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Sleeping Dolphins

November 8, 2007

A listener asks: Why don’t dolphins drown while they sleep?


Surviving an underwater snooze. I’m Bob Hirshon and this is Science Update.

Listener Parsa Heidarpoor of Iran wrote to ask why dolphins don’t drown while they sleep. We turned to comparative anatomist Joy Reidenberg of Mt. Sinai School of Medicine.

JOY REIDENBERG (Mt. Sinai School of Medicine):
Dolphins don’t drown while they’re sleeping because they’re never really fully asleep.

She explains that dolphins have been observed sleeping with one eye open and one eye closed, suggesting that part of the brain remains conscious during sleep.

The animals are probably sleeping with half of the brain at a time. The other half is therefore maintaining their ability to breathe.

Unlike humans who breathe automatically, dolphins have to make a conscious effort to breathe. With half their brain still active, they can rise to the surface periodically to take in air. If you have a science question, call us at 1-800-why-isit. If we use your question, you’ll win a Science Update Mug. I’m Bob Hirshon, for AAAS, the science society.