Do Whales Sleep?

Whales do sleep, but their sleep is quite different from what we typically understand as sleep in humans. Whales, like all cetaceans, have a unique way of sleeping that allows them to remain conscious enough to breathe. Unlike humans, who breathe automatically even while unconscious, whales must come to the surface of a body of water to breathe. This means they cannot afford to be completely unconscious, as they would risk drowning.

To manage, whales engage in a fascinating process known as unihemispheric slow-wave sleep. This means that one hemisphere of the whale’s brain remains active while the other rests. This allows whales to maintain enough awareness to surface for air and to keep an eye out for potential threats. Dolphins, which are also cetaceans, also keep half of their brain awake to regulate breathing while they sleep.

Large whales often sleep by floating horizontally just below the water’s surface. They periodically move their flukes, which are their uniquely shaped tails, to rise above the water for a breath. This surface-sleeping behavior allows them to rest while still being able to breathe and stay alert to their surroundings.