Researchers observing marine mammals in far northern seas seem to push out controlled streams of bubbles to help stay afloat during short rest periods sticking straight up.
A team attached tracking tags to whales to record resting patterns in the wild in their usual habitat.
The work hints that the whales' large heads appear not to throw off balance while at rest.
Several of the cows have been seen floating upside down below the surface to conserve energy.
Posing like that could offer support to cows feeding calves between feedings, members of the team point out.
These shifts in buoyancy add to the limited record of cetacean idle states, the authors note, in plain language.