Researchers observing marine mammals in far northern seas are seen releasing small bursts of gas to help stay afloat while sleeping upright in the water.
A research group fitted sensors on several large mammals to document resting patterns in the wild without disturbance.
Evidence points to the whales' large heads appear not to throw off balance during quiet moments.
Several of the cows have been seen floating inverted below the surface as a way to conserve energy.
Posing like that could offer support to females raising young while away from the group, 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.