[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Arms into wings



><<extant birds use flight feathers (as defined by their aerodynamic
>properties) for brooding, not brooding feathers for flight. I'm quite sure
>that many, many more birds use their wings for flying than for brooding. So it
>is much more straightforward to regard brooding as a flight exaptation rather
>than flight as a brooding exaptation.>>

In fact most modern birds do NOT use their feathers for most brooding,
wing-feathers or otherwise.  Since the major purpose of brooding (certainly
of incubation) is to transfer heat from the parent, insulating structures
such as feathers are actually counterproductive.  Birds generally develop a
bare area, the brood patch, for this purpose.

Wings can be used for shading or to protect young from rain, but I hardly
think this could have driven their evolution.  The best evidence for this,
to me, is the reduction of wing feathers in flightless birds.  If brooding
were a major factor in selecting for well-developed wing-feathers  I would
expect these to be retained in flightless birds, which brood their young in
the same manner as flying birds.  Why, for example, would ostriches have
large remiges, but not emus or rheas?

On the other hand, flightless birds with large remiges (eg the Kagu) DO use
the feathers for display, so we know that this is a valid non-flight
purpose for them.  By contrast, the chief evidence for brooding in
dinosaurs comes from a fossil that - let's remember this point - shows no
trace of feather imprints.  We simply do not know if Oviraptor had large
remiges, reduced remiges or no remiges at all, whatever we may know about
Caudipteryx.
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@home.com