Juncos are so commonplace around the bird feeder that they rarely draw a long look, unless I’m exercising my curiosity about behavior. But this one drew a long stare because of a back full of white feathers, a partial albino.
A true albino bird is very rare. It would have no pigment in its feathers, bill or legs and its eyes would appear pinkish-red, because the blood vessels can be seen when the typically dark color is missing.
A deficiency in this pigment (melanin) creates white feathers. Pigments absorb some wavelengths of light and reflect others. What we see as color are specific reflected wavelengths of light when they stimulate receptors in our eyes.
The red patch on a red-winged blackbird’s wing appears red because the melanin absorbs all wavelengths except the longest one, which is reflected and we see as red. The bird’s black feathers are black because the pigment absorbs all wavelengths.
(Blue and iridescence are structural colors not produced by pigments, a topic for another day.)
A feather is made of keratin, which is naturally whitish. Take away the melanin, and you’re left with white. Or a simple reduction in melanin may create a paler shade (schizochronism), sometimes challenging birders trying to identify a seemingly unusual species.
Other types of color variation are called melanism (extra dark plumage from excessive pigment), xanthochronism (yellowish or orangish plumage), and erythrism (reddish), all rare in the wild.
Albinism is normally caused by a genetic mutation that can be inherited if both parents have the albino gene. If it’s hereditary, then a new set of feathers will carry the same white pattern.
Researchers have found that parasites, injury, shock and malnutrition also may lead to a form of albinism. Diet also can create color changes and can be reversed with a different diet. The pinkish color of roseate spoonbills comes from carotenoids in some of the crustaceans that they eat.
Partial albinism in barn swallows near the Chernobyl nuclear power plant in 1986 was basically nonexistent until the accident; by 1991, the partial albino rate was 15 percent, a rate not duplicated in any other bird species in the world.
According to the “Handbook of Bird Biology,” sunlight can lighten feathers, too, although it’s not a form of albinism. American kestrels in Michigan and Arizona look similar when in their fresh fall molt. A few months later, the Arizona birds are much paler than their Michigan counterparts.
Regardless of cause, it’s rare to see even a partial albino bird. It’s more common in robins than any other wild bird species; about 8 percent of all North American full or partial albino wild birds were robins (house sparrows were second), but even that translates into about one in 30,000 robins (someone works hard at compiling these statistics).
Being an albino or partial albino bird catches our attention; unfortunately, it makes a bird stand out for predators, too. The greater the lack of pigment, the weaker the eyesight and the higher the danger of going blind from the sun without the protective coloration, making an albino bird an easier target for predators and usually leading to a shorter life span.
Since potential mates usually recognize each other by visual clues delivered by feathers, some albinos may not be able to attract a mate. A flock of the same species will often shun an albino.
Melanin plays another, less obvious role that has only surfaced in the last few decades. Pigments appear to make feathers stronger and more resistant to abrasion; feathers with color last longer than white ones.
Whatever the cause or ramifications, an albino or partial albino is certainly an eye-catcher.
Columnist Sharon Wootton can be reached at 360-468-3964 or www.songandword.com.
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