Yep, I think Chris Hill is right. White feathers probably grow in in
places where the feather follicle is injured in some way rather than just
anywhere a feather is lost. However, I would think that injury is not the
likely cause of a lot of the white-feathered birds we've been discussing,
like the various white-backed/tailed chickadees. What's left? Are the
alternatives genes and some more systemic pathology? Would a genetic
tendency toward albinism manifest itself in scattered white feathers or
even in local, symmetrical white patches? Likewise, would some problem
with diet or toxins manifest itself in this way?

If there were periods during which there is some reason why feathers grew
in without pigment, this should manifest itself in the patterning of white,
with only the feathers growing in at these times being white. With what we
know about patterns of molt, this would cause symmetry in white patches in
wing and tail feathers but not necessarily body feathers. And some of the
wing feathers--probably especially the secondaries--and some of the tail
feathers could be white in species in which both are molting
simultaneously. This might be a fruitful track to follow. If this *were*
the case, it would be extremely unlikely for a given bird to molt in the
same feathers white each year. If it did, then it points to something else
as a cause. Watch those mutant chickadees, tweeters!

Lots of questions to be answered--and birds as a group are the best-known
animals!

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