How Dolphins Sleep Without Drowning: Half a Brain at a Time

Bottlenose dolphin surfacing in open water — A bottlenose dolphin. Only half of the brain sleeps at a time, so breathing never stops. Photo: NASA — Public domain

Dolphins breathe on purpose, so a full night of unconsciousness would kill them. Instead they shut down one half of the brain at a time, keep one eye open, and some species barely stop moving for days.

Dolphins swimming together in a pod — Dolphins rest in pods, keeping one eye on each other while they sleep-swim. Photo: NASA — Public domain

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Photography credits: NASA (Public domain) via Wikimedia Commons