Most animals have eyelids that close when they sleep, but some animals sleep with their eyes open. Nocturnal animals sleep during the day and are awake at night, while other animals sleep at night and are awake during the day. Animals need different amounts of sleep and sleep in a wide variety of positions. Some sleep for just a few minutes each day.
Animals who sleep with their eyes open
Cows sleep with their eyes open, as are rabbits. They mostly sleep during the day, but the way to tell if they are asleep is if their noses stop moving. Dolphins and porpoises sleep while using only half their brain at a time, as do ducks and pigeons. Whales appear to sleep with their eyes open, too. Birds that migrate can sleep and fly at the same time. Most fish sleep with their eyes open, as do sharks. Snakes don't have eyelids, so they appear to sleep with open eyes. Walruses are able to sleep and swim underwater, or they can sleep on land where they hook their tusks onto land or ice to stay in one place. They sleep 19 hours at a time, but might not sleep for 3 days.
How much sleep do different animals need?
Animals that need the most sleep include the koala, who need 22 hours of sleep in each 24-hour-day, and the sloth, who sleeps 20. The brown bat sleeps 82.9% of their day, or 19.9 hours. Their sleep is more like a nap, lasting a few minutes at a time. The giant armadillo and the North American opossum both sleep 19 hours daily, while the lemur can sleep up to 16 hours. On the other hand, some animals rarely sleep at all. The giraffe sleeps less than 1 hour a day. They can sleep for five minutes at a time and get only a half hour of sleep each day. The horse, who sleeps while standing, sleeps less than 3 hours. Donkeys also sleep for 3 hours, while sleep need just a bit more- 3.8 hours each day. Cows are said to sleep 3.9 hours daily. Some animals are awake in the daytime and are called diurnal animals, while those who are active and awake at night are called nocturnal. In general, smaller animals sleep more than the larger ones, but there are some exceptions, such as lions and tigers, who both sleep between 14 and 16 hours each day.
Sleep position of various animals
Humans sleep lying down, but other animals sleep in different positions and places. Leopards sleep in trees, and bats sleep hanging upside down and clinging with their feet. Some animals are able to sleep underwater, such as seals and hippos.