Do whales sleep? © iStock

Do whales sleep?

Do whales dream of aquatic sheep?

Asked by: Steven Collins, by email 

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Whales, dolphins and porpoises need to retain conscious brain activity in order to take a breath because they must be able to tell that their blowhole is at the surface. To get around this, they only sleep with one hemisphere of the brain at a time. This resting state is more like a very light nap and the whale can still swim at the same time.


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