Written by: Mallorie Stallings
Updated February 25, 2021
As humans, we feel our best when we’ve had a good seven to nine hours of shuteye. What feels like a reasonable amount to us is excessive to much of the animal kingdom. Sure, lions and koalas can snooze for hours on end, but many animals sleep very little. In fact, some animals sleep so little that they would consider your afternoon power nap to be a full night’s sleep.
Why do some animals sleep less than others? There are exceptions to every rule, but in general, large animals tend to sleep fewer hours (1) than smaller ones. Some grazing animals also get by on less sleep than their hunting counterparts, since they need to spend so much of their day eating to survive.
What animal sleeps the least? In order from most to least sleep, we'll look at seven animals that get by on surprisingly little sleep.
Sheep - Five Hours per Day
Sheep are diurnal like humans, with much of their sleep taking place at night. In total, they may only spend five hours asleep (2). Ruminant animals like sheep must spend much of their day upright in order to eat, which limits their ability to sleep lying down. As a result, they may spend as little as 2.5% of their sleep in REM. By comparison, humans spend up to 10 times that amount (3) in REM.
REM sleep is also shorter in prey animals like sheep, since spending too much time in that stage of sleep can make them more vulnerable to attack. Sleeping in a herd offers them some protection against predators.
Giraffes - Four to Five Hours per Day
How long do giraffes sleep? Somehow, the tallest animal in the world gets by on very little sleep. In total, a giraffe sleeps around 4.6 hours per day (4). As grazers, giraffes spend most of their day eating. Much of their sleep takes place in short naps lasting 35 minutes or less. They can sleep lying down or standing up.
Horses - Four Hours per Day
Horses spend the bulk of their day eating or resting. Resting accounts for five to seven hours, with as few as four hours (5) of that time fully asleep. Like giraffes, horses can sleep standing up — but only as long as they’re not in REM sleep. During REM sleep, the brain temporarily paralyzes muscles, preventing humans and animals alike from acting out dreams and injuring themselves. Horses can spend 30 minutes each day (6) in REM sleep, but they need a comfortable place to lie down to do so. You can tell a horse has entered REM sleep when they fall or lie down (7).
Elephants - Three to Four Hours per Day
As grazing animals, elephants have short sleep needs. In all, the average elephant may only sleep two hours per day (8). That two-hour figure is only an average, and some elephants have been observed traveling for nearly two full days, without any sleep, to escape poachers. Due to their grazing and itinerant behavior, elephants choose new sleep spots each night. They can sleep standing up or lying down.
Deer - Three Hours per Day
Deer are crepuscular animals (9), which means that they are most active in the twilight hours. Deer can sleep standing up or lying down (10). Either way, they always keep their noses and ears alert so they can run away if a predator approaches. They may even peek their eyes open to look around.
Walruses - Two Hours per Day
Walruses can spend up to 84 hours swimming continuously (11). Given that they can stay awake for more than three days, they certainly deserve a spot on our list. When they finally get a chance to rest, walruses may sleep while floating in the water, lying along the sea bottom, or leaning against something in an upright position.
Walruses can sleep on both water and on land, but they prefer to snooze on shore, and will spend up to 75% of their time on land asleep. In total, they might spend two to 19 hours resting, and sleep in short bursts of three to 23 minutes (12).
Migrating Birds - One Hour per Day
When considering which animal sleeps the least, it appears that migrating birds may be the answer. These animals are the ultimate multitaskers, having figured out a way to sleep while they fly. Birds have the ability to sleep unihemispherically (13), which means that one side of their brain sleeps, while the other stays awake. This enables them to keep one eye open and maintain flight while migrating.
Alpine swifts have been documented flying for 200 days nonstop (14), while frigate birds sleep for less than 1 hour per day during a 10-day flight. When they reach land, these birds catch up on sleep just like walruses do, and may sleep for up to 13 hours per day.
Is There an Animal That Never Sleeps?
It’s unclear (15) whether or not all animals need sleep. One commonly cited study concluded that bullfrogs don’t sleep (16). However, that study relied on a narrow definition of sleep, which scientists have since reconsidered.
Mammals have evolved (17) to need varying amounts of deep and REM sleep. Some species can get by on very little REM sleep (18), and others can survive in hibernation for years at a time. Even brainless animals like the jellyfish seem to display a sort of sleep-like state (19).
Sleep is as fascinating and as varied as the animal kingdom itself. As researchers continue to explore the origins and benefits of sleep for animals, they find clues that help us also better understand the sleep of humans.
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