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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