ZAP’S FACTS!
WHALES

Whales sleep with half their brain awake at a time.

One half rests while the other keeps swimming, breathing, and watching.

2 min read
Whales sleep with half their brain awake at a time.
THE FULL STORY

Whales have a problem most mammals don’t. They breathe air, but they live in water. If a whale slept like we do - completely shut down for hours at a time - it would simply drown. Holding your breath is a conscious act in a whale’s body.

Their solution is one of the strangest sleep patterns in the animal kingdom. Whales (and dolphins) sleep with only half their brain at a time. One brain hemisphere shuts down and rests; the other stays awake and keeps the body swimming, breathing at the surface, and watching for danger. After a while, the two halves swap.

You can sometimes see it in resting dolphins and whales: they swim slowly with one eye open and the other eye closed. The closed-eye side of the brain is the one asleep. The open eye is the one still on guard.

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