Feathers help raptors stay warm in the winter and cool in the summer.
For a bird to keep its body temperature just right, it has to get assistance from the thousands of feathers covering almost its entire body.
Each feather on a bird is controlled by a muscle, which does this very well. In the winter, a bird will raise its feathers and interlock them together. This creates a pocket of air, which heats up and insulates them from the cold. No wonder down jackets and blankets are so comfortable!
In the summer they will raise the feathers but keep them open, not interlocked, and this allows air to flow through them, cooling off the bird. A great ability for birds throughout the world, from the Antarctic to the African desert.
So when you see a raptor sitting on a power pole in the winter and it looks huge, it is just keeping itself warm in its down jacket.
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