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Re: Archaeopteryx with bird book, was Re: Archaeopteryx flight
At 09:15 PM 10/22/2005, Jaime A. Headden wrote:
Patrick Norton (email@example.com) 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.>
The origin and relationships of the cathartid vultures are still not
quite settled, though they certainly arose independently from the old
world vultures (both groups are known as fossils from both
hemispheres, by the way).
Perhaps still three. Most ciconiiforms are feather-heads, rather than bald.
Storks, among herons and ibises, tend towards bald faces, but a complete bald
head is known in a few species, as well as the bald ibis (*Geronticus*), and
among storks specifically we have a clade of leptoptiline ciconiid storks
including the jabiru (the latter -- *Jabiru* -- a close ally of the marabou,
*Leptoptilos*, and they have at times been synonymized), with *Ciconia* and
*Anastomus* having a fully-feathered head and *Mycteria* having a half-bald
face, less bald than the bald ibis.
It is, of course, probably unlikely that herons, ibises and storks
are each other's closest relatives anyway - and besides, except for
the marabou and the adjutants none of these birds, including the
jabiru and bald-headed ibises, are scavengers.
This, as with other ciconiiforms, as well as the colors, may indicate a display
function for the brightly colored, patterned, and wattled faces of marabou,
jabiru, other storks and vultures.
I think that this is likely in some species (turkeys, for example!),
particularly those in which the juveniles have feathered heads. Note
that this is also the case for some non-scavenging passerines (eg the
Wattled Starling Creatophora cinerea of Africa, which loses head
feathering and develops fleshy wattles in the breeding
season). Unfeathered heads are known in many birds that are not
scavengers, including galliforms (argus pheasant. turkey, guineafowl
etc), many ratites, two species of parrot, a number of cotingas,
friarbirds etc. For some of these the loss of head feathering has
been associated with a diet of large, fleshy fruits, for the same
reason that vultures that plunge their heads into messy carcasses are
supposed to have lost their head feathering.
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