Research teams studying whales near polar waters seem to push out puffs of air to help stay afloat while sleeping sticking straight up.
A research group fitted sensors on whales to record natural sleep behavior without disturbance.
The work hints that the whales' large heads appear not to disrupt stability during quiet moments.
A number of adult females have been seen floating upside down off the bottom of the ocean as a recovery method to conserve energy.
That posture could also help cows feeding calves in the gaps between meals, researchers say.
That documented habit may expand461 research on animal rest, scientists add.