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BIRD
COLUMN FOR August 17, 2003 By Benjamin P. Burtt Now and
then albino birds are reported. These
are birds that have white feathers in place of the usual colors of their
normal plumage. These
white feathers may cover the whole bird, but usually they only replace part
of the feathers. Such a bird is said
to have partial albinism. Such a
condition is quite rare,. Two
scientists who studied birds by capturing and banding them, handled some
30,000 birds over a period of 10 years. Only 17 of those birds had albinism
to any degree. This is less than half
of 1%. For the
average person who knows the common birds around his home, a partially albino
bird is unlike any bird ever seen before.
We tend to identify birds by the color of the different parts of the
body. Quite naturally, the observer assumes that the bird is some new species
that wandered by. If a bird
is carefully described to me, I can usually say that there is no bird around
here that normally has that plumage and that it is probably some common bird
with abnormal plumage colors. Once you
realize that it is probably a common bird then you can consider the shape and
size and ask what species it might it be? You can also ask, what birds are
mingling with it? Last year
I was contacted by Don and Marge Svedman of Manlius who had a partially
albino female cardinal in their yard. When it
first appeared in February of 2002, the male was feeding the albino as they
do in courtship at that time of the year. It is still around their property
now and a photograph taken by Svedman appears with todays column.
This beautiful bird is a partially albino female
cardinal that has been living in Manlius for two years. (Courtesy of Don
Svedman ) I am very
pleased to be able to share this image with you for very few people ever have
a chance to see such a bird. You will
notice that there is red in all the usual places where red appears on a
female cardinal. It is on the tip of
the crest, on the wings, tail and beak.
In other words the red pigment was not altered. What is missing is the
normal brown color of the female and those feathers have no pigment and
appear white. This is
the result of a genetic change and a chemical is missing that is needed to
make the colored pigment. As far as we know, this bird had this plumage when
it first fledged. In some
cases, a patch of white feathers will appear on a bird that up to then has
had its usual colors. This can be caused by an injury, some dietary
deficiency or some hormonal change at the time the feathers are developing. A British
bird bander trapped the same blackbird every year and in the fifth year, the
bird had patches of white all over its body that were not there
previously. Another became
progressively white over a three year period. Totally albino
birds are those in which all the feathers are white. The eyes, leg and bill
will have a pinkish tinge because the color of the blood shows through when
there is no pigment in the tissue. Such birds
are extremely rare in the wild. They are conspicuous and more likely to be
caught by predators. They often have weak eyesight and the lack of pigment
makes the feathers brittle. Such feathers often wear out before the next molt
and the bird will not be able to fly well. One other
problem when there are many white feathers, is that the bird is not
recognized by prospective mates or others of its own kind. One
scientist reported a pure albino female red-winged blackbird in an immense
September flock that was chased repeatedly by its companions. It always returned to the flock to be
chased again. The
Manlius female cardinal shown in the illustration apparently is recognized as
a cardinal by the male. I suspect that it is the red color in all the right
places that identifies her and whether the rest of the bird is the usual
brown or whether it is white apparently does not matter. With a few
species, it is normal for the plumage to become white and then change back
each year. The ptarmigan is a brown, grouse in the summer that gradually
becomes white each fall. This is not albinism. It lives in the open country
far north beyond the limit of the trees. It is also found at high altitude in
the Rocky Mountains. The white
plumage makes the bird hard to see in
the winter snow. In the summer it becomes brown again. That color then
matches the bare and rocky terrain where it breeds. One time
on a family summer trip to the Rockies years ago, we all watched a ptarmigan
slowly walking across a rocky slope only 20 feet away. When it stopped
moving, it blended so well with the background that it just disappeared! |
