Do these wild "partial albinos" (leucistics?) tend to appear at times of the
year when the species in question are known to be molting?

Re predators, we have had a Chestnut-backed Chickadee with a bright-white
tail in our yard off and on for the past week or so and it is certainly
conspicuous, but I wonder how much of its conspicuousness is due to perceived
anomaly. In a sharpie's eyes is it any more conspicuous than, say, a
junco? (Has anyone done experiments on perception/predation of bird prey in
raptors? Kiltie in Fla was looking at detection of melanistic [all-black]
squirrels, expecting that raptors would find them more conspicuous than
the standard grey-brown models, but as I recall he did not find a significant
difference in frequency of attacks on the two colors in his experiments.)
And is there really a lack of predators in urban environments? We
see on average a sharpie, a Cooper's, or a Merlin in the backyard each week
(all three in the space of an hour one day), and in addition to these airborne
threats the birds in our neighborhood (ne Seattle) have to contend with a
multitude of cats. The density of bird-specific raptors may be less on
average in urban environs, but how much less, and is the overall predator
pressure less when cats are factored in (cf. estimates from British
studies of "billions" of birds killed annually by house cats)?

Re environmental bleaching, it seems to me that anomalous white areas
that involve scattered entire feathers and/or strong symmetry are much
more likely to be developmental in origin.

David Wright
dwright at u.washington.edu

> On Thu, 16 Mar 1995, Dennis Paulson wrote:
>
> > 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
> >
> >
> >
>