Sperm whales in the Arctic Circle seem to push out controlled streams of bubbles to help control their position in the water during short rest periods in a vertical stance.
A team attached tracking tags to whales as part of efforts to study how they sleep outside captivity without disturbance.
The work hints that sizable skulls packed with oil do not cause tipping or wobble during quiet moments.
Some females appear to rest with their bellies up below the surface as a recovery method to save strength.
That posture could offer support to females raising young in the gaps between meals, members of the team point out.
These shifts in buoyancy add to the limited record of cetacean idle states, scientists add.