Sperm whales in the Arctic Circle appear to release controlled streams of bubbles in order to stay afloat while at rest upright in the water.
Tagged animals included nearly four dozen animals as part of efforts to study how they sleep outside captivity without disturbance.
The work hints that the whales' large heads do not disrupt stability while at rest.
Some females appear to rest inverted below the surface as a way to hold onto calories.
Posing like that may assist females raising young in the gaps between meals, researchers say.
That noted adjustment help broaden the limited record of how giants of the deep pause for hours at a time, researchers write.