Every animal with a brain needs sleep — and even a few without a brain do, too. Humans sleep, birds sleep, whales sleep and even jellyfish sleep. Sleep is universal “even though it’s actually very ...

This is read by an automated voice. Please report any issues or inconsistencies here. Animals such as penguins and frigatebirds have evolved extreme sleep strategies — naps that last a few seconds, ...

Sleeping underwater might sound peaceful — but for ocean animals, it’s a matter of survival. Some dolphins sleep with one half of their brain at a time, keeping one eye open to avoid danger and ...

Sleep in fish may look different from humans, but rest is essential for survival. Here’s what experts have to say about fish sleep. A protective mucous cocoon surrounds this parrotfish as it sleeps in ...