Human beings have a pretty straightforward sleep schedule of 8 hours a night, but our pals in the animal kingdom vary much more depending on their needs.
Sleeping animals are vulnerable to getting attacked by predators, so it’s in their best evolutionary interest to develop ways to protect themselves during sleep. That’s why cows and sheep sleep in a herd, as there’s strength in numbers. Otters hold hands during sleep, or wrap themselves in seaweed to protect their young and stay afloat. You can often find them floating at the surface of the water, lying on their backs in a relaxed pose.
Lions sleep in short bursts throughout the day and night in order to capture their prey as it becomes available. It’s interesting to note that this is analogous to the polyphasic sleep schedule that Leonardo Da Vinci and Thomas Jefferson adhered to - as if people who avoid a conventional sleep schedule are ready to “strike” at their creativity or ingenuity at any moment. Animals that eat less calorie dense food generally need more sleep, while herbivores are awake more of the day to get their proper nourishment.
Giraffes sleep no longer than five minutes at a time fully standing. A sleeping animal of that size is a tempting prey for a predator, and standing up would be a long, awkward process for a giraffe that would make it extra vulnerable. This is why giraffes sleep with one eye open to remain ready to run.
Koalas may have the most uncommon sleep habits. They don’t get much energy from their eucalyptus-based diet, so sleep nearly 15 hours a day, with most of their time awake spent eating or lounging around.
Primates, which includes humans, sleep in a concentrated period of the day, a pattern known as uniphasic sleep. Both birds and marine mammals are able to sleep through unihemispheric sleep, in which animals sleep in only one brain hemisphere at a time. This is how birds can remain flying, and dolphins and whales continue to swim and see through one eye.