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

[Tim Williams <twilliams_alpha@hotmail.com>]

Patrick Norton  wrote:

> 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.

I'm not so sure that the link between New World vultures (Cathartidae) and 
storks (Ciconiidae) still has much support these days.  See, for example, 
the morphological analysis of Mayr and Clarke (2003), which has cathartids 
as falconiforms.

> 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.

This is partly true.  But if the carcass is much bigger than the scavanger 
then this also necessitates the scavenger inserting its head and neck deep 
into the carcass.  This is frequently the case with vultures when feeding on 
the carcasses of pachyderms and large ungulates - especially after all the 
best bits had been taken by those carnivores higher up in the pecking order.

> 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.

I think this is apples and oranges.  Some vultures cannot actually access a 
fresh carcass by themselves - their beaks and talons are incapable of 
ripping open the hide of large mammals.  So, this means they either have to 
access the innards via available orifices (mouth, anus), or wait for another 
carnivore to tear open the hide (like a lion or hyena).  In any case, 
getting inside a carcass is not always so easy for a vulture or marabou.   I 
would guess that it is much easier for a raven to get inside a dead coyote 
than a vulture to get inside a dead wildebeest or elephant.

> 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.

But many vulture species are actually highly specialized for scavenging.  
Sure, some vultures also kill their own prey (small prey), but vultures have 
a specialized strategy for feeding off carcasses, and their morphology 
reflects that.  I think there is good evidence that the naked head and neck 
is an adaptation to a particular type of scavenging, not just being a 
scavenger per se.

Cheers

Tim