When birders head into the field and see a certain species, they expect that bird to have certain plumage colors, but conditions such as bird melanism can drastically change a bird’s appearance. These amazingly dark birds can be startling to see and challenging to identify, but birders who understand this type of coloration can appreciate a melanistic bird's plumage and uniqueness.
What Is Melanism?
Melanism, or melanosis, is a condition caused by a genetic mutation that gives a bird excess amounts of melanin or dark pigmentation in its feathers. This makes the feathers much darker than normal plumage, and many melanistic birds appear completely brown or black or may only show accents of other colors. There are two ways melanism can affect birds’ plumage:
- Normally dark markings, such as a bib, hood, eye line, malar stripe, or wing bars, are bolder and noticeably “overrun” their typical boundaries
- All the plumage is darkened and appears completely dark brown or black with very little variation overall and other typical markings are obscured by the deep color
Just like with leucism or very pale plumage, melanism can vary for different birds. Some individuals will show much darker plumage than normal with very obvious color changes that make them nearly unrecognizable. Other birds will have less noticeable color changes, particularly if they already have dark markings and such changes may be less prominent.
Dark Morphs and Melanism
While a true melanistic bird is rare, many bird species have regular color morphs that show some degree of melanism. This creates a dark variation of the bird’s typical plumage, and birders can learn to recognize the most common of these birds without difficulty. Two species with well known dark morphs are red-tailed hawks and ferruginous hawks.
In domestic birds, such as game birds or poultry bred in captivity, pet birds, or specially bred pigeons, melanistic plumages may be highly desirable for their unique appearances. Birds showing abnormally dark coloration may be bred to one another to ensure the genes are passed to another generation and more dark birds are hatched in subsequent broods.
Of course, some birds such as common ravens, rooks, black vultures, and many blackbirds have naturally dark plumage. While these birds may appear almost entirely black, this is natural coloration for their species and they are not considered melanistic.
How to Identify Melanistic Birds
When a bird’s typical plumage and field marks can no longer be seen, identification can be more challenging. When looking at a melanistic bird, it is impossible to rely on color alone to determine the species, since much of the color will be overshadowed by the darker plumage. Instead, birders should pay particular attention to the bird’s size and shape, behavior, feeding, range, and song. If the bird is found in a flock, its associates can be strong clues about the species, even in mixed flocks. Carefully examining the bird’s legs, feet, eyes, and bill is also useful, as melanism only affects the feathers and other body parts, such as a pale bill, colored legs, or bold eyes, will be unchanged.
Effects of Melanism on Birds
Whereas leucism can be dangerous for birds because it robs them of camouflage, melanism can be beneficial by helping conceal birds more fully. Melanistic birds in cold weather climates can also absorb solar radiation more efficiently through sunning, helping them regulate their body heat without expending as much energy. Studies of other melanistic animals, particularly felines, have indicated genetic links between melanism and stronger immune systems, which may give melanistic animals and birds better resistance to diseases. It is believed that these positive benefits may have helped give rise to the common dark color morphs of different bird species.
Of course, a bird with melanism may still have difficulty attracting a mate because their coloration is not the expected breeding plumage. Too much melanin in feathers may also rob the birds of some feather flexibility, which could lead to brittle feathers that are subject to damage more easily. This can affect a bird's flight ability, decreasing its essential agility and making it less maneuverable in the air.
Any abnormally colored bird can be a treat for birders to see. By understanding what bird melanism is and how it affects plumage, birders can easily identify melanistic birds and appreciate their uniqueness.