Herb Curl wrote:

>Cormorants seem like a rather independent lot, off the colony, with some air
>drying, and some not, with little or no interaction, so signalling appears
>unlikely to me.

I'd argue with you about the "little or no interaction," as I've watched
d-c cormorants coming into roosts quite a few times, and I've frequently
seen them land next to another bird, with much pecking and sometimes wing
waving, with one (rarely both) birds displaced. These are at roosts such
as ropes or tree branches, where the cormorants spread out (eventually,
very evenly) along the linear extent of the available space. Two wing
lengths apart is a pretty good description of the interbird distance. I've
seen one land next to or even on another bird on top of a piling and
displace it very effectively, and I could envision the bird on the piling
being more visible with its wings out. I think there's much competition
for roost sites, in fact, but by no means am I vigorously espousing the
"territorial-signal" hypothesis; I think it bears thinking about, that's
all.

Herb again:

>Do Cormorants have much of an oil gland? You (or at least
>I) don't see them preening like lots of other aquatic birds. Moreover, they
>don't seem to be as bouyant; most of their bodies are underwater when
>they're surfaced. Anhingas also hang their wings out to dry and don't
>appear very buoyant either.

They do seem to be less buoyant than other birds, and I have hypothesized
that the ability to wet their plumage allows them to stay under water more
effectively. Their hunting method is to move slowly along the bottom and
search for fish, so being highly buoyant means they'd have to expend a lot
of energy to stay down and to stay at one level. "Wetter" feathers might
facilitate this, and then they'd have to be dried. However, by no means do
cormorants get thoroughly wetted, as they'd die in cold water. Anhingas,
which swim slowly under water and spear fish they encounter, would benefit
from a similar adaptation. It may be that some cormorants such as
Brandt's, which hunt a lot more near the surface, aren't similarly adapted.
Pelagics, on the other hand, seem to eat mostly bottom fish, but they
might hunt differently than double-crests.

I don't think there's any real confirmation of the wing-drying hypothesis
(nor rejection, of course). I don't disagree strongly with it, but I
consider it as among those "explanations" that are long-established without
a whole lot of evidence. These pat explanations often discourage further
thought or research, as you know. And this is one that I think could be
tested rathe easily, a fine student project or WOS project.

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