Air sacs turn a resting walrus into a float
A walrus has expandable air sacs in its throat. When it fills them with air, they add buoyancy around the neck and chest, helping the animal float with its head above the surface. That matters during rest: keeping the nostrils clear of the water lets a walrus breathe without swimming or paddling continuously.
The sacs work like a built-in flotation aid, but they are not a substitute for active swimming in every situation. A floating walrus can still move when it needs to; the extra lift simply makes staying at the surface less effortful while it rests.
Rest without losing access to air
For an animal that spends much of its life in cold water, resting at the surface creates a simple problem: it must breathe. The air sacs help solve it by holding the head in a useful position while the body floats. The key is not keeping the whole animal motionless, but reducing the work needed to keep its nose above water.
