[Tweeters] More on white-spotted Dark-eyed Juncos
dennispaulson at comcast.net
Sat Mar 7 12:34:12 PST 2009
I agree that feathers don't change color, once grown, except by the
gradual fading that goes on over the year in many birds.
And indeed an injury could easily damage the sites from which
individual feathers grow, to the point of them not producing pigment.
Poor nutrition when feathers are growing in may cause them to have
inadequate pigment production, and I believe that has been claimed as
a possible cause of pale wings in some crows, usually juveniles.
However, I can't imagine any sort of injury or condition that would
cause the white-cheeked junco syndrome. I think, as in all the
chickadees in Seattle that have a lot of extra white in their
plumage, it's a genetic mutation of some sort. I don't know any more
about it than that, except I would look at the patterns of other
sparrows (the closest relatives of juncos) to see if the same
feathers that are white in the juncos are part of a pigment group in
any of their relatives. In other words, is there something about the
cheeks being a special group of feathers in the junco evolutionary
line. Developmental pathways in bilaterally symmetrical organisms are
usually symmetrical, so a mutation or physiological cause of some
sort would likely cause a symmetrical abnormality.
Just because of all the white-feathered chickadees in our yard over
the years, and having seen numerous birds that seem the same from
year to year I strongly suspect that most cases of leucism represent
a permanent plumage situation, not altered by molt. But I have no
other evidence than that.
Speaking of that, we have had those leucistic chickadees in our yard
ever since moving here in 1991, but none in the past two years, so
apparently that genetic line has died out here. For the most part, it
seems to me that the more common a species is and the more easily we
see it, the more likely someone will report these abnormalities. On a
theoretical basis, I would have doubted if they are any more frequent
in juncos or Black-capped Chickadees than in any other bird, but I
may be very wrong on that. I've never seen a Chestnut-backed
Chickadee with white feathers.
One more thing. When I was in London years ago, I was shocked at the
white-feathered birds in city parks. I saw white-feathered
Blackbirds, European Starlings, and House Sparrows within a few
minutes of one another in one park. I felt strongly that it was the
reduced number of predators in such a place that allowed these
mutations to persist. If anyone goes to Hyde Park any time soon, let
me know if they're still around.
On Mar 7, 2009, at 12:00 PM, tweeters-
request at mailman2.u.washington.edu wrote:
> Date: Fri, 6 Mar 2009 23:55:42 +0000 (UTC)
> From: johntubbs at comcast.net
> Subject: [Tweeters] More on white-spotted Dark-eyed Juncos
> To: tweeters at u.washington.edu
> Hi everyone,
>> From replies both on and off list, it's apparent that white-
>> cheeked (or almost white-headed) Dark-eyed Juncos (DEJU) are
>> definitely out there in the population. Off list, one person
>> indicated that there is a theory that a window-crash injury to a
>> bird could cause issues that would lead to a lack of melanin (the
>> pigment that causes dark colors in feathers) in certain areas. If
>> I recall correctly, fully-grown feathers are lifeless (similar to
>> toenails and fingernails in humans) and it would therefore not
>> seem possible for an injury to affect pigment in a fully-formed
>> feather.Â It also (an assumption on my part) seems unlikely that
>> an injury would cause the lack of pigment in a specific area or
>> feather tract, as appeared to be the case in the bird in our
>> yard. It would seem more likely to be something atypical in the
>> genetic code of a bird that would cause the unusual pigmentation.
> Dennis P. and others out there - are there any indications of
> environmentally (injury) induced white plumage? Are there any
> studies indicating that 'once a leucistic bird, always a leucistic
> bird' - i.e. the abnormal plumage is repeated in subsequent
> moltings? Or is this one of the many areas about birds that are
> not completely understood yet?
> John Tubbs
> johntubbs at comcast.net
> Snoqualmie, WA
1724 NE 98 St.
Seattle, WA 98115
dennispaulson at comcast.net
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