Question

Birds have been observed puffing

up their feathers under certain
conditions. By trapping air
between feathers, this behavior
helps the bird do what?

Answer 1

the air pockets help the bird keep its body heat in its feathers keeping it warm.

Answer 2

It's an important part of the bird's ability to maintain its body temperature.
Air is a poor conductor of heat, so the air trapped among the feathers
prevents the loss of heat in cold atmosphere, and prevents overheating
in hot atmosphere. Much like our wearing several layers of clothing.