An avian oddity was recently spotted at the BFS — a pied leucistic California Towhee. Leucism is caused by a defect in melanin deposition. Some leucistic birds have uniformly reduced pigmentation all over their bodies and other — those with pied leucism — deposit melanin normally in some feathers, but not in others, causing white patches or spots.
Pied leucistic California Towhee in a Skunkbrush in the East Field
A normally pigmented California Towhee in a Blue Elderberry tree.
Not surprisingly, little is known about the genetics of leucism in wild birds. In mice, pigs, and humans white spotting can be caused by defects in the kit gene, which encodes a membrane receptor signalling protein that directs melanocytes to their normal locations.
According to some reports leucistic birds do not survive as long in the wild because they are more easily spotted by predators, while other studies suggest there is no difference in life-span in some cases.
You can read more about albinism and leucism in this article from Cornell University’s Project Feeder Watch.