15 Incredible Animal Sleeping Behaviors

Without the luxury of sleeping masks or relaxing soundtracks, animals rely on the tools nature has given them to rest. As a result, many have developed extraordinary methods to ensure they get the sleep they need.

1. DOLPHINS

Dolphins are fascinating creatures, often admired for their cuteness, intelligence, and sometimes unsettling sexual behaviors. However, their sleep habits are just as intriguing. Dolphins can experience deep sleep, called "logging," during which they appear as a log drifting on the water's surface. Even more astonishing, they achieve this state by shutting down half of their brain, along with the eye opposite that hemisphere. The other half of the brain and the opposite eye remain active to stay alert for potential threats, such as predators or other dolphins. This half-brain sleep cycle also signals when it's time to surface for air. Every couple of hours, the resting and active brain halves swap places. This remarkable sleep behavior is shared by other animals, including fruit bats, porpoises, iguanas, seals, birds, and ducks.

2. SPERM WHALES

In 2008, researchers stumbled upon a group of sperm whales sleeping vertically in the water off the coast of northern Chile. The sight was remarkable, but then things took an unexpected turn. These whales, previously thought to rest only one side of their brain at a time, like dolphins and some other whales, didn't react to the approaching boat. It wasn't until one whale was unintentionally nudged that the group stirred and quickly swam away. This discovery revealed that sperm whales sleep differently from their relatives, with full sleep cycles occurring near the surface. They remain still and don't breathe during their naps, and if this is their only sleep type (it remains unclear if they also use half-brain sleep), their relatively brief sleep sessions could make them the least sleep-dependent mammals.

3. GIRAFFES

Giraffes don't sleep for long periods, similar to sperm whales. They only manage around 20 minutes of sleep daily, mainly to avoid predators. Their towering height makes it tricky for them to catch a quick nap, but when they do curl up for some rest, it's undeniably cute.

4. SEA OTTERS

Sleep for otters isn't just about avoiding predators; they also need to keep from drifting away. While resting, sea otters float on their backs, sometimes in groups or nestled in seaweed forests. To prevent themselves from floating apart, they often hold hands.

5. ALBATROSSES

The albatross, a majestic sea bird, spends most of its time soaring through the skies on the hunt. With such a busy lifestyle, it doesn't have much opportunity for rest, so it's believed that albatrosses sleep while in flight. Alpine swifts are also thought to do this, as well as migratory Swainson's Thrush, which take many short power naps, each lasting only a few seconds.

6. DUCKS

Ducks don't just sleep with one eye open—they sleep in formation. When it's time to rest, ducks line up in a row, with those at the ends keeping one eye open to watch for predators, while the other eye closes. Meanwhile, the ducks in the middle get to rest fully, closing both eyes. This strategy of single-hemisphere sleep by the ducks on the ends ensures the safety of the entire group.

7. MEERKATS

Meerkats spend their nights in intricate burrows, which feature elaborate tunnels and cozy underground sleeping chambers. These social creatures live in groups called mobs or gangs, which can include up to 40 members, each led by an alpha male and female. They sleep in piles, huddling together for warmth and to protect their leaders at the bottom of the heap. Other animals, such as puppies, squirrels, and bats, also cuddle up during sleep to stay warm (humans included).

8. HORSES, ZEBRAS, AND ELEPHANTS

These are the animals known for standing while they sleep, remaining alert by resting on their feet. They can lock their legs in a position that requires little muscle effort, a remarkable ability known as a 'stay apparatus.' While this is impressive, horses (and even cows) need to lie down occasionally because they can't enter REM sleep while standing. Flamingos also stand to sleep, primarily because their natural habitats don't offer many comfy spots for resting.

9. BROWN BATS

On the opposite end of the sleep spectrum from sperm whales and giraffes are brown bats, who sleep an impressive 19 hours each day. These nocturnal creatures hang upside down for their naps, a position that provides greater efficiency, as their delicate wings are better suited for takeoff from this posture. After bats, the longest sleepers are armadillos, opossums, sloths, tigers, and of course, domestic cats. Keep that in mind next time you ask your cat to be more productive.

10. SHARKS

Many sharks must keep swimming constantly to breathe, passing water over their gills for oxygen. However, some species have evolved spiracles—small openings behind the eyes—that enable them to take in oxygen even when they're stationary. Generally, sharks' sleep is considered more of a restful idle state rather than a full shutdown. Research on the spiny dogfish suggests that its movement might be controlled by the spinal cord instead of the brain, meaning sharks could potentially rest their minds and keep moving. Some scientists also think that certain white sharks might face the current while still, letting water flow over their gills effortlessly.

11. WALRUSES

Walruses have a remarkable ability to sleep while swimming. They're the kind of creature who can doze off just about anywhere—whether it's holding their breath for up to five minutes underwater, or taking a lengthy nap on land for up to 19 hours. They’ve earned that rest, though—walruses are known to swim continuously for up to 84 hours. While sleeping in the water, they make use of pharyngeal pouches—special air pockets in their bodies that function like a natural life vest, keeping them afloat while they rest.

12. DESERT SNAIL

It might seem like a snail's life would be pretty low-energy, but these little creatures can sleep for literally years. A particularly famous case involved an Egyptian desert snail that was presumed dead by a British Museum staff member who attached it to an ID card. Four years later, the staff discovered a trail of slime on the card, and when they removed the snail's shell, it crawled out alive.

13. FROGS

Frogs survive the winter through hibernation, much like their larger, furrier counterparts, but their abilities are even more extraordinary. Equipped with natural antifreeze, frogs can survive freezing temperatures. While ice may form in their body cavities and under their skin, the glucose in their organs prevents them from freezing solid. When frozen, a frog stops breathing, and its heart stops beating. But once the spring thaw arrives and the temperature rises, the frog's body comes back to life, resuming its normal functions.

15. BEARS

Bears don't have particularly unique sleep patterns, except for during the winter months when pregnant mothers are hibernating. During this time, their heart rates drop, and they stop eating, drinking, urinating, defecating, or moving around. However, despite being deep in hibernation, mother bears will wake just enough to give birth. The newborn cubs then nurse from their sleeping mother for several months until she eventually wakes up and leads them into the world.

16. APES

Scientists are investigating apes to understand human sleep patterns and how they might have influenced our evolution. Research shows that animals like orangutans, gorillas, and chimpanzees prefer curling up to sleep, much like humans. They also build nests or seek out safe platforms to sleep on, helping them avoid predators and sleep more soundly compared to species like baboons that sleep upright. This opportunity for a longer, more restorative rest may have been key to our evolutionary development, contributing to our intelligence over time.

This article was originally published in 2015.