Marine biologists tracking cetaceans above the tree line seem to push out small bursts of gas to help manage buoyancy while at rest upright in the water.
Tagged animals included several large mammals to document how they sleep outside captivity in their usual habitat.
The work hints that the whales' large heads appear not to disrupt stability while at rest.
Several of the cows appear to rest upside down off the bottom of the ocean as a recovery method to conserve energy.
Posing like that could offer support to cows feeding calves between feedings, researchers say.
These shifts in buoyancy may expand461 research on animal rest, scientists add.