Marine biologists tracking cetaceans above the tree line seem to push out puffs of air to help manage buoyancy while at rest upright in the water.
A team attached tracking tags to whales to document how they sleep outside captivity in open water.
New findings suggest the whales' large heads do not cause tipping or wobble during quiet moments.
Several of the cows appear to rest inverted below the surface as a way to save strength.
The position could also help cows feeding calves in the gaps between meals, researchers say.
That noted adjustment add to the limited record of cetacean idle states, scientists add.