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In a message dated 10/16/02 4:23:37 PM, [log in to unmask] writes:

>Ehrlich, et al. (The Birder's Handbook)...
>Cormorants - only for drying, not thermoregulation
>Anhingas -  primarily thermoregulation
>Vultures - both

For those that don't have the book handy or at all:
Page 25 & 27 in the Birder's Handbook: "Spread-Wing Postures"

"The structure of cormorant and Anhinga feathers decreases buoyancy and thus
facilitates underwater pursuit of fishes. Hence their plumage is not
water-repellent, but 'wettable.' .... the degree of waterproofing of feathers
is primarily due to their microscopic structure, not to their being oiled. In
addition to helping wing feathers to dry, other suggested functions for these
postures include regulating body temperature..., realigning of feathers,
forcing parasites into motion to ease their removal, and helping the perched
bird to balance."

"Spread-wing postures may serve different purposes in different species.
Anhingas, for example, have unusually low metabolic rates and unusually high
rates of heat loss from their bodies. Whether wet or dry, they exhibit
spread-wing postures mostly under conditions of bright sunlight and cool
ambient temperatures, and characteristically orient themselves with their
backs to the sun. thus, it appears that Anhingas adopt [this] posture
primarily...to absorb solar energy to supplement their low metabolic heat
production and to offset partly their inordinately high rate of heat loss due
to convection and (when wet) evaporation from their plumage."

Cormorants have a different plumage setup, the book goes on to say, in that
"only the outer portion of the feathers is wettable, so an insulating layer
of air [remains] next to the skin when [these birds] swim underwater." Also
why cormorants can be seen in cooler climes farther north than Anhingas.

Turkey Vultures, and I'd wager to say Black Vultures, "maintain their body
temperature at a lower level at night than in the daytime. Morning
wing-spreading should provide a means of absorbing solar energy and passively
raising their temperature to the daytime level." I'm sure folks have seen
them in the morning, perched on telephone poles or whatever and facing the
rising sun with their wings spread, at least partially.

Sarah Linney
Cocoa, FL
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