Re Stuart's question, I wonder if we can just see white feathers more
easily on black birds. A few white feathers on a sparrow just might not be
as conspicuous at a distance as they would be on a crow or blackbird.
Blackbirds were among those I saw in London with white feathers on them,
but I have seen it a fair amount in the closely related robins here. Every
museum collection contains some neat partially albino robins. Obviously
another generality is that we will see albinism more in the most common
birds. I've seen it in this area only in common birds--red-tailed hawk,
western sandpiper, dunlin, barn swallow, red-winged blackbird, robin, crow,
black-capped chickadee that I can recall at the moment. A house sparrow at
our feeder now has two white tail feathers, again making me realize how
much more exciting watching birds is when you can recognize an individual
bird.

About your bleach hypothesis, JoLynn. I'm perfectly willing to concede it
may be as likely as either of mine! But I'll stand fast on my "we don't
have a clue" hypothesis. The two black-capped chickadees that I described
at the beginning of the winter are still coming to the feeders; they seem
as healthy as the "normal" birds. They may disappear when the flock breaks
up into territorial pairs, which should happen very soon.

Fault barring is an interesting phenomenon also mentioned by Stuart. Fault
bars, or growth bars, are actually thought to represent daytime and
nighttime growth, which probably happen at different rates and thus cause
the bars; thus each pair of bars represents one day's growth. This is
still an untested hypothesis. Good vs. poor nutrition would show up by the
width of the bars in comparisons among individuals. This is still a
scarcely tested hypothesis.

The technique of using growth bars to determine something about a bird's
nutrition, health, growth rate, etc., which has been termed
ptilochronology, has only been recently examined. Two review papers to
check are by Thomas Grubb in Auk 106: 314-320, and Auk 109: 673-676, but
see a critique of the usefulness of growth bars by Mary Murphy in Auk 109:
676-680.

Next time you pick up a dead bird or examine a museum specimen, look for
these bars on the tail feathers. I think you could see them in a closely
scrutinized live bird, but I guess I haven't tried it! Sparrows are good
subjects.

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