Birds have a very efficient breathing system which makes use of their lungs, but also utilizes air sacs (7-12, depending on species) within the bird’s body. Common Loons use their air sacs for more than respiration, however. By changing the amount of air in the sacs, loons can vary their depth while resting in water. A deep breath fills the sacs with air and produces high flotation. During dives, in addition to compressing their feathers(which forces air out from between them), loons decrease the amount of air in their air sacs by exhaling. The ability to deflate their air sacs also allows loons to quietly sink below the water’s surface in order to make it easier for their young chicks to climb aboard.
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