held together by hooks are so close to each other that not even smoke can
pass through them. If these hooks are somehow unlocked, it is enough for
the bird to shake itself or to put its feathers in order with its beak, to make
the feathers return to their previous state.
In order to survive, birds must always keep their feathers clean, neat and
ready for use. For the care of their feathers, they use oil sacs at the bottom
of their tails. They take some oil with their beak, and then clean and polish
their feathers. In swimming birds, this oil prevents water from reaching
their skin when they are in the water or in the rain.
In addition, birds can prevent loss of body heat by ruffling their feathers in
cold weather. In hot weather, on the other hand, they keep their body cool
by smoothing their feathers.
Each group of feathers in a particular part of the body has particular func-
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