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Re: Point of brooding is...



John Bois wrote:

>> We have NO evidence that these animals sheltered their young
>> after hatching (living megapodes do not, so the behaviour is not even
>> universal among living birds).
>
>Without arguing against your position--this behavior may be (probably is)
>derived. 

Agreed.

>Who do you mean here?  I would argue that a prime benefit of brooding is
>to keep egg temperature elevated, thus increasing the rate of embryonic
>development allowing for greater organogenesis without spending eons at
>the nest. So brooding-to-keep warm should primarily be associated
>with endotherms.  Aren't birds the only warm-blooded egg layers around (I
>know there is a snake which can shiver itself warm)?

This is not, as I understand, what Tom Hopp is talking about.  As I pointed
out, an incubating bird keeping its eggs (or hatchlings) warm generally is
interested in transferring heat to them from its own body, and does so via
a vascularized patch of bare skin on the belly, the brood patch.  Feathers
are actually counterproductive here as their insulating nature prevents
heat flow from the parent's body, rather than faclitating it which is what
this type of brooding requires.

My understanding is that Tom Hopp is proposing that the evolution of wing
feathers (remiges) was driven by the need to brood.  Clearly if this is the
case (and I am highly skeptical that it is) it could not have been for heat
transfer, as remiges cannot function in that way.  Many modern birds do use
the remiges, though, to shade the young or protect them from rain - and I
suppose it is possible that remiges used in this way could help retain heat
around the young as they would restrict air movement, though I know of no
research on this point.

--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
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