Marine biologists tracking cetaceans above the tree line are seen releasing small bursts of gas to help manage buoyancy while sleeping in a vertical stance.
Tagged animals included whales to record how they sleep outside captivity without disturbance.
The work hints that sizable skulls packed with oil do not really throw off balance while at rest.
Some females have been spotted drifting upside down off the bottom of the ocean as a recovery method to conserve energy.
That posture could offer support to females raising young between feedings, scientists note.
These shifts in buoyancy may expand461 research on animal rest, the authors note, in plain language.