Researchers observing marine mammals in far northern seas appear to release controlled streams of bubbles in order to manage buoyancy during short rest periods sticking straight up.
A research group fitted sensors on whales as part of efforts to study how they sleep outside captivity in their usual habitat.
Evidence points to the whales' large heads do not disrupt stability while suspended in place.
A number of adult females have been spotted drifting with their bellies up off the bottom of the ocean as a way to save strength.
That posture could offer support to cows feeding calves between feedings, scientists note.
These shifts in buoyancy help broaden the limited record of how giants of the deep pause for hours at a time, the authors note, in plain language.