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Re: Archaeopteryx with bird book, was Re: Archaeopteryx flight
Tim Williams wrote:
I can answer that question in more than one way. Firstly, there are two
separate families of vultures (Old World and New World) that evolved
independently. There is also the marabou stork, a scavenging bird that
also has a bald head. So, that's three separate examples of baldness
associated with scavenging in large birds.<
Although the old and new world vultures are veiwed as not sharing recent
common ancestors, the new world vultures are viewed as arising from the
stork lineage (see Sibley and Alquist, 1990). So this narrows the list to
two taxa of bald headed scavengeres, at most.
Secondly, the life-style of scavengers like vultures is very specialized.
They will plunge their neck and heads deep into the carcass, and some
species specialize on feeding on the viscera (accessed via the anus). The
naked head and neck of vultures and the marabou is an adaptation to feeding
on (or rather, *within*) large mammal carcasses, from which they will gulp
down large chunks of flesh or viscera.<
The feeding behavior of vultures is in large part a function of their size.
If you are a big avian scavenger, you can't physically enter into the body
cavity of most dead animals, so, by necessity, you have to insert your head.
But small scavengers (like corvids---and Archie, by the way) are/were able
to hop inside a rib cage of a relatively small animal without much problem.
This is well documented, and I have personally flushed several scavenging
ravens from deep inside the chest cavity of a coyote.
The thing that bugs me about the often-stated idea that bald heads in birds
are somehow a preferred adaptation for a scavenging lifestyle is that there
isn't a shred of evidence to support it. One, maybe two, taxa of large avian
scavengers are bald, but the large majority of avians who scavenge for a
living are not.