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.
What Is Melanism
Melanism, or melanosis, is a condition caused by a genetic mutation that gives a bird excess amounts of melanin in its feathers. This makes the feathers much darker than normal plumage, and many melanistic birds appear completely brown or black. There are two ways melanism can affect birds’ plumage:
- Normally dark markings are bolder and noticeably “overrun” their typical boundaries
- All the plumage is darkened and appears dark brown or black
Just like with leucism, melanism can vary for different birds and some individuals will show much darker plumage than normal, while other birds will have less noticeable changes in their coloration, particularly if they already have dark markings.
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 morph variation of the bird’s typical plumage, and birders can learn to recognize the most common of these birds without difficulty. Two species with the most well known dark morphs are red-tailed hawks and ferruginous hawks.
How to Identify Melanistic Birds
When a bird’s typical plumage 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 these physical features are not affected by melanism.
Effects of Melanism on Birds
Whereas leucism can be dangerous for birds because it robs them of camouflage, melanism can actually be beneficial by helping conceal birds more fully. Melanistic birds in cold weather climates can also absorb solar radiation more efficiently, 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.
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.
Photo – Melanistic Mallard Hen © Howard Cheng