Hi Phillip
I might have misread your posting but I don't think that anyone is
suggesting that the crest feathers on the bushlark (or any other
species) were somehow acting as little conductors or "heat sinks".
Feathers just don't work that way.
I don't think that anyone is saying that the crest feathers on the
bushlarks are modified to form a longer crest in any way either.
Rather, the suggestion is that by raising feathers, especially around
apteria - feather free patches - that some heat transfer takes place,
resulting in cooling (as long as the surrounding air is not hotter
than the bird's body temperature, which is around 40 to as much as 44
degrees, as I recall). This is known as "ptilorection".
There appears to be evidence that crest raising in Singing Bushlarks
takes place in hot weather in conjunction with "panting" and nobody
has yet stated that they have witnessed this species raising its
crest in cool weather. This may mean that they are raising their
crest feathers as a type of ptiloerection.
At least that is my take on the discussion.
Happy birding
Ricki
Belrose, Sydney
On 13/12/2006, at 12:21 PM, Philip Veerman wrote:
There is a curious thing about this discussion: Birds can raise or
lower their feathers and do so to assist heat loss or transfer. I
don't see how the issue of crests is relevant or helps (though it
is lateral thinking and innovative). I agree with others that the
issue is raising the feathers, rather than the feathers being
modified (longer) into crests. Crests simply exist as the feathers
at the top of the head are longer than usual, or longer than
needed, to provide the ordinary layering required to insulate the
bird's body (or head in this case). Crests exist for display or
communication function (and are often coloured or shaped for the
purpose). It is hard to conceive how, having longer feathers than
usual, could assist in heat loss. If anything, shorter or less
dense feathers would help.
Philip
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