How Do Animals Sleep? The Sleeping Habits of Different Species

December 18, 2019 | Casper Editorial Team
illustration of a polar bear sleeping illustration of a polar bear sleeping illustration of a polar bear sleeping

Almost all animals do have some sort of pattern when it comes to sleep, but sleep times vary across the animal kingdom. While some creatures sleep for over 18 hours each day, others don’t need more than a few seconds of shut-eye at a time.
 
Habitat, cold-blooded vs. warm-blooded anatomy, brain size, feeding patterns and many more factors contribute to animals’ sleep patterns.
 
As a general rule, genetically similar species will have similar sleeping habits. Because of this, we’ve separated different species below and highlighted some specific organisms within each section.
 
From sharks to puppies, wild creatures are fascinating and their bedtime routines are no different. Every little bit we learn about the other organisms that surround us can help protect the wild places in which we live.
 
In order to spark curiosity in the next generation of biologists and scientists, we’ve attached printable educational activities to help kids learn about sleeping habits in some of the wildest places on earth.
 
a fox sleeping next to a ball toy and a bone

Do All Animals Sleep?

It’s unknown if all animals need sleep, but it’s essential for most in order to function normally. The brain’s metabolism — or the chemical processes required to keep the body in order — depends on sleep to recharge. This process is relatively similar in all animals.
 
Without sleep, the brain begins to shut down. The longest recorded awake time for a human is 264 hours (about 11 days). Hallucinations, memory loss and mood swings are noted side effects of staying awake for long periods of time, but they’re all temporary. The individual who stayed awake for 11 days recovered after a couple days with normal sleep. The animal kingdom, so it seems, is the same way.
 
In the animal kingdom, sleep is more complex. Because most animals are at peak vulnerability when sleeping, it’s rarely seen as a luxury.
 
01 Chart - 2

Which Animals Sleep the Most?

Sleep duration can range from a couple hours to nearly 24 in the animal kingdom. These patterns not only aid health, but more so to keep them safe from predators. Living organisms have adapted to incorporate sleep into their daily life. Bears, for example, are able to hibernate for many months at a time during months where food is scarce and the air is cold — but, they even need their regular night-to-night shut-eye, too.
 
Below are some of the animals that sleep the most on average:
 

  • Brown Bat: 20 hours per day
  • Lion: 19 hours per day
  • Giant Armadillo: 18 hours per day
  • North American Opossum: 18 hours per day
  • Tiger: 18 hours per day
  • Cat: 14 hours per day
  • Dog: 13 hours per day

Each amount of sleep is dependant on the environment, it’s important to note. A wild dog will sleep much less than a domestic one. A bear in the wild will have different sleep habits than one in a zoo.

02 Dog, owl, bear

Sleeping Habits of Land and Air Mammals

Many land and air mammals need a particular type of sleep called Rapid Eye Movement (REM) sleep. Animals like dogs, primates and yes, humans, experience REM sleep. This is a mammal’s deepest phase of sleep and the portion of a night’s rest where dreams occur.
 
One reason mammals need REM sleep is to keep the skull and brain warm. In turn, this keeps bodily functions normal and regenerative processes running smoothly. Metabolism and the ability to process food is one function particularly influenced by REM sleep.
 
Without REM sleep, most mammals can die, because the body will essentially shut down. For some animals, like owls, this changes with age. Owlets will spend almost 50 percent of sleep in REM, while adults it’s closer to 25 percent.
 
Not all mammals need REM sleep, though — bears and other hibernating animals don’t experience it at all. While in winter dormancy, an animal’s metabolic processes are 20 times slower than when awake. Hibernating animals generally have a body temperature that’s just one degree Celsius higher than the air around them. This means that for the winter months, hibernating animals sleep at a level much deeper than REM in order to conserve energy.
 
03 Whale, dolphin, shark

Sleeping Habits of Marine Life

Marine organisms have vastly different sleep patterns compared to land and air animals. Whales, for example, float vertically with half of their brain awake while they sleep. Whales only nap for about 7 percent of the day for up to 10 minutes at a time. This lack of sleep is thought to be due to their predators’ eating habits.
 
Dolphins, on the other hand, sleep vertically at the surface of the water. Sometimes called “logging,” dolphins will remain almost completely still and slowly take in air. In order to do this, they also sleep with one side of their brain engaged.
 
Almost all species of shark sleep the same way that dolphins do. However, the nurse shark is one exception and can sleep completely still on the ocean’s floor.
 
Fish also go in and out of sleep frequently — both to avoid predators and to filter oxygen properly. They will stop swimming and float, or remain dormant in between natural structures under the water for protection and bob up and down.
 
04 Frog, newt, salamander

Sleeping Habits of Amphibians

Not much research has been done on the sleeping habits of amphibians. It’s not fully known if frogs sleep. They have been observed sitting still and closing their eyes while sitting on foliage — which is assumed to be their sleep state, but researchers are still unsure.
 
Some species of newts, though, are able to achieve deep sleep. In hot climates, certain species of this amphibian will burrow deep into the ground. By doing this, they can find moisture and avoid predators for hours at a time.
 
Similarly, the barred tiger salamander burrows deep into the ground and spends most of its time here, both awake and asleep. The main difference with this animal, though, is that they are nocturnal. This means that during the day they will enter deep sleep and emerge once the sun goes down for brief hunting stints.
 
05 Snake, crocodile, alligator

Sleeping Habits of Reptiles

Depending on the species, reptiles have different sleeping habits. Snakes, for example, don’t have eyelids — meaning they can’t close their eyes for sleep. Instead, they sit very still with their eyes open, as brain functions slow down and the entire body rests.
Snakes also hibernate in colder states during winter months, and in the south where the weather is warmer, they brumate — or slow down their metabolism without sleep.
 
Crocodiles also sleep with half of their brain “on.” Unlike other species lower on the food chain, the main reason crocs sleep like this is to be alert for nearby prey. While asleep, they will leave one eye open (which is connected to the “awake” side of the brain).
 
Crocodiles are also primarily nocturnal, meaning they need to stay semi-alert during the daytime as this is when some of their prey is active. Because it’s generally colder at night, living organisms use less energy keeping themselves warm than if they were nocturnal. This is one reason why many nocturnal animals, like the crocodile, are cold-blooded.
 
American alligators have an interesting variation on traditional hibernation. In extreme temperatures, the animal creates a “gator hole.” These 65-foot long tunnels fill with mud and water, and the alligator remains dormant during intense periods of heat or cold — but, unlike hibernation, it is completely weather dependant. In typical weather, similar to crocs, alligators are nocturnal but can wake during the daytime to hunt and stay safe.
 
06 Bee, fly

Sleeping Habits of Insects

Most insects do sleep — in fact, they’re a lot like humans. Bees, for example, will nap during the day when there is little work to be done on the hive.
 
Fruit flies also sleep. Similar to humans, they are responsive to sleep-altering chemicals like caffeine. These bugs also go through similar circadian rhythms as mammals, meaning that their body functions are dependent on solid, regular sleep. While it’s unknown if REM sleep is reached, fruit flies regenerate and build important mechanisms in the body while asleep.
 
Cockroaches also depend on regular sleep. Cockroaches keep their eyes open during sleep because they (and many other insects) don’t have eyelids. However, these bugs fold their antennae down to protect important organs and vulnerable areas while sleeping.
 
Animals and a human sleeping next to each other on a cozy Casper mattress. Illustration.
 
Knowing about the animal kingdom is important because humans are a part of it! While animals sleep differently, most of them do sleep. Try these out with your little explorer on your fresh resting place, a new Casper mattress.