How do dolphins sleep without drowning?
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Dolphins aren't like fish, which can breathe underwater.
They're mammals. That means they must get to the surface to breathe air.
They can only hold their breath under water for about seven minutes. That includes everyone's favorite, the bottlenosed dolphin.
So how do these watery animals sleep? They simply shut one eye at a time.
While sleeping, dolphins let one half of their brains nod off. The other half keeps an eye out for trouble. For instance, if the left side of the brain is sleeping, the right eye stays open.
So they always know when it's time to surface and breathe. And when they quickly need to get out of possible trouble.
Sleeping dolphins switch from one side of their brain to the other about every two hours. They do it until they get a full eight hours of sleep a day.