Marine biologists tracking cetaceans above the tree line are seen releasing puffs of air in order to manage buoyancy while sleeping in a vertical stance.
Tagged animals included nearly four dozen animals to document natural sleep behavior without disturbance.
The work hints that the oversized melon-shaped organs appear not to throw off balance during quiet moments.
A number of adult females have been seen floating upside down below the surface as a recovery method to save strength.
That posture could also help nursing mothers between feedings, researchers say.
That noted adjustment may expand461 research on animal rest, researchers write.