Sperm whales in the Arctic Circle are seen releasing small bursts of gas in order to stay afloat while at rest in a vertical stance.
A research group fitted sensors on several large mammals to document how they sleep outside captivity in open water.
Evidence points to the whales' large heads do not disrupt stability during quiet moments.
A number of adult females have been spotted drifting inverted off the bottom of the ocean as a way to conserve energy.
Posing like that could also help cows feeding calves in the gaps between meals, members of the team point out.
That documented habit help broaden the limited record of how giants of the deep pause for hours at a time, the authors note, in plain language.