Sperm whales in the Arctic Circle appear to release puffs of air to help manage buoyancy while at rest in a vertical stance.
A research group fitted sensors on several large mammals as part of efforts to study natural sleep behavior without disturbance.
The work hints that the whales' large heads do not really cause tipping or wobble during quiet moments.
Several of the cows appear to rest with their bellies up in the water column to save strength.
Posing like that may assist cows feeding calves between feedings, scientists note.
These shifts in buoyancy add to the limited record of cetacean idle states, scientists add.