16 Weird Sleep Habits in the Animal World

two otters floating on backs and holding hands to stay together

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As humans, we're familiar with the importance of sleep. Each night, we crawl into bed hoping to squeeze in the recommended seven to nine hours. But for many other members of the animal kingdom, the sleeping experience is quite different. From the creatures that sleep nearly 20 hours each day to those that slumber with only half their brain at a time, here are some of the more unusual ways some animals doze off.

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adult elephant sleeping while standing up, leaning trunk against thick tree

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A 2017 study found that elephants in the wild sleep for just two hours every day. And those two hours aren't uninterrupted — they occur in spurts over several hours. Compare this to their captive counterparts that, without having to worry about predators, doze for up to seven hours a night.

To obtain this information, scientists from the University of Witwatersrand in Johannesburg, South Africa put collars and small monitors on two wild female elephants and recorded their movements for a month. Sometimes the creatures lay down, but most of the time they slept standing up. They weren't picky about where they slept, and their level of physical activity during the day seemed to have no impact on how long they dozed.

The study poses the question of if the two-hour rest time makes elephants the shortest-sleeping mammals, but they have competition for this title in the giraffe.

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baby giraffe sleeps on ground with neck wound and head resting near rump

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In the wild, these lumbering giants can go weeks without sleep — though that skill is borne out of necessity. Being large and slow, adult giraffes are constantly on guard against predators. When they do snooze, it's often standing up to avoid having to take time they may not have to get their lanky legs off the ground.

This is primarily for adult giraffes, however. Baby giraffes get to sleep lying down; their legs are tucked under them and their neck twists around so their head can rest on or near their rump, as shown above.

Remarkably, giraffes only sleep for five minutes at a time for a total of around 30 minutes a day.

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Sperm Whales

sperm whale sleeping perfectly vertical underwater

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In 2008, a group of researchers was studying calls and behavior in sperm whales off the coast of Chile when they happened upon something new: a pod of sperm whales sleeping so soundly in the water that none of them saw or heard the boat coming. This was particularly surprising because whales are unihemispheric sleepers, meaning they only sleep with one half of their brain at a time while the other half stays awake.

The whales rested perfectly upright and bobbed vertically in the water — some with their noses above water, some completely underwater. This behavior is called drift-diving. They only moved after the small boat accidentally bumped one of them, making them all swim away.

Based on this, researchers believe that sperm whales do sleep fully while drifting for 10 to 15 minutes at a time, during which they don't breathe.

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three ducks uniformly sleeping in row

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There is general consensus that ducks sleep with one eye open, and sleep researchers at Indiana State University wanted to learn more about it. They found interesting trends by filming the slumber of a group of mallard ducks.

First, the ducks almost always slept in rows or cliques. Second, the ducks at the end of the row kept open the eye facing away from the group, sleeping unihemispherically like sperm whales. Meanwhile, the ducks in the middle of the group closed both eyes.

This is likely a defense behavior, with the ducks on the end serving as lookouts for predators while the middle ducks sleep.

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bottlenose dolphin asleep at surface with head poking above water

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Dolphins are another animal that rests only half its brain at a time. For them, however, it is not just to watch out for predators. As mammals, dolphins need to breathe, but they do not do it involuntarily like humans; when they rest, they must be awake enough to rise to the surface regularly to take a breath so they do not suffocate in their sleep.

When dolphins want to enter a deeper sleep, they float horizontally near the surface with their blowholes above the water. This behavior is called logging because the still, floating dolphin looks like a log in the water.

These sleeping techniques aren't practiced by dolphin babies and their moms, however. Baby dolphins don't sleep at all in their first month of life; they swim continuously to keep safe from predators and maintain body temperature as they develop blubber. The mothers of those newborns follow suit, getting almost no sleep to protect the calf as it grows.

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three walruses huddles asleep on ice bed in water

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The walrus is an equal-opportunity sleeper. It can sleep anytime, anywhere, whether it's floating in the water, lying on the ground, or leaning on another walrus. Researchers have even noticed walruses resting in water while using their tusks to hang from ice floes.

When walruses sleep in the water, they can only do so for minutes at a time before they need to come up for air. But on land, they settle into a deep sleep that can last up to 19 hours.

Don't let that make you think they're lazy animals though. Walruses can have periods of activity where they stay awake and swim for up to 84 straight hours. When it's finally time to sleep, they need it.

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group of bats covering themselves with wings, sleeping upside-down from cave ceiling

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It's well known that bats sleep upside down, but do you know why? Bats do this because their wings are not strong enough for them to take off from the ground. To make up for this, the creatures keep themselves suspended in the air so they can use gravity and drop into flight from their perches.

Bats stay in that upside-down sleeping pose for a long time, too. In fact, bats are some of the sleepiest creatures in the animal kingdom. The little brown bat, for example, sleeps an average of 19 hours each day.

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two zebras sleeping by resting their heads on each other's backs

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Zebras often sleep standing up so they can stay on alert for predators. To do this, they use what's called a "stay apparatus," which is a group of muscles, tendons, and ligaments that allows them to lock their joints, most importantly, their knees. Once their joints are locked, they can drift off without having to engage any muscle groups, letting them relax without worrying about falling over.

When they sleep in this position, it's more of a nap than a deep sleep. They do need to lie down once in a while to achieve REM sleep.

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Sea Otters

close up of two otters lying on their backs asleep in water and holding hands

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When sea otters sleep, they float on their backs on the surface of the water. As such, there is worry about separation. To ensure they don't drift away while they slumber, they've been known to hold hands in pairs and small groups.

Sea otters also wrap themselves in a strand of seaweed growing on the ocean floor to use as a kind of anchor. When a baby sea otter — called a pup — is too young to float on its own, it sleeps on its mom's belly as she floats on her back.

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Migratory Birds

alpine swift bird soaring against clear blue sky with wings open

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Migratory birds such as the alpine swift (pictured) and the albatross spend much of their lives traveling or on the hunt; researchers have found that alpine swifts can stay in the air for 200 straight days without landing. So, when do they sleep?

These birds are multitaskers that can sleep (and eat) while flying. Scientists believe that birds, like whales, ducks, and walruses, are unihemispheric sleepers. They sleep while gliding and soaring — whenever they're not flapping.

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group of meerkats huddle in the shade and sleep on top of each other in pile

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Meerkats live in underground burrows in groups called mobs or gangs. Housing as many as 40 meerkats, the burrows contain numerous sleeping chambers, including ones used only when breeding.

When meerkats lie down to rest, they do so in heaps, piled on top of each other for warmth. The matriarch is typically buried deepest in the group so she gets the best sleep possible. The meerkats on the outside don't reach REM sleep so they can stay alert and watch for predators.

In the summer, the meerkats may spread out more and sleep above the ground.

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tiger shark cruises over white sand bottom of the ocean

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Much about how sharks sleep is unknown, but there are some things we understand. For sharks to breathe, they must pass water over their gills. That's why most sharks sleep while moving. Smaller species of shark — such as the nurse shark — are exceptions, as they can use their spiracles (small holes behind each eye that aid in breathing) to force water over their gills while they lie still on the ocean floor.

In 2016, we learned more when researchers filmed a great white shark sleeping. The footage, which was captured by a robotic submersible near Mexico’s Baja California Peninsula, showed a female great white swimming closer to the coast in shallow waters as night fell. She faced directly into strong currents with her mouth open, likely so that water could continue to pass over her gills. Her swimming slowed, making researchers believe she was asleep, and they marked this as a sleeping behavior.

The footage was shared as part of Discovery's annual Shark Week. See it here:

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brown and tan snail shell hidden among wet ground with twigs and dead leaves

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We are all familiar with hibernation, which is when certain animals conserve their energy by lowering their metabolisms and "sleeping" through cold months. Some snail species hibernate, but that's not all — they also estivate. Estivation is the summer version of hibernation, in which animals enter a prolonged dormant state to protect themselves from dryness and dangerously high temperatures. Snails can estivate for years.

In 1846, a British museum worker found the shell of an Egyptian land snail, assumed it was empty, and attached it to an identification card. Four years later, someone noticed traces of slime on the card. It was put in water, and when the shell came off the card, the live, awake snail crawled out. It was estivating all that time.

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brown frog sleeping in opening between light tan rocks

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Like snails, frogs use both hibernation and estivation as sleep strategies. Frogs that estivate are found mainly in Africa and South America. During dry spells, they burrow into the soil and shed several layers of skin to form a cocoon, leaving their nose exposed to breathe. When the rain comes again, they shed the cocoon and climb up to the surface.

Some aquatic frogs hibernate underwater, resting atop or partially buried in the mud to ensure access to oxygen-rich water. Terrestrial frogs, like the wood frog and American toads, hibernate by burrowing into the soil below the frost line or hiding in cracks in logs or rocks.

But many animals hibernate and even estivate. What makes the frog so interesting is its biologically built-in antifreeze system. As ice crystals form in its body (in its bladder or under its skin), a high concentration of glucose in the body keeps major organs from freezing. The heart may stop beating and the frog may stop breathing, but come spring, it will thaw and return to normal.

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grizzly bear sleeping on a large log in the rain

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There may not be any animal as famous as bears when it comes to hibernation, but they have a lesser-known special hibernation skill: giving birth.

A pregnant bear that settles in to hibernate will rouse herself briefly to deliver one or more cubs. Then, she'll quickly return to sleep as her cubs nurse and snuggle up to her to keep warm. So, she not only gives birth while hibernating, but she also cares for and supports her newborns.

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chimp sleeps on side in bed of fluffy grass

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Chimpanzees like to curl up to sleep the same way humans do. They even use twigs and leaves to construct nests for sleeping high up in trees, much like human beds. However, they are extraordinarily picky when it comes to these beds.

Research has shown that when choosing locations for their nests, chimps are particular about the trees they use, honing in on those with stiff branches and minimal distance between leaves. Then, after taking so much care to find the perfect tree to build the perfect nest, a chimp will use it just once. After one night's sleep, the chimp will leave the nest behind and construct a new one for the upcoming night.