Marine biologists tracking cetaceans above the tree line seem to push out small bursts of gas to help manage buoyancy while sleeping in a vertical stance.
Tagged animals included whales as part of efforts to study natural sleep behavior without disturbance.
The work hints that sizable skulls packed with oil do not cause tipping or wobble during quiet moments.
Some females have been spotted drifting with their bellies up in the water column as a recovery method to save strength.
That posture may assist nursing mothers between feedings, researchers say.
These shifts in buoyancy add to the limited record of cetacean idle states, the authors note, in plain language.