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Bird wings do have arteries and veins.   As Brad alluded, these vessels are
not generally set up for serious heat transfer (e.g., rete mirabile) in
birds (anhingas in particular?).   A spread wing should absorb heat better
across its total surface better than a folded wing, and this might at least
slightly increase conductive heat transfer to wing vessels, even without a
rete or other specialization.  But a spread wing would also lose heat via
convection more rapidly than folded wing, and by evaporative heat loss if
the wing is wet.

A spread, wet wing will undoubtedly dry faster than a folded wing (unless
it's raining)... sometimes the simple, obvious explanation is the best.
Even IF the spread-wing behavior does aid in thermoregulation, it would be a
great stretch (ahem) to claim that this is the MAIN reason for the existence
of the behavior.

If we step back and look at a slightly bigger picture, both cormorants and
anhingas have this stereotyped behavior and they both have peculiarly
"wettable" feathers.  Wing spreading helps dry wet wings, whether or not one
wants to regard this as the main reason for the behavior or not.
Interested physiologists have apparently discounted thermoregulation via
wing-spreading in cormorants.  Anhingas and cormorants are thought to be
sister groups -- that is, they share a unique common ancestor not shared
with other birds.  The simplest explanation of the observed (reported)
pattern is that wing-spreading dries the wettable wings of both cormorants
and anhingas, and that it MAY have some additional thermoregulatory benefit
in anhingas.  If either benefit is  "primary" in anhingas, from an
evolutionary perspective it would have to be wing-drying .

David Wright
Miami Shores

on 10/15/02 7:38 PM, Robert Kelley at [log in to unmask] wrote:

> Your remark that Anhingas do not have veins in their wings may be true.
> It was March or April of 1975 when Tom Lodge and I were given the lecture
> By Oscar T. Owre, but there is no question that he asserted that the
> PRIMARY reason for wing spreading in Anhingas was heat gain. His argument
> was quite persuasive(as always carefully thought out and presented). It is
> a shame that he did not publish it.
> Bob Kelley
> University of Miami
> Coral Gables, FL
> [log in to unmask]
>
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