Thursday, March 9, 2017

Thomas Spence's beautifully pale Pine Siskin

Last week I received an email from WTIP listener Thomas Spence, asking about a beautiful, extraordinarily pale finch, which he correctly identified as a “leucistic Pine Siskin,” with some help from David Brislance. Tom sent me photos of the bird, alone and with other siskins.

Tom is a carpenter and was doing work with some guys at a house just west of Grand Marais. He writes, “The saws were set up on the deck, outside, while we worked inside. The huge flock of siskins would hit the deck feeders when we went inside from making a cut, then all fly off when we opened the door to go back out. At one point, I noticed a single, starkly contrasting bird on the feeder. I quickly ran to the truck for the camera, returned and it was still there. It fed and sat in nearby trees for 15-20 minutes.”

Finches often gather in mixed flocks, making identification of one in weird plumage a bit trickier—you can’t just assume that a single pale finch within a flock composed entirely of goldfinches or siskins or redpolls will belong to that same species. But Tom’s excellent photos clearly establish the identification. His outlier bird had a longer, more slender bill than a goldfinch or redpoll. It wasn’t pure white—there was the tiniest hint of streaking beneath that also confirmed that it was a siskin. And to top it off, it had pale yellow on the wing and base of the tail, exactly where siskins usually show some yellow—though usually a more bright and intense hue.

Pine Siskins normally have a dark bill and feet, but they were pink in Tom’s bird. Fortunately, the bird had a dark eye, indicating that it has better prospects for longevity than an albino—the lack of pigment in albino eyes, which makes them appear pink, allows more sunlight to reach the retina, leading eventually to blindness in creatures that don’t have the option of wearing sunglasses.
When I took ornithology, we learned to describe this plumage type as “dilute,” and would have called the bird leucistic. If the bird had patches of pure white, making it piebald in a pattern or piecemeal, we learned to call it a “partial albino.” Now it’s gone out of vogue to refer to partial albinism, because being an albino results from a specific genetic condition that an animal either has or does not have.

When we threw "partial albino" out the window as a description for patchy white birds, “leucistic” became a catchall term referring to any plumage abnormality of a bird being whiter or paler than normal, in either a piebald, black-and-white sort of pattern, in being solid white with any color at all in the eyes, bill, or feet, or in overall dilute colors. Use of that term now seems worthless to me, because the word "leucistic" now refers to so many completely different kinds of plumage abnormalities. Ironically, many biologists consider leucism a genetic trait like albinism, so without a DNA test, if we shouldn't refer to an animal as a partial albino, we shouldn’t refer to one as leucistic, either.