Dolphins sleep with half their brain awake!

½ a brain at a time

Dolphins can't just switch off and snooze like we do. Instead, they can rest one half of their brain at a time while the other half stays more alert.

This unusual trick helps them keep breathing and stay aware of what's happening around them.

Graffiti-style painting of a pink and purple dolphin gliding through bright blue painted water, from the book Sleep, Nap, Snooze.

Now You Know!

A sleeping dolphin may keep one eye open while the other one gets a break!

The open eye is connected to the side of the brain that's staying more alert.

How does a dolphin sleep?

How long?
In several periods throughout the day and night
When?
Day and night
How?
One half of the brain at a time

From Sleep, Nap, Snooze

Semi-Sleeping

The dolphin is one of the strangest sleepers featured in Sleep, Nap, Snooze: The Bed Habits of Animals.

Explore the Book

Keep snoozing...

Discover All Animal Sleep Facts

For parents & teachers

Is this really true? Sources & further reading

Yes. Dolphins can use a form of sleep called unihemispheric slow-wave sleep. During this type of sleep, one cerebral hemisphere rests while the other remains comparatively alert. Eye state can also be asymmetric, which is where the familiar idea of a dolphin sleeping with one eye open comes from.

Animal:: Dolphin
Scientific name:: Tursiops truncatus

Source: Lyamin et al., research on unihemispheric sleep in bottlenose dolphins.

Read the research