When I was in London many years ago I noted an amazingly high frequence of
partially albinistic birds, and my hypothesis was that these birds existed
in the city because there were few bird predators to home in on them.
Albinism is probably selected against rapidly in nature, so we probably see
a lot fewer of them than hatch out of eggs.

That hypothesis is still valid, but an alternative one to consider is that
some dietary lack or inbalance is manifesting itself in these birds that
spend all winter at bird feeders. I know wild birds in captivity sometimes
change color at a molt.

Dennis Paulson, Director phone: (206) 756-3798
Slater Museum of Natural History fax: (206) 756-3352
University of Puget Sound e-mail: dpaulson at ups.edu
Tacoma, WA 98416