In today’s birding column, I answer my readers’ questions. The three questions I am asked most frequently are as follows: What is this hawk that keeps coming to my backyard feeder? Will you please stop writing so many columns about sea birds? What was that weird white bird I just saw?
The answer to the first question is easy. It’s a sharp-shinned hawk or a Cooper’s hawk. Both specialize in hunting smaller birds. They are similar in appearance and regularly haunt feeders. The Cooper’s hawk is more likely in winter.
To the second question, the answer is no. Hey, you chose to live in a coastal state. Birding columnists in Vermont never write about sea birds.
The third question requires a more thorough response. I often am asked to identify photos of weird birds. Most turn out to be common species with a pigment challenge. Birds get their color in several ways. Blues and greens tend to be structural colors, which means that microscopic structures in the feathers refract light in those hues. Count blue jays and bluebirds among them. Most birds get their colors from chemical compounds called pigments that reflect light. Many birds have a combination of structural and pigmented colors.
Melanin is the pigment responsible for blacks and browns. Most animals produce it. It’s the pigment that colors human skin. Melanin may interact with other pigments, producing various colors. Carotene is responsible for many of the red colors in nature. While birds’ bodies produce their own melanin, carotenes are ingested in the bird’s diet. Cardinals get it from berries. Flamingos get it from shrimp. There are variations on these pigments, and there are a few other less common pigments responsible for bird color, but together they combine to color the bird according to its genetics. Unless genetics screw up.
Albinism is a genetic mutation that prevents a bird from producing melanin. Even the eyes are pink, because pigments aren’t present to block the color of the interior blood vessels. It’s unusual to see a true albino in nature. Predators spot them too easily. Furthermore, melanin plays a constructive role in stiffening and strengthening feathers and in shielding the bird from sun damage.
An albino does not need to be completely white, however. A bird may be able to produce some types of melanin but not others. A bird that cannot produce any melanin may still absorb carotene from its diet. A whitish cardinal that shows some red but no black is an albino. Even birds that get their color from structure rather than pigment can be albino. The blue in a blue jay is the result of refracted light rather than any kind of blue pigment, but light refraction requires the underlying color to be black.
It also is possible to produce too much melanin. This rarer condition is called melanism, in which even light-colored feathers are darkened.
Leucism is the most common pigment disorder. It results from a bird’s inability to produce melanin in some parts of the body, while other parts are colored normally. Results vary widely. Some birds are almost completely white, while in other birds, the leucism is limited to a single feather. The majority of leucistic birds are white in patches. These are the bird photos I receive most often. Some common birds, such as chickadees and robins, seem particularly prone to the condition.
Dilution is another plumage abnormality. These birds produce melanin in low concentrations. The blacks and browns are present but severely washed out. Sun damage may bleach these birds even further. I have not seen many diluted birds, but I was inspired to write this column because I chanced upon a diluted house finch last week. His coloration pattern was normal but almost completely faded. He was ghostly pale, but all the usual streaks and bars were discernable. Two days later, a friend sent a similar photo of an American goldfinch.
I have long argued that color merely serves to confuse birders. It distracts us from observing other field marks and behaviors. Should you chance upon a pigment-challenged bird, this will be your opportunity to practice your identification skills. Note behaviors and other features, such as bill size and shape. Whatever it is, it’s probably a locally common bird. Expect the expected. The odds of finding a bird that is both locally rare and pigment deficient are astronomically small.
I’m swinging for the fences next week. I’m writing a column about a Cooper’s hawk chasing a leucistic sea bird.
Bob Duchesne serves as a Maine Audubon trustee and vice president of its Penobscot Valley Chapter. Bob developed the Maine Birding Trail, with information at mainebirdingtrail.com. Bob can be reached at duchesne@midmaine.com.