Wednesday, December 11, 2013
By HERB WILSON
We have been having an odd visitor at our feeder. It's a male hairy woodpecker with a difference. Instead of black and white feathers and red on the nape, many of the typically white feathers are buff- colored.
A hairy woodpecker at a Maine feeder has buff-colored feathers in places that are usually white. The even distribution of the brownish feathers suggests they are not a result of staining by tree tannins.
Herb Wilson photo
Such variants occur regularly in hairy woodpecker populations in western North America and in the southern United States, but this morph is a first for me in New England.
Woodpecker specialists have found some hairy woodpeckers whose feathers were stained by tannins from trees, imparting a brown to cinnamon coloration. But the fairly even distribution of the buff on our woodpecker suggests the coloration comes from pigments laid down in the feathers.
The aberrant plumage of this hairy woodpecker got me to reminisce about other birds I have seen with unusual appearances.
Albino birds lack any pigment whatsoever in their feathers. Such birds lack the enzyme tyrosinase, an essential enzyme needed to make the pigment melanin. The feathers are therefore pure white. Albinos also lack coloration in their legs, feet and bill.
The eyes of true albinos appear pink because no melanin is present in the iris of a bird's eye, allowing the pinkish color of the blood vessels of the eye to be seen through the iris. The lack of melanin in the iris diminishes the vision of an albino.
Albinos have it rough: their white plumage makes them conspicuous and their reduced visual acuity makes it harder to detect approaching predators.
A bird with white feathers is not necessarily an albino. For example, a snowy egret has all white feathers. The bird does not deposit melanin in the feathers when they are being formed. The dark legs and eyes indicate that these long-legged beauties are not albinos.
I've had the pleasure of seeing an albino house sparrow, conspicuous among a flock of 20 others in normal plumage. I've also had a fleeting glimpse of a pure-white European starling.
But two other albinos are even more memorable, both seen during my college days. One was an albino Northern mockingbird, a strikingly beautiful wraith. You have likely seen Northern mockingbirds exposing their white wing patches with a distinctive two-step motion. The flashing white can be seen for quite a distance.
Ornithologists are still not sure of the purpose for the behavior. I think it is used mostly to either court females or deter other males. Other ornithologists think otherwise, suggesting the display is used to scare insects, making them fly up and become easy prey for the mockingbird.
Whatever the function of the display, I felt some empathy toward this albino mockingbird. It had the motion of displaying its wing patches down perfectly, but of course the white patches were no different from the rest of the plumage. The bird did not have an inkling that it was colored differently from normal Northern mockingbirds.
The other albino was a bird seen in Salisbury, Mass., over a Presidents Day holiday. A group of us drove from Baltimore to New England in search of various northern owls. A snowy owl was high on our list, most of us never having seen one before, and we'd had reports of several snowy owls in Salisbury.
En route, we saw an all-white bird perched about halfway up a large oak tree. Remarking to ourselves that the perch seemed to be an odd place for a snowy owl (they are usually perched on or near the ground), we jumped out of our cars in the cold air and set up our scopes. It was not a snowy owl but rather a red-tailed hawk. It was a magnificent bird. We later found snowy owls, but that albino red-tail remains a much more memorable bird.
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at email@example.com.