How do whales sleep if they need air?

DW (English)

Whales and other cetaceans are mammals that have adapted to life in the water, but they still must surface to breathe. That makes sleeping a challenge. This week's viewer question comes from Richard M. in Tanzania.

Transcript

00:00Today's viewer question comes from Richard M. in Tanzania.

00:09Do whales sleep?

00:14Whales and dolphins are mammals that have adapted perfectly to life in the water.

00:20Unlike fish, which have gills, whales and dolphins breathe with lungs like we do,

00:26so they have to surface regularly to tank up on air.

00:30When the animals breach like this, every breath has to be coordinated with their movements.

00:36For this and other reasons, whales and other cetaceans have developed sophisticated sleep techniques.

00:46Many marine mammal species, including dolphins, only switch off half their brains when they sleep.

00:53The other hemisphere remains awake, reminding them to come up for air at regular intervals.

01:00They also keep only one eye open.

01:03Usually it's the one that's opposite the awake half of the brain.

01:08Researchers have discovered that the animals have a resting phase thanks to this half-sleep,

01:14even when they remain active.

01:17Not all cetaceans sleep in the same ways.

01:20There are major differences in terms of duration and position.

01:25Pods of pilot whales, for example, migrate through the water at a steady speed.

01:31They sleep horizontally and move constantly, directly on the surface.

01:38That allows them to breathe in a regular fashion.

01:43For all whales, it's important not to sink too far beneath the waves when resting,

01:49which is why some sleep suspended vertically in the water column, close to the surface.

01:57That makes it easier for them to come up for air.

02:04Humpback whales have even been observed suspended head down in the water.

02:09They can sleep in that position for up to half an hour at a time.

02:14Sperm whales are also known for slumbering in the water column.

02:19They arrange themselves heads up vertically in groups just beneath the surface

02:24and have a kind of internal alarm that ensures they'll surface before they run out of air.

02:30So both halves of the brain can sleep simultaneously in sperm whales, just like in us humans.

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