Jim Rosso wrote about wing spreading in cormorants. Thanks much for doing
the research, Jim, and I hope you find the J. Exp. Biol. article.

>I read a short article in the Wilson Bulletin (100:140-144) Wing spreading in
>Chilean Blue-eyed Shags. It had this conclusion "The hypothesis that
>wing-spreading in the Chilean Blue-eyed Shag serves primarily to dry feathers
>is supported by our observations that wing-spreading was often associated
>with preening, most wing-spreading birds had wet plumage, and shags did not
>return to the water immediately after wing-spreading."

I think this conclusion is surely justified, although I've been surprised
to see Double-crested with their wings spread several times during light
rains. It may be that even during a light rain the spreading still
contributes to drying. But darn it, why don't Brandt's and Pelagic do it?
They must really be different in some way ecologically and/or anatomically.

>Another short article published in Ibis (120:540-542) has a different
>conclusion. A Possible Function of the Wing-drying posture in the Reed
>Cormorant. "I suggest that the conspicuous open-winged posture in the Reed
>Cormorant and other species may have as its primary function the
>advertisement to other cormorants that here is a profitable fishing area, and
>that to join that particular roosting assemblage will be mutually
>advantageous."

It may be that there is more than one function to wing spreading in
cormorants, but I question this one, based on the fact that many cormorants
feed at long distances from where they roost, and they spread their wings
while at these roosts. Seems to much time delay to function as "here is a
profitable fishing area." The Pygmy Cormorant of India spreads its wings,
and the ones I've seen were roosting solitarily, as do Anhingas (and it
certainly can't explain the phenomenon in vultures & storks).

Want to stop in at one of our local museums and examine cormorant feathers,
Jim? No, too late, you're going to work next week. Work, argghh!

Dennis Paulson, Director phone: (206) 756-3798
Slater Museum of Natural History fax: (206) 756-3352
University of Puget Sound e-mail: dpaulson at ups.edu
Tacoma, WA 98416