What is Bird Melanism?
Bird Melanism: This is a genetic mutation that results in excess dark pigment production known as melanin. Melanism is a dominant allele, which can be passed on to the next generation.
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Depending on the extent of the melanism in an individual, the bill and other bare parts of the body can be very dark or only a darker version of the typical bill and skin color.
Do all melanistic birds look alike?
No, the mutation itself happens in varying degrees, which results in different levels of melanin production. Being genetically controlled, each individual shows a unique degree of melanism. Some birds show black plumages, others brown, or a combination of both.
Interestingly, temporary melanism can also result from a bird’s diet. Seeds with high oil content appear to prompt a higher production of dark pigment in a bird resulting in dark plumages than birds feeding on a different diet.
Read about Bird Albinism.
What is adaptive melanism?
Adaptive melanism implies that dark or melanistic individuals are better fitted or adapted to the prevailing environment. This adaptation comes in the form of being better camouflaged, making dark individuals less conspicuous to predators.
Being less conspicuous to predators generally results in dark individuals living longer and producing more offspring. Since melanism is a dominant trait, dark or black plumages may become widespread in the population living in an environment that favors dark plumages.
Do you have examples of adaptive melanism in Birds?
The more common cases of adaptive melanism in birds apparently respond to the darkening of their habitat due to pollution.
• House sparrows (Passer domesticus) were noticed to increase in melanistic birds during the industrial revolution of 1930,s. Dark birds appeared to be better camouflaged against the trees and walls that were darkened by pollution.
• Vermillion Flycatcher (Pyrocephalus rubinus) is perhaps the best know and better-studied case of adaptive melanism that has resulted from industrial pollution. In the heavily polluted city of Lima-Peru, nearly half of Vermillion Flycatchers are melanistic. Melanistic birds range from brown, sooty brown to blackish. Studies have demonstrated that only the population within the city of Lima carries melanistic genes. Populations outside the city, in non-polluted areas, are not melanistic and are genetically different from the city birds.
Related: Bird Plumage: Patterns & Functions
Do melanistic birds have problems with having different plumages?
It appears that melanism in birds, and other animals, does not imply detrimental effects. In fact, melanism appears to be beneficial depending on the habitat where melanistic animals occur.
- A decreased risk of predation: Most birds rely on their plumage to blend in the habitat they use. Melanistic birds that resulted from industrial pollution appear to blend in their environment darkened by pollution better than birds of the typical plumage.
- No apparent plumage deterioration: Melanin, a dark pigment, is an important structural component of a feather. The added melanin results in a plumage more firmly cohesive than normal plumages. It is thought that melanistic individuals are more robust than individuals with typical plumage.
- Ability to Find Suitable partners: In some birds, plumage and feathers of the body play an important role in courtship display. It is likely that not having the right plumage coloration makes melanistic birds not recognizable by potential mates. However, in populations of birds that include melanistic individuals, dark individuals seem not to have difficulties finding mates.
Related: A Guide to Bird Feathers
How to Identify melanistic Birds?
Seeing a melanistic bird in a place where such plumage is unexpected is sure to call an observer’s attention. At first, such plumage may bring confusion, but at a closer look, you will likely be able to arrive at the correct bird identity.
Most melanistic birds have darkened versions of the typical plumage. Identifying these birds is relatively easy despite their unusual plumage.
Pure sooty or black melanistic birds are relatively rare. To identify them:
- See the other birds that are associated with the melanistic bird. Compare the bill color, length, shape, eye and leg color, and behavior to find similarities with the other birds. The single dark bird in a flock is likely the same species as the birds that accompany it.
- If the melanistic bird is alone, see the habitat type, size, shape, and behavior. These clues should give you an idea of which species are expected in the area the melanistic bird is more likely to be.
Conclusion:
Melanism in birds is rare overall. Melanism is a dominant allele and may become increasingly widespread in populations where birds adapt to prevailing environmental conditions. Melanistic birds generally are a darkened version of the typical plumage. Depending on the degree of melanism, the bill, legs, and base skin may be darker or of the color of normal plumages.
Birders rely on plumage as the primary clue for bird identification. An atypical bird plumage is likely to cause temporary confusion, but taking the clues suggested here, it is likely that you will be able to arrive at the correct bird identification.
References:
- Industrial melanism in the Vermilion Flycatcher (Pyrocephalus rubinus): the first case in a vertebrate? Conference Paper • October 2011 with 27 Reads. Conference: Conference: 2011 Society for Advancement of Hispanics/Chicanos and Native Americans in Science National Conference.
- Begon, M., Townsend, C. R., Harper, J. L. (2006). Ecology: From individuals to ecosystems. 4th ed., Blackwell Publishing Malden, Oxford, Victoria.
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