Primate Study

UNIT 2 PRIMATE BEHAVIOUR

Contents
2.1 Introduction
2.2 Activity Pattern
2.3 Social Organisation
2.4 So What Sort of Behaviours do We See in Primates?
2.5 Rhesus Monkey (Common Monkey)
2.6 Papio (Commonly Known as Baboons)
2.7 Presbytis (Hanuman Langur)
2.8 Lesser Apes (Siamangs and Gibbons)
2.9 Great Apes: Orangutan
2.10 Chimpanzee
2.11 Gorilla
2.12 MAN and Other Primates
2.13 Summary
2.14 Glossary
References
Suggested Reading
Sample Questions

Learning Objectives &

MAN is a primate. However, it is difficult to understand why he behaves
differently under different situations. At the same time, it is not possible to study
man in the laboratory. In order to understand his changing behaviour, emotions,
etc., under different conditions, it is important to study the behaviour and social
structure/organisation of non-human primates and then extrapolate that to MAN.
Once you have studied this unit you will be able to understand
Ø primate behaviour under different ecological conditions; and
Ø insight into the behavioural variables as seen in MAN.

2.1 INTRODUCTION
The very fact that non human primates have been so frequently used in biomedical
researches shows that structurally, physiologically and behaviourally, they display
greater similarities to the Homo sapiens.

It is only on man’s closest relatives, the non-human primates, that behavioural

studies can be conducted and extrapolated to MAN. The social behaviour of the
non-human primates may be viewed as a simplified model of human behaviour.

So the question arises as to how we can study primate behaviour? Study of their
behaviour in captivity is not their natural behaviour but conditioned behaviour.
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Thus, we need to understand how they adjust into their environment, i.e., to Primate Behaviour
understand the life style/behaviour of our non-human primate relatives in their
natural habitats. This depends on a number of variables, including different types
of trees on which they move, sleep and collect food (amount and types of food
needed as also food distribution across the habitat occupied) during different
seasons. As such, non human primates occupying different environments must
meet different demands. Many of the behavioural differences prevalent among
them reflect adaptations to this diversity. For instance, different primate groups
live within a single forest but move and feed on different levels and or on different
types of trees (e.g. bamboos, palms, vines, etc.). Most primates eat a variety of
foods resulting in differential development of teeth. For example, insectivores
have pointed cusps on their teeth, plant gum eaters have typically sturdy incisors
and sometimes canines that protrude forward for scraping off gum, frugivores
have wide incisors and low rounded molar cusps for scraping out the fruit from
the rinds, and folivores have sharp ridged molars for shearing leaves into tiny
bits.

The ultimate needs of human and non-human primates are not as divergent as
they appear since the survival of both depends upon the conservation of the
natural habitats. Rapid urbanisation and industrialisation is not only forcing the
non-human primates to move into smaller home ranges but it is also disturbing
their ranging patterns (due to destruction of trees, undergrowth and arboreal
pathways), group structure, dominance, etc. Such demographic changes and
ecological disturbances transform their behaviour as well as movement patterns,
temporarily if not permanently.

Researchers on the above lines reveal that urban primates depict higher
competition and aggressive instinct than their forest counterparts. On the contrary,
the role of leadership and dominance is much more defined amongst the forest
primates in tune with the exigencies of the environment. Aggression is quite
common among the urban primates whereas communication is well developed
amongst the forest monkeys. Seasonal changes in the ecosystems and the annual
variations in the weather year after year influence their daily activity pattern.

2.2 ACTIVITY PATTERN

Primates normally begin their day early in the morning and retire to their sleeping
areas (usually trees, abandoned buildings, etc.) in the evening. Their major
activities that occupy them most of the day are eating, travelling and resting;
they have well defined areas through which they move in groups in search of
food and places to rest or sleep. Grooming, playing, fighting and mating activities
occupy a small fraction of their time budget. Of course, the amount of time they
spend in each of these activities varies according to the season, availability of
food, and the habitat occupied by them.

All primates have a home range or territoriality which they defend from other
groups. The neighboring groups actively defend the boundaries of their home
ranges. Ranges of non-territorial primates may overlap. At times, when different
groups occupying the same territory come face to face, an encounter occurs leading
to fight with the lesser dominant group yielding to the higher-ranking group.

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Primate Study
2.3 SOCIAL ORGANISATION
Living in social groups is one of the significant characteristics of primates. They
solve their major adaptive problems within this social context. Social groups
among non-human primates probably formed due to two main selection pressures:
predation (gaining protection by living in groups) and group life (increasing the
efficiency in acquiring food sources in the forest). The richness of the environment
determines the composition of the population, a poor habitat supporting fewer
non-human primates than the richer one.
Many different patterns of social organisations exist among the primates. Usually,
the primate social group includes members of all ages and both sexes. This
composition does not vary significantly during the annual cycle.
The following are the main social groups that can be encountered among the
living primates:
v Solitary individuals, e.g. a mother and her dependent offspring, adult males
and adult females.
v Family, or monogamous pairs (a mated pair and their young ones).
v Multi-male groups (several adult males, several adult females, and their
young ones).
v Offspring and (perhaps) several non-sexually active females.
v Uni-male groups.
v Single male (or harem) groups (a single adult male, several adult females,
and their offspring).
v All female groups (several adult females and their offspring).
v All adult male groups.
These categories reflect the sizes of the social groups. But medium sized groups
of about a dozen individuals can have either one or several males. In any case,
groups of a given size need not have the same internal structure. This applies to
dominance hierarchies. For instance, in multimale groups of macaques and
baboons, there is a clear rank order among the adult males, whereas it is absent
in the multimale groups of spider monkeys and chimpanzees. Besides these,
there are other social groups such as foraging and hunting groups.

Group life is likely to increase competition for resources and any benefits of
groups must outweigh the costs of such competition. The nocturnal primates
live in monogamous family groups. They are not gregarious animals. The diurnal
species usually live in relatively large and stable groups. Most of the diurnal
species form sizeable groups.

For all primate species, the primary social link is the mother-infant bond. In
group living primates, relationships between females and successive generations
of their female off springs usually form the core of the group. Primate social
groups are stable only in a relative sense, as individuals migrate between them
when they become sexually mature. In most of the groups, males leave the group
whereas females remain behind.

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Mating and Paternal Care Primate Behaviour

Mating and paternal care are the keys to successful reproduction. From amongst
the primates, females must make a substantial commitment of time and energy
to pregnancy and lactation once they have conceived. This naturally leads females
to emphasise parental care.

Females in Groups
The females generally protect themselves by living in groups. As a consequence,
the males usually compete for control over such groups of females. A single
dominant male might be able to keep other competitors away when groups are
small (e.g. less than 10 females) and thereby monopolise matings with the females
within the group. Primates living in more open country like the baboons and
macaques are exposed to much greater risks of predation and thus tend to live in
larger groups. As groups become large, a male cannot prevent other males from
joining his group. This also leads to competition for access to females for mating.

In large multimale groups like baboons and macaques, males are usually organised
in a dominance hierarchy. Most of the matings are generally performed by one or
two ‘top’ ranking males.

Home Range/Territory
This is an area in which the non-human primates normally confine themselves
for their day-to-day activity. This may or may not change during the individual’s
lifetime. The changes vary according to both the species and their sex. Home
range is often described as an area, which provides the animal or group of animals
with food.

Individuals or groups of most of the non-human primates actively defend part or

all of their home range against other members of their own species with displays,
vocalisations and interactions. On the other extreme, baboons have an extensive
overlapping area between their home ranges, within which groups usually avoid
each other. The degree of territoriality depends on the costs and benefits of
defending resources as in the case of scarce water resources, food resources, and
so on.

2.4 SO WHAT SORT OF BEHAVIOURS DO WE SEE

IN PRIMATES?
Social Grooming
Social grooming is a regular primate activity. Allogrooming (others) is an
important affiliative mechanism. It can be used to fortify links: subordinate
animals tend to groom more dominant ones; males groom females for sexual
access.
Social grooming is an important and a unique primate entity since it facilitates
social cementing of the organisation of the group. This activity eases the
interaction between the individuals where there is a possibility of friction and/or
aggression thus resulting in the establishment and/or strengthening of friendly
social relations among the animals within the group. It plays an important role in
the life of most of the non-human primate. It also helps in keeping the body
clean since it removes parasites and debris from the fur and the skin. 27
Primate Study Parental Care
An infant usually depends upon its mother for 2-6 months after birth for food,
etc., depending upon one’s size, etc. Most infants are usually carried by their
mothers for a further period of 6 to 12 months. The infants also depend upon
their mothers for support during fight or for protection against danger for another
3 to 4 years. Some females as among baboons and rhesus monkeys have longer
inter-birth intervals enabling the mothers to invest more time and energy in the
care of each infant.

Reproduction
In all primates, except for humans (and perhaps Chimpanzees), the females are
seasonally or cyclically receptive. This is usually associated with visual changes
such as genital swelling clearly indicating that the females are experiencing heat.
Pair bonding of any sort is rare among primates though Gibbons seem to be life-
long monogamists. Also some New World monkey groups such as marmosets
have only one reproductively active pair in any group. Chimpanzees have been
seen to have consortships of several weeks where copulation is frequent.

Mother-Infant Relationship
It has been observed that this mother infant bonding is required to allow the
infant to be able to interact properly as an adult. This attachment between the
mother and her infant which begins at birth itself is the most fundamental social
unit within the primate social relations and begins at birth itself. Infants are
mostly cared for by their mother. Primates learn what to eat, where to find food,
how to eat different foods, mating rituals, social structure, and females learn
maternal behaviour.

Dominance
Primates are mostly group-living animals and tend to form “dominance
hierarchies”. These hierarchies are also referred to as status rank. A dominant
individual always gets priority and even in a confrontation his is usually the last
word.
Animals higher in the hierarchy tend to displace lower ranked individuals from
resources like mates, space and food. The hierarchy is not a fixed one and depends
on a number of changing factors such as age, sex, body physique, aggression and
even intelligence perhaps.
Dominance serves to organise social interactions. Since the primates are born
within the group and grown therein, they learn the processes and norms of
behaviour by sheer observation. This helps in avoiding chaotic and unpleasant
situations within the group.
Males are generally dominant over females in most of the non-human primate
societies. Higher ranking males are also responsible for protecting the group,
particularly the females in estrus or with off springs, from predators or from
attack by other groups.

Aggression
Aggression is either intra- or inter-specific and is generally associated with one
or more of the following: competition for food, defense of an infant by its parents,
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struggle for dominance or change in social status, failure to comply with signals,
the consort formation at oestrus, and changes in the internal biological state of Primate Behaviour
the animal. Aggression builds up spontaneously and must be released. It has
been shown that hierarchies are considered to reduce the amount of aggression
but when hierarchies are most rigid, aggression is most common.

Communication
The communication system of the non-human primates which includes scents,
body postures, gestures, and vocalisations as monkeys and apes is rather an
expanding field. From the human perspective, we often find it easier to associate
sounds with specific meaning, whereas among the non-human primates, gestures
and actions are often used. Presentation and mounting behaviour is often used to
diffuse potentially aggressive situations. Yawns exposing teeth are often threats,
like direct eye contact. Facial expression is important too. It’s very obvious in
chimpanzees: their expression often appears all too human-like, but other primates
also use stereotyped eyelid flashes or lip slaps.

‘Display’ communicates to other members one’s emotion such as greeting, fear,

threat, happiness, danger, pain, hunger, courtship etc., through a wide variety of
body movements, facial expressions, vocalisations and olfactory signals. A display
primarily communicates information that is useful to an individual of the group,
to the social group to which he belongs and to other species.

We have now familiarised ourselves with basic behavioural characteristics of

non human primates. Let us now examine the behavioural aspects of some
common non human primates such as Rhesus monkeys, baboons, presbytis and
great apes (Orangutan, Chimpanzee and Gorillas).

2.5 RHESUS MONKEY (COMMON MONKEY)

Hindus regard the rhesus monkey as God Hanuman and as such it is considered
as sacred in India. These monkeys are omnivorous feeders and often raid cultivated
fields and gardens.

Social Behaviour
They live in large multimale-multifemale groups. Macaques (rhesus monkey)
live in troops of varying sizes in which both males and females have well-defined
rank. Ranking females benefit from easier access to food and water, space, and
grooming partners. Their group sizes range from 5 to 80; at times groups as large
as 125 individuals are also encountered. Macaques have a variable social structure.

Matrilineal hierarchies are very strong. As in many Old World monkeys, females
get genital swellings when they are in oestrus (sexually receptive). This occurs
often in multimale groups. In this way, all the males become aware that the
female is for copulation. For this purpose, they compete with one another and
ultimately the stronger male will copulate with her.

After a conflict, they have a ritual reconciliation behaviour in which the

subordinate presents its hindquarters to the dominant, which clasps the presenter
by the rump. The dominant animal may present to a low-ranking individual to
reassure or pacify it. This eases the tension between individuals. Grin, teeth
chattering, and lip-smacking are other signs of submission. Grooming is a form
of social interaction that promotes appeasement and group cohesion. The teeth- 29
Primate Study chattering face is a greeting or appeasement signal. When attacked by a high-
ranking animal, a stump tail macaque may redirect its aggression by attacking a
nearby subordinate.

Sexual Behaviour
Male rhesus monkeys make intense sexual friends. Males, especially younger
ones, use a number of ritualised erotic “greeting” gestures with one another,
including embracing, face-licking or kissing, fondling or grabbing of the erect
penis, mounting and rump fingering.

Reproduction
Dominant males copulate with high-ranking females throughout their oestrus
cycles. When low-ranking males mate, they are often interrupted by the dominant
male; to avoid interruption, they mate while he is mating with another female
(www.cellar.org).

Vocalisations
The most common vocalisation of rhesus monkeys is a ‘coo’ used when
approaching other group members to avoid aggression and initiate grooming or
other friendly interactions.

2.6 PAPIO (COMMONLY KNOWN AS BABOONS)

Baboons have complex social systems. The average size for a baboon troop is
closer to 40-80 individuals (at times as large as 200 individuals). All live in a
multimale - multi-female social group. Males fiercely defend the group. Baboons
normally sleep in large troops, no matter what their foraging patterns are, in
some high place where they are protected from predators. Mutual grooming
functions as a strong social bond.

Dominance
All baboons have strong dominance hierarchies where ranks are inherited from
the females. Females outnumber male group members, though males tend to be
dominant, herding females around and determining their foraging direction. The
highest ranking male of the group is dominant over all other males and females.
There is a ranking system between the females that is established at birth. A
daughter assumes the rank just below her mother. The ranking of the females is
stable, where as that of the males frequently changes. The dominant male is
challenged by other males who want to be in the highest ranking position.

Males will often, though not always, live elsewhere. Male olive baboons use
infants as “social buffers” in dominance struggles. Males may change troops
more than once in the course of their lives.

Reproduction and Lifespan

Baboons attain sexual maturity from 3.5 to 6 years (approx) whereas the males
become mature when they are of 60 months. Oestrus cycles run roughly for 30-
35 days. Gestation time varies from 170-190 days with most falling around 180
days. Infants are born throughout the year. Baboons live around 35-45 years.

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Communication Primate Behaviour

Baboons communicate through a variety of facial, gestural, postural, olfactory

and vocal means. Lip smacking is associated with affiliative behaviour.

2.7 PRESBYTIS (HANUMAN LANGUR)

Activity Pattern
The word “langur” means “long tail” in Hindi language. They are generally shy
creatures, spending most of their time in the trees, although some langurs spend
a major part of their time on the ground. Langurs are most active in the early
morning and late afternoon. They sleep in a shady grove during the hot midday
hours. Feeding occurs at dawn and again during the evening. The Hanuman
langur often feeds in troops, which contain males and/or females of various ages.
A troop of langurs returns to the same resting place every night. They sleep on
the extremities of branches, a precaution against large beasts of prey. Groups
may forage over several kilometers in the course of a day.

Their home range varies between .05-13 km for groups containing both males
and females, and 7-22 km for all-male groups. A portion of the home range is a
core area in which most of the time is spent.

Social Behaviour
Langur groups range between 13-37 individuals. But this can swell up to 125
when several groups gather at rich food areas. Groups usually consist of 8 - 125
individuals. Males without females form bachelor groups of 2-32. Langurs have
variable social structure: one male-multifemale, multimale-mutifemale, all
females with infants and adolescent males and females and all male groups.
Bisexual groups usually contain between 10 and 30 members – one adult male
besides adult females, young individuals of both sexes and infants. All male
troops are more variable in number, and comprise solely of adult and subadult
males. Larger groups may break into subgroups in some seasons. In the groups
with several males, the high-ranking males can mate with any female, while the
other males can only mate when they can sneak by the high-ranking males.

Females stay in the same home-range for their whole lives in association with
their mothers, grand-mothers, sisters, daughters and aunts. These home ranges
slightly overlap.

Reproduction
The young ones are weaned in 10-12 months. Female langurs become sexually
mature at 3-4 years, and the males at 4-5 years. They however do not mate until
they attain 6-7 years of age. Gestation lasts for about 190-210 days. Mothers
usually bear one infant at a time. The oestrus cycle is about 24 days long. But if
the infant is lost, cycles can resume within 8 days. The normal interval between
births is 15-24 months.

Infanticide
When a male takes over a troop, he will kill the infants to gain a reproductive
advantage. Normally, a female takes around nine months to wean her young one
and another year or so to be sexually receptive again. Infanticide serves to shorten
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Primate Study this waiting period as females whose infants have been killed will be in oestrus
shortly. As such the new male will establish himself as the leader.

Locomotion
They move through the forest and on the ground quadrupedally. Langurs also
use a leaping gait on trees through the forest. Their tails can be up to three feet
long and are used as balancing rods (like a bamboo pole) for swinging in the
trees. Langurs can be entirely terrestrial or entirely arboreal depending on the
ecological situation. In areas where trees are scarce, the langurs adapts well to
life on the ground. When on the ground, langurs walk or run on all four feet. In
the trees, they are remarkably agile. Langurs can jump horizontally from 3-5 m.
The grasping capacity of their hands and feet allows them to move on the trees at
great speeds.

Communication
Presenting behaviour is performed by the female to elicit copulation from the
male. From this condition the male understands that the female is ready for
copulation. Head-shaking precedes the display of the female presenting behaviour.

In the morning, the resident male in a group of females gives long-distance shouts,
viz., whoop, whoop! They produce a variety of sounds, e.g., a joyous “whoop”,
a guttural alarm, and a booming whoop.

Lifespan
Langurs can live up to 20 years in the wild and about 25 years in captivity.

2.8 LESSER APES (SIAMANGS AND GIBBONS)

The lesser apes are monogamous and live in small stable family groups consisting
of an adult male and an adult female (for life) and their immature off springs.
Unlike great apes, these lesser apes do not make sleeping nests. They simply
sleep (in sitting posture) between the forking branches of the trees.

They have a throat pouch (also known as gular sac) which enables them to make
louder calls. This hooting can be heard up to longer distances (approx 2-3 kms)
through the dense rain forests. These apes in the morning make loud territorial
hooting calls and menacing gestures signaling their presence in the area. Such
calls warn others to stay away from their territory particularly from the local
fruit trees. These diurnal apes are otherwise quite social animals. They are
territorial and emigrate from their natal groups around adolescence.

2.9 GREAT APES: ORANGUTANS

Orangutans are the largest and rarest of the great apes. They are found in the
tropical rain forests of Borneo and Sumatra in the southeastern islands of Asia.
Males often grow to over 150 pounds with a high degree of sexual dimorphism.

They are arboreal and good climbers having much longer arms than legs. But on
the ground, they have an obliquely quadrupedal mode of locomotion, generally
knuckle walking.

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Orangutans are intelligent, peaceful and predominantly frugivores. Adult males Primate Behaviour
and females forage independently in their habitat.

Social Behaviour
Orangutans have little social organisation, their maximum group size being the
mother with her infant. A couple may have brief associations when the female is
in oestrus. A few orangutans may congregate at a good fruit tree. Orangutan
adult males mostly lead a solitary life, except when they copulate with females.
This is probably because their food is scattered thinly throughout the rain forest.
Further they need lots of food owing to their being large creatures.
Their population densities range from 0.2 to 5.0 individuals per sq km. Local
variation has been reported in the social structure of the orangutans. Adult males
occupy larger home ranges than adult females and are hostile to one another.
Males’ home ranges are often 2 - 6 sq. km. in size, and overlap the ranges of
several females.
To avoid violent disputes, males make distinctive ‘long call’ unique to orangutans
which produces a booming sound that can be heard up to 1km away. In this way,
males avoid each other.
Orangutans are active during the day and are almost exclusively arboreal. They
forage in the early morning, resting during the midday heat and resume their
activity in the afternoon. They live alone in large territories probably due to their
eating habits.
Orangutans also construct a sleeping nest high up in the trees to rest at night. But
only the lighter female and juveniles do this. The heavier males usually sleep on
the ground. Each night, they construct nests out of leaves and branches. The
nests are of a platform style ranging from 40 to 60 feet high in a tree.

Reproduction
Orangutans have a very low reproductive rate. They mature and become capable
of reproducing when they are 7 to 10 years old by which time they attain their
adult size. The males however continue to grow until they are 10 years old and
do not have successful mating until they are about 14 years of age.
A female usually has her first infant at the age of 12-15 years. It gives birth to
one offspring at a time. They give birth once in every 3-8 years. Their gestation
period is 227 to 275 days (8 to 9 months). The young ones are not weaned from
their mothers until they are 3 ½ years old. The female orangutans have an estrous
cycle of about 30 days in length.
The male and female adults come together only for a brief period of courtship.
For purposes of mating, males prefer fully adult females. The choice of sexual
partners is very much a prerogative of females. When she is ready to mate, the
female listens to the loud calls of males following which she reaches out to one
of them for mating.

Mother - infant
Like human children, orangutan babies have to be taught everything that they
need to know to survive. Since males have nothing to do with the female after
mating, the mother takes the responsibility of teaching the infant. The mother
even feeds her baby pre-chewed food until it can eat on its own.
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Primate Study A newborn orangutan weighs 2 kg and remains totally dependent on the mother
for the first 18 months. A female adult usually establishes a territory near her
mother often overlapping with hers. A male travels far away to establish a separate
territory.

Life Span
Orangutans live about 50 to 60 years in captivity while their life span in the wild
is only 40 to 50 years.

Locomotion
Orangutans have longer and more powerful arms than other great apes. Their
arms measure 2.2 m across in their outspread position. They are longer than their
height. In contrast, their legs are short and weak. Too heavy to brachiate, the
adult orangutans swing slowly, not letting go of a branch until they reach the
next branch. They usually move slowly and deliberately using all the four limbs.
Orangutans usually move in the forests by swinging from one branch to another
called brachiating. On the ground, they usually walk on all fours. Though they
have really mobile joints, they do not really swing like the gibbons. It is more
like climbing with four hands. Adult males get so big that they sometimes have
to get down and walk from one tree to the next!

As one of man’s closest relatives, the orangutan (Asiatic great ape) or commonly
referred to as ‘man of the forest’, is a severely endangered species.

Communication and Vocalisation

Orangutans are quieter but make very long, loud calls that can be heard through
forests for up to 1 km for territorial and courting purposes. Males have a large
throat sac that lets them make these loud calls. They scream when scared, and
males sometimes roar.

Tool Use
Orangutans show a remarkable ability to arrive at certain trees just when their
fruit is ripening. Like other great apes, they have been observed to use tools but
less extensively than has been observed in chimpanzees.

They use sticks for digging and winkling out edible seeds from a spiny fruit
case, or use a stick even to hit a snake. They may also use sticks to fight each
other or scratch themselves.

2.10 CHIMPANZEE
Chimpanzees are diurnal, semi terrestrial and generally frugivorous. During the
dry season seeds, nuts, flowers, leaves, resin, eggs , etc., form the important food
resources.

Social Behaviour
Chimpanzees are social animals and are active during the day (diurnal). Their
social structure can be categorised as fusion-fission. They live in small, stable
groups (called communities or unit groups) of about 40-60 individuals who would
defend a common territory. Smaller subgroups of 6-7 chimpanzees stay together
34
for a while, with the membership changing over time. A 38 year long study in the
Gombe Stream Reserve revealed that the number of individuals in the main Primate Behaviour
study community ranged between 40 and 60.

Chimpanzees live in relatively large and complex social groups based on

permanent relationships among males. All chimpanzees are highly sociable.
Common chimpanzees live in loose, extended groups that may include more
than 100 animals. Social-bonding among them is not as strict or structured as in
gorillas and relations within a group are complex. It is hard to identify groups
because their members travel around individually, in pairs and other combinations.
But they usually forage alone.

Grooming one another (cleaning the hair of another chimpanzee) is an important

activity by which they maintain positive relationships. This kind of behaviour is
a major occupation among chimpanzees. Males do social grooming with a wider
range of individuals than females do. Grooming plays a vital role in establishing
and reinforcing bonds. Chimpanzees are particular about their territoriality.

Like other apes, they build bowl shaped sleeping nest in trees with leaves and
other plant material usually at a height of 6-25 m from the ground for safety
from predators. Every evening, chimpanzees construct a new “sleeping nest” in
the trees where they curl up and sleep. They use the same nest for several nights
if the troop is not on the move. They keep their nests clean. Each adult makes its
own nest, only young chimpanzees share their mother’s nest, until the next baby
is born.

Dominance
Within the community, there is a linear hierarchy with one of the males emerging
as number one (or alpha). All adult males dominate all females. The males of a
community regularly patrol their boundaries. Adolescent females may migrate
into a new community permanently. When they become pregnant, they move
back to their own natal group.

Hierarchy is based on age and size as well as on alliances and friendships. A

male chimpanzee gains rank or dominance on the basis of his mother’s higher
rank. In such fluid communities, aggressive behaviour is common which seldom
results in outright violence.

Male chimpanzees proclaim their dominance with spectacular charging

displays during which they may hurl themselves along the ground, or stand
upright, slap their hands, stamp their feet, drag branches, or even hurl rocks
(www.janegoodallug.org).

Sexual Behaviour
Mothers engage in sexual activity fairly often with their infants. Young females
typically experience a one-to-three year period of long adolescent sterility
following their first menstruation. During this period, they mate heterosexually
without conceiving. Incestuous matings between adults are not common
(www.forum.philosophynow.org).

Reproduction
There is no distinct breeding season among chimpanzees. They mate whenever
a female ‘comes in season’ whereupon she develops massive pink swellings on
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Primate Study her hind region lasting two to three weeks or more and occurring every four to
six weeks. This condition is an invitation for males for copulation. Chimpanzees
attain full growth and are able to reproduce by the age of 12-13 years. Female
chimpanzee’s pregnancy period lasts 8.5-9 months. They usually have a single
baby at a time; twins are rare. The female gives birth once every 4 to 5 years. The
gestation period ranges from 230 to 250 days (8 to 9 months). The females are
good mothers and raise their young ones alone.

Infanticide
Infanticide is common among them. This generally happens when there is a
change in the leadership as it immediately leads to the weaning females coming
in estrus; thereby the new leader can have sexual relationship with the adult
females to raise his own offspring.

Tool Use
Chimpanzees have opposable thumbs (although much shorter than the human
thumb) and opposable big toes capable of a precision grip, which enables them
to use tools especially in extracting ant and termites out of a mound and or a
ground as also to crack open nuts with a stone using a hard platform. Chimpanzees
have been observed to use sticks to obtain ants and termites to eat and to scare
away intruders. They also use chewed up leaves as a sponge to sop-up water to
drink.

Life Span
Chimpanzees live about 50 to 60 years in captivity while their life span in the
wild ranges from 35-40 years. Like most animals, they survive for longer period
in captivity.

Locomotion
Chimpanzees’ arms are longer than their legs which enable them to reach out to
fruits growing on thin branches that would not support their weight. This also
helps them climb trees and brachiate (swing from branch to branch by their
arms). Chimpanzees can also walk upright (on the two legs in the bipedal
position), when carrying something in their hands or when looking over tall
grass.

Chimpanzees are known as “knuckle walkers” because they place their soles
and the back of the finger joints on the ground. They are terrestrial creatures.
While most primates walk on the flats of their hands, chimpanzees walk on their
knuckles with their hands turned over. This type of walking is typical of not only
chimpanzees but also of gorillas. Chimpanzees usually walk using all fours (on
the soles of feet and the knuckles of their hands).

Communication and Vocalisation

Chimpanzees have complex communication methods involving facial
expressions, gestures and calls. Their crying calls warn other chimpanzees of the
likely danger in the area. Such danger calls can be heard through the forest for
about 2 miles (3 km). When they spot food in abundance, chimpanzees bark
loudly to call others in their group to a feast.

36
The intra-group communication is mostly achieved through posture, gesture or Primate Behaviour
facial expression, and submissive signals of crouching, presenting the rump and
holding the hand out accompanied by pant-grunts or squeaks.

2.11 GORILLA
These are the largest of the primates in the world weighing up to 400 pounds.
Their build is much heavier than that of chimpanzees. Further, they have big
canine teeth and much larger stature. They are diurnal, terrestrial apes. Some of
them prefer arboreal climbing. Gorillas possess widely set and deeply sunken
eyes and flaring nostrils. They inhabit lowland and montane forests with a
discontinuous distribution in equatorial Africa.

Ecology
Gorillas are mostly folivorous. They eat fruit, leaves, bark, ants, and bamboo
shoots. They never eat all the leaves from a single plant. Instead, they leave
plenty of leaves so that the plant can replace the leaves quickly.

Activity Pattern
The activity pattern of the gorillas depends upon the food availability, social
conditions and their reproductive status. Gorillas are shy, social animals and are
most active in the morning.

Gorillas are active during the daytime. They wake up just after sunrise (troop
rises between 6 A.M. and 8 A.M.) and search for food such as leaves, buds,
stalks, berries, bark and ferns, which they consume and rest and relax. During
midday, adults usually nap while the young play games. Gorillas do not appear
to drink water but derive the same from their juicy diet. They feed again in the
afternoon, finally retiring for the night in nests made of twigs and leaves. Unlike
the chimpanzees, they construct nests of leaves on the ground for sleeping at
night.

Home Range
Gorilla groups wander about within a home range of 10 to 40 sq km (4 to 15 1/
2 sq mile), which is not defended or marked at the boundaries. Some conflicts
may arise with neighboring groups, but encounters are generally avoided by
communications such as drumming on the ground from a distance.

Social Behaviour
Gorillas live in structured family groups with a polygynous mating pattern. The
gorilla’s social system is usually composed of a single adult male with multiple
females. They live in small groups (bands or harems) consisting of close family
members and other relatives (6–7 individuals) that may number up to 30
individuals. The adult females maintain hierarchy within the group which they
pass on to their offspring.
A typical harem is a closely-knit group including a dominant male, one or two
subdominant males, and several mature and young females. Some groups may
contain only the dominant male, two or three females and the young. males are
normally driven out of a harem once they reach an age of 11-13 years. Males
may form all male groups or travel lonely until the opportunity to start their own
harem arises. 37
Primate Study Dominance
The gorilla is essentially a peace-loving creature that would rather retreat than
fight except in circumstances when its life is threatened and retreat is impossible.
However, once provoked, an adult male will attempt to intimidate his aggressor
by standing on his legs and slapping its chest with cupped hands, simultaneously
roaring and screaming. Adult males perform elaborate displays, including chest
beating, running sideways and tearing up vegetation to frighten an intruding
male or similar other threat. Males also use these displays as a show of dominance
within the group. Adult females can become aggressive while defending their
infants, or while helping each other to drive out rowdy, young adult males. The
dominant male leads the family group and decides where the members should
feed and sleep. Females are strongly bonded to the male.
Grooming
Grooming one another (cleaning the hair of another gorilla) is a major occupation
among gorillas in a band. Female gorillas not only groom their offspring but also
one another and the dominant male. Unlike most other primates, each gorilla
takes care of its own toilet routine. Mutual grooming is quite rare among the
gorillas.
Reproduction
Females reach sexual maturity during 6-9 years of age. Males become sexually
mature in the wild between 8 and 9 ½ years of their age and in captivity as early
as 6 ½ years. Males are not considered fully mature until they become about 15
years old. The oestrus cycle lasts 26-30 days. Gorillas do not have a distinct
breeding season. Gestation lasts from 250 to 285 days. In the wild, female gorillas
usually deliver their first offspring at their age of 10½ years old and subsequently
at four-year intervals.
Locomotion
Gorillas walk in an obliquely quadrupedal mode of locomotion by actually using
their knuckles to support part of their weight. However, they do stand erect on
occasions. Gorillas perform knuckle-walking by using both their legs and long
arms. They can climb trees but do not do so very often because of their heavy
weight.
Communication and Vocalisation
Gorillas generally communicate with each other using many complicated sounds
and gestures. Some of their gestures range from chest-beating, high-pitched barks,
lunging, throwing objects to staring, lip-tucking, sticking out the tongue, sideways
running, slapping, rising to a two-legged stance, etc.(www.animalcorner.co.uk).

2.12 MAN AND OTHER PRIMATES

Macaques are the favorite animals for laboratory tests. Tests on the rhesus macaque
resulted in the discovery of the Rh (rhesus) factor in 1940. This is a hereditary
blood antigen. When Rh and non-Rh blood samples are mixed during blood
transfusions, fatal reactions can occur. The crab-eating macaque was the clinical
test animal for the development of the polio vaccine.
Orangutans have senses very similar to ours, including hearing, sight, smell,
taste and touch.
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Chimpanzees on occasions exhibit such behaviours as group hunting, food sharing Primate Behaviour
and tool making which were once considered as the exclusive trait of humans.
These behavioural traits suggest close anatomical and behavioural kinship
between Homo sapiens and chimpanzees. They have senses very similar to ours,
including hearing, sight, smell, taste and touch. Chimpanzees are very intelligent
and can learn even extremely complex tasks. Chimpanzees are the most violent
primates besides humans!
It is hardly impossible to emphasise the importance of friendly physical contact
in maintaining good relationships among chimpanzees. Social grooming is one
remarkable trait which is probably the most important social behaviour (in humans
as well), serving to maintain or to improve friendships within the community as
also to calm nervous or tense individuals.

2.13 SUMMARY
Non human primates are referred to as Man’s closest relatives. Therefore, in
order to understand Man’s changing behaviour and emotions, etc., under different
conditions, it is important to study the behaviour and social structure/organisation
of non-human primates, man’s closest relatives, and then extrapolate that to MAN.
In this Unit, we briefly discuss the behaviour of our closest relatives, i.e. the
non-human primates.
Major activities that occupy these primates most of the day are eating, traveling
and resting, grooming, playing, fighting and mating activities.
For all primate species, the primary social link is the mother-infant bond. In
group living primates, relationships between females and successive generations
of their female off springs usually form the core of the group.
We find in this unit that the frequently observed primate activity is social
grooming. It helps to strengthen links. The mother-infant relationship is the most
fundamental social unit within the primate social relations and begins at birth
itself.
Primates are mostly group-living animals and tend to form “dominance
hierarchies”. These hierarchies are also referred to as status rank. Dominance
serves to organise social interactions. Since the primates are born within the
group and grown therein, they learn the processes and norms of behaviour by
sheer observation. Aggression is either intra- or inter-specific.
In this Unit, it is observed that the primates have a very interesting system of
communication amongst themselves. For example, ‘display’ primarily
communicates information that is useful to an individual of the group, to the
social group to which he belongs and to other species. This mode of
communication conveys to other members of the group, one’s emotion such as
greeting, fear, threat, happiness, danger, pain, hunger, courtship, , etc., through a
wide variety of body movements, facial expressions, vocalisations, and olfactory
signals.
Macaques are the favorite animals for laboratory tests. Tests on the rhesus macaque
resulted in the discovery of the Rh (rhesus) factor in 1940.
Baboons have complex social systems. They live in a multimale - multi-female
social group. Baboons normally sleep in large troops, no matter what their foraging
patterns are, in some high place where they are protected from predators. Mutual
grooming functions as a strong social bond. 39
Primate Study The word “langur” means “long tail” in Hindi language. They are most active in
the early morning and late afternoon. Feeding occurs at dawn and again during
the evening. Langur groups may forage over several kilometers in the course of
a day. A troop of langurs returns to the same resting place every night.

The lesser apes (siamang and gibbon) are monogamous and live in small stable
family groups consisting of an adult male and an adult female (for life) and their
immature offsprings. Unlike great apes, these lesser apes do not make sleeping
nests. They simply sleep (in sitting posture) between the forking branches of the
trees (www.miamimetrozoo.com).

Orangutans, the largest and rarest of the great apes, have senses very similar to
humans, including hearing, sight, smell, taste and touch; are usually frugivores.
Chimpanzees are diurnal, semi terrestrial and generally frugivorous. During the
dry season seeds, nuts, flowers, leaves, resin, eggs etc. form the important food
resources. Chimpanzees on occasions exhibit such behaviours as group hunting,
food sharing and tool making which were once considered as the exclusive trait
of humans. Gorillas are the largest of the primates in the world weighing up to
400 pounds. They are diurnal, terrestrial apes. Some of them prefer arboreal
climbing. Gorillas possess widely set and deeply sunken eyes and flaring nostrils.

These behavioural traits speak of the close anatomical and behavioural kinship
between man and chimpanzees. These non-human primates have senses very
similar to ours, including hearing, sight, smell, taste and touch. Chimpanzees
are very intelligent and can learn even extremely complex tasks but are the most
violent primates besides humans!

2.14 GLOSSARY
Alpha male/female : highest ranking individual within a dominance
hierarchy.
Arboreal : tree dwelling.
Affiliative behaviour : behaviours which promote group cohesion (friendly/
positive gestures), e.g. grooming, touching, and
hugging
Brachiation : locomotion by arm swinging.
Crepuscular : active during twilight hours.
Diurnal : active during day time.
Dominance : ability to intimidate others.
Estrus : period in which an adult female is sexually receptive.
Frugivorous : fruit eating.
Gestation : conception and development of young one in uterus.
Grooming : cleaning of body surface by licking, nibbling, picking
with fingers or kind of manipulation.
Home range : area of land used.
Infanticide : killing of infants.
Mating : having sex.
Matrilocal : residence with mating female.
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New World : American mainland. Primate Behaviour

Nocturnal : active during night.

Old World : Europe, Africa and Asia.
Patrilocal : living with male.
Perineal : area in between anus and the pubic arch.
Quadrupedal : walking on four limbs.
Rank : position or status in hierarchy.
Reproductive success : number of surviving offspring of an individual.
Sexual dimorphism : difference in the body size and form of the males and
females.
Terrestrial : living on ground.
Territory : area which is exclusive and defended.
Weaning : gradually stop breast feeding.

References
www.animalcorner.co.uk accessed on 21-03-2011
www.cellar.org accessed on 30-05-2011
www.forum.philosophynow.org accessed on 11-02-2011
www.janegoodallug.org accessed on 16-02-2011
www.miamimetrozoo.com accessed on 02-05-2011.
Suggested Reading
Bramblett, C.A. 1976. Patterns of Primate Behaviour. California, Mayfield
Publishing Company.
Kummer, H. 1971. Primate Societies. Chicago, Aldine Publishing Company.
Nelson, H. and R. Jurmain 1988. Introduction to Physical Anthropology. New
York, West Publishing Company.
Seth, P.K. and S. Seth 1993. Structure, function and diversity of Indian rhesus
monkey. In New Perspective in Anthropology Ed. P.K. Seth and S. Seth. New
Delhi, M.D. Publications Pvt Ltd. pp 47 – 82.
Sample Questions
1) How does home range influence behaviour of primates?
2) What is the role of a female in estrus within the social structure of the group?
3) How do sleeping sites, food, and water resources affect the social structure
of primates?
4) Compare and contrast the social behaviour of rhesus monkey and apes.
5) Write short notes on
a) Territoriality
b) Dominance and aggression
c) Prosimians and insectivores.

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