For the Birds Radio Program: Blue Downy Woodpecker
Today Laura Erickson talks about a peculiar Downy Woodpecker. 3:32
I got a phone call from one of my Madison, Wisconsin, friends a couple of weeks ago. Steve Lang is a fine bird photographer with whom I’ve collaborated on a few magazine articles, and he’d just been to an area feeder photographing an odd Downy Woodpecker. And this was one odd bird—all the feathers that should have been white were vivid blue—almost as dark blue as an Indigo Bunting on the face, belly, back, and even the dots on its wings.
This bird has been coming to the same feeder since before Thanksgiving. The people who have been watching it are mystified, as is everyone I’ve talked to about it. Most feather oddities—from the white feathers on albinos and partial albinos to the dark feathers on melanistic birds—are caused by genetic mutations that cause the bird to manufacture more or less pigment than normal.
But blue isn’t caused by a pigment at all. It’s what’s called a structural color, resulting from the pattern of growth of the outermost layer of cells on the feather. The underlying pigment of a Blue Jay feather is grayish brown. Of course, that underlying pigment contributes to the shade of blue, and so this Downy’s feathers are obviously pigmented. White is also considered a structural color, taking its glistening quality from the arrangement of the feather’s cells. So it’s possible that this bird has a genetic mutation making it produce a pigment, and its cell arrangement makes the feathers appear blue. Of course, there is also a very real possibility that the whole thing is a hoax, and some trickster dyed it blue. One ornithologist who looked at the bird through a telescope thought he may have detected blue on the bird’s legs, which would indicate that it was dipped in dye. But others who saw it close up thought the legs and feet looked normal. I’m hoping scientists at the University of Wisconsin will soon catch the bird for banding. They can examine its legs and also pluck one or two back feathers to examine under a microscope.
I often hear about odd birds at feeders. The most common abnormalities are albinos—birds with varying amounts of white in place of their normal color because the bird is producing no pigment at all in these areas. Some birds produce less pigment than they should, making all their feathers appear lighter and creamier than normal—there are several scientific terms for this, the most descriptive and perhaps most accurate being dilute plumage. When birds produce more pigment than normal, taking on a darker color, they are called melanistic. Some feather colors result from the combination of two different pigments. Parrots are green because of gray and yellow pigments inside cells that are structured to reflect blue. When a parrot can’t make gray pigment, the yellow pigment dominates the blue structure, producing abnormally yellow feathers described as schizochroic.
Whether it’s an albino, melanistic, schizochroic, or dilute, birds of a feather may flock together, but a blue woodpecker is definitely a horse of a different color. As we learn more about this odd little Downy, we’ll let you know about it.