Biology Reference
In-Depth Information
www.tc.umn.edu/~devo0028/contact.htm.
) But as long as it's acting normally and staying
well out of reach, it's doing fine and will be better off if left alone.
Q I saw a chickadee at my feeder with a bill so long and curved that it was having
trouble eating. What was wrong with it?
A
A large number of chickadees and other birds in Alaska have been developing unusual
bills, often overgrown or crossed, in the past two decades. The outer sheath of the bill is
made of a type of keratin, much like your fingernails, and in these birds this protective
sheath is growing abnormally.
Colleen Handel, a biologist with the USGS Alaska Science Center, has documented
bill deformities among 30 species in Alaska, from ravens and magpies to chickadees and
nuthatches, and compiled records of at least 2,100 individual deformed chickadees in
Alaska between 1991 and 2009 and 420 individuals of other species since 1986. She has
been actively soliciting reports of deformed birds from outside Alaska but has received
only 30 reports of deformed chickadees and 110 reports of other species from the rest of
North America. Alaska has the largest concentration of bill deformities ever documented
in the world.
Blood tests on birds with deformed bills found damaged DNA, consistent with envir-
onmental contamination or disease, though there have been no other obvious indications
of disease. The reports cluster in late winter. Birds manufacture their own vitamin D, as
we do, from exposure to sunlight, and vitamin D helps us absorb calcium. So chickadees
visiting feeders, eating a higher proportion of seeds than they do on a natural winter diet
of insect eggs and pupae, may be vulnerable to calcium deficiencies during the time of
yearwhensunlightislowest.Thisdoesn'texplainthenumbersofother,unrelatedspecies
that don't visit feeders but still exhibit deformed bills.
