A simple question like “where do orcas sleep?” may seem innocuous, but it’s one that leads to a lot of questions about whale behavior as a whole. Marine mammals like whales and dolphins live their entire lives in the ocean, and they must constantly come to the surface for air, so how do they manage to get some rest?
Orcas are able to do this in part by logging, or resting for short periods of time. The rest is not deep sleep, as they need to remain conscious and alert for threats, but it allows them to reduce fatigue and improve their performance. They also take naps during the day to make sure they’re getting enough sleep.
Researchers have found that orcas spend seven percent of their time sleeping in the water. They have found that captive killer whale mothers and newborn calves spend much of their time logging, which is sleeping vertically on the surface of the water in a position where their blowhole (the flap of skin they open and close to breathe) is closed.
They do this in order to prevent themselves from drowning or releasing too much carbon dioxide, which they are unable to do when surfacing for air. This is because they must consciously rise to the surface to breathe, which is why it’s necessary to keep their blowhole closed during these periods of rest.
Scientists have observed that humpback whales rest motionless on the water’s surface in similar ways for increments of 30 minutes, but they cannot sleep this way for very long because they need to be aware of their surroundings and on the lookout for sharks. Similarly, newborn killer whale calves and dolphins do not sleep at all for the first month of their life, even though they spend hours floating motionless and closing their eyes like other adult orcas.