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Brooding over dinos



On a previously much abused thread, Ronald Orenstein wrote:
<If feathers (or some feathers) were only of use during brooding, and if this
activity were restricted to certain seasons, I would have expected that they
would be lost through moult during the rest of the year (very much as many
modern birds lose specialized display plumes outside the breeding season).  As
feathers, once damaged, cannot be repaired, moult ensures a fresh set at the
start of the new season.>
    We agree, so far.
<However, I would add that in modern birds wing-feathers are only rarely
used in brooding, and then only in extreme situations in birds that nest in
open, hot areas . . . . . So unusual is wing-brooding in birds that I find it
hard to imagine this having been a major factor in their evolution; . . . . I
would a priori favour thermoregulation . . . . or display, . . . . or both.>
    I can't allow the first sentence above to go unchallenged.  As Mark Orsen
and I have learned in putting together our Dinofest 98 lecture, the literature
abounds with photos and life histories of birds that use their wing feathers
in brooding.  Admittedly you have to dig, because, as near as I can tell,
brooding behavior is somewhat taken for granted, and often not described as
elaborately as song, foraging, fighting and courtship. Often it is mentioned
just in passing, but it is there nonetheless, and widespread.  In our talk,
(and in the up-coming manuscript for the symposium volume) we showed photos of
wing feather coverage of young by: a duck, an eagle, a falcon, a gull, a
flamingo, an ostrich, and a doggoned old chicken, which just might be the best
example of all.  This pretty much blankets the phylogeny of birds, so please
don't try to convince me it's rare.  It's nearly ubiquitous, and therefor
probably ancient.
   Regarding thermoregulation: yeah, I'll go with that.  How about
thermoregulation of hatchlings?  Under the wing?
    Regarding display: personally, this is my most un-favorite explanation for
evolution of anything.  It seems to me, that with a few exceptions, what birds
are displaying, when they display, is their fitness to raise a brood or to
kick butt (same as raise a brood).  Display only makes sense to me if it shows
off some other quality that is the REAL reason for displaying in the first
place (bright plumage = health; unbroken wing/tail feathers = ability to
forage, ability to shelter young, ability to fight).  Display for its own sake
seems very dubious to me as an ORIGIN to anything.
    Tom Hopp