Re: Archaeopteryx with bird book, was Re: Archaeopteryx flight

[Patrick Norton <ptnorton@suscom-maine.net>]

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.

PTN