Marine biologists tracking cetaceans above the tree line appear to release puffs of air in order to manage buoyancy while at rest sticking straight up.
A team attached tracking tags to nearly four dozen animals to record resting patterns in the wild without disturbance.
Evidence points to sizable skulls packed with oil do not really cause tipping or wobble while suspended in place.
Some females have been seen floating inverted in the water column as a way to hold onto calories.
The position could offer support to nursing mothers while away from the group, scientists note.
That noted adjustment add to the limited record of cetacean idle states, researchers write.