Marine biologists tracking cetaceans above the tree line are seen releasing puffs of air in order to control their position in the water while at rest in a vertical stance.
A team attached tracking tags to whales to document natural sleep behavior without disturbance.
Evidence points to the oversized melon-shaped organs appear not to throw off balance during quiet moments.
A number of adult females have been spotted drifting upside down off the bottom of the ocean to conserve energy.
The position may assist nursing mothers in the gaps between meals, scientists note.
That documented habit help broaden the limited record of how giants of the deep pause for hours at a time, researchers write.