result, the alpha male secures 90 to 100 percent ,,, AA01, ,1 1110y,i/ , 9144‘(,11
o *tif , -,•91 \ hi; 01,1 NIV,))40, ,,
of all copulations at the nesting colony. A \
V
Resource-defense and female-defense polygyny may evolve
\ • \I 414 ,
when male parental care is less important to female reproductive suc-
cess than other factors, such as safe nesting sites or rich food supplies ..;,,)410%
on a territory. Freed from the demands of paternal behavior, males can
‘1110 " ‘‘‘ A1•04ii‘14114
compete among themselves for key resources that females desire, or
can compete directly for clusters of females, depending on the condi- , , ,

tions that determine the distribution of females.

1'4 ilii„414
Cornell Laboratorq of Ornithologq Handbook of Bird Biologq
6.76 John Alcock Chapter 6— Understanding Bird Behavior 6.77
a. Satin Bowerbirds at Avenue Bower b. MacGregor's Bowerbirds at Maypole Bower In any population, only one or a very few males are chosen by most
of the receptive females over the course of the breeding season. As a
result, many male Satin Bowerbirds fail to secure a single partner in a
given year, even though they may be inspected by a large number of
highly selective females.
The mating behavior of Satin Bowerbirds has many similarities
to that of most other lek polygynous birds. For example, males of the
White-bearded Manakin of South America defend small saplings
within a display court cleared of leaves (Lill 1974) (see Ch. 7, Sidebar
1, Fig. F, as well as Track 16 on CD or cassette). Groups of males have
their display courts close together. When a female appears, males
rocket from their sapling perches to the ground and back, cracking
their clubbed wing feathers together to add an acoustical component
to their display. Females appear highly choosey, and most pick the
same individual from among the battery of potential mates. After cop-
Figure 6-41. Bowerbird Courtship: The bowerbirds of Australia ulating, the female goes off to rear her offspring without male parental
and New Guinea have substituted the building and decorating of assistance; the male resumes his energetic attempts to attract addi-
complex structures for elaborate displays and plumages. Males
tional mates. Many other manakin species have similarly spectacular
of most of the 18 species, true to their name, build bowers on the
ground at which they accumulate a variety of brightly colored ob- displays (Fig. 6 42).
-

jects—flowers, butterfly wings, fruit, feathers, bright leaves, and The evolutionary basis of lek polygyny is especially difficu It to ex-
so on. The bower, which may be one of several different types, at- plain because it would seem more profitable for males to compete for
tracts females who visit for courtship and mating, and then depart
resources that attract mates than to devote their energies to defending
to nestaloneelsewhere. a. Satin BowerbirdsatAvenue Bower: The
Satin Bowerbird builds a type of bower termed an avenue bower. territories used solely as a platform for highly bizarre displays. In the
The male constructs two parallel walls of interwoven twigs stuck environment of some species, however, neither resources nor females
in the ground, the avenue between the walls giving the bower its may be clumped spatially, greatly raising the energetic cost for males
name. He aligns the bower along a north-south line, at the north to attempt to defend resources or females. If, in addition, males can-
end of which is a display court. This he decorates with numerous
not contribute usefully to the welfare of their young (perhaps because
colorful objects, which may be natural or human-made; he shows
a strong preference for shiny, blue items. A visiting female enters their presence at a nest would make it much more conspicuous to
the avenue and watches the displaying male from within it. If the efficient nest predators), parental-assistance monogamy also cannot
female signifies her willingness, the male enters the avenue and evolve. Under these special conditions, the absence of any other prof-
mates with her. b. MacGregor's Bowerbirds at Maypole Bower:
itable mating tactics for males makes lek polygyny the default mating
The MacGregor's Bowerbird builds a maypole bower, a central
system.

01I
pole with a circular display court at its base. The male chooses
a thin sapling, which he surrounds for much of its height with
horizontal piles of sticks, their ends decorated with hanging items c. Vogelkop Bowerbird with Maypole Bower with a Hut
such as regurgitated fruit pulp. At the pole's base he constructs Reproductive Behavior: Polqandrii
a display court in the form of a circular mat of compressed moss Another kind of mating system that is extremely rare in birds is
with a rim. Objects such as seeds or woody black fungi are used
a form of polyandry in which one female forms pair bonds with two
to decorate this court. During courtship, male and female move
back and forth around the court, keeping the maypole between
or more males, as seen in the Spotted Sandpiper, most jacanas, and
them. When the female stops moving, the male expands his bright certain phalaropes (Oring 1985). The behavior of female Spotted
orange head plume, shaking it from side to side while remaining v" . Sandpipers and Northern Jacanas (see Fig. 4-18b for Wattled Jacana)
behind the maypole; he then moves forward and mates with 711 resembles that of males engaged in resource-defense polygyny. They
the female. c. Vogelkop Bowerbirds at Maypole Bower with a - -
defend territories that contain safe nesting sites and access to food.
Hut: A more complex maypole bower, with an open-sided,
hut-like structure over the circular display court, is built by Females with adequate territories attract males, who settle there, build
theVogelkop Bowerbird. Its roof of sticks, several feet high, nests, accept the clutch of eggs that their partner donates to them, and
is supported by a vertical sapling, and the floor beneath it incubate and care for the young when they hatch—all without female
is cleared of litter. The male decorates the floor with nu-
assistance. Instead, females devote themselves to securing sufficient
merous neat piles of decorative objects, carefully sorted
by color, which in the case of perishable items like flowers
food to produce another clutch of eggs and, in the case of the Spot-
and fruit, he replaces daily. The impression is of neatly kept ted Sandpiper, to acquiring another territory in competition with rival
garden beds, and in fact another common name for this spe- females. Females that succeed may attract a second male; when he
cies is the Vogelkop Gardener Bowerbird. accepts the clutch, he, too, is abandoned and must provide all the

Cornell Laboratorg of Ornithologq Handbook of Bird Biologq

6.78 John Alcock Chapter 6— Understanding Bird Behavior 6.79
Figure 6-42. Group Courtship Display of the a parental care. In the Northern Jacana, a female's territory may be suf-
Blue Manakin: The manakins, which range
ficiently large and rich in resources to attract several males, each one
from central Mexico to northern Argentina, are
noted for their stereotyped courtship behavior. of which nests in the successful polyandrist's domain.
Although the plumages of the males of most of In contrast, the polyandrous female phalarope does not defend
the 59 species are quite colorful, they are none- a useful territory, but instead directly locates a male, defending him
theless modest when compared to those of the against competing females until he accepts her clutch. She then pro-
birds-of-paradise (see Fig. 3-10). Each male
duces a second clutch, if possible, and tries to find and defend another
manakin performs a species-specific series
of precise and intricate courtship maneuvers, male to incubate her eggs and attend the young for a time after they
which are often accentuated by sounds, but hatch.
are enhanced only secondarily by plumage The evolution of polyandrous mating systems of the sort descri bed
b
displays.
here poses special problems for evolutionary biologists—puzzles that
Male manakins perform in traditional dis-
play areas known as courts, many of which have have not been fully solved. The key puzzle is why males would enter
been used for generations. Depending on the polyandrous pairings, which require that they fertilize only some of the
species, some courts are on the forest floor, and eggs produced by their partner, who has additional mates. But perhaps
others are in trees. All the courts meet certain in cases of this sort one parent is as successful as two would be in caring
requirements, such as the appropriate number
for a clutch of eggs and the resulting youngsters. Furthermore, there is
and size of the saplings, twigs, and branches for
maneuvers; and must have a clear and unob- evidence that, in the Spotted Sandpiper at least, adult males slightly
structed approach, enabling females to see the outnumber adu It females, providing opportunities for females that des-
performances and reach the courts readily. In ert their first partners. Given these two factors, if females consistently
some species the males perform on their courts
do not care for their eggs, mated males are left with two options: to
alone, but in others several males perform in
interacting groups (see Fig. 6-47). abandon the clutch, which will then fail, or to stay put, providing the
The Blue Manakin of South America, shown necessary parental care by themselves, and thus making the best of the
here, is one species that performs a cooperative situation that arises from the absence of an incubating partner.
display. In this species, three, or sometimes
more, males display to females from a vine a
few feet above the forest floor. In this drawing, Mate Choice: Extrapair Copulations in Birds
birds #1, #2, and #3 are males, and the fourth
bird is a female. a. The female perches at one
Although most birds pair off one male to one female, in recent
end of the vine and the males crouch along the years infidelity has been discovered to be far more common than once
vine, oriented toward her, quivering and giving believed. Many supposedly monogamous birds are effectively polyga-
rhythmic, twanging calls. b. The male closest to mous, with individuals of both sexes sometimes copulating with more
the female (male #1) jumps up and flies toward
d than one partner in a breeding season (Birkhead and Moller 1992).
her, briefly hovering, then flies toward the far
end of the line of males. c. Male #1 lands on Copulations with birds other than one's mate are termed extrapair
the perch at the far end of the line of males, but copulations (EPCs).
faces in a direction opposite to that of the other, Evidence for extrapair copulations comes from two sources:
males. Meanwhile, the other males have all
direct observation of marked individuals showing that some mate
sidestepped along the perch, moving one place
forward, male #2 now being the closest to the
with several different partners, and molecular studies of the paternity
female. d. Male #2 now jumps up and hovers of clutches of young, which sometimes reveal that the presumptive
before the female, then flies back toward the far father cannot possibly have been the actual father for all of the young
end of the line. Male #1 swivels to face in the under his care.
same direction as male #3. e. Male #2 lands at
The use of DNA fingerprinting (analysing DNA from different
the end of the line, facing in a direction opposite e
to that of the others. This sequence proceeds, individuals to determine sufficient structural details to identify indi-
each male describing a circular flight path away viduals and their relatives with a high degree of certainty) and other
from the female, attaining such speed that the related genetic techniques has established that pair-bonded females
display eventually resembles a rotating wheel of
sometimes copulate outside the pair bond at times when they are
birds. The joint display ends when the dominant
male flies up in front of the other males and gives fertile. In one study of wild Zebra Finches, for example, DNA fin-
a shrill call, causing them to disperse. The dom- gerprinting demonstrated that 2 of 82 offspring were definitely not
inant male then proceeds with a solo display fathered by the male paired to the mother, indicating a relatively low
of slow-motion flights to and from the perch, frequency of infidelity in this population. In contrast, about a quarter
which, if the female is sufficiently impressed,
of all female Tree Swallows in one population were estimated to have
culminates in copulation. Adapte4 from draw-
ings by William C. Di lger. engaged in at least one EPC.

Cornell Laboratorq of Ornithologq Handbook of Bird Bioio9q

6.80 John A lcock Chapter 6— Understanding Bird Behavior 6.81
An even higher degree of infidelity has
been recorded in the Superb Fairywren (Fig.
6-43), which forms breeding pairs that oc-
cupy year-round territories in suitable habitat
in eastern Australia. Males help their mates
defend the territory and feed the young, par-
ticularly in the fledgling stage, and so might
have been considered more or less typical
monogamous birds were it not for careful
observation of color-banded individuals by
several Australian ornithologists. They found
that while a male's partner is building a nest
and incubating eggs, he is likely to visit other
females on neighboring territories. There the
"philandering" male courts his neighbors'
Figure 6-43. Superb Fairywren: Male mates, often displaying his iridescent blue crown and cheek patches b. Magnificent Frigatebird
in breeding plumage. These year-round while carrying a yellow flower petal in his beak. Resident males attack
residents of eastern Australia appear Figure 6-44. Elaborate Male Orna-
intruders to the extent that they can detectthem, but "phi landerers" are
monogamous, but close study has re- ments: a. Greater Bird-of-paradise:
vealed that they commonly engage in
extremely persistent, especially with respect to females in their fertile
A male displays his ornate plumage.
extrapair copulations. Photo by C. H. phase—the week they lay their clutches of eggs. Drawing by Robert Gillmor. b. Mag-
GreenewalVVIREO. To determine whether fairywren intruders fertilize some eggs laid a Greater Bird-of-paradise nificent Frigatebird: A male with its
by their neighbors' mates, Raoul Mulder (1994, see Suggested Read- gular sac expanded into a scarlet bal-
loon during display. Photo courtesy of
i ngs) employed DNA fingerprinting to check the paternity of nearly 200
Lee Kuhn/CLO.
nestlings in his study population in Canberra. He found that more than disproportionate share of all the extrapair fertilizations in his large
three-fourths of this sample had been fathered by intruder males—not study population of Superb Fairywrens.
the mothers' pair-bonded partners. Females in this population clearly
engaged in EPCs at times when their eggs could be fertilized. Mate Choice: Whq Do Some Birds Displaq
The benefits of EPCs to outsider males are obvious. They visit
nearby territories at times when their own regular partners are not Elaborate Ornaments?
fertile, and if they succeed in fertilizing a neighboring female, their In a great many species of birds, including any number that are
"extra" offspring will be cared for by another male. In this way a suc- at least superficially monogamous, males possess striking plumage,
cessful "philanderer" can raise his lifetime production of surviving off- combs, wattles, inflatable sacs, and the like (Fig. 6-44; also see Figs.
spring at relatively little energetic cost to himself (at least with respect 3-6, 3-43, and 6-40). Previously, we noted that males of the "mo-
to parental care). nogamous" Superb Fairywren show their iridescent cheek and crown
The benefits of EPCs to females are less obvious. Outsider males feathers to prospective mates. Males of the familiar Barn Swallow, a
do not usually assist parentally, eliminating extra parental care as a similarly "monogamous" species, possess two unusually long outer tail
possible incentive for females. In the European Dunnock, however, feathers, which females examine when selecting a male with which to
females that mate with several males do get help from their multiple breed (Fig. 6-45). Anders Moller (1 992) has shown that both the length
partners in taking care of the young. and symmetry of these tail ornaments influence a male's chances of
To account for EPCs in Superb Fairywrens, some researchers acquiring a mate early in the breeding season. Only males with rel-
have suggested that females gain sperm with unusually "good genes" atively long and symmetrical outer tail feathers are likely to attract a
through extrapair matings with superior males. According to this hy- mate soon enough to be able to father two broods in one breeding
pothesis, females evaluate the health, longevity, or competitive ability season in northern Europe, where Moller did his research.
of neighboring males and then copulate with the best of the lot, en- Although elaborate ornaments and complex displays occur in
dowing their offspring with hereditary traits superior to those of their certain "monogamous" species, lek polygynous species exhibit some
pair-bonded partner. of the most extreme examples. The males of one bird-of-paradise have
If this hypothesis is correct, many females should select the same beautiful powder blue plumes, which they can erect and vibrate whi le
males for their EPCs. Mulder's DNA fingerprinting work showed that hanging upside down from a perch to display to a potential mate. The
one male, two of his sons, and a grandson were responsible for a highly orange inflatable sacs of Greater Prairie-Chickens come into play

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6.82 John A lcock Chapter 6 — Understanding Bird Behavior 6.83
Figure 6-46. Number of EyespotsVersus
Symmetrical Asymmetrical +1
Mating Success of the Male Peacock:
Petrie and Halliday (1994) captured

Cha nge in Average Numbe r o f Cop ula tions

male Indian Peafowl between breed-
0 ing seasons and removed 20 eyespots
(by snipping them out) from their trains,
• then returned them to the wild. Males
with the number of eyespots reduced
averaged 2.5 fewer copulations during
the following breeding season than in
previous seasons, compared to a control
-2 group who showed no such decline in
number of copulations. This difference
between the experimental and control
groups was statistically significant. Pre-
-3
vious field observations had shown that
the males with more eyespots in their
trains obtained more copulations during
-4 a breeding season. These data provide
evidence that females choose males on
Barn Swallow the basis of the number of eyespots in
Experimental Group: Control Group: their trains, and thus that the elaborate
Museum Specimens
6 Males, 15 Males,
trains of peacocks evolved through fe-
20 Eyespots Removed Trains Unaltered
male choice. Adapted from Petrie and
From Each Train
Figure 6-45. Symmetrical and Asymmetrical Barn Swallow Tails: According to a study carried out by Moller (1992) in northern Halliday (1994).
Europe, both the length and symmetry of the outer tail feathers of male Barn Swallows appear to influence a male's ability to attract
a mate early enough in the breeding season to be able to raise two broods of young. In these photographs of museum specimens,
with the mating success of their owners. She and her colleagues found
note the similar-length outer tail feathers on the bird on the left, compared to the very different lengths of the two outer tail feathers
of the bird on the right. Photo courtesy of Marie Read/CLO. that 50 percent of the variation in the number of copulations secured by
males at one lek could be attributed to variance in eyespot number. In
when males boom out their mate attraction calls while performing a other words, why a few males did very well in the mating game while
courtship dance in front of observant females that have come to the most did poorly could be explained in large measure by the differences
lek to select a mate. Wild male peacocks erect, spread, and shiver in their numbers of eyespots.
their overblown, magnificently patterned, blue-and-green "tail" under It was possible, however, that females were not focusing on eye-
similar circumstances (see Fig. 3-6). spots, but on some other aspect of the male's appearance or behavior
The peacock's train constitutes the classic example of an elab- that happened by chance to be correlated with eyespot number. Petrie
orate male ornament, but only in recent years have hypotheses on its therefore devised an experiment in which she decreased the number
evolution been rigorously tested, by Marion Petrie and her co-workers. of eyespots in some males to test the prediction that these birds would
One idea long deemed plausible is that a female preference for males suffer a decline in mating success (Fig. 6-46). She and her co-workers
with elaborate trains has produced sexual selection via female choice captured six males, and from each snipped out 20 of the outermost
for this male attribute. eyespots—one from the end of each of 20 tail feathers—and released
Sexual selection is a form of natural selection that occurs if their subjects. During the following breeding season, they observed
individuals differ in their ability to acquire mates. Such differences the 6 experimental males as well as 1 5 control males whose tails had
typically arise because males differ in their competitive ability or be- not been altered. They found that on average the controls mated about
cause males differ in their attractiveness to the opposite sex. (In some as often as they had in preceding seasons. In contrast, the experimental
species, males can exert sexual selection on females through mate males (with fewer eyespots) averaged 2.5 fewer matings that year—a
choice, but this is an exception to the rule.) Thus, with respect to the significant decline and one that supports the hypothesis that female
peacock's tail, it is possible that males with elaborate trains are better choice by peahens is responsible for the evolution of elaborate trains
able to intimidate rival males and so keep them away from females. But with hundreds of eyespot ornaments.
it could also be that males with highly decorated tails are especially But what do peahens gain by choosing certain males? Let's
attractive to receptive fema les. Petrie chose to examine the second pos- consider three major alternative explanations: the good genes, the
sibility (Petrie and Halliday 1994,
see Suggested Readings). She asked runaway selection, and the direct benefits hypotheses (Ryan 1997;
whether peahens exerted sexual selection in favor of males whose tails Reynolds and Gross 1990) (Table 6-3). Earlier we noted that the good
were ornamented with a larger number of eyespots. She predicted that, genes hypothesis had been invoked to explain the readiness of fe-
if they did, the number of eyespots in male trains would be correlated male fairywrens to copulate with males other than their pair-bonded

Cornell Laboraton4 of OrnitholoBtf Handbook of Bird Biologq

6.84 John A lcock Chapter 6— Understanding Bird Behavior 6.85
Table 6-3. The Reproductive Benefits Gained by Females in Choosing Nonpaternal Sexual Partners with To discriminate among the
Elaborate Ornaments: Three Hypotheses three hypotheses is difficult, be-
cause they tend to produce many
Hypothesis Benefit to Choosy Females of the same predictions. However,
if females benefit by securing
Good Genes Both male and female offspring receive genes that enhance sperm with survival-enhancing
their chances of surviving to reproduce successfully. genes for their offspring from
genetically advantaged males
Runaway Selection Male offspring receive genes that produce elaborate (the good genes hypothesis),
traits that enhance their sex appeal but may reduce their longevity. then the offspring of preferred,
highly ornamented males should
Direct Benefits Females gain improved survival or fertility by avoiding diseased have lower mortality rates than
males or those likely to provide infertile sperm. The quality and offspring of less ornamented,
condition of a male's elaborate traits may signal his health status. less attractive individuals. This
prediction has been tested. Petrie
discovered that the offspring of
partners. However, as discussed below, the evidence cited in favor peacocks with more elaborate
of this hypothesis (the fact that females tended to prefer a very few trains grew faster and survived
males in the same paternal line) actually supports all three competing better than youngsters whose fathers had tails with fewer eyespots. Figure 6-47. Cooperative Courtship
hypotheses. This result is clearly consistent with the good genes hypothesis— Display of the Long-tailed Manakin:
Good Genes: The same few males may be chosen because their offspring apparently inherit genes that improve the viability of both
Males of this beautiful Central American
species form long-lasting teams of co-
genes confer survival advantages on their offspring. "Good genes" are sexes, rather than only making male progeny more attractive to females operatively displaying males. Typically
those that contain information that translates into superior foraging (as expected from the runaway selection hypothesis). However, to also two males—an alpha and a beta—call
ability, greater skill in dealing with predators, or better capacity to hold eliminate the direct benefits hypothesis, we still need to know whether together in a highly coordinated fashion
territories—all useful survival aids. the differences in growth and survival of the young birds occurred be- from the forest canopy. Once a female
Runaway Selection:Another possibi I ity is thatfemale mate choice has been attracted, they descend to a
cause some were infected with contagious disease or parasites thattheir display perch to perform an intricately
is adaptive strictly because the sons of males with elaborate ornaments mother picked up through contact with an infected male. Researchers choreographed courtship display that
will inherit these attributes and thereby become irresistible to females. are still studying peacocks and other species, trying to untangle the pos- closely resembles that of the 81 ue Mana-
In addition, the daughters of these choosy females will inherit a pref- sible explanations for why females choose carefully among potential ki n (see Figure 6-42). The top-ranking
erence for the extreme ornaments that make males attractive to many male invariably secures the majority of
mates.
matings, leading biologists to speculate
other females. As a result, they too will tend to mate with attractive
on why the beta male should engage in
males and produce sons of great sexual attractiveness. Therefore, the cooperative courtship with little appar-
evolution of mate choice and sexual ornaments can be driven entirely Mate Choice: ent reproductive advantage—especially
by the aesthetic preferences of females, whether or not males with the
preferred ornaments survive as well as males without them.
Whti Cooperate in Courtship Displaqs? since DNA analysis has determined that
the two males are not related. Never-
A special evolutionary puzzle associated with mate choice is theless, by cooperating, the beta male
Incidentally, the technical term "runaway selection" is used
exhibited by males of the Long-tailed Manakin, which cooperate with benefits by establishing his right to take
because mathematical models have shown that once female mate over the top rank and monopolize fe-
one another in attracting mates (Fig. 6 47). David McDonald's long-
-

preferences and male preferred traits are inherited together, the stage males when the alpha male finally dies
term study (McDonald and Potts 1994, see Suggested Readings) reveals (McDonald and Potts 1994). Here, two
is set for a runaway process in which ever more extreme preferences
that males of this extraordinarily beautiful Central American bird form males, top and bottom left, perform a
and bizarre ornaments can spread through a species.The trains of pea-
courtship display teams of up to 13 members, headed by an alpha and leapfrogging display, one in midair and
cocks, the bowers of certain bowerbirds, and the remarkable plumes the other movi ng toward the female (bot-
beta male. The alpha and beta males often stay together for two or more
of some birds-of-paradise are all candidate products of runaway selec- tom right) on the display perch. Photo by
years, spending most daylight hours at a perch in the forest where the
tion, although as noted, these structures conceivably can be produced Marie Read.
pair sing their loud and ringing mate-attraction song to le do in perfect
- -
by good genes or direct benefits selection as well.
unison over and over again—up to 335 times per hour. Occasionally
Direct Benefits: The third possibility is a straightforward one,
the alpha or beta male leaves temporarily, in which case another team
namely that females benefit by mating with certain males because
member may join the remaining bird for duets that last until the higher-
they are least likely to infect the females with a disease, mites, or some
ranking individual returns to reclaim his place.
other affliction. Th is hypothesis is called the direct benefits hypothesis
Should a female arrive at the lek arena, the two males begin a joint
because the female herself derives reproductive advantages (improved
visual display, leapfrogging over each other on their perch in a stereo-
health) through her choosiness in mating.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

6.86 John A Icock Chapter 6 — Understanding Bird Behavior 6.87
this prediction was difficult, because there seemed to
0\0
be no way to locate and follow the offspring of a set of
females for the long time required before the sons of
those females became part of alpha-beta partnerships.
(Males do not appear to become betas until they are at
least four years old.) Fortunately, McDonald and his
co-worker Wayne Potts could use molecular genetics
technology to establish that any two alpha-beta partners
Siblings = 50% were no more likely to share genes in common than two
-4(
Isolo
individuals drawn at random from the manakin popu-
lation as a whole. Thus, they could reject the indirect
fitness hypothesis.
The direct fitness hypothesis produces testable
predictions, too. If beta males cooperate with alpha
males to establish their "right" to eventually become

d f Cousins =12.5% the top bird, they should move up as soon as the alphas
disappear. McDonald has seen only 11 males become
alphas in his 10-year study—a testimony to the lon-
gevity of these birds. In every case, however, the new
Figure 6-48. How Relatives Share typed fashion, or flying together with exaggerated wi ngbeats back and
top manakin was the previous beta male, not a lower-
Genes: Related individuals share some forth over the arena. On most occasions, females watch and then leave,
of the same genes, having inherited them ranking individual.
but once in a while, after a prolonged spell of cooperative display by
from their common ancestors. A parent Furthermore, females (who also live for many
the two males, females submit to mating. Because McDonald had
and his or her offspring share exactly years) are faithful to a particular mating arena, so when
50% of their genes, because the child color-banded 33 alpha-beta pairs, he could determine the distribution
a beta male assumes the top rank, he tends to secure
receives half of its genetic complement of matings among the males in his study. Over 10 years, he recorded
from its father and half from its mother. sexual access to the females who came to the arena in previous years Figure 6 49. Sibling Rivalry in Nestling
-

263 copulations, of which 259 were secured by the alpha male, who
Full siblings share on average 50% of to mate with the prior, generally older, alpha. Thus, there is a potential Great Egrets: Nestling egrets of various
may retain his top-bird ranking for up to 8 years. species often fight aggressively with their
their genes. This is because, through reproductive payoff for the patient cooperator who secures the beta
each parent, there is a 25% chance that From an evolutionary viewpoint, this result is most surprising. nestmates. Fierce blows from thei r strong
position in a cooperative team. bills can be lethal, especially if one of
any given gene possessed by one sibling How can it be adaptive for the nonmating male to engage in what
will also be in the other (For gene A, for the nestlings is smaller and weaker than
may be years of mutual display, if during this time the male has almost
example: there's a 50% chance of Mom the others, as happens when egg laying,
giving it to sibling 1, and a 50% chance
no chance to mate? McDonald tested two alternative hypotheses on Parental Behavior: Wht1 Do Some Birds Ignore and thus hatching, is staggered. Here,
of Mom giving it to sibling 2. The chance
this phenomenon: (1) the beta male is related to the alpha male, and the nestling on the left pecks at one of its
that both those events will occur is 50% therefore helps propagate his genes indirectly by raising the repro- Lethal Aggression Among Their Nestlings? squabbling siblings. Parent egrets ignore
x 50%, or 25%). To find the probability ductive success of his relative with whom he shares some proportion In most birds, both males and females help feed and defend their sibling aggression, and researchers have
suggested that siblicide may, in fact, be
that any gene possessed by one sibling of his genes (the indirect fitness hypothesis), and (2) the beta male offspring, especially in species with altricial young (those that hatch
is shared by the other, you must add adaptive behavior from the perspective
gains reproductive success himself, albeit long-deferred, by virtue from the egg in a featherless, helpless state). Given the high level of of the parent birds. See text for further
together the probability that it is shared
of reaching alpha status when his long-term partner dies (the direct parental care in so many birds, it is surprising to observe parent Cattle explanation. Photo courtesy of Douglas
through Mom and the probability that
it is shared through Dad (25% through fitness hypothesis). The point is that individuals can propagate the Egrets standing calmly on the nest while at their feet one offspring bat- Mock.
Mom plus 25% through Dad), resulting genes underlying their behavioral abilities in either way: (1) by help- ters a sibling to death. The absence of parental intervention in this and
in the 50% average of shared genes be- other cases of siblicide is yet another major evolutionary puzzle: how
ing relatives leave more descendants than they would have without
tween siblings. Using similar reasoning,
their help, or (2) by reproducing personally and transmitting copies of can it be adaptive for parents to accept a reduction in the number of
grandparents and grandchildren share
an average of 25% of their genes, as their genes to their offspring. Helping relatives (Hypothesis 1) can be their offspring (Mock et al. 1 990) (Fig. 6-49)?
do aunt/uncle and niece/nephew pairs. adaptive because related individuals share some of the same genes as Researchers have offered several hypotheses on why siblicide is
Cousins, on average, share 12.5% of a result of having inherited them from their recent common ancestor. paradoxically adaptive from the parental perspective. One possibility
their genes.
For example, full brothers have an average of 50 percent of their genes is that parents permit an offspring to eliminate nestlings that would
in common because they had the same mother and father (Fig. 6-48). A have little chance of surviving to adulthood, due to the scarcity of food
bird that helps his brother reproduce is really reproducing by proxy, be- for parents to provide to their offspring. Inadequate amounts of food
cause many of his genes will be present in his nephews and nieces. brought to the nest result in increased conflict among nestlings.
The indirect fitness hypothesis yields the prediction that alpha This argument is founded on the recognition that "reproductive
and beta males will be fairly closely related to one another. Testing success" is measured not in terms of the number of eggs laid or nestlings

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

6.88 John A lcock Chapter 6— Understanding Bird Behavior 6.89
produced, but by the number of offspring that reach the age of repro- Figure 6-50. Helpers at the Nest in
duction and pass on genes received from their parents. If Cattle Egret the Florida Scrub-lay: In cooperatively
breeding species, such as the Florida
parents that divide a limited quantity of food among three nestlings
Scrub-Jay pictured here, the breeding
wind up having three small, weak fledglings that all die before repro- pair receives help from their non-
ducing, then they will contribute no genes to the next generation. In breeding adult offspring from previous
contrast, egret parents with siblicidal offspring may wind up feeding /11
years. These "helpers at the nest" aid
their parents in territorial defense, in
just one or two nestlings, so survivors fledge at a heavier weight and
.sw/A , ,;;. • attacking would-be predators, and in
may well live long enough to breed. I
bringing food for the young—who are, in
Parent egrets incubate their eggs in ways that promote siblicide, actuality, the helpers' younger siblings.
suggesting that tolerance of siblicide is adaptive. The birds start incu- >
bating as soon as the first egg is laid. Because eggs are laid one per day,
at one- to two-day intervals, the first egg hatches sooner than the sec-
ond, which hatches before the third, so the first nestling gets a head start
in growth over its siblings. This process is called asynchronous hatch-
ing. The senior chick's size advantage allows damaging attacks on the
smaller siblings, so it is invariably the last-hatched youngster that dies
from the sibling's blows, or is forced out of the nest to starve.
Parent egrets could make it much tougher for one offspring to
dominate the others if they simply waited (as many other birds do)
to begin incubation until the complete clutch had been laid, leading
to synchronous hatching. Instead, the use of asynchronous hatching
suggests that creating unequal, frequently lethal competition within
their brood is adaptive for egrets.
This argument has been tested by circumventing the effects of
the incubation pattern. Researchers shuffled very young nestling
Cattle Egrets among a number of nests. In some nests, the resulting
experimental brood consisted of three nestlings all the same age and
size; in others the three nestlings were 1.5 days apart in age and of Z--
different sizes, as in natural sibling groups. As predicted, adult birds ;iii .
-/-io' • • ,
endowed with same-age nestlings actually reared fewer fledglings (1.9
on average) than those that had received nestlings of different ages (2.3 , ••"
fledglings on average) (Mock and Ploger 1987). • 5'4
,,..

:4
/
•
,"7
' ler9/7-

Parental Behavior: Mil Are There "Helpers at the

Nest" That Care For Someone Else's Offspring?
however, some possible Darwinian solutions to the paradox posed by
In a surprising number of bird species, breeding pairs receive
nest helpers. These hypotheses have historically been placed in two
"parental" assistance from some other adults that do not reproduce,
categories by behavioral biologists. Included under the ecological
but instead adopt the role of "helper at the nest." In the Florida Scrub-
constraints category are explanations for helpers that focus on the pos-
Jay, one of the best studied of these cooperative breeders, thanks to
sible costs to young birds of dispersing from their natal territory. Within
Glen Woolfenden and his colleagues (Woolfenden and Fitzpatrick
the benefits of philopatry (staying at home) category are hypotheses
1984), extended family groups of up to eight birds occupy and defend
that focus on the possible benefits to young adults of remaining with
a single territory, communally bringing food to the young and repelling
their parents (Table 6-4).
predators such as snakes (Fig. 6-50).Yet only two members of the flock
So, according to one of the constraints arguments, young Florida
reproduce in any given year.
Scrub-Jays may stay at home with their parents because their breeding
The behavior of the nonbreeders is surprising from an evolutionary
habitat is already saturated with territory owners (see Ch. 1, Sidebar
perspective because they appear to reduce their own reproductive
2, Fig. C). An attempt to find a suitable site under these conditions is
success while raising that of others, precisely the sort of self-sacrific-
likely to fail, while exposing the young bird to predators and the risk
ing behavior that Darwinian theory cannot accommodate. There are,
of starvation.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologg

6.90 John Alcock Chapter 6— Understanding Bird Behavior 6.91
Table 6-4. Two Approaches to Understanding the Puzzle of "Helpers at the Nest" In species with family groups, a combined cost-benefit approach
yields an additional series of predictions about the helpers and their
chances for personal reproduction. A central prediction is that if a
Disadvantages of Leaving Home: Ecological Constraints
nonbreeding helper gets a significant chance to reproduce, it will
1. Few vacant territories of good quality available do so, rather than accepting permanent nonbreeding status. In the
2. Few suitable breeding partners available Florida Scrub-Jay, helpers often become breeders, moving into vacant
3. Little chance of successful reproduction for birds until they gain "parenting" experience breeding niches in neighboring territories when reproducing adults
disappear, or breeding in their natal territory when a parent or step-
Opportunities for "Stay-at-Homes": Benefits of Philopatry parent dies.
1. Survival improved via group membership Likewise, in the Seychelles Brush-Warbler, ornithologist Jan
2. Chance to improve the survival of close relatives Komdeur (1 992) found nest helpers to be commonplace on one is-
3. Chance to acquire superior territory, either by monitoring vacancies in neighboring sites or by land where the warbler was abundant. If helpers remain where they
inheriting natal territory were born because suitable breeding habitat is in short supply, then we
can predict that they should quickly switch to personal reproduction
when transplanted into an area with no competitors. To test this pre-
Adapted from Emlen (1994). diction, Komdeur moved helpers from their original island to another
one where the warblers were previously absent. As predicted, the
transplants immediately set up territories, attracted mates, and began
In addition, those young scrub-jay adults who stay with their nesting. Furthermore, their offspring did not stay at home, but dispersed
parents are in a position to benefit from their philopatry—they can into the unsaturated habitat on the island, where they, too, attempted
assist their parents in the rearing of additional siblings. If their helpful to reproduce personally rather than helping at a parental nest. This
behavior results in the production of siblings that otherwise would not result provides one more demonstration of the evolved ability of birds
have survived, the helpers have in effect advanced the propagation of to behave in the "best interests" of their genes. (Sidebar 6: Bird Families
their own genes. As noted earlier, close relatives share a substantial as Models for Understanding Ourselves)
proportion of their genes. In this sense, the special "self-sacrificing"
behavior of helpers has the same genetic consequences as having some
offspring of their own (parents are no more closely related to their own How to Studtj Bird Behavior Yourself
offspring than they are to their full siblings; on average, they share 50
percent of their genes with each [see Fig. 6-48]). As a result, helping at
■ Taking the time to watch how birds behave is something that most
amateurs feel is less rewarding than the search for as many species as
the nest can in theory persist over evolutionary time as a consequence
possible. As a longtime bird-lister myself, I know the thrill of racking
of the indirect fitness gains derived by helpers. In the case of the Flor-
up a big total for a day and the even bigger thrill of seeing a species
ida Scrub-Jay, helpers can sometimes more than double the number of
that I have never seen before. But as a behavioral biologist I also have
fledglings produced by their parents, judging from the fledgling output
experienced the pleasure of really observing a species—getting to
of adults with and without helpers at the nest.
know what it does and why it does it. This experience of discovery
Stephen Emlen (1982) points out that the two categories of
and understanding is one I recommend highly. There are plenty of
hypotheses, those that focus on the costs of dispersal and those that
opportunities for you to have this experience as well. The behavior of
emphasize the benefits of staying at home, are complementary, not
a huge number of bird species, even common ones, is incompletely
mutually exclusive. If dispersal carries a high cost, the benefits of stay-
described and poorly understood. The Birder's Handbook (see Sug-
ing home need not be great for a young bird to gain in the long haul by
gested Readings) is a particularly good source for what is and what is
becoming an adult helper at its parents' nest. Thus, the two factors can
not known about the behavior of North American species. With only
work together to create durable families of breeders and helpers.
a few thousand professional ornithologists in the world, dedicated
Furthermore, both types of hypotheses yield the same central pre-
amateurs can make contributions to the field of bird behavior at many
diction: nonbreeding helpers should be the offspring of the adults they
different levels.
assist. The prediction holds in many cases (but not in all). In the Florida
At one level, the bird watcher who wishes to expand his or her
Scrub-Jay, for example, long-term studies of marked individuals have
horizons need only slow down and spend some time with the birds
revealed that nest helpers are usually adu It sons of the breeding pair. The
encountered on a walk. A little patience, the willingness to sit quietly,
same is true for the Superb Fairywren, whose "monogamous" breeding
a notebook and pencil, and a permanent record book for transcribing
pairs are sometimes helped by up to three sons from previous breeding
attempts. In the White-fronted Bee-eater, both sons and daughters may one's observations are a starting point. There is real pleasure to be
stay with their families, helping to rear still more siblings. (Continued on p. 6.96)

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

6.92 John Alcock Chapter 6 — Understanding Bird Behavior 6.93

Sidebar 6: BIRD FAMILIES AS MODELS

FOR UNDERSTANDING OURSELVES
Stephen T. Emlen and Natalie J. Demong

Cooperatively breeding species

such as the Florida Scrub-Jay, the
White-fronted Bee-eater, and the
Seychelles Brush-Warbler described
in the text are of interest for reasons
extending far beyond their help-
ing behavior. They are interesting Parents
because they live in family groups.
a. Human Extended Family b. White-fronted Bee-eater Family
Mature offspring frequently delay
their dispersal and remain with their Figure B. All in the Family: a. Human Extended Family: Authors Stephen T Emlen and Natalie J. Demong are second and third
parents for significant portions of from left, at back. Photo courtesy of Stephen T Emlen. b. White-fronted Bee-eater Family: Five family members huddle together
their adult lives. Parents themselves in the chill of an East African dawn. Photo by Natalie]. Demong.

form long-term pair bonds, and both Focal Male

mother and father contribute to the The evolutionary biologist starts of time to fine-tune our behaviors for social groupings. The reason is that
care of the young. The result is a by assuming that whatever heritable interacting optimally with different intact families are composed of ex-
multigenerational family structure behavioral tendencies we possess types of family members. tremely close genetic relatives—par-
that bears an uncanny resemblance would have been selected during the And this is where the value of ents and their grown offspring. Such
to our own family systems (Figs. A, Unpaired, tens of thousands of years that we lived avian studies comes in. Birds provide relatives share genes with one an-
B). The obvious question is: Can we Widowed Brother as hunter-gatherers. The reasoning is excellent model systems for under- other by virtue of common descent
learn anything about ourselves by that humans ceased the hunter-gath- standing human family behavior for (see Fig. 6-48). An individual that
studying family-dwelling birds? erer way of life and started living in two reasons. First, over 300 species helps other family members is thus
The study of human behavior (in large, permanent settlements only of birds are known to live in multi- indirectly helping itself. If such help
this case, of human family dynamics) very recently, after the domestication generational family groups very leads to higher survival of the next
has typically been the research do- of food plants some 12,000 years ago. similar to our own. Birds, more than brood of young, the result is the pro-
main of social scientists, particularly Even though our social way of living most mammals, and even more than duction of additional close relatives.
sociologists and psychologists. has changed immensely si nce the dis- most primates, offer the most com- If such help reduces the work load of
Twenty years ago, most social sci- covery of agriculture, there has been parable family models to humans. one's parents and allows them to live
entists believed that culture alone insufficient time for natural selection Second, avian behavior is largely to breed again, the result is the same. 6
determined human behavior, and to have significantly altered most her- free of cultural influences. If there The helper receives indirect genetic
that heritable influences were of mi- Unpaired Son Unpaired Daughter Unpaired Sister itable components of social behavior. are universal rules governing family benefits in direct proportion to how
nor, if any, importance. Th is view has Thus, to the degree that we carry heri- interactions among birds, then such closely it is related to the birds that
changed radically with the explosion Figure A. Genealogy of a White-fronted Bee-eater Extended Family: This coopera- table behavioral tendencies, they will rules are likely candidates to be her- it helps. The closer the kinship, the
of human genome studies, however, tively-breeding, EastAfrican species lives in extended family groups within large col- be for behaviors that were adaptive itable predispositions in ourselves. greater the tendency for animals to
and it now is generally recognized onies. Fully grown offspring frequently delay their own breeding, instead remaining to our ancestral hunter-gatherer way We then can ask whether these cooperate. This line of reasoning is
that virtually every human behavior with their family of origin and helping their parents or other family members raise of life. same rules are useful in predicting known as "kin selection theory."
develops through a complex in- young. The result is a multigenerational family structure similar to our own. For ex- What is known about the social our own behaviors in different family We should therefore expect to
terplay of both genetic and cultural ample, the paired male labeled "focal male" has an unpaired son and daughter, a life of our pre-agricultural ancestors? situations today. find ektensive cooperation and
influences. widowed brother, and an unpaired sister available to help him and his mate in their helping within intact families. This
Anthropologists agree that the social
breeding effort, as well as potential help from his parents, should they fail to breed Kinship and Cooperation in
Let us assume for the moment that core of hunter-gatherer societies con- expectation is borne out by data.
themselves. From Emlen, S. T, P H. Wrege, and N. J. Demong. 1995. Making deci-
genes do influence our behavior— sisted of multigenerational extended Intact Avian Families More than 90 percent of bird species
sions in the family—an evolutionary perspective. American Scientist 83(2): 148-157
that we carry heritable tendencies (p. 150). Reprinted with permission. family groups. We thus have had a What might such basic rules be? that live in multigenerational fami-
to behave in certain more or less long history of interacting not only Let us start by examining intact avian lies practice cooperative breeding,
predictable ways in specific social with mates and offspring, but also families—those in which the two similar to that of the Florida Scrub-
situations. How can we determine with replacement mates (steppar- parents stay together as a breeding Jay, White-fronted Bee-eater, and
what these predispositions might ents), half- and stepsiblings, in-laws, pair. There is an important biological Seychelles Brush-Warbler, in which
be, and how might such knowledge and other assorted family members. reason to expect such families to be nonbreeding adults commonly help
be useful? Natural selection has thus had plenty more harmonious than other types of to rear offspring that are not their

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

6.94 John A 'cock Chapter 6 — Understanding Bird Behavior 6.95

own. In essence, parents living with territory of its own outside of thefam- new family, the two sets of offspring lies are less stable than intact fami- The escalation of divorce rates is statistically more likely to occur, and
their grown offspring can count on ily. Stepparent-stepoffspring matings will be totally unrelated to each other lies. The incidence of subsequent di- leading to a further transformation to occur more intensely, in stepfam-
a built-in "work force" to help with have been reported in Stripe-backed (they will be stepsiblings). The large vorce is higher in second marriages, from nuclear to single-parent (typ- ily situations than in intact families.
the task of child rearing. In stark con- Wrens, White-browed Scrubwrens, differences in relatedness will result and increases with the number of ically mother) families. This further However, as family members (and
trast, such cooperation is practically and White-fronted Bee-eaters. In in a host of competitive interactions stepchildren present. Children in exacerbates the already reduced family counselors) become more
unknown in avian species that live in such cases, the remaining biological within the new family. stepfamilies also leave home signifi- support system, creating a child- aware of this increased potential for
any other type of social grouping. parent opposes such matings, result- Consider the formerly reliable cantly earlier than children in intact rearing situation that had no ante- conflict, all participants can learn to
There is a second reason to ex- ing in intense aggressive interactions "work force" of grown offspring that families. cedent in our ancestral family en- become more sensitive to it. We then
pect increased harmony in intact within the family. routinely helped their parents in Of what possible value is knowing vironments. Whatever our heritable can be better prepared to deal with
families. Competition over mates is Stepparents also have little bio- intact family situations. In the new that we share with birds a propensity decision-making rules might be, they family problems early on, in ways
commonplace in most avian species. logical incentive to provide care for stepfamily environment, these older to behave in similar ways in similar were never adapted to single-parent that promote harmony and stability.
their dependent stepchildren. In fact, offspring will be related to future family situations? First, it suggests child-rearing situations. We have Biological predispositions are just
But there is little or no such sexual
from a stepparent's point of view, any young produced by the new breed- that the same evolutionary logic used created a culturally novel social sit- that—predispositions. Unlike birds,
competition among members of in-
time or effort spent investing in the ing pair only as half-siblings (they to predict avian social interactions uation—one for which our inherited we humans can use our intellectual
tact family units. Recall that family
mate's previous offspring may be a have only one parent in common). also correctly predicts some of our predispositions have prepared us resources to consciously modify be-
members are close genetic relatives.
waste, especially if it delays its own They thus stand to gain only half as own patterns of family interactions. poorly. Incorporating this evolu- haviors we judge to be undesirable.
It is well known that incestuous
reproduction with the new mate. If much in indirect fitness benefits by This justifies the comparative use of tionary perspective on child care, The study of avian family dynamics
matings (those with close relatives)
food is scarce, competition from helping. Kin selection theory pre- avian family systems as models for however, can help us as we seek to contributes to this process by identi-
can have harmful genetic conse-
the mate's previous offspring may dicts that such offspring will be less better understanding ourselves. build societal alternatives to replace fying situations where family conflict
quences, so natural selection has
decrease the chances of survival of willing to help in the rearing of half- Second, such information can the family-based child support sys- is most likely to occur, and by helping
fostered mechanisms that help birds
its own, younger offspring. Thus the or stepsiblings, a prediction borne help us, as a society, to better antici- tem that operated in our past. us to understand why such conflict is
recognize and avoid inbreeding with
stepparent is predicted to offer only out by studies of Florida Scrub-Jays, pate the problems that accompany Another lesson to be learned sometimes so difficult to eliminate.
close kin. Sons rarely compete with
minimal, if any, care for its stepoff- White-fronted Bee-eaters, and Sey- the changes in family composition from the study of avian families is So the next time you read about
their fathers, and daughters rarely
spring.This prediction is again borne chelles Brush-Warblers. occurring today. A century ago, how we, as individuals, can bet- family members in some avian spe-
compete with their mothers, for
out by data from family-dwelling When all these data are com- most people lived in extended fam- ter anticipate and deal with family cies helping at the nest, stop and
sexual access to a parent's spouse.
birds. bined, the unavoidable prediction ily situations. Mothers had access to changes in our own lives. Recall the think about the potential importance
Likewise, siblings don't seek sexual
Under some circumstances a step- is that stepfamilies will be less stable the built-in support system of other data on increased conflict in avian of such discoveries. By seeking and
relations with one another, despite
parent may even benefit by forcibly than intact families. There are fewer extended family members who as- stepfamilies. Should those of us who interpreting patterns in bird behavior,
their frequent social interactions. The
terminating all care from others to its reasons for the offspring to stay home sisted with the tasks of child rearing. are stepparents, stepchildren, or we discover that the importance of
result of this avoidance of incestuous
stepoffspring. The extreme example and help, and the reduced degree of This work force was largely stripped stepgrandparents be discouraged by avian research often extends well be-
matings is increased family har-
of this behavior, infanticide, is well kinship among family members will away, however, with the shift from these findings? We think not. Rather, yond the birds themselves. It offers
mony—especially compared to the
documented not only in birds, but lead to increased conflict, even be- extended to nuclear families that oc- we should accept what evolutionary instruction that is directly relevant to
courtship disruption, mate guarding,
and other sexually-related aggressive
also in mammals, including rodents, tween the remaining parent and its curred in the early 1900s. theory predicts: conflict and strife are the drama of our oWn lives. ■
social carnivores such as lions, and new mate. We know of no studies an-
behaviors we see in non-family-
many species of primates. The risk alyzing the rate of "divorce" among
living species.
of infanticide is greatest when the parents in avian stepfamilies, but we
stepparent is of the dominant sex (in predict it will be high.
Behavior in Avian Stepfamilies
birds, generally the male).
Harmony in family interactions
If the new couple succeeds in hav- Implications for Human
may evaporate if a bird parent dies
ing offspring of their own, conflicts of Families
or divorces. if the remaining parent
interest are even further intensified. The profound disruptions we find
takes a new mate, the equivalent of a
This occurs because so many dif- in the social dynamics of avian step-
stepfamily is created, and the family
ferent degrees of relatedness now families closely mirror those found in
dynamics can instantly become con-
exist within the family. For example, human stepfamilies. Large-scale so-
tentious on a number of fronts.
when the original parent takes a new ciological studies consistently show
Consider the "rule" of avoidance
mate and produces a new brood, that human stepparents do invest less
of incestuous matings. Unlike the
it is equally related to all its own time and effort in the offspring from
original biological parent, a step-
offspring, both new and old. But their partner's previous marriage
parent is not genetically related to its
its new mate is related only to the than they do in their own children;
new mate's previous offspring. Their
new offspring. The two parents will
relationship thus is not bound by any that stepchildren are at greater risk
therefore disagree about how much for sexual and physical abuse than
incest restriction. A stepparent may
investment to allot to the various children in intact families; and that
find a willing partner among its ste-
youngsters in the stepfamily unit.
poffspring (or vice versa), especially children report more conflicts with
And if the stepparent should bring half-siblings and stepsiblings than
if the stepoffspring has only a mini-
previous offspring of its own into the with full siblings. Further, stepfami-
mal chance of finding a mate and a

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

6.96 John A lcock Chapter 6— Understanding Bird Behavior 6.97
gained from looking at a bird long enough to see what it is eating, what So, for example, to test the Table 6-5. The Scientific Method
plant it is pollinating, what displays it employs when interacting with hypothesis that anting was food-
conspecifics, and so on. gathering behavior, you would (1) Choose a question to study: Questions are usually generated
Perhaps the next step is to join established research projects; need to watch carefully for in- based on prior observations or known problems.
many of these are led by university types ranging from professors with stances of "anting" jays picking Example: Is nesting success in American Kestrels related to nest-
teams of observers to graduate students in need of a volunteer. Re- up ants and swallowing them. cavity orientation?
search projects are also coordinated by nature centers, bird research Observations from a single jay
organizations, government agencies, and various other nonprofit
(2) Restate the question as a hypothesis that can be tested:
would not be adequate. Records
groups. Chapter 10 gives more details on how to get involved in re- (Note: not all scientific inquiries involve hypothesis testing.)
that fai led to indicate total time of
search projects. observation, total number of ants Example: American Kestrels have higher nesting success in south-
east-facing cavities compared to cavities that face in other direc-
The truly dedicated amateur can consider a project of his or her picked up, and total number of
tions.
own design. But it is only fair to say thatthe job is a challenging one.The ants consumed (if any) would be
first task is to identify a behavioral trait that warrants further research of little value. (3) Design a systematic study to objectively test the hypothesis:
from a personal or scientific standpoint. To this end, there is no substi- At some point early in the Study designs can be quite complex and should include plans
tute for curiosity. If you observe a bird doing something puzzling that process, it would help to have for statistically analyzing the data.
piques your curiosity, you have a start. As this chapter has emphasized, access to a university library Example: You will determine the compass azimuth and fate of
behavioral biology presents two general kinds of puzzles: the problem carrying ornithological journals American Kestrel nesting attempts in your study area. Then you will
of internal or proximate causes, and the problem of evolutionary or such as TheAuk, The Condor, The compare nesting success of kestrels in southeast-facing cavities to
that of kestrels nesting in cavities that face in other directions using a
ultimate causes. To develop a research project, you must know whether Wilson Bulletin, and The Ibis as
chi-square test for independence.
the puzzle requires exploring the underlying proximate causes or the well as behavioral journals such
long-term evolutionary causes. So, for example, you may wonder why as Animal Behaviour, Behavioral (4) Collect unbiased data following the methodology set forth
Bluelays sometimes stretch on the ground near an ant nest, apparently Ecology and Sociobiology, Be- by the study design:
permitting the ants to "attack" them (see Fig. 3-22). You could focus on haviour, and Ethology. General Example: Without biasing nest outcome, monitor each kestrel nest
the proximate cues for the behavior: Do parasites cause the skin to itch? ornithology textbooks, the Stokes and determine its fate and orientation.
Do Blue Jays seek ant nests only when the air temperature is high? Or Nature Guides, and behavioral (5) Analyze the data using appropriate statistical techniques and
you could investigate the reproductive, evolutionary benefit of the odd texts (see Suggested Readings interpret the results in statistical and biological contexts:
"anting" behavior: Do the ants remove skin and feather parasites that and Ch. 2, The Birder's Essential
Example: Statistically compare rates of nesting success for American
reduce the birds' vigor? Is the behavior a way to find food, luring the Resources) also may help you Kestrels using southeast-facing cavities versus those in cavities that
ants close enough to be eaten? The research you do depends entirely track down what already has face in all other directions.
on the kind of hypothesis you select to test. been done to address a specific It is found that 52% of southeast-facing nests were successful,
As we have seen, a good way to investigate evolutionary causes of hypothesis or question, so that whereas 46% of nests facing in other directions were successful.
behavior is to ask, "Why would the bird do such-and-such, given that you do not simply repeat another When a chi-square test for independence is done, the differ-
ence in nesting success between southeast-facing cavities and
the action carries with it some obvious disadvantages in terms of repro- person's study.
cavities that face in other directions is found to be not statistically
duction?" Anti ng is of evolutionary interest precisely because anting If you can find research pa-
significant.
birds appear to both expose themselves to predators and to waste time pers related to your own interest,
. (6) Draw conclusions and confirm or reject the hypothesis:
that could be spent in other, more productive, behaviors. you may be able to contact the
Example: Nesting success in American Kestrels is not significantly
Having selected a puzzle and developed one or more possible authors, some of whom may be higher in cavities that face southeast. Reject the hypothesis pro-
solutions, the next step is to test the hypothesis, or better still, several willing to assist you in various posed in step (2).
alternative hypotheses. This task involves thinking of testable predic- ways. Publishing a paper on a
tions (behaviors or circumstances that you should be able to observe if completed research project is a (7) Devise new hypotheses for future testing and repeat Steps 1
the hypothesis is correct) (Table 6-5). Testi ng to see if your expectation difficult, but highly rewarding,
through 7:
matches reality is full of pitfalls and pleasures. Your goal is to collect part of the scientific process. It is Example: American Kestrels have higher nesting success in north-
west-facing cavities compared to cavities that face in all other direc-
enough quantitative data to determine if the prediction was accurate a great thrill to carry a behavioral
tions.
or not, and thereby to reject or confirm the hypothesis that gave rise to project through from start to fin-
it. This requires, among other things, a great deal of patience, neutral ish. (8) Report the results of your study to share the information with
note-taking, precise record-keeping, a clear view of what observations others
are pertinent, and avoiding overinterpretation or biased analysis of
(9) Consider new questions:
what the birds are doing.
Example: Is nesting success in American Kestrels related to nest-cav-
ity height?

Cornell Laboratorj of Ornitholo8q Handbook of Bird Bioloaq

6.98 John Alcock

Suggested Readings
Alcock, J. 1993. Animal Behavior: An Evolutionary Approach. Fifth Edition.
Sunderland, MA: Si nauer Associates.
A general behavior text that covers many of the same topics presented in
this chapter in more detail and with a wider range of animal examples.

Brown, J. L. 1987. Helping and Communal Breeding in Birds. Princeton, NJ:

Princeton University Press.
An advanced text on a highly fascinating evolutionary issue, the occurrence
of helpers at the nest and other forms of reproduction by social birds.

Ehrlich, P. R., D. S. Dobkin, and D. Wheye. 1988. The Birder's Handbook.

New York: Simon & Schuster.
Summarizes much of the knowledge of the behavior of North American
birds. Includes a short section on how amateurs can contribute to orni-
thology.

Heinrich, B. 1989. Ravens in Winter. New York: Simon & Schuster.

One of the best books ever on the scientific method applied to a problem
in bird behavior.
Vocal Behavior
Lorenz, K. Z. 1952. King Solomon's Ring: New Light on Animal Ways. New
York: Thomas Y. Crowell Co.
1' 1
A classic text that presents the ethological perspective, especially on the
proximate causes of bird behavior. Donald E. Kroodsma
Stokes, D. and L. 1979-1989. A Guide to Bird Behavior, Vols. Ito III. Stokes
Nature Guides. Boston: Little, Brown and Company.
Think, every morning when the sun peeps through
Fora selected list of common birds, gives detailed life history information;
descriptions of displays, songs, and calls; and suggestions on how to observe The dim, leaf-latticed windows of the grove,
the behaviors. How jubilant the happy birds renew
Their old, melodious madrigals of love!
Tinbergen, N. 1953. The Herring Gull's World: A Study in Social Behavior of And when you think of this, remember too
Birds. London: Collins. 'Tis always morning somewhere, and above
Another classic account of bird behavior that presents the ethological The awakening continents, from shore to shore,
perspective, especially on the ultimate causes of Herring Gull behavior. Somewhere the birds are singing evermore.
—Henry Wadsworth Longfellow
Some representative recent short articles on bird behavior that are
exciting and readable: It's four in the morning, Sunday, mid-June, atop my usual
fire tower at Mount Lincoln in western Massachusetts,
Heinsohn, R. 1995. Raid of the red-eyed chicknappers. Natural History and already I sense the impending frenzy. Off and on all
104(2): 44-51. night long the Whip-poor-will has been singing vocif-
erously, earning his alternate name of "nightjar." But others now begin
McDonald, D. B. and W. K. Potts. 1994. Cooperative display and relatedness to stir. As the eastern sky hints of the sunrise, Ovenbirds increasingly
among males in a lek-mating bird. Science 266:1030-1032.
launch from the ground into the canopy and sometimes beyond, re-
Mulder, R. A. 1994. Faithful philanderers. Natural History 103(11):56-63. leasing their energetic, jumbled bursts of song, which seem to have
been pent up all night long. Minutes later, the American Robins are car-
Petrie, M. and T. Halliday. 1994. Experimental and natural changes in the oling. The two other thrush songs soon follow, the flutelike ee-oo-lay
peacock's (Pavo cristatus)train can affect mating success. Behavioral Ecol- of the Wood Thrush (Fig. 7 1) and the ethereal, downward-spiraling
-

ogy and Sociobiology 35:213-217. vee-ur, vee-ur, veer, veer of the Veery. I know the Eastern Towhee will

Cornell Laboratorq of Ornithologq

7.2 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.3
be next—he almost always is, seeming to flaunt his entire repertoire Figure 7-3. Blue Jay Tending Nestlings:
The success of any bird is measured in
of four different songs as fast as he can.
the currency of offspring. Individuals
As four-thirty approaches, others join in. Three warblers, the that are better at using their sounds to
Chestnut-sided, Black-and-white (Fig. 7 2), and Black-throated Blue,
-
manage their environments will, on
aggressively announce their presence, and the staccato, mach i ne-gu n- average, produce more young, passing
I ike fire of the Chipping Sparrow jars the air. Below me, the Eastern some of their favorable genes for sound
production on to those young. Photo
Phoebe continues to rapidly alternate his two song forms. I'm sure the
courtesy of Isidor Jeklin/CLO.
distant Black-capped Chickadee has been whistling for some time,
too, but he's just now caught my attention. The crows, jays, vireos, and
others have all chimed in, and by quarter to five there's no doubt—ev-
eryone is present and accounted for.
With my trained ear, I not only can identify who is making each
sound, but also can hear a little of what each bird is doing. The Oven-
birds abandon their flight songs and settle low in the canopy to repeat
their tea CHER, tea CHER, tea CHER song. The towhee gradually
- - -

Figure 7-1. Wood Thrush: One of the eases his pace and increasingly repeats each different song several
first and last singers of the day, a Wood social environment for its own selfish gain (Fig. 7 3). Each manager
times before introducing the next. Others slow down, too. The Chip- -

Thrush serenades residents of eastern

ping Sparrow lengthens his familiar, dry trill until he's singing the way is in turn managed by other individuals, of course, so compromises
forests with its melodic, flutelike phras-
es. Photo by Lang Elliott. the field guides dictate. As the minutes tick away, one of the phoebe's must be reached and agreements brokered. Sounds play a key role in
two songs predictably comes to predominate. Near sunrise, the war- the entire process (Smith 1977, 1996).
blers switch from their aggressive dawn song to a daytime song, one This chapter is all aboutthe sounds birds useto manage their daily
used more in the presence of their female friends. During all this time, I ives.The goal is to help you, the student, understand what birds do and
the chickadee has been whistling his hey sweetie on a series of dif-
-
why they do it, to the best of our current knowledge. After reviewing
ferent frequencies. And so much more is happening, I am sure—my what sound actually is, you'll learn about the repertoires of sounds
nonavian senses give me just a hint of all that transpires during these that birds use, how songbirds (and parrots and some hummingbirds)
dawn events. learn many of their sounds just as we learn our speech, and how other
Each of these birds, and each of the others whom I've slighted in species (such as flycatchers) don't seem to learn. You'l I also learn how
this all-too-brief glimpse of dawn at Mount Lincoln, is on a mission.The brains control songs in birds, how a bird can sing a duet all by itself
mission continues through the morning, the afternoon, into the next with its two voice boxes, how sounds of some birds differ from place to
day, the next week, month, year, and throughout life. The mission is to place and from one generation to the next, and why birds duet, mimic,
succeed, in evolutionary currency, by surviving and reproducing, and and make the particular sounds they do. In Sidebar 6, Listening onYour
each tiny note of each sound a bird makes during the mission is geared Own, I suggest several listening exercises to help you get started.
to increasing the likelihood of success. For each bird, the ultimate goal The objective, in short, is to help you appreciate the extraordinary
is to perpetuate itself. In all bird species, success for a male requires world of bird sounds that surrounds us. I know that as I revel in the
a female, and success for a female requires a male. Nearly all of what dawn aural feast served to me every summer day, throughout New
we hear from the birds on their mission is the negotiating, cajoling, England and elsewhere as dawn circles the globe, windows are being
persuading, and impressing that accompany the selfish games required slammed so that unappreciative humans can slumber another hour
for success. or so. My wishes are to open each reader's mind to the world of bird
Evolution occurs as each individual attempts to perpetuate itself sounds, so that we not only hear but see and feel these sounds; and to
in whatever selfish way it can. Males interact to establish a hierarchy hear windows opening wider at dawn, to let the sounds of our natural
and to impress potential mates, either directly or indirectly. Females world permeate our lives.
assess possible mates by listening carefully to the male interactions and
proclamations. Once paired and raising a family, a male and female
further negotiate, on a daily basis, how much effort each contributes. What is Sound?
Figure 7-2. Black-and-white Warbler:
Also, females of ostensibly monogamous species sometimes choose ■ Consider a musical instrument such as a drum. Pounding on the
to mate with males other than their social partners; much of the male tightly stretched skin of the drum makes it vibrate, which sets into
The Black-and-white Warbler sings his
high, thin wee-see, wee-see, wee-see noise we hear during the dawn chorus may actually be geared toward motion the air around it. As the vibrating skin moves outward, it com-
from a high branch in mixed woodlands these extrapair encounters. Just as we would manage a stock portfolio presses a band of air; when the skin moves inward, the air that rushes
of eastern North America. Photo by Lang for maximum financial gain, each bird uses its sounds to manage its into the space formerly occupied by the skin is thinned. This suc-
Elliott.

Cornell Laboratorq of Ornitholo8q Handbook of Bird Biolvi

7.4 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.5
• •
. • • • .*. • • • • • ••

. ••
•

About 20 kHz

. .1
LYI
16

15
kHz

—
t Bat Sonar (40-100+ kHz)

a b d e f
14 -

Drumstick Drumskin Drumskin Drumskin Drumskin Much Later

Strikes Drum Depresses Vibrates Upward Depresses Vibrates Upward Drumskin Stabilizes
13-
• Full Range of
Dots Represent Molecules of the Gases that Compose Air
Human Hearing 12 -

a: Stationary drumskin just before it is struck; air molecules uniformly distributed

11 —

b: After drumstick hits drumskin, drumskin depresses, thinning nearby air

c: Drumskin vibrates upward, compressing nearby ai r; previous band of thinned air has propagated
upward 10-
d: Drumskin vibrates downward, thinning another band of air; previous bands of thinned and Blackpoll Warbler
compressed air have propagated upward 9 -

e: Drumskin vibrates upward, compressing yet another band of air; previous bands continue to
propagate upward 8— ■ Cape May Warbler
f: Much later, after drumskin has ceased to vibrate, air molecules return to uniform distribution ■ Cedar Waxwing
B 7—
Figure 7-4. Generation of a Sound Wave cessive compression and thinning (or rarefaction) of air molecules is B
Through Air: A sound wave consists of transmitted to air farther away and constitutes a sound wave traveling Yellow Warbler
6
a series of alternately compressed and
thinned bands of air molecules propa-
through space (Fig. 7 4).
- I
Optimal Range of
Common
On the familiar piano, the heavy wires that produce the lowest 5 Yellowthroat
gating through air. Here, the vibration of Human Hearing
a drumskin (shown greatly exaggerated), C vibrate only 32.7 times per second, and the thin wires that produce Dark-eyed Junco
4
alternately reduces and increases the
density of the air nearby, and this "wave"
the highest C vibrate more than 4,000 times per second. The number Human I Field MBlack-capped
of times this cycle of compression and rarefaction occurs per second Female Voice Sparrow • Chickadee
of sound travels upward and away from
the drum. For convenience, the "wave"
is shown here in a narrow arc above each
is the frequency, which is measured in cycles (waves) per second, or
Hertz (Hz), named after Heinrich Hertz, a German pioneer in the
0
0
3

2
Veery, House Sparrow, N. Cardinal
I White-throated Sparrow

drum; in reality, the wave would consist study of sound. The lowest frequency most*hu mans can hear is about Canada Goose,
of bands of air moving outward in all 20 Hz, and the highest is about 20,000 Hz. Fortunately for us, most —C2 Mallard
directions, like ripples of water from a
bird sounds are in the range that we hear well, from about 2,000 Hz
1
Barred Owl
■ Eastern Screech-Owl
stone dropped into a pond. 0 Human Male Voice
(or 2 kilohertz [kHz]; 1 kilohertz = 1,000 Hertz) to about 7,000 Hz 0 2— Mourning Dove, Great Horned Owl
C'
(7 kHz) (Fig. 7 5). Some birds, such as pigeons, can hear sounds of
-
C-3 C2 \ Ruffed Grouse Drum (40-100 Hz)

a lower frequency than we can, and some owls can hear sounds of
lower intensity than we can. For the most part, however, laboratory Figure 7-5. Typical Frequency Ranges of Selected Bird and Human Sounds: Average frequency ranges, shown in kilohertz (kHz;
1 kilohertz = 1,000 Hertz), of various bird songs, bat sonar, and human voices and hearing. Also shown are musical notes. C' is
tests have not shown any truly superior general hearing ability among
middle C on a piano, C' to C5 are the first through fifth Cs above middle C (C 4 is the highest Con a piano), and C' to C-3 are the
birds (Dooling 1982). three Cs below middle C. Note that the Cs are not evenly spaced because the relationship between frequency (cycles or waves
per second) and pitch (a musical note on a scale) is not linear, but logarithmic. Because human speech is very complex, with
many harmonics and different frequency ranges for different types of sounds (for instance, an "s" sound is in a different frequency
Seeing Sounds: Sonagrams and Oscillograms range than an "cc" sound), the ranges shown here for human voice are only rough approximations. Human hearing ranges vary
We humans rely heavily on our vision, and our relatively un- from person to person, and the exact endpoints are hard to determine, as indicated by the fading bars.
trained ears often have trouble appreciating sound. One way to en-
hance our hearing and listening skills is to convert the bird sounds to
graphs that we can see and study. These graphs take two forms, called

Cornell Laboratort of Ornitholom Handbook of Bird Biolo,914

7.6 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.7
sonagrams and oscillograms (wave forms). Although studying these 5.0- a. Black-capped Chickadee Sonagram Figure 7-6. Sonagram and Oscillogram
graphs seems somewhat daunting at first, a little experience shows that of Black-capped Chickadee Song (Track
1, 2nd Song): a. Sonagram: A sonagram
the graphs can be very helpful in understanding how to think about 4 5-
is a representation of a sound plotted as

Frequency (kilohertz)
and listen to bird sounds. frequency (measured in thousands of
First examine the sonagram, using the simple whistled song of the 40- cycles per second [kilohertz]) versus
Black-capped Chickadee as an example (Fig. 7-6a & Track 1; see "Use time in seconds. The volume (loudness)
of CD with ChapterText," below). The vertical axis is frequency, mea- is roughly indicated by the darkness of
3.5-
the notes. The more pure the tone, the
sured in kilohertz.The horizontal axis is time. Field guides describe the Hey Swee - tie
smaller the frequency range of the note at
chickadee's song as fee-bee, or hey-sweetie, with the first part slightly any given point in time. In this sonagram
higher in frequency than the second. The sonagram of this whistled of a Black-capped Chickadee song, the
song clearly shows two whistles, each about 0.4 seconds in duration, pure, whistled quality of the notes, as
well as the rhythm, can be seen easily. b.
with about 0.2 seconds between them. The first whistle is at about 4.0
05
Oscillogram: An oscillogram represents
1.0 1.5
kHz, roughly the highest C on a piano, and the second one is about 00 20
a sound in terms of relative loudness
Seconds
400 Hz lower, at about 3.6 kHz. (vertical axis) versus time (horizontal
One feature of our chickadee's hey-sweetie doesn't show very axis). The vertical axis actually gives a
b. Black-capped Chickadee Oscillogram
measure of the increase and decrease in
clearly on a sonagram, however, and that is the relative loudness of
15 air pressure (in micropascals) associated
the sounds. If we listen carefully, we can hear two syllables within the with the sound wave (see Fig. 7-4), which
sweetie, because a subtle but clear drop in loudness occurs in about 10 determines the loudness. Therefore, the

Pressure (m icropasca ls)

the middle of the whistle. Although the relative intensity of a sound is louder the sound, the greater the height
reflected in the darkness of the sonagram, the second graph form, the and depth on the vertical axis. Note that
frequency cannot be determined from
oscillogram, reveals it far better (Fig. 7-6b). Time in the oscillogram
an oscillogram. In this oscillogram of
is again shown on the horizontal axis, but relative intensity is on the Hey Swee - tie the same Black-capped Chickadee song
vertical axis, so the louder a sound is, the greater the height and depth pictured in (a), the greater loudness of
0 the first note, and the two-part nature
of the wave on the oscillogram. We now see in our two graphs not
of the second note, the sweetie, can be
only patterns in frequency but patterns in amplitude; the whistles are -15
seen more clearly than in (a).
clearly not the same intensity throughout, and the audible break in
-20
sweetie is evident. 00 0.5 1.0 2.0
1.5
By using both the sonagram and the oscillogram to help us "see" Seconds
bird sounds, we can begin to appreciate the finer details of what we
hear. Consider another example of a song with pure whistles, the
White-throated Sparrow's old sam peabody peabody peabody (Fig.
7-7 & Track 2). These songs are introduced by two or three relatively
long whistles, each on a slightly different frequency; in some indi-
Use of CD with Chapter Text viduals successive notes rise in frequency and in some they fall, but the
overall pattern is unmistakable. The last part of the song, the peabody
Please note that there is a CD (compact disc), narrated by MargaretA. Barker, to accompany this chapter. It is attached portion, clearly shows three notes coupled together to form each pea-
to the inside back cover of this book. As you read through the chapter and sidebar text, in addition to the usual figure body, even though the human ear has to listen carefully to distinguish
references (for example, Fig. 7—n), you will encounter the word Track followed by a number. This tells you to stop the three parts. The patterns of frequency are visible in the sonagram,
reading and listen to the appropriate selection on your CD; you will be able to directly punch in the number afterTrack
and patterns of amplitude are especially clear in the oscillogram.
as the track number on the CD. The CD tracks for sidebars are integrated with the tracks for the chapter text, such that
In sharp contrast to whistled sounds, such as the chickadee's
if you read the sidebar at the time it is referred to in the text, you can continue your CD tracks in numerical order.
In many instances, a CD track is linked to a sonagram, which appears in the text as a regularly numbered figure.
hey- sweetie and the sparrow's peabody, are "noisy" sounds, which
These situations will be indicated by the reference: (Fig. 7—n &Track n) in the text. In these cases, the sonagram shows consist of a broad span of frequencies at an instant in time. Noisy
a portion of the CD track you are listening to (for exactly which song or portion, refer to the figure caption); you will sounds appear on a sonagram as vertical lines, not horizontal ones.
want to look at the sonagram as you listen to the CD. On a sonagram, the snap of a finger and the slam of a door appear as
Appendix A of this chapter is a list of the tracks and a description of their contents. For many tracks, the information noise. When a woodpecker taps on a tree, the sound is noise because
in the CD narration will be sufficient to al low you to understand what you are listening to. For some tracks, however, different parts of the tree vibrate at many different frequencies.
especially those with no associated sonagram, more detailed information will be helpful.This additional information The drumming sounds of three different woodpecker species
is included in the track descriptions in Appendix A. ■ nicely illustrate this noise and show how patterns of noise can be
highly distinctive (Fig. 7-8 & Track3, Track 4). The fi rst two species, the
Downy Woodpecker and Hairy Woodpecker, look a lot alike, but can

Cornell Laboratorq of Ornithologq Handbook of Bird Biologti

7.8 Donald E. Kroodsma Chapter 7 -Vocal Behavior 7-9
Figure 7-7. Sonagram and Oscillogram 5.5 - a. White-throated Sparrow Sonagram be distinguished by their size or by Common Yellowthroat
of White-throated Sparrow Song 4111. ei m I their unique vocalizations. They
(Track 2, 1st Song): Like the song of 5.0 -
„.atim
the Black-capped Chickadee, the song
differ, too, in the rate at which they

Frequency (kilohertz)
of the White-throated Sparrow consists
4.5 - drum. Surprisingly, the larger Hairy
entirely of pure whistles, each note on 4.0 -
Woodpecker drums faster than the
nearly a single tone. Although there is Downy. Counting the number of
some variability among individuals, 3.5 - 101".. OW". WSW MIAOW IIIINIAVO
pulses in a second shows that, in
most songs follow the same general pat- Poor Old Sam Peabody Peabody Peabody Peabody
tern: the first two or three notes are long 3.0 - our example, the Hairy Wood- 2 i - ty witch - i - ty witch - i - ty witch ...
00 0.5 1.0 1.5 2.0 2.5 3.0 35 40
and solid, and the last three or four notes pecker has about 26 drums per 0.0 0.5 1.0 1.5 20
are divided into three parts each. The first Seconds second and the Downy only 15. Seconds
notes may be lower or higher than the
The third species, the Yellow-bel-
last, and occasionally one is divided
like the later notes. The song is often
lied Sapsucker, after which the Cornell Laboratory of Ornithology's bird Figure 7-9. Sonagram of Common Yel-
described as old sam peabody peabody b. White-throated Sparrow Oscillogram sanctuary was named, adds a unique rhythm to its drumming, deliv- lowthroat Song (Track 6, 3rd Song):
peabody because it resembles the folk ering taps not at the constant rate of the Downy and Hairy, but starting Common Yellowthroat songs vary
Pressure (m icropasca ls)
50
tremendously from bird to bird, but all
song-but here poor old sam is used at fast and ending at a slower pace (Fig. 7 8 & Tradc 5).
-
have in common a pattern of three or
the beginning, because there are three
four notes (three in this example) usu-
notes. a. Sonagram: Note how clearly 41411111-1M-01140--- ally described by birders as witchity.
frequency differences are shown. b. Os-
cillogram: Rhythm is stil I evident, but not
Understanding Complex Songs This pattern is typically repeated three
-50 Sonagrams and oscillograms help us to visualize more com- times in a song.
frequency. Note that the division of the Poor Old Sam Peabody Peabody Peabody Peabody
peabody notes into three parts is much plex sounds, too. The song of the Common Yellowthroat can be heard
more clear in the oscillogram than in the 0.0 05 0 15 2.0 2.5 3.0 3.5 4.0 throughout much of North America. The song is rendered as witchity-
sonagram. In addition, the oscillogram Seconds witchity-witchity by field guides, so we know to search on a sonagram
more clearly shows that all the notes are
approximately the same loudness.
for some kind of a complex repeating pattern of individual notes (Fig.
7 9 & Track 6). Each witchity consists of three or four dark notes on
-

the sonagram, and successive

Eastern Towhee
witchities appear identical. This
pattern occurs in almost every yel-
lowthroat song. When the tape is
Figure 7-8. Sonagrams of Woodpecker Hairy Woodpecker Downy Woodpecker slowed to one-half or one-quarter
Drums (Track 3, 1st Hairy W. Drum; speed, we can more easily fol-
Track 4, 1st Downy W Drum; Track 5,
low each note. Halving the tape
2nd Y-b. Sapsucker Drum): In contrast 4
to pure tones, harsh, "noisy" sounds speed also halves the frequency, of
a)
appear on a sonagram as tall, vertical 0 3
course, so the song sounds much
bands consisting of many different lower.
frequencies at any given point in time. 2
The drink-your-teaeeee of
•
These "broad-band" sounds are typical 3
of woodpecker drums and pecks, as
the Eastern and Spotted towhees
C- 1
well as many mechanical sounds such is also familiar throughout North
as clapping hands or the slamming of a 0.0 0'5 10 1 5 0' 0 05 10 1.5 America, although the western
Drink your tea ee - ee - ee - ee
door. The Hairy Woodpecker, in spite of Seconds Seconds Spotted Towhees often seem to 2
its larger size, drums consistently faster 00 0.5 1.0 1.5
omit the drink-your in their songs.
than the Downy Woodpecker. In this Yellow-bellied Sapsucker Seconds
example, the Hairy Woodpecker gives The classic song has a couple of
I I i k t I I
26 drums per second, and the Downy introductory sounds, starting with a high drink followed by a lower- Figure 7-10. Sonagram of Eastern
Woodpecker, 15. The Yellow-bellied frequency your. Then the song typically concludes with a series of Towhee Song (Track 7, 1st Song): The
Sapsucker drum is distinctive, varying 1 I 1 1 III 1 identical units, or syllables, often repeated so fastthat we cannot count
classic Eastern Towhee song begins
in rate and generally slowing down to- with two relatively slow introductory
ward the end. Woodpecker drums may them (Fig. 7 10 & Track 7). Given the repetitive nature of this song notes-a higher, then a lower one-of-
-

be given by both sexes, and function to ending, perhaps the teaeeeee would be more appropriately rendered ten described as drink-your. These are
declare a territory and to attract a mate. as tetetetete. The chosen example at normal and slowed speeds clearly followed by a trill (tea-ee-ee-ee-ee)-a
They are faster and more regular than the series of rapidly repeated units or syl-
shows these features of the song.
more leisurely pecks used to find food. lables. Songs vary greatly among birds,
O .r 5 1.0 1.5 2.0 2. 5 3.0 One final example illustrates especially well how "seeing" the however, and each individual male may
Seconds song as a sonagram helps us appreciate what we are hearing. The song sing up to eight different song types.

Cornell Laboratory of Ornitholos Handbook of Bird Biologq

7.10 Donald E. Kroodsma Chapter 7—Vocal Behavior 7.11
Figure 7-11. Sonagram of Winter Wren Winter Wren of sonagrams representing the vocal repertoire of that individual. In
Song (Track 8, 1st Song): The song of
this way, we gradually begin to understand how the bird uses this vocal
the Winter Wren is one of the longest
8 repertoire in different social contexts.
and most complex among North Ameri-
6
can birds. The high, rapid, piccolo-like
4 1.1f\,4\ 64‘,‘f ell'if#101e9 This approach has revealed that birds have a relatively limited
sounds race by as a series of different
2:0 selection of types of vocal signals (signals are vocalizations that have
trills, sometimes separated by individual 00 - 1.0
evolved for a specific function). For now, we'll consider "song" one
notes.

Frequency (kilohertz)
8 type of signal; even though a Brown Thrasher, for example, might
6 ANN *V have thousands of different songs, all seem to serve the same func-
4
4.0 tion (see Song Repertoires, later in this chapter). Consider again the
3.0
Black-capped Chickadee (for good accounts of chickadee behavior,
8- see Hailman 1989; S. M. Smith 1991; and Hailman and Ficken 1996)
6-
4
A1,,.,1,,1,0 4 14, (Fig. 7 12). Extensive tape recording, creation of sonagrams, and clas-
-

5:0 6:0 70 ._D sification of sound structure has shown that chickadees have about 14
different kinds of sounds. Three sounds are frequently used, highly dis-
tinctive, and readily recognized by anyone who watches chickadees
6 44)rat
y f \ PP 1111411111114111A for even a short time. One of these is the hey-sweetie, identified as
the "song" because the male usually sings it loudly from an exposed
8.0 9.0 10.0 perch, as if he were proclaiming his territory or serenading a female.
Seconds
Another vocalization, the one for which the bird was named, is the
chick-a-dee call, often heard in winter flocks and near winter bird Figure 7-12. Black-capped Chicka-
of the Winter Wren, especially from western North America, has been
feeders (Fig. 7 13a & Track 9). The birds give this call in a variety of
- dee: Resident in woodlands, clearings,
referred to as "the pinnacle of song complexity" (Kroodsma 1981). The parks, and suburban areas throughout
contexts, including when they seem mildly alarmed, as at humans or
songs of these wrens are truly remarkable; they can be 10 seconds or the northern United States and much of
other animals. The third common vocalization is the "gargle," a com-
longer, but the wren sings successive notes so rapidly that all we hear Canada, the Black-capped Chickadee
plex sound used mostly by males in aggressive interactions over short is one of the most familiar birds and a
is a blur. Once we slow the song down, however, we can appreciate all
distances (Fig. 7 13b & Track 10).
- common visitor to feeders. The male's
of the finer details and begin to hear what we see in the sonagram. At distinctive fee-bee orhey-sweetie song is
These three sounds are the most common, but careful study
one-half and especially at one-quarter normal speed, the listener can one of the earliest avian "signs of spring."
has revealed that Black-capped Chickadees make about 11 other
clearly identify each note the wren produces (Fig. 7 11 & Track 8). - Sung frequently in late winter as the day-
vocalizations. These have been given a variety of names: faint fee- light periods begin to lengthen, the song
Dissecting the sounds of the wren and the other species in this
bee, subsong, broken dee, variable see, hiss, snarl, twitter, tseet, high serves to proclaim a territory and impress
fashion gives us a new appreciation of the complexity of bird sounds.
zee (alarm zee), scream, and squawk. These vocalizations occur in a females. Photo by Lang Elliott.
By using sonagrams, and to a lesser extent osci I lograms, we can also
wide variety of contexts. Mates in the vicinity of the nest give a "faint
begin to "see" the finer details of what birds do with their sounds.
fee-bee," which is basically a fee-bee (or hey-sweetie, as I prefer) but
We add a dimension to our listening skills that enhances our overall
much softer.Young male and female birds, beginning at about 20 days
experience and appreciation for bird sounds. Throughout this chapter
of age, give "subsong," a variable whistled performance in which the
we illustrate sonagrams for you to inspect, accompanying them with
young birds seem to be practicing their song. Chickadees "hiss" when
recordings so that you can improve both your seeing and hearing of
they are cornered, as in a nest cavity; this hiss may be a kind of mim-
bird sounds.
icry evolved to make predators think they are dealing with a snake at
close quarters. Chickadees "snarl" in fights and "twitter" to mates near

Vocal Repertoires the nest. They give "high zees" when they detect a predator or other
alarming object; high-frequency alarm calls can be difficult to locate,
■ Our experience tells us that birds produce a tremendous variety of warning chickadees (and other birds) of the danger without revealing
sounds. How can we begin to make sense of this great diversity? The the caller's location to the predator. Chickadees "scream" when cap-
best way is to start with an individual bird. Professionals who study tured, as in a mist net, and "squawk" to the young in the nest.
bird sounds often mark a bird, usually with a distinctive combination
of colored leg bands, and then follow it, often for days at a time, and
sometimes year after year. The researchers record all sounds the bird
The Problem of Meaning
makes and carefully document the context in which each sound was The total repertoire or vocabulary has been established for very
used. Next, they make sonagrams for each recording so that the anat- few species, and is as thoroughly documented for chickadees as for
omy of each sound can be studied in more detail. Finally, they sort all any other birds. Yet those who study such repertoires worry that we
the sonagrams by shape and combination of notes to establish a library humans don't really classify signals the way the birds do. The sonagram

Cornell Laboratorq of Ornithologq Handbook of Bird Biologt

 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.13
Figure 7-13. Sonagrams of Black- a. Black-capped Chickadee chick-a-dee Call anything, or does absence of a particular note convey something
capped Chickadee Chick-a-dee and special? Do chickadees send different messages with all of these vari-
"Gargle" Calls: In addition to its ations? We simply don't know.
hey-sweetie song, the Black-capped 10

Chickadee has about 13 different calls

The "gargle" is another "combinable" vocalization, in the sense
9
in its vocal repertoire. a. Chick-a-dee that the component parts can be rearranged to form different vocal-
8 A
Calls (Track 9, 1st Call): The chickadee izations. Each gargle consists of two to nine short notes, which are
7
is named for its chick-a-dee call, used drawn from a pool of about two dozen notes in each local population
in winter flocks and often heard at bird 6-
of birds. The notes used in any one gargle are thus only a sample of the
feeders. Each flock has a distinctive 5-
chick-a-dee call, and new birds who local population, and each bird combines and recombines the notes to
4-
join a flock change their call to match produce a tremendous variety of different gargle calls. To simplify our

Freqi
that of their new flockmates. The call 3-
view of chickadee communication, we combine all of those variations
is given frequently when two or more 2- into a single category, the gargle. But the birds undoubtedly hear so
different flocks interact. The call may
contain up to four different types of Chick - a- dee - dee - dee - dee - dee - dee - dee - dee much more in a given gargle than we humans can begin to appreci-
notes, referred to by researchers as A, 00 0.2 0.4 0.6 0.8 1.0 1.2 1'4 18 2'0
ate. Although we lump the hundreds of qualitatively different gargles
B, C, and D, in various combinations. Seconds into a single class, the chickadees probably attend not only to different
Most commonly, however, it consists of sequences and combinations of elements, but to fine nuances of pro-
a few introductory notes (chosen from
b. Black-capped Chickadee "Gargle" Call nunciation as well. In our attempt to understand a complex situation,
A, B, and/or C) followed by a series of D
notes—the sonagram clearly shows the we may have unjustly oversimplified what the birds are doing.
broad-band nature of the raspy-sound- Consider an analogy with human speech. The words "I love you"
10
ing D notes. Note that our example can be said in many ways, and we are primed to hear these subtle nu-
contains only three types of notes, A,
ances in how our language is used. The emphasis, for example, can be
B, and D. b. "Gargle" Calls (Track 10, Q.) 8
_c
1st Three Calls): The "gargle" call is 0 on any one of the three words, and the implications for the resulting
7 statement are profound. The statement can stress who loves (I), the
very complex and highly variable—the
same individual may give many dif- U6 type of relationship (love), or who is loved (you). The inflection of the
CU
ferent versions. It is used most often by statement can rise, thus questioning the statement, or fall, which can
t:3"- 5
males in aggressive interactions over
13")- 4 have different meanings depending on the context. An alien unfamiliar
short distances. The sonagram shows
three gargles given consecutively by with our communication might fai I to appreciate these nuances, just as
one bird, and even here the variability we, aliens to the birds, undoubtedly fail to appreciate the finer points
is apparent. of their expressions.
Even the simple hey-sweetie song varies in ways that are only
00 0.5 1.0 1. 5 2.0 2.5

Seconds
recently being appreciated (Horn et al. 1992). If you listen to a B lack-
capped Chickadee during the early morning, for example, you hear
the typical hey-sweetie over and over. The song is simple and doesn't
is a crude way to picture a sound, as we appreciated when we com- seem to vary. But listen to 10, 20, or 30 songs, and suddenly you'll hear
pared the osci I logram and the sonagram. The osci I logram nicely shows a change that seems, in context, rather dramatic. At some point, the
relative amplitudes, but not frequency; the sonagram shows relative bird transposes this simple hey-sweetie by a couple of hundred Hertz,
frequency well, but amplitude poorly. The main problem is that we either up or down, and then resumes singing the hey-sweetie on this
have little idea what features the birds really attend to. We humans can new frequency. A few hundred Hertz may not sound like much, but the
classify sounds by relatively gross features on the sonagrams, and we human ear is very good at comparing two signals given in succession,
can correlate these sound categories with general social contexts, but and the shift is indeed dramatic (Track 11). Careful analysis has now
we undoubtedly fail to appreciate the finer details of what birds really shown that a chickadee can sing its hey-sweetie on many different
hear and respond to.
frequencies. So how many different hey-sweetie songs does the male
In fact, the birds themselves may hear and use a far greater variety chickadee sing? Perhaps an infinite number, if we "split hairs"? Do we
of sounds than we appreciate. Reconsider that "simple" chick-a-dee
vastly oversimplify the chickadee's communication system by saying
call (see Fig. 7-13a). This call consists of four different notes, which
that it has only one hey-sweetie song? Furthermore, even successive
might be identified as A, B, C, and D. Most chick-a-dee calls contain
hey-sweetie songs on the same frequency may vary in subtle ways—in
these four notes, but the birds deliver them in different combinations
duration or patterns of loudness, for example. We can hear and see
and differing numbers of times, to form hundreds of qualitatively dif- these subtle variations when we graph the songs, but we don't yet know
ferent kinds of calls. Does ABCD convey information different from whether they are meaningful to the chickadees.
ABCDD, for example? Does the number of repetitions of a note mean

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

7.14 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.15

Song Sidebar 1: WINNOWS, SNAPS, AND SPRING THUNDER-

The amazing variation in one type of signal, the songbird's "song,"
of which the hey-sweetie is an example, has received special attention
NONVOCAL SOUNDS
from researchers. "Song" has been defined in numerous ways, but it is Sandt1 Podu Ika
generally accepted that songs are loud vocalizations, often delivered
from an exposed perch, with the presumed function of attracting mates
The melodies put forth by singing
or repelling territorial intruders. It's tempting to let the definition
birds appeal to our love of music and
of song go at that, because no entirely adequate definition can
dominate the spectrum of natural
be found (Spector 1994). Although the distinction between sounds we hear around us, yet the
"song" and "call" is a somewhat arbitrary one devised by many nonvocal sounds birds make
humans, our general definition ordinarily works well. It are equally dramatic and engaging.
works because most birds dosing—they use special be- Discussed here are only a few.
haviors to try to attract mates or defend territories. Remove a
female from a male songbird, for example, and he soon begins Woodpecker Drumming
singing, announcing with great vigor his bachelorhood and thus his You have already listened to the
availability. Because songs are often sung loudly and persistently, they drumming of several different wood-
Figure A. Ruffed Grouse Drumming: A male Ruffed Grouse "drums" by cupping his
peckers. Most of these short "drum
are the most noticeable vocalizations that we hear from birds. wings and then bringing them upward and forward with such force that he compresses
rolls" differ markedly from the more a parcel of air between his chest and wings, creating a sound wave without his wings
In functional terms, woodpeckers "sing" as they drum on a tree,
quiet, irregular, leisurely taps wood- and chest ever touching. He repeats this "thump" in a series, beating faster and faster
and snipes "sing" during aerial displays as wind rushing over their tail peckers make while searching for until the thumps become a whir. The sound is so low in frequency (40 Hz) that a hu-
feathers produces winnowi ng sounds (Sidebar 1 :Winnows, Snaps, and food or excavating a nest site (Track man may not even notice it, or may write it off as a distant car starting, unless he or she
Spring Thunder: Nonvocal Sounds). Most birds "sing" vocally, how- 12). Drumming, like song, is clearly is listening carefully. The male usually drums while standing on a hollow log, which
ever, although the complexity of "song" varies widely among species. meant to be noticed by other mem- serves as a resonating chamber—amplifying his message that he owns the territory
and is available to mate. Drawing by Charles L. Ripper.
In some, such as the Winter Wren, the song is by far the longest and bers of the same species. The per-
most complex vocalization produced. In others, however, the "song" former chooses a dry branch, hollow
Figure 7-14. Female Northern Car- can be much simpler than "calls"—for example, the hey-sweetie song log, drainpipe, or tin roof—anything but Doc Allen's frames revealed that touching (Fig. A). Each stroke of his
dinal Singing: In most species just the that will make a good loud noise— the male stood crosswise on his log, wings produced a muffled thump.
of Black-capped Chickadees is much simpler than their gargle call.
male sings, but Northern Cardinals are and then lets loose with a roll. One braced on his tail, and cupped his He started slowly, stroking faster and
one common exception. Other North
Songs can be "musical" or not, according to our ears; what's important
particularly creative Yellow-bellied wings, bringing them forward and faster until the thumps merged to a fi-
American species in which females to remember is that beauty lies in the ears of the beholder.
Sapsucker drummed on a garbage upward with such force that he com- nal whir (Fig. B & Track 13). The male
occasionally may sing include Purple In some species both males and females sing (Fig. 7-14), but in can lid! Both males and females pressed a parcel of air between his proclaiming his territory and avail-
Finches, Gray Catbirds, Baltimore Ori- our northern temperate zone we hear mostly males, because they are drum, to proclaim territory and as a chest and wings, creating a sound ability to any passing female can be
oles, House Finches, Rose-breasted
the ones who are primarily responsible for defending territories and part of courtship. Although they may wave without wings and chest ever heard up to 1/4 mile (0.4 km) away,
Grosbeaks, and Black-headed Gros-
beaks. attracting mates (see Duetting, later in this chapter, for more on female have many different "signal posts"
song, especially in the tropics). Hence, in this chapter the singer is within their territory, they usually fa-
usually referred to as "he." vor one or two that are particularly
The songbirds are a group of about 4,600 species renowned for well-placed or resonant. Drums are
their singing ability. Unlike some other bird groups, songbirds learn one of the first bird 'songs" heard in
the late winter woods—a sign that
their songs, which can therefore be especially complex (more on this
behavior patterns are changing and
topic later, in theVocal Development section). If we accept that sorting
spring is on its way.
based on sonagrams gives a crude indication of how many different
songs a bird can sing, we discover vast differences among species. The Ruffed Grouse Drumming
chickadee is a songbird with a very simple song repertoire, essentially In the predawn hours of early May,
one basic hey-sweetie that varies in frequency. Except for these slight 1932, ArthurA. Allen hid in Sapsuck-
differences in frequency, all hey-sweetie songs look basically the same er Woods near the drumming log of
on sonagrams. Some other species also have simple repertoires; Chip- a male Ruffed Grouse, and through
ping Sparrows, Indigo and Lazuli buntings, Common Yellowthroats, slow-motion photography and sound
Ovenbirds, White-throated Sparrows, and White-crowned Sparrows recording, solved the mystery of how Figure B. Sonagram of Ruffed Grouse Drum (Track 13, 1st Drum): Each thump pro-
"spring thunder," as he called it, was duced by a drumming Ruffed Grouse is made up of a broad band of frequencies, but
all use one basic song form in their singing. The sequence of notes in
produced. Until then, people had lasts only a short time. Note that the frequency scale here is in Hertz, whereas most
their songs, as revealed by sonagrams, remains essentially unchanged
speculated that grouse pounded their other sonagrams in this chapter are scaled in kilohertz (1,000 Hertz).
from one song to the next.
wings on a log or beat them together,
(Continued on p. 7.19)

Cornell Laboratorq of Ornithologq Handbook of Bird Biolo94

7.16 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.17
but the frequency of 40 Hertz is so m) up, and then dives to achieve the
low that it sounds soft even from very necessary speed of 24 to 52 mph (39
close. Why so low? No one knows to 83 km/h). In the midst of the dive,
for sure, but the lower limit of hear- the performer spreads his tail, caus-
ing of one of the Ruffed Grouse's ng the ai r to vibrate the stiff, modified
most powerful enemies, the Great outer feather on each side of the tail,
Horned Owl, is 60 Hertz. Perhaps in which produces a whistle-hunn sound
past generations any grouse drum- that can be heard up to 1/2 mile (0.8
ming at a higher frequency was km) away. Because the beating wings
also proclaiming the availability of send air over the tail in pulses—not
dinner to an owl, and was eaten. in a steady stream—the whistle-hum
Through natural selection, then, the is a rapidly pulsing woo-woo-woo-
sound may have evolved to its cur- woo, rather than a continuous sound
rent low frequency. (Fig. E) (Track 15).
To hear "spring thunder," visit a Either sex may winnow to pro-
northern woods in spring at dawn claim territory, and the male may do
or dusk, when the drumming is most so to court a female. That the sound
frequent. Males also drum all night is indeed produced by feathers and
under strong moonlight, and oc- not voice was demonstrated by
casionally in the fall or during the placing tail feathers of a European Figure D. American Woodcock Courtship Display: At dusk and dawn, and on moonlit
day. Listen carefully, for the sound Snipe in a wind tunnel, producing nights, the male American Woodcock performs his spring ritual throughout the eastern
is easy to miss. You may even be the whistle-hum sound with no bird United States in small clearings in fields or wet meadows. He begins on the ground
lucky enough to discover a male's with a series of nasal peents during which he often faces different directions—thus
Specialized present. (Because the airflow over
drumming site—usually a big, the sound may seem to vary in loudness. Then he takes silently to the air and ascends
Primaries the feathers was steady, this sound
gradually. As he climbs higher he flies in wide spirals, making musical twittering
mossy, hollow log. A pile of drop- did not pulse.) sounds with his wings (see Fig. C). At the peak, as much as 300 feet (approximately
pings and a flattened patch worn in Figure C. American Woodcock in Flight: The outer three primary feathers of each wing If you visit a marshy field during 100 m) in the air, he begins vocal chirps as he zig-zags downward. For the last part
the moss from many years of grouse of the male American Woodcock are unusually narrow and stiff; when he flutters his twilight, listen carefully, and look for of the descent he is silent. When he returns to the ground, near where he began, he
feet may confirm your find. If a log wings rapidly during the flight portion of his courtship display, the air vibrates these
a performer circling overhead. If the resumes his "peenting."
is not available he may use any el- feathers, and they produce a high twittering noise.
sky is light enough, you will be able
evated site, such as a mossy mound to watch its dives, and to see it spread
or a stone pile. A grouse may have Aldo Leopold in "Skydance" from A chirps—to the careful listener strain- its tail feathers as you hear the haunt-
several other drumming logs in ad- Sand County Almanac, ing to catch a glimpse of the tiny dot ing sound.
dition to his primary one, so don't be against the dusky sky, a clue that he is
surprised if you hear him drumming . suddenly the peenting ceases on his way down (Fig. D) (Tradc 14). Other Nonvocal Noises
from more than one location in his and the bird flutters skyward in To view the "skydance" of the Birds seem to use every avail-
territory. a series of wide spirals, emit- woodcock, dress in dark clothes and able method of nonvocal sound
ting a musical twitter. Up and listen in open fields for the peenting production.
American Woodcock Display up he goes . . . the twittering call at dusk. When the performer A number of birds, including
Another nonvocal performance louder and louder, until the takes to the air, quickly move in a storks, herons, owls, roadrunners,
captivates nature-watchers in east- performer is only a speck in the little closer. Before the bird drops out and Tree Swallows, snap their jaws
ern North America each spring—the sky. Then, without warning, he of the sky, crouch down or hide near together in various displays, but
courtship display of the American tumbles like a crippled plane, a shrub, then remain still until he is wing noises are the most common.
Woodcock. In open, wet fields, giving voice in a soft liquid up again. Displaying males are quite Grouse and quail wings thunder as
males display briefly at dawn and warble that a March bluebird sensitive to disturbance, however, so the birds burst from cover when dis-
dusk—the times of day when the might envy At a few feet from stay far enough away to let the male turbed, perhaps startling predators
light intensity changes most rapid- the ground he levels off and continue uninterrupted. and buying a few precious seconds
ly. The outer three primaries of each returns to his peenting ground, for the fleeing bird. Mourning Dove
wing are narrow and stiff, and when usually to the exact spot where Common Snipe Winnowing and Common Goldeneye wings
a male flutters his wings rapidly, the Figure E. Common Snipe Winnowing: Circling more than 300 feet in the air over
the performance began, and Over wet pastures and meadows whistle in flight, and the wings of
wet meadows and pastures, Common Snipe perform their territorial and courtship
air vibrates these specialized feath- there resumes his peenting. throughout northern North America, Rock Doves may hit each other over display in the springtime twilight. Termed "winnowing," after the rapid, whistle-hum
ers to produce a high twittering (Fig. yet another springtime ritual is car- their backs, making a loud clapping woo-woo-woo-woo produced during one portion, the display may be given by either
C). The performance begins on the Although the twittering dur- ried out each dawn and dusk: the noise in flight. Hairy Woodpeckers, males or females. To make the noise, the performer must reach a minimum air speed
ground with a series of nasal, vo- ing the upward spirals is nonvocal, winnowing of the Common Snipe. Chuck-wi I l's-widows, and Common of around 24 mph, which it achieves by diving. In the middle of the dive it spreads
calized peents similar to the call of at the peak, 300 feet (90 m) in the The displaying bird circles high Poorwil Is clap their wings in a sim- its tail, causing the air to vibrate the outer tail feathers, which produces the haunting
a nighthawk. Then, as described by air, the bird begins a series of vocal overhead, 300 to 360 feet (90 to 110 ilar way in territorial defense, as do sounds that can be heard up to 1/2 mile (0.8 km) away.

Cornell Laboratorq of Ornitholooti Handbook of Bird BioloBti

7.18 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.19

Short-eared Owls in their shallow ing growls and rapid firecracker-like struments"—the "jug band crowd"
courtship dives. Many humming- snaps. The sounds are produced by evolved using whatever raw material
birds, too, make buzzes or shrill striking together the stiff, narrow, was available to make their sounds.
whistles with their wings in their outer primaries, or the thickened And they use their feather-whirring,
territorial and courtship flights. The secondary feather shafts (Fig. F) feather-rattling, beak-snapping, and Eastern Towhee Repertoire
Common Nighthawk dives deeply (Track 16). wing-whacking in the same ways
in courtship, and at the bottom, his This dazzling variety of nonvocal other birds use vocalizations—to at- Song Type 1
wings make a low roar like someone sounds demonstrates the remark- tract mates and defend territories. ■
blowing across the top of an empty able flexibility of evolution. Natural
cu
bottle. selection doesn't "design" systems Suggested Readings cu
o8
Manakins, a huge group of Neo- from scratch fora specific purpose; it Al len, ArthurA. 1987. SpringThunder
tropical birds, produce an assortment works instead on existing behaviors 6
in Sapsucker Woods. Living Bird (-)

of nonvocal noises during courtship. and structures, sustaining those that Quarterly. 6(4):8-11. (First printed a) 4
White-bearded Manakins form leks most improve survival and repro- in The Cornell Plantations, Spring a-
of up to 60 males. In dramatic court- duction. Most birds communicate 1947.) Lt. 2-

ship displays, they hop back and vocally using the syrinx, whose
One of the Lab's founders, DocAl- 0.0
main purpose is sound production. 0.5 1.0 1.5
forth between saplings, and slide len, recounts a trip into Sapsucker Seconds
down the trunks, their wings mak- But others use less conventional "in-
Woods on the day he and his Song Type 2
equipment-laden colleagues cap-
tured for the first time the thunder

Freq uency (kilohertz)

of a drumming Ruffed Grouse.
8-

6-
Leopold, Aldo. "Skydance" in A Figure 7-15. Eastern Towhee: The male Eastern Towhee
Sand CountyAlmanac. Ballantine sings his song from moderately high, exposed perches 4-
Books, NY. 1949. within his territory—often a location along a forest edge
or in an open woodland. Photo by Lang Elliott. 2-
A beautifully written essay de-
scribing the American Woodcock
Other species have much larger repertoires (Krebs and Kroodsma 00 0.5 1.0 1.5
and its aerial display. The book is Seconds
1980; Kroodsma 1986). An Eastern Towhee (Fig. 7 15) may sing three
-
a classic, containing numerous
passionate, yet ecologically infor- to eight different drink - your- tea songs; each song form has a distinctive Song Type 3
mative, essays about wildlife in the structure and sequence of notes, and the differences are visible on
American midwest. Aldo Leopold sonagrams and audible to anyone who listens carefully (Fig. 7 16 & -
8
is one of the founders of the field of Track 17). Over a period of five to ten minutes, a male typically sings 0
•_
wildlife biology and the environ- 6
ten to thirty renditions of one song form, but he then abruptly switches
mental movement in the United to another form, and eventually another, until he returns to sing, with
States. great fidelity, the first song you heard. The towhee thus partitions his
song performance into three to eight different songs. A male Song
Sparrow typically has 8 to 10 different songs. Each one is repeated
00 0.5 1.0 1.5
often, and this repetition is an integral part of his singing activities. Seconds
Even more impressive are Marsh Wrens; in eastern North America,
Figure F. Courtship Display of the White-bearded Manakin: Males of this chickadee-sized lekking species (see Ch. 6, Repro- males have about 50 different songs apiece, and males in the western Figure 7-16. Sonagrams of Eastern Tow-
ductive Behavior: Lek Polygyny) display in groups of up to 60 individuals, each on his own small arena or "court," often within states have about 150. Northern Mockingbirds typically sing 100 to hee Songs (Track 17, 1st, 4th, and 7th
yards, sometimes feet, of his neighbors on the forest floor. Females actively participate, although males frequently display when 200 songs. The largest repertoire found so far, however, is that of the Songs): Three different song types from
no females are present. Each tiny arena is kept clear of leaves by the male, and has several small, thin saplings growing within the same Eastern Towhee. Note that
Brown Thrasher. When thousands of sonagrams of a male thrasher
it. The male leaps rapidly around his arena from sapling to sapling, giving loud, firecracker-like snapping noises with each leap. although none of the songs match the
were sorted into different categories, he was estimated to sing well "classic" song type shown in Fig. 7-10,
In intense excitement he may give volleys of snaps, resulting in a loud ripping sound. He may repeatedly travel in one direction
(1), suddenly changing to ricochet back and forth between two saplings (2). Each time the male lands, he does so in a horizontal over 2,000 different songs (Fig. 7 17).
- they all follow the general pattern of be-
position, flaring out his white beard. When a female joins him, the display becomes still more frenetic, both birds leaping around ginning with one or several introductory
in the above manner together, sometimes following each other, sometimes moving in opposite directions and passing each other notes and ending with a trill. The note
in midair. Often the male jumps to the ground (3), then springs up onto a sapling (4), giving a sound partway between a grunt The Structure and Function of Sounds and trill types differ from song to song. A
and a hum, then continues leaping around the arena. If the female accepts the male, she remains immobile on a sapling, and he male may have a repertoire of between
The structure of a song or other sound is a combination of all the
uses the grunt-jump (4) to land well above her. He then slithers rapidly down the sapling (5) to land on her back, and copulation 3 and 8 different song types, and he usu-
features that form that sound, as typically detected on a sonagram. ally sings each one 10 to 30 times before
occurs. The snaps, rips, and grunts are nonvocal sounds, thought to be produced by the male manakin's specialized wing feath-
ers. Females do not make these sounds. These features include the duration of the sound, the overall frequency, switching to a different type.

Cornell Laboratort of Ornitholo9q Handbook of Bird Biolom

7.20 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.21
Figure 7-17. Brown Thrasher: The larg- Figure 7-18. Sonagrams of Alarm Calls
est song repertoire known belongs to dpm.#001110110111 (Track 18, 1st A. Robin Call, 1st T. Tit-

Frequency (kilohertz)
the Brown Thrasher, who can sing up mouse Call, 1st Two 8-c. Chickadee
to 2,000 different song types, a few of 6 Calls): The alarm calls of many birds are
them imitating the songs of other spe- similar—a high, narrow-frequency note
cies. He usually repeats each song type that begins softly, increases in amplitude,
4
two or three times, quickly moving on and then fades away. Sounds with these
to the next. characteristics are particularly difficult
2 to locate, thus allowing a bird that spots
American Robin
a predator to warn other individuals (of
both its own and other species) without
0.0 0.2 0.4 0.6 0.8
giving away its location to the predator.
The examples shown are the high zee
.-wwww.....mr iammi
8 ,11111111.1 calls of the American Robin, Tufted Tit-
1fr
mouse, and Black-capped Chickadee.
Note that although the high-frequency
nature of the calls can be seen from
the sonagram, the amplitude changes
are not visible—they would require an
oscillogram to be distinguished. Note
also that the time scale for the American
Tufted Titmouse Robin calls (which last longer) is differ-
ent from that of the other two species.
00 0 1
. 02 03

0 1111111111111.ftommir _ 4001111111SMINIIIII ■Rimir--

whether the sound is a relatively pure whistle or reaches across a broad

spectrum of frequencies at once, whether individual sound units are
repeated, and so on.
To some extent, the functions of vocal signals dictate their struc-
Black-capped Chickadee
ture. When a hawk flies overhead, for example, small birds typically
freeze and produce a high, narrow-frequency call that begins softly, 00 0.1 0.2 0.3
Seconds
increases in amplitude, and then fades away; sounds with these char-
acteristics, such as the high zee of the chickadee, are difficult to locate
(Fig. 7 18 & Track 18). When songbirds "mob" an owl, however, they
-

dive and swoop at the predator, making seemingly daring passes at it; carries a long distance through the forest even though it is given from
calls in this situation are harsh, broad-band noise, and easily located near the ground. The low-frequency, often tremulous whistles asso-
(Marler 1955) (Fig. 7 19 & Track 19). In general, aggressive sounds
- ciated with tropical forests are in many cases voiced by ground-dwell-
are often broad-band noise emphasizing low frequencies, whereas ing birds, such as tinamous (Fig. 7 21) (Track 20). -

appeasing sounds are higher in frequency (Morton 1982).

The type of habitat in which a bird sings also can influence song Our understanding of the meanings of avian vocalizations to
structure, because certain songs transmit better in some habitats than other birds is truly in its infancy. Our current classifications may bear
in others. Songs of the Great Tit (an Old World chickadee relative) little resemblance to how birds actually hear and use their vocal sig-
differ consistently between forests and more open woodlands; forest nals, and we must remember that our ultimate goal is to ask the birds
songs are simpler, lower in frequency, and contain more pure tones themselves how they do this. Experiments in the laboratory and the
(Fig. 7 20). Perhaps the most striking effect is the use of low-frequency,
- field in which we attempt to interact with birds by playing sounds
fairly pure tones near the ground, especially in tropical forests. Al- to them over loudspeakers are probably the best way to understand
though low-frequency sounds travel best in any habitat, in some hab- birds, and these experiments are just beginning (Dabelsteen and Mc-
itats ground-dwelling birds are "forced" to use low-frequency sounds Gregor 1996; McGregor and Dabelsteen 1996). Only when we can
because sounds higher than one or two kilohertz do not transmit well actually converse with birds in a meaningful way will we truly begin
owi ng to reflections off the ground (Wiley and Richards 1982).The very to appreciate what it is like to be one. Until then, we remain as aliens,
low-frequency drumming display of the Ruffed Grouse, for example, pondering the meaning of all that birds say.

Cornell Laboratory of OrnitholoBq Handbook of Bird Biolcm

7.22 Donald E. Kroodsma Chapter 7 — Voca 1 Behavior 7.23
Figure 7-19. Sonagrams of Mobbing a
Calls: In contrast to alarm calls, mob- Blue Jay 14
bing calls of many different species tend Mobbing Calls

Freq uency (kilohertz)

12
to be broad-band, raspy sounds. These
are relatively easy to locate, allowing 10
an individual bird scolding a predator
to quickly attract other individuals, of-
ten of several different species, to form 6
a mobbing flock that is more likely to
drive the predatoraway. a. (Track 19,1st
Five Seconds of Blue Jay Calls, 1st Three
House Wren Calls, 1st Five Seconds of
Tufted Titmouse Calls): Blue Jay, House :4
Wren, and Tufted Titmouse mobbing
House Wren
calls—note the similarity among the dif- 14-
Mobbing Calls
ferent species in the structure of this call.

Frequency (kilohertz)
12-
b. (Track 19, 1st Six Seconds of Calls):
Mixed-species mobbing flock from Ar- 10-
izona, including Mexican Chickadee,
Western Tanager, and Red-breasted 8-

Nuthatch, all with similar broad-band

6-
calls.
4-

2-

2 4 6
Tufted Titmouse Figure 7-20. Effect of Habitat on Great
Mobbing Calls Tit Song Structure: In more forested
14
areas (left), the song of the Great Tit (an
12
Old World chickadee relative) is simpler,
4)-
-0 of lower frequency, and contains more
10
Vocal Development pure tones than songs from Great Tits
that live in more open woodlands (right).
O.) 6
■ Birds clearly produce a variety of sounds, but how do they know The difference is thought to result from
which one to use and when to use it? After a parent incubates an egg for the different sound transmission prop-
CU
the appropriate length of time, a tiny nestling emerges. Its first sounds erties of the two habitats. The dense for-
est vegetation interferes more with the
are soft peeps, given perhaps in response to siblings or to parents who
transmission of sound waves, distorting
2 4 provide warmth and food.The nestling grows and eventually becomes sounds to a greater extent than does the
Seconds a fledgling, a yearling, and finally an adult. During this development, vegetation of open areas.
various sounds appear in turn to enable the growing bird to manage its
b
16 Mixed-Species Flock Mobbing Calls social environment. How does the bird know when to use what kind of
vocalization? Is it a little robot, with all its vocalizations encoded in its
14 genes, to be uttered automatically in the appropriate circumstances?
Or is development more complex, with the young bird learning much
12 Mexican
of what it knows from other individuals, much as we humans learn
Chickadee
Freq uency (kilohertz)

Red-breasted
Western our language from adults who were, in evolutionary terms, successful
10 Nuthatch
Tanager
before us?
The reason vocal development has been such an intriguing focus
of interest is that certain groups of birds are clearly not robots in their
development. Most of the interest has been on the song of songbirds,
such as wrens, sparrows, thrushes, mockingbirds, warblers, swallows,
and crows. In all songbirds that have been studied, researchers have
0.■ ;•••1
discovered some kind of learning. Just as in humans, this learning
involves listening to a model sound, memorizing the model, and
practicing until the sound matches with great fidelity the young bird's
memory of the original sound.

Cornell Laboratorq of Ornithologq Handbook of Bird Biolom

 7.24 Donald E. Kroodsma Chapter 7—Vocal Behavior 7.25

Vocal Development in Songbirds

Among birds, the "songbirds" are especially successful. Com-
prising about 4,600 of the world's roughly 10,000 bird species, they
are one of two suborders within the Order Passeriformes (the "perch-
ing birds") (Fig. 7 22). The songbirds are well known for their corn-
-

dippers,
lyrebirds,
Old World swallows,
bowerbirds,
flycatchers, chickadees,
fairywrens,
thrushes, titmice,
logrunners,
mockingbirds, nuthatches,
shrikes, vireos,
thrashers, creepers,
crows, magpies,
catbirds, bulbuls,
jays, nutcrackers,
New World starlings, kinglets,
birds-of-paradise, larks, wagtails,
(tyrant) waxwings, Old World
Old World flowerpeckers,
flycatchers, silky-fly- warblers, etc.
orioles, cuckoo- sunbirds,
becards, catchers, etc.
shrikes, drongos, wood-warblers
ovenbirds, Old World
bushshrikes, etc. (New World
woodcreepers, Insect-Eaters
warblers),
antbirds, Thrush tanagers,
cotingas,
Relatives Weaver sparrows,
manakins, etc.
Relatives buntings,
Crow
New World
Relatives
pittas, blackbirds,
New Zealand
broadbills New World
wrens
orioles, finches,
Parvorder Corvida Parvorder Passerida Hawaiian
honeycreepers,
weavers,
whydahs, etc.

SUBORDER TYRANNI SUBORDER PASSER!

(SUBOSCINES) (OSCINES, "True Songbirds")

ORDER
7 PASSERIFORMES
(PERCHING BIRDS)

Figure 7-22. Passerine Taxonomic Tree: Traditional clas- cepted interpretation, based on the work of Charles Sibley and
sification of birds was based on anatomical similarities and Jon Ahlquist The suborderTyranni consists of three groups: one
differences among various species. The order Passeriformes containing the New Zealand wrens, a second containing the
(the passerines or perching birds) has long been recognized pittas and broadbills, and a third composed of the remaining
to consist of two major divisions, which differ in their syrinx suboscines (entirely restricted to the Americas). The suborder
musculature: suborder Tyranni (the suboscines or non-oscine Passeri is divided into two groups: parvorder Corvida contains
passerines) and suborder Passeri (the oscines or true songbirds). the crows and their relatives, parvorder Passerida contains the
Figure 7 21. Tinamou in Rain Forest Vegetation: Tinamous—ground-dwelling, chickenlike birds of Central and South Ameri-
-
Data from molecular biology, particularly the technique of thrush relatives, Old World insect-eaters, and weaver relatives.
DNA-DNA hybridization, recently have been used to develop Source material from Distribution and Taxonomy of Birds of the
ca—give haunting, low-frequency, tremulous whistles that ring through the rain forest in the early and late twilight hours. Low-
frequency sounds travel best in any habitat, especially dense jungle vegetation, and may avoid interference from sound waves modern theories of how bird groups are interrelated. The much- World, by Charles G. Sibley and Burt L. Monroe, Jr, 1990.
reflecting off the ground, which may be a problem with sounds higher than one or two kilohertz. simplified passerine taxonomic tree presented here is a well-ac-

Cornell Laboratort of Ornitholo94 Handbook of Bird Biologq

7.26 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.27

plex songs, which to human ears are often beautiful (Fig. 7 23) - bird is given a live bird to interact White-crowned Sparrow
(Tradal); (Fig. 7 24) (Track 22). By definition, most bird spe-
- with, learning after day 50 becomes
8 Normal Song
cies "sing." That is, they use a loud vocalization to attract somewhat easier, but never as easy,
4l' mates or defend territories. In this way, even nonsongbirds it seems, as during those early

Frequency (kilohertz)
/ 7
such as shorebirds and owls "sing." Not all songbirds, weeks of life. Other songbirds, such
6
however, produce "beautiful" songs (consider the song as Swamp Sparrows, Marsh Wrens,
of a crow), but they're songbirds nonetheless, based and Zebra Finches, also learn best 5

on their evolutionary history. The songbirds are so during this early period (Baptista 4
named because they typically sing so frequently 1996).
3
and so conspicuously—at least from the human The extent to which birds can
perspective. learn later in life varies among spe- 2
00 0!5 1 1:5 2:0 2:5
Songbirds also imitate sounds. Caged birds cies. Northern Mockingbirds can Seconds
have been kept for centuries, for example, and add new sounds to their complex 8 Isolate Song
trained to sing a variety of sounds often unchar- repertoires as adults, so repertoire

Frequency (kiloher tz)

7
acteristic for their species.Various Island Ca- sizes may increase steadily with
6
nary strains have been selected to produce age. Other species that mimic
different kinds of songs, so the genes of the also are reported to acquire songs 5
different strains now dictate what range of song throughout their lives. In most spe-
4
syllables the birds learn (Mundinger 1995). cies, however, individuals seem to
In the laboratory, we can readily demonstrate the song- develop a repertoire of sounds dur- 3

learn ing potential of birds. In North America, the White-crowned ing their first year and then rarely, 2
00 0.5 1.0 1.5 2.0 2.5
Sparrow has been a favorite study species (Baptista 1996). If re- if ever, modify it. One male Red- Seconds
searchers take a sparrow from a nest in the wild at eight or nine days of winged Blackbird, for example,
Figure 7-23. Common Nightingale:
age and keep him in the laboratory where he can't hear any of his spe- sang the same six songs over a period of five years in a Tallahassee, Figure 7-25. Sonagrams of White-
Lauded by romantic poets and song writ-
cies' natural songs, he develops a highly abnormal song (Fig. 7 25 & Florida, marsh (Kroodsma and James 1 994). crowned Sparrow Normal and Isolate
ers over the centuries, the nightingale's -

Song (Track 23, 1st Normal Song, 1st

exquisite, melodious song, often sung Track 23). Expose the young male to songs of an adult White-crowned Birds are selective in what they learn. A young White-crowned
Isolate Song): The normal song of an
at night, gives this otherwise modest Sparrow, however, and he learns to sing the details of the tutor song. Sparrow does not learn just any bird song it hears. It seems that the adult White-crowned Sparrow (top
European bird its fame.
Regardless of where the young bird was born, he can learn a wide components of the song must match, to some extent, characteristics sonagram) is a complex mix of pure
range of White-crowned Sparrow songs, taken from anywhere in the of some innate knowledge of song that the young bird is born with. If tones, buzzes (the large, dark, broad-
geographic range of the species. Details of the youngster's song match he hears both Song Sparrow and White-crowned Sparrow songs, he'll band note ending at about 1.5 seconds),
and other notes. When a young male is
those of the song with which he was tutored, detail for detail. learn the White-crowned Sparrow songs. If he's housed with a singing
taken from a nest in the wild at 8 or 9
Most songbirds seem to have what is called a "sensitive period" Song Sparrow, however, his physical and vocal interactions with that days of age and raised in the laboratory
for song learning. It is during this relatively brief time that birds are bird may override his inborn tendencies, and a young White-crowned without hearing any further songs of his
best equipped to memorize the details of a tutor song. For the White- Sparrow can then, under some circumstances, learn to sing Song Spar- own species (bottom sonagram), he de-
velops an atypical song that is much less
crowned Sparrow, model songs from a loudspeaker in the laboratory row songs (Baptista 1 996).
complex than normal songs.
seem to have the greatest impact from day 15 to about day 50. Songs How songbirds learn to sing is worth considering in some detail
heard after day 50 seem to be far more difficult to learn. If the young (Kroodsma 1993). Nestlings can hear within a few days of hatching,
and they begin their practice singing shortly after leaving the nest, at
Figure 7-24. Musician Wren: The small,
about three weeks of age. The earliest "subsong" is barely perceptible,
brownish-orange Musician Wren of the
Amazonian rain forests is far more often even to someone listening only a wing's length away. Among birds
heard than seen. It more than makes up hand-raised in the laboratory, this early practice typically occurs in
for its small size with its long, loud, com- a fledgling that recently has been fed. He (and in some species, she)
plex, melodic song, considered by many perches, resting comfortably, even appearing to doze with eyes closed
people to be among the most beautiful
of all bird songs—perhaps because it
and head tilting to one side. All the bird's systems appear to be com-
resembles our notion of music quite pletely at rest, but soft whispers, accompanied by barely perceptible
closely. Photo by J. Dunning/VIREO. throat movements, reveal that inwardly the future maestro has begun
his work. If this resting state is disturbed, as by a sibling or curious
human, the youngster breaks abruptly from his apparent slumber and
becomes fully alert, producing no more evidence of practice.

Cornell Laboratorti of OrnitholoBq Handbook of Bird Biolo9i

7.28 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.29
This song practice gradually becomes louder, more persistent, The young Bewick's Wren in the garden just outside my daugh-
and more structured, and the sounds begin to resemble the adult song. ter's window was also practicing. H is task was to master a vocabulary
In juvenile males of the nonmigratory Bewick's Wrens that I studied in of about 16 different songs from his male neighbors. His eventual goal
the Willamette Valley of Oregon, this process was especially evident was to take one of these 16 songs and sing it 20 to 50 times in suc-
(Fig. 7 26). A typical young male left his parents' territory by four to
-
cession, giving each rendition crisply, confidently, and consistently,
five weeks of age, and a few weeks later was already defending the ter- with no mistakes or wavering. Then he would introduce another of
ritory he would hold for the rest of his life. On that territory, the quality the 16 songs, and eventually another, until slowly, methodically, over
of the practice singing gradually improved, until songs matched, detail several hours, he had worked his way through his entire song reper-
for detail, the songs of adult neighbors. Although the young male was toire. If each song were paraphrased into English, one might imagine
capable of learning his father's songs during the first four or five weeks an adult Bewick's Wren proclaiming from the treetops a series of 30
when he was cared for by his parents, he rejected his father's songs in "Good morning's," then 30 "How are you's?," 30 "Keep out's," 30
favor of songs from his new home. "Be my Valentine's," and so on, in a nice orderly progression, with
The practice singing (subsong) of a young songbird, such as the pauses of five or six seconds between each two-second song. (We're
Bewick's Wren, is remarkably similar to the practice speaking (bab- paraphrasing in this way merely to show that the songs are different;
bling) through which humans progress as toddlers. Consider my to the birds, the songs may all carry the same meaning even though
daughter's babbling when she was about a year and a half old. I have they sound different.)
numerous recordings of her early speech attempts, but my favorite is But the practicing youngster gets it all wrong. Like my daughter,
when she was sitting in her highchair, looking out the large picture he takes bits of sounds out of context and strings them together in a con-
window to the garden, and perhaps to the Oregon Cascades beyond. tinuous, nonsensical sequence, such as "BeGoodYouAreKeepIngOut-
With no one else in the room, she babbled and babbled. The sounds of OrnTimeMy . . ." The sounds lack the crispness and confidence of an
one segment (Track 24) were "bow wow . . . wow wow . . . bow wow adult's, and no two attempts at the same sound are alike. Eventually
. . . wee wee wee . . . hi daddy ba ma wow wow wow . . . daddy! da this young wren will be as competent as his father, just as each young
daddy bow wow bow wow . . . dere's da ditty . . . hey ditty . . . hey h uman eventually masters the fine art of his or her spoken language
daddy . . . nyeh . . . no . . . down." Clearly evident in this practice are (Fig. 7-27 & Track 25).
simple syllables and entire words that she will eventually incorporate
into her adult speech. The "bow-wow" refers to a dog, and "ditty" to
Bewick's Wren
kitty. "Daddy" is unmistakable, as are "no" and "down." The "wee wee
wee" shows good recall of the little piggy's homeward cry. Importantly, 8 Adult Song

Frequency (kilohertz)
no dog or kitty was in the room, nor was Dad, who was hiding around
the corner with his microphone. She took all of these elements of the

17
6-
vocabulary out of their appropriate context and strung them together
in what was, by adult standards, a nonsensical practice session.
4-

Figure 7-26. Bewick's Wren: The Be- 2

wick's Wren, an active, noisy resident of 00 0 5. 1:0 1'5 2.0 2.5 3:0 3.5 4.0
dry, scrubby areas and most common in
8 Subsong
the western United States and Mexico, is

Frequency (kilohertz)
well known for its variable song. Males
have a repertoire of 9 to 22 different song

it
6
types, but repeat each one many times
before switching to another. Photo by J.
HoffmanNIREO. 4

2
0.0 0'5 05
- 2:0 2:5 3:0 3'5 4:0
Seconds

Figure 7-27. Sonagrams of Adult Song and Subsong of Bewick's Wren (Track 25, 4th Adult Song, 1st Subsong Phrase): The adult
song of the Bewick's Wren (top sonagram) is a complex assortment of notes, trills, and buzzes, similar to that of a Song Sparrow. In
contrast the subsong (practice song) of young Bewick's Wrens (bottom sonagram) is rambly and long, with less distinct notes, and
is different each time the bird sings. Note that the young bird's sounds between 1.0 and 2.0 seconds are similar to those produced
by the adult between 7.5 and 3.0 seconds, but are in reverse order.

Cornell Laboratorq of Ornitholo94 Handbook of Bird Biologi

 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.31
7.30
Black-billed
Memorization, recall, and a good ear all are crucial in this learn-
Scythebill
ing process, for both songbirds and humans. The young songbird first
memorizes a song, which it can do as early as 15 to 20 days of age.
Days, months, or even a year later, when the youngster begins his prac-
tice singing, he recalls that memory and tries repeatedly to produce
a copy of what he remembers. Successive corrections to the practice
sounds eventually result in a perfect copy of the remembered song.
Hearing is thus crucial to both the initial memorization and the later
production of that sound.
Chances are you'll be able to hear young birds practicing if you
listen carefully during late summer and early fall. Practice songs are
less structured and more rambling than the adult male song. Bewick's
Wrens and Song Sparrows are good subjects, but young of many spe-
cies practice during the late summer. Scissor-tailed
Flycatcher

Vocal Development in NonsonBbirds

We can better appreciate song development in songbirds by un-
derstanding how sounds develop in other bird groups. Consider the
close relatives of the songbirds, the suboscines (Kroodsma 1 988). The
songbirds (also called oscines) and suboscines are the two suborders
Banded
of the order Passeriformes; they are "sister groups," each other's closest Pitta
Guianan
living relatives (see Fig. 7-22). Just a handful of suboscines live in the
Cock-of-the-rock
Old World, but about a thousand species occur in the New World, in-
cluding antbirds, antwrens, woodcreepers, cotingas, and flycatchers.
Of all suboscines, only a few flycatchers reach North America (Fig.
7-28).
Song development by the Alder and Willow flycatchers clear-
ly illustrates the striking difference in song development between
suboscines and songbirds. Current field guides describe these two
flycatchers as essentially identical in appearance, and only in 1 973
did the American Ornithologists' Union officially recognize the then Long-tailed
"Trai I l's Flycatcher" as really consisting of two species (see Fig. 2-15). Manakin
The only reliable way to identify these two species is by their voices.
The Alder Flycatcher sings a fee-BEE-o (also described as free-BEE-er)
song, and the Willow Flycatcher, a FITZ-bew song; never does the
same bird sing both (Track 26).
I n an experiment, you ngAlder and Willow flycatchers were taken
from their nests at about 10 days of age. The young Wi I low Flycatchers
were then trained over loudspeakers with Alder Flycatcher songs, and
Alder Flycatchers were trained with Willow Flycatcher songs, in an
attempt to confuse the birds in their singing. Although the young birds
Figure 7-28. Suboscine Diversity: The suboscines are one of that, like nuthatches, search bark for insects; antbirds, such as
from fee-BEE-o nests heard FITZ-bew and the young FITZ-bew birds the two suborders of the order Passeriformes. A few species the Ocellated Antbird, which follow army ant swarms to prey
heard fee-BEE-o, the young birds were not confused. Remarkably, and of suboscines live in the Old World, including the secretive on the insects and other small animals flushed up by the ants'
so unlike songbirds, these young flycatchers developed perfectly nor- pittas, long-legged ground-dwellers in tropical areas, and the passing (see Ch. 9, Sidebar 3: Ant Followers); cotingas, such
mal songs of their own species. The experience with the wrong songs New Zealand wrens (for example, the Rifleman), which may as the Guianan Cock-of-the-rock, large, stocky, fruit-eating
be the most ancient group of passerines. Most suboscines, birds, many of whom have bizarre courtship displays; and the
caused no problems (Kroodsma 1996a).
however, live in the Neotropics, with only one group, the brightly colored manakins (see Fig. 6-42), such as the Long-
How Alder Flycatchers develop their songs is especially fasci- flycatchers, containing species that reach as far north as the tailed Manakin, small, chunky, fruit-eaters, also with unusual
nating. This process was first discovered in the field and then con- United States. Neotropical groups include the woodcreepers, courtship behaviors.
firmed in the laboratory. During the first few days out of the nest, the such as the Black-billed Scythebill, woodpecker-like birds

Cornell Laboratory of Ornithology Handbook of Bird Biology

7.32 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.33
young flycatchers usually remain near each other in a small family
flock. When the fledgling brothers and sisters get separated, they use
a particular vocalization as a contact call, as if to keep tabs on each
other and perhaps to announce their location to their parents, who are
still feeding them. This call is an unmistakable, although scratchy and
uncertain, rendition of what will eventually become the adult song,
the fee-BEE-o. Thus, as soon as young Alder Flycatchers leave the nest, Figure 7-29. Anna's Hummingbird: Al-
though most nonpasserines do not ap-
they are already uttering what will clearly become their adult song.
pear to learn their songs, hummingbirds
In the laboratory, the process is the same: a young bird that has just are one exception, as was demonstrated
left the nest gives this call repeatedly when separated from its siblings. by raising youngAnna's Hummingbirds,
This call, clearly the precursor of the adult song for these suboscines, a common species along the Pacific
coast of the United States, in the labo-
is already being used at day 14, the age at which young songbirds are
ratory.
just beginning to memorize the sounds they will later produce.
Follow-up experiments with the Eastern Phoebe, another fly-
catcher species, reveal that no matter what environment they are
raised in, young flycatchers seem to know the proper songs to sing.
These three species are only 0.3 percent of the 1,000 or so suboscines,
so generalizing to the whole suborder would be unwise. Nevertheless,
some clues from other species, such as the contact calls used by young
birds and the lack of geographic variation (see Variation in Space and Vocal development in other groups is more like that of subos-
Time, later in this chapter), suggest that the song development of most cines and seems to involve little, if any, imitation. Doves and pigeons,
suboscines may resemble that of these flycatchers. for example, develop normal vocalizations without learning them
One additional piece of evidence shows just how different the from adults; hybrids between dove species produce vocalizations
flycatchers are from the songbirds. Like humans, songbirds must be intermediate to those of their parents, again suggesting that the vo-
able to hear themselves vocalize during the developmental process. calizations are coded in the genes and not learned by imitating other
Deaf humans cannot learn to speak properly, and deaf songbirds can- adults. Roosters develop normal crowing calls even if they cannot hear
not learn to sing properly. Their learning is impaired because, to com- themselves, again suggesting that learning is unnecessary. Scientists
pare their practice sounds to the remembered model sounds, both the have studied vocal development in few other groups, but believe that
young human and the young songbird must hear themselves vocalize. for most groups, no striking evidence of vocal learning will be found.
Flycatchers, however, are different. Eastern Phoebes develop normal The logical question at this point is "Why?" Why do the songbirds
song even if they can't hear themselves practice. Brain differences learn, whereas most of their close relatives, the subosci nes, appear not
between songbirds and suboscines tend to confirm this relationship to? Do the songbirds have some special advantages that the subos-
between learning and hearing, and to further reinforce the differences ci nes lack? Although we have a few hints about some subtle aspects of
between the two groups (see Control of Song, later in this chapter). song development (see Songbird Diversity, below, on styles of learning
Vocal development in other orders of birds, collectively called among wrens), we simply do not know the answer. Presumably the
the "nonpasserines" (i.e., "not the order Passeriformes") is less well ancestor of songbirds acquired the ability to learn, so learning evolved
studied, but what we do know can be compared to the development only once in the songbird lineage; in the suboscine lineage, however,
of songbirds and suboscines. In only two other orders, the parrots learning occurs among bellbirds, but apparently not among most other
(Psittaciformes) and the hummingbirds (Apodiformes), does extensive species, such as flycatchers. But what advantage might a songbird such
learning seem to occur. Parrots, of course, are renowned for their abil- as a wren have over a suboscine such as a flycatcher? What does learn-
ity to imitate human speech in captivity (Pepperberg 1 990; see Ch. 6, ing accomplish? Clearly each of the roughly 400 flycatcher species in
Sidebar 1: Bird Brains), although we know little about how that ability the world is highly successful at perpetuating itself, as is each of the
to imitate is used in the wild. That some hummingbird species learn roughly 75 species of wrens. Once learning evolved, wrens, like many
was demonstrated by raising young Anna's Hummingbirds (Fig. 7 29) - other songbirds, developed large song repertoires and local dialects,
in the laboratory (Baptista and Schuchmann 1990). Furthermore, the but wrens don't appear to be any more successful, in any sense of the
existence of hummingbird dialects, in which neighboring groups of word, than flycatchers. We can't say that learning is any better than
birds sing different songs, also shows that some species, such as the not learning, even though, as one ranking of the world's best songsters
tropical Little Hermit, learn songs. (For more on dialects, see Variation shows, we especially appreciate the music of the songbirds (Harts-
in Space and Time, later in this chapter.) horne 1973). We are left with a big mystery on why songbirds are the

Cornell Laboratorc1 of Ornithologq Handbook of Bird Biologq

7.34 Donald E. Kroodsma Chapter 7—Vocal Behavior 7.35
way they are—they're special singers (see Fig. 7-50). Work in lower Mich- Indigo Bunting Songs
because they learn, but we don't know igan has shown that "neighborhoods"
a. Territory Holder
why they evolved the ability to learn in of different songs occur side by side, 9-

Frequency (kilohertz)
the first place. and that young males and females typ- 8-

ically breed in neighborhoods where 7-

they were not born. When a young 6-

Songbird Diversitq 5-
male settles on a territory during his
With well over 4,000 species of 4
first breeding attempt, he usually has
songbirds, trying to generalize about 3
an odd song, one that is unique to him
how "the songbird" develops its song is 2
and that typically bears little resem-
dangerous. Our only valid conclusion 0
blance to his father's song. Over time, b. Neighbor
may be that some evidence of learning s-
however, he usually changes his song

Frequency (kilohertz)
has been found in all songbirds studied 8-
to match the song details of an imme-
to date. But howdifferent species learn 7-
diate territorial neighbor, thereby per-.
varies considerably. 6-
petuating the local neighborhood of 5-
4
Natural selection has presumably
songs (Fig. 7 31 & Track 27). In some
-
4-
molded the developmental process in
way, a young male must gain social 3-
each species so that individuals de-
advantages by matching the songs 2-
velop the best sounds for managing the
of his immediate neighbors. A better o 3
behavior of other birds of the same spe-
understanding of the song's function, q c. Stranger
cies. At one extreme are species such
such as exactly why the male sings and

Frequency (kilohertz)
8
as White-crowned Sparrows, in which
who listens and is influenced by it, may 7
young birds must be tutored with adult
someday help us to understand why 6
songs and learn perfect detai Is of songs.
young males imitate their neighbors in 5
At the other extreme are species such
this way. 4
as the Gray Catbird (Kroodsma 1996a)
Young Song Sparrows develop
(Fig. 7 30). A young catbird in the
-
their songs in much the same fashion, 2
laboratory does not seem to need ex- 2
but the process seems more complex
posure to normal catbird song (at least Seconds
because each sparrow has a repertoire
Figure 7-30. Gray Catbird: The Gray not after the age of 8 to 10 days, when the young were taken from
Catbird seems to require less learning
of 8 to 10 songs (Beecher 1996) (Fig. 7 32). In a Seattle, Washington Figure 7-31. Sonagrams of Indigo Bun-
-

the nest in this study). Apparently normal repertoires of hundreds of ting Song from Neighbors and Strang-
to acquire its song than most songbirds, population, young males don't settle down immediately, but rather
typical catbird sounds develop in birds isolated from adult songs at er: Songs of Indigo Buntings consist of
since young taken from nests in the wild seem to range over the territories of four or five adults late during their
this early age. Catbirds are highly atypical in this regard, because the a few notes or syllables, each generally
at 8 to 10 days and kept in isolation hatching year.The young males learn the songs from adults in this small repeated two or three times. Although
develop normal catbird songs. Like its young of most songbird species develop abnormal songs if they are
neighborhood, and seem to follow two primary rules in the learning each individual bird sings only one song
close relatives, the mockingbirds and isolated in this way. Nevertheless, studies in both the laboratory and
process. First, they learn a complete song from a particular bird and type, songs vary from bird to bird in both
thrashers, this mimic is able to imitate
nature show that catbirds can imitate both their own and other spe- length and content. Furthermore, birds
the songs of other birds, so some degree don't cobble together songs by taking pieces from different songs or
of song learning must occur. Photo by
cies, so vocal learning does occur in catbirds. It's just that imitating often sing shortened versions of their
different males. Second, they learn the most common songs, so that if one song type, especially during terri-
Lang Elliott. other adult catbirds doesn't dominate the song-development process
all five adults in the neighborhood share a song, the youngster is espe- torial encounters. Young birds change
as it does in so many other species.
cially likely to learn it; songs unique to a single adult are far less likely their songs to resemble those of their
Why the young sparrow imitates his neighbors so perfectly but neighbors, creating pockets of birds with
to be learned. Over the winter, the young male sparrow either takes
the young catbird "improvises" his unique repertoire are mysteries. similar songs. a. Territory Holder (Track
over the territory of an adult who has died or simply usurps an area for
Before we can understand these differences among species, we need 27, 3rd Song): Relatively short song of
himself in this neighborhood. one territorial bird, with three different
to know more about the daily life of the sparrow and the catbird,
These rules for learning maximizethe chance thata male wi II sing syllables that are repeated. b. Neighbor
more about whom each individual expects to influence with its vo-
songs of surviving males in the neighborhood where he will breed. Like (Track 27, 2nd Neighbor Song): Song
calizations, and how those birds are "persuaded." We must follow of a bird who holds a territory adjacent
the Bewick's Wren and the Indigo Bunting, neighboring males then
them in nature, from hatching to adulthood. to the bird in (a). Note how similar the
share similar songs. Sharing the same song repertoires must somehow two songs are. c. Stranger (Track 27, 1st
In most studies of this sort, like that of the Bewick's Wren dis-
enhance the birds' abilities to interact with and influence other birds Stranger Song): Song of a bird who is a
cussed earlier, the young birds have been found to be especially good
in their social environment. Somehow, a bird who imitates the right stranger to the birds in (a) and (b). Note
at learning the songs of other adults in their immediate neighbor- how different the song is from that of the
songs must increase his ability to guard or acquire resources, such as
hood. Consider yearling Indigo Buntings, for example (Payne 1996) other two birds.

Cornell Laboratorq of Ornithologg Handbook of Bird Biolom

7.36 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.37
a territory or a mate, but the exact process by which the occurs throughout North, Central, and South America,
bird gains this advantage is unknown. in a variety of habitats. In some places, the Sedge Wren
One final example illustrates the same phe- I ives in communities that are stable throughout the year,
nomenon of neighbors sharing signals and also provides like the Marsh Wren of western North America. In those
an instructive counterexample. Marsh Wrens in western communities, one would therefore predict that Sedge
North America learn each other's songs, so they have Wrens should behave more like the Marsh Wrens of
nearly identical repertoires (see Fig. 7-51). They often western North America than like the Sedge Wrens of
engage in a startling display of what is called matched North America. A study in Brasilia National Park con-
countersinging (for additional discussion, see Song Rep- firmed just that. There, male Sedge Wrens imitate their
ertoires, later in this chapter, and Verner 1976). Males neighbors and countersing in the same kinds of intricate
have large repertoires of over one hundred song types, matching displays found among western Marsh Wrens.
and they often hurl identical songs back and forth. One Thus, the stability of the habitat, year-round residency,
male sings A, and his neighbor counters with A; B from and familiarity with neighbors seem to influence how
one, B from the neighbor; C, C; D, D; and so on. The songs develop and, consequently, how the songs are
songs are sufficiently different that a human listener can used in interactions among birds (Kroodsma 1996a).
readily tell when the males are matching each other in The focus in this section has been on songbirds
this fashion (Track 28). Many western Marsh Wren pop- and song, because that's where researchers have done
ulations are resident year round, and males thus come the most work. But we have much to learn about songbirds, and even Figure 7-33. Sedge Wren: The tiny Sedge
to know each other. They imitate each other's songs, as more about other birds and about vocalizations other than songs. Wren breeds in wet, grassy meadows.
shown in laboratory studies, and males in a marsh in- Unlike its close relative, the Marsh
Among "nonsong" vocalizations of songbirds, a variety of develop-
Wren, the Sedge Wren seems to invent
teract in intricate ways with their shared vocabularies. mental patterns occur. Both the gargle and the chick-a-dee calls of most of its 100 or more song types,
Figure 7-32. Song Sparrow: In late sum- With a premium on neighbors sharing nearly identical vocal reper- the Black-capped Chickadee are learned, for example. The gargle rather than learning them by copying
mer and fall of their hatching year, the toires, Marsh Wrens are thus I i ke the Bewick's Wren, the Song Sparrow, varies among populations, and birds undoubtedly learn the gargle of the songs of other Sedge Wrens. Photo
young Song Sparrows studied in Seattle, by Lang Elliott.
and the Indigo Bunting, although the number of signals involved and the population in which they settle. Also, the chick-a-dee call differs
Washington by Beecher (1996) learned
some of their 8 to 10 song types from oth-
the complexity of the vocal exchanges seem to have escalated. among flocks, and when a chickadee joins a winter flock, its chick-
er males in the area in which they would You can easily hear this kind of matched countersinging among a-dee call converges on the call structure of its new flock (Nowicki
eventual ly settle. Young were more likely Marsh Wrens in any marsh in western North America—my favorite is 1989). The other calls of chickadees are less well studied.
to learn songs shared among several ter- Coyote Hills Regional Park southeast of San Francisco. In the East, the A variety of other calls are also learned among songbirds. Some
ritorial birds than less common songs.
Tufted Titmouse and the Northern Cardinal are good subjects. Listen calls of American Goldfinches and related species are learned; the
Photo by Marie Read.
carefully and you may be able to hear how males within a species calls of members of a pair may converge on one another, such that
interact with each other, hurling the same song form back and forth. pairs within a larger flock can be identified based on call structure. In
In contrast, the Sedge Wren of North America seems to do little Europe, the "rain call" of the Chaffinch is also learned, so local dialects
of this kind of intricate countersinging (Kroodsma, Liu, et al. 1999) of this call can be found (see Song Dialects, later in this chapter).
(Fig. 7 33). In the laboratory, Sedge Wrens do not imitate songs the
- Learning seems to play no role in the development of many other
way Marsh Wrens do. They learn a little, but mostly they seem to songbird vocalizations. Calls of the Eastern and Western meadow-
"improvise," inventing 100 or more good "Sedge Wren" songs using larks, for example, seem not to be learned. Where these two species
some kind of inborn song generator.Thus, no two males share identical meet in the Great Plains, they can learn each others' songs, but the
repertoires, so when they sing to one another, they cannot match each call notes enable us (and probably the birds) to identify the birds to
other. This kind of development is apparently ideal for the lifestyle of the appropriate species (Lanyon 1969). Call notes are discussed in
Sedge Wrens in North America. They are somewhat nomadic birds, more detail in Sidebar 5: "Call Notes" and Their Functions, near the
unpredictable in their breeding locations within and between seasons, end of this chapter.
and they seem to go where the habitat is most suitable. As a result,
neighboring males are relative strangers to one another, and they com-
municate not with identical song types, butwith generalized songs that Control of Song
declare "Sedge Wren" without getting into matching details. ■ Birds have several calls and sometimes hundreds or even thou-
These examples suggestthat carefu I imitation of neighbors is espe- sands of different songs. Some of these are learned, but others are not.
cially important in stable neighborhoods, where birds getto know each How does the brain control these vocalizations? Where in the brain is
other and can interact with shared identical songs. Nature provides an knowledge of these signals stored? How does the syrinx, or voice box,
exciting test of this proposed relationship between learning, improvis- produce the signals? What seasonal factors influence the endocrine
ing, and degree of familiarity with one's neighbors. The Sedge Wren system, and how does the endocrine system in turn control song?
Cornell Laboratorg of Omithologg Handbook of Bird Biolopq
7.38 Donald E. Kroodsma Chapter 7—Vocal Behavior 7.39
How the brain controls song in songbirds is an exciting research Wood Thrush Figure 7-35. Sonagram of Wood Thrush
Song Showing Contribution from Each
area (Brenowitz and Kroodsma 1996). This brain control system was Simultaneous Output Syrinx #1
Half of the Syrinx (Track 29, 4th Normal
discovered somewhat by serendipity, during a study of song learning.
aLLL
8- from Two Syrinxes Song, 3rd Song at One-Half Speed): The
Researchers had known for some time that the voice box consists of song of the Wood Thrush allows the

Frequency (kilohertz)
7-
two independent units, located where the trachea splits to form the Syrinx #2 contributions from each half of the
6-
syrinx to be distinguished fairly easily.
two bronchi. On top of each bronchus is a voice box (Fig. 7-34). One
5- You can see from the sonagram that the
nerve travels down the left side of the neck to innervate the left voice middle and final trills are made up of
4-
box, another down the right side of the neck to the right voice box. Syrinx #1 components that are generated simulta-
This "dual innervation" gives birds independent control of each voice 3- neously—these appear to be produced
box. In several species that produce two sounds at once, blocking the
signals from one nerve eliminates one of the two sounds. Some bird
2-

1-
Pr. rtr tr Syrinx #2 from different halves of the syrinx. Note
that the designations "Syrinx #1" and
"Syrinx #2" are purely arbitrary, serving
songs clearly demonstrate this dual innervation and control of the 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 only to differentiate the sounds from the
two voice boxes. Wood Thrush songs, for example, often contain two Seconds two halves. Which half of the syrinx pro-
sounds produced simultaneously; one voice box controls the higher- duces which sounds is not known.
pitched sound and the other, the lower-pitched sound. In essence, the
Tracing these nerves back into the brain led to the discovery of
Wood Thrush can sing a duet with itself (Fig. 7 35 & Track 29).
-

a series of cell groups involved in both hearing and producing songs.

All cell groups were interconnected in the way one would expect if a
young bird had to compare its own songs with a remembered version
before trying again (Fig. 7 36).The overall size of these control centers
-

Figure 7-34. The Syrinx: The bird's voice in the brain is proportional to the size of the bird's song repertoire. In
box, the syrinx, is really a pair of cham- Zebra Finches, females do not sing, and the song control centers of the
bers located along the trachea, where it Trachea female are much smaller than those of the male. In species in which
splits to form the two bronchi heading
to the lungs. The chamber of the syrinx,
females do sing, these control centers are correspondingly larger.
like the rest of the trachea and bronchi, Within species, too, the more songs a male has, the larger his song
Syrinx (Voice Box)
is kept open by rings of cartilage. The control centers are likely to be. Thus, male Island Canaries or Marsh
muscles of the syrinx control the details Wrens with larger repertoires are likely to have larger song control
of song production (see Fig. 4-77). The
more complex syringeal musculature of
songbirds allows them to produce more Important
Hearing Region
intricate songs than other taxonomic
groups of birds (see Ch. 4, Sidebar 2, Vocal
Fig. A). Center
Muscles of
Syrinx Brain

Lungs
Figure 7-36. Song Control Centers
in Avian Brain (Section through a
Songbird's Brain as Seen from the Side):
Song development and production are
controlled by an elaborate network of
nerve cell groups and neural pathways
in the avian brain. The system's inter-
connectedness is essential because, to
Nerve to Spinal
Muscles Cord learn songs correctly, young male song-
birds usually must hear and remember
of Syrinx /
7 the songs of adult male conspecifics,
then later compare their own practiced
Cell Groups Involved in Song Control songs with the remembered versions
before further refining their efforts. Note
Song Production Pathway that this is a highly simplified diagram
Cartilaginous Rings
of Syrinx of the system. For more information, see
Song Learning and Recognition Pathway
Brenowitz and Kroodsma (1996) and
Pathway Linking Hearing and Song Production Systems DeVoogd and Lauay (2001).

Cornell Laboratorq of Ornitholo8q Handbook of Bird Biologq

7.40 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.41

bird groups (Gahr et al. 1993)? The brains of those subosci nes that do
Day Length Gonad Size Hormone Song Control Singing
Increases 4 Increases 4 Production
Increases
Centers in Brain
Stimulated
Rate
Increases
not learn their songs differ remarkably from those of songbirds, and
searches for a comparable control system among the subosci ne groups
have failed. To be sure, some neural network in the brain controls
LATE WINTER EARLY SPRING LATE SPRING ■■••• ♦ vocalizations, but nothing like the one in the songbird brain has been
found. Some kinds of control centers have been found, however, in
Figure 7-37. Pathway by which Day centers than males with smaller repertoires. Species with huge song parrots and a hummingbird, the two other bird groups in which vocal
Length Affects Singing Rate: In late repertoires, such as the Brown Thrasher, also have enormous song learning has been documented. The control centers differ in the three
winter, the increasing day length stimu-
control centers. groups that learn, however, suggesting that brain structure and vocal
lates the gonads to grow larger, which
in turn increases the output of gonadal Also intriguing is how the characteristics of these song control learning arose independently in these three orders.
hormones. One effect of the gonadal centers change with the seasons (Nottebohm 1987). They appear to When I think of how birds sing, I like to recall that Winter Wren
hormones is to stimulate the song con- shrink during the nonbreeding season, when hormone levels are low, song we heard earlier. Study the sonagram and listen to the slowed-
trol centers in the brain, which causes and enlarge again during the breeding season, when hormone levels down tape once more (see Fig. 7-11 & Track 8). Each song consists
neural changes that increase the amount
of singing.
are high. Careful work has also shown that new neurons are being born of a hundred or more brief sounds, each pronounced with precision
in some of these control centers—an activity not previously thought to in both time and frequency, and all placed in a consistent sequence,
occur in the adult nervous system of any vertebrate! Th is neural control so that the wren produces a remarkably complex song with unfailing
network is a stimulating model for understanding how brains control accuracy. Somehow the young bird memorizes that song from other
behavior, and the songbirds provide an exciting diversity of species in adults, storing all the bits of information somewhere in his tiny brain.
which to explore how nature has shaped control in different ecological That he recalls the details of his memory and sends the correct neural
circumstances. messages to the voice boxes, and that those tiny muscles contract in
Why these brains change with the seasons is somewhat contro- such a controlled sequence to produce such eloquence, I find simply
versial. The first ideas came from studying Island Canaries and Zebra astounding. Western Winter Wren males learn not one but dozens
Finches. The canary's brain changes with the seasons and the canary of these complex songs, and western Marsh Wrens learn up to two
learns new songs each year; the finch brain does not change and the hundred. My mind simply boggles at the thought. For those who know
finch does not learn new songs each year. Were the brain changes birds, the phrase "bird brain" takes on new meaning!
necessary for the new learning? That idea was quickly refuted when
researchers discovered that other species, such as the Eastern Towhee,
seasonally change their brains but not their songs. Perhaps, then, the Variation in Space and Time
brain changes so that birds can learn to recognize, though perhaps not
sing, the songs of new neighbors each year. Maybe—and maybe not.
■ What is especially fascinating about signal variation is the great va-
riety of patterns (Kroodsma 1986). Questions abound! Why don't male
As scientists study the brains and songs of more species we may start
White-throated Sparrows match the songs of a local neighborhood
to see some patterns and better understand why these brains work the
the way males of the closely related White-crowned Sparrows do?
way they do.
Why does the hey-sweetie of the Black-capped Chickadee occur from
The endocrine system, too, is intricately involved in bird song.
Maine to British Columbia when songs of other species are so much
Many of the song control centers in the songbird brain contain re-
more local? In short, why do species differ in how their signals vary
ceptors for gonadal hormones, so as day length influences the size and
from one population to the next (over space) and in how their signals
hormonal output of the gonads, it indirectly affects the brain. Length-
vary from one generation to the next (through time)?The birds use each
ening days cause the production of more hormones, which activate
signal in some way to interact with and influence other individuals,
cells in the song control centers and stimulate neural changes, which in
and the patterns of variation must be well adapted for communication.
turn cause singing (Fig. 7 37). The combined effect of all these factors
-

The goals in studying this variation are first, to document the patterns
first begins to surface in northern climates on those occasional warm
of variation, and second, to understand the relationship between the
sunny days in January. It is then that, at least in the Midwest and north-
patterns and their functions. In this section, we focus first on how
eastern United States, we hear songs from Northern Cardinals, Tufted
species differ and how we can use these differences to identify each
Titmice, Black-capped Chickadees, and other residents, all of whom
species. Then we study some of the variation that is so important to
are undergoing a physiological transformation, from their gonads up
the birds but is usually less appreciated by humans. We'll learn how
to their brains.
signals vary from bird to bird, population to population, and generation
The song control centers of songbirds are clearly involved in
to generation. Throughout, our goal is to understand how sounds vary
the learning and production of songs, and these neural centers have
and ultimately whythey vary the way they do, although answers to the
been identified in all major songbird groups. But what about other
"why" are few, so far.

Cornell Laboratorq of Ornitholo8q Handbook of Bird Bioiogq

 7.42 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.43

Species Differences
As we listen to the great diversity of bird sounds and study field
guides and associated sound guides, we appreciate that each species
makes different sounds. We can identify the Chipping Sparrow's dry
trill, and the trained, professional ear can (usually!) distinguish the
a
Chipping Sparrow's trill from the similar songs of the Pine Warbler,
Dark-eyed Junco, and Swamp Sparrow. During its normal daily ac-
tivities, each bird typically interacts only with other members of its own
species, because they're the ones it must compete or cooperate with
to achieve success. Evolution has thus insured that these interacting
birds share vocal signals, either by inheritance, for sounds encoded in
genes, or by vocal traditions, for sounds transmitted by learning.
Humans use these species differences in a variety of ways. The
sounds are indispensable in survey work, for example. In many hab- Male 2 Male 3
itats, especially in dense tropical forests, few birds are seen but many
are heard. It is thus the birds' voices that enable us to determine the
relative abundance of different species in different habitats. Or con- b
sider the work of Bill Evans at the Cornell Laboratory of Ornithology
(Sidebar 2: Listen Up!). Most small birds migrate at night, when they
are invisible, at least to our eyes. But many of them call, and the calls
they use in flight are distinctive enough that sophisticated computer-
recognition software can automatically identify many night-recorded
sounds to the correct species. By recording sounds raining from the
sky, the abundance of some Neotropical migrants can be determined,
day after day, year after year, and these kinds of data are extremely
valuable in our conservation efforts. Song of Male 1 Male 2

Individual Variation
We humans can easily identify each other by our distinctive voic-
es, and research clearly shows that birds can recognize each other
by voice, too (Stoddard 1996). This ability to recognize individuals
was first demonstrated with the songs of the Ovenbird (Weeden and
Falls 1959). Each male has his own unique rendition of the tea CHER -

song. Differences in the songs of individuals can be seen clearly in

7 sonagrams, but, more importantly, some ingenious field playback ex-
periments have demonstrated that the birds use those differences to
identify each other (Fig. 7-38). Thus, males defending territories get
Song of Male 3
to know their neighbors and the songs they sing. A neighbor singing
from the appropriate location may be acknowledged with a few songs
in return, but if the neighbor sings from the "wrong" location, or if a
strange bird delivers an unfamiliar song anywhere in the area, the terri-
torial male responds more aggressively. Clearly Ovenbirds can identify
each other by their distinctive songs, and they take advantage of those Figure 7-38. Neighbor Recognition in Ovenbirds: Many territorial birds learn to recognize the songs of their neighbors—a fact
differences to help maintain their territories. established by numerous experiments over the years. A typical experiment might proceed as outlined here: a. Male Ovenbirds
1, 2, and 3 occupy territories in a line, as if along a stream; males 1 and 2, and males 2 and 3 have shared borders. b. If male 1 is
This individual recognition is especially easy in Ovenbirds,
removed, and his song is played from the common boundary between 1 and 2, male 2 responds little, if at all. Male 2 has come
because all males have a single song that is unique. Just as a unique to know that particular song from that location. c. If, however, the song of male 3 is played on the boundary between males 1 and
fingerprint identifies each human, a song identifies each Ovenbird. 2, male 2 responds very aggressively. The wrong song coming from that boundary means that the status quo has been disturbed,
and boundaries need to be reestablished. Thus the experiment demonstrates that male 2 can use the differences in the songs of
(Continued on p. 7.47) males 1 and 3 to know who is singing from what location.

Cornell Laboratory of OrnitholoA Handbook of Bird BioloBq

7.44 Donald E. Kroodsma Chapter 7—Vocal Behavior 7.45
On a good night the myriad voices
Sidebar 2: LISTEN UP! flow by all night long in ever-varying
a. American Redstart b. Veery
Bill Evans Track 31, 1st Call Track 32, 1st and 2nd Calls composition: a wonderful intermin-
glingof soft phews, quees, and wheers
8 of migrant thrushes and Rose-breast-

I
One mid-September night my Dad North America, thousands of calls birds, migrate at night, vocalizing
pointed out the calls of night mi- may be heard by listeners on the while they fly. Warbler and sparrow ed Grosbeaks; pinks of Bobolinks;
grating birds—faint peeps and tseeps ground (Fig. A). prehistoric-sounding squawks from
calls are typically short, high-pitched
6 herons and bitterns; lisping tseeps
passing high above our backyard in In the spring of 1985, I heard an notes, not unlike a single field cricket
southern Minnesota. I was just 15, astounding flight whi le camping on a chirp (Track 30) (Fig. Ba & Track 31). and tzeeps of sparrows and warblers;
and 10 more years would pass be- bluff along the St. Croix river in east- a plethora of strident shorebird calls;
Thrush calls are beautiful, mellow 4
fore I really noticed these voices in ern Minnesota. An avid birder, I lived notes, lower pitched than warbler and many other sounds that thrill and
transit again. This time I would find
my own calling.
for the short spring migration and
the chance to see colorful migrating
and sparrow calls. My Dad, after
walking home from work early in 2
4 perplex the listener (Fig. Bc & Track
34) (Track 35) (Fig. Bd & Track 36)
Twice a year, millions of birds flocks refueling before heading to the morning, told me of a large flight
(Track 37) (Fig. Be & Track 38). There
migrate across the Americas to northern breeding grounds. But on of thrushes he'd heard descending is no better way than through hours
and from ancestral breeding and the night I heard that incredible flight of such peaceful listening to ponder
from night migration. He described 00 0.5 1.0 0 0 0.5 1.0
wintering grounds. The migrations so clearly, I realized that if I knew the the mystery of these ancestral migra-
some of the calls as sounding almost
c. Bobolink d. Upland Sandpiper tions: little songbirds traveling thou-
of most species occur under cover callers' identities, I could sit out at like a cat's meow. I think he may 8 8-
Track 34, 3rd Call Track 36, 1st Call sands of miles twice each year, often
of night, and many vocalize during night in a lawn chair and view in my have been hearing Veery night flight
to the same wintering and breeding

Frequency (kilohertz)
their flights. The calling has long mind the species composition of this calls (Fig. Bb & Track 32). Others
been thought to help birds keep in clandestine symphonic transit. The 6 6- grounds.
have likened the night flight notes
contact with one another as they thought was overwhelming! One can only imagine what the
of the Swainson's Thrush to calls of
migrate, allowing them to form Many people have heard flocks Native Americans may have heard
the spring peeper, a small tree frog
4 4- and thought of the great migra-
and maintain in-flight associations of Canada Geese migrating at night. common throughout most of eastern
tory flights. Night calling has been
in the darkness. Some suggest the Even though you can't see them, you North America (Track 33).
r
calls may serve as air traffic control.
But no one knows to what extent
they act as a method of information
exchange. Whatever their purpose,
know they are Canadas because
you've heard the calls during the day.
But what most people don't realize
is that all North American warblers
Many people, in fact, are unaware
of songbird night calls because they
mistake them for insects, frogs, or
even cats! To hear the calls, find a
2 2-
rfr studied by modern science for the
last 100 years or so, although with
remarkably little progress. For unlike
Canada Geese, whose calls are the
0.0 0.5 1 0 0 0 0.2 0'4 0 '6 0. 8 same night and day, many migrant
on a good migration night in eastern and sparrows, and many other song- quiet place away from traffic, loud
e. American Bittern land birds use call types during noc-
insect noise, and other environ-
Track 38, 2nd Pair of Calls turnal migration that are rarely given
mental noise such as streams or
during the day except in specific
wind. It helps to find the highest place
behavioral situations. When I began
around in order to get as close to the
studying night calls, I was able to rec-
migrants as possible—although
ognize distinctive call types at night,
you can often hear good flights in
but even with a decade of birding
low-lying areas as the birds descend
experience, I could not associate
from night migration, typically in the
most of them with particular species.
hours before dawn. Choose a night
2 I relished the few published articles
during spring or fall migration when
on night flight calls I could find (see
the winds are favorable for a flight
Ball 1952, Graber and Cochran 1959
(see Fig. 5-64). Then sit back, relax,
0.5
and 1960, Graber 1968, and Tyler
and listen up toward the night sky. 00 1.0
Seconds 1916).Then I heard about the Cornell
I've taken many people out to
Laboratory of Ornithology's Library
listen with me. They often have
of Natural Sounds (LNS), the largest
trouble hearing calls at first. But
natural sound archive in the world. I
then, as if some kind of acoustic Figure B. Sonagrams of ight Flight Calls of Migrants: a. American Redstart (Track 31,
came to work at LNS in 1988 with the
door opens, they hear a call, and 1st Call): Most warbler night flight calls are short and high pitched. b. Veery (Track 32,
hope of finding clues to many of my
then another, and their ears quickly 1st and 2nd Calls): Thrush night flight calls are lower, longer, more mellow notes than
those of warblers. The Veery says veeree orveer in night flight. c. Bobolink (Track 34, unknown calls.
become focused on what to listen
Figure A. Bill Evans Listens to Night Migrants: Researcher Bill Evans listens to the 3rd Call): The pink used during night migration is the same as the common daytime I gradually realized, however, that
for. It's like magic when, in a mat-
calls of night migrants flying overhead. On a good migration night in eastern North flight call note. d. Upland Sandpiper (Track 36, 1st Call): The night flight call is a short, no one knew the identity of most
ter of moments, they tune in to the
America, listeners on the ground may hear thousands of calls, even without the help upward-slurred whistle—repeated quickly a few times. e. American Bittern (Track night flight calls and only a handful of
abundance of beautiful voices from
of microphones, from quiet, high places such as hilltops. Photo by Tim Gallagher. 38, 2nd Pair of Calls): The deep croak of a migratingAmerican Bittern is similar to the recordings existed. I was faced with
passing migrants. croaks of night-herons—note the broad band of frequencies in each note. the challenge of identifying nearly all

Cornell Laboratory of Ornithology Handbook of Bird Biology

7.46 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.47
the night flight calls of migrant land of Tennessee Warbler, Nashville each can be established. In NewYork Thus, the memory needed to recognize all of one's neighbors is limited,
birds—a quest I pursued with a three- Warbler, Orange-crowned Warbler, State, after listening to thousands of and distinguishing neighbors is especially easy. This kind of neighbor
part strategy. First, because some and Black-throated Green Warbler, hours of recordings, I have found that
recognition has now been shown in a number of species in which each
species' night flight calls are similar for example. I also would like to be thrushes typically pass over one of
male has essentially a single songform: Indigo Bunting, White-crowned
to their daytime calls, by intensively able to document the range of varia- my recording stations in one to two
listening to diurnal call notes from tion of each species' cal Is. The typical
Sparrow, White-throated Sparrow, and Common Yellowthroat (Stod-
minutes. Therefore I can assume
birds that I could see, I was able to night flight calls of the Ovenbird and that thrush calls separated by more dard 1996).
find matches to many of my un- the American Redstart, for instance, than two minutes are very likely to To easily hear differences among individuals, try listening care-
known night flight calls. Second, are clearly distinct, but some call be from different individuals. One fully to males of some species in which the male sings only a single song
by extensively recording night flight variations of each are quite similar additional way to sort a night of type. In addition to those mentioned above, Chipping Sparrows, Field
calls in different geographic regions, to one another. calls into individuals is to record in Sparrows, and Prothonotary Warblers are good subjects. For many
I was able to narrow down the possi- Since learning to recognize many stereo—from two carefully placed of these species, you can learn to recognize individual birds by their
bilities for the unknown calls by cor- night migrants by their calls, one of microphones. When two birds pass unique songs.
relating the geographic distribution my major focuses has been to mon- by together, stereo recordings often
But neighbor recognition also has been demonstrated in species
of particular calls with the known itor these calls across eastern North reveal their separation in space to a
with much larger repertoires. Song Sparrows may have up to 10 different
geographic regions through which America to gather information on careful listener. Although progress so
particular species migrate. Similarly, their migration routes and changing
songs apiece, but they can still recognize their neighbors, even though
far is encouraging, further research
I was able to gain clues by correlating abundance. Counting the number on counting techniques is needed to the neighbors may collectively have over 50 songs. This neighbor rec-
the time of year I recorded certain of calls from each species over a develop a reliable method of moni- ognition is based on the birds' remarkable memory for different song
call types with known migration particular recording site each night toring migration through recording forms. Memory of this sort is important because monitoring the be-
times of certain species. is relatively simple, but translat- night flight calls. havior of one's competitors is essential to breeding success. A stranger
In 1994 I began an association ing those totals into the number of One exciting possibility is auto- introduces great instability into a neighborhood; the immediate threat is
with the Cornell Lab of Ornithology's individuals passing by is a much mating the collection and analysis probably to the territory, and later to the female. Songs of strangers thus
Bioacoustics Research Program more difficult task. For example, if I of night flight calls using comput- provoke strong responses. Responses to neighbors are not so strong,
(BRP). The computer program "Ca- count 35 Great Blue Heron calls in ers that can detect and identify the
because a truce has typically developed, in which each bird has come
nary" developed by BRP became my one evening, how many individuals various calls from a tape. Harold
to accept the other as a neighbor. The neighbor with the familiar song
primary tool, allowing me to easily have flown by? One bird might pass Mills, in the Lab's Bioacoustics Re-
make sonagrams from my record- over a recording station and call only can still pose a great threat, however. Male Red-winged Blackbirds, for
search Program, recently developed
ings of night flight calls. With these once, whereas another may call 10 a prototype software program that, example, often inseminate the females on neighboring territories. In
detailed "pictures," I could now vi- times during its transit. Because of when given a tape with a selection Song Sparrows, it is again neighbors who are especially l ikely to steal
sually pick out differences between such variations in individual call of known night flight calls, was able real estate. Using sound to monitor these potential threats to one's suc-
calls that previously had sounded rates, I cannot simply total the calls to identify them to species or species cess is therefore indispensable (Sidebar 3: Pushing the Limits: New
the same to my ear. With sonagrams, each night, but also must look at complex, and to total the number of Computer Techniques for Studying Bird Song).
it was also much easier to compare their pattern of occurrence. There calls of each. Once this procedure Birds also use vocalizations other than territorial song to rec-
my night flight calls to daytime calls are several ways to do this. One is is perfected, an array of night flight ognize individuals (Beecher and Stoddard 1 990). Bank Swallows live
from known species—many night to carefully examine sequences of call monitoring stations can be set up
in colonies, and once the young leave the nest, they mix with young
flight calls are so brief that it's nearly calls. As a bird approaches, passes across the continent, interconnected
impossible to hear the differences
from other nests (Fig. 7 39). Parents use the distinctive vocal signatures
-
over the recording site, and heads via the Internet. Such an array could
between them, even if you listen away I often hear a sequence of provide us with real-time bird migra- (Continued on p. 7.53)
very carefully. weak calls, followed by loud ones, tion maps analogous to the weather Figure 7-39. Bank Swallow Young: After
After 10 years of research, I now then weak ones again. Thus I can radar loops we watch on television fledging, young Bank Swallows gather
have a fairly good understanding acoustically follow the progression news—we could broadcast bird together with young from other nests
of the night migration language of of some individual birds over the migration TV into America's living to form large groups. Parent birds are
birds in eastern North America. I recording station. Another way to room, follow the progress of our fa- still able to single out their own young,
can identify nearly all the night flight estimate numbers of individuals vorite species during their migration, however, by recognizing their voices.
calls heard in this region to species from a recording of a night's calls and automatically track changes in (See Ch. 8, Recognition Between Par-
or to "species complex"—a group of ents and Young.) Photo courtesy of Mary
is to determine the time it takes for bird populations. That's the dream
Tremaine/CLO.
closely related species. But much a bird of a particular species to pass we are currently working toward
work remains. I would like to be overhead—in other words, to appear here at the Lab. Stay tuned! ■
able to distinguish the similar calls and disappear on the tape. Luckily,
of each species within the species species have fairly consistent flight
complexes—to separate the calls speeds, so average transit times for

Cornell Laboratorq of Omithologq Handbook of Bird Bioloti

7.48 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.49

Sidebar 3: PUSHING THE LIMITS: NEW COMPU I ER TECHNIQUES Figure A. (Continued)

the researcher might switch to a song
that closely resembles the song that
b. Comparison of Piano Score and Sonagram of Wood Thrush Song
FOR STUDYING BIRD SONG 4/00MIIMMNINimmiiii%
the subject bird is singing, engaging
him in "matched countersinging"
John Bower -•4.411.• (see Marsh Wren discussion in
Songbird Diversity, earlier in this
My admiration for the pioneers of MEM 1=1■1

chapter). Or the researcher can play

bird song research, who faced the a. Piano Score of Wood Thrush Song
a longer song than the subject sang,
daunting task of studying bird song
8va. or choose to overlap the subject's
without modern technology, never
iitivret a song by instructing the computer to
wavers. These turn-of-the-century . , •4
a FAING11 =' ./ UM IN a I / JIMIN ■
11"/"IrrrIliMMIN aIIIIII1 play a song while the subject bird is
researchers studied song by trans- II.,=VJ MN 111111111111111 = /117 I 111/1•111111VIIIII ■4
•1".4r11.25=11L11
I /4111KiNIIMIGIIIIIPPANWJIIILII II" IN Gill NEM/ ad il 11 IC.11.11m em Ira I still singing his song.
lating the songs they heard into stan- IN /IIII1 ■=IIIII I LA= ■
IIM=u MIMIIIIIMANIIIII :INV I
..-
But do birds really respond dif-
dard musical notation, and assigning
words to the phrases the birds were 4.,0 -- • -
Ii°
ferently to the two types of playback
experiments? Peter McGregor (Co-
singing. Such translations, although II. 1-111.! ill I IM ■1111151bIall Iiii 8-
I Es ■ V_I■M3111r11111111111=11NIIIIIIIIEMI penhagen University) and co-work-
the only technique available at the '
, e
7- ers answered this question by mea-
time, were very limiting: at best they
suring 26 different aspects of singing
were gross approximations of the 6-

Frequency (kilohertz)
behavior in Great Tits subjected to
complex information transmitted
both traditional playback and inter-
when a bird sings (Fig. Aa & Track 5
39; Fig. Ab & Track 40). The mod- :Mg n
_■1 -4
pp 2:: 1
_-- 4/44 active playback (in which songs were
lWM IN IM 4 ..... chosen to match the type and/or
ern era of bird song studies began ._i ■--.Isr Animmer--,-.~4.1 NI EN IW MIVIE I IN' BUIL:1[1
in the 1940s when the invention
MIK1111111111111111111r-M1111•P!./ ■1111= I - U U I MEN/ ING.11
3- tam /---- structure of the song the subject bird
I ?"" •11 I
-
was singing). It turned out that birds
of magnetic tape recorders and the
sonagram allowed the preservation
2- 11117,11.111 approached the speaker in response
to either playback experiment, indi-
and objective analysis of natural 1-
cating that Great Tits mistook both
song. These two technologies have
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 types of playbacks for intruders. The
been the basis for a half century of
Seconds subjects sang differently in response
great advances in our understanding
to the two types of playbacks, how-
of avian communication. Now, as
territory a researcher places a speak- answer these questions—although ever. When interactive playback was
the 21st century begins, we find our-
er just outside the territory boundary they allow the researcher to start an used, subjects waited longer before
selves riding a new technological 64 and plays a Song Sparrow recording acoustic interaction with a bird, she singing, and tended to match aspects
revolution: the development of fast, d 1t made several miles away (see Fig. 7- of the playback song structure (for
powerful, and portable computers. 41111Wm"11111111711Eff 0— w "MIII• •111 11 ■ cannot continue the interaction in
h111111=111111111111111111•/ MAIN - I • IIMPNI.Aralll I example, the number of phrases in
IN 111 ■■ 32 for Song Sparrow picture). A male any realistic way since she is limited
Here I describe three new computer- V I41.1.111MECOMMI I MEW I
Song Sparrow will almost always re- to the series of songs on her playback the song) more than when traditional
based techniques that hold great
spond to this experiment by singing tape. playback was used. Another dif-
promise for furthering our under-
• and approaching the speaker. Typi- In contrast, interactive playback ference was that birds sang shorter
standing of avian communication. •
• cally, he will continue to sing for long experiments allow researchers to songs after the interactive playbacks
periods if the playback continues. engage the bird in a realistic bout of ended than after traditional play-
Interactive Playback
This experiment, repeated for many acoustic interactions. To do this, the backs, suggesting that responding to
The first new technique, inter-
species, has shown that territorial researcher first stores many recorded interactive playbacks may be more
active playback, allows researchers
FigureA. Piano Score and Sonagram of Wood Thrush Song: a. Piano Score (Track 39): males consider song sung near their songs on a portable computer. Once tiring. Clearly, these birds considered
to interact more realistically with the
Early bird song researchers did not have sophisticated computers, microphones, tape territory by an unfamiliar bird to be she starts an interaction with a bird, the two types of playbacks to be very
birds they are studying. In traditional recorders, and other equipment used to study bird song today. They listened carefully,
a threat, and that the territory holder she can continue the interaction different things.
(non-interactive) playback experi- and often used musical notation to describe the songs they heard. In 1921, F Schuy-
uses his song to confront intruding by choosing from the many songs Two other studies have used inter-
ments the researcher plays tape ler Mathews published his Field Book of Wild Birds and Their Music, a collection of
males. But how do males use their stored on her computer. Return- active playback to examine the fine
recorded songs through a speaker musical scores representing the songs of birds common in the eastern United States.
Shown here is the Wood Thrush score from that book. In Track 39 you will hear this songs during these encounters? What ing to our Song Sparrow playback details of how birds interact acous-
to a bird, and notes or tape records
Wood Thrush score played on a piano. b. Comparison of Sonagram and Piano Score information in the song is important example, if the researcher is using tically. Torben Dabelsteen (Copen-
the subject bird's response (see Fig.
(Track 40, 3rd Song): A comparison of one portion of the Wood Thrush piano score for the communication between the interactive playback, once she has hagen University) had observed that
7-55). Traditional playback experi-
with a sonagram of a single phrase from a Wood Thrush—note that the introductory territory holder and his foe? For that elicited song from the territorial territorial male Eurasian Blackbirds
ments have played an important role
notes to the song, audible at close range and on Track 40, were removed from the matter, how would an intruder use male she can engage him in dif- matched the "intensity" of their
in deciphering the functions of song.
sonagram to better match the piano score. his song in this situation? Traditional ferent kinds of acoustic interactions. songs (as measured by their singing
Consider the following experiment:
playback experiments cannot fully For instance, with a click of a mouse, rate, loudness, and the amount of
after mapping a male Song Sparrow's

Cornell Laboratorq of 0 mithologq Handbook of Bird Biologg

7.50 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.51
"twittering" contained in the song) Multichannel Recording tory holder, as well as monitor the tory!" Furthermore, neighbors' song My recordings of an entire field of Computer-Based
to the level of threat they felt from Whether studying naturally oc- challenger's singing, and the singing rates appear to be closely related to Song Sparrows are providing some Song Recognition
neighboring males. Using inter- curring bird song, or using traditional of all the other birds in the field. Early the movements of the challenger. of the first glimpses into the singing A third technique that holds tre-
active techniques, Dabelsteen then or interactive playback, techno- results from my study are showing Again, it appears that neighbors dynamics of an entire neighborhood mendous potential for changing how
found that his subjects reacted most logical limitations have kept scien- interesting patterns in the singing may be singing in proportion to their of songbirds. we study avian communication is
aggressively when the intensity of the tists from studying the interactions between the males involved in a perceived threat from the challenger. computer-based recognition of bird
playback song increased in parallel of more than two birds at once. Yet territory battle, and among the other
with the intensity of the subject's birds do not live in isolation—com- birds in the field. Challengers almost
Channel
reaction. Playbacks that presented munication often involves a whole always sing at the highest rates in the Number
songs of different intensities in ran- neighborhood of birds. My research, minutes before they intrude into the 1
dom order elicited less aggression made possible by the engineering established male's territory. Interest-
from the subjects. Interactive play- feats of computer programmers in ingly, the challenged males respond
back thus enabled Dabelsteen to the Bioacoustics Research Program in markedly different ways—ranging
discover that the order in which at the Cornell Lab of Ornithology, from singing in intense bouts at rates
an intruder sang songs of different aims to overcome this limitation by that nearly match the challenger, to
intensities was an important part recording the vocalizations of an en- singing less often and irregularly.
of the meaning communicated to a tire neighborhood of birds on mul- These findings raise more questions
threatened territorial male. tiple, widely spaced microphones. than they answer. For instance, why
Bonnie Nielsen and Sandra Veh- By placing eight microphones along would the challenger advertise his at-
rencamp (University of California at the perimeter of a nine-acre (22-ha) tack through a high song rate instead
San Diego and Cornell University) field, I am able to record simultane- of engaging in a quieter ambush-type
have used interactive playback to ously the singing of the 14 territorial attack? Is he using his high song rate
5
look at how territorial Song Spar- Song Sparrows, as well as the songs to intimidate the bird he is about to
rows interact acoustically during of many other species. When I return challenge? Are challenged territory
4$ I
intrusions. They hypothesized that
male Song Sparrows send aggressive
threats to other males by switch-
to the lab, I play the eight-channel
recording into the computer. During
analysis, sonagrams from all eight
holders sending specific messages
through their differing singing behav-
iors, and, if so, what are those mes-
, att It)
toLL #101t•
N2 to D
ing song types at the same time as microphones scroll across the mon- sages? I hope that questions such as
their rival (synchronized song-type itor—a visual feast of all the singing these can be answered by observing !ern: ts,- ;;%+SIT: *TA' ;'
switching), and by matching the song from an entire field of birds! (Fig. B & more naturally occurring territorial NN2 NN3
being sung by the rival (matched Track 41) From these sonagrams, I first conflicts, and through the use of in-
countersinging). They tested both of document each bird's repertoire of teractive playback experiments.
these hypotheses through a series of song types so that I can recognize in- If I expand my view to all the
interactive playback experiments in dividual singers by their songs alone. birds in the field, I find that the entire 10 Seconds
which they instructed their computer With that knowledge, I can exam- neighborhood's song production
Ch Challenger
to engage in synchronized song-type ine any tape from my study site and increases shortly before a territorial
D Defender
switches, to match the song types determine which birds are singing, battle occurs. Does this mean thatthe N Neighbor
sung by the subject, or to do neither. what they are singing, and when they entire neighborhood is aware that a NN Non-neighbor
They found that subjects responded sang. Furthermore, by measuring the battle is about to take place? Are
Figure B. Sonagrams of Songs of Several Territorial Song Spar- challenger was trying to expand his small territory (newly
with the most aggression when differences among the times a given other males doing the bird equivalent
rows Recorded Simultaneously by Eight Microphones (Track acquired two days earlier) by stealing parts of neighbors' terri-
the computer matched their song song arrives at each different micro- of shouting, "Fight! Fight! Fight!?" A
41): This multichannel sonagram is of a 10-second recording tories. Other Song Sparrows singing in this sonagram were two
types, with an intermediate amount phone, the computer can calculate closer look shows that not all birds males (N1 and N2) whose territories were adjacent to those of
made by John Bower at 7:06 A.M. on April 17, 1998 in Ithaca,
of aggression when the computer a precise location for each singer. In in the field sing at equal rates. Birds NY using an array of eight microphones arranged around the the combatants, and four non-neighbors (NN 1 to NN4) from
engaged in coordinated song-type this way, I am able to preserve and re- whose territories border the territory edge of a field in which several male Song Sparrows held the other end of the field.
switching without matching, and create the entire acoustic scene that of the bird being challenged tend to territories. Simultaneous recordings from the eight micro- Song Sparrow N1 starts the activity by singing toward
with less aggression when neither occurs in my study site. sing at higher rates than more distant phones are shown stacked from top to bottom, with channel the defender (notice how this song is represented strongly
occurred (Nielsen and Vehrencamp I am using this technique to ex- birds. Perhaps these birds are more 1 (recorded from microphone 1) on top and channel 8 (from in channel 2, less strongly in channels 1 and 3, and weakly
1995). The work of these pioneers microphone 8) at the bottom. As you read through this visual in channels 5 through 7). The challenger then sings toward
amine the acoustic interactions of threatened by the instability that
representation of auditory changes in time and space, you will the defender (again strongly picked up in channel 2 but also
in interactive playback already has Song Sparrows when new males often occurs after a territorial battle,
notice that many of the same songs are recorded at multiple in other channels) and the defender sings in response. At
revealed new layers of complexity in challenge established territory and are sending their own message to
microphones. Computer analysis of the tiny differences in the same time as this activity, NN1, NN4, and NN2 sing in
the communication systems of terri- boundaries. With my system, I can the challenger and challenged birds: channels 8 and 5. Neighbor N2 then sings in response to the
arrival times at different microphones allows the spatial loca-
torial birds. Many more fascinating record how the challenge affects "Whichever of you loses, don't think tions of the birds to be calculated. defender (channels 7 and 6, and represented more faintly in
discoveries await us. the singing behavior of the terri- about trying to move in on my terri- The recording was made two minutes before a territorial channels 1 through 3 as well). Finally NN3 sings in channel
fight between the challenger (Ch) and the defender (D). The 8, his song appearing in channels 3 and 4 as well.

Cornell Laboratorti of Ornithologq Handbook of Bird Biologq

7.52 Donald E. Kroodsma Chapter 7—Vocal Behavior 7.53
song. This technique is deceptively cies by sound alone. Very few orni- are used together. For instance, of their young to identify them in large flocks of other young Bank
simple in concept—the computer thologists have the knowledge to do conducting an interactive playback Swallows. This kind of parent-offspring recognition seems less well
compares a recorded song, or some this. This problem was made obvious experiment while the microphone
developed in Barn Swallows; young Barn Swallows are less likely to
feature of the song, with a stored tem- by the tragic death of Ted Parker, who array is running will give us a much
mingle with birds from other nests because their parents don't nest in
plate to determine which species or died in 1993 when the small plane in finer glimpse into how a community
even which individual sangthe song. which he was riding crashed during
large colonies like Bank Swallows. Numerous experiments show, too,
of birds responds to the carefully
In practice, building a template that a recording trip in Ecuador. Ted was controlled singing of our artificial that in many species, mates recognize each other. Sometimes they do
can distinguish a particular bird's arguably the greatest human resource intruding male. Or, using automated so under conditions that seem overwhelmingly difficult to us, such as
song from natural and man-made for Neotropical bird song identi- recognition to analyze tapes made in a huge colony of penguins or seabirds. As in humans, recognizing
background noise is a challenging fication who ever lived. His ability to with a microphone array in a little- individuals is the foundation for social relationships, and individual
task. Early development of this tech- identify bird sounds was legendary. studied tropical habitat may result in recognition by voice can be expected in almost every social situation
nique in the Bioacoustics Research During visits to the Library of Natural a much better look at which animals that birds encounter.
Program is focusing on automated Sounds, for example, it was com- (birds or otherwise) use that habitat,
recognition of the calls of nocturnal mon to sit Ted in a quiet room and and where in the habitat they are
migrants (see Sidebar 2: Listen Up!), play tape after tape of unidentified found. Clearly, exciting times are Song Dialects
but many other applications are wait- Neotropical bird sounds recorded ahead for the application of new One feature of variation in the songs of songbirds has attracted
ing to be tried. For instance, if I want by other people. Occasionally Ted computer technology to the study of special attention: song dialects (Lynch 1996; Payne 1996). We humans
to compare how often each Song would be stumped, but more often avian acoustics. ■ have dialects in our speech, of course; Americans all recognize "south-
Sparrow at my study site sings on he would calmly say something like,
ern drawls" and r-less Bostonians, and experts can often pinpoint a
days when territorial conflict is high "Phlegopsis nigromaculata, Black- Suggested Readings
versus days when it is low, I currently Spotted Bare-Eye." Ted's knowledge person's place of origin by the subtleties of these different accents.
Bower, J. L. 2000. Acoustic Interac-
need to spend hours and hours wea- of Neotropical sounds was so com- Songbirds have dialects, too. Dialects in both speech and song are
tions during Naturally Occurring
rily "browsing" through tapes stored plete that he was often able to guess Territorial Conflict in a Song Spar-
a consequence of vocal learning. Humans learn their speech, and
on the computer. Soon, and much to correctly where mystery recordings row Neighborhood. Dissertation. songbirds learn their songs, and if individuals remain at the location
my relief, the computer may spend were made by the complex of spe- Cornell University. where they learned their vocal signals (or if newcomers learn the local
the night analyzing my tape while I cies present on the recording. Ted's dialect), then individuals in a given geographic location come to use
Dablesteen, T., and S. B. Pedersen.
sleep, greeting me in the morning death was a tremendous loss, but the same local dialect.
1990. Song and information about Figure 7-40. White-crowned Sparrow:
with a list of who sang what, when, we are fortunate that his legacy of
aggressive responses of blackbirds, The term dialect is typically used to signify any clusteringof sim- Many aspects of the White-crowned
and from where. approximately 15,000 carefully cat-
Turdus merula: evidence from in- ilar vocalizations that is a consequence of learning. Dialects can thus Sparrow's singing behavior have been
Computer-based recognition of aloged recordings are archived in the well studied, including its song dialects
teractive playback experiments consist of only a few birds or of thousands, depending on how learn-
bird song also holds great promise Macaulay Library of Natural Sounds. (regional differences in song). Because
with territory owners. Animal ing and dispersal affect the distribution of vocalizations in a particular
for advancing the conservation of It would be a great contribution to each male sings only one song type,
Behaviour 40: 1158-1168. species. Each neighborhood of like-singing Indigo Buntings could be
Neotropical birds. Ornithologists of- conservation, and an honor to Ted, dialects are particularly easy to identify.
ten warn that the extinction of many if we could use those recordings to McGregor, P. K., T. Dabelsteen, M. called a dialect, as could the megapopulation of Black-capped Chick- Photo courtesy of Mike Hopiak/CLO.
bird species is inevitable unless we program a computer with the ability Shepard, and S. B. Pedersen. 1992. adees extending from Maine to
conserve critical tropical habitat to recognize Neotropical species by The signal value of matched sing- British Columbia, whose mem-
from ever-increasing human de- their sounds. Such a program would ing in Great Tits: evidence from
bers sing very similar versions of
struction. But which habitats are most enable tropical bird recordists to interactive playback experiments.
the hey-sweetie song.
important to save? A major problem record the sounds of a particular Animal Behaviour 42: 987-998.
Hearing song dialects re-
in answering this question is that we habitat and location, and rely on the Nielson, B. M. B., and S. L. Vehren-
quires a good ear, but a skillful
know very little about the population computer to determine what species camp. 1995. Responses of Song
distributions of Neotropical birds.
listener can hear dialect differ-
were singing at that location. In this Sparrows to song-type matching
Censusing birds in the Neotropics way, the knowledge required to make via interactive playback. Behav- ences in the songs of many song-
is no easy task. Because visual iden- good conservation decisions in the ioral Ecology and Sociobiology bird species. Dialects have been
tification is difficult at best in many Neotropics would be improved. 37: 109-117. especially well studied in the
tropical habitats, census workers are Stap, Don. 1994. Remembering Ted White-crowned Sparrows of the
faced with the daunting task of identi- These three techniques will be Parker. Living Bird, Winter 1994, coastal chaparral in California
fying thousands of Neotropical spe- even more powerful when they 13(1): 24-25. (Baker and Cunningham 1985)
(Fig. 7-40). There, boundaries
between dialects are so sharp
that, near Point Reyes Bird Ob-
servatory, one can stand facing
the Pacific Ocean and hear songs
of one dialect to the left and an-

Cornell Laboratonj of Ornithologq Handbook of Bird Biologq

7.54 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.55
other to the right. Distinguishing dialects is especially easy in this spe- some way different, and these odd songs can then become the basis for
cies, because each male uses a single song form, and each song thus a new dialect. As suitable habitat areas expand, they eventually contact
identifies the dialect (Fig. 7 41 & Track 42). Laboratory experiments- other expanding areas of suitable habitat. It is at these locations of sec-
have shown that males usually learn their songs rather early in life ondary contact that boundaries between dialects form (Fig. 7 42). -

(see Vocal Development in Songbirds, earlier in this chapter), so the The formation of dialects in this manner is relatively straight-
dialects clearly result from each male learning his song, then staying forward. More controversial is what maintains boundaries once they
within the region where he learned it to breed and defend a territory. have formed. Dialects and their boundaries remain fairly stable over
Just how do these sparrow dialects form? As humans who build time, so one can predict that males within a given area will sing a cer-
houses in California chaparral have discovered, sometimes tragically, tain dialect. The central question is this: How socially and genetically
the chaparral is a fire climax community. Vast stretches of the habitat isolated are the birds in different dialects? The degree of isolation is
routinely burn, temporarily destroying good sparrow habitat. The determined in large part by when and where young sparrows learn
destruction is part of normal renewal, however, and when pockets of their songs and enter the breeding population. Because we know that
suitable habitat again become available, the sparrows rei n habit them. dialects tend to remain stable, two possibilities exist. First, males may
Founding birds can have songs that are incompletely learned or in learn their songs before leaving their fathers' territories, keep the same
songs in later life, and settle in their fathers' dialect regions. Second,
Figure 7-41. Sonagrams of White- White-crowned Sparrow Dialects young males may move to new dialect areas and modify their songs
crowned Sparrow Dialects (Track 42, to match the new dialect.
2nd Oregon Song, 1st California Song, 9
Occasionally, females also sing, and like males, young females
2ndAlberta Song): Representative songs 8 learn their songs early in life. A female might use her memorized song,
Frequency (kilohertz)

from three different White-crowned

7 whether she sings it or not, to choose a male with the same kind of
Sparrow dialects, one in Oregon, one in
California, and one in Alberta, Canada. 6 song. What is especially intriguing is the possibility that most young
Note that although each song follows birds, both males and females, electto remain in or return to their natal
5
the same general pattern of pure tones,
4 dialect, so that the learned songs promote the isolation of the birds in
buzzes, and other notes, the details of
note structure and order vary from song 3
the different dialects. This kind of isolation could enhance genetic dif-
to song. ferences among populations, eventually leading to differences so great
2
that the populations become different species. Perhaps, it has been
00 0.5 1.0 1.5 2.0 2.5 hypothesized, the song-learning ability of songbirds, together with
early learning and dispersal more within than between dialect areas,
#2 (California)
has been instrumental in generating so many songbird species.
Frequency (kilohertz)

Exactly what young White-crowned Sparrows do, however, is

largely unknown. Laboratory experiments show that young males
certainly are with their fathers long enough to learn their songs, and
they learn most readily during that time. But laboratory experiments
also show that, under the right social conditions, birds can modify their
songs later in life. Banding studies in the field show that some young
..ffloommonal

males remain in their natal dialect area, but some also move across
dialect boundaries and learn the songs at the new location. Merely
knowing that young males opt for both choices doesn't, however,
9 #3 (Alberta)
address the critical question: Does the dialect boundary in any way
8
inhibit dispersal? Do fewer birds cross the dialect boundary than one
Frequency (kilohertz)

would expect by chance? If the dialect boundary in any way restricts

7
dispersal, then mating opportunities are also relatively restricted, to
6
birds with a similar singing background. Unfortunately, testing these
5 ideas in the field is extremely difficult, so we still do not know, with
4
3

2
IC\ ■
,1 41 4; confidence, how these dialect boundaries affect dispersal and mating
opportunities in the White-crowned Sparrow. Most young songbirds
are adept at learning songs while they are with their fathers, but the
influence of the father's songs on dispersal and on the range of songs
0.0 0'5 l'O l'5 2'0 i5 that a young male (or in some cases, female) finds acceptable remains
Seconds to be determined.

Cornell Laboratory of Ornithology Handbook of Bird BioloBq

 *A
7.56 Donald E. fKroodsma Chapter 7 —Vocal Behavior 7.57

All
b A
A

A A

Pacific-slope Flycatcher Cordilleran Flycatcher

Geographic Variation in Suboscine Vocalizations Figure 7-43. Pacific-slope Flycatcher

Dialects occur in learned vocalizations, such as the songs of and Cordilleran Flycatcher: Because
most suboscines do not learn their songs,
KEY songbirds, but how much do non learned vocalizations change over little regional and individual variability
geographic space?Very little, it seems.The songs of theAlder Flycatcher occurs among groups that interbreed.
Suitable Habitat are an unmistakable fee BEE o from Maine to British Columbia. No
- - Differences in songs, then, may indicate
detectable local variation occurs in these songs. The same general genetically separate groups, and can
be valuable clues to separating species
Burned Area pattern is found among other suboscines. The songs of these birds are
that appear very similar in other ways.
not learned, but instead seem to be a more or less "direct readout" of Until 1989, these two birds of western
A Individual White-crowned Sparrow
the genes. Apparently, the genes that dictate the fee BEE o of the Alder
- - North America were both considered
Al White-crowned Sparrow Dialect 1 Flycatcher don't vary from coast to coast in North America. to be Western Flycatchers, but differ-
ences in their songs alerted researchers
Because songs are a good indication of a bird's genetic back-
A2 White-crowned Sparrow Dialect 2 to their other differences. Finding that
ground, songs of flycatchers and undoubtedly other suboscines can they were also different genetically al-
A3 White-crowned Sparrow Dialect 3 help us to determine which populations of birds belong to which spe- lowed researchers to separate them into
cies—that is, the songs are good "systematic" characters. During the the coastal Pacific-slope Flycatcher and
Figure 7-42. Development of White-crowned Sparrow Dialects: White-crowned Sparrow dialects occur in small patches with 1960s, for example, investigators discovered that the two groups of the more interior Cordilleran Flycatcher.
sharply defined boundaries in the coastal chaparral (dry areas with low shrubs) of California. These dialect patches develop in Photos by R. and N. Bowers/VIREO.
theTrai I I's Flycatcher differed consistently in voice, suggesting that the
concert with the natural cycle of fire and regrowth that maintains the habitat: a. Established population of White-crowned Spar-
two groups did not interbreed. The voice difference helped to identify
rows. b. Fire temporarily destroys a large part of the suitable sparrow habitat. c. Over time, isolated pockets of suitable habitat
develop within the burned area as vegetation regrows. Dispersing White-crowned Sparrows (A 1, A2, and A3) colonize these areas the two populations as two species, the Alder Flycatcher and Willow
of renewal. If a founding sparrow's song happens to be slightly different from that of the original population, it can become the Flycatcher. More recently, researchers recognized that the Western
basis for a new dialect. d. As suitable habitat expands, the colonist populations of Wh ite-crowned Sparrows increase. Still isolated Flycatcher consisted of two different groups, each with its distinc-
from the original population, their young learn only the local songs. e. Eventually the subpopulations (Al, A2, and A3) contact
tive songs (Johnson and Marten 1988). Study of genetic characters
other areas of expanding suitable habitat; it is at these locations of secondary contact that boundaries between dialects form.
showed that the songs identified different genetic populations, and
the two groups were recognized as distinct species, the Pacific-slope
Flycatcher and the Cordilleran Flycatcher (Fig. 7 43).
-

Cornell Laboratorg of Ornithologii Handbook of Bird Biologq

7.58 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.59
The songs of suboscines can be especially useful in charting the
unknown avian biodiversity in the tropics (Kroodsma et al. 1996). A Chipping Sparrow Songs
remarkable series of studies throughout the Neotropics by Wesley 9
Lanyon used the songs of Myiarchus flycatchers (the group containing
the Great Crested Flycatcher of North America) to help identify the
7 MUM
different species in the group (Lanyon 1978). We know very little, how-
5
WM=
3 111M111
ever, about antbirds, woodcreepers, flycatchers, cotingas, manakins, MI 1 MI 2 MI-3
- - MI-4 MI-5
and other suboscines from the New World tropics. Systematists who
Shared Unique
classify bird species currently differentiate most species on the basis of
plumage patterns or other morphological characters, but experience
AMIN. mean
has shown that such characteristics can be misleading (Fig. 7 44).
Plumage patterns might not vary much over a vast geographic area
simply because the habitat favors a certain type of cryptic pattern. Be-
-

•••
OREN anus
MA 1- MA-2 — MA-3 MA-4 MA-5---
haviors such as songs, which are used to identify mates for breeding,
could be a more reliable indicator of which birds are capable of mating 0.25 seconds
with one another, which in turn helps us to define species. Tape-re- MI Michigan
cording and analyzing songs from these Neotropical suboscines may MA Massachusetts
thus be the fastest way to chart their diversity, and speed is important,
because habitats and the birds themselves are disappearing rapidly.
make sense—a bird who shares a vocal signal with either immediate Figure 7-45. Chipping Sparrow Songs
neighbors or more distant birds must gain some social advantage that from Two Populations: Individual male
The Diversitq of Geographic Patterns in Songbirds Chipping Sparrows each sing only one
leads to a particular pattern of geographic variation. But learning what
Some songbird songs appear in geographic patterns other than song type—a trill made up of one simple,
these social forces and advantages are awaits further field work. repeated syllable. The song type comes
the sharply defined dialect areas of the White-crowned Sparrow. And,
In some species, the same songs recur throughout the geographic from an apparently limited pool of song
just as the functions and consequences of White-crowned Sparrow
range of the species. Within any population of Chipping Sparrows, types used by all the populations of this
dialects remain unknown, so do the reasons for these other patterns species. The song types are not distrib-
for example, many different song types exist with little sharing among
(which are described below). In some way, these different patterns must uted in dialects, but rather throughoutthe
males, but songs found in one population can also occur in other pop-
range of the species, such that in any pop-
ulations across North America (Borror 1959). It seems that Chipping ulation, a few songs will be shared among
Sparrows sing a limited number of song forms, each of which could several males, but most will be sung by
perhaps occur in any population; these song forms are distributed not only one male. Illustrated in the figure are
Figure 7-44. Identifying Flycatchers: Is five songs from a Michigan population
in local dialects but throughout the range of the species (Fig. 7 45). -

it a Swainson's, Brown-crested, Short- (MI-1 through MI-5) and five songs from a
Also widely distributed are the hundred or so components from which Massachusetts population (MA-1 through
crested, or Dusky-capped flycatcher?
These Neotropical flycatchers are so sim-
... ' • '''. . - ' . •'-‘-'> 4.4.=
. :;
the Indigo Bunting song is constructed; local dialects in buntings are MA-5). Within a given population, some
ilar in appearance that the most reliable formed not so much by the types of elements used, but by their par- songs are sung by only one bird (songs
way to distinguish them is by song. .....1, ticular combinations. 3, 4, and 5) and some are shared or at
,:i z.4,
4.4u4-2,..4 0 %,: least very similar (in Michigan, MI-1 and
1:1Wl:4,1 i .13 The whistled hey-sweetieof the Black-capped Chickadee has an
MI-2 are the same; in Massachusetts,
especially puzzling geographic distribution. Like the Alder Flycatcher, MA-1 and MA-2 are the same). Between
„, 'N-.4.14.-,y- tk,
cc~ai 0 *it `,--..,.; 0- the chickadee uses the same song from Maine to British Columbia. populations, the same is true: songs MI-3,
MI-4, MI-5, MA-3, MA-4, and MA-5 are
Patterns of whistles are the same in both frequency and amplitude, and
each unique, but some songs are found
birds use the same rules to transpose their songs in frequency. Such
in both populations: MI-1 and MA-1
consistency in a learned song across an entire continent is remarkable. are the same, and MI-2 and MA-2 are
How the chickadees maintain such a stereotyped learned signal over the same. In this example it is simply by
such a vast geographic expanse remains a mystery; the more typical chance that the same two songs shared
songbird pattern is to show at least some form of local variation. within populations (songs 1 and 2) are
also shared between populations. Note
Some intriguing local populations with song forms other than the
that the "songs" shown are actually just
hey-sweetie do occur, however. One is on Martha's Vineyard, a small short segments from the entire songs—in
island off the coast of southeast Massachusetts (Kroodsma, Byers, et actuality, Chipping Sparrow songs con-
al. 1999). There, males also whistle, but the two whistles are on the sist of much longer trills, repeating the
same syllable around 20 or more times.
same frequency, with no drop between the first and second whistles.
Adapted from Kroodsma (1996a).

Cornell Laboratory of Ornithology Handbook of Bird Biology

7.60 Donald E. Kroodsma Chapter 7 - Vocal Behavior 7.61
Furthermore, song dialects occur on the island, so that males in differ- be relatively isolated from mainland North America. Perhaps
ent areas use different songs (Fig. 7 46 &Track43). On the far western
-
isolated pockets of chickadees also occurred in some western
end of the island, at Gay Head, songs typically consist of two whistles, states, so songs in those areas also had a chance to diverge from
both on the same frequency, but with an amplitude break in the first, the standard hey-sweetie. We don't know whether these vocally
not the second, whistle. Instead of hey-sweetie, the males sing sweetie- distinct populations are genetically distinct, or if a female of one
hey, and the males sing this song on two frequencies, one noticeably tradition would accept a male from another.
higher than the other. On the eastern end of the island, near Edgartown, Work with chickadees in the laboratory has only enhanced
however, males have more complex songs, with two amplitude breaks the mysterious nature of chickadee song (Kroodsma et al . 1995).
in the first and one in the second whistle (swesweetie-sweetie). That If male chickadees from normal hey-sweetie populations are
song also occurs on a high and low frequency. In other parts of the is- tutored with normal hey-sweetie songs in the laboratory, they
land, males sing a sweetie-sweetie, and sometimes the high frequency develop highly abnormal songs, unlike anything one would
song is different from the low frequency song; a typical combination expect from a chickadee in nature. Although the whistled tonal
throughout the center of the island is for a male to sing a high frequency quality remains, the songs consist of from one to seven or more
sweetie-sweetieand a low frequency sweetie-hey. A second pocket of different whistles on a variety of frequencies (Track 44). Fur- Figure 7-47. Blue-winged Warbler: Blue-
song differentiation occurs in Oregon and Washington, where males thermore, males develop repertoires of up to three different winged Warblers, Neotropical migrants that
breed in brushy fields in the northeastern
sing a bewildering variety of whistled songs. The patterns on Martha's song forms. Groups of males isolated from one another even
United States, have two different categories of
Vineyard and in Oregon and Washington thus differ markedly from develop different "dialects." In the laboratory, the true potential songs. One, the well-known bee-buzz, is used
those elsewhere in North America. for chickadee singing is unleashed, as it seems to be, at least in most in the presence of females, and varies little
How do these regional differences in song arise? Martha's Vine- part, on Martha's Vineyard. Over most of the North American throughout the range of the species. The other
continent, some social factors must restrict song variation to type of song, used at dawn and in very aggressive
yard is aboutfour miles off the coast of New England, so birds there may
situations, is more variable and occurs in dia-
the simple hey-sweetie, transposed in frequency; in the highly
lects. Photo by Lang Elliott.
artificial laboratory environment, those forces are absent, per-
Figure 7-46. Sonagrams of Black- Black-capped Chickadee
mitting both song repertoires and dialects. But what are the
capped Chickadee Songs from Martha's
Vineyard (Track 43, 5th and 6th Western 4.6 Martha's Vineyard West social forces? Is it the female who sets standards for what songs
Songs, 3rd Eastern Song): On the island are to be sung? Among songbirds, the female is believed to
4.4
of Martha's Vineyard, Black-capped select a mate, not vice versa. Female Brown-headed Cowbirds
Frequency (kilohertz)

Chickadee dialects exist that are very

different from typical Black-capped
Chickadee song. At the far western end
4.2

4.0
* Mil V614
respond differently to the different songs of males, and in that
way "instruct" males about which songs to sing to be especially
of Martha's Vineyard, at Gay Head (up- Swee - tie Hey successful in acquiring a mate (West and King 1996). Perhaps
per sonagram), males tend to sing each 3.8 the female chickadee, too, has certain inviolate standards for
song all on one frequency, with the am- her mate's song. Or do male singing contests in some way limit
plitude break in the first whistle rather 3.6
variation on mainland North America? Future work must, in
than the second(sweetie-hey). Birds sing
the song on two different frequencies, as 3.4 Swee - tie Hey some way, ask the chickadees to help answer these questions.
illustrated in the sonagram. At the east- The diverse patterns of geographic variation are puzzling,
3.2
ern end of the island, near Edgartown but some hints as to why songs vary in these ways are found in
(lower sonagram), males also sing each 0.0 0.5 1.0 1.5 2.0 2.5 3.0 certain warblers, and, perhaps surprisingly, the Black-capped
song all on one frequency, but have two
amplitude breaks in the first whistle, and 4.6
Chickadee again (Kroodsma 1996a). Among certain warbler
Martha's Vineyard East
one break in the second (swesweetie- groups, males have two categories of song forms (Kroodsma
sweetie). The first swe is not clearly vis- 4.4 1989; Spector 1992). One category seems to be used espe- Figure 7-48. Chestnut-sided Warbler: Like the
Frequency (kilohertz)

ible in the sonagram, existing as just a

4.2 cially with females. Examples include the beee-buzzzz of the Blue-winged Warbler, male Chestnut-sided
small blip on the first "note." It would be
easier to distinguish in an oscillogram.
4.0
1)\1414 oft Blue-winged Warbler (Fig. 7 47) (Track 45) and the pleased-
-

pleased-pleased-to-MEETCHA of the Chestnut-sided Warbler

Warblers have two different song categories.
The familiar p leased-pleased-p leased-to-meet-
Eastern birds, like western birds, sing Swe swee - tie Swee - tie cha songs, often termed the "accented-ending
the song at two different frequencies, 3.8 (Fig. 7 48) (Track 46). Sonagraphic analyses show that these
-
songs," are used in association with females,
but only the higher frequency song is song forms vary little over the entire geographic range of the and vary little throughout the bird's range. The
illustrated here. 3.6 so-called "unaccented ending song" is used at
species. The birds use a second category of song at dawn and
dawn and in highly aggressive situations, and oc-
3.4 in highly aggressive situations, when males are countersinging
curs in dialects. Migrating from the Neotropics
with one another, especially near territory boundaries. These to the northeastern United States and Canada,
3.2
songs occur in dialect patterns, with songs often changing over these birds breed in second-growth deciduous
0.0 0.5 1.0 1.5 2:0 2.5 3.0 short distances. woodlands and along forest edges. Photo by
Seconds Lang Elliott.

Cornell Laboratory of Ornithology Handbook of Bird Biology

7.62 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.63
FLORIDA MASSACHUSETTS neighborhood, he announces that he has a history in that neighborhood
Bird 26 Bird 28 Bird 29 Bird 31 Bird 32 Bird 33 and belongs there; others listening know he has survived in the local
29A a 31A 33A area long enough to be an acknowledged resident. By advertising ste-
111111111
ARRAtilli
reotyped signals familiar to all birds of their kind, on the other hand,
4

2
males hope to attract a female, regardless of her locality of origin.
29B
8
31B 32B 33B
The same patterns of familiarity are undoubtedly expressed in the
7171711k 1114114001 geographic distribution of songs of other species. The Eastern Towhee
■MEMILIM ■ li
2
provides a good example (Fig. 7 49). At the Archbold Biological Station
-

in Florida, the Eastern Towhee is believed to be a resident species. Males

31C

11111
probably stay on their territories throughouttheir lives and cometo know
111111111111111
each other well. These males use song repertoires that almost perfectly
2

0.5 sec match the songs of their neighbors. Furthermore, songs changeover only
1-4 33D
short distances, so males within small neighborhoods can match each
• 1411441L
other with their songs but cannot match males even from nearby areas. In
contrast, Eastern Towhees of the northeastern United States are migratory
26E
IA
and are on their territories only a few months each year. Consequently,
11M1
TIT 7 ITV these birds are undoubtedly less familiar with each other, and the songs
— 711/1,1.11 I.1
of neighboring males differ considerably. The tight vocal communities
0.5 sec of Florida are nowhere to be found. Residency and familiarity thus seem
b. Less Similar Song Types Among Migratory Towhees
to be correlated with the tight vocal communities of males who use the
a. Highly Similar Song Types Among Resident Towhees
same song repertoires (Ewert and Kroodsma 1994).

Figure 7-49. Song Sharing Among Mi- Among these warblers, it seems that a male attempting to attract
grant and Resident Eastern Towhees: a female succeeds best if he has a highly stereotyped signal that all Song Change Over Time
Within some songbird species with song
females can recognize. Females of many songbird species tend to Because song is learned, it has a high potential to change over
repertoires, as demonstrated here with
the Eastern Towhee, a greater degree of disperse farther than males, so an especially stereotyped male signal both space and time. Our examples have shown that song patterns in
song sharing occurs among populations will be unmistakably recognizable to all females, no matter where they space vary considerably from species to species, and even within spe-
that are resident than among breed- fledged. When males address other males on neighboring territories, cies. How signals change over time also varies considerably among
ing populations that are migratory. however, some advantage must accrue to having a local signal. Exactly species.
a. Sonagrams of Highly Similar Songs
how males sing just a few territories away might not matter, as long The most impressive long-term study of how bird song changes
of Neighboring Resident Males from
Corkscrew Swamp Sanctuary, Florida: as males remain on or return to their own territories year after year, as over time focused on the Indigo Bunting (Payne 1996) (Fig. 7 50). -

Five songs each are shown from Birds they often do. Throughout their entire geographic range, these buntings use about a
26, 28, and 29 (columns), although their The Black-capped Chickadee helps to solve this puzzle, too. Dur- hundred different song elements. Each male uses only about six of the
complete repertoires are slightly larger.
ing the breeding season, the whistled song seems to be used (in part) hundred to produce his song, however, and the combinations of those
Similar song types are compared in rows.
Song types A, B, and C are identical in to attract a mate; unpaired males, for example, sing their hey-sweetie elements vary locally, so small neighborhoods occur in which local
all three birds, and song types D and E all day long. After pairing, they use this song less often. Another, more males come to use the same combination of elements (see Fig. 7-31).
are shared between birds 28 and 29. complex vocalization, the gargle, is used in especially aggressive sit- How these dialects form, who copies whom, and how songs
Song types 26D and 26E are unique. b. uations. This call varies locally, from one population to the next. change over time are especially fascinating. Consider what you might
Sonagrams of Less Similar Song Types
of Neighboring Migratory Males from In the warblers and chickadee, then, the vocalization used in hear over a summer if you monitored a local bunting population. Bun-
Western Massachusetts: Complete song more aggressive contexts varies from place to place, in dialects. Far tings migrate, living during the North American winter in the southern
repertoires of each bird are shown, but more stereotyped over geographic space are the songs used when a United States and on islands in the Caribbean. Older male buntings,
only one pair of songs is identical: 328 male is unpaired and prospecting for a female. Because these two those two years and older, typically return to the same territories as
and 338. Terminal trills are identical Figure 7-50. Indigo Bunting: Breeding
songbird groups are in different evolutionary lineages, this pattern in previous years, and their songs usually do not change from year to
only in the following pairs of songs: along woodland edges and clearings,
31A and 32A; 328 and 338; 31C and must have evolved independently at least two times. Together, these year. When yearlings (birds hatched the previous year) return to breed,
and in old fields with young trees
33C. Adapted from Ewen and Kroodsma groups strongly support the idea that the variability of signals over however, their songs are initially unique, typically unlike the songs of throughout most of the eastern, central,
(1994). space relates to their function. any males from the previous year, including their fathers. During their and southwestern United States, these
These patterns of variation actually express patterns of familiarity first adult year, many of these yearlings change their songs to match Neotropical migrants have often been
the focus of bird song researchers. Of
or hoped-for familiarity among individuals. By singing local songs in those of the older birds in their immediate neighborhood. In this way,
particular interest is how their dialects
aggressive contexts, males identify the neighborhood of males in which small pockets of birds, all within earshot of one another, come to sing develop and change over time. Photo
they hope to have influence. If a male's songs match those of the local highly similar songs. by Lang Elliott.

Cornell Laboratorq of Ornitholom Handbook of Bird Biolom

7.64 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.65
Not all copies of bunting song are exactly like 11 Marsh Wren (Eastern) Figure 7-52. Sonagram of Eastern
the model, however. Perhaps an element is added, 10 Marsh Wren Song (Track 47, 8th Song):
From Stanton and Norfolk, Nebraska
or perhaps one is dropped. Thus, annual changes ac- 9
east to the Atlantic Ocean, Marsh

Frequency (kilohertz)
cumulate in a given song as it is copied from male to 8 Wrens typically start their songs with a
male. New songs also are introduced to a population 7 nasal buzz, then give a musical trill that
when yearling males keep their unique songs, as they sounds somewhat like a stick being run
6
sometimes do, or when older males from other loca- quickly along a picket fence. Although
5 each male may sing 50 or more different
tions immigrate into a population. All of these factors,
4 songs, each follows this basic pattern.
especially the new songs of immigrating males, con-
3
tribute to a rapid turnover of song forms within local 'I
populations. Each year, many songs are introduced 2
Buzz
and many songs are lost in a local population, and only 1

a few are copied and maintained from one year to the 00 0:2 0.4 0'6 0.8 1.0 12 14 1 .6 18
next. The net result of all these processes is that bun- Seconds
ting songs in a given neighborhood continually and
relatively rapidly evolve overtime. Almost a complete
turnover of songs occurs in a given neighborhood over
a period of 10 or so years. 11 - Marsh Wren (Western) Figure 7-53. Sonagram of Western
Songs of most species don't change at such a 10 . Marsh Wren Song (Track 48, 4th Song):
From Erikson, Nebraska west to the
rapid pace, however. Songs of the White-crowned 9
Pacific Coast, Marsh Wrens have loud,
Sparrows in certain California dialects have remained

Frequency (kilohertz)
8 raucous, buzzy, and coarse songs, often
highly stable over several decades. As more and more 7 ending with a raspy, noisy note. Unlike
species are studied, and as locations are revisited in the songs of eastern Marsh Wrens, they
6-
the future, we will better understand how and why do not begin with a faint buzz. Males may
5- sing more
ore than 150 different songs.
Figure 7-51. Marsh Wren: Breeding in songs change or don't change over time.
4-
cattail and bulrush marshes throughout
most of the northern United States and 3-
southern Canada, the small, brown Dialects Over Broad Regions 2
Marsh Wren looks much the same from
Distributions of non learned songs, such as those of flycatchers,
coast to coast. But song differences be-
tween eastern and western birds reveal provide good clues about evolutionary h istories and species relation- 00 0:2 0:4 0.6 08 1.0 1.2 1.4 1'6 1.8
two distinct subgroups that do not ap- ships, but the learned songs of songbirds also can provide information
Seconds
pear to interbreed. Males often perch about evolutionary history (Martens 1996). Several informative pat-
atop a cattail to deliver their bubbly,
terns of learned song occur in North America, and the Marsh Wren
squeaky songs. Photo by Marie Read.
provides a good example (Kroodsma 1983) (Fig. 7 51). Field guides
-

typically identify a single species of Marsh Wren, because the birds

look about the same from coast to coast, but careful listening reveals
two distinctly different Marsh Wrens in North America. Near Stanton reveals another major difference. The western males sing about three
and Norfolk, Nebraska, for example, males typically introduce their times as many songs as the easterners (roughly 150 versus 50). In south-
songs with a nasal buzz and then produce a relatively musical series central Saskatchewan, Canada, these eastern and western males occur
of repeated notes. From there to the Atlantic Ocean, that basic song in the same marshes along the Qu'Appel le River.
pattern is consistent; even though a male sings fifty or more different The simplest explanation for the origin of these regional differ-
song types, each type is of this basic formula (Fig. 7 52 &Tradc47). Just
-
ences lies in the distribution of habitats during periods of North Amer-
a few miles to the west of Stanton and Norfolk lies Erikson, and farther ican glaciation. When glaciers advanced, they must have isolated two
west the Valentine National Wildlife Refuge. B irds at those two loca- Marsh Wren populations, one in the west and the other in the east.
tions use songs very different from those of their eastern relatives. These Over thousands of years, the song differences we hear today developed
western songs are loud, raucous, buzzy, noisy, and coarse, and some in these two isolated populations. As the glaciers receded, the avail-
include loud, penetrating whistles modulated rapidly in frequency. able habitat increased, and the two populations then met in the central
Most striking is the tremendous diversity of songs. Never are songs Great Plains. Even though males of the two groups can learn each oth-
introduced by the faint buzzy note of the east, and often songs include ers' songs, as has been shown in the laboratory, in nature they tend to
or end with a raspy, noisy note (Fig. 7 53 & Track48). Further analysis
-
maintain their distinctiveness, and few hybrid singers occur.

Cornell Laboratort1 of OrnitholoBq Handbook of Bird Biologq

7.66 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.67
What happens at these zones of secondary contact depends on
how much each group has evolved during isolation (Rising 1983).
Sidebar 4: DO BIRDS THINK?
The two Marsh Wrens appear sufficiently distinctive that they breed Donald E. Kroodsma
primarily within their own groups, and future work may confirm that
Please Note: In this sidebar, I have used words like "mind," "think," "reason," "saying," or "choose."These are con-
we should recognize two species. The same pattern has occurred in troversial words and are avoided by some scientists who believe these words are too anthropomorphic—attributing
other taxon pairs, such as Eastern and Western meadowlarks, Eastern human abilities to animals. To be more objective, for example, some would argue that we should substitute the words
and Western kingbirds, Indigo and Lazuli buntings, Bullock's and "brain and behavior" for "mind." I respect those concerns, yet find it convenient to think anthropomorphically. We
Baltimore orioles, and Rose-breasted and Black-headed grosbeaks. often can reliably predict the behavior of animals when we attribute human abilities to them. An animal might behave,
Each of these eastern and western forms is currently recognized as for example, as if it had a mind that thought or reasoned carefully about the possible choices and their consequences,
a separate species; presumably the populations evolved sufficient and then chose an appropriate response. The danger lies in our accepting these descriptions as an explanation ofwhy
differences during isolation to prevent mating in most cases when the animal behaves the way it does, rather than just as a tool to help us predict how animals will behave.
they came back in contact. Current field guides lump the eastern and
western counterparts of the Northern Flicker into a single species, sug-
Just what goes on in the "minds" of reactions, and then choose an appro- behave. Before we can understand
gesting that the evolutionary changes were not as great for this bird. birds as they communicate with one priate response. The most impressive how their brains are functioning, we
Songs of the kingbirds and flickers are not believed to involve learning, another? When male Marsh Wrens example is Alex, an African Grey Par- need to describe more carefully just
and their songs would therefore reflect genetic differences among the hurl songs back and forth to one rot, who has been taught to use Eng- how birds interact with one another.
populations. Although songs of the songbirds (wrens, meadowlarks, another, or when warblers "choose" lish to communicate with his trainers; When Marsh Wrens countersing
buntings, orioles, grosbeaks, and towhees) are learned, the learned to use an appropriate song from their his ability to reason and think is truly with identical songs, for example,
traditions are sufficiently stable that they still reflect past evolutionary repertoire, are their minds simply act- impressive (see Ch. 6, Sidebar 1: Bird we need to know answers to a whole
history. As illustrated by the laboratory-reared Black-capped Chick- ing like programmed robots? When Brains). He can, for example, exam- series of questions. When does this
a female hears a male sing, do her ine an object and identify its color, matched countersinging occur?
adees who sang truly innovative songs and by the eastern or western
mind and body react in some prepro- shape, or material. Even more strik- What is the social relationship of
Marsh Wrens who learned songs of the other wren, these songs have a
grammed fashion? Do birds respond ing, he can survey a tray of objects the two (or more) males engaged in
strong potential for change.Yet some social forces, undoubtedly those
and counter-respond by using some and identify how they are all similar this behavior? Who leads and who
that involve individual attempts to manage one another, seem capable mechanical, turn-taking rules? Are (for example, color) or all different follows in these exchanges? How do
of conserving the learned qualities of songs over extraordinarily long these interactions just an example (for example, shape), but if asked these exchanges vary during the day
periods of time. of "stimulus and response"? I don't "What's similar," and all the objects or throughout the season? Does mat-
Other recently discovered examples occur in North America, think so. are different, he'll respond by saying ing status, age, relative dominance,
too, such as the Winter Wren (Kroodsma and Momose 1991). Males Scientists are becoming increas- "nothing." He thus also knows the ab- or how well the interactants know
of eastern North America have one to at most three different, relatively ingly interested in trying to under- sence of a quality, an ability that we each other affect how each male
complex songs. Males of western North America have even more stand how the minds of animals think of as an abstract concept. Alex participates? Those of us who study
work. This exciting new area of clearly begins to threaten some of birds are convinced that these wrens
complex songs and much larger repertoires. We don't know where
study in animal behavior is termed our unfounded notions about "bird- must weigh many of these factors and
the dividing line is between the two types or whether they interbreed,
"cognitive ethology." We know that, brains," and at the same time forces us then choose an appropriate way in
but they behave very differently, and future field guides will probably
physiologically at least, other animals to rethink just how different our own which to interact with singing neigh-
acknowledge these differences and identify them as two different function much like we do; our bod- abilities are from a parrot's. Parrots bors. But, as scientists, we realize that
species. ies all follow certain natural rules in are undoubtedly not unique among we must go to the field and collect
duplicating genes, processing foods, birds, and other birds must have some data on how the birds behave. Only
and the like. Perhaps, too, the brains of these same abi I ities. Ravens, for ex- when we have fully described these
The Functions of Song of other animals share many traits ample, seem remarkably intelligent
(Heinrich 1995). Once other birds
complex interactions will we begin
to understand how the wren's mind
■ Most investigations of the function of bird vocalizations have focused with our brains, and perhaps other
animals "think," too. We're con- have been taught to use English or sees the world.
on the loud "songs" of songbirds. These are the most extravagant and fident, of course, that our thinking another communication system that Consider one final example
noticeable sounds birds make, and it is no wonder that they have at- and logic are superior, both qualita- we can understand, perhaps we will based on research by Munn (1986).
tracted so much attention. Just how did such "songs" evolve, and what tively and quantitatively, and that no begin to grasp the differences both In Peruvian rain forests, flocks of birds
good are they, anyway? How are they used? What are their functions? other animals are as "self-aware" or among birds and between birds and move throughout both the understory
(Sidebar 4: Do Birds Think?) "self-conscious" as we are. The goal humans. Eventually, we also hope to and the canopy. The composition of
Two broad functions for bird song are generally accepted. One is of much current research is to identify improve our understanding of what each flock is highly predictable,
that songs help to defend a territory. If one plays a song of a Chipping just how different the minds of other birds are saying to each other during and consists of a dozen or so mated
animals are. their daily activities. pairs, each of a different species.
Sparrow from within a Chipping Sparrow territory, the local territorial
In certain situations, we know that As we ponder the mental powers Foraging behaviors differ among the
male responds aggressively. Males of many species go so far as to at-
birds act as if they can weigh mul- of birds, we begin to realize that we species within each flock, with the
(Continued on p. 7.69) tiple factors, think about possible need to know more about how they foraging habits of each mated pair

Cornell Laboratorq of Ornitholoei Handbook of Bird Bioloel

7.68 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.69

Figure 7-54. House Wren Attacking

Loudspeaker: Evidence that one func-
tion of bird song is to defend a territory
comes from playback experiments, in
which songs are broadcast from a loud-
speaker. If the song of a House Wren is
played within the territory of a House
Wren, for example, the male usually
will respond aggressively, and may even
attack the speaker.

tack the loudspeaker (Fig. 7 54). Even better evidence that songs help
-

to keep out other males has been derived from "speaker replacement"
experiments (Krebs et al. 1978). In these experiments, researchers re-
move a male from his territory and replace him with tape players and
a series of speakers. Playing songs from different speakers simulates
the presence of the territorial male. Intruders are more likely to invade
territories from which no song is broadcast, showing that song does
say "Keep Out" to other birds (Fig. 7 55).
-

Speaker replacement experiments remove the male from the ter-

ritory and leave the songs. In another twist to testing song function,
Figure A. White-winged Shrike-Tanager Gives a Deceptive Alarm Call to Gain a ForagingAdvantage: White-winged Shrike-Tan-
agers lead permanent mixed-species flocks in the rain forest canopy of the Peruvian Amazon Basin, maintaining flock cohesion the songs can be removed from the territory, leaving the males. This
by means of loud vocalizations throughout the day. The shrike-tanager obtains food by capturing insects flushed by the flock's entails temporarily muting a male by puncturing one of the air sacs in
movements. It also acts as flock sentinel, giving alarm calls at the approach of bird-eating hawks and thus warning its flockmates, his respiratory system. He then can't maintain enough pressure in his
which react by freezing in place or diving for cover. Ornithologist Charles A. Munn noticed that during aerial chases of insects
respiratory system to produce songs and typically loses his ability to
by one or more of the flock's members, the shrike-tanager sometimes joined in the pursuit and gave its predator alarm call—even
though no actual predator was present. He suggests that the shrike-tanager is "crying wolf," giving the alarm call deceptively to
defend his territory, so intruders are more likely to invade. Both types
distract the other birds and thus enhance its own chance of capturing the insect prize. Here, a White-winged Shrike-Tanager (left), of experiments show that song is crucial to defending a territory.
giving deceptive alarm calls, follows a Yellow-crested Tanager (right), which is distracted from chasing a large insect, while other Song, however, is not the only vocal keep-out signal that birds
members of the foraging flock react to the false alarm by taking cover. use. Birds of many species defend territories during the nonbreeding
season, and they typically use a simpler call to broadcast territorial
probably complementing those of others in the flock not been distracted that after these false alarms I have un- rights at these times. A male or female Northern Mockingbird on a
other pairs. One pair is of particular by the false alarm. contested access to some particularly
winter territory, for example, uses a loud "chuck" to announce its pres-
interest here—the "sentinel" spe- If we were the sentinel bird, we attractive prey item."
ence. A warbler on its winter territory in the Caribbean does not sing,
cies. Individuals of this species often might be thin king something like the Unfortunately, we do not know
but rather uses a simple call note to declare territorial rights.
perch in the open, sallying out to following: "The dangers from preda- exactly what transpires in the brain
capture prey items flushed by their tors are high, and my flockmates must of this sentinel individual. Nor do we The other major proposed function for bird song is to attract and
flockmates (Fig. A). These sentinels attend to my alarm calls. I'll be honest know what other birds are thinking as stimulate a female (Searcy andYasukawa 1996). Evidence for this func-
are so named because they are the most of the time, so that I remain cred- they use their vocalizations during tion, although largely circumstantial, is highly believable. Unpaired
first to spot predators, and an alarm ible, but on occasion I can 'fib'. My their daily activities. Given how dif- males of most species typically sing all day long, and paired males
by the sentinel alerts flock members false alarms will be relatively few, so I ficult it often is for us fellow humans sing far less often. If a paired male loses his female, he typically reverts
to impending danger. On occasion won't be found out. An inquiry might to understand each other, we may be to abundant singing. The amount of song coming from a male is thus
the sentinels seem to sound an alarm be made, but the jury won't be able to pessimistic about ever understanding a good indication of his pairing status. Experiments with European
when no predators are present. As a distinguish between slight incompe- the thoughts, feelings, or motives of
Starlings and European Pied Flycatchers have shown that nest boxes
result, others in the flock freeze or take tence, a trigger-happy alarm tendency these birds. Therein, however, lies
from which male songs are played attract females. Curiously, the same
cover, allowing the sentinel to sally that simply fires falsely on occasion, the challenge for those of us intrigued
forth and capture a prey item that
songs attracted male starlings and male flycatchers, so the situation is
or a true intent on my part to deceive. with how the minds of our feathered
might have been hotly contested had It's just a coincidence, I would insist, friends work. ■ a little more complex than it initially seems!

Cornell Laboratorq of OrnitholoBq Handbook of Bird Biologq

7.70 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.71
In the laboratory, too, females that have been tested typically pre- territory for several species (Searcy and Yasukawa 1 996). Males with
fer songs of their own species. The response used to assay a song is the extra food have been more persistent singers, and in some species the
"precopulatory display," a tail-up display by the female that initiates more persistent singers attract the first females in the population. A
mating (Fig. 7-56). In these experiments, females typically display female could use the amount of song to judge a male's abil-
more to songs of their own species than to songs of other species, fur- ity to obtain a good territory, or perhaps to indirectly
ther implicating a mate-stimulation function for song. judge the quality of the territory, which might be im-
All these birds might be reading far more subtle cues than simple portant as a food supply for herself and her young.
presence or absence of the song, however. The amount of song from Pause briefly now and think about all of the infor-
a territory, for example, could indicate the relative health of a male. A mation available in the singing of a typical songbird in
territory rich in food can supply its owner with energy more quickly North America. A single song identifies the species and (for
than a poorer territory, so a male on a good territory can sing more. By the vast majority of species) the sex. For songs thatvary geo-
experimentally supplementing the territory's food, researchers have graphically, the song also identifies the regional location of
documented the relationship between amount of song and quality of the singer. Birds typically don't sing during the nonbreeding
season, so a singer is in reproductive condition, on territory,
and available for mating(with either his social partner or any interested Figure 7-56. Precopulatory Display of
Pairs in Experimental Area
female). At any instant, a listener can probably judge the distance of Female Song Sparrow: To initiate cop-
Territories Occupied Removed and Replaced Territories Occupied
ulation, many female songbirds give a
Experimental Design Before Removal of Pairs with Loudspeakers After Removal of Pairs the singer, not so much by the loudness but by the degeneration of
"precopulatory display" with the tail up
sound quality over distance. The relative amount that he sings may and the wings down or outand quivering.
reveal the quality of his territory, because it takes less time to eat on a In the lab, females will give the display
good territory, which leaves more time to sing. His general health can in response to song alone, and they dis-
be revealed not only by the amount he sings, but perhaps also by the play more to songs of their own species
E than to songs of other species—a good
CU
size of his song repertoire or by the consistency with which he delivers
indication that one function of song is to
his complex songs. If he sings all day long, he reveals his mating sta- attract and stimulate a mate.
tus: he's probably a bachelor, or if he already has a mate, he's ready
8 Hours After
for another (for example, Marsh Wrens are polygynous, with males
Removal
often having harems of females). If he is of a species that uses different
songs in different contexts (for example, a Chestnut-sided Warbler),
he immediately reveals his mood, because he uses different songs
Control in love and war. His repertoire size may also impart information to a
Sound careful listener. In some species, such as Song Sparrows and GreatTits,
Control
Control repertoire size seems to predict longevity fairly well. If he's a Northern
Silent
ilen
Mockingbird or another species in which birds add to their repertoires
in successive years, he reveals his age. Finally, if a male's songs match
Experi-
those of his local neighborhood, he reveals that he probably has lived
mental
10 Hours After in the neighborhood long enough to establish his local identity.
Removal A singer tries to manage others of his species, and the others try
in turn to manage him, all for selfish gain; over evolutionary time, ploy
Figure 7-55. Speaker Replacement Experiments: These experi- Eight hours later, new males had moved into the five territories and counterploy have led to a communication system that reveals
ments with GreatTits (chickadee relatives common in temperate in the control areas, but not into the experimental areas. In
an extraordinary amount to those who are ready to listen. Birds, of
zone woodlands of the Old World) were done to demonstrate Experiment 2, conducted a month later, a similar procedure
that song alone, even without the presence of the territorial pair, was followed, but the areas receiving control and experimental
course, are primed to hear all of this information in songs and calls,
keeps intruding birds out of a territory. The experiments were treatments were changed. Ten hours after birds were removed, and to act accordingly. Birds rely far more heavily on their ears than
conducted near Oxford, England in early spring, a time when four males had moved in, leaving the experimental area empty we do (even though, surprisingly, laboratory tests show that our ears
males are prospecting for new territories. in Experiment 1, the except for one small portion at the extreme edge. In both experi- are sufficient to hear most of the same details that the birds hear), and
eight territorial pairs in the study area were captured on one ments, the experimental areas were eventually invaded by new
birds must be prepared, at any instant, to interpret correctly a sound
morning. Three territories (those in the "experimental" area) males, but not for about two and a half days. Both experiments
each were occupied by four loudspeakers broadcasting the clearly demonstrate that Great Tit song functions to defend a ter- that warns of a life-threatening emergency or predicts an unexpected
songs of the former residents all day, in a pattern resembling ritory. Over the longer term, however, intruding birds were able opportunity, perhaps for mating. Those who listen and hear succeed
natural singing. Two territories (those in the "control sound" to learn that the loudspeaker was not a real bird, and that the reproductively over evolutionary time, so the survivors we listen to
area) were occupied with loudspeakers broadcasting a sound experimental territories were not actually occupied. Adapted
today are the summa-cum-laude graduates in the fine art of listening
similar to Great Tit song, but played on a tin whistle. The other from Krebs (1976).
three territories (in the "control silent" area) were left empty. (Sidebar 5: "Call Notes" and Their Functions).
(Continued on p. 7.75)

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7.72 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.73

Sidebar 5: "CALL NOTES" AND THEIR FUNCTIONS

Donald E. Kroodsma
Birds use a tremendous diversity of Waxwings appear to be nonterrito- those variants seem to be correlated ent sounds are broadly classified as
vocalizations. But, of course, they rial throughout the year; they nest in with particular contexts. Some vari- "alarm and distress calls"; some of
don't classify all of their vocal- loose clusters and forage together at ants are given during flocking, some these calls seem to be used in spe-
izations into the two categories of fruit crops when away from the nest. when the male and female are nest cific contexts, such as when hawks
"songs" and "calls," as we so often Waxwings thus have no need to building, some during courtship are near, but the so-called "hawk
do, so let's explore exactly what birds broadcast ownership of a territory, feeding, some by nestlings, and so alarm call" also is given to raccoons!
do a little more closely. because defending the feeding ter- on (Howell 1973). Waxwings un- Both males and females use "feeding
Perhaps it's most useful to start ritory at rich, ephemeral food sup- doubtedly use the subtleties of these calls" when feeding the young, as
with the idea that birds use sounds plies would not be economical (see vocalizations to communicate with well as "courtship calls." Males also
to manage other individuals for self- Ch. 6, Sidebar 4: Living in Groups). each other in ways that we have not give "flight calls" when leaving the
ish gain. For almost all passerine But don't males need to "sing" to yet even imagined. territory, or just before flying.
species and many nonpasserines, impress their mates? Apparently not. Especially intriguing, !think, are a
too, one particular sound seems to Intriguingly, the waxy red tips of the Red winged Blackbirds
- variety of calls that males use as they
stand out. That sound is loud and secondary feathers on the wing may Our knowledge of vocalizations perch on their territories (Beletsky et
often repeated persistently from a be an index of a bird's age or health and their functions in other species al. 1986). Investigators have estab-
prominent post. The vocalization (Fig.A) and it is possible thatthe birds is equally rudimentary. Consider the lished seven broad categories of
can be rather simple, as in a Black- assess and try to impress one another Red-winged Blackbird, for example these sounds: check, chuck, chick,
capped Chickadee, or the number with the quality of their "waxwings" (see Fig. 7-62). The male clearly has chonk, chink, peet, and cheer.
of different building blocks within (Mountjoy and Robertson 1988). a set of "songs," loud vocalizations Neighboring males tend to use the
the vocalization can number in the The "wax" on the wings may be the that he broadcasts, apparently in an same call, such as the check, but
thousands, as in a Brown Thrasher. functional equivalent of intersexual attempt to defend his territory and at- then they all seem to switch to an-
For temperate zone birds, it's usu- aspects of "song" in other species, tract mates. Like a typical songbird, other call, and eventually another.
ally the male who "broadcasts" this and as a feature of waxwing plumage he learns those songs from other male Waves of call usage spread through-
vocalization, but in more tropical evolved to take on that function, the blackbirds (Marler et al. 1972). Fe- out the marsh, like shock waves
areas, where females and males song may have been lost. That's only males have some loud vocalizations, spreading out from an epicenter,
remain paired year round, females a guess, but this line of thinking is too. One is the chit, which is often de- and anyone patiently sitting and
often broadcast, too. It thus seems instructive, I think, because itfocuses livered immediately after the male's listening beside a red-wing marsh
that most species have a "need" for on how individuals of a particular song, so that the two vocalizations will hear these events. But what are
this particular vocalization, which species evolve to manage others, and overlap; this "duet" between males the males doing? Do any of the dif-
seems to be to announce ownership it considers the management game and females is frequently heard in ferent sounds that we hear convey a
of a particular territory or mate, or in the context of all of the other attri- marshes throughout North America special meaning about a particular
to try to attract (or maybe impress or butes of that particular species, such (see Fig. 7-63 and Track 62). The circumstance within the marsh? Or
stimulate) a mate. We label this par- as plumage. Because no two species chit seems to encourage the male to perhaps the vocalization itself has
ticular vocalization a "song." are alike, we don't expect them to guard the female's nest against pre- Figure A. Cedar Waxwing: One songbird without a song is the Cedar Waxwing. These no special significance, but rather it
nonterritorial birds nest in loose clusters, feed together on fruit-bearing plants that are is the changing from one vocaliza-
have the same sets of tools to manage dation and to discourage him from
often in large clumps, and may use the quality or number of their waxy red wing tips (see
Cedar Waxwings one another, either. harassing her (Beletsky and Orians tion to the next that has particular
inset) to impress potential mates. Because song was not needed to defend a breeding or
But, itseems that not all songbirds If Cedar Waxwings don't sing, 1985). The female has a second loud meaning. Perhaps by simply switch-
foraging territory, or to attract a mate, it may have been lost through natural selection.
sing. Apparently some species don't what do they do? Their sounds have vocalization, the teer, but this one is Photo courtesy of John Dunning/CLO. Inset photo courtesy of E. J. Fisk/CLO.
ing from one vocalization to another
need a loud, complex vocalization been broadly classified into two apparently used in aggressive con- the males can monitor changing
that is broadcast far and wide. The categories, the bzeee call and the texts with other females (Beletsky a female's forebrain; perhaps her less interesting becomes the question conditions within the marsh, such
Cedar Waxwing, for example, has seee cal I. The difference in these two 1983) (Track 51). These two loud vo- non learned vocalizations originate of whether a particular vocalization as approaches by a predator.
no recognizable "song," at least as sounds can be heard easily, because calizations apparently do not need from some more primitive part of her is a song or a call.
we have come to know song in many the bzeee has a buzzy or rattl ingqual- to be learned from other females, brain, as do simpler vocalizations Red-winged Blackbirds use a American Goldfinches
other species (Howell 1973; Witmer ity, and the seee is a high-pitched, because they develop normally in (that is, "calls") in some other spe- tremendous variety of other vocal- Vocalizations of another common
et al. 1997). Given that most other hissy whistle (Track 49 [bzeee];Track females who are isolated from other cies. Notice that we can probably izations, too, as summarized byYas- bird, the American Goldfinch, illus-
songbirds have "songs," it seems 50 (seee]). Careful analysis reveals, female vocalizations during and after gain a better understanding of the ukawa and Searcy (1995). "Contact trate how different one species can
likely that waxwings evolved from however, that the birds use a great the nestling stage (Armstrong 1994). female vocabulary without labeling calls" are given repeatedly by males be from another. Perhaps the most
an ancestor with a typical song, diversity of subtle variants (too sub- If these sounds are not learned, per- those vocalizations as either "calls" on a territory or by both sexes as distinctive sound from goldfinches
but that the waxwings simply lost tle to be distinguished by the human haps they are not even controlled or "songs." In fact, the more we un- they forage. "Threat calls" are given (and other members of this cardue-
that song over evolutionary time. ear), especially of the bzeeecal I, and by the "song control centers" in derstand how sounds are used, the in aggressive contexts. Many differ- I ine subfamily, including siskins and

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

7.74 Donald E. Kroodsma Chapter 7—Vocal Behavior 7.75

Dawn Chorus
Some of the most remark-
able singing occurs at dawn, es-
pecially in temperate zones (Sta-
icer et al. 1996). Most birds are si-
lent the entire night, presumably
roosting quietly somewhere on
their territory. But beginning an
hour or so before sunrise, males
begin their dawn chorus. Each
species chimes in at a slightly dif-
ferent light level, often beginning
Figure B. American Goldfinch Contact Call:American Goldfinches give their contact call, a sweet, twitteryper-ch i k o ree, during
- - with American Robins, and other
the rising, rapid wingbeat portion of their undulating flight. When a male and female form a pair bond, each changes its contact species join in a rather regular se-
call to match that of its mate, probably allowing them to distinguish their partners even in a large flock of goldfinches.
quence. The quantity and often
the quality of singing during this
redpolls) is what has been labeled songbird. Each male phoebe loudly together, because they seem to time differ markedly from singing
their "contact call." We typical ly hear proclaims his territory and presumed sound alike and, on the sonagrams, during the rest of the day (Track 53, Track 54). Figure 7-57. Chipping Sparrow: Like
this vocalization as goldfinches fly interest in mating with two different look alike. Determining which of many other birds, the Chipping Spar-
Species vary considerably in how they behave at dawn. Dur-
overhead in their characteristic un- "song" forms, the phoe be and the
- these two possibilities is true awaits row sings with more energy at dawn
ing daytime singing, an Eastern Towhee sings one song form (say, A)
dulating flight pattern, the per chik-
- phoe bree (see Sidebar 6, Fig. A; and
- further study. than at other times of the day. At dawn,
o ree contact call occurring during
- Track 69), neither of which is learned,
over and over, and then introduces another (say, B), then another, and a male often sings short bursts of song
the rapid wing beats rather than the but male and female phoebes use a perhaps another, until he has delivered his entire repertoire of three from the ground, quite a contrast from
The vocabularies of birds are
brief, wings-folded descent (Fig. B) variety of other sounds, too. The truly rich. In studies of bird sounds, to eight song types over a period of an hour or so. His singing pattern the much longer trills delivered later
(Track 52). A paired male and female most common sound is described by might be illustrated as AAAA . . . BBBB . . . CCCC . . . and so on. The in the day from high in a tree. Photo by
researchers have been initially at-
Lang Elliott.
change their contact calls to match Smith as a "clear, sweet, weak chip," tracted to study those loud vocal- pattern is one of "eventual variety," in which a male repeats one song
one another, and this social learning or simply a tp, and it is given in a va- izations produced so persistently type many times before "eventually" proceeding to the next type. At
from one's mate undoubtedly enables riety of contexts. It typically is used ("songs"), and most of the literature dawn, however, the towhee sings with "immediate variety," perhaps
a bird to identify its partner, even in in aggressive encounters, but it also on birds sounds is therefore about delivering all of his song types in 20 to 30 seconds: ABCABCDEDE.
a large flock of birds. Adult cardu- is used by lone birds, such as when these "songs." But birds clearly use The singing is far more energized and dramatic than it is during the
eline finches can relearn these calls foraging during migration or even on a variety of other sounds, too. When daytime.
throughout life, apparently as social the nonbreeding grounds. If a preda- studying these "call repertoires,"
partners change. When at least sev- tor is encountered near the nest, this
Chipping Sparrows also sing differently at dawn (Fig. 7 57). A
-
our initial approach has been to
en years old, for example, one cap- call becomes more emphatic. The typical daytime song is about two seconds long, and consists of per-
lump similar sounds into a given
tive adult male Pine Siskin learned same vocalization seems to serve category, thereby hoping to see haps 20 repetitions of a single song element. The male pauses 10 or so
the flight call of its new cage-mate, a variety of purposes, and thus the some order in how birds commu- seconds between successive songs (Track 55). While singing, the male
a female Eurasian Siskin. This form actual meaning of the vocalization nicate. We thus identify "begging typically sits on an exposed perch high in a tree. At dawn, however, a
of lifelong call learning from social may depend on the circumstance in calls" or "alarm and distress calls" male often sits on the ground near a male from a neighboring territory
partners probably occurs throughout which it is used (Smith 1969). Alter- or "contact cal Is." As we explore the and delivers bursts of song as if they were shot from a machine gun. He
the cardueline subfamily. natively, of course, the birds may be details of these vocalizations within sings two or three elements of the song, pauses briefly, sings another
more attentive to the details in this and among categories, however, I burst followed by a pause, and so on (Track 56). As with the towhee,
Eastern Phoebes chip call than we are. Perhaps they am convinced that we will be flab-
The vocalizations of the Eastern
the vocal display seems highly energized, even frenetic.
produce and detect subtle differ- bergasted at the richness of the mes-
Phoebe (see Smith 1969) provide a ences in these calls, and those subtle
Other species use entirely different songs at dawn than during the
sages that are communicated and at
final example illustrating the diver- differences have meanings to which day. Certain warblers that have two song categories use their aggressive
the richness of the details to which
sity of vocal behaviors among pas- we are not privy. In a crude first as- birds are attentive. ■ songs for the first 30 to 60 minutes of the morning, after which they
serines. The phoebe is a flycatcher sessment, researchers have lumped lapse into a slower-paced delivery of their other song. A male Yellow
and therefore a suboscine, not a all of these different vocalizations Warbler uses about 12 songs delivered with immediate variety during'
his dawn chorus, and after half an hour or so he switches to his single
daytime song type. The male reverts to songs of his aggressive dozen
during daytime encounters with other males, too, but the singing is
never as energized as at dawn. American Redstarts behave similarly,

Cornell Laboratorq of Ornithologq Handbook of Bird Biolo9q

7.76 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.77
although songs of their aggressive repertoire more typically number
only three or four. Some flycatchers, too, such as the Eastern Wood-
Pewee (Fig. 7 58), use qualitatively different songs at dawn (Craig
-

1943) (Track 57; Tradc 58).

The drama at dawn is truly extraordinary, as if so much pent-up
energy is unleashed. But why? Why such a burst of energy at dawn,
and again, why does that energy reveal itself in such diverse ways?
Researchers have proposed many ideas for why dawn singing is
so dramatic (Staicer et al. 1996). Perhaps males sing at dawn because
that is the best time to attract females, especially those who have
migrated and arrived overnight. Conditions at dawn are often calm,
too, so song at that time carries the maximum distance. Furthermore,
during the dawn chorus conditions are often too dark to forage, so
singing then is an efficient use of time. Or perhaps singing at dawn is
especially important for territory defense; dawn follows the longest
period of inactivity, and predation occurs at night, too, so dawn might
be an important time for a bird to proclaim "I am still alive" and "This
territory is still mine."
Figure 7-58. Eastern Wood-Pewee: The energized displays and often dramatic interactions, such
Breeding in woodlands throughout the as those of Chipping Sparrows, suggest that during the dawn chorus
eastern United States, the Eastern Wood-
is when patterns of social dominance are established and daily re-
Pewee gives its plaintive, slurred-whistle
song differently at dawn than later in the confirmed. Little is known about dominance patterns among males
day. At dawn, the singing rate is faster, on adjacent territories, but females may attend to such displays and
and an extra song type, the ah di dee,
- -
make mating decisions, both intrapair (between mates) and extrapair
may be added to the daytime pee ah- -
(with a bird other than the mate), based on male singing exchanges.
wee and wee ur songs. Photo by Lang
-

Elliott.
So many extrapair fertilizations take place in some species, such as the
Indigo Bunting and Red-winged Blackbird, that any kind of ritualized
display that establishes male hierarchies and broadcasts information
about them would benefit listening females. A female Black-capped
Chickadee, for example, will mate with males other than her social
partner, and her extrapair gambit tends to be with a male higher in
the dominance hierarchy than her own mate (S. M. Smith 1988). She
could base her decision on her knowledge of dominance hierarchies
established during the winter flocks, but that knowledge is probably
reinforced by information she gleans from the dawn performances of
males in the population. For many species, perhaps singing at dawn
is a formal way to establish and monitor social relationships and hier-
archies, giving individuals in complex societies the information they
need to make wise decisions.
The dawn chorus probably serves multiple purposes, with the
emphases undoubtedly varying from species to species, just as social
environments and management differ among species. Our failure to
understand the full implications of the dawn chorus, however, in no
way diminishes the drama played out each morning in these extraor-
Figure 7-59. Dawn Chorus: At dawn, the woods, fields, and marshes come alive with song, as every male bird seems to be
dinary singing displays (Fig. 7 59).
-

proclaiming his territory and existence anew. Although many hypotheses exist to explain why birds sing so much and with such
energy and variability at dawn, the phenomenon remains poorly understood—one of the many mysteries surrounding why birds
sing as they do.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

7.78 Donald E. Kroodsma Chapter 7—Vocal Behavior 7.79
butions are equally complex, exchanges are highly coordinated and
precise, and both sexes participate frequently (Fig. 7 61 & Track -

Carolina Wren Duet

60).
Surveys show that most duetting species live in the tropics. Trop-
ical duetting species include certain types of parrots, woodpeckers,
antbirds, flycatchers, shrikes, and wrens, among others. Males and
females of many tropical species maintain prolonged monogamous
pair bonds and live year round on a given territory. Both males and
Tea - ket - tle Tea - ket - tle Tea - ket - tle Tea ket- females thus have a considerable year-round investment in two re-
• sources, the mate and the territory. Loss of either resource reduces the
40.
14- chance of surviving and breeding, so it isn't surprising that a female
would vocally announce her presence and intentions as consistently
0.0 0:5 1.0 1 5 20 2.5
Seconds . and persistently as her mate.
In temperate zones, pair bonds are often markedly different
Figure 7-60. Sonagram of Carolina
Wren Duet (Track 59, 6th Song): The
Duetting (Morton 1996). In many migratory species, males typically arrive on
territory a week or so before females.The male sings to establish the ter-
loud, rollingteakettle-teakettle-teakettle A mated male and female communicate frequently, and many
of the male Carolina Wren is a familiar species do so vocally. In some species these exchanges are simply ritory and attract a female, and once the female arrives she specializes
sound in woodlands throughout most in egg laying and raising the family. The season is short, and within a
overlapping bouts of calling, but in others they are antiphonal—that
of the eastern and midwestern United few weeks the male and female separate and migrate to nonbreeding
States. Each male may sing 25 or more
is, the male and female rapidly alternate their contributions—and are
quarters agai n. The many temperate zone females who solicit matings
different song types, but each consists highly coordinated. These "duets" of different species differ in a num-
from males who are not their mates don't have the major investment
of a syllable with approximately three ber of ways, including the nature of the overlap between male and
in either the territory or the mate that tropical females do. Accordingly, Figure 7-61. Sonagram of Bay Wren
parts (tea-ket-tle), usually repeated three female (from synchrony to antiphony), how often mates join in duets, Duet (Track 60, 1st Song): The Bay
or four times. Once in a while, the female
how precisely the vocal exchanges are timed, and the relative quality temperate zone females duet and sing less, and manage their social
Wren, like most duetting species, lives
may add a coarse rattle to the end of the environment in other ways.
and complexity of the male and female sounds (Farabaugh 1982). in the tropics. Residents of rain forests
male's song, creating a simple "duet."
Wrens of the genus Thryothorus provide three good examples of One of the most conspicuous examples of duetting that does from Nicaragua to Ecuador, the male
occur in North America involves the Red-winged Blackbird, which and female sing complex duets so well
the range of vocal duets. The duet of the Carolina Wren, a common coordinated and intertwined that their
songbird of the eastern United States, is perhaps the least impressive nests in marshes throughout the continent (Fig. 7 62). Males and fe-
-

respective contributions to the song are

(although we can be confident that it works well for the wrens them- males perform a duet similar in complexity to that of the Carolina nearly impossible to distinguish without
Wren. In this blackbird, males sing their konk-a-ree song over and careful study.
selves). Male Carolina Wrens sing a loud, resounding teakettle-tea-
kettle-teakettle, each song consisting of a complex syllable (teakettle)
repeated several times. On occasion, the female appends to this song
9- Bay Wren Duet
a coarse rattle or churr—unmistakably the female Carolina Wren an-
nouncing her relationship with her mate (Fig. 7 60 &Track 59). The
-

quality of male and female utterances differs markedly, females are

8 d1 00
only occasional participants, and the timing of the male and female 7
contributions does not appear to be well coordinated.
The female's performance is more male-like in Rufous-and-white 6-

Frequency (kilohertz)
Wrens from Central America. Male and female songs, each a series of
pure whistles, appear to be equally complex. In this wren, the female's 5
song is slightly higher in frequency than the song of her mate. The
two birds may deliver their songs separately or simultaneously, but 4- t
if they are delivered together, they simply overlap and are not highly r
3
coordinated.
Most extraordinary are the complex, highly coordinated duets
2- 11!
some species sing. So coordinated are these singing efforts that the
male and female contributions are impossible to differentiate unless
1-
the birds are a considerable distance apart. Among the Thryothorus
wrens, the Buff-breasted Wren, Bay Wren, Riverside Wren, and Plain
Wren sing duets of this sort. In these duets, male and female contri- 0 2 3 4 5 6
Seconds

Cornell Laboratorq of Ornithologq Handbook of Bird Biologg

7- 80 Donald E. Kroodsma Chapter 7—Vocal Behavior 7.81

Red-winged Blackbird Duet No.

• 11211,

Frequency (kilohertz)
6 cc
5

0 0 0. 2 0.4 0.6 0.8 1.0 1.2 1.4

Choice: Extrapair Copulations in Birds). Who mates with whom among Figure 7-63. Sonagram of Red-winged
these duetting species, how long the pair remains together, how stable Blackbird Duet (Track 62, 1st Song):
/./
In the simple duet of the Red-winged
local territories are, and other life history characteristics might all af-
Blackbird, the female produces a loud
fect male and female vocal interactions. Future research mustfocus on series of notes during the last half of the
correlations between the types of duets and features of life histories, male's raspy konk-a-ree song. In this
but as yet the necessary studies simply haven't been done. sonagram, the dashed lines denote the
approximate area in which the male's
song is overlapped by the female's; the
exact end of the male's song is difficult
to distinguish, because it is obscured by
One fascinati ng consequence of song learning is mimicry (Baylis the female's song.
1982). Some species learn not only their own songs but the songs of
other species. In North America, the Northern Mockingbird is perhaps
the best example; males sing up to 200 different songs, and a consid-
98
erable number are clearly derived from other species such as Wood
Figure 7-62. Female and Male Red- Thrushes, Northern Cardinals, Eastern Phoebes, and Blue Jays (Fig.
winged Blackbird Duetting: Common 7 64a & Track 63; Tracks 64-65; Fig. 7 64b & Track 66; Track 67).
- -

breeders in fields and marshes through- over, eventually switching to another song form. Each male has four Renowned mimics occur on other continents, too; the lyrebirds in Aus-
out North America, male and female
to six different konk-a-ree songs, and a careful listener can hear when tralia are remarkable, as is the Lawrence's Thrush of South America.
Red-winged Blackbirds sometimes per-
form a simple duet. the male switches from one song form to the next (Track 61). Males Species nottypically thought of as mimics also occasionally learn
are frequently polygynous, with more than one female nesting on the the vocalizations of other species. Blue Jays imitate the calls of Red-
territory. Females often respond to male songs, producing a loud series tailed, Red-shouldered, and Broad-winged hawks, for example. Eu-
of notes during the last half of the male song (Fig. 7 63 & Track 62). If
- ropean Starlings, closely related to mockingbirds, are excellent mim-
you visit any marsh with blackbirds and listen to the male's songs, you ics. Occasional examples of mimicry in other species are especially
JI
can identify how often he changes from one konk-a-ree song type to intriguing because they show birds' remarkable flexibility and also the
another, and also listen to the patterns of response by the female. risks of song learning. Well-documented examples include a Vesper
We don't know why males and females interactwith each other in Sparrow and House Wrens singing songs of the Bewick's Wren, and an
exactly the ways they do. We are still learning much about male-female Indigo Bunting and a Common Yel lowthroat singing a Chestnut-sided
relations; only within the last 10 years, for example, have researchers Warbler song. It seems that a fairly large number of these occasional
discovered that a female doesn't always mate with her social partner, mimics are unpaired, suggesting that males who learn the wrong songs
and often seeks copulations outside the pair bond (see Ch. 6, Mate often fail to pass their genes to the next generation. Selection against

Cornell Laboratorq of Ornitholojcj Handbook of Bird Bioloffi

7.82 Donald E. Kroodsma
r Chapter 7 —Vocal Behavior 7.83
a extensive repertoire of African sounds on the nonbreeding grounds
Northern Cardinal
during the European winter. The warbler then uses his enhanced rep-
ertoire on his European breeding grounds.
Two especially fascinating examples of mimicry suggest very
,

specific functions. Indigobirds of Africa are brood parasites that lay

their eggs in the nests of firefinches (Payne 1973) (Fig. 7 65a). Each
-

0.0 0.5 10 15 20 25 3.0 3.5 indigobird species lays its eggs in the nest of one firefinch species, and
the firefinch raises the indigobird young. The young of the indigobird
Northern Mockingbird Mimicking Northern Cardinal have converged in appearance and begging calls on the young of the
•
firefinch, so the firefinch cannot identify the intruders and throw them
6
out of its nest (Fig. 7 65b). Young male indigobirds also mimic the
-

songs of their hosts. Young females undoubtedly imprint on the songs

of their host species, too, so male and female indigobirds can use a

0:5 1.0 1.5 2:0 2:5 3:0 3.5 4.0

a. Adults Figure 7-65. Fire finch (Host) and In-
Seconds HOST PARASITE digobird (Brood Parasite) Adults and
b Killdeer Gaping Nestlings: The indigobirds of
Africa parasitize the nests of firefinches;
r each indigobird species lays its eggs in
ft the nest of one particular species of fire-
finch, and the firefinch raises the young.

•
a. Adult Red-billed Firefinch and its
Host, the Village Indigobird: Although
1.0 1.5 the adults look fairly different, the eggs
and young as well as the songs of the
two species are very similar. The same is
Northern Mockingbird Mimicking Killdeer
true for other indigobird-firefinch pairs.
Red-billed Firefinch Village Indigobird b. Gaping Nestling Indigobird and Fire-
(Lagonosticta senegala) (Vidua chalybeata) finch Pairs: The colors and patterns on
the gape of each nestling indigobird spe-
cies have evolved over ti me to closely re-
semble those of their host species. Here,
b. Nestlings note the similarity between the nestling
0.0 0'5 1.0 1.5 2.0 Village Indigobird and its host, the
Seconds
Red-billed Firefinch; and between the
nestling Purple Indigobird and its host,

•
Figure 7-64. Sonagrams of Northern birds who learn the wrong songs may thus be very strong, so "mistakes" the Jameson's Firefinch. Firefinch photo
Mockingbird and Model Songs: North- are not perpetuated. by C. H. GreenewalVVIREO. Indigobird
ern Mockingbirds may sing up to 200
different songs, many of them learned
by mimicking the songs of other species.
Their ability to mimic is so good that not
Researchers have proposed a number of hypotheses on why birds
mimic. An occasional bird may mimic because it has been deprived
of hearing songs of its own species, a condition that can be readily
• photo courtesy of Dr. Robert B. Payne.
Drawing adapted from Payne (1973).

only do the copied songs sound very simulated in the laboratory. More interesting, however, are persistent
authentic to our ears, but sonagrams of Red-billed Firefinch—Host Village Indigobird—Parasite
mimics such as the Northern Mockingbird. Mockingbirds are highly
the mimicked songs closely resemble (Lagonosticta senegala) (Vidua chalybeata)
those of their models. One can read- aggressive, and they possibly may use other species' songs to threaten
ily distinguish mockingbird songs from them and so keep territories more to themselves. For example, if a
their models, however, by listening to Northern Cardinal hears the resident mockingbird utter a cardinal
the pattern of singing: the mockingbird
song, does he notice? Is he reminded of aggressive interactions, per-
rapidly repeats each song a few times
(usually four or more), then moves right
haps back at the winter feeder, or of a confrontation just the day before,
on to another song type. a. Northern all of which might shift the cardinal's use of his territory? Or perhaps
Cardinal (Track 63, 1st N. Cardinal the cardinal is oblivious to the mockingbird's crude renditions of his
Song, 1st N. Mockingbird Song): The songs. Th is possibility has never been thoroughly investigated. Perhaps
breaker, breaker, breaker cardinal song. Yellow
learning the songs of other species is simply an easy way to develop a
b. Killdeer (Not Made from Track 66, but Jameson's Firefinch—Host Purple Indigobird—Parasite
large repertoire of diverse sounds, which might be used to impress a Pink
Similar to 1st and 2nd Killdeer Songs; (Lagonosticta rhodopareia (Vidua purpurascens)
1st and 2nd N. Mockingbird Songs). female. This idea is supported by the Marsh Warbler, which learns an jamesoni) Blue-black

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

7.84 Donald E. Kroodsma Chapter 7—Vocal Behavior 7.85
particular firefinch song to find one another and mate. This complex Figure 7-67. Ruby-throated Hum-
set of adaptations, involving mimicry not only of songs but of nestlings mingbird Dive Display: Used in both
and their begging calls, occurs throughout the group of indigobirds territorial defense and courtship, the
Ruby-throated Hummingbird Dive
and firefinches.
display combines a stereotyped flight
The second example involves mimicry of alarm calls (Morton pattern with a wing buzz. The display
1976). The female Thick-billed Euphonia of the Neotropics uses the consists of a U-shaped dive that the bird
mobbing calls of other species when her nest is threatened. In this way, performs back and forth, making a loud
she attracts birds of the mimicked species to help her ward off predators buzzing noise with his wings at the bot-
tom of each dive.
at her nest. Mimicry thus seems to be a vocal tool that enables eupho-
nias to use other species for selfish gain in predator defense. Those
"used" individuals of other species aren't necessarily deceived to their
disadvantage, however, because it could be in their best interest, too,
to drive off a predator in their general vicinity.

Flight Songs
Although most birds sing while perched, others sing in flight. ,................„
Wing Buzz
Many shorebirds deliver their songs high above their breeding grounds.
(---1---)
American Woodcock fly above their display grounds, singing not only
on the wing but with their wings; snipe "sing" with their tails. Other
shorebirds produce long, complex songs in flight. Eurasian Sky Larks,
the subject of many a romantic poet, impress us by delivering their
seemingly unending soliloquy from great heights (Fig. 7 66). Hum-
-

mingbirds, too, often combine flight and sounds—either vocalized or

wing-produced—in their impressive courtship displays (Fig. 7 67). -

Singing birds attempt to maximize the influence of their songs.

Open-country birds have few high perches from which to broadcast Some species, however, don't quite fit this comfortable expla-
their songs, so taking to the air seems like the obvious choice. Hence, nation for flight songs. The Ovenbird, a common warbler of forests
most birds with flight songs are birds of grasslands or the arctic steppe. in northeastern North America, is a prime example. Especially near
The extra energy required to deliver the songs must be rewarded by an dawn and dusk, but even in the middle of the night, the Ovenbird
increase in the area over which the song can be heard. launches from near the forest floor up into the canopy and some-
times even beyond. If you listen carefully, you hear the elements of the
normal Ovenbird song, the familiar tea CHER, tea CHER, tea CHER,
- - -

embedded in the long, jumbled stream of the flight song, but someone
unfamiliar with the Ovenbird would be hard-pressed to identify the
source of this odd song (Track 68). Why does the Ovenbird perform
such "ecstasy flights," as they have been called? We can only guess.
To anyone listening, the energetic song makes an emphatic statement,
especially in the relative calm of night or predawn. A song delivered
high above the forest floor must also carry farther. Who's listening,
and who cares? Do females of neighboring territories take note? Are
males serving notice of territorial rights? Until we better understand
relationships between males and females, both within and between
territories, these puzzles will remain unsolved.

Figure 7-66. Sky Lark: The subject of Song Repertoires

many a romantic poet, a male Sky Lark,
The style of song development influences song repertoire size
a Eurasian species, delivers his long,
twittery song from high over his grassy
(Kroodsma 1988). Species that apparently do not learn songs, such as
habitat. most suboscines, tend to have small repertoires. The Alder Flycatcher

Cornell Laboratorg of OrnitholoBti

Handbook of Bird Biologq
7.86 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.87
Table 7-1. Average Repertoire Size and Delivery Style for Selected North American Species: Average number of one song does not do for a Chipping Sparrow? Why is more better in
songs in the song repertoire of individuals of selected species; even within species, repertoire size may vary widely
some species?The answer to this question has focused, not surprisingly,
with geographic location, lifestyle, or age. Delivery style (in what pattern the songs are sung) is given for typical,
daytime singing. "Eventual" refers to a bird that sings with "eventual variety" repeating one song type many times on what we presume to be the two main functions of bird song: territory
before going on to a different song. "Immediate" refers to a bird that sings with "immediate variety," typically defense, and mate attraction and stimulation. In stylized displays such
singing each song type once, and then moving on to another song type. Several species that sing with eventual as the dawn chorus, larger repertoires might help males display their
variety during the day, such as the the Eastern Towhee and Eastern Phoebe, sing with immediate variety at dawn. prowess and defend their territories. Common Nightingales in Europe
Although listed as singing with eventual variety, Eastern Phoebes, when excited, and male Red-winged Blackbirds,
(Todt and Hu ltsch 1996) and Marsh Wrens in western North America
when courting a female, may sing with immediate variety. For more information, see Stoddard (1996).
(Verner 1976), for example, seem to duel with their large repertoires;
Average males can match each other with the same song type, refuse to match,
Species Repertoire Size Delivery Style jump ahead to the next song in the sequence, overlap a neighbor's
songs, or alternate with a neighbor's songs. The complexity of interac-
Indigo Bunting tions can be dizzyi ng. Verner reported, for example, that Marsh Wrens
White-throated Sparrow would match a sequence of as many as 10 songs from a loudspeaker;
but because males in the local marsh sang songs in a predictable
White-crowned Sparrow 1
sequence, the males could sing each song before the tape recorder,
Ovenbird 1 not after. The male could actually anticipate which song would come
Common Yellowthroat 1 next and sing it before the "intruder" did! Recent studies show that this
kind of matched countersinging can be important in directing threats
Alder Flycatcher 1
to particular individuals and in mediating interactions (Nielsen and
Eastern Phoebe 2 eventual Vehrencamp 1995). Females might somehow be more impressed both
Eastern Wood-Pewee 3 immediate by larger repertoires and by the way a singer uses his repertoire.
Certain evidence supports these ideas on the functions of reper-
Willow Flycatcher 3 immediate
toires. In the laboratory, females do respond more to a greater variety
Eastern Towhee 6 eventual of song. Measuring a female's responses in nature, however, is more
Red-winged Blackbird (male) 6 eventual difficult, because the male she seems to pair with isn't necessarily the
one from whom she collects sperm to form her family. Recently, by
Western Meadowlark 8 eventual
using DNA to identify parentage, Hasselquist et al. (1996) showed that
Song Sparrow 9 eventual female Great Reed-Warblers in Sweden tend to pick extrapair partners
Northern Cardinal 9 eventual who have especially large repertoires. We need more studies of this
Tufted Titmouse 10 eventual sort to determine how females use male song repertoires.
In at least two species, the Great Tit and the Song Sparrow, males
Bewick's Wren 16 eventual
with larger repertoires survive longer than males with smaller reper-
Carolina Wren 25 eventual toires (McGregor et al. 1981; Arcese 1989). One is tempted to con-
Red-eyed Vireo 50 immediate clude that having a large song repertoire somehow causes a male to live
longer, but it is perhaps more likely that good health permits both the
Marsh Wren (Eastern) 50 immediate
longer life and the development of a larger repertoire in youth. Young
Eastern Meadowlark 55 eventual male Bewick's Wrens, for example, learn more songs if they hatch early
American Robin 70 immediate in the breeding season than if they hatch late; early-hatching birds have
more time to learn songs before their first winter, and they may have
Sedge Wren 100 immediate
a chance to select the best territory, too. In some species, such as the
Marsh Wren (Western) 150 immediate Northern Mockingbird, birds with larger repertoires are older, because
Northern Mockingbird 200 immediate males continue to add songs to their repertoires throughout life. For
Brown Thrasher several reasons, then, males with larger repertoires in some species
2,000+ immediate
are likely to be healthier and better at surviving, and both males and
females are undoubtedly sensitive to these badges of success. How
has but one song, the Eastern Phoebe two, the Willow Flycatcher three.
the large repertoires are associated with success and how they might
In contrast, song learning has enabled the songbirds to evolve huge
actually help achieve success in some species remain exciting topics
repertoires. Eastern Meadowlarks have 55 songs, Rock Wrens 200, and
for future research (Sidebar 6: Listening on Your Own).
Brown Thrashers 2,000 (Table 7 1). -

But what do 2,000 songs accomplish for a Brown Thrasher that

(Continued on p. 7.91)

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

7.88 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.89

Sidebar 6: LIS t LNING ON YOUR OWN songs that occur before your song is daytime singing, choose the Eastern many communities, American Rob-
repeated. Now repeat the entire pro- Towhee, Field Sparrow, or a warbler, ins seem to be the first to sing, and
Donald E. Kroodsma cess for several other songs that you such as the Chestnut-sided or Blue- other species join in a rather regular
have come to recognize. Calculate winged. Or, listen to a Song Sparrow, sequence.
All too often, people stop listening to the grand average, and you will have and study how many times he repeats If you are interested in listening
but later in the day more and more parts: a few barely audible notes at
a singing bird once they have iden- a rough estimate of how many dif- each song type. Pick almost any spe- more to the sounds of birds, the
of the songs are of the phoe-be type the beginning, a loud middle portion,
tified it. But that's when the fun can ferent songs the individual sings. cies, and note how much more ener- whole world is your theater. Wher-
(Fig. A & Track 69). Under what cir- and a softer concluding section. Fo-
begin! By keeping your ears tuned gized the singing seems at dawn than ever you travel, birds will be vocal-
cumstances do the proportions of cus on the loud, highly musical mid-
in a bit longer, you can discover the Dawn Chorus later in the morning. izing, and if you listen carefully you
these two songs change in the male's dle portion of the song (Fig. C & Track
variety of songs that a particular bird Learn to appreciate how birds of It's also fascinating to document can learn to enjoy eavesdropping on
singing? 71). Each male has a repertoire of four
sings and some of the ways he uses many species sing at dawn, and con- how birds contribute to the dawn the birds as they go about their daily
To hear a song repertoire, listen to eight phrases he may choose from
his songs. Below I describe several to a Song Sparrow deliver one song to use here, and he uses one per song.
trast their dawn behavior with what chorus of a given location. Each I ives. ■
ways to increase your listening en- they do later in the day. For a dra- species chimes in at a slightly dif-
over and over, sometimes varying the He often (but not always) sings songs
joyment. matic difference between dawn and ferent light level, for example. In
ending a bit, and then abruptly move with different "middles" in a regular
to the next song type. He'll sing eight order: if a male's four types of phrases
Individual Variety or so different kinds of songs, and if are identified as A, B, C, and D, for
Follow a male Black-capped you have a good ear, you may be able example, the first song will have A,
Chickadee during the dawn chorus, to become familiar with all eight (Fig. the second B, and so on; every fifth
and hear him shift the frequency of B & Track 70). The same exercise can song will have the same sound. By Figure B. Sonagrams of Song Sparrow
his hey-sweetie songs. Or, identify be done with Eastern Towhees or listening carefully, you can learn Song Types (Track 70, 1st Song of Song
the two song forms of Eastern Phoe- Red-winged Blackbirds. to identify the different sounds and Type 1, 1st Song of Song Type 2): Com-
bes, the phoe-be and the phoe-bree. to determine, by ear, the repertoire mon throughout North America, each
Both songs start with essentially the Wood Thrush Song Repertoires size of those middle portions of the male Song Sparrow has a repertoire
same sound, the phoe, but one ends of approximately 8 or 9 different song
Wood Thrushes provide special song. If your ear is good enough, you
types, all often clumped under the rough
in a raspy be and the other ends in opportunities to challenge your lis- should even be able to tell if you have
description maids, maids, maids put on
a stuttered, higher bree. At dawn, tening skills and identify their reper- the same Wood Thrush returning to the teaeeeee kettle-ettle-ettle. Although
males tend to alternate the songs, toire size. Each song consists of three your woodland in successive years. the details of each song type differ tre-
Because our memories are not so mendously, many songs stick to the basic
good from year to year, consider re- pattern of a couple of repeated introduc-
cording your bird in one year so that tory notes (maids, maids, maids), then a
you can compare the songs from year jumble of buzzes and notes in the middle
to year; even a crude tape recording (put on the teaeeeee), and a final trill (ket-
tle-ettle-ettle). If you listen carefully to a
of the songs will help—don't worry
singing male, you will hear him repeat a
about having expensive equipment.
song type many times, perhaps varying
the ending a bit; then you will hear him
Northern Mockingbird and switch to another type, repeating it many
Red-eyed Vireo Repertoires times before moving on to another song
Once your ears are sharpened up, type. Sometimes a singer delivers most
try this special challenge. Northern of his repertoire before repeating a song
Mockingbirds and Red-eyed Vireos type, and at other times one or more song
types may be given much more often than
usually have huge song repertoires,
others. The two song types shown here do
but you may be able to estimate the
not fit the general pattern—but they are
number of different song types each still typical Song Sparrow songs. Song
male sings! These birds tend to sing Type 1 has two different sets of introduc-
with immediate variety: cycling tory syllables repeated twice each, then
through their whole repertoire before a longer trill, and a varied non-trill end-
repeating any one song type. Listen ing containing a buzz. Song Type 2 has
FigureA. Sonagram of Eastern Phoebe Dawn Song (Track 69, Sonagram not Produced carefully to an individual singer, and an introductory trill of three syllables, a
from Track 69, but Similar to 1st and 2nd Songs): Throughout the eastern United States longer trill, then a jumble of buzzes and
pick out an especially distinctive
and much of Canada, the familiar song of this common flycatcher is a welcome sign notes. In Track 70, the Song Sparrow
song. Then count how many other
of spring. The Eastern Phoebe has two song forms, phoe-be and phoe-bree. Although sings Song Type 1 three times, Song Type
songs occur before you hear the same
both begin with a single harsh phoe note, the phoe-be ends with a raspy be, and the 2 three times, and then repeats Song Type
phoe-bree, with a stuttered, higher bree. The phoebe tends to alternate the two songs song again. Repeat this process sev- 1 three times, varying the endings a bit.
at dawn—and a portion of dawn singing is shown in this sonagram. Later in the day, eral times for that unique song, and This is a more rapid switch in song types
mostly phoe-be song types are given. then calculate the average number of than is typical.

Cornell Laboratorq of Omithologq Handbook of Bird Biologq

7.90 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.91
The thought of dawn sweeping around the globe every 24 hours
is uplifting and powerful for me. Like a giant player piano, the Earth
plays on and on, year after year, century after century, from ages past
into the indefinite future. Always, somewhere, the birds are waking,
Wood Thrush and always, somewhere, they are singing. I like to picture humans in
all types of dwellings, around the globe, in the northern and south-
Loud, Highly ern hemispheres, tracking this dawn chorus by throwing open their
Musical Middle Terminal windows, letting this marvelous bird music help us greet each new
Portion Trill
of Song day. The sun's first light, the waking birds, and opening windows thus
10 - continually accompany each other around the globe.
And all that goes on as these birds communicate with each other
Frequency (kilohertz)

8- is truly astounding! The goals of each individual, to survive and leave

offspring, are rather simple, and the role of sound in achieving this
6-
mission is extraordinary. I hear short songs, long songs; simple songs,
4- Soft complex songs; musical songs, harsh songs; duets and solo perfor-
Introduct
Notes mances; simple repertoires, huge repertoires; and much, much more.
2. Song with A-type
Young songbirds are learning, practicing, babbling as they copy older
Middle Portion
birds, who pass traditions on to future generations. Ears are poised,
brain cells are processing, nerves are firing, and tiny muscles in dual
voice boxes respond, creating sounds that we have come to recognize
and love.
So many species, each different from the other. And each is suc-
cessful in its own special way, having survived eons of time to travel,
together with us, on this planet Earth. Why each species is the way it
Song with B-type is remains one of the great evolutionary puzzles that we face in trying
0 Middle Portion to decipher how these birds communicate with each other. We have
10
so much to learn, and the more we learn, the more we appreciate all
of these birds for what they are. May the sounds of birds fill your life.
N
L..
a.)
Pe Throw the windows open, and enjoy!
0
6
0Q.) 4 Suggested Readings
LL. 2 Song with C-type Armstrong, E. A. 1963. A Study of Bird Song. New York: Dover.
Middle Portion
0.0 0:5 1.0 1.5 Like the book byThorpe (see below), this book reviews the study of bird song
Seconds in its infancy during the 1960s. Armstrong was a British clergyman whose
spare-time passion was studying birds, especially the Winter Wren.
Figure C. Sonagrams of Wood Thrush Song Types (Track 71, 1st Song (A), 2nd Song Catchpole, C. K., and P. J. B. Slater. 1995. Bird Song: Biological Themes and
(B), and 3rd Song (C)): The beautiful song of the Wood Thrush is made up of three Variations. Cambridge, England: Cambridge University Press.
different parts: a few simple, soft introductory notes; a loud, complex, highly musical
middle portion; and a final soft trill. The description ee-oo-lay often applied to the
An excellent review of the study of bird song, written with a wide readership
song refers only to the middle portion. Although the beginning and end portions may in mind. Chapters cover production and perception, how song develops,
vary, the differences are subtle and often hard for a human to detect by ear. To learn getting the message across, when birds sing, recognition and territorial
to listen to repertoires, focus, instead, on the middle portion, which also varies. Each defense, sexual selection and female choice, themes and variations, and
male has a repertoire of four to eight different phrases that he may choose from to variation in time and space.
put here, and he uses one per song. Songs with three different "middles," A, B, and
Greenewalt, C. H. 1968. Bird Song: Acoustics and Physiology. Washington,
C, are shown here. In Track 71 the Wood Thrush sings songs with their middles in the
following order: A, B, C, D, B, C, A, D, A, B.
D.C.: Smithsonian Institution Press.
A classic. Written by an "amateur ornithologist" but a superb scientist, win-
ner of the Cornell Lab of Ornithology's Allen Award for his contributions
to ornithology. A fine, early treatise on how birds sing.

Cornell Laboratorq of Omithologq Handbook of Bird Biolo9i

7.92 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.93
Hartshorne, C. 1973. Born to Sing. Bloomington: Indiana University Press.
One of my favorite books, by a philosopher who loves bird sounds. The
Appendix A:
author ranks birds by the quality of their music, listing the bestsingers in the
world. Not always accepted as scientifically authoritative, but a delightful
DESCRIPTIONS OF TAPE / CD TMCKS
tribute to one man's passions. Track 1: Black-capped Chickadee Hey-sweetie Song more slowly than in drumming. In addition,
Jellis, R. 1977. Bird Sounds and Their Meaning. London: British Broadcast- (Fig. 7-6): Recorded February 20, 1988 in these foraging pecks are much softer than
ing Corp. New York by Gregory F. Budney. drumming, as is usually the case, because the
A good introduction to bird sounds for those who love birds but have little bird is not selecting a resonant branch to hit.
Track 2: White-throated Sparrow Song (Fig. 7-7): Re-
knowledge of bird behavior. Examples in the text are primarily of birds from Recorded in Oregon by David S. Herr.
corded in Ontario, Canada by William W. H.
the British Isles or continental Europe. Gunn. Track 13: Ruffed Grouse Drumming (Sidebar 1, Fig. B):
Kroodsma, D. E., and E. H. Miller, Editors. 1982. Acoustic Communication Recorded in Oregon by David S. Herr.
Track 3: Hairy Woodpecker Drumming (Fig. 7-8): Re-
in Birds. 2 Volumes. New York: Academic Press. corded in California by Geoffrey A. Keller. Track 14: American Woodcock Peenting and Aerial
Nineteen authoritative chapters on how birds produce and perceive sounds, Display: You will hear three peents from the
Track 4: Downy Woodpecker Drumming (Fig. 7-8):
on how sounds are designed, and on song learning and its consequences. male on the ground, then wing twittering as
Recorded in Oregon by Geoffrey A. Keller.
Includes some of the finest summaries on duetting, mimicry, and other he takes to the air and spirals upward. At the
topics that are not a focus of the 1996 volume by the same editors. Track 5: Yellow-bellied Sapsucker Drumming (Fig. peak, you will hear the twittering change to a
Kroodsma, D. E., and E. H. Miller, Editors. 1996. Ecology and Evolution of 7-8): The third drum, which is quieter than more "chirpy" quality as the male begins to
Acoustic Communication In Birds. Ithaca, NY: Cornell University Press. the others, is another bird answering the first. vocalize during his descent. When he reaches
Recorded in Ontario, Canada, by William W. the ground, you will hear him give two more
The most recent compendium, written by 39 experts on bird sounds. Each
H. Gunn. peents. In an evening or morning of display-
author wrote about his or her professional interest. The 26 chapters in this
ing, the male intersperses aerial flights with
book suggest abundant research activities for those wishing to study devel- Track 6: Common Yellowthroat Song (Fig. 7-9): You
sequences of peenting that vary in length. Re-
opment, repertoires, geographic variation, signal processing, how birds will hear three songs at normal speed, two at
corded on May 22, 1951 in Ithaca, New York
interact with each other, or a host of other topics. one-half normal speed, and then two at one-
by Arthur A. Allen.
Smith, W. J. 1977.T he Behavior of Communicating:An Ethological Approach. quarter normal speed. Recorded in New York
Cambridge, MA: Harvard University Press. by Steven R. Pantle. Track 15: Common Snipe Winnowing: You will hear
An excellent book about communicating in general, not just about birds three sets of woo-woo-woo-woo as the bird
Track 7: EasternTowhee Song (Fig. 7-10):You will hear
and not just about vocalizing. Many insights into why animals behave as dives during its aerial display and spreads
three songs at normal speed, then two at one-
they do. its tail. The sound is produced at high flight
half normal speed. Recorded in New York by
speeds when air vibrates the spread outer tail
Thorpe, W. H. 1961. Bird Song. Cambridge, England: Cambridge University Arnold van den Berg.
feathers. Recorded in Alaska by Leonard J.
Press. Track 8: Winter Wren Song (Fig. 7-11): You will hear Peyton.
Written by a pioneer in the study of bird song, this book reviews what was two songs at normal speed, one at one-half
known in the early 1960s.
Track 16: White-bearded Manakin Wing Sounds at Ac-
normal speed, and then one at one-quarter
tive Lek: You will hear occasional growls and
normal speed. Recorded in Oregon by Geof-
various types of wing snaps, all produced by
frey A. Keller.
striking together specialized wing feathers.
Track 9: Black-capped Chickadee Chick-a-dee Calls Sounds from three different males displaying
(Fig. 7-13a): Recorded in NewYork by Robert simultaneously at lek. Recorded on January 29,
C. Stein. 1983 in Cauca, Colombia by Mark Robbins.
Track 10: Black-capped Chickadee"Gargle" Calls (Fig. Track 17: EasternTowhee,Three SongTypes (Fig. 7-16):
7-1 3 b): Recorded on July 4, 1979 in NewYork This track was created so that you will hear
by Andrea L. Priori. three repetitions of SongType A, three of Song
Type B, and then three of Song Type C. In this
Track 11: Black-capped Chickadee Song Sequence with
example, the intervals between songs have
Frequency Shifts: You will hear four songs at
been shortened compared to typical Eastern
one frequency, then one at a lower frequency,
Towhee singing. All songs were recorded in
one at the first frequency, one again at the
the field from one singing male. Recorded on
lower frequency, and then two at the original
April 8, 1987 in Florida, by Donald E. Kroods-
frequency. All songs from one bird, as sung in
the field. Recorded in May 1996 in Massachu- ma.
setts by Donald E. Kroodsma. Track 18: "High Zee" Alarm Calls (Fig. 7-18): You
Track 12: Hairy Woodpecker Foraging Pecks: Note the will hear a series of alarm calls, first from an
American Robin, next from a Tufted Titmouse,
irregular rhythm, with pecks paced much
and finally from a Black-capped Chickadee.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

7.94 Donald E. Kroodsma Chapter 7 — Vocal Behavior 7.95
American Robin recorded on August 3, 1990 Kroodsma. Adult song recorded in May; sub- at one-half normal speed. Recorded in New night-herons. Although this example contains
in Deer Park, in the Upper Peninsula of Michi- song, in August. York by Arthur A. Allen. pairs of calls, they are more typically given as
gan, by Lang Elliott. A Broad-winged Hawk single notes. Recorded in mid-October 1989
Track 26: Alder and Willow Flycatcher Songs: You will Track 30: Black-and-white Warbler Night Flight Calls:
was perched nearby, and the robin was clearly in southern Alabama by Bill Evans.
first hear Alder Flycatcher songs, often de- Like most warbler night flight calls, these are
responding to the hawk. Tufted Titmouse re-
scribed as fee-BEE-o or free-BEE-er. Note the short, high, and cricket-like. Recorded in late Track 39: Piano Music RepresentingWoodThrush Song
corded in Texas by Geoffrey A. Keller. Black-
soft beginning to the song, and the accent on April 1989 in eastern Florida by Bill Evans. (Sidebar 3, Fig. Aa): You will hear the piano
capped Chickadee recorded in Ontario, Can-
the second syllable. Then you will hear Wil low music from the score representing Wood
ada by William W. H. Gunn. Track 31: American Redstart Night Flight Calls (Side-
Flycatcher songs, usually described as FITZ- Thrush song shown in Sidebar 3, Fig. Aa. This
bar 2, Fig. Ba): Like the night flight calls of
Track 19: Mobbing Calls (Fig. 7-19):You will hear a se- bew. The latter have a harsh beginning, with the is from Field Book of Wild Birds and Their Mu-
the Black-and-white Warbler, the American
ries of mobbing calls, firstfrom a Blue Jay, next accent on the first syllable. Although the songs sic, written by F. Schuyler Mathews in 1921.
Redstart's calls are short, high, and cricket-
from a House Wren, and then from a Tufted sound somewhat simi lar, they are an easier tool
like. Recorded in mid-May 1989 in eastern Track 40: Wood Thrush Song (Sidebar 3, Fig. Ab): You
Titmouse. You will then hear a sequence of for distinguishing these two species than are
Florida by Bill Evans. will hear a series of Wood Thrush songs. The
mobbing calls from a mixed-species flock their nearly identical appearances. Alder Fly-
third song, chosen for its similarity to one
that includes Mexican Chickadee, Western catcher songs recorded in Ontario, Canada by Track 32: Veery Night Flight Calls (Sidebar 2, Fig. Bb):
phrase from the piano music played in Track
Tanager, and Red-breasted Nuthatch. Blue William W. H. Gunn. Willow Flycatcher songs Veery night flight calls, like those of other
39, is shown in the sonagram in Fig. Ab. Note
Jay recorded in New York by Hugh Mclsaac. recorded in Oregon by Geoffrey A. Keller. thrushes, are lower, longer, and more mellow
that you will hear soft introductory notes in
House Wren recorded in Alberta, Canada by than those of warblers. The Veery says veeree
Track 27: Indigo Bunting Song (Fig. 7-31): You will first the third song of Track 40, although they were
William W. H. Gunn. Tufted Titmouse record- or veer in night flight. Recorded in late August
hear the song of a territorial male, then the removed from the sonagram in Fig. Ab to bet-
ed in Texas by Geoffrey A. Keller. Mobbing 1988 near Ithaca, New York by Bill Evans.
song of a male who holds an adjacent ter- ter match the piano score. Recorded in New
flock recorded in the fall of 1980 in a dry oak
ritory. Note how similar the two songs are. Track 33: Swainson's Thrush Night Flight Calls: This York by Arthur A. Allen.
woodland in Arizona by Randolph S. Little.
Then you will hear the very different song of a flock of Swainson's Thrushes migrating over-
Track 41: Songs in Song Sparrow Neighborhood (Side-
Track 20: GreatTinamou Song: Recorded on December 3, male who is a stranger to these two birds. Note head sounds a great deal like a pond full of
bar 3, Fig. B): This 10-second recording was
1992 in Zancudo Cocha, Napo Province, Ecua- that the first song of the territory holder, the calling spring peepers (small tree frogs). Re-
made using an array of eight microphones ar-
dor, by David L. Ross and Gregory F. Budney. second song of the neighbor, and the second corded in mid-September 1990 in Ithaca,
ranged around the edge of a field in which
and fourth songs of the stranger are notice- New York by Bill Evans.
Track 21: Common Nightingale Song: Recorded April several male Song Sparrows held territories.
ably shortened versions of each bird's song.
18, 1997 in Taliouline, Morocco by Arnold Track 34: Bobolink Night Flight Calls (Sidebar 2, Fig. The singing you will hear occurred two min-
Although each Indigo Bunting has only one
van den Berg. Bc): The pink note you will hear from a night- utes before a territorial fight. You will hear the
song type, males often shorten their songs
migrating Bobolink is the same as the common entire 10-second recording twice. Recorded
Track 22: Musician Wren Song: Recorded on August 27, in various ways, especially during territorial
daytime flight call note. Recorded in mid-May April 17, 1998 at 7:06 a.m. in Ithaca, New
1982 at Cocha Cashu, Manu National Park, encounters. Territorial male and neighbor re-
1989 in eastern Florida by Bill Evans. York by John Bower.
Madre de Dios, in Amazonian Peru by Theo- corded at Point Pelee, Ontario by William W.
dore A. Parker, III. H. Gunn. Stranger recorded in Bloomington, Track 35: Rose-breasted Grosbeak Night Flight Calls: Track 42: White-crowned Sparrow Song Dialects (Fig.
Indiana by Geoffrey A. Keller. The night flight call of the Rose-breasted Gros- 7-41):You will hear three songs from a dialect
Track 23: White-crowned Sparrow Normal and Isolate
beak is a mellow whistle, similar to that of the in Oregon, three from a dialect in California,
Songs (Fig. 7-25):You wi I I first heartypical adult Track 28: Marsh Wrens in Matched Countersinging:
Swainson's Thrush, but slightly higher in pitch and three from a dialect in Alberta, Canada.
songs, then atypical songs, much less complex, The first example you wi II hear was fabricated
and somewhat off-key. The same call is given by Oregon dialect recorded by Geoffrey A. Keller,
from a bird taken from a nest in the wild at eight using recorded songs from western birds. It
family groups in late summerto maintain contact California dialect recorded by Wi lliam R. Fish,
or nine days of age and raised in the labora- illustrates matched countersinging, in which
with one another. Recorded in mid-September and Alberta dialect recorded byWil I iam W. H.
tory without hearing any further songs of his one bird (Bird A) sings a song, then his neigh-
1991 in Oneonta, New York by Bill Evans. Gunn.
own species. Normal song recorded in Oregon bor (Bird B) sings a very similar song. Then
by Geoffrey A. Keller. Isolate song recorded in Bird A sings a different song and Bird B again Track 36: Upland Sandpiper Night Flight Calls (Side- Track 43: Black-capped Chickadee Unusual Song from
May 1976 by Mark Konishi. matches the song of Bird A. This pattern con- bar 2, Fig. Bd): The Upland Sandpiper's night Martha's Vineyard (Fig. 7-46): You will first
tinues with a number of different songs, just flight call is a short, upward-slurred whistle hear a bird from Gay Head, at the western
Track 24: Babbling of 1 1/2-year-old Child: A sample of
the way neighboring western Marsh Wrens that is repeated quickly a few times. Recorded end of the island, then a bird from Edgartown,
human speech development that parallels the
often sing. The second example is a recording in mid-August 1989 in west-central NewYork at the eastern end. Birds at Gay Head record-
subsong of birds. Donald E. Kroodsma record-
made in the field in California of two Marsh by Bill Evans. ed on May 10, 1994 and birds at Edgartown
ed his daughter at home in Oregon in 1972.
Wrens actually engaged in matched counters- recorded in May 1996, both by Donald E.
Track 37: Barn Owl Night Flight Calls: The Barn Owl's
Track 25: Bewick's Wren Adult Song and Subsong (Fig. inging. The first example was fabricated from Kroodsma.
night flight call is a piercing, raspy hiss, much
7-27): You will first hear typical adult songs, songs recorded May 19, 1985 in Coos Bay, louder than the begging hiss of a juvenile Track 44: Black-capped Chickadee Abnormal Song
then typical practice songs (subsong) from Oregon by Geoffrey A. Keller. The second ex- Barred Owl. Recorded in June 1990 in Enfield, from Lab-tutored Bird: You will hear highly
a young bird. Note that the practice songs ample was recorded March 21, 1996 in Wild New York by Bill Evans. abnormal songs from a Black-capped Chick-
are long and rambly, with less distinct notes Gustin, California by Joe Brazie.
than in the adult songs. Both songs recorded adee from a normal population (one that sings
Track 38: American Bittern Night Flight Calls (Side-
in 1970 in Corvallis, Oregon by Donald E. Track 29: Wood Thrush Song (Fig. 7-35): You will hear the typical hey-sweetie song) in Amherst, Mas-
bar 2, Fig. Be): The deep croak of a migrating
five songs at normal speed, then three songs sachusetts. This bird was reared in the lab and
American Bittern is similar to the croaks of

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

7.96 Donald E. Kroodsma Chapter 7 —Vocal Behavior 7.97
exposed to typical hey-sweetie songs. Under different variants in different contexts, such Track 56: Chipping Sparrow Dawn Song: At dawn the like the mobbing or scolding calls of many
these conditions, male Black-capped Chicka- as in flocks, during courtship, during begging, male Chipping Sparrow usually sings from the species. (In the first example, the female gives
dees develop songs with the typical whistled, or during nest building. Recorded in Ontario, ground, delivering very short trills separated two scolding notes; in the second, she gives
pure-tone quality, but containing from one Canada by William W. H. Gunn. by short pauses. Note how different this pat- four notes.) In this "duet," the female's notes
to seven or more different notes on a variety tern is from that of typical daytime singing obscure the end of the male's song, at least to
Track 50: Cedar Waxwing Seee Calls: The other cat-
of frequencies. Recorded March 19, 1990 by (Track 55). Recorded in California by Matthew our R
manF Recorded in California by
egory of Cedar Waxwing calls (see Track 49)
Donald E. Kroodsma. D. Medler. William Fish.
are the seee calls. These are high-frequency,
Track 45: Blue-winged Warbler Song:You will first hear hissy whistles, generally pure tones all on one Track 57: Eastern Wood-Pewee Daytime Song: In typi- Track 63: Northern Cardinal Song; Northern Mock-
the well-known beee-buzzzzsong, used most frequency. Seee calls commonly are given by cal daytime singing the male Eastern Wood- ingbird Mimicking Northern Cardinal (Fig.
by males in the presence of females. This song flock members during take-off or landing, or Pewee irregularly alternates between a whis- 7-64):You will first hear the breaker, breaker,
varies little throughout the range of the spe- in flight, and one often can determine when tled pee-ah-wee and a wee-ur. Recorded in breakersong of a Northern Cardinal, with sev-
cies. Then you will hear the male's aggressive a flock is about to take off by the change from Manitoba, Canada by William W. H. Gunn. eral introductory notes. Then you will hear a
song, used at dawn and in very aggressive situ- bzeee calls to seee calls. Seee calls also are Northern Mockingbird mimickingthe breaker,
Track 58: Eastern Wood-Pewee Dawn Song: At dawn
ations. This song varies more, and occurs in given when there is a disturbance, such as a breaker, breaker portion of Northern Cardinal
and dusk the Eastern Wood-Pewee gives his
dialects. Beee-buzzzz recorded in Ohio by predator, near a bird's nest. Recorded in Or- song. Northern Cardinal recorded on May 19,
"twi I ight song," which adds a slurred, whistled
Randolph S. Little. Aggressive song recorded egon by Geoffrey A. Keller. 1989 in Concan, Texas and Northern Mock-
ah-di-deeto the other two daytime song forms
June 11, 1981 in Massachusetts by Donald E. ingbird recorded on May23, 1988 in Del Rio,
Track 51: Red-winged Blackbird Female Teer: Female (seeTrack 57). Recorded in Nebraska by Geof-
Kroodsma. Texas, both by Theodore A. Parker, Ill.
Red-winged Blackbirds appear to give the frey A. Keller.
Track 46: Chestnut-sided Warbler Song: You will first loud teer vocalization in aggressive encoun- Track 64: House Sparrow Song; Northern Mocking-
Track 59: Carolina Wren Duet (Fig. 7-60):You will hear
hear the familiar pleased-pleased-pleased- ters with other females. Recorded in Massa- bird Mimicking House Sparrow:You will first
one song type from a male Carolina Wren; it
to-MEETCHA, often termed the "accented- chusetts by R. Simmers. hear the series of chirps that passes for House
follows the typical pattern of a syllable with
ending song" because of the emphasis placed Sparrow song. Then you will hear a North-
Track 52: American Goldfinch Per-chik-o-ree Calls: approximately three parts (tea-ket-tle) repeat-
on the meetcha portion. This is used by males ern Mockingbird mimicking House Sparrow
The twittery, lilting per-chik-o-ree call of the ed three or four times. But, on the first, fourth,
in association with females, and varies little chirps. House Sparrow recorded in Massachu-
American Goldfinch is typically given by birds sixth, and eighth songs, the female Carolina
throughout the range of the species. Then you setts by C. S. Thomas; Northern Mockingbird
in flight. Recorded in Ontario, Canada byWi I- Wren adds a coarse rattle to the end, creating
will hear the so-called "unaccented-ending recorded in Texas by Theodore A. Parker, III.
liam W. H. Gunn. the simple duet of this species. This selection
song," used at dawn and in highly aggres-
Track 53: Dawn Chorus in New York: This chorus was also illustrates the variability in this species' Track 65: Blue Jay Jaay Calls; Northern Mockingbird
sive situations. This song occurs in dialects.
duet. Note that in the first song, the female Mimicking Blue Jay:You will first hear a series
Accented-ending song recorded in Ontario, fabricated from songs recorded by David
begins her portion well before the end of the of Blue Jay jaaycal Is (used to assemble a flock,
Canada byWi I liam W. H. Gunn. Unaccented- L. Ross and Gregory F. Budney in three dif-
male's song; in the second and seventh songs, or as alarm or mobbing calls). Then you will
endi ng song recorded in June 1990 in the town ferent locations in eastern deciduous forests
she inserts just a short buzz in the middle of the hear a Northern Mockingbird mimicking the
of Florida in the Berkshire Mountains of west- in New York. Species sing in approximately
male's song. Recorded by Eugene S. Morton. jaay calls of Blue Jays. Blue Jays recorded on
ern Massachusetts by Donald E. Kroodsma. the following order: Scarlet Tanager, B lack-
May 2, 1982 in NewYork by Andrea L. Priori;
and-white Warbler, Worm-eating Warbler, Track 60: Bay Wren Duet (Fig. 7-61): It is nearly im-
Track 47: Marsh Wren Songs from Eastern North Amer- Northern Mockingbird recorded in Pennsyl-
Mourning Dove, American Crow, Ovenbird, possible to distinguish the male and female
ica (Fig. 7-52): Recorded at Long Lake Na- vania by J. C. Glase.
Wood Thrush, Yellow-billed Cuckoo, Red- contributions to this complex duet from the
tional Wildlife Refuge, Moffit, North Dakota,
eyed Vireo, Winter Wren, Yellow Warbler, Bay Wren without carefully following the Track 66: Killdeer Songs; Northern Mockingbird Mim-
by Geoffrey A. Keller.
Indigo Bunting, Tufted Titmouse. sonagram of the duet in Figure 7-61. Recorded icking Killdeer (Fig. 7-64): You will first hear
Track 48: Marsh Wren Songs from Western North on March 3, 1991 in the Province of Heredia, a series of Killdeer songs. Then you will hear
Track 54: Dawn Chorus in French Glen, Oregon: Spe-
America (Fig. 7-53): Recorded in Oregon by Costa Rica by David L. Ross. a Northern Mockingbird mimicking Killdeer
cies sing in approximately the following or-
Geoffrey A. Keller. songs. Killdeer recorded in Montana by Geof-
der: Red-winged Blackbird, Yellow-headed Track 61: Red-winged Blackbird Konk-a-reeSongTypes:
Track 49: Cedar Waxwing Bzeee Calls: Cedar Wax- freyA. Keller; Northern Mockingbird recorded
Blackbird, Yellow Warbler, Cedar Waxwing. You will hear one konk-a-ree song type from
wings have no real "song," in the sense of a in Pennsylvania by). C. Glase.
Recorded in habitat dominated by juniper, one male (designated Bird A), repeated two
loud vocalization that is broadcast repeatedly sage, and bunchgrass on June 13, 1993 by times; then you will hear a different konk-a- Track 67: Northern Mockingbird Song Sequence: A
from a prominent post. Instead they have sev- David S. Herr. ree song type from a different male (Bird B), delightful sample of singing by a Northern
eral different types of calls that researchers repeated two times. First song type recorded in Mockingbird. Note the typical mockingbird
Track 55: Chipping Sparrow Daytime Song: In typical
have broadly classified into two categories: New York by Randolph S. Little; Second song singing pattern of rapidly repeating each song
daytime singing the male Chipping Sparrow
bzeee calls and seee calls. The bzeee calls, as type recorded in Ontario, Canada by William type many times, then moving right on to the
perches high in a tree and gives a simple, long
you will hear, are high-frequency notes with W. H. Gunn. next song type without any pause. It is this
trill—approximately 20 repetitions of a single
a buzzy or trilled quality, and are quite vari- singing pattern that gives away the identity of
element—usually lasting about two seconds. Track 62: Red-winged Blackbird Duet (Fig. 7-63): You
able. Although humans cannot determine the the singer, not necessarily the specific content
He then pauses around 10 seconds before will hear the male begin his konk-a-ree song,
subtle differences by ear, they are visible on of his songs. Handbook of Bird Biology edi-
singing again. Recorded in Washington by then, toward the end of the song, the female
sonagrams, and the birds appear to use the tors' best guess as to the sequence of model
David S. Herr. gives several harsh notes that sound very much

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

7.98 Donald E. Kroodsma
songs sung is: Red-winged Blackbird, Blue sonagram in Fig. A, but it is nearly identical
Jay, American Robin tuckcall note, unknown, to the recording used. In both, the Eastern

8
American Kestrel killy killy killy call, North- Phoebe alternates his two song forms, phoe-
ern Cardinal, unknown, unknown, unknown, be and phoe-bree, beginning with the phoe-
Tufted Titmouse, Wood Thrush, Empidonax be. Recorded in Ohio by Randolph S. Little.
flycatcher whit call (one time), Northern
Track 70: Song Sparrow Song Sequence (Sidebar 6, Fig.
Flicker kleer call, Carolina Wren, unknown.
B): You will hear one male Song Sparrow sing
Recorded in June 1994 in Groton Plantation in
a song type (designated Song Type 1) three
Luray, South Carolina by Gregory F. Budney.
times, then sing another song type (Song Type
Track 68: Ovenbird Flight Song: Note the typical tea- 2) three times, and finally repeat Song Type 1
CHER, tea-CHER, tea-CHER song of the Oven- three ti mes. Th is is a natural recording, but the
bird (a shortened version, with only three tea- singer switches song types after fewer repeti-
CHERs) toward the middle of this long jumble tions than is typical. Recorded in NewYork by
of notes given as the singer launches himself Matthew D. Medler.
high into the air. Recorded at dusk on June
8, 1994 in Seney National Wildlife Refuge in
Michigan's Upper Peninsula by Lang Elliott
Track 71: Wood Thrush Song Sequence (Sidebar 6, Fig.
C): If you just focus on the musical "middle"
Nests, Eggs, and Young:
portion of the songs, the singer here sings songs
and Ted Mack.
with their middles in the fol lowing order:A, B,
Track 69: Eastern Phoebe Dawn Song (Sidebar 6, Fig.
A): Note that this recording of Eastern Phoe-
be dawn song was not used to produce the
C, D, B, C, A, D, A, B. See caption for Sidebar
6, Figure C for more information. Recorded in
New York by Arnold van den Berg.
Breeding Biologui of Birds
David W. Winkler

They sit for months at a time, huddled together against

4 winds up to 60 mph (90 km/h) and wind chills of -150
degrees F (-100 degrees C) in the black ever-night of Ant-
arctic winter, each incubating a single egg on top of his
feet under a flap of densely feathered skin. When the sun returns to
the Antarctic, the mates of these male Emperor Penguins return, after
many days' journey over pack ice. They relieve the fathers and feed
the recently hatched chick, which until now has been fed only a thick
soup from the esophageal lining of the father. As each male departs
for the distant ocean, he begins a long series of solitary trips for food to
feed the rapidly developing chick—a series of forays, nest duties, and
exchanges that, with luck, will culminate over six months from laying
with the production of an independent descendant....

In the dank, steamy forest of eastern Australia, a male brush-tur-

key (a type of megapode) tends his mound—a pi le of rotting vegetation
that can be as much as 16 feet (5 m) high and 40 feet (12 m) across,
containing many tons of material; the nest site may have been continu-
ously used for over a thousand years. Poking his bill into the mound he
methodically monitors the progress of the fermentation within—he is
a living thermostat, adding or removing vegetation from the mound to
maintain temperatures and humidities near its core that are ideal for

Cornell Laboratorg of Ornithologq

8.2 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.3
the development of the eggs of his species. of habitats with a rich diversity of strategies.Th is chapter explores these
Females are attracted to males according strategies, following the breeding cycle from nest building, through
to the quality of the mounds they maintain egg laying and incubation, to chick rearing and interactions between
and defend, and, after laying her egg, a parents and offspring after the young fledge.
female will never see her young again. The Over the past 40 years biologists have developed a rich set of
chicks that emerge from these eggs are the ideas known as life history theory to explain the diversity in breeding
most well-developed chicks of any bird, strategies. This theory sheds light upon the evolution of life history
and they flutter away from the mound as traits, such as number of offspring and age of first reproduction, which
soon as they dig their way out, to live lives are closely connected to the most fundamental processes of life: sur-
of independence from the very start.... vival and reproduction. In discussing the life histories of birds, I will
try to provide an inkling of the larger theoretical issues as we pass by.
Far to the north and months later, in a cool, Even the most vagabond bird must settle down long enough to rear its
English oak wood, a female Blue Tit returns to young, and ornithologists have thus been able to gather more infor-
her nest after a short absence (Fig. 8-1). She mation about the breeding life histories of birds than any other aspect
climbs into her nest hole and clears the moss of avian biology. In writing this chapter, I have taken examples from
and fur off the eggs—she had covered them my own reading and experience; by the chapter's end I hope you will
just before she emerged to make a quick dash feel empowered to ask questions of the birds in your world, as I have
from the nest to defecate and grab a morsel of of the birds in mine.
food. She is sitting on a clutch of 17 eggs, and
as soon as these myriad young hatch, she and
her mate will engage in a two-week marathon Survival
of feeding—gathering food from dawn to dusk
and bringing it to the nest at rates of up to 500
■ Biologists today view life histories as the ways in which organisms
compete with others of their species to leave the greatest number of
visits per day. When the young tits flutter from
descendants, and thus genes, in future generations. A key concept in
the nest, they will seek shelter in high, dense
life history theory is that trade-offs exist among different life history
Figure 8-1. Blue Tit at Nest Hole: vegetation. There they will be fed for another week or so, at ever de-
Like their North American relatives,
traits. The most common trade-off is between increased reproductive
creasing rates, until the young become independent and depart their
the chickadees, Blue Tits of Eurasian output and decreased survival—survival of both the parents and the
natal territory for a life of perpetual risk....
woodlands nest in cavities and lay large offspring they produce. These trade-offs are reflected in the consid-
numbers of eggs. Through natural selec- -----
erable variations in the reproductive effort and survival of birds: A
tion, these short-lived birds have traded At the edge of the same British wood is a most puzzling sight: a
Blue Tit may produce more than 15 fledglings in one summer, but has
a high annual survival rate for the op- small warbler feeding a fledgling that is many times its own size. The
portunity to rear many offspring each at best a 50 percent chance of surviving to the next year. In contrast, a
hapless parent seems in danger of being swallowed by the offspring it
year. Photo by D. J. Saunders/Oxford Royal Albatross produces at most one fledged young every two years,
Scientific Films. is feeding, as one of ornithology's most intriguing dramas is played out
but the adult's annual survival rate is over 95 percent. No matter how
once again. The large young is that of a cuckoo. The bird that inspired
prodigious or restrained a bird's reproduction, its lifetime output is
the cuckoo clock is actually a so-called "brood parasite"—the original
usually just adequate, on average, to replace losses to mortality. (You'll
dead-beat parent—relying on other species to incubate and rear its
hear more about this in Chapter 9.)Variation in mortality is one of the
young. This parasitic habit has arisen at least six times in the evolution
principal ways that natural selection can sift among the variants in a
of birds. It relies on a carefully cultivated deception that prevents host
population: the least fit are more likely to die before passing on their
parents from rejecting the parasite's young, a deception that in different
genes. Thus, mortality, as unfortunate as it may seem on an individual
parasites has led to the evolution of a suite of mimetic and aggressive
basis, is one of the wellsprings of the great diversity of reproductive
ploys unparalleled in the feathered world....
(and all other) traits that we see in birds, and it is a natural place to begin
this chapter's exploration of the breeding life histories of birds.
■ Despite these different scenarios, however, there is no essential vari- A great deal remains to be learned about the survival rates of birds,
ation in the reproductive challenge that these and all other adult birds
but several generalities emerge from the studies available:
face: finding a safe place to lay their eggs; ensuring that the eggs receive
the warmth they need for the developing embryos within to hatch; and (1) Larger bird species tend to have higher survival rates than smaller
then ensuring that the young are well fed, increasing their chances of ones, especially among closely related species (Table 8-1). (This
surviving to independence and then perpetuating the parents' heritage. rule generally holds among all animals.) For example, adult swans
Clearly, birds manage to meet the reproductive challenge in a variety have an 80 to 98 percent chance of surviving to the next year,
whereas their small cousins, the ducks, have annual survival rates

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 8.4 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.5
of only about 40 to 60 percent. In general, most big birds (gull
Table 8-1. Annual Adult Survival Versus Weight: Larger adult birds tend to survive better from one year to the next size or larger) have annual adult survival rates between 70 and 95
than smaller birds, but some exceptions are evident. For example some seabirds, such as the Sooty Shearwater percent, and most small birds (robin size and smaller) have annual
and Northern Fulmar, are particularly long-lived for their weight. Unless otherwise indicated, all weight data from adult survival rates between 30 and 60 percent. A few groups ap-
Dunning (1984) and survival data from Welty and Baptista (1988), after Lack (1954).
pear to be distinctive, however: penguins have comparatively low
survival rates for their size, and swifts and hummingbirds survive
longer than one might expect from their small size. The ecological
Species Annual Adult Survival (%) Average Weight oz (g) reasons for these distinctions are not known.

(2) Immature birds nearly always have lower survival rates than birds
Blue Tit 30 0.4 (11)* that have reached reproductive age. For example, in their first few
years, gulls have average annual survival rates of 30 to 50 percent,
Barn Swallow 37 0.7 (19)
whereas older birds survive at about 80 percent per year (Fig.
Song Sparrow 30 0.8 (21) 8 - 2)

European Starling 47 2.9 (80) female (3) Birds in tropical areas tend to have higher survival rates than their
3.0 (85) male relatives at higher latitudes. Studies of color-marked passerines in
the tropics indicate that over 80 percent of adults survive each year,
American Robin 52 2.8 (77) whereas only about 50 percent of similar-sized songbirds in the
Blue Jay 55 3.1 (87) temperate zone survive each year (see Ch. 5, Patterns of Migration,
Table 5 - 2).
California Quail 50 6.1 (170) female
(4) Birds have higher survival rates than mammals of a similar size.
6.3 (176) male
Because very few birds approach humans in mass, however, most
Figure 8-2. Typical Survivorship Curves:
Sooty Shearwater 91 10.3 (287) birds have substantially lower survival rates, and consequently Graphs showing the approximate num-
shorter life spans, than humans.The mammalian exceptions to this ber of individuals of different species
Northern Fulmar 94 17 (479) female
mammal-bird comparison are bats, whose relatively high survival remaining alive at different ages, out
21.8 (609) male of a starting group (cohort) of 1,000
rates approach those of similar-sized birds.
individuals of each species. Relative
American Coot 40 20 (560) female
age, rather than absolute age, is shown,
26 (724) male Once the period of low survival early in the life of an immature because of the very different life spans of
bird is past, the adult experiences a constant probability of surviving the species. Typical invertebrates such
Black-crowned Night-Heron 70 31.5 (883) as the oyster produce vast numbers of
any given year for most of its remaining life. Ecologists define survi-
young, but few survive to adulthood
Herring Gull 70 37.3 (1,044) female vorship as the proportion of the individuals born at the same time (a
(note the sharp reduction in survivors
43.8 (1,226) male cohort) that survive to a given age. Plotting survivorship relative to age at a young age). Once oysters reach
yields a curve for birds that is distinctly different from our own: like a certain age, however, their chance
Mallard 52 38.7 (1,082)
birds, humans have a period of high mortality in the very early years of of surviving each year remains high
life, but after that period is past, we have very high survival rates until (as indicated by the nearly horizontal
White Stork 79 107-125 (3,000-3,500)*
portion of their curve). Humans have a
late in life, at which time our mortality rates climb steeply (see Fig.
Canada Goose (canadensis race) 84 118 (3,314) female very short period of high mortality just
after birth (not shown due to scale), but
136 (3,814) male 1000 after that, their chance of surviving each
Yellow-eyed Penguin 90 year remains very high until late in life,
185 (5,200)*

Number of Survivors (Log. Sca le)

when mortality rates rise again. Birds
8 Tundra Swan 92** 221 (6,200) female also have high mortality rates at a young 8
age. Once they reach about one year of
254 (7,100) male 100
age, however, their survival rate remains
Royal Albatross 97 296 (8,300)* quite constant (but lower than that of hu-
mans or oysters) for the rest of their lives.
*Weight and survival data from Brooke and Birkhead (1991) Unlike humans, birds rarely live long
**Survival data from Limpert and Earnst (1994). 10 enough to experience greater mortality
due to old age. Bird survivorship curve
based on actual Herring Gull data from
Paynter (1966), in which only 60 percent
of the birds survived their first year, but
90 percent survived each later year.
Relative Age

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

8.6 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.7
8-2). Most birds do not live long enough to experience the senescence Figure 8-4. Zitting Cisticola: The di-
that causes this climb in mortality rates late in our own lives. This, minutive, warblerlike Zitting Cisticola
(also known as the Fan-tailed Warbler)
coupled with the generally lower survival rates of birds, means that
holds the record for rapid attainment
they face prospects very different from our own during adult life. So, of reproductive maturity. Formerly
before reading on, consider for a moment what it would be like to face classified with Old World Warblers,
a constant and substantially higher risk of mortality throughout your cisticolas are now placed in their own
adult life; think what this risk would do to the potential for social ties family. Although most cisticolas are
strictly African, this common species
outside the family, and what havoc it would wreak with our insurance
ranges from Africa into southern Eu-
premiums! rope, Asia, and even northern Australia,
Some birds put more effort than others into reproduction—gen- inhabiting a variety of wet and dry grass-
erally yielding more offspring, but at a cost of decreased survival for lands, marshes, and agricultural fields
in both temperate and tropical regions.
the parents. For example, a Northern Cardinal that puts too much
The polygynous male weaves a number
energy into rearing offspring during one breeding attempt may de- of bottle-shaped nests on his territory,
press its own survival to such an extent that it will end up producing suspending them from grass stems. Indi-
fewer. offspring in the long run than another Northern Cardinal that vidual females choose a nest, add a lin-
ing, and raise young with no additional
puts less energy into the current breeding attempt and saves more
help from the male, while he continues
for its own survival, thus elevating its chances of producing more to build more nests and display for
young in the future. Over evolutionary time, the way in which this more females. The breeding season
trade-off between parental survival and offspring production plays situation in which their annual survival rates are declining, and the is long, lasting up to seven months in
itself out may set the optimal balancing of costs and benefits at very curious biologist thinking about the evolution of life history traits in Mediterranean regions and Japan, and
birds can consider a bird that is in the early years of its reproductive most of the year in tropical Africa. In a
different levels of effort for different species (Fig. 8 3). A key factor in
-
Japanese study, Ueda (1985) found that
this balance is the change in the number of offspring that a bird can life to be essentially equivalent to one that is much farther along. This
11 percent of the breeding females were
expect to produce in the future. For example, if a bird is faced with makes a big difference for the field biologist gathering data on the juveniles—nesting in the same breeding
a future in which the prospects for its own survival are beginning to breeding biology of wild birds: discriminating the ages of breeding season into which they fledged. One fe-
birds is much less important than it would be in life-history studies male, banded as a nestling, laid her first
decline, then it will produce more offspring overall if it puts more
egg merely 27 days after fledging, and
into reproduction immediately. In some birds, such as scrub-jays, of many other organisms, such as mammals or fish.
another female, just 46 days after fledg-
gulls, and terns, for which much data on banded and recovered Recall that immature birds have lower survival rates than adults, ing. On average, juvenile females were
individuals has been obtained, researchers can detect a decline in and the transition to a fairly constant survival rate usually occurs as successful as adult females in their
annual survival rates very late in life. Pugesek (1981) has reported when a bird reaches reproductive maturity. Most songbirds reach breeding attempts. The Zitting Cisticola
maturity a little less than a year after fledging. However, females of is the only species whose range extends
that the effort put into reproduction by very old California Gulls
into the temperate zone that is known
increases, possibly as an evolved response to this late senescence. some small tropical species with very long breeding seasons can
to complete two generations within
As already noted, however, the great majority of birds never face a initiate their own breeding attempts just a few weeks after fledging the same breeding season. Photo by D.
(Fig. 8 4) laying eggs and rearing young in the same breeding sea-
- — Tipling/VIREO.
son into which they hatched! At the other extreme are some large
Figure 8-3. Reproductive Strategies:
eagles, condors, and albatrosses, which can take up to 12 years to
Over their lifetimes, birds produce off-
spring in a range of different patterns. reach reproductive maturity.
Shown here are two extremes. The Increasing the survival prospects of their young is one of the
Eurasian Tree Sparrow produces many principal ways that birds can increase their reproductive output, and
young each year of its relatively short
much of the breeding biology explored here is adapted to achieve this
life, whereas the Yellow-eyed Penguin
Eurasian end. Before examining these strategies, however, it is worthwhile to
produces fewer young per year, but
0.3 Tree Sparrow
lives much longer—sometimes 20 years briefly consider the principal threats to young. The most pervasive is
or more. Producing large numbers of predation. Recall that adult birds have higher survival rates for their
young per year apparently places such size than mammals. Many researchers believe that this high survival
an energetic burden on parents that
results from their ability to escape predators through flight. Viewed
their long-term survival is reduced.
Natural selection thus imposes an evo- from this perspective, the act of settling down at a single spot to rear
lutionary trade-off. species must choose young is a very significant departure from the avian lifestyle. Indeed
either longer lives or a higher rate of for many birds, such as swifts and pelagic seabirds, the only time
reproduction. Adapted from Ricklefs
they come down from the sky for a significant period is when they
(1973b, p. 410). 0.0
0 5 10 15
breed. Many nest predators will take sitting adults as well as eggs
Age (Years) or young, so incubating birds of all species, not just waterfowl, are

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 8.8 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.9

Table 8-2. Nest Predation Rates on North American Passerines: Presented here for a selection of passerines is the percentage of
nests lost to predators each breeding season, on average. Some of the percentages may include cases in which only some of the
eggs or young were taken by predators. Note that the sampling methods vary greatly from study to study. In addition, predation
rates may vary widely from year to year, and among different regions and habitats. Thus, these predation rates may not be directly
comparable to one another, and must be viewed with some caution.

% Nests Lost
Species to Predation Location Reference

Yellow-billed Cuckoo 39% Arkansas (Martin 1993a)

Eastern Phoebe 49% Southern Indiana (Weeks 1979)
71% Central Appalachians (Hill and Gates 1988)
Greater Pewee 42% Southeastern Arizona (Chace and Tweit 1999)
Acadian Flycatcher 39% Arkansas (Martin 1993a)
a. California Gull b. American Crow Red-eyed Vireo 49% Arkansas (Martin 1993a)
Warbling Vireo 38% Arizona (Martin 1993a)
Figure 8-5. Predation on Adult Birds at literally "sitting ducks" for predators (Fig. 8-5). The loss of an incu- Carolina Wren 64% Northwestern Alabama (Haggerty and Morton 1995)
Nest: Although nest predators usually bating parent is relatively rare, but eggs and young can be consumed American Robin 39% Pacific NW of N. America (Sal labanks and James 1999)
destroy and eat only eggs or nestlings,
by predators at an alarming rate: predators commonly destroy close 54% Arizona (Martin 1993a)
occasionally they kill adult birds on the
nest. a. California Gull: This California
to half the nests in most forest-nesting passerines (Table 8-2). Some Wood Thrush 40% Arkansas (Martin 1993a)
Gull incubating in a colony at Honey of birds' most engrossing nesting habits are antipredator adaptations HermitThrush 83% Arizona (Martin 1993a)
Lake, California was killed and eaten at to protect both parents and young. From swifts building their nests on American Redstart nearly 52% New Hampshire (Sherry and Holmes 1992)
night, along with its eggs. Photo courtesy cliffs and under waterfalls, Killdeer with their nearly invisible eggs and
of David W. Winkler. b. American Crow: Black-and-white Warbler 26% Arkansas (Martin 1993a)
nests, and lapwings and geese with their pugnacious nest defense, to
This female American Crow and her Hooded Warbler 47% Arkansas (Martin 1993a)
nestling were killed and eaten overnight Southern Penduline-Tits and thornbills whose nests have false open-
44% Pennsylvania (Evans Ogden and Stutchbury 1994)
in their nest by a Great Horned Owl. ings, much of the breeding biology of birds appears to be an effort
Photo by Kevin J. McGowan. 30% Ohio (Evans Ogden and Stutchbury 1994)
to evade or fool predators. Notoriously effective predators include
36% Ontario, Canada (Evans Ogden and Stutchbury 1994)
monkeys, raccoons, skunks, weasels, cats, opossums, and arboreal
Ovenbird 24% Michigan (Hann 1937)
snakes (Fig. 8-6). Among birds, the most effective nest predators in
forested habitats appear to be crows and the crowlike, Australasian 29% Arkansas (Martin 1993a)
currawongs and their relatives; in marine habitats, the top predators 70%* Central Illinois (Robinson 1992)
are skuas, jaegers, gulls, and frigatebirds. Important nest predators Worm-eating Warbler 21% Arkansas (Martin 1993a)
sometimes come from surprising groups: mice and chipmunks are Orange-crowned Warbler 33% Arizona (Martin 1993a)
significant predators in North America, toucans in the Neotropics, and Virginia's Warbler 31% Arizona (Martin 1993a)
Great Spotted Woodpeckers in Europe. In Africa, a large bird of prey Red-faced Warbler 40% Arizona (Martin 1993a)
called the African Harrier-Hawk specializes on bird nests. MacGillivray's Warbler 49% Arizona (Martin 1993a)
Other sources of mortality tend to be much less constant. Weather Yellow-rumped Warbler 38°k Arizona (Martin 1993a)
is probably the most important after predation. Although high rainfall, Western Tanager 45% West-Central Idaho (Hovis et al. 1997)
tides, or winds can cause the wholesale destruction of nests of marsh 30% Northeastern New Mexico (Goguen and Mathews 1998)
birds or colonial birds nesting on low islands, weather more often af- 46% Arizona (Martin 1993a)
fects the eggs or nestlings indirectly by reducing food supplies. Forced Scarlet Tanager 69-78%** Illinois (Brawn and Robinson 1996)
8 to leave the nest for extended periods in search of food for their own Green-tailed Towhee 61 0/0 Arizona (Martin 1993a)
maintenance, parents often lose their eggs or young to exposure or White-throated Sparrow 35% Adirondack Park, New York (Tuttle 1993)
starvation. Birds that feed on flying insects can be especially vul-
45% Algonquin Park, Canada (Falls and Kopachena 1994)
nerable to cold, because their prey may still be present but unable to
Dark-eyed Junco 31 0/0 Arizona (Martin 1993a)
fly: In three years out of ten, cold fronts lasting two or more days and
Indigo Bunting 75% Indiana (Carey and Nolan 1979)
passing through during the nestling period have halved the fledgling
43% Arkansas (Martin 1993a)
production of Tree Swallows nesting near Ithaca, New York (McCarty
Black-headed Grosbeak 23% Arizona (Martin 1993a)
and Winkler 1999). In tropical and desert areas, fledgling production
can be severely depressed by unpredictable periods of extended rain * An unusually high predation rate; data from small forest fragments.
or drought. ** Sample Size = 4 nests.

Cornell Laboratort1 of Ornithologq Handbook of Bird Bio1o9,1

8.10 David W. Winkler
r Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.11
breeding season. In a given year, the length of time over which most
temperate zone birds can potentially breed is no more than about three
months; in the tropics, the season of potential reproduction may extend
to as much as six months.
In an influential early paper, Baker (1 938) introduced the con-
cepts of ultimate and proximate factors (see Ch. 6, Questions About
Behavior) to explain variation in the timing of the breeding seasons of
birds. One of the most common proximate factors influencing the start
of breeding is day length. Through an elaborate chain of physiological
steps within the bird's body, day length serves as the cue that tells most
birds the season (see Fig. 7-37 for how day length affects one aspect
of breeding behavior—singing rate). Ultimate factors, by affecting the
survival and reproduction of birds' ancestors, have caused each popu-
lation to evolve the breeding time that works best for its members, on
a. Eastern Chipmunk b. Bullsnake average. For most species, the food supply for the developing young is
the ultimate factor that seems to have most strongly influenced breed-
ing time. In the annual cycle, birds need the greatest food resources
when feeding large young, and most species, at least in the temperate
zone, appear to time their breeding seasons to match the period of
peak demand with the peak in food availability (Fig. 8-7). This syn-
chronization can explain much of the variation in breeding time that
we see: Goldfinches are the only common birds in North America that
feed their young thistle seeds (most songbirds bring insects to their
young), and goldfinches breed one to two months later than other
songbirds, coordinating their nestling feeding with thistle availability.
Many birds of prey, such as Great Horned Owls, breed very early in
the season—laying their eggs as early as November and December
in the southeastern United States—because their large young take a
c. Pied Currawong d. Brown Skuas
long time to develop. By starting early, the owls can synchronize their
period of peak energy demand with the peak availability of vulnerable
Figure 8-6. Nest Predators in Action: Parasites also can have devastating impacts on fledgling pro- young mammals and birds in early summer. One raptor, Eleonora's
Eggs are vulnerable to attacks from a wide duction. Seabirds that nest in dense island colonies, such as boobies,
range of predators. a. Eastern Chipmunk
Falcon, has switched its predominant prey base for rearing young to
pelicans, and gulls (see Fig. 6-15a), can be wiped out by viruses or the plethora of migrant land birds that pass through the eastern Med-
Raiding American Robin Nest: Chip-
munks consume significant numbers of other pathogens passing swiftly through the colony. For birds nesting iterranean in the fall; its late-summer laying insures that the nestlings
eggs in North America, even from nests in a more dispersed fashion, brood parasites often cause significant will reach the stage at which they require the most energy just when
high in trees. Photo by Bruce D. Thomas. mortality. Cowbirds have been found to parasitize up to 100 percent of most is available.
b. Bullsnake Eating Long-billed Curlew the Wood Thrush nests in woodlots in Illinois (Robinson and Wilcove
Egg at Nest: Snakes consume numerous One familiar bird, the Rock Dove, comes close to avoiding breed-
eggs and young in a variety of habitats.
1994) and parasitism by cuckoos in the Old World can foil over 70 ing seasons altogether. Although it breeds more commonly in spring
Photo courtesy of Mary Tremaine/CLO. percent of the nesting attempts of their hosts (Liversidge 1971). and summer, the Rock Dove can be seen throughout North America in-
c. Pied Currawong Stealing Egg from Many of these high parasitism rates cannot be sustained by the cubating or feeding nestlings in the most inclement weather of deepest
Willie-wagtail Nest: In forests, crows host populations: cowbird parasitism, for example, is threatening
and the crowlike Australasian cur- winter. Its native relative, the Mourning Dove, also has an uncommonly
the survival of several species of birds in North America, including long breeding season—about six months in New York (Bull 1985).
rawongs are the most significant nest
predators. Photo courtesy of Richard Kirtland's Warbler and Bell's and Black-capped vireos. Doves and pigeons may be able to breed when other birds cannot
Major, Australian Museum. d. Brown
because they feed their young nestlings crop milk (see Fig. 4-99b). A
Skuas Consume an Egg: In marine
parent may be able to secrete crop milk while subsisting on a seed diet
habitats, the skuas—large, predatory
relatives of gulls—are among the most
The Timing of Breeding that would not meet the nutritional needs of very young nestlings.
effective nest predators, along with jae- ■ In his novel, Ape and Essence, Aldous Huxley explored how different Pigeons and doves have uncommonly /ongbreeding seasons, but
gers, gulls, and frigatebirds. Photo by R. a few birds have uncommonly variable breedi ng seasons. Birds of des-
our social and emotional lives would be if we restricted our breeding
and N. BowersNIREO.
to a discrete period in the annual cycle. Imagine how intense those ert areas, especially in southern Africa and Australia, nest in extremely
weeks would be! Then consider that most birds have just such a limited unpredictable environments. Whether their environments can support

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

8.12 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biology of Birds 8.13

breeding depends entirely on whether rains have fallen recently. The

crossbills of the Northern Hemisphere face unpredictability of a similar
SPECIES FOOD sort (see Fig. 4-119). Like their relatives the goldfinches, crossbi I Is feed
their young on a diet of seeds, but they require the seeds of pine and
/ Eleonora's Palearctic spruce trees, not thistles. Seed crops in these trees are notoriously vari-
Falcon Migrant Birds able from year to year, and crossbi I Is range over enormous distances
searching for stands of trees with sufficient seed production to support
a breeding attempt. As in birds of tropical deserts, the reproductive
systems of crossbi I Is are primed to go into action whenever promise of
Red-billed Insects
sufficient food for breeding is encountered, and crossbi I Is have been
Quelea
recorded breeding in every month of the year! Note that these birds
with highly flexible breeding seasons are responding to food supply
as both the proximate cue and the ultimate selective force for timing
Tree Insects their breeding.
Swallow

Key Breeding Territories

Food Availability
Fledglings
American Seeds, ■ During the breeding period, nearly all birds defend some kind of ter-
11111111111111111 Goldfinch Especially
Nestlings ritory. Although the size and function may vary widely among different
NE Eggs Thistle
species, mostterritories include at leastthe nest site.The majority of spe-
cies, including warblers, vireos, thrushes, sparrows, most other song-
Boreal Small birds, and many woodpeckers, live completely within their territory
11•1111111111111111111111•M Owl Mammals during the breeding season—mating, nesting, and feeding there.
A number of other species defend smaller territories—usually
just the area immediately around the nest—sharing neutral feeding
F M A ' M ' J . A S O N D grounds with other conspecifics with little or no aggression. Grebes,
Month swans, harriers, goldfinches, and blackbirds—especially Red-winged
and Yellow-headed blackbirds—have this type of territory. Red-wings
place their nests rather close together in a marsh, roadside ditch, or wet
field and feed together nearby. If they visit your feeder in the spring,
Figure 8-7. Breeding Time and Food Abundance: Most bird and other late summer flowers. They breed one to two months
you may notice several males eating together peacefully at one time.
species time their breeding so that the period when they need later than other songbirds, apparently to match nestling feed-
the most food resources—while feeding large young—coin- ing to thistle abundance. Breeding data based on Middleton If a male intrudes near another's nest, however, he is fiercely attacked.
cides with the yearly peak in the young's food supply. This (1993). Many birds of prey breed extremely early in the year, In birds that nest colonially, such as penguins, albatrosses, petrels, pel-
chart, indicating the months when eggs, nestlings, and fledg- temperate zone species frequently laying eggs during winter. icans, gannets, cormorants, herons, gulls, and terns, the territory may
lings typically are present, as well as the approximate seasonal Because their young take a long time to develop, starting early
be tiny—restricted to just enough space around the nestto allow mating
patterns in the availability of food for the young, illustrates this allows the parents to have older nestlings and fledglings during
correlation for selected species with different types of prey. early summer, when their prey—vulnerable young mammals
and nesting activity without physical contact with neighboring pairs.
Eleonora's Falcon nests relatively late in the year, taking ad- and birds—are at peak. Boreal Owls also breed fairly early, pro- Indeed, some of these territories appear to be separated by the distance
vantage of the abundant avian migrants passing through the ducing large young by summer, but for different reasons. Their an incubating bird can reach with its beak: in exactly the same habitat,
eastern Mediterranean region in the fall, which provide ample primary prey, voles, peak in autumn, well past the fledgling nests of the large Peruvian Pelican are placed around two per square
food for older nestlings and fledglings. Data are based on Walter stage, but the vole supply in summer appears to be sufficient
yard, whereas those of the smaller Guanay Cormorant are at three per
(1979). Nesting on the African savannas, Red-billed Quelea for feeding young. Early breeding is probably advantageous
feed their nestlings exclusively on insects for their first five because both juveniles and their parents have more time before square yard (Welty and Baptista 1988).
days, although the adults are primarily seed-eaters. They breed winter to increase their fat reserves and to complete their post- A few breeding birds defend territories that do not include the nest
during the rainy season, when insects are the most abundant. nesting molt. In addition, young fledged earlier have more time site. These include leks, used only for male display and mating (see Ch.
The "food" graph for quelea actually indicates monthly rain- to develop their hunting skiI Is before winter, and early breeding
6, Reproductive Behavior: Lek Polgyny); and feeding territories, such as
fall, which is directly correlated with insect abundance. Data adults increase their chances of producing a second brood.
courtesy of Jim Dale. Tree Swallows and most other temperate Note that the Boreal Owl's small size and consequently faster
the flower patches defended by many hummingbirds (see Ch. 6, Side-
zone passerines that feed insects to their young begin breeding rate of development allow it to breed slightly later than many bar 4, Grouping Versus Territoriality). Several species defend separate
in the spring, matching their time feeding older nestlings and larger birds of prey: eggs laid in mid-March produce fledglings feeding and nesting territories: Seaside Sparrows defend a feeding area
fledglings to the high insect abundance of late spring and sum- by mid-May. Data from Korpimaki (1987) and Korpimaki and right along the shore in addition to their brushy nest site well above the
mer. Data courtesy of David W. Winkler. Unlike most songbirds, Hakkarainen (1991).
high-tide line; and in Southern California, Phainopeplas defend their
American Goldfinches feed their young on the seeds of thistles

Cornell Laboratory of Ornithology Handbook of Bird Biology

 8.14 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.15
nest site in trees in the canyon bottoms and commute to their hillside parakeets) observed by Krebs (1998) were destroyed by other Crimson
foraging territories, which contain stands of buckthorn trees that bear Rosellas during laying. Beissinger et al. (1998) demonstrated how ef-
their principal food, a berry (Walsberg 1977). fective nest defense can be: when they set out experimental nest boxes
The territorial system may also vary within a species, depending with eggs, 75 percent of the clutches were destroyed by Green-rumped
on local ecological factors. Most Song Sparrows, for example, stay Parrotlets (small Neotropical parrots) within three days, whereas only
within their territories in the breeding season—mating, nesting, and 4.5 percent of the clutches were destroyed in control nests defended
feeding there. But when the density of nesting birds is high, as on some by Green-rumped Parrotlet pairs. Other birds will go so far as to kill
islands off the coast of British Columbia, each male may defend only a the young of conspecifics: unmated male Barn Swallows sometimes
small mating and nesting area, joining other males to feed in one area kill other Barn Swallows' nestlings by grabbing them and throwing
without aggression. them to the ground.
A few birds also defend territories outside the breeding season. Breeding interference also may result in birds rearing young that
For example, Northern Mockingbirds often defend their berry-rich are not their own. Studies with individually marked birds have shown
wintering area as vigorously as they do their breeding territory. Snowy that in most species "monogamous" males will try to sneak copu-
Owls, which breed on the arctic tundra, defend winter territories a bit lations with females other than their mates whenever the opportunity
further south that contain fields and edge habitat rich in their chief prey, arises; these extrapair copulations allow them to father more young,
rodents (Boxal I and Lein 1982). Other birds known to defend winter thus further promoting their genes without increasing their parental
territories include, in North America, Loggerhead Shrikes, American care duties. Mated females, also, may seek extrapair copulations with
Kestrels, Red-headed Woodpeckers, Sanderlings, and many other mated or unmated males they deem "good genetic material" (see Ch.
shorebirds. On their wintering grounds in Africa, Common Nightin- 6, Mate Choice: Extrapair Copulation in Birds)—and their mates may
gales, European Robins, White Wagtails, and wheatears also defend end up rearing young that are not genetically their own. Very recently,
territories. For the most part, however, nonbreeding birds move in aided by DNA comparisons, researchers have discovered that many
flocks of single or mixed species, or move around an undefended species regularly lay eggs in the nests of conspecifics. Over 185 spe-
home range either singly or loosely associated with their mate. Even cies not previously considered parasitic—especially colonial birds,
in species that are territorial in winter, individuals can switch to flock- waterfowl, and other precocial birds—are now known conspecific
ing whenever a predator appears or when so many intruders attempt brood parasites (Rohwer and Freeman 1989; Rothstein and Robinson
to get at the defended resources that territorial defense is no longer 1998; Semel and Sherman 2001; Eadie et al. 1998).
possible. By defending an area for breeding, birds isolate themselves from
others, thus decreasing their vulnerability to interference with their
courtship and nesting activities. Although maintaining any kind of
Functions of Breeding Territories exclusive space is clearly helpful, larger territories provide more iso-
Although territories are costly to defend—in terms of time, en- lation than smaller ones—but they also cost more in time and energy
ergy, and personal risk—birds benefit from them in many ways. Living to defend.
in a familiar area allows birds to evade predators more readily, because
they know the most protected spots and the best hiding places. Birds
also may be able to find food more easily in a familiar area, and de- Nests and Nest Building
fending areas with adequate food secures thatfood supply for the bird's
own use. But why does defending an exclusive area become crucial to ■ No branch of ornithology has a greater disparity between our current
most birds in the breeding season? level of understanding and what our understanding could be than the
Researchers believe that the primary benefit a bird gains from a study of nests. Only insects exceed birds in the diversity and sophis-
breeding territory is that it reduces the chances that other members tication of the nests they build, and a tremendous amount of literature,
of the same species will interfere with its breeding effort. Although much of it from the 19th century, qualitatively describes the nests and
8
at first glance most breeding birds appear relatively faithful to their nest-building behavior of birds (Sidebar 1: Neat Nesting Facts). How-
mates and at peace with other members of their species, this scenario ever, a quantitative literature that includes a rigorous scientific approach
rarely survives close scrutiny. Female Warbling Vireos, for example, to asking and answering questions about nest function and construction
regularly steal nest material from each other's nests (Howes 1985). is in its infancy. Across the entire spectrum of birds, from common back-
Many birds destroy the eggs of conspecifics: Marsh Wrens and House yard birds to exotic species in far-off lands, interesting and compelling
Wrens routinely puncture conspecifics' eggs, and roughly 10 to 20 questions wait to be answered. I will ask a few of these questions in the
percent of the nests in Cliff Swallow colonies studied by Brown and pages to come, but I wish to emphasize here that many of these questions
Brown (1988) lost at least one egg to conspecifics. In Australia, more can be answered with no specialized tools or techniques. I encourage
than 50 percent of the clutches of Crimson Rosellas (bright red and blue (Continued on p. & 18)

Cornell Laboratori1 of Ornithologq Handbook of Bird Biologq

8.16 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biology of Birds .8.17

Ducks even occasionally incubating simultaneously.

Sidebar 1: NEAT NESTING FACTS . \ \
Even more rarely, two different species may share a
(

Podulka nest. In Florida, a Great Horned Owl moved into a Bald

Eagle's nest, each incubating their own eggs just a few feet
../r
• apart. (Great Horned Owls often completely take over
Birds can fly and we can't—that alone is enough to inspire
our awe and fascination for these small, feathered bundles
.= •

4, ; -".■
----47i
- A.,
'._,- "--4.- --. b
-:4
S eagle nests.) In Denver, Colorado, an American Robin
and a House Finch shared the robin's nest (Bailey and N ie-

,-.-,
of energy. But birds also have adapted to almost every .1,--,-•%■\ drach 1936). The female House Finch laid six eggs in the
1 lc.'.' - - ..1Z.-
-- 7---- --' Ib. /4'' '
habitat on land, and in building their nests and raising their / ■ .
• 17:„.,--....,4. „.. -- ,-:- robin's nest, and both pairs fed both species of nestlings.
young they regularly carry out tasks that seem nearly im-
possible to us. Below are some of the feats accomplished
by birds—some routine and some quite unusual—as they
41'r::::61;:-
ittiil:t:%
._;,f . y
:,--_,Wi
: _...4

--.%:.4 ,f,77
Aro'
'le "-y.:t5._
The larger robin young eventually smothered the nestling
finches, but the adult House Finches continued to feed the
i.,,, young robins, even after they had left the nest.
go about breeding.
1 a'-------_.. .---,-
-
WW1
i 4•0

"--#7- '" -•/' 40Mdr/

, 7"sli
.---
...

_ Feeding the Young

Nests Figure B. Canyon Wren Nest ofOffice Supplies: An enterprising Young birds, like most babies, are a lot of work right
Unusual Nest Sites Canyon Wren in Fresno, California adds yet another rubber from the start. Experiments with young nestling crows
Although most birds place their nests on the ground, band to its nest. The nest, weighing 2.5 pounds (1.1 kg), was
determined that they must eat one-half their body weight
located in an office building and was constructed entirely from
in vegetation, in cavities, or on rocky ledges, a few indi- each day just to stay alive, but that they could easily con-
office supplies—a total of 1,791 items.
viduals have fledged young from more mobile sites. An sume their full weight daily. In the wild, nestling Belted
Ash-throated Flycatcher in Colton, California nested in FigureA. White-necked Raven in Barbed Wire Nest: Birds may Kingfishers may devour up to 1.75 times their weight in
a crevice in an active steam shovel that moved up to 200 make creative use of the materials on hand in constructing their in Eurasia must hammer on a tree about 100,000 times to
fish each day (White 1939). In general, older nestlings
feet (61 m) a day; a Barn Swallow nested on a slow-mov-
nests. White-necked Ravens sometimes include barbed wire, excavate their nest cavity (Cuisin 1983); and Hamerkops
consume greater amounts of food, but their intake is a
and occasionally may build a nest entirely from it. may make roughly 8,000 trips over four months carrying
ing narrow-gauge train in British Columbia, Canada; and smaller fraction of their weight—only about 25 percent.
both Prothonotary Warblers and Tree Swallows have suc- ti rely of facial tissue, White-necked Ravens occasionally sticks and grass to build their huge nest mounds (see Fig.
One fledging-age American Robin described by Allen
cessfully nested on ferryboats moving back and forth daily use only barbed wire (Fig. A), a Ruby-throated Hum- 8-38) (Kahl 1967). The pendulous cup nest of one AI-
(1961), however, was fed (by researchers) as much as it
across rivers. mingbird on Long Island, New York relied solely on fiber- tamira Oriole in Mexico contained 3,387 pieces of grass,
would eat, and it managed to down a full 14 feet (4.3 m)
Birds also are good at adapting to whatever nest sites glass roofing insulation, and a Carolina Wren used mostly many of which were three to four feet (0.9 to 1.2 m) long.
of earthworms!
are available. On treeless islands, birds that typically nest hairpins. In Bombay, India, crows included 25 pounds (One wonders whether the bird's nest construction or the
To keep the food flowing, most parents make nu-
in trees, such as American Robins, may place their nests (11 kg) of gold eyeglass frames stolen from an open shop researcher's job of counting each piece of nest material
merous trips to their nest. Skutch (1976) determined that
right on the ground. window in the structure of their nest; and, off the coast of was the more difficulttask.)The Edible-nest Swiftlet, which
most small songbirds feed each of their nestlings an av-
Labrador, Double-crested Cormorants—who routinely constructs its nest almost entirely of saliva (see Fig. 4-93),
erage of 4 to 12 meals per hour. This can add up quickly:
obtain nest material under water—salvaged pocketknives, must work for five or six weeks to build up its nest, even
Sizes of Nests a European Pied Flycatcher, during one nest cycle, may
men's pipes, hairpins, and combs from a sunken trading though its salivary glands enlarge greatly during the nest-
Using primarily their beaks and feet, birds build a visit the nest 6,200 times with food (Welty and Baptista
bewilderingly diverse array of nests, ranging in size from vessel to use in their nests (Forbush 1925-1929). In Fresno, ing season (Stresemann 1927-1934).
1988). One male House Wren in Illinois feeding 12-day-
the tiny cups of the Bee Hummingbird of Cuba, just 0.8 California a Canyon Wren placed its nest on the beam of old nestlings by himself may hold the record, however.
inches (2 cm) across and about 1 inch (2.5 cm) tall (around an office building, and keeping with the office theme, Nest Sharing and Reuse
He brought food to the nest 1,217 times between 4:15
the size of a large thimble), up to the enormous mounds constructed it entirely out of office supplies such as paper Sometimes more than one nesting pair may benefit
A.M. and 8:00 P.M.—an average of once every 47 seconds!
of megapodes, which weigh many tons. The largest nests clips, pins, rubber bands, thumbtacks, shoelaces, needles, from a bird's labor in constructing a nest. Large nests, in
Birds that bring larger prey feed their young much less of-
in North America, however, are built by Bald Eagles. The wire, matches, and toothpicks-1,791 items in all (Fig. B). particular, may be used year after year by the same pair
ten. Golden Eagles, for example, bring a rabbit or grouse
record is probably held by one near St. Petersburg, Flor- The large nest—nearly 8 inches (20 cm) high—weighed a or a succession of different pairs. Bent (1937) reported
to their nest about twice a day, and Bald Eagles bring prey
ida that was 20 feet (6 m) deep and 9.5 feet (3 m) across full 2.5 pounds (1.1 kg). three different Osprey nests occupied continually for 41,
four or five times a day.
(Broley 1947). One near Vermilion, Ohio is thought to Birds frequently use animal hair in their nests, espe- 44, and 45 years. And, the large platform nest of a White
Some birds travel great distances to find food for their
have weighed about two tons when it came crashing down cially in the lining, but one Loggerhead Shrike in Florida Stork in Germany was occupied from 1549 through at least
1930! One nest built in a tall chestnut tree near Saybrook, young. Seabirds are famous for this (see Feeding the
(Herrick 1934). The mud nest of the Rufous Hornero of built its nest almost entirely of hair from a nearby dead
Connecticut served four species in four years: built by a Young, later in this chapter), but even the Common Swift
South America (see Fig. 8-34d) weighs up to 11 lb (5 kg), cow. Birds don't always wait for hair to become avail-
Cooper's Hawk that used it one year, it was taken over by of Europe may fly a total of 621 miles (1,000 km) each
nearly 70 times the weight of its 2.6-oz (75-g) builder. able, though. Tufted Titmice may pluck hair from living
Great Horned Owls, then Red-tailed Hawks, and finally day to gather food for its two or three nestlings (Welty and
We would be busy for quite some time if compelled to opossums, woodchucks, squirrels, or people, and Black-
Barred Owls; each spent a breeding season in the nest Baptista 1988). North of the Arctic Circle, parents may
construct a 9,000-lb (4,000-kg) mud globe using our lips capped Chickadees may grab hair from sleeping raccoons
(Bent 1938). gather food over a longer workday (Welty and Baptista
and toes! (Lynn Leopold, personal communication).
Occasionally, two females or pairs of birds may occupy 1988): one female Bluethroat (an Old World flycatcher)
the same nest at the same time. Two Long-billed Curlew fed her young from 3:00 A.M. to 11:45 P.M.—a 21-hour
Odd Nest Materials Nest Construction Feats
Birds are equally resourceful when selecting nest mate- If you have ever watched a bird build a nest, you prob- females shared a nest containing a large number of eggs, day shift! ■
rials. Although most species prefer certain materials when ably thought it looked like hard work—and apparently, it presumably laid by both females. Two Song Sparrow pairs
they are available, sometimes other substances are more is. Barn Swallows may make more than 1,200 trips with a have done likewise, as have two Wood Duck females. In Note: Unless otherwise indicated, the facts presented above are
mouthful of mud to build their nest; Black Woodpeckers each case, females shared incubation duties—the Wood from Terres (1980) and Kress (1988).
accessible. AWarblingVireo in California built its nesten-

Cornell Laboratory of Ornithology Handbook of Bird Biology

8.18 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.19
readers to relentlessly ask "why?" Why do goldfinches Figure 8-9. Birds Nesting in Association
line their nests with the down from thistle seeds? Why do with Social Insects: Many tropical birds
build their nests near or in the nests
so many birds (hummingbirds, Blue-gray Gnatcatchers
of aggressive ants, wasps, or termites.
(Fig. 8 8), the nuthatch-like sittellas of Australia and
-
These insects do not bother the birds,
New Guinea, Long-tailed Tits of Eurasia, and others) but do provide protection from nest
plaster lichens on the outside of their nest cups? Why predators. a. Nest of Rufous-naped

does the Cliff Swallow build its nest without any of the Wren in Ant-Acacia Tree: The Rufous-
naped Wren—a large, boldly patterned
vegetation that the Barn Swallow uses to build its mud wren of dry tropical forest and thorny
cup? Why don't all swallows use feathers to line their scrub in Central America—often places
nests as do Tree, Barn, and Bank swallows? Does the its nest in an ant-acacia tree. These trees
same species nesting in different parts of the continent are covered with large thorns which,
formidable predator-deterrents them-
build a different kind of nest? (Enlist some pen-pals or
selves, are inhabited by acacia ants
join the CLO's Birdhouse Network to find out!) These that attack any animal that comes near
sorts of questions will lead inevitably to questions about the tree. In addition, certain aggressive
the costs (in terms of parental effort and risk) and benefits wasps also tend to nest in ant-acacias, for
protection against predatory army ants.
(in terms of greater nest safety) of various sorts of nest
Rufous-naped Wrens nesting near the
construction and placement, and only when hundreds nests of these wasps fledge more young
of people begin asking such questions will a modern than wrens that do not, because they
Figure 8-8. Lichen-covered Nest of science of nest study be possible. gain the wasps' protection from nest-
Blue-gray Gnatcatcher: The small, robbers such as white-faced monkeys
a. Nest of Rufous-naped Wren in Ant-Acacia Tree (Joyce 1993). Here, two Rufous-naped
compact, cup nest of the Blue-gray
Gnatcatcher, usually saddled atop a Functions of Nests Wrens approach their nest (center) near
a wasp nest (cylindrical structure on the
horizontal limb, is neatly bound together
Nests are primarily structures to hold and protect the eggs and, in left) in an ant-acacia tree in Santa Rosa
and to its supporting branch with spider
webs. Pieces of lichen camouflage the
many species, the developing young. In some species, the nest takes National Park, Costa Rica. b. Black-
outside so well that from a distance the on additional functions: some birds roost in their nests even when they headed Trogon Nesting in Termitary: A
nest may look like just another bump are not breeding, and others use them to attract mates. Some nests have variety of tropical birds place their nests
on the branch. Photo courtesy of David inside termitaries (active termite nests),
secondarily taken on important functions in courtship: many bird spe-
Allen/CLO. including this male Black-headed Tro-
cies I imittheir courtship behavior to the vicinity of the nest, and mutual gon peering from its nest hole in Santa
nest building is a common aspect of pair formation and solidification. Rosa National Park, Costa Rica. Termites
Nevertheless, providing a safe haven for eggs and young is the main use digested wood and their own feces
function of nearly all nests. to construct their nests, forming a hard,
carton-like mound into which birds
Clearly, one of the principal requirements for a nest and its site may dig their nests. As a bird digs into
is to thwart predators, and birds have evolved many adaptations to do the mound, the termites seal the exposed
so. One of the most interesting is placing the nest near insects or other walls, so that the bird's nest and the ter-
animals that keep predators away. Many tropical birds, for example, mites' living chambers are not in direct
contact. Other term itary-nesters include
nest on or very near the nests of aggressive wasps (Joyce 1993) or in
many other New World trogons, several
acacia trees tended by aggressive ants (Young et al. 1990), both of parrots, nearly half the kingfishers, and
which attack mercilessly any of a large suite of potential predators that some jacamars and puftbirds. In Peru,
approach their nest or nest tree (Fig. 8 9a). No one yet knows how
-
Brightsmith (2000) found that Tui and
(or why) the nesting birds are spared the insects' attacks. Violaceous Cobalt-winged parakeets, as well as
Black-tailed Trogons, prefer termitaries
Trogons of the Neotropics dig their nest cavity right inside a large paper that also house colonies of aggressive,
wasp nest, and other trogons, many kingfishers, and various parrots, biting ants. Brightsmith suggests that the
including the Orange-fronted Parakeet, dig their nest tunnel into an ac- ants, which have a distinctive odor, may
tive termite mound (Fig. 8 9b). In the Old World, House Sparrows and
-
protect the birds' nests either directly
by attacking potential predators, or
European Starlings often nest near Imperial Eagles; and in the tundra,
indirectly because their odor masks the
Snow Geese, Brant, and Common Eiders often nest near a Snowy Owl, smell of a bird's nest or in some other way
whose presence discourages attacks by arctic foxes. The ploverlike b. Black-headed Trogon Nesting in Termitary discourages predators from searching for
WaterThick-knee of Africa nests along sandy shorelines near breeding nests. Inset shows male Black-headed
Trogon. Photos by Marie Read.
crocodiles (Gill 1990).

Cornell Laboratorq of Ornitholop Handbook of Bird Biologq

8.20 David W. Winkler Chapter 8 —Nests, Eggs, and Young: Breeding Biologq of Birds 8.21

Predation pressure on bird nests is general ly thoughtto be greatest faces, holes and cracks of every type, branches of all diameters, bare
in the tropics, and many species there build nests that are extremely ground, as well as myriad human artifacts (skyscrapers, out-buildings,
small for the bird's size, apparently to escape detection (Snow 1976) bridges, telephone poles, signs, oil pumps, old boots and hats): nearly
(Fig. 8 10).
- anything that would support a nest has been called into service (Fig.
Nests also provide shelter from the elements. The microcl i mates 8 11). Nest sites need not even be stationary: robins, swallows, and
-

around and in many nests are much more favorable than those in the phoebes have been reported to nest on active ferries.The variety of nest
Figure 8-10. Pompadour Cotinga and surrounding environment. For example, temperate-nesting humming- sites is so diverse as to defy classification. The one factor common to
Nest: Many tropical birds, such as this
birds choose nest sites under overhanging trees to minimize heat loss successful sites, however, is that they are protected from predators and
Pompadour Cotinga from the rain for-
ests of South America, build relatively at night (Calder 1973); some gulls place their nests in shade to reduce the elements, and close to the food supply for hungry nestlings.
small nests and lay few eggs. Ornitholo- the risk of overheating and dehydration for the nestlings (Wi nnett-Mur- Some species seem to have much more specific nest site require-
gists believe these tiny nests are less ray 1979); and the enclosed nests of many desert birds provide shade, ments than others, and the Kirtland's Warbler may be one of the most
noticeable to the numerous tropical
preventing the overheating of eggs (and the parents incubating them) demanding. This endangered species, which breeds exclusively in a
nest predators. In 1924, a New York
Zoological Society expedition led by during the day (Yom-Tov and Ar 1980 [19811). Nests also contain the 100-by-60-mile (161-by-97-km) area in northern Lower Michigan,
William Beebe discovered the nest pic- eggs and young to keep them from rolling out: New World orioles and requires a specific combination of plants of particular sizes for suc-
tured here. Located 60 feet (18 m) up in their large, tropical relatives the oropendolas, as well as the Old World cessful nesting. It places its nest on the ground among grasses, arched
a stand of bamboo, the nest was a loose weavers (distant relatives of House Sparrows), build their nests at the over by the living lower limbs of pines, usually jack pines between 6
tangle of woody tendrils, so open that the
tips of very long, thin branches, probably as an adaptation against and 18 feet (2 and 5.5 m) tall (Fig. 8 12). Smaller pines are too dense
-
egg was visible from below, and so small
that the "entire nest was eclipsed by the predation by monkeys and other mammals.Their deep, enclosed nests near the base; older trees have too many dead limbs at the bottom. The
feathers of [the incubating female's] help prevent the eggs from falling out as the nests swing wildly in the stand of jack pine must be at least 80 acres (32.4 hectares) in size, with
breast" (Beebe 1924, p. 114). a. Female wind—a frequent result of their precarious location. numerous openings to admit sunlight and keep the lower limbs of the
Pompadour Cotinga on Nest: This wa-
pines green (Fig. 8 13).
-

tercolor was painted by Helen Tee-Van,

a member of the expedition. b. Nest and
Before humans arrived on the jack pine plains of Lower Michigan, Figure 8-11. Great Kiskadee (Pitan-
Diversitq of Nest Sites I ightning-ignited fires burned sections of the forest at frequent intervals,
Egg of Pompadour Cotinga: A photo of gus sulphuratus) and Plain Thornbird
the nest and egg, taken by Herman Rog- Birds nest in virtually every terrestrial or shallow water habitat on creating an ideal nesting area for the Ki rtland's Warbler. Somewhere in (Phacellodomus inornatus) Nests on
ers and John Tee-Van, both expedition earth—from the surfaces of lakes to rock niches above timberline, and the forest area, newly growing young jack pines of just the right height a Windmill: Birds are known to place
members. From: "The Rarest of Nests on from deep tropical caves to the howling, frozen barrens of Antarctica. their nests in all sorts of seemingly odd
were always available. When humans began prohibiting forest fires,
the Tallest of Grass Stems," by William places, including various structures built
Other than the surface of the open ocean and thin air, it is difficult to life became difficult for the Kirtland's Warbler. The pines grew too big
Beebe, September 1924. Bulletin of by humans. This Great Kiskadee nest was
the New York Zoological Society 27(5):
think of a habitat birds do not use for nesting. Furthermore, the sites and too thick to satisfy its needs. The story has gone full circle, however. constructed on top of an existing Plain
114-118. birds use within those habitats are similarly diverse. Featureless cliff Humans, conscious at last of the bird's dilemma, now burn sections of Thornbird nest in a completely exposed
setting within the supporting structure of
the pine forest regularly on the Kirtland's Warbler Management Area
a windmill on a working ranch in the Ila-
near Lovells, Michigan.This burning, combined with cowbird trapping nos of central Venezuela. The inset shows
to reduce brood parasitism, appears to be effective, as the number of a closer view of the nest indicated by the
Kirtland's Warblers have increased since 1990. arrow. Photo by Jason A. Mobley.

Figure 8-12. Male Kirtland's Warbler

at Nest: The endangered Kirtland's
Warbler breeds only amid thick stands
of medium-sized jack pines in northern
Michigan. It conceals the nest among
dense grasses on the ground, usually
right near the trunk of a pine (not vis-
ible). The lower branches arch over the
nest—a cup of dry grasses, sedges, and
pine needles lined with finer grasses,
hair, and moss stems. Here, a male visits
a nest with young nestlings. Photo cour-
tesy of Bill Dyer/CLO.

a. Female Pompadour Cotinga on Nest b. Nest and Egg of Pompadour Cotinga

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 8.22 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.23
Figure 8-13. Nesting Habitat of Kirt- In a California orchard, American Crows nesting early in the
land's Warbler: The only habitat in which season before the trees had leaves chose sites an average of 12.2
Kirtland's Warblers will nest is jack pine
rows from the edge. Later in the season, when leaves were out and
stands of at least 80 acres (32.4 ha), with
trees usually 6 to 18 feet (2 to 5.5 m) tall. the foliage was more dense, the crows nested an average of only 8.8
In such a stand, sufficient sunlight filters rows from the edge. Thickness of cover was undoubtedly a factor in
through the limbs to keep the lower their choice of nest site (Pettingi II 1972).
branches green—a critical nesting re-
quirement for the warbler. This jack pine
stand in Crawford County, Michigan, has Nest Site Selection
been burned to provide suitable nesting
habitat. The birds first breed in a stand
The decision of precisely where to put the nest is ultimately up
about six years after it has burned. Photo to the female (she has veto power!), and in many polygynous spe-
courtesy of J. Surman/CLO. cies (pheasants, grouse, Ruffs, manakins, cotingas, birds-of-paradise,
and others) the female is left with all domestic duties. In species in
which nest sites are limited, the male often displays for a mate from
a potential nest site (as in bluebirds [Fig. 8 15], swallows, and wrens
-

Seasonal Changes in Nest Sites

Many species choose different types of nest sites at different
points throughout the breeding season. Early in the season, for ex-
ample, Eastern Towhees, Field Sparrows, and Song Sparrows place
most of their nests on the ground. Later, they nest in low shrubs (Fig.
8 14). Because these birds usually begin nest building before the
-

shrubs have leafed out, the ground provides much better cover for
their early nests. But once the shrubs have leaves, they apparently pro-
vide safer nest sites than the ground. American Robins usually place
their first nests of the breeding season low in a protected evergreen
tree. Later in the season, however, they usually choose a higher site
in a deciduous tree (Sallabanks and James 1999).
Figure 8-14. Seasonal Changes in Nest
Height of Field Sparrows: In a central
Illinois study site containing grassland, 30 —
shrub, and woodland areas, Best (1978)
Average Nest Height (Groun d to Upper Rim, in Inches)

found that the average height of Field

Sparrow nests increased as the breeding
season progressed. Birds placed most
early nests in stands of dead grasses, but
placed later ones in shrubs, small trees,
and living herbaceous vegetation such 20 —
as black raspberries and goldenrod, as
well as in dead grasses. The latest nests Figure 8-15. Eastern Bluebird Wing-Wave Display: In this common visual display of Eastern Bluebirds, the male or female slowly
were almost all in shrubs and small trees. raises one or both wings, sometimes quivering them, while singing or chattering. Wing-Wave may be given during courtship or
8 These birds begin to nest early in spring nest site selection, or as a greeting between the pair in a variety of situations. Nest site selection also involves flight displays in
before leaves have emerged, when dead which the male flies with slow, deep, butterflylike wingbeats; hovers in front of the nest hole; or flies oddly, with the wings mov-
grasses provide the best available cover. ing out of synchrony and at varying speeds—all while singing or chipping. Stokes and Stokes (1989, pp. 318-319) describe one
10 -
Increasing nest height as the season common nest site selection scenario:
progresses may partly reflect additional
When a female first arrives on the [male's] territory, or the pair arrive together, the male [give a flight display], ending up
opportunities for hiding nests in vege-
at a prospective nest site. Here he will cling to the entrance or a nearby perch and do Wing-Wave while continuing his singing.
tation. Because nest height in trees and
After this he may go to the nest hole and, while clinging to the entrance, rock back and forth, putting his head and shoulders
shrubs continued to increase even after
in and out of the nest hole and looking around between each rocking motion. He may be carrying a bit of nest material while
the leaves were fully out, however, Best
doingthis. The male may also land on the nest box with his backtothefemale and spread his tail and droop his wings, exposing
suggests that other factors also may in-
May June July August his vibrant blue back. He may lift and quiver his wings and pivot, appearing to dance.
fluence nest height. Error bars represent
one standard deviation. In this photo, a male raises both wings in a Wing-Wave display. Photo courtesy of IsidorJecklin/CLO.
Month Nest Built

Cornell Laboratory of Ornithology Handbook of Bird Biologq

8.24 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biology of Birds 8.25
Figure 8-16. Male Marsh Wren Dis-
playing at"Courting Nest": Male Marsh
Wrens construct numerous (often 20 or
more) "courting nests" on their ter-
ritories. These unlined, globular struc-
tures are woven from cattail leaves and
grasses and have a side entrance. When
a female arrives on a male's territory she
visits his nests and then, if she chooses
him as a mate, adds a soft lining to one or
builds another nest herself. As the female
inspects nests the male escorts her, giv-
ing a display in which he fluffs his breast
feathers and cocks his tail over his head
(as pictured here). He also may sing rap-
idly, quiver his wings, and/or sway from
side to side. (Males also give this display
to other males during territorial inter-
a
actions near boundaries.) Researchers
hypothesize that the remaining court-
ing nests may help to deceive predators
(Leonard and Picman 1987), and they Figure 8-17. Tricolored Blackbird Nest-
may have other uses as well: the pair may Site Demonstration Display: Tricolored
renest in one if their eggs are destroyed; Blackbirds nest in dense colonies in
adults may roost in them at night; fledg- marshes, fields, and blackberry thickets,
lings may take shelter in them; and they primarily in central California. Males set
may be used for winter shelter where up their small territories before pairing,
wrens are year-round residents. Photo each singing from the highest perch
by Marie Read. available. a. When a male spots a female
flying overhead, he gives a Song-Spread
[Fig. 8 16]) or from a territory where the male knows the whereabouts
-
display: he lowers and spreads his
of likely nest sites (as in marsh-nesting blackbirds [Fig. 8 17]). In other
- wings and tail, erects his neck feathers,
species—such as gulls, many passerines, and even some polyandrous and sings. b. Then he elevates his wings
to a V shape and lowers and spreads his
ones such as jacanas—the choice of a nest site appears to be the result
tail again. c. He moves down into the
of a negotiation between the male and female, with each considering vegetation, continuing to display, as the
sites identified by their mate. female follows. He may point his bill at
In species in which pair members communicate over the choice possible nestsites, move it back and forth
rapidly, and pick up nesting material. d.
of a site, that communication is usually mediated by stereotyped dis-
At a potential nest site, the female also
plays that often involve the ritualized placement of nest material or
may pick up nest material and display
pointing at the nest site. This stage of the reproductive cycle is hard to with the male. This sequence of male-
study, because birds tend to be less committed to a breeding attempt female interactions, described by Ori-
when it is just beginning than when they have progressed to the point of ans and Christman (1968), is termed the
Nest-Site Demonstration display. Often,
laying eggs or hatching chicks: slight disturbances from observers may
when a female flies over a colony of dis-
cause them to abandon the breeding effort. As a result, ornithologists playing males, many give a Song-Spread
have done less work with individually marked birds at this stage than and disappear into the vegetation nearly
at later stages. So if you see a bird acting strangely early in the breeding simultaneously. Adapted from a drawing
season, pay particular attention, as you may see the details of nest site by Gene M. Christman, in Orians and
Christman (1968).
selection unfold as very few others have.

Diversity of Nests
The nests that birds actually build in their selected sites also are
remarkably diverse. I will attempt a provisional classification of nest
types, mostly based on shape, but beware that there are many other
criteria we could use to classify nests that might be more meaningful
to the birds: these groups merely look similar to us. d

Cornell Laboratory of Ornithology Handbook of Bird Biology

8.26 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biology of Birds 8.27
The simplest nest is no nest. In a number of species, nesting in- Figure 8-19. Great Potoo Egg on Dead
volves selecting a nest site but no construction of any nest whatsoever. Branch: Like most of its nightjar relatives,
the Great Potoo of South America builds
All brood parasites fall within this group, and the final section of this
no nest at all. Instead, it may lay its single
chapter discusses their breeding biology. Some megapodes (chicken- egg atop a tree stub—the egg fitting into the
like birds of Australasia) lay their eggs on bare rocks warmed by the natural depression so closely that it is dif-
sun, murres lay their eggs directly on exposed rock ledges, and New ficult to dislodge. Incubating birds sit in an
World vultures and condors lay their eggs on the bare floors of shal- upright posture, looking remarkably like
an extension of the tree. Drawing by Dr.
low caves. White Terns of tropical seas lay their single egg on bare C. J. F. Coombs.
branches (Fig. 8 18), as do the potoos of the Neotropics (Fig. 8 19;
- -

also see Fig. 3-56). Emperor Penguins transfer their single egg to the
top of the male's feet as soon as it is laid, and the "nest" is formed by
the male's feet below and a loose bulge of skin above (see Fig. 4-100).
Most nightjars, including nighthawks and Whip-poor-wills, build no
nest at all (Fig. 8 20), laying their eggs on the forest floor, on sand bars
-
Figure 8-20. Whip-poor-will Eggs in "Nest": Like
in rivers, or even on flat, graveled roofs. Some species can move their most other nightjars, the Whip-poor-will builds no
eggs to a different site in the midst of incubation. nest. Instead, it lays its two eggs directly on a bed of
dead leaves on bare ground in open woodlands, of-
The nest of many more species is a simple scrape (Fig. 8 21). -
ten near the edge of a clearing. The nest site is bathed
For example, the nest of many plovers (including the Killdeer), terns, in a mixture of sunlight and shadows, rendering the
and skimmers is a very shallow depression, often containing no nest incubating bird nearly invisible against its surround-
material, or simply lined with a few flat pebbles. These species don't ings; it will not flush unless an intruder approaches
closely. Photo courtesy of Bill Dyer/CLO.
even create a depression if the substrate for nesting is too hard. Many
Antarctic-nesting penguins build up their scrape on frozen substrate
by moving pebbles around.

a. Egg Perched on Tree Fork b. Adult and Chick a. Black Skimmer Nest Scrape b. Gentoo Penguin with Chick at Nest
Figure 8-18. White Tern Nesting: The pelagic White Tern, nesting on tropical ocean island, often places its single egg directly in
a fork or depression in a horizontal branch, constructing no nest of any kind. Although the egg may be perched precariously, the Figure 8-21. Nest Scrapes: The nest of many plovers, terns, skimmers, and penguins is a scrape: a shallow depression with little or
incubating birds seem to have little trouble settling on or rising from the egg without knocking it down. a. Egg Perched on Tree no nest material, sometimes lined with a few flat pebbles. a. Black Skimmer Nest Scrape: The Black Skimmer's nest is an unlined,
Fork: The male and female take turns incubating the cryptically colored egg until it hatches at about 34 days. Photo byA. Forbes- shallow depression 5 to 10 inches (13 to 25 cm) across, within a colony of skimmers on open beaches or sand bars. Although
Watson/VIREO. b. Adult and Chick: The chick remains on the branch where it hatched, attempting to hold on tightly with its sharp placed above the normal high-tide line, it may be destroyed by unusually high tides during storms. Photo courtesy of Platt/CLO.
claws, while the parents bring food and provide warmth until it is ready for flight. If the chick falls to the ground, which occasionally b. Gentoo Penguin with Chick at Nest: Gentoo Penguins breed on subantarctic islands and the Antarctic Peninsula, in colonies
happens during severe storms, it is ignored by the parents and soon dies from hunger and exposure. Adults also ignore eggs that of 2 to nearly 10,000 pairs. The nest, placed on ice-free ground on a beach, hill, or grassy area, is a platform of stones built up
are moved just a few inches from where they were laid. The precise location of the egg or young is thus quite important, and birds from the ground, 4 to 8 inches (10 to 20 cm) high and 18 inches (45 cm) across. At the center is a small cup lined with smaller
return year after year to nest in the exact same fork or depression they used the year before. Photo by R. L. PitmanNIREO. stones and, depending on the location, with vegetation. Here, an adult tends its chick in a nest on the Falkland Islands. Photo by
Wolfgang Kaehler.

Cornell Laboratory of Ornithology Handbook of Bird Biology

8.28 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.29
Figure 8-22. Platform Nest of Turtle Figure 8-25. Floating Platform Nest
Dove: Like most doves and pigeons, of Black Tern: Nesting in loose groups
the Turtle Dove builds a small, flimsy in shallow freshwater marshes with
platform of twigs for its two white eggs. emergent vegetation such as cattails,
This nest, lined with finer materials the Black Tern builds a flimsy, floating
such as roots, grass stems, and leaves, nest that is commonly destroyed by
is usually placed about 3 to 8 feet (1 to wind, waves, or changes in water level.
2.4 m) off the ground in a tree or shrub, The nest, just 0.8 to 2.4 inches (2 to 6
sometimes loosely clustered with other cm) high and 0.8 to 2 inches (2 to 5 cm)
Turtle Dove nests. Breeding in northern above water, is often built on an existing
Africa and the western Palearctic, Turtle floating mat of dead marsh vegetation.
Doves live in mixed habitats with open The terns pile dead vegetation from the
ground for foraging and trees or shrubs surrounding water upon the mat, then
for nesting and roosting. Drawing by Dr. shape it into a shallow cup for the eggs.
C. J. F. Coombs. The eggs are well adapted to their soggy
environment, having extra pores to help
them tolerate their constantly water-
soaked conditions (Davis and Acker-
man 1985; Firstencel 1987). Photo by
Marie Read.
Platform nests consist of a very shallow depression in the top
of a mound of nest material. They vary tremendously in complexity,
from the flimsy platform of twigs put together by the Mourning Dove and grebes and some terns build floating rafts of aquatic vegetation,
and most of its relatives around the world (Fig. 8 22), to the massive
- upon which the shallow nests sit (Fig. 8 25). The Horned Coot of
-

structures, sometimes containing thousands of sticks, built by storks or South America builds an interesting variation on this type of platform
large birds of prey such as Ospreys and eagles (Fig. 8 23). Birds can
- nest (Fig. 8 26). Nesting on high Andean lakes with little aquatic veg-
-

build platform nests anywhere they find support of sufficient strength, etation, these birds pile stones in the water to make a mound upon
and the type of support used can vary considerably within a species: which the shallow nest of vegetation is built (Goodfellow 1977). The
many herons, cormorants, storks, and raptors build platform nests of accumulation of stones, built up by several pairs over a few years, may
twigs in trees, but will nest on the ground on protected islands if no be 3 feet (1 m) high and up to 13 feet (4 m) in diameter and may weigh
trees are available. Flamingos build short pedestals of mud (Fig. 8 24), - over a ton (907 kg).
The Oilbird of northern South America uses quite unusual ma-
terials to build its platform-like nest high on a ledge jutting from the
wall of a cave. The bulky nest—a short, truncated cone topped by a
shallow depression—consists mainly of regurgitated fruits and seeds

Figure 8-26. Horned Coot Nest on

Figure 8-23. Platform Nest of White Stone Mound: Breeding on high-al-
Stork: The beloved White Stork of Eur- titude Andean lakes with little vege-
asia builds a massive platform of sticks tation, the Horned Coot places its nest
and earth up to six feet (two meters) on a cone-shaped mound of stones
across, topped by a shallow cup of finer that it creates in shallow water. The
materials such as grass and sometimes stones, which can weigh as much as
rags or paper. It often nests on human- a pound (0.5 kg) each, are brought to
built structures such as walls, ruins, the mound one-by-one. The pile—ac-
churches, roofs, or (as pictured here in Vegetation cumulated by several pairs over sev-
Poland) on chimneys. The nests are used eral years—may reach up to 3 feet (1
year after year,
, the birds adding new ma- m) high and 13 feet (4 m) in diameter,
terial as necessary: one nest in Germany Figure 8-24. Greater Flamingo Nesting Colony: Found in isolated pockets in certain and may weigh as much as a ton (907

Up to 3 feet ( 1 meter)
was occupied from at least 1549 through tropical or high-altitude areas around the globe, flamingos nest in large colonies in kg). The mound ends below the water's
1930! Despite centuries of protection in the mud flats around shallow, alkaline, soda lakes and salt lagoons. Their nests—cir- surface, and the birds pile vegetation
Europe, White Storks have declined dra- cular mounds 14 inches (35 cm) across and up to 12 inches (30 cm) high, wider at the on top, forming a nest that rises one to
matically since the early 1900s, much to base—are topped by a shallow depression for their single egg. The height protects the two feet (0.3 to 0.6 m) above the water.
the dismay of people who believe that a egg and nestling from flooding, and also keeps the nest cooler than the surrounding Although laborious to build, these
stork nesting on their roof brings good ground—which, in the black mud around Lesser Flamingo nests at Lake Magadi, Ke- island nests are protected from terres-
luck. Photo by Liz and Tony Bomford/ nya, may reach as much as 167 degrees F (75 degrees C) (Welty and Baptista 1988). trial predators. Drawing by Dr. C. J. F.
Oxford Scientific Films. Photo by E. BartelsNIREO. Up to 13 feet (4 meters) Coombs.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

8.30 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.31
mixed with the bird's own excrement, and grows
higher each year as more and more material is
added (Fig. 8 27).
-

The majority of bird species in the world build

some sort of cup nest. The smallest are those of
hummingbirds, and probably the largest are built
by large crows and ravens. Cup nests can be com-
posed of a wide variety of materials: most common are
, P))),011111, small twigs and dried grass, but quite a few species use
mud (Rowley 1971). Smaller species, such as hummingbirds
Figure 8-27. Oilbird at Nest: The night- and gnatcatchers, often use spider webs in conjunction with
jar-like Oilbird of northern South Amer- lichens and "vegetable down" from seeds (Fig. 8 28).-

ica, nearly the size of a small crow, nests Ornithologists often distinguish cup nests on the basis of how they
high on a ledge inside a cave. The bulky
are supported. Statant cups are built on top of a hard physical support
platform nest—a short, truncated cone
topped by a shallow depression—con- or supports (Fig. 8 29). Some, such as the nests of Horned Larks and
-

sists of regurgitated fruits and seeds Bobolinks, are built directly on the ground. The nests of Horned Larks
mixed with the bird's own excrement. It often are made in open country, commonly placed within the hollow a. Bobolink b. American Robin
grows higher as more material is added
of the hardened hoofprint of a cow or horse—an arrangement that
each year. Adapted from a drawing by
places the eggs slightly below ground surface, thus protecting them 2 Feet (61 cm)
Robert Gillmor.
from most foot traffic if the large mammals should return. Most nests
built in shrubs and trees also are statant, from the loose piles of twigs
and grass built by most songbirds, to the massive mud nests built by the
enigmatic Magpie-larks, White-winged Choughs, and Apostlebirds of
Australia. Pensile cups are supported by their rim with the belly of the
cup hanging unsupported beneath (Fig. 8 30). Such nests are built
-

by New World blackbirds, vireos, and kinglets; by many songbirds

c. American Crow d. White-winged Chough

Figure 8-29. Statant Cup Nests: Cup nests built on top of hard sticks, twigs, bark, vines, and sometimes mud, the nest is lined
physical supports, including the ground, are termed statant with softer materials such as grasses, plant fibers, moss, feath-
cups. They vary widely in location, material, and size, and are ers, or fur. It usually is about two feet (61 cm) across and about
built by birds from many taxonomic groups. a. Bobolink: In 4.5 inches (11.4 cm) deep. Note one newly hatched chick in
hayfields and large, grassy meadows, the Bobolink builds a this nest. Photo by Kevin McGowan. d. White-winged Chough:
shallow cup of coarse dead grass and weed stems, lined with Inhabiting dry woodlands in eastern Australia, the gregarious,
Figure 8-28. Anna's Hummingbird on finer grasses or sedges. The nest is often placed in a small hollow crowlike White-winged Chough lives in an extended family
Nest on Pine Cone: Hummingbirds, on the ground—either natural or formed by the female—and group whose members cooperate to build and tend their mud
such as this Anna's of western North well-hidden among dense grass and weeds. Photo by Marie nest. Saddled across a horizontal branch, this nest is a huge
America, often incorporate spider webs Read. b. American Robin: On the fork or horizontal branch of a cup of mud lined with shredded bark, grass, and fur. Mixed
into their tiny cup nests. The sticky webs tree or shrub, or on the ledge of a house, barn, or other building, with the mud are grass stems and bark, which the birds use as
help attach the nest to a branch, large the American Robin places its fami I iar cup nest of grasses, weed wicks to gather mud, and then incorporate into the nest. The
leaf, or pine cone (as shown here). The stems, and mud. See Figure 8-50 for details of structure and structures are 8.5 inches (22 cm) across with walls 3 inches (8
webs also may help the female to stick nest building. Photo by Hal H. Harrison. c. American Crow: In cm) thick, and may weigh 5 pounds (2.3 kg) when dry. They last
bits of lichen or bark to the outside of a large tree or shrub, 10 to 70 feet (3 to 21 m) above the ground, for many years, and sometimes are reused by the birds. Photo
the nest so that it blends into nearby the American Crow builds its huge nest on the base of a branch by R. BrownNIREO. Please note that the photos shown here
branches or tree trunks. Photo taken in against the trunk or in a vertical fork. A large, bulky basket of are not to scale.
the Sonoran Desert, Arizona, by John
CancalosiNalan Photos.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

8.32 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.33

a. Red-eyed Vireo b. Golden-crowned Kinglet

a. Baltimore Oriole b. African Masked-Weaver

Figure 8-30. Pensile Cup Nests: Cup nests suspended from branches by their rims are called pensile cups. a. Red-eyed Vireo:
Hanging from a horizontal forked twig in a deciduous or mixed forest, the Red-eyed Vireo's nest is a delicate, compact cup of
bark strips, grasses, pine needles, rootlets, and weeds. It usually is held together and bound to its supporting branches with spider 0,
2
411-1630111bY
,
webs and cocoons (not visible in this photo), and sometimes is decorated outside with lichen, paper birch bark, or paper from
wasps' nests. Photo by Marie Read. b. Golden-crowned Kinglet: Breeding mainly in old, dense spruce or fir stands in the boreal
and subalpine forests of North America, the tiny Golden-crowned Kinglet places its nest high in a conifer, suspended from a twig
fork or several small side branches. The deep, thick cup of mosses and lichens is bound together and to its supports with spider
webs and hair, and lined with small strips of inner bark, fine black rootlets, hair, and feathers. The well-camouflaged nest is just
2.75 inches (7 cm) across and 3.75 inches (9.5 cm) high, and the rim curves inward at the top, forming a snug hollow below. From
A Guide to the Nests, Eggs, and Nestlings of North American Birds, 2nd Edition, by Paul J. Baicich and Colin]. 0. Harrison, 1997.
Reprinted by permission of Academic Press.

in Australia and Asia; and by a host of orioles and flycatchers, and

their relatives in the Old World. Exploring whether this type of nest
has any intrinsic advantages over cup nests would be interesting. My
impression is that most birds would be better off building a cup nest,
but that pensi le nests are an adaptation for nesting on emergent vege-
tation in marshes or on thin, distal branches (probably for protection c. Planalto Hermit
from predators), neither of which offer support from below. Pensile
nests with deeper and deeper cups grade into pendulous cups, which Figure 8-31. Pendulous Cup Nests: Very deep cup nests sparrow, displays by hanging under the nest (as shown here),
are entered from the top and have the nest chamber anywhere from suspended from their rims are termed pendulous cups. a. fanning his wings and calling. If a female accepts a nest, she
Baltimore Oriole: In open woodlands, forest edges, riverside lines it with leaves and grass flower heads, then lays eggs and
around 4 inches (10 cm) to over 1 yard (1 m) below the supports from
trees, and shade trees throughout the eastern and central United tends the nest herself, while the polygamous male courts other
which they hang (Fig. 8-31). Such nests are usually woven from plant
States, the Baltimore Oriole firmly attaches its nest to a twig fork females. Photo by M. P Kahl/Photo Researchers. c. Planalto
strips or fibers, and they are characteristic of the New World orioles, near the end of a slender, drooping branch of a tall, deciduous Hermit: This South American hummingbird creates an inter-
oropendolas (see Fig. 6-39), and caciques, as well as some weavers in tree—usually 25 to 30 feet (7.6 to 9.1 m) above the ground. The esting pendulous cup variation. It suspends its minute nest
the Old World. Adherent cups are made of mud or saliva and rely on deep, hanging pouch, up to 8 inches (20.3 cm) long, is tightly cup from a twig or leaf tip by a single support, adding a long
woven from long plant fibers, strips of vine bark, grasses, strings, streamer of vegetation below as a counterweight—to keep the
chemical forces to hold the nest to a vertical surface. Many swifts use
and sometimes Spanish moss, and lined with fine grass, soft nest upright. The Sooty-capped Hermit builds a similar nest, but
a considerable amount of saliva to hold their nests together and to the plant down, and hair. Photo by W. Greene/VIREO. b. African for its counterweight attaches tiny pebbles or lumps of dry clay
nesting surface. The African Palm-Swift goes the extra step of gluing its Masked-Weaver: The male African Masked-Weaver weaves an to a spider web streamer. Both birds must build much of their
eggs to the padlike vertical nest, incubating them from a vertical posi- oval nest of grass strips and reeds, suspending it from a droop- nest on the wing, as their nest sites provide no place to perch.
tion (Fig. 8-32). The use of saliva culminates in the Edible-nest Swiftlets ing branch of a tree or between several reed stems, often over Drawing by Dr. C. J. F Coombs.
water. The striking, yellow-and-black male, about the size of a

Cornell Laboratort of Ornithologq Handbook of Bird Biologq

8.34 David W. Winkler Chapter 8 — Nests, E55s, and Youn8: Breedin8 Biology of Birds 8.35

of Southeast Asia, which often build their nests entirely of saliva (see
Fig. 4-93). These nests, the key ingredient of the great Asian delicacy
bird's-nest soup, are harvested in the vast nesting caves by workers on
rickety skyscraperlike scaffolds of bamboo (Valli and Summers 1990).
When the first nest is taken a swiftlet pair will often hurriedly build
another, but the replacement nests usually contain bits of vegetation,
and thus are much less valuable than those of the first harvest. The Barn 1
11
Swallow, as well as many other swallows in the Old World, build their
cup nests of mud mixed with straw (Fig. 8-33). Similar adherent nests
are sometimes made by phoebes.
A
Some species, especially those that nest on the ground amid
some vegetative cover, build domed nests. These are cups with a wo-
a. Eastern Meadowlark b. Ovenbird
ven dome overhead that probably mainly helps to conceal the eggs or
nestlings. In North America, species such as meadowlarks and snipe
build domed nests in grassy areas, and Ovenbirds build them in for-
ests (Fig. 8-34a and b). The House Martin, an Old World relative of
the Barn Swallow, builds the walls of its mud cup all the way up to an
overhanging surface, thus incorporating the overhang as the top of its
nest and leaving only a small opening to enter the cavity—presumably
Figure 8-32. African Palm-Swift Eggs
Glued to Vertical Nest: Most swifts
a strategy to exclude predators (Fig. 8-34c). This species often nests in
use saliva to hold their nest material dense colonies on favorable sites inaccessible to predators, however,
together and to glue their nests to verti- leading some researchers to suggest that the nest closure may also re-
cal surfaces, but the African Palm-Swift duce the frequency of unsolicited extrapair copulation attempts from
also uses saliva to glue its eggs to the
neighboring males in the colony. Note that I have placed the House
nest! The soft, padlike nest is glued to
the underside of a vertical palm leaf, and Martin's nest with domed nests, even though it does not actually build
thus the eggs would fall out if not held the top of the dome, as do the other species mentioned here. This is a
in place. The bird incubates in a vertical good example of how fuzzy and subjective these nest categories re-
position, holding onto the nest with its
ally are. The Rufous Hornero builds a nest that is even more difficult
feet. Drawing by Charles L. Ripper. Entrance
to categorize: a cup of grasses enclosed in hardened mud, complete Egg Chamber Chamber
with an entrance chamber (Fig. 8-34d). c. House Martin d. Rufous Hornero

Figure 8-34. Domed Nests: Cup nests with a woven roof formed, and the martin builds the walls right up to the overhang,
Figure 8-33. Adherent Cup Nest of Barn to help conceal the eggs or young are termed domed nests. leaving only a tiny opening into the nest cavity, which is lined
Swallow: Inhabiting open areas through- a. Eastern Meadowlark: In open fields and grasslands, the with soft materials. Photo by Mark Hamblin/Oxford Scientific
out most of North America and Eurasia, Eastern Meadowlark builds its large, domed nest in a shallow Films. d. Rufous Hornero: In the grassy plains of southern
the Barn Swallow originally nested in depression in the soil amid dense vegetation. The nest, often South America, the thrush-sized Rufous Hornero (called "El
caves. By the mid-1900s, however, it topped by an arched roof that leaves a large side entrance, is Hornero" or "the ovenbird" in South America, owing to its nest
had shifted to nesting almost exclu- composed of dry grass and weed stems interwoven with the shape) constructs a two-chambered nest of mud (or, in some
sively in open buildings such as barns; surrounding living plants, as visible here. Photo courtesy of W. areas, sand and cow dung), with some grass and hair mixed in.
and under bridges, docks, culverts, and R. Spofford/CLO. b. Ovenbird: On the open forest floor, the The domed nest, nearly one foot (30 cm) high, usually sits fully
similar structures. To build their nests, female Ovenbird creates a depression in the leaf litter. She then exposed atop a stump, post, or limb, and may weigh up to 11
which are frequently reused, the birds weaves dead leaves, plant stems, twigs, and bark into a domed pounds (5 kg). The upper diagram is a front view of the nest,
gather mud—often mixed with grass nest with a small side opening that is invisible from above. The showing the entrance chamber. Below is a vertically sectioned
stems—in their beaks, then plaster it as result looks somewhat like an old-fashioned oven, giving the nest: the right half contains the entrance chamber and dividing
pellets (up to 1,400 [Moller 19941) to species its common name. Photo courtesy of Mike HopiaW partition; the left holds the egg chamber, lined with grasses and
a vertical wall, slightly below the roof, CLO. c. House Martin Feeding Young at Nest: Domed nests feathers (not visible here). The nest hardens to the consistency
as in the nest shown here. The shallow, usually are topped with nest material, but the House Martin of cement and is so crack-proof that in 1958 Brazilian health
semicircular cup is lined first with fine uses an overhang as a cover. This common Eurasian swallow workers carefully copied the bird's sand/dung formula and
grass stems, horsehair, or algae strands, places its nest on a vertical wall beneath an overhang—either plastered 200,000 huts, reducing infestations of the reduviid
and then finally with abundant feathers the eaves of a house (as shown here) or a projecting rock ledge, bug, which thrives in crevices and carries the fatal Chagas'
from poultry. Nests also are placed on a on a cliff. The bird first plasters mud and bits of straw to the disease. Nests can last up to eight years, and may be reused by
horizontal support such as a beam, and vertical surface. Then it adds a new mud layer only about 0.5 many other species. For photo of bird and partially completed
often are in small, loose colonies. Photo inches (1.2 cm) thick each morning, thereby allowing each nest, see Fig. 4 118. Adapted from Welty and Baptista (1988),
-

courtesy of]. R. Woodward/CLO. layer to dry before adding the next. Eventually a mud cup is after Pycraft (1910).

Cornell Laboratory of Ornithology Handbook of Bird Biology

8.36 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.37
A globular nest results when the top of a dome nest is com- Figure 8-36. Southern Penduline-Tit
pletely enclosed. Usually entered through a hole in the side, these Nest with False Entrance: Hanging
spherical nests are characteristic of most wrens. Anyone who has from a twig several yards off the ground,
the globular nest of the Southern Pen-
seen the grassy sphere built by Cactus Wrens, usually within the
duline-Tit of southern Africa has two
spiny arms of a cholla cactus, can appreciate how nest construction entrance holes on the side. The bot-
combined with nest placement can protect the young from both the tom hole, more prominent, is a false
elements and predators (Fig. 8-35). In a spiny shrub in the same entrance leading to a small, dead-end
desert habitat, the chickadee-I ike Verdi n builds a smaller globe nest chamber. Just above this entrance is the
true entrance, a narrow slit concealed
out of spiny twigs, orienting the spines to the outside. Thus spines
in the projecting upper lip of the false
on both the nest and its supporting shrub discourage predators. The entrance. Most of the nest is made from
Black-billed Magpie of Eurasia and western North America builds fine, woolly plant and animal materials
a similar domed nest of thorny twigs, occasionally inserting short felted into a tough, clothlike material;
but the lips, floor, and roof of the true
strands of barbed wire! Southern Penduline-Tits, African relatives
entrance tube are coated with coarse
of the Verdin, build globular nests of grass and plant down that can spiderwebs. Thus, when the bird closes
include a false entrance, apparently to foil predators (Fig. 8-36). The the tube the sides cling together, making
false entrance is a prominent hole on the side of the nest that leads the true entrance virtually invisible, and
to a dead-end chamber, whereas the true entrance is concealed in a presumably thwarting predators. When
not breeding, up to 18 of these social
slit in the projecting upper lip of the false entrance.
birds may roost in one nest. a. Photos of a
A globular nest with an entrance tunnel is termed a retort nest. Nest in Cape Province, South Africa: In
These are common among the mud-nesting swallows, and in the the left photo, only the false entrance is
grass nests of many African weavers and New World swifts in the visible. In the right photo, the true en-
trance also is visible as a wide slit above
genus Panyptila (for example, Goodfellow 1977) (Fig. 8-37). The
the false entrance. Photos courtesy of
lengths of these tunnels can vary from an inch or two (a few cm) to C. J. Skead. Reprinted by permission
over a yard (meter). Once again, the traditional explanation for the of B i rd I ife South Africa/The Ostrich. b.
b
elongation of these tunnels has been defense against predators—but Cross Section through Nest: In the left
this does not seem to be the whole story. Access to the nests of mud- diagram, the true entrance is closed. In
the right diagram, the entering bird has
nesting swal lows, especially those of the large species that build very
pushed the true entrance open.
thick mud walls on their tunnels, can be very difficultfor all predators
except snakes. But predators such as monkeys and large birds can rip
into grass nests, no matter how long their tunnels. The length of the
tunnel often varies considerably among closely related species, and
evaluating their effectiveness against predators of all sizes, as well
as their possible role in reducing extrapair copulations and brood
parasitism within and between species, would be interesting.

Figure 8-35. Cactus Wren Nest in

Cholla Cactus: Inhabiting open areas
of the southwestern United States and
northern Mexico, the large Cactus Wren
usually places its conspicuous nest in a
cholla cactus, as shown here, or in a
thorny shrub. The globular nest is a
bulky sphere of plant stems and grasses
one foot (30 cm) or more across with an
entrance tunnel about 6 inches (15 cm)
long. The nest deters predators through
its shape and location, rather than
camouflage. Photo by Jim MerliNalan
Photos.

Cornell Laboratorq or 0 rnitholom Handbook of Bird Biologq

8.38 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.39
A few species build a mound nest. This chapter began with a
brief account of a mound nest built by a male brush-turkey, a type
of megapode (see Fig. 6-36). Not all megapodes build mounds, but
among those that do, considerable variation exists in the type and size
of mound built. Megapodes are the only birds that use the nest itself,
rather than the parent's body, as the source of heat for the developing
embryos. Among passerines, only a few species build true mounds.
Social Weavers—small, seed-eating, African relatives of House Spar-
rows—build a large, colonial nest that is essentially a large haystack
in a tree (Sidebar 2: Social Weavers). On a smaller scale, Palmchats
build colonial nests up to one yard (one meter) in diameter high in
palm trees in the Dominican Republic, and Monk Parakeets build
large, colonial stick nests in their native Patagonia (southern South
America) and in parts of the United States from Miami to Chicago in
which escapees have established colonies. The other notable mound
builder is the odd, heronlike Hamerkop of Africa, pairs of which build
a. Cliff Swallow nest mounds of sticks up to 6.5 feet (2 m) high and wide, usually in a
Figure 8-37. Retort Nests: Globular nests with entrance large tree (Fig. 8-38).These nests contain up to 8,000 sticks and weigh
tunnels are called retorts. a. Cliff Swallow: Breeding in
up to five hundred pounds (several hundred kg) (Goodfellow 1 977).
dense colonies of up to 3,500 active nests under overhangs
of bridges, cliffs, or roofs, Cliff Swallows prefer to place The nest chamber lies in the center of the mound and is connected to
their grass-lined, mud nests on a vertical wall just below the outside by a mud-lined tunnel. For some unknown reason, the birds
an overhang. Late arrivals to the colony, finding this prime add a variety of carrion, feces, and scraps to the top of the mound after
location used up, usually build their nests right below and
the eggs have hatched; perhaps they are erecting an olfactory smoke
connected to the first tier, slightly offset (see top left photo,
showing a vertical wall face). The gourd-shaped nests, with
screen to protect their young?
entrance tunnels projecting outward 6 to 8 inches (15 to 20 The final set of nest types is burrows or holes. Some species ac-
cm) and facing down at the end, are constructed entirely tually excavate their own holes, whereas others, the cavity adopters,
from pellets of mud (each representing one beakful), vis- obtain a nest cavity created by physical forces, such as decay or ero- Figure 8-38. Mound Nest of Hamerkop:
ible as tiny lumps in the two photos at right. When building b. Red-vented Malimbe The heronlike Hamerkop ofAfrica builds
sion, or by other species. Among the excavators, there are two types:
nests, Cliff Swallows apparently assess the composition of a massive nest mound of sticks, often in
nearby mud, and choose the types that best adhere to walls those that excavate wood and those that excavate sandy soil. Some a tree fork, measuring up to 6.5 feet (2
(Robidoux and Cyr 1989). The mud walls of the nest protect wood excavators are familiar to everyone: all woodpeckers in North m) in diameter and weighing up to 500
eggs and young from wind and rain, and also keep the inside (Continued on p. 8.41) pounds (907 kg). The central nest cham-
of the nest warm at night—up to 13 degrees F (7 degrees C) ber is lined with sticks positioned so that
warmer than the surrounding air. The entrance tunnel tradi- no jagged ends project inward. It con-
tionally has been thought to deter predators, but it also may nects to a mud-lined entrance tunnel up
reduce interference from neighboring Cliff Swallows, which to 2 feet (0.6 m) long, which opens to the
frequently steal grass (and wet mud) from each other's nests, outside near the bottom of one side of the
and may destroy eggs and parasitize nearby nests either by mound (the opening is not visible in this
laying directly in them or by transferring their own egg to drawing). The roof, reinforced with mud
them in their beaks. Note the pale foreheads of adults, vis- and grass to make it waterproof, may be
ible in some entrance holes, and the partially completed up to 3 feet (1 m) thick, and has been
nest in the lower right comer of the left photo. Top left photo known to support the weight of a human.
courtesy of MaryTremaine/CLO; top right, courtesy of Peter The nest may take six or seven weeks to
Stettenheim; bottom right, courtesy of lsidor Jeklin/CLO. b. build, and may be reused in later years.
Red-vented Malimbe: This African weaver builds a retort Other species sometimes benefit from
nest with a spectacular entrance tunnel up to 2 feet (60 cm) the Hamerkop's construction: small
long. Although the walls of the nest chamber are thickly wo- birds such as weavers, mynas, and pi-
ven, the walls of the tunnel are more open, the fibers forming geons may attach their nests to active
a criss-cross pattern that acts like a transparent net Hamerkop mounds; small mammals
a clear view of a bird inside. Crook (1960) described an such as genets may move in; and var-
entering, in-flight bird as dramatically sweeping downward ious raptors may evict the Hamerkop
to the tube entrance and then "diving upwards into lit] with and takeover its nestsite. In addition, old
closed wings, the momentum carrying ]it] to the top of the nests may be occupied by cavity-nesting
tube...without [touching] the fabric." Drawing by Dr. C. J. geese or ducks, or bysnakes. Drawing by
F. Coombs. Dr. C. J. F. Coombs.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

8.40 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.41
Figure A. Social Weaver: Looking
Sidebar 2: SOCIAL WEAVERS something like small, brown-
Figure 8-39. Woodpecker Nest Cavity:
This longitudinal section shows the nar-
capped versions of their relatives,
Sandi,/ Podulka the House Sparrows, Social Weav-
row entrance and deep, unlined nest
chamber in firm wood typical of most
ers live in the arid scrublands of woodpecker nests. Photo courtesy of
southwest Africa, where they for- John H. Gerard.
In the arid scrublands of southwest Africa, Social Weav-
age on the ground for insects and
ers—small, seed-eating House Sparrow relatives (Fig.
seeds. These highly social birds
A)—build enormous communal nest mounds in sturdy,
feed and nest in groups, roosting
isolated trees or on telephone poles (Fig. B). The mounds,
communally in their nests at night
which are occupied year round, may house more than 100 and during the hottest parts of the
pairs of birds, and may be more than 25 feet (7.5 m) long, day. Drawing by Robert Gillmor.
15 feet (4.5 m) wide, and 6 feet (2 m) high.
The mound is not woven, but thatched from piles of
coarse, dry grasses brought by flock members. Numerous
fine twigs are also incorporated into the huge domed roof,
which provides protection from predators and helps to
shed the rain. Once the roof is complete, the birds ex-
cavate separate nests from below by pushing in or nipping
off grass stems to create an oval chamber and then adding
grasses to extend an entrance tunnel downward from the
chamber (Fig. C). Eventually, a monogamous pair will
occupy each nest chamber. The mounds may be used for
many generations, and as new nests are added below, the
old ones may be filled in with straws.
In addition to providing a communal breeding site for
this highly social species, the huge nest mounds provide
thermal mass to help moderate the wide daily temperature America are capable of excavating their own nest cavity (although
fluctuations typical of the arid habitat. By absorbing the some reuse cavities from year to year) (Fig. 8 39). Worldwide, no
-

sun's heat during the day, the grass mound buffers the ac-
other birds are as adept as woodpeckers at excavating cavities, al-
tual nest chambers from becoming too hot; duringthe cool
though many species of parrots, barbets, toucans, nuthatches, and
nights the mound radiates back its absorbed heat, adding
to the heat of hundreds of bird bodies to keep the nests chickadees are capable of modifying a pre-existing hole to suit their
warm. On cold winter nights, internal nest temperatures needs. Many species in many different avian families excavate cavities
have been measured at 32 to 41 degrees F (18 to 23 degrees in sandy soil, and, in contrast to the machinery needed to be able to
C) above the external air temperature (White et al. 1975). excavate sound wood (strong, sharp beaks; sturdy skull bones; stiff
These "heated" nest chambers reduce the metabolic needs tail feathers for support), soil excavators often have no specialized
of roosting Social Weavers, which reduces the amount of
adaptations for the task. Good examples in the temperate zone are the
food they must eat. They also allow the birds to breed at
Bank Swallow (Fig. 8 40) and the Belted Kingfisher (Fig. 8 41), both
- -
any time the erratic rains provide a sufficient food sup-
ply, even in winter when night temperatures routinely fall of which loosen soil with their bills (which are adapted for specialized
below freezing. Winter breeding may be advantageous foraging, not digging) and clear the tunnel of soil with their weak feet.
because the birds' major predator, the cape cobra, is in- Similar examples of soil excavators abound in the tropics (bee-eaters
active then. The greater effectiveness of large nest mounds Figure B. Communal Nest of Social Weavers: This large nest [Fig. 8 42], motmots, Crab Plovers) and among seabirds (shearwaters,
-

at buffering nest chamber temperatures is thought to have mound in an isolated tree in Kalahari Gemsbok National Park,
petrels, storm-petrels, puffins).
driven the evolution of such large communal nest struc- South Africa is typical of the communal breeding mounds built
Many cavity adopters that nest in tree holes rely on other species
tures in this species (Collias and Collias 1984). ■ by flocks of Social Weavers. Individual nest tunnels are recog-
(usually woodpeckers) to make their holes. The avifauna of Australia,
nizable as loose clumps ofgrass hanging down from the bottom.
Note that at least two birds are visible one flying upward to however, contains a particularly high proportion of cavity adopters, yet
enter a nest tunnel, and another perched on the bare limb ex- no woodpeckers I ive in Australia. How can this be? Apparently, the Eu-
tending to the lower right—both dwarfed by the massive nest.
calyptus trees that dominate the Austral ian landscape are particularly
Photo by Richard Packwood/Oxford Scientific Films.
liable to develop cavities through fungal action on scars left by fallen
limbs. And indeed, many species throughoutthe world adopt natural ly
Figure C. Individual Nest Tunnels of Social Weavers: This photo occurring tree holes or niches in rock. The wheatears of Eurasia are par-
looks straight up at the bottom of a Social Weaver nest mound
ticularly interesting in this regard. These sparrow-sized birds usually
in a tree in Namibia. Each hole is the entrance to a tunnel that
leads to the oval nest chamber of an individual pair. Photo by build their nests in little caves beneath boulders, and they sometimes
Jan Halaska/Photo Researchers. (Continued on p. 8.44)

Cornell Laboratorq ofOrnithologq Handbook of Bird Biologq

 8.42 David W. Winkler Chapter 8— Nests, Eggs, and Young: Breeding Biologq of Birds 8.43
Figure 8-41. Kingfisher Nest Tunnels:
All kingfishers nest in holes. Some adopt
.1 0 cavities in trees, others dig nests in active
termite mounds, and others, as shown
here, dig burrows in earthen banks.
a. Belted Kingfisher Excavating Nest
Tunnel: While his mate calls nearby,
a male Belted Kingfisher takes his turn
digging the nest tunnel with his beak,
kicking out loosened dirt. Birds usually
dig in the early morning, their tunnels
often extending 12 inches (30 cm) after
the first day. The entrance hole is about
4 inches (10 cm) in diameter, and the
bottom of an active hole has a distinct
furrow on each side where an entering or
exiting bird's feet scrape the dirt. b. Belt-
ed Kingfisher Nest Tunnel (Side View):
Belted Kingfishers usually nest near wa-
‘,1
ter, digging their tunnels into steep dirt
a. Belted Kingfisher Excavating Nest Tunnel
or sand banks with no vegetation on the
face and usually just herbaceous plants
on the top, minimizing the chance of hit-
ting roots. The tunnel entrance is high,
14 to 15 inches (36 to 38 cm) below
b. Two Nestlings Survey their Surroundings the top of the bank, probably to deter
predators and avoid flooding. The tunnel
is usually 3.3 to 6.6 feet (1 to 2 m) long,
Figure 8-40. Bank Swallow Nest Tunnels:
occasionally reaching 15 feet (4.5 m),
Ranging through much of North America and
a. Bank Swallow Colony and it slopes upward to the nest cham-
Eurasia, Bank Swallows breed in dense colo-
ber, probably to keep out water. The
nies often having several hundred active nests,
nest chamber is unlined, but once birds
but occasionally containing as many as 2,000.
begin to incubate, regurgitated pellets
a. Bank Swallow Colony: Bank Swallows lo-
of undigested fish and insect parts may
cate their colonies in nearly vertical sand or .1000$41 0)44140000
accumulate, somewhat cushioning the
dirt banks, usually near water. Common sites
eggs (see inset). Nest information from
include sand and gravel pits (as shown here),
Hamas (1994) and Michael J. Hamas
road cuts, and eroded stream banks—places
r. (personal communication). c. Com-
where the substrate is fairly crumbly for dig-
mon Kingfisher Feeding 14-Day-Old
ging, but not so loose that tunnels will col- b. Belted Kingfisher Nest Tunnel
Nestlings: After the first few days, parent
lapse. Although not evident from this photo,
Common Kingfishers of Eurasia bring
the birds usually dig their tunnels near the top
small whole fish to their young. The six
of a bank, where the soil is firm and the nests
or seven chicks each may consume 15 or
are farthest from climbing predators. Not all
more fish per day, keeping their parents
burrows visible in a colony are active—some
busy. Photo by Angelo Gandolfi/BBC
remain empty from previous years, and others
Natural History Unit.
were started by young or unmated birds and
never completed. Both sexes dig the burrow,
using their beaks and feet, progressing up to 5
8 inches (12.8 cm) each day. Tunnels average 2 to
3 feet (0.6 to 0.9 m) in length, but occasionally
reach 6 feet (1.8 m). Photo courtesy of Lang
c. Chicks Inside Nest Chamber Elliott/CLO. b. Two Nestlings Survey their Sur-
roundings: Photo courtesy of Lang El I iott/CLO.
c. Chicks Inside Nest Chamber: At the end of
the tunnel, the male and female build a nest
of grass, weeds, and rootlets, adding a lining
of feathers after the eggs are laid. These three
nestlings are almost ready to fledge. Photo by
Mike Birkhead/Oxford Scientific Films.
c. Common Kingfisher Feeding Nestlings

Cornell Laboratorq of Omithologq Handbook of Bird Biologq

8.44 David W. Winkler Chapter 8—Nests, Eggs, and Young: Breeding Biologq of Birds 8.45

Figure 8-43. Mud "Cavity Nest" of Rock

Nuthatch: In their treeless, rocky hab-
itats in the Middle East, Rock Nuthatches
must create their own nest cavities. They
plaster mud (or in dry periods, dung) to
a rock wall, building up a massive hemi-
sphere with a funnel-shaped entrance
tunnel. The thick-walled nests—located
under a rocky projection, around a crev-
ice in the rock, or on a steep rock face (as
shown here)—may reach 10 inches (25
cm) across and weigh up to 77 pounds
(35 kg). Inside, the birds build a large
nest cup of moss, hair, and feathers.
Drawing by Dr. C. I. F. Coombs.

a. White-fronted Bee-eater Colony b. European Bee-eater Feeding Nestling

Figure 8-42. Bee-eater Nest Tunnels: line the nest and its entrance with large numbers of pebbles—up to
Like many of their kingfisher relatives,
the colorful bee-eaters of the southern
thousands in long-established nests. Debate continues aboutthe func-
tion of this behavior, but the pebbles may, in part, signal the quality of
4
Old World nest in tunnels that they dig
into a bank or flat ground. a. White- a male to his mate before egg laying, and also may aid in thermoregu-
fronted Bee-eaters at Nest Colony: lation of the nest or in protecting the nest or the incubating female from
Inhabiting the hot African savannas, predation (Leader and Yom-Tov 1998). Apparently, all nuthatches are
White-fronted Bee-eaters breed during
cavity adopters, and many species use mud to narrow the entrance to
the dry season, but dig their tunnels
into sand or dirt banks at the end of the a hole in a tree branch or under a flap of tree bark. Rock Nuthatches
previous wet season, before the soil is of the Middle East have no trees in which to nest, so they use a niche
too hard-baked. White-fronted Bee-eat- in a rock face instead. Upon this niche they add a large mud nest with
ers nest in colonies, and each tunnel is
walls over 0.75 inches (2 cm) thick, up to 10 inches (25 cm) across,
dug and tended by the members of a
complex, extended family group. The
and weighing up to 77 pounds (35 kg) when dry (Goodfellow 1977)
tunnels, which may be up to 3 feet (1 (Fig. 8 43). Many other birds use mud to modify adopted cavities, but
-

m) long, end in an unlined, oval nest most design the entrance to allow the passage of the parents. The spec-
chamber, which may acquire regur- tacular exception is the hornbills of Africa and Asia, named for their Figure 8-44. Red-billed Hornbill
gitated pellets of hard insect parts as Female and Young in Nest: At the
large bills, which superficially resemble those of toucans. Most species
incubation proceeds. In this intensively beginning of incubation, Red-billed
studied colony in Kenya, note the col- in this family adopt a tree cavity for their nest. The cavity is enclosed
Hornbills of Africa plaster up most of
ored wing tags (appearing mostly as light with mud, and the female is left inside, incubating the eggs and later the entrance hole to their cavity nest
patches), which researchers have placed feeding the nestlings with food supplied by the male through a small with mud, leaving the female captive
on the birds for individual recognition.
slit in the mud wall of the nest. The female goes through a rapid molt inside for the 25-day incubation period
The birds in this photo are socializing and part of the 45-day nestling period.
at their nest tunnels, as they do each
of her feathers while in the nest, and her old molted feathers, together
There, the female depends on her mate
morning and evening. Photo by Peter H. with the shed feather shafts of her young, combine with many weeks'
to deliver provisions, both for her and
Wrege. b. European Bee-eater Feeding feces to create a mess without rival in the feathered world (Fig. 8 44).
-
the young, through a tiny sl it. During this
Nestling: Although bee-eaters special- In some species the female emerges part-way through the nestling time, feathers from the molting female
ize on venomous, flying insects such as combine with feces from both the young
period to help the male gather food, and in others, mother and young
honeybees, they often bring larger prey, and mother to create quite a mess in the
such as this dragonfly, to their young. emerge together. It must be a special day for the hornbill family when,
nest. Part-way through the nestling stage
The nestlings have enlarged papillae at the end of the nestling period, mother and young burst through the the female emerges to help the male
along the ankle (the upper section of the mud wall to pursue life outside in fresh air! feed the growing young. One side of
tarsometatarsus—see Fig. 1-11), and this tree cavity was replaced with glass,
they shuffle around the nest and tunnel allowing photographers and researchers
on their entire foot, as do humans, rather The Evolution of Nest Construction to observe nest activity. Photo by Alan
than on their toes, as do most other birds. Root/Oxford Scientific Films.
The enlarged ankle is visible in this one- The remarkable diversity in nest construction and placement
week-old nestling, which has crawled displayed by birds around the world tempts ornithologists to try to
out of the nest chamber to meet its reconstruct the evolution of nest-building behavior. Unfortunately,
parent. Photo by Alain Christof/Oxford no simple scenario seems widely applicable. There are certainly
Scientific Films.
birds considered to be relatively primitive that build very simple

Cornell Laboratorc of Ornithologu Handbook of Bird Biologq

8.46 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.47
nests, but many primitive birds build complicated nests, and many Interestingly, in the evolutionary sequence for nest building in
more-recently evolved birds build simple nests. Nest-building be- swallows, cavity adoption arises after at least burrow nesting. Thus,
havior has clearly evolved very differently in various bird groups swallows that use no special motor patterns for making a nest evolved
throughout the world, as the groups are molded by quite different from ancestors who already had evolved techniques for digging bur-
selection pressures. As a result, scenarios for the evolution of nest rows. This discovery, based on DNA-DNA hybridization studies (Win-
building seem to work best when applied to single groups of birds. For kler and Sheldon 1993) and confirmed by comparing sequences of
example, Winkler and Sheldon (1993) found an ordered progression mitochondrial DNA (Sheldon et al. 1999) is counter to the intuitively
of nest types within the swallows of the world (Fig. 8 45): the most -
appealing notion (Mayr and Bond 1943) that cavity adopters are more
primitive swallows today are burrowers, whereas mud nesting and primitive. Not only does this finding remind us how often our intuitions
cavity adoption came later in the group's diversification. Among can lead us awry in evolutionary biology, but it highlights the impor-
species that build mud nests, it appears that species with open cup tance of context in understanding the evolution of life history traits.
nests arose before those with closed cups, which in turn led to spe- The great majority of cavity-adopting swallows live in the Americas,
cies that build retorts. Note, however, that the evolutionary history so this new nesting trait apparently evolved in the New World after an
and relationships among species with these nest types may be very ancestral Old World group colonized there.
different in a different family of birds.

Nest Lining
One of the most interesting aspects of the nesting biology of birds
Cliff Swallow (N. America)
e..-1 Cave Swallow (Mexico and the Caribbean) is the diversity of materials they use to line their nests (Fig. 8 46). A sur-
-

Mud Retorts
- ‘4 South African Swallow (S. Africa) prising number of species, ranging from raptors to starlings and swal-
Rufous-chested Swallow (Africa)
lows, line or adorn their nests with green plant material (Fig. 8 47). -

Early authors, failing to see a function for this "decoration," wondered

Closed Mud Cups ci House Martin (Palearctic)
if these birds might simply be expressing an aesthetic sense, but recent
Barn Swallow (Holarctic) research indicates that the green plants are carefully selected to bring
Open Mud Cups
Rock Martin (S. Africa) chemicals that repel or kill insects into the nest (Wimberger 1984;
Clark and Mason 1988).
Mud Nesters
Another habit found in a wide variety of phylogenetic groups that
tempts observers to ascribe aesthetic motives to birds is using feath-
al Tree Swallow (N. America)

^ 11111k Burrow Nesters

Cavity Adopters Cavities

Burrows
Purple Martin (N. America)
Northern Rough-winged Swallow
(N. America and Mexico)
ers to line nests. Anyone with a down coat has been comforted by the
habit of most female waterfowl to line their nests with down feathers
pulled from their breasts (see Fig. 4-124a), but several songbirds line
Bank Swallow (Holarctic) Violet-green Swallow
(Western N. America and Mexico) their nests with feathers that are not their own. For instance, many
Blue-and-white Swallow (Neotropics)
Brown-chested Martin (S. America)
species of swallows collect feathers for their nest lining, and in some
Ancestral Swallows
species competition for feathers is intense—sometimes even leading
(Burrow Nesters?) Banded Martin (Africa)
to serious fighting (Fig. 8 48). In recent experimental work on Tree
-

Swallows, Winkler (1993) demonstrated that young grow faster in

nests lined with more feathers, suggesting that the fights might well be
Gray-rumped Swallow (Africa) worth the risk in this species. Other birds that gather feathers include
kinglets and the Long-tailed Tit of Europe. Long-tailed Tits must be the
champions of feather collecting: their oval nests (Fig. 8 49), made of
-

a felt of wool, moss, and spider webs, are lined with between 1,000
Black Sawwing (Africa) and 2,000 feathers (Goodfellow 1977)! One can only wonder how
these birds find so many.
Figure 8-45. The Evolution of Nest-Building Behavior in Swallows: This diagram, based on the degree of similarity among DNA Even within a closely related group of birds, interesting differ-
sequences of the different species, illustrates the probable order in which different types of nest building behaviors evolved in ences often exist in the types of nest linings chosen. For example, most
swallows. At each fork, a subset of birds diverged from the ancestral group, following evolutionary paths that led to the repre- thrushes build a nest of twigs, grass, and leaves cemented together with
sentative species alive today. Species listed for each nest type are selected examples, not an inclusive list. The ancestral swallows
mud and lined with fine grasses. In contrast, the SongTh rush of Eurasia
probably were burrow nesters, from which at least two different burrow-nesting lineages split off. Interestingly, one of these led to
cavity adopters—a counter-intuitive progression, as one might expect birds that build their own nests to arise from those that do
does not add a soft lining, but elaborates the mud portion of the nest
not. From other burrow nesters arose the mud nesters, first those that build open mud cups, and later those building more closed into a hard, smooth lining, sometimes in combination with wet rotten
cups and retorts. See text for more details. Adapted from Winkler and Sheldon (1993). (Continued on p. 8.50)

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

8 48 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.49
Figure 8-47. Purple Martin Nest with Green Leaves: Many birds, in-
cluding Purple Martins, House Sparrows, European Starlings, American
Crows, and some raptors, add green leaves to their nests—either placing
them around the edges or directly in the nest (as shown here). Many spe-
cies replenish the leaves daily throughout the incubation and nestling
periods. Researchers believe these leaves are added because they repel
or kill ectoparasites, but more study of this phenomenon is needed.
One species, the European Starling, does appear to choose leaves high
in compounds with these properties (Clark and Mason 1988). Because
Purple Martins nest colonially in adopted cavities, people often try to at-
tract them by putting up multi-roomed nest boxes or by hanging clusters
of hollow gourds with entrance holes. The top of this gourd house has
been removed to reveal the nest inside. Photo by Hal H. Harrison.

Anhinga Nest Lined With Leaves

American Goldfinch Nest Lined With Plant Down

Cooper's Hawk Nest Lined With Bark

Sandhill Crane Nest Lined With Twigs

a. Tree Swallow Bringing Feather into Nest b. Tree Swallow Nest Lined with Chicken Feathers

Figure 8-48. Tree Swallows and Nest

Feathers: Many swallows, such as Tree
Swallows, line their nests with feathers
that are not their own. a. Tree Swallow
Bringing Feather into Nest: This female
has found a large feather for her nest,
which is located in a natural tree cavity.
Photo by Marie Read. b. Tree Swallow
White-breasted Nuthatch Nest Lined With Wool and Fur Piping Plover Nest Lined With Broken Shells Nest Lined with Chicken Feathers: This
elegant nest is lavishly lined with chick-
Figure 8-46. Nest Linings: Birds line their nests with a remarkable diversity of materials. Many, particularly passerines, use soft en feathers. Note the white eggs typical
plant materials such as grasses, moss, bark fibers, or down—especially cattail and thistle down, as in the American Goldfinch of cavity nesters. Photo by Mark Wilson/
nest pictured here. Anhingas and some waders include leaves in their nest lining. Some raptors and other large birds may use WILDSHOT. c. Tree Swallows Fighting
more coarse plant materials such as twigs—as in the Sandhill Crane nest shown here, located in a sphagnum bog—or bark chips, Over a Feather: Feathers can be hard
as in the nest of the Cooper's Hawk, which usually is lined with outer bark from oaks or pines. Chickadees, Ovenbirds, White- to find, so competition for them may
breasted Nuthatches, and others often construct a soft lining of animal hair. Many beach-nesting shorebirds, such as the Piping be intense, sometimes involving serious
Plover, line their simple nest hollow with a few broken shells. Keep in mind that a single species may use widely different nest fights. Because young Tree Swallows
materials in different habitats, and that these photographs provide only examples of typical nests. American Goldfinch photo by grow fastest in nests lined with the most
Hal H. Harrison/Photo Researchers; Anhinga and Cooper's Hawk photos by Hal H. Harrison; Sandhill Crane courtesy of L. H. feathers, the fighting among parents may
Walkinshaw/CLO; White-breasted Nuthatch courtesy of Bill Duyck/CLO; Piping Plover courtesy of John Gavin/CLO. c. Tree Swallows Fighting Over a Feather be worth the risk of injury.

Cornell Laboratorc1 of Ornithologq Handbook of Bird Biologq

8.50 David W. Winkler Chapter 8—Nests, Eggs, and Young: Breeding Biologq of Birds 8.51

Figure 8-49. Long-tailed Tit at Feather- Figure 8-50. Nest Construction in the
lined Nest: The 5-inch (13-cm) oval nests American Robin: American Robins
of Long-tailed Tits are felted from wool typically spend five to six days building
and moss, bound together with spider their cup-shaped nest, placing it on a
webs, and covered with lichen. After fork or horizontal branch of a tree, or on
about nine days of nest building, the pair the ledge of a building. The nest is about
spends the next one or two weeks gath- 6 to 7 inches (15 to 17.5 cm) across on
ering feathers for the cozy lining—usu- the outside, with an inner cup for the
ally bringing the 1,000 to 2,000 feathers a. Gathering Outer eggs about 4 inches (10 cm) wide and
to their nest one at a time, from locations Wall Material 2.5 inches (6.25 cm) deep. Both male
up to several hundred yards away. Small and female bring nest material (with
birds in cold regions often line their nests the male's contributions being fewer
heavily, and these Eurasian tits have and smaller), but the female actually
found an extremely effective insulating constructs the nest. It consists of three
material. Photo by David Hosking/Photo 4 layers, which are built sequentially. a.
Researchers. Gathering Outer Wall Material: For
the coarse outer wall, the birds make
many trips bringing twigs, rootlets,
b. Shaping Outer dead leaves, moss, coarse grasses, and
Wall sometimes man-made materials such as
paper pieces to the nest site. They often
choose wet materials, because they are
more pliable. b. Shaping Outer Wall:
Once the pair has accumulated enough
material, the female squats in its midst,
rotating left and right (as shown by col-
ored arrow) and pressing down, thereby
wood, dung, or peat glued together with saliva (Goodfellow 1977). using her body to shape the material into
a rough cup. The birds may then bring
Most warblers I ine thei r nests with fine, dried grasses or hair, but Worm- c. Gathering Mud
more material and repeat the shaping
eating Warblers line their nests entirely with the hairlike stalks from the process. c. Gathering Mud: The second
spore capsules of the hair moss (Polytrichum) and occasionally with layer, inside the outer wall, is formed of
the stalks of maple seeds (Bent 1953). Do the species that make such mud. Visiting banks of streams, edges
highly specific and idiosyncratic choices of lining materials reap some of puddles, or other muddy places, the
female picks up pellets of mud or earth-
advantage? It would be very interesting to find out!
worm castings in her bill, sometimes
using a wick of vegetation to carry them
(see Fig. 8-53), and plasters them inside
Nest-building Behavior the nest. d. Shaping Mud Layer: After
The behaviors that birds use in building nests vary in complexity d. Shaping Mud Layer incorporating numerous mud pellets
with the elaborateness of the nest: a scrape with no lining is clearly a lot into the nest walls, the female again
squats inside and rotates her body left
less demanding than a hanging retort. Species that build platform nests
and right, shaping the mud into a cup by
seldom require any specialized fabrication methods: a foundation of pressing with her breast and the wrists
coarse sticks is laid across the supporting branches and other sticks are of her wings. e. Gathering Lining: While
added until the bulk of the platform is built. Finer sticks and a lining, the mud is still damp, the robins bring
if any, are then added. fine, soft, dead grasses for a nest lining.
f. Shaping Lining: The female shapes the
The cup nesters, however, use some specialized motor patterns in
lining by pressing it into the mud layer,
construction. To build a cup nest, most species loosely weave together e. Gathering Lining rotating her body as before. Once the
coarser material for the outside, then weave inner layers of finer mate- nest is complete, she usually begins to
rials to support the lining, if any (Fig. 8 50). In species with pendulous
-
lay eggs within a few days.

nests, these weaving motions have been elaborated and perfected

through natural selection to produce walls of considerable integrity
and tensile strength. But the height of avian weaving technique is
reached in the globular nests of the African weavers. These birds use
a variety of knots in their constructions, producing nests of consid-
erable durability and unrivaled intricacy (Fig. 8 51). The Common
-

f. Shaping Lining
(Continued on p. 8.54)

Cornell Laboratorq of Omithologg Handbook of Bird Biologq

8.52 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.53
Figure 8-51. Nest Construction in the Village
Weaver: Males of theVillage Weaver, common in
open areas throughout much of Africa, use com-
plex weaving techniques to build their retort nests,
Outer Shell which are hung from the ends of long branches.
(Woven) Males learn the details of weaving and nest shap-
ing through experience--the nests of yearlings
are usually crude and messy. This species and its
nest building have been thoroughly described by
Collias and Collias (1984). a. Nest Colony: Males
place their nests in colonies, most often in acacia
trees, but sometimes in other trees such as this
palm. b. Longitudinal Section: The oval nest is
6 inches (15 cm) wide, with an entrance tunnel
Antechamber 2 to 4 inches (5 to 10 cm) long that may provide
Egg and Brood
Chamber protection from predators such as snakes. The
thick, thatched ceiling and the outer roof provide
Threshold
(Bottom of Ring) protection from rain and sun, and the threshold
helps to prevent the eggs and young from rolling
out of the nest as it sways in the wind. c. Male in
Nest at Ring Stage: The male starts his nest by
tearing long, flexible strips from living grasses or
Entrance palm leaves, and winding these securely around
a downward-facing, forked twig. He then gath-
e. Stages in Nest Building ers the dangling ends of the strips and weaves
a. Village Weaver Colony them together, forming a ring that becomes the
b. Longitudinal Section Through Village Weaver Nest
perch from which he weaves the rest of the nest,
beginning with the roof. d. Nest Early in Roof-
Building Stage: Note the intricate interweaving of
the grasses in the roof. e. Stages in Nest Building:
Perched on the threshold at the bottom of the ring
and always facing the same direction, the male
weaves the roof, egg chamber, and antechamber.
Loop Tuck Simple Loop Interlocking Loops The bright yellow-and-black male then displays
from his nest to attract a female, and if one accepts
his nest (after careful inspection), he builds an en-
trance tunnel. The female does no actual weaving,
but lines the egg chamber with grass leaves, soft
grass heads, and sometimes feathers. The male
may then build additional nests to attract more
females—sometimes having as many as five ac-
tive nests at the same time. Although he uses about
300 grass stems in the shell of each nest, he can
complete an entire structure in one day, and if any
one of his nests is not chosen by a female, he dis-
mantles it and begins another in the same place. f.
Spiral Coil Simple Weave Alternately Weaving Techniques Used by True Weavers (sub-
Reversed Winding family Ploceinae) in Nest Building: The Grosbeak
Weaver constructs its primitive nest with simple
loops and tucks (top row). The Red-billed Quelea
and Red Fody use spiral coils in their crudely
woven nests. The Village Weaver, however, uses
more sophisticated stitches—attaching the roof to
c. Male Village Weaver in Nest at Ring Stage
the support twigs with alternately reversed wind-
ing, using the simple weave in the egg chamber,
and placing half hitches throughout the nest.
The more complex overhand and slip knots are
only occasionally used by weavers. Photo a by E.
Half Hitch Overhand Knot Slip Knot Daeschler/VIREO. All other photos and drawings
d. Nest Early in Roof-Building Stage
courtesy of Nicholas E. Collias.
(Figure continued on next page) f. Weaving Techniques

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

8.54 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biology of Birds 8.55
Figure 8-52. Common Tailorbird Nests: Figure 8-54. Cliff Swallow Gathering
The female of this common warbler of a Beakful of Mud: Cliff Swallows may
India and Southeast Asia creates a fun- fly up to several miles from their nests
nel-shaped cradle for its fluffy cup nest to gather mouthfuls of pure mud from
by piercing a series of small holes near beside streams, lakes, or temporary
the edges of one or more leaves with its puddles. Their adherent retort nests are
bill, then sewing them together with plant made entirely from mud and then lined
fibers, cobwebs, or silk from cocoons. with grass. Mud-collecting is carried
Nest construction, which lasts about four out by both members of a pair, often
days, may be hampered by threads break- in large, synchronized groups of birds
ing and leaves tearing. The bird may form from the same colony. Photo courtesy
the cradle by curling one large leaf and of Cliff Beittel.
sewing the edges together (see photo) or
by sewing two to four different leaves to-
gether (see drawing). The leaf cradle helps
to disguise the nest cup and protects it
from heavy tropical rains. Although
Common Tailorbirds frequently nest
near humans, especially in city gardens,
their well-camouflaged nests seldom are
noticed. Photo by Pat Louis/Valan Photos;
drawing by Charles L. Ripper.

Tailorbird, a well-known warbler (family Sylviidae) in Southeast Asia, the most common way that birds incorporate mud into a nest, and it is
creates a funnel-shaped cradle for its soft cup nest by piercing a series used by thrushes (such as the American Robin), and some flycatchers,
of small holes near the edges of two large, living leaves. It then sews such as the Eastern Phoebe. The only birds that build an adherent nest
the leaves together with plant fibers, cobwebs, or silk from cocoons by of mud are the mud-nesting swallows. And those species that build a
placing these fibers in the leaf holes, and drawing the leaves together retort (for example, the Cliff Swallow) have evolved the further inno-
(Fig. 8 52). Much less well understood is how the felted nests of such
- vation of transporting mouthfuls of pure mud to the nest (Fig. 8 54);-

species as Long-tailed Tits (see Fig. 8-49), Bushtits, and pendu I i ne-tits most other mud-nesting swallows use a wick, incorporating it into the
Figure 8-55. Carolina Wren Gathering
manage to hold together, but certain lichens may provideVelcroTm-like nest. Selecting the right mud to meet the extraordinary engineering Nest Material: Beaks evolved to procure
adhesion (Hansell 2001). demands of their nests must require considerable discernment (Kilgore food, not to carry nest material, but nest-
Within the mud-nesting birds, a great variety of construction and Knudsen 1977; Robidoux and Cyr 1989); I wonder how well we building birds must use the only tools
methods are used (Rowley 1971). If you have ever watched an Amer- they have available. This Carolina Wren
would do at such a task?
may have grabbed more dried leaves and
ican Robin build a nest, you may have seen it take a beakful of vege- Birds carry out all the digging, weaving, and plastering required grasses than intended, ending up with
tation, often dried, dip it into a source of mud, then transfer this wick— to construct their various nest structures with the only tools available a considerable beakful of nest material!
and all the mud that adhered to it—back to its nest (Fig. 8 53). This is
- to them—their beaks and feet. But as you watch a female oriole weave Photo by Marie Read.
long strands of grass into an intricate
Figure 8-53. American Robin Using
hanging basket, you might forget that
Vegetation Wick to Gather Mud: Most beaks and feet evolved primarily for
birds that use mud to construct their other purposes. Beaks evolved to ob-
nests gather it by taking a beakful of tain food efficiently; not to carry sticks,
vegetation and dipping it into the mud
gather mud, pile up vegetation, sew
source. Then they add the entire vege-
tation "wick" and its mud coating to leaves together, and weave grasses (Fig.
the nest. This American Robin is adding 8 55): the kingfisher's beak evolved to
-

a mud wick to her nest on a nest shelf. catch fish, not to dig tunnels in earth.
Note that the nest is still unlined at this
Feet evolved to walk, run, perch, swim,
stage of construction (see Fig. 8-50).
Photo courtesy of Hal H. Harrison.
and wade across snow and lily pads; not
to dig tunnels, scrape, stamp, and gather
and hold nest materials. Woodpeckers
are perhaps an exception, as their means
of finding food and digging nest cavities
are similar: chiseling into wood.

Cornell Laboratory of Ornithology Handbook of Bird Biolo g y

8.56 David W. Winkler Chapter 8 —Nests, Eggs, and Young: Breeding Biologq of Birds 8.,)%
Sex Roles in Nest Building In many sexually dimorphic species with brighter
Birds vary considerably in the roles that each sex takes in nest males (for example, tanagers, warblers, and New World
construction, but within certain groups, sexual roles tend to be fairly blackbirds), the female often takes on the bulk of nest-con-
consistent. For example, in hummingbirds and other species with struction duties, perhaps because she is less likely to be
strong sexual selection on males—such as many cotingas (see Figs. detected by predators. But much is yet to be learned about
1-66 and 1-67), birds-of-paradise (see Fig. 3-10), manakins (see Figs. sex roles in building: why don't male vireos (who look just
6-42 and 6-47), and grouse—the female does all the work of nest like their mates) help to build the nest? And why is the gaudy
construction. In polyandrous species, such as phalaropes and jacanas male Magnificent Frigatebird the one who builds the nest
(see Fig. 8-126), the male does all the nest building. In many species with material brought by the female?These and many other
in which the male and female are similar in appearance—for example, questions wait to be answered.
gulls, corvids, herons, and swallows—the male and female take a
near-equal share in nest building. In these species the male often gath-
ers most of the material, and the female actually places it in the nest
Duration of Nest Building
(Fig. 8 56). In other species whose males and females appear similar,
-
The length of time that a bird takes to build a nest
depends upon the type of nest (simple or elaborate), the
including wrens and raptors, the male takes the lead in nest building
season (early or late in the breeding season), and the cli-
as well, with the female often adding only the lining when the nest is
finished. Curiously, wrens and raptors also happen to construct many mate. A passerine building a simple cup nest in northern
North America spends about six days: three days on the
surplus nests on their territories. Although the functions of these extra
outer layer and three on the lining. In contrast, a passerine
nests are open to debate, they may allow rapid renesting if a nest is lost
to predators or competitors (Newton 1979). Extra nests built by males such as an antwren in Panama takes 10 to 15 days (Russell
Greenberg, personal communication). In the Neotropics,
may also help to attract a female, as in Winter Wrens (Evans and Burn
a Great Kiskadee (a flycatcher) takes 24 days to build its
1996) and some populations of Marsh Wrens (Verner and Engelsen
1970). Is it possible that such an advantage may have "gone wild" in bulky, domed nest; and the Chestnut-headed Oropendola
takes about a month to construct its long, pendulous nest. The short Figure 8 57. Huge Platform Nest of
the elaborate courtship structures made by bowerbirds (see Fig. 6-41) -

breeding season in the higher latitudes apparently forces birds to build Osprey: Fish-eating Ospreys always
(Borgia 1985)? Could the extra nests of some species also serve as nest near water, building their enor-
decoys to throw off potential nest predators? faster. In the lower latitudes, where the breeding season is prolonged,
mous platform nests atop a variety of
there is no such pressure. Birds build leisurely, working on their nests structures: large dead trees (as pictured
perhaps only a few hours each day. here), cliffs, cacti, buoys, utility poles,
Some birds take less time to build their second or third nests of or nest platforms. On small islands, they
the breeding season. American Robins, for example, take an average may nest on the ground. The nests, built
of large sticks—sometimes including
of five to six days to build their first nest of the year, but may build a
debris such as rakes, brooms, shoes,
new nest in two to three days if the first nest is destroyed (Kendeigh and dolls—are lined with inner bark,
1952). grasses, and vines. Nests may be more
than 10 feet (3 m) high and often grow
bigger each year, as birds reuse them for
Nest Appropriation and Reuse many generations, adding material with
each use. Photo by R. Day/VIREO.
Most cup-nesting species—even those, such as woodpeckers,
that build energy-demanding nests—tend to build a new nest each
year. This makes sense because once a nest has been used, especially
if it has supported young all the way to fledging, it often has outlived its
usefulness. The accumulation of odoriferous nest contents probably
makes most used nests more vulnerable to predators than new ones.
In addition, old nests often contain large numbers of ectoparasites that
could harm the developing young. Nevertheless, eagles, Ospreys, and
some other large birds do reuse nests for generations (Fig. 8-57), and
Figure 8 56. Great Blue Heron Pair Nest Building: In Great Blue Herons and many other species in which the sexes look alike,
-

the male gathers sticks and twigs and brings them to the female, who stays in the nest and arranges the nest materials. In the left
recent observations (Davis et al. 1994) suggest that Eastern Bluebirds
drawing, the male presents a stick to the female. Often this presentation involves much display, especially early in the nest build- prefer to nest in boxes that contain an old nest. The ectoparasites
ing process, when the female performs a Stretch Display (see Fig. 6-18b) and takes the stick. Then, in another display called Bill in many old nests are part of a complex living community in which
Clappering, the male points his bill toward the female, rapidly clicking the bill tips together in the air. In the right drawing, the some animals feed on feces, uneaten food, and bits of castoff skin and
female inserts a stick into her platform nest while the male looks on. Drawing by Richard P Grossenheider, from Miscellaneous
feather sheaths; others prey on living nestlings; and some are actually
Publications—Museum of Zoology, University of Michigan, Number 102.

Cornell Laboratortj of Ornithologq Handbook of Bird Biologq

8.58 David W. Winkler Chapter 8—Nests, Eggs, and Young: Breeding Biologq of Birds 8.59
Figure 8-58. Parasitoid Wasp Laying parasites (termed parasitoids) on these para- Figure 8-60. Prothonotary Warbler in
Eggs in Blowfly Pupa: One might think Nest Cavity: Most New World warblers
sites (Fig. 8 58). Is it possible that in some com-
-

that freshly built, insect-free nests would nest on the ground or in vegetation, but
munities of nest invertebrates, the older nests the Prothonotary Warbler of the eastern
be the most desirable to breeding birds,
but some insects that dwell in nests are have a higher preponderance of parasitoids, United States, which breeds in swamps
actually beneficial to birds because they thus making them more suitable for nesting? with standing dead trees and in wooded
parasitize insects that parasitize the Ornithologists are just beginning to investigate bottomlands along streams, places
birds. These so-called parasitoids—such its nest in natural cavities (as shown
this question, and much remains to be learned
as this gnat-sized female chalcid wasp, here), abandoned woodpecker holes,
Nasonia vitripennis—may be more prev-
about the interactions among parasites, para- and nest boxes—usually low and over
alent in used nests, and may render these sitoids, and nesting birds. This example illus- or very close to water. The male places
older nests more desirable to breeding trates how ornithologists, to really understand the nesting biology of moss (up to 3 inches 18 cm] deep) in a
birds. The larvae of this Nasonia wasp number of potential nest sites, and the
the species they study, need to be broadly trained zoologists!
will hatch and devour the blowfly pupa, female completes the nest cup with
In some birds, the advantages of using old nests must outweigh more moss, rootlets, bark, and plant
thus killing an insect that feeds on the
blood of nestlings, especially in cavity the disadvantages, because many species appropriate the nests of other down, lining it with finer materials. The
nests. Photo courtesy of John H. Werren, species. Solitary Sandpipers and Bonaparte's Gulls, nesting in northern only other New World warbler that nests
Copyright 1980. in cavities is the Lucy's Warbler, found
boreal forests (taiga), appropriate the nests of land birds in small spruce
in the western United States. Because
trees (Fig. 8 59). House Sparrows use the old nests of a variety of other
-
so few New World warblers nest in cav-
birds from American Robins to Cliff Swallows, in addition to other ities, this breeding behavior probably
appears to be a more significant innovation, as most other hawks and
niches and cavities of all sorts. Great Horned Owls often use the large evolved more recently in this group
warblers do not nest in cavities (Fig. 8 60). Most nest appropriators
-
than the building of other types of nests.
nests of other species, such as Red-tailed Hawks or even squirrels. The
wait until the nest builder is finished with the nest, but European Star- Photo by G. BaileyNIREO.
large, thorny nests of South American thornbirds are used by at least
lings, House Sparrows, and House Wrens take over active cavities or
11 other species, including flycatchers, tanagers, and chachalacas
boxes of other birds; wrens go so far as to puncture the eggs of birds
(Lindell 1996). Sometimes the old nest is used simply as physical sup-
whose nests they fancy, and House Sparrows often kill resident birds
port for the building of a new nest: Mourning Doves place their flimsy
to obtain their cavity.
stick nests on almost any elevated support, including the old nests of
Most New World swallows, including Purple Martins and Tree,
robins, grackles, or Brown Thrashers. The Little Swift of Africa adopts
Northern Rough-winged, andViolet-green swallows, are totally reliant
old mud retorts made by Lesser and Greater striped-swallows, often
on cavities made by other species or natural processes, but even in swal-
affixing white feather "decorations" around the entrance.
low species that build their own nests, such as Barn and Cliff swallows,
Some of the most dedicated nest appropriators are species that
individuals often will reuse the nest made by another of their species.
nest in cavities in trees or in holes in a bank or cliff. Great Crested Fly-
catchers, chickadees, and Eastern Bluebirds are North American cavity
adopters (also called "secondary cavity nesters") who share this habit
with close relatives elsewhere in the world. The adoption of tree holes
EBBS
for nesting by American Kestrels and ProthonotaryWarblers, however, ■ One of my most pleasant memories from years of studying California
Gulls breeding in the Great Basin is the image of hundreds of clutches
Figure 8-59. Bonaparte's Gull Nest- displayed before me on an expanse of sand as the parents rose into the
ing in Spruce Tree: Bonaparte's Gulls, air, each clutch with its own variation on the typical shape and color
which nest near lakes, rivers, or bogs of the species, and each glowing softly in the early morning light, like
in the northern boreal forests of North
agates or opals being offered by a dealer in gems (Fig. 8-61). Indeed,
America, may either use the abandoned
nests of land birds or build their own. birds' eggs are one of the most beautiful productions of life on earth.
Their nests are typically located on a
horizontal branch of a spruce tree, 4 to
15 feet (1.2 to 4.6 m) above the ground. E88 Structure
Photo courtesy of Sam Grimes/CLO. The beauty of birds' eggs is testimony to millions of years of el-
egant engineering by natural selection, allowing them to survive on
dry land and thus develop under a variety of environmental conditions.
In contrast, the eggs of fish and most amphibians can only survive in
water, tying these animals to an existence wholly or partially depen-
dent upon water. Ancestral reptiles, however, evolved a hard-shelled
egg with internal membranes—which kept the embryo in the watery
medium required for development—freeing these animals from I iv-

Cornell Laboratorq or Ornithologq Handbook of Bird Biologti

8.60 David W. Winkler Chapter 8—Nests, Eggs, and Young: Breeding Biologq of Birds 8.61

Figure 8-61. California Gulls at Nest

Colony: The clear blue water of Mono
Lake provides a stunning contrast to both
the white breasts of nesting California
Gulls and the white rocks encrusted
with tufa (calcium carbonate) in the
background. This breeding colony, lo-
cated on an island, is one of the largest
in North America. The salty lake is high
in bicarbonate ions, and where rainwa-
ter carrying dissolved calcium flows into
the lake, calcium carbonate precipitates
out underwater, form ing the tufa crust on
the volcanic rocks. When the lake water
was diverted for use in Los Angeles, the
water level dropped dramatically, ex-
posing the tufa-encrusted rocks. Photo a. Short-beaked Echidna Adult (left) and Young Hatching from Egg (right)
courtesy of David W. Winkler.

Figure 8-62. Egg Diversity: Eggs that develop

outside the parent's body vary widely among
different groups of animals, but each must
contain all the water and nutrients required by
the embryo to develop from a single cell into
a hatchling. a. Short-beaked Echidna Adult
and Young Hatching from Egg: The foot-long
(1/3-meter), hedgehog-like echidnas (or
spiny anteaters) of Australia, Tasmania, and
New Guinea use their snouts and long, sticky
tongues to feed on ants and termites. Unlike
all other mammals, these monotremes—an
order of mammals containing only echidnas
and the platypus—lay eggs that develop out-
ing in or near water. Thus began the long evolution of land animals, side the body. After a 21-day gestation period,
including birds. the female lays a leathery, grape-sized egg and
places it in a pouch on her stomach. Ten days
Bird eggs are large—no bird has an egg as small as thatfrom which
later, a semi-transparent hatchling emerges,
each of us spru ng.The only mammals with eggs similar to those of birds using its egg tooth and a hard bump on its nose
are the monotremes—echidnas (spiny anteaters) and the platypus of b. Spotted Salamander
(visible here) to break through the shell. Just
Australasia. Thei r eggs develop outside the body, unlike those of all oth- one-half inch (13.5 mm) long, it remains with
its mother for six to eight months, first nursing
er mammals (Fig. 8 - 62a). Most snakes, lizards, and turtles also lay large
while in her pouch, and later in the burrow
eggs (Fig. 8 - 62b and c). The embryos in the large external eggs of birds, Adult photo by Dave Watts/Nature Focus.
reptiles, and monotremes—unlike most mammalian embryos—must Hatchling photo by Rismac/Nature Focus.
develop entirely independent of their parents for resources.Th us for the b. Female Spotted Salamander Laying Eggs:
long developmental journey, a bird embryo must be packed with al l the Lacking a hard outer shell, the eggs of most
amphibians are embedded in a jellylike
protein, carbohydrates, fats, and water that it will need to develop into
material, and must remain moist. The female
a hatch I ing. For all the resources it must contain, the egg begins life as a spotted salamander, 6 to 8 inches (15 to 20
single cell with just one copy of each parent's genes on board: indeed, cm) long, attaches her single oval egg mass 8
the egg of an Ostrich is the largest living cell on earth. to underwater sticks or plants. About the size
of a tennis ball, the mass may contain up to
Before going into the details of egg structure, step into your kitchen
200 eggs. Photo by Dwight R. Kuhn.
and refresh your memory of the major features of an egg (Fig. 8 - 63). As c. Female Prairie Skink Guarding Eggs: Rep-
you crack the egg, notice how the brittle mineral shell is held together, tile eggs, like bird eggs, are adapted to survive
just like the layers of auto safety glass, by a thin membrane to which it away from water, but their shell is less brittle,
adheres at its inner surface. (There actually are two membranes here: and more leathery, than that of bird eggs. The
female prairie skink—a shiny lizard of the
one sticks tightly to the shell; the other, surrounding the egg white or
U. S. Midwest—guards her eggs throughout
albumen, is the one that can be frustrating to peel off a hard-boiled the incubation period. Photo courtesy of
egg.) Once you have broken through these two outer membranes you Harry W. Greene. c. Prairie Skink

Cornell Laboratorti of Ornithologq Handbook of Bird Biologq

8.62 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologu o f Birds 8.63
Outer Shell Lighter Yolk Germinal Figure 8-64. Egg Structure: This longi-
Membrane (Deposited Spot tudinal section of a domestic chicken
Darker Yolk
During Night) egg shows the major parts of a bird egg.
(Deposited
During Day) Vitel line Membrane The outer circle around the yolk con-
tains the chalaziferous layer of albumen,
which surrounds the yolk and attaches
Chalaza to the far ends of the egg as the cha-
lazae. The next circle in from that is the
Air Space vitelline membrane, which contains the
yolk. Note the five pairs of dark and light
Inner Shell
Membrane yolk bands, which indicate that this egg
took five days to "yolk up." See text for
Albumen Layers: a detailed description of each structure.
Chalaziferous (Dense) Drawing by Charles L. Ripper.
Inner (Watery)
,lk . 11hum< vi Fibrous (Viscous)
t1 hite , Outer (Watery) Outer Shell
Membrane [ Shell

a. Visible Parts of a Raw Egg b. Hard-boiled Egg with Membranes

Figure 8-63. Chicken Egg Photos: a. Visible Parts of a Raw Egg: If you crack a chicken egg into a bowl, you will see the clear, watery
females often prepare yolks in all the ova they will need for a com-
albumen (the egg white) and the yellow yolk, which is held together by the virtually invisible vitelline membrane. The stringy,
whitish coils on each side of the yolk are the chalazae. You also may notice that the yolk rotates such that a circular, white spot
plete clutch (and often in at least one more ovum) before any eggs
on its surface (barely visible in the center of this yolk) faces upward. If the egg were fertilized, this tissue, termed the blastoderm, are laid. During the preparation period, termed "yolking up," yolk is
would make up the tiny developing embryo. b. Hard-boiled Egg with Membranes: If you gently crack open a hard-boiled egg, deposited within the vitel line membrane in alternating bands of darker
you may be able to find the two shell membranes. The outer shell membrane clings tightly to the inside of the shell, coming off and lighter yolk, producing a structure resembling the growth rings
with it. The inner shell membrane adheres stubbornly to the egg white—usually frustrating anyone who tries to peel it off. Photos
of a tree in cross section. Because these bands alternate on a daily
courtesy of Marie Read/CLO.
cycle (light being deposited at night and dark during the day, when
can spill the contents of the egg into a bowl. There you can see the yolk the female is ingesting food rich in pigments), the yolk ring structure
surrounded by the white, now released from its membrane. The yolk it- can be used to determine how long birds take to prepare their yolks
self is surrounded and held together by the vitelline membrane, which for laying (Grau 1976). The one structure interrupting the concentric
is hard to see, but is what you rupture when you "break" a yolk. You rings is a cylinder of light yolk that stretches from the yolk's core to its
may notice that the yolk rotates such that a circular, white spot on its surface, upon which sits the germinal spot. This is the site where the
surface is upward in the dish .Th is tissue, termed the blastoderm, would embryo will develop, first as a flattened disc called the blastoderm on
make up the tiny developing embryo if the egg were fertilized. If you the yolk's surface, and eventually growing to fill the entire egg (Fig.
have ever tried to separate a yolk from the white, you have encountered 8 65). The lighter-colored yolk of the germinal spot and the column
-

some gelatinous, stringy parts of the albumen, often milky white in on which it sits also is lighter in weight, and the yolk rotates so that the
color, which are hard to separate from the yolk. These are the chalazae, developing embryo always floats to the top during its development, no
which surround and protect the yolk and may appear twisted. matter which way the egg is turned. Unfortunately, the layers of yolk
Now that you know the general layout of an egg, look in greater are hard to see without freezing, fixing (adding a stabilizing chemical),
detail at the structure and function of its parts, beginning with the yolk and staining the yolks.
(Fig. 8-64). The yolk contains essentially all the lipid (fat) and most of The yolk would actually float up against the shell if it were not
the protein for the developing embryo. The relative sizes of the yolk cradled at the center of the egg by the chalazae, which envelop the
and white vary according to the type of young that will hatch: in spe- yolk and attach to the far ends of the egg. The twisted, cordlike chala-
cies with precocial chicks that are very well developed at hatching zae allow the yolk to rotate (see Fig. 8-64). The chalazae are similar in
(such as ducks, geese, and grouse) the yolks tend to make up a larger composition to the remainder of the albumen, which is mostly water
proportion of the total egg mass than in species with altricial young and protein. The viscosity of the albumen varies with the proportion of
(such as passerines). water and protein it contains. Immediately surrounding the yolk and
The yolk is the first part of the egg constructed by the laying forming the chalazae is a very thin layer of viscous albumen. Around
female. Before the yolk passes down the oviduct for the addition of this central complex of yolk and albumen is a thin layer of watery
albumen and shell (see Fig. 4-111), the yolk of most eggs undergoes albumen, then a thick layer of more viscous and variably fibrous al-
rapid growth over a period of about five days to two weeks; but birds, bumen (the largest component of the albumen), and then finally a thin
especially songbirds, usually lay an egg a day (and never more). layer of watery albumen right beneath the shell (for much more on egg .
Because the yolk preparation time is longer than the laying interval, (Continued on p. 8.68)

Cornell Laboratorq of Ornitholog,1 Handbook of Bird Biologg

8.64 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.65

Figure 8-65. Embryological Development of a Chick: Selected stages in the development of a domestic chicken embryo. The egg
schematics are approximately life-size with the parts drawn to scale. Note that an embryo's stage of development at a particular
time varies not only between species, but also within species, owing to changes in incubation temperature, egg freshness at the
start of incubation, season, egg size, and other factors. CAM inset for 7-day embryo adapted from Patten (1971). All other photos
and drawings courtesy of Drew M. Noden, Department of Biomedical Sciences, Cornell Veterinary College.

TOP VIEW TOP VIEW TOPVIEW 4 DAYS

18 HOURS 36 HOURS

AT LAYING Eye Primordium

Heart
Midbrain
Blastoderm
Cells

Somites
- 2 mm
Primitive Streak (Future Vertebrae)
Diameter
(- 2 mm Long)

- 6 mm _

(- 4 mm Long)

36 Hours: Cells continue to divide and begin to specialize,

so that many parts of the body—such as the circulatory, Embryo
digestive, and nervous systems—begin to differentiate.
AT LAYING The first somites (segments that will become vertebrae
4 DAYS
and muscle) develop at about 20 hours. By 36 hours, the
embryo has about nine somite pairs, and buds for the eyes
are clearly visible.
Allantois

Outer Shell

At Laying: By the time an egg is laid, the egg cell already has 18 Hours: Some blastoderm cells move to the mid- 4 Days: The four main extra-embryonic membranes (which protect and nourish the growing embryo,
begun to divide, producing a flattened disc of cells called the line, forming a trough (lighter area) with raised sides but do not form part of the adult body) have formed as foldings or outpocketings of the embryo. The
blastoderm, which lies on the upper surface of the yolk. (dark lines) called the primitive streak. Most tissues yolk sac surrounds the yolk—a store of fat and protein for the embryo; the amnion becomes filled
of the embryo form in or adjacent to this structure, with fluid and surrounds the embryo, allowing it to move and stay moist, and keeping its various
and it establishes the body axes: cranial-caudal, growing parts free from sticking to or blocking one another; the allantois forms a receptacle for
left-right, and dorsal-ventral. Here, the cranial end metabolic wastes; and the chorion surrounds the embryo and other three membranes. The chick's
can be distinguished as the dark area where cells are body has bent and twisted so that it lies with its left side on the yolk sac, and numerous body parts,
more closely packed. Eventually, the raised sides fold such as the wing and leg buds, are clearly visible. The heart has been beating for a full day.
inward over the groove and meet to form a tube, the
neural tube—a precursor to the spinal cord. (Figure continued on next page)

Cornell Laboratorq of Omithologq Handbook of Bird Biologq

8.66 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.67
7 DAYS 9 DA YS
15 DAYS

- 18mm- -21 mm-

Carbon
Through 15 Days: The embryo is much larger and
Dioxide
Porous Sh II covered with down; it has small claws on
Out
the toes and scales on the legs.
Oxygen
In
A mn iotic Cavity
Nitrogenous
'Wastes Segregated
and Stored in
Allantois

20 DAYS

CAM =
Allantoic Vein
Chorion & Yolk
Allantoic Artery
Allantois Sac
4***41'-'444.
Or-
441. ;xi ∎ To Embry.
y
Food Materials )4.
Stored in Yolk Sac
Amnion
Vitelline Artery Vitelline Vein
(Blood Flow Back to Yolk (Carries Nutrients from
Sac to Complete Cycle) Yolk to Embryo)

20 Days: The embryo is almost fully de-

veloped and will hatch in about one day. It
has used up most of the yolk and albumen,
9 Days: The embryo appears much more birdlike, having a lon- but the yolk sac remains attached to its
ger beak and longer and more distinct digits. It has a skeleton of abdomen, and will be brought into the
cartilage, partly formed eyelids, and small bumps on the skin abdomen during hatching. Because the
called feather papillae, which are the beginnings of feathers CAM no longer met the embryo's needs,
7 Days: Most organs are taking shape, notably the huge eyes. Each wing and leg is differentiated into three sections, the digits are on day 19 the embryo poked its beak into
(not visible in photo). The allantois and chorion have fused
separated by grooves or webs, and the beak is prominent, with a tiny egg tooth (see 9-Day photo). The allantois presses against the airspace at the blunt end of the egg and
against more of the eggshell, expanding the CAM. The albumen
the chorion along a portion of the eggshell, and the two fuse to form the CAM (chorioallantoic membrane). Via the numerous began air breathing (see Fig. 8-66b).
continues to shrink as the chick uses up water and protein, and
blood vessels of the CAM and pores in the eggshell, the embryo receives oxygen from outside the egg and expels carbon dioxide
water evaporates through the shell.
(see inset).

Cornell Laboratorq of Ornithologq Handbook of Bird Biologtj

8.68 David W. Winkler Chapter 8 —Nests, Eggs, and Young: Breeding Biologq of Birds 8.69
structure see the Romanoff's (1 949) classic The Avian Egg). In addition coat the egg's surface, cutting off gas exchange. Researchers have dem-
to providing nearly all the water and much of the protein for the devel- onstrated that applying just one-half drop of oil per day to a Mal lard egg
oping embryo, these layers of albumen serve admirably to protect the kills the embryo after just a few days. Even one-tenth that amount of
embryo from physical damage, provided the shell is not broken. oil killed up to 90 percent of the embryos (Graham 1989). Adult birds
The shell is the developing embryo's first line of defense (Fig. 8- exposed to low levels of pesticides or oil in water may bring enough
66a), and it is much thicker and stronger than those of other terrestrial back to the nest on their belly feathers to kill their eggs.
egg-laying vertebrates. But increased thickness also has disadvantages, How gas exchange takes place is apparent to anyone who opens
for all the embryo's gas exchange must occur across the shel I. The egg a fertile chicken egg containing an embryo at an advanced stage of
contains all the water and other raw materials necessary for embryonic development. The entire inner surface of the shell is covered with a
development, but it cannot contain all the oxygen required to fuel membrane that is richly invested with blood vessels. This chorioal-
metabolism for growth, nor can it hold all the carbon dioxide and lantoic membrane ("CAM" for short) is formed from the fusion of two
waste water produced by the embryo during growth.To get around this embryonic sacs, the chorion and the al lantois (see Fig. 8-65, 7 days).
problem, the developing embryo must be able to "breathe" through its The chorion is the outer membrane surrounding the entire avian em-
shell—and breathe it does. Eggs lose, on average, 18 percent of their bryo, and is homologous (evolutionarily related) to the mammalian
mass between laying and hatching (Rahn and Ar 1974), mostly from membrane, also called the chorion, which forms much of the placenta
water loss during metabolism of the embryo. in most mammals. The al lantois is a sac into which the developing bird
The eggshell's porosity can also put the embryo at risk. Pollutants embryo shunts all metabolic wastes that cannot evaporate through the
such as oil from oil spills can enter the egg and poison the embryo, or shell, such as uric acid crystals. The CAM, the remarkable structure

b. Shift to Breathing Air in Chicken

a. Outer Layers of the Eggshell
Outer Shell Air Space Inner Shell Egg Tooth
Membrane Membrane

Amnion

Calcite Crystals

Outer Shell Membrane

. .. .. .. ....
Chorioallantois-
• -
.✓ Day 19: Air Breathing Begins
Days 5-18: Gas Exchange Through CAM Day 19 + 6 Hours: Chick
4
$.
Breathes Atmospheric Air
Figure 8-66. Embryonic Gas Exchange: a. Outer Layers of the Eggshell: This cross section of the outer layers of a bird egg covers a
Inner Shell depth of about 0.016 inches (0.4 mm). The outermost layer is the cuticle, a thin layer of organic material. Underneath is the shell
Membrane proper, composed of columns of calcite crystals and traversed by pores, which terminate in the loose, fibrous outer shell mem- 8
brane. Below that is the inner shell membrane, a thinner and less coarse layer whose inner surface, termed the "film," is apparently
,
'?•.w.74:.'"?*.:7r,'„ 7 a continuous sheet. Attached to the film is the chorioallantoic membrane (CAM), the respiratory organ of the embryo, which is
homologous to the placenta of mammals. Venous blood (lighter) pumped by the embryonic heart flows to the CAM, where it is
4..
replenished with oxygen that has diffused into the egg through the pores. At the same time, carbon dioxide diffuses out of the venous
blood. Oxygenated blood (darker) then travels to embryonic tissue. Drawing courtesy of Patricia J. Wynne. b. Shift to BreathingAir
lb 4111 Eb110 IMO Q. ID • 111111 • OD 4110 in Chicken: On day 5, the CAM begins to cover the inner shell membrane with a network of capillaries that carry out gas exchange
for the embryo. Water vapor also diffuses continually from the egg, and the liquid water that evaporates is replaced by gas to form

027 Chorioallantoic Membrane

Venous Blood an air space at the blunt end of the egg. On day 19, however, the embryo pokes into the air space with its beak and begins to breathe
air, inflating its lungs and air sacs for the first time—although the CAM continues to function. About six hours later (in the chicken)
Oxygenated Blood
the chick breaks through the eggshell with its egg tooth and begins to breathe atmospheric air, as CAM function begins to wane.
(Figure continued on next page) Drawing courtesy of Patricia J. Wynne, based on one by Hans-Rainer Duncker of the University of Giessen.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

8.70 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.71
formed by the fusion of these membranes, serves as the functional As a general rule, larger birds tend to lay
equivalent of the embryo's lungs throughout development. larger eggs, although the eggs of larger species
As the embryo develops, the chorioallantoic membrane covers are generally a much smaller proportion of their
more and more of the inner surface of the shell. At the same time, body size: an Ostrich egg is 1.7 percent of the
as water within the egg is used up and evaporated out through the female's weight, whereas a wren's egg is 13.0
shell, the air space between the two shell membranes at the blunt percent of the weight of the female that lays it.
end of the egg gradually expands (Fig. 8-66b). (This is the air space Conspicuous and spectacular exceptions to this
that you can see at the blunt end when you peel a fresh hard-boiled rule include the kiwis, which lay eggs that are
egg.) The buoyancy imparted by this growing air space is valuable to each 25 percent of the female's body weight
field ornithologists who wish to check the developmental progress of (Fig. 8 70). Not surprisingly, kiwis lay at most
-

an egg: they can simply place an egg in water and note the position two eggs in one clutch! The ecological pressures
in which it settles or floats to get a fairly accurate indication of how that might have selected for such large eggs are
much longer the embryo within must develop before hatching (Fig. not well understood.
8 67). (Although water vapor moves readily through the shell, the
- Many other interesting variations in egg
shell membranes do a good job of keeping liquid water outside, as size occur among birds. In their first nesting
well as inside, the egg. So ornithologists needn't worry about drown- attempts, females of many species lay smaller
ing the embryo during their brief "float test.") eggs than more experienced breeders, and birds that lay large numbers Figure 8-68. Ostrich and Hummingbird
So, next time you crack open an egg for breakfast, pause for a of eggs have some tendency to lay smaller eggs. The eggs of precocial Egg: Nearly 7 inches (18 cm) long, the
egg of the Ostrich is the largest of any
moment to reflect on this elegant engineering that natural selection birds tend to be larger than those of altricial birds of a similar size
living bird. The world's smallest eggs,
hath wrought... And enjoy your omelet! (Fig. 8 71). For example, a crane (with precocial young) and an eagle
-
barely one-half inch (13 mm) long—just
(altricial young) of similar body weight lay eggs of about 4.0 and 2.8 the size of a pea—are those of several
percent of the parent's body weight, respectively. Because precocial West Indian hummingbirds. Ap-
Egg Size species spend longer in the egg than altricial species—reaching a more proximately 5,500 hummingbird eggs
The largest eggs of living birds are those of the Ostrich, mea- advanced developmental stage before hatching—their eggs must start
would fit inside an Ostrich egg. Photo
suring roughly 7 by 5.5 inches (18 by 14 cm) and weighing nearly 3 by Runk/Schoenberger/Grant Heilman
with a greater supply of nutrients for the embryo. Some brood para- Photography.
pounds (1.4 kg) (Fig. 8 68). But Ostrich eggs seem small when com-
-
sites—the Common Cuckoo of Eurasia, for example—lay small eggs
pared to those of the extinct elephantbirds of Madagascar (see Fig. relative to their body size. This could be an adaptation to match the
5 48), which measured up to 14.5 by 9.5 inches (37 by 24 cm) and
-
egg sizes of their hosts, or it could allow the parasites to lay more eggs
may have weighed as much as 27 pounds (12 kg). One of these eggs per season, thus placing eggs in more host nests and increasing their
could have held the contents of at least 150 chicken eggs. The small- chances of hatching and survival. Egg size among closely related spe-
est eggs are laid by hummingbirds.Those of two West Indian species, Figure 8-69. Egg Size Diversity: The
cies tends to be much less variable than other aspects of birds' breeding
the smallest of all birds, measure from 0.4 to 0.5 inches (1 0 to 13 mm) biology, such as clutch size and number of broods per season. eggs of the now-extinct elephantbirds
Figure 8-67. Egg Buoyancy and Embryo in length and weigh less than 0.04 ounces (1 g): approximately 75 of of Madagascar were enormous-14.5
Development: As the developing em- these would fit inside a large chicken egg (Fig. 8 69). inches (37 cm) long and weighing up to
-

bryo uses water and additional water 27 pounds (12 kg). Twice the length of
evaporates from the shell, air moves in an Ostrich egg, they could have held the
to replace it, gradually expanding the air Elephantbird contents of more than 11,000 humming-
10-
space at the blunt end of the egg. To de- bird eggs! The eggs of most songbirds are
termine the approximate developmental sized somewhere between the egg of a
stage of an egg, ornithologists can place chicken and that of a hummingbird.
it in a jar of water, noting the position and
height at which it floats. A freshly laid egg
will remain on the bottom, the air space Ostrich
too small to noticeably affect the egg's Q)

buoyancy. By about halfway through U

Air Space
development ,the air space has grown
large enough to raise the blunt end of
the egg off the bottom, but will not cause
it to float. As the air space enlarges, the
\ Developing
Embryo

Chicken

egg gradually floats higher in the water,

0 Hummingbird
with more protruding above the surface
Freshly-laid Egg Midway Through Late Developmental 0
in the later developmental stages. This 0
Embryo Development Stage
technique may be used quickly in the 0 5 10 15 20 25
field, without harming the egg. Inches

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

 8.72 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologq of Birds 8.73
Figure 8-70. X-ray of Brown Kiwi with a. Egg Shape Chart b. Egg Shape Examples
Egg in Oviduct: The grouse-sized kiwis
of New Zealand lay eggs that are larger
with respect to their body sizethan those
of any other bird—typically 18 to 25
percent of the female's body weight.
The eggs are incubated for nearly three Spherical
months, mostly by the male, until the (or Round) Elliptical (or
active chicks emerge—fully feathered Oblong Oval) American Golden-Plover
Cylindrical (or
and with open eyes. This X-ray shows Short Pyriform
Long Elliptical)
a fully formed egg in the oviduct of a
female Brown Kiwi. Photo courtesy of
Otorohanga Zoological Society, New Common Loon
Zealand. Subelliptical to
Long Oval

Tawny Owl
Elliptical
Short
Subelliptical Subelliptical
Long Subelliptical
EA9 Shape (or Fusiform or Biconical)

Egg shape varies from long pyriform, through oval, to nearly

spherical, with oval (typified by chicken eggs) being the most com-
mon (Fig. 8 72). The diameter and muscular tension of the oviduct Red-necked Grebe
-
Common Murre Long Subelliptical
during eggshell formation presumably determine the egg's shape, and Long Pyriform
almost all egg shapes conform to those of a single mathematical family
of "path curves" (D. E. Baker, personal communication). But within Figure 8-72. Egg Shape Diversity: Bird eggs vary greatly in
shape. Not only do they vary from species to species, some-
this family of curves is a broad variety of shapes, and adaptations to the
Short Oval times they differ within a species or even within a single clutch.
post-laying environment often accountfor the egg shape of a given spe- Oval a. Egg Shape Chart: Different references use different terms
cies. Murres, colonial seabirds that place their eggs directly on narrow, (or Ovate) Long Oval for egg shapes. Illustrated here are some of the most common
Figure 8-71. Egg Size in Altricial Versus (or Elliptical Ovate)
Precocial Birds: Although adult Killdeer often slanting, ledges high above the sea, have eggs that are remarkably terms, based on the system proposed by F. W. Preston (1953).
Note that there are four basic shapes (middle column): ellip-
and meadowlarks are approximately pointed at one end, and large and rounded at the other (pyriform).
tical, subelliptical, oval, and pyriform, with a short and long

0
the same size, the Killdeer lays larger These eggs always roll in a tight circle—a distinct advantage for eggs
eggs and incubates them for longer pe- version of each. A shortened elliptical egg, for example, is
so vulnerable to rolling off a perilous edge (Fig. 8 73). Traditionally,
-
spherical. b. Egg Shape Examples: Some cavity nesters, such
riods-24 to 26 days, compared to the
meadowlark's 13 to 15 days. Whereas ornithologists have assumed that their shape evolved to prevent them as owls and kingfishers, have fairly rounded (elliptical) eggs,
the altricial young meadowlark hatches from rolling off their ledge, but the eggs of most other cliff nesters are whereas all shorebirds (such as the American Golden-Plover)
have very pointed (pyriform) eggs, which fit more compactly

1
as a helpless nestling, whose eyes re- not pointed and the eggs of all shorebirds have a similar shape despite Short Pyriform in the nest (see Fig. 8-74). The large eggs of the cliff-nesting
main closed for the first five days, the Pyriform
being laid in flatland nests with no danger of rolling anywhere. Shore- murres also are pointed (long pyriform); several hypotheses
Killdeer chick is precocial—it emerges (or Conical)
from its egg able to see, run around, and
birds usually lay four eggs, pointed at one end, that fit symmetrically Long have been proposed to explain the function of this shape (see
Pyriform Fig. 8-73). The eggs of loons, grebes, and cormorants are
pick up its own food. Therefore, the Kill-
deer requires a larger egg and a longer quite elongated. The majority of birds, however, have fairly
developmental period inside the egg. oval eggs. Reprinted from Manual of Ornithology, by Noble S.
Drawing by Charles L. Ripper. Proctor and Patrick]. Lynch, with permission of the publisher.
S Copyright 1993, Yale University Press.

Precocial

Figure 8-73. Common Murre Egg on Ledge: The eggs of Common Murres—co-
lonial seabirds that place their eggs directly on narrow, rocky ledges—are pointed
Day-old Chick
Day-old Nestling atone end and rounded at the other (long pyriform). This shape causes the eggs to
roll in a small circle, so ornithologists have traditionally assumed that it evolved to
keep the eggs from rolling off their ledges. However, the similar egg shape of non-
cliff-nesting shorebirds, and the lack of a similar egg shape in other cliff nesters,
both cast some doubt on this explanation (see text for more information). Drawing
Killdeer Meadowlark by Margaret LaFarge, from The Audubon Society Encyclopedia of North American
Adult and Egg
Adult and Egg Birds, by John K. Terres, 1980. Published by Alfred A. Knopf, New York.

Cornell Laboratorq of Ornithologq Handbook of Bird Biologq

8.74 David W. Winkler Chapter 8 — Nests, Eggs, and Young: Breeding Biologui of Birds 8.75
and compactly in the nest with their pointed ends inward (Fig. 8 74).
- Figure 8-76. Diversity of Egg Markings:
If you disarrange the eggs in a shorebird nest, the bird will point them Bird eggs may be decorated with a va-
riety of markings, which they acquire in
all inward again before resuming incubation. The compactness of the
the female's oviduct as they rotate while
clutch may be important because shorebirds lay large eggs in propor- pigment is deposited. Rapid rotation and
tion to their body size (see Fig. 8-80), and may need to conserve heat descent through the oviduct results in
particularly well in their far northern nesting habitats. With the eggs Wreathed Capped Overlaid Scrawled Streaked more streaking, and slower movement
closely packed together, there is no wasted space to interfere with the leads to more spotting. Because the
large end of the egg travels through the
transfer of heat from the parent's body to the developing offspring.
oviduct first, it often picks up more pig-
ment, which may be concentrated into
a wreath or cap. Eggs of open-nesting
Egg Surface Texture birds tend to be pigmented heavily—the
Most eggs have a smooth, matte finish like that of a chicken or markings provide superb camouflage,
Figure 8-74. Compact Clutch of Pip- protecting the eggs from visual pred-
robin, but the variations are many. The surface may be deeply pitted as Marbled Dotted Spotted Splashed Blotched
ing Plover: The eggs of all shorebirds ators, and also may prevent the eggs
are pointed at one end, allowing the in the eggs of Ostriches and storks; chalky as in grebes and flamingos;
from overheating by shielding them
clutch (usually four eggs) to fit together or glossy, like glazed porcelain, as in tinamous (Fig. 8 75). The egg of
-
from intense solar radiation (see text).
tightly with their pointed ends toward the Guira Cuckoo of Asia has a chalky latticework