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.
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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.