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size & insulation (naked chicken)

Greetings Schmidt,

Clearly no lliving birds has evolved featherlessness, regardless of size.
The largest birds, such as ostrich, that inhabit warm climes have large
bare areas on the flanks under the wing. They will spread their wings
when heat stressed and use the area for cooling. Many small birds, where
ever they live will do the same thing. However, most of the cooling in
birds comes from evaporative water loss. You can observed the gular
fluttering in many birds on hot days. The water economy of many birds
allows them to occupy just about every place on earth.

There are  many examples of mammals, on the other hand, with little or
very sparse pelage. Humans are one, but also horses, cows, marine mammals
(but not marine birds), etc. We assume that primitively they have heavier
coats. Further, there are mammals, now hairless, that had very hairy
ancestors. Think of elephants and Mammoths (and other Pleistocene
species). Living mammals that are small and hairless, range to naked mole
rats (admittedly, they live in very controlled environments

I think it best not to think of a 'body size (where) feathers become
unneeded to retain body heat', as you suggest. Feathers can also be
protective, where mammals evolve a very thick hide. This may be another
weight conserving factor in birds. Surface color can also influence
thermoregulation. Whie surfaces are reflective (gull in the open) and
black strongly absorbs heat. Ironically, birds like ravins and crows
(whihc are essentially all black, inhabit some of the warmest areas, and
are subject to intense insolation.


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