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Sarah Linney wrote:

In a message dated 10/12/02 7:47:01 PM, [log in to unmask] writes:

>> The cormorants may have been drying their wings, but the anhingas were
>>thermoregulating.

>I have not heard that before. Is it not true that both cormorant AND
>anhingas have to dry their wings after feeding and bathing due to the
>fact that their feathers are not water-repellent as both genuses lack the
>oil glands other birds use while preening to help waterproof their
>feathers?

First, the plural of "genus" is "genera."  Second, Bob Kelley's original
assertion that "the wings have a network of veins under them..." is false.
Except for a very small portion near the "armpit" and the rather stubby
and slender forearm bones, themselves, a bird's wing is composed of
feathers, which, once fully formed, have no connection whatsoever to the
circultory system.  They could no more be involved in the direct transfer
of heat to the blood than could a mammal's hair, no matter what color they
are.  The purpose of feathers (other than flight) is actually the opposite
of heat conduction, namely insulation.  The only way a bird could directly
absorb heat from the sun would be through bare parts, which would include
some small bare areas under the wing, near the base.  Now, there's a
possibility for what the anhingas and cormorants are doing.  Next time you
see them, study their orientation to the sun.  Do they seem to be aiming
their bare armpits toward or away from the sun?  If the former, they could
be trying to warm up.  If the latter, they could be trying to cool down,
taking advantage of some convection across the shaded bare portions.
Either of these is a voluntary form of thermoregulation.

Of course, it's still possible they're drying their wings. The feather
structure of both anhingas and cormorants is different from that of other
diving birds such as ducks and grebes; namely, their feathers (that
includes the wing feathers) are wettable (I'm pretty sure they do have a
uropygial or preen gland, but preen oil is not really what makes a duck's
feathers waterproof).  Hence the fact that we've never heard the saying
"like water off an Anhinga's back."

Brad
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Brad Bergstrom, Ph.D., Professor           TEL  229-333-5770 /-5759
Department of Biology                      FAX  229-245-6585
Valdosta State University                  e-mail: [log in to unmask]
Valdosta, GA 31698-0015                    Home: 229-333-0743
           Home Page-- http://www.valdosta.edu/~bergstrm/
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