How Animals Sleep: Explore the Sleep Habits of 17 Animals

Different animals have quite a few variations in the way they experience sleep. Habitat, brain and body size, anatomy, and feeding patterns all affect how animals sleep. Some examples of animal sleep patterns include:

1. 1. Armadillos: Armadillos are nocturnal animals that dig burrows to sleep underground for up to 16 hours a day. They’re mostly active at night, spending the bulk of their time foraging for food.
2. 2. Birds: Birds experience similar sleep phases to mammals in shorter sleep cycles. They can keep half of their brains awake during rest, also known as unihemispheric sleep. Birds can retain their muscle tone while in a deep sleep, which allows them to sleep while perched or hanging upside down. Like some other marsupials, birds can put their body into torpor, a state of reduced physiological activity that allows them to conserve energy by lowering their body temperature, and their metabolic and heart rate. This state is beneficial for birds that live in colder climates.
3. 3. Brown bats: The nocturnal brown bat gets a hardy amount of sleep, resting for around 19 hours per day in the upside-down position, which allows them to wake and drop into flight with minimal energy expenditure.
4. 4. Cats: Cats are hardwired to be more active during the twilight hours. They usually get 15 to 20 hours of daily sleep through naps rather than long segments of rest. During sleep, their hearing and smelling senses remain sharp—an evolutionary characteristic that aids in their survival against predators.
5. 5. Dogs: Like humans, dogs also follow a circadian rhythm, experiencing wakefulness during the day and sleepiness at night. However, they are also social sleepers, adapting the schedule of their owner. Dogs are polyphasic sleepers, which means they will sleep multiple times throughout the day, rather than one segment. A single sleep session lasts about 45 minutes for dogs, totaling around 10 to 14 hours of daily sleep. Dogs also experience rapid eye movement sleep, also known as REM sleep, which means they can dream.
6. 6. Dolphins: In the 1970s, the Russian biologist Lev M. Mukhametov found that dolphins swim half-asleep, resting one half of their brain first and then alternating to complete a full sleep cycle. Dolphins sleep for about eight hours a day, resting each half of the brain for four hours at a time because they have to tell their brain to continue breathing. They can drown if their brain activity shuts down for deep sleep.
7. 7. Frigatebirds: These seabirds, common in the tropical Pacific, can soar for two months without touching down. Researchers recently discovered frigatebirds doze off mid-flight—napping in 10-second bursts, accumulating about 45 minutes of daily sleep.
8. 8. Fruit flies: Even the fruit fly needs to sleep. Fruit flies are capable of producing slow-wave sleep and have been observed resting for 10 hours a night. Like humans, fruit flies experience diurnal sleep, which means they rise with light and sleep when dark.
9. 9. Giraffes: Giraffes need less sleep than most animals—calves get four hours of sleep per day, while adults average five minutes per session. Researchers believe that adult giraffes sleep so little because of their vulnerability to predators. During sleep, giraffes sometimes wrap their long necks around their back and rest their heads on their butts, like a pretzel.
10. 10. Koalas: These herbivores sleep in trees, getting anywhere from 16 to 22 hours a day. This long sleep gives them enough time and energy to digest the fibrous eucalyptus leaves they eat while staying safe from any ground predators.
11. 11. Opossums: Nocturnal opossums spend their nights hunting for food and sleep during the day, around 18 hours. They don’t hibernate in the winter, but they decrease their activity to increase their fat storage to stay warm in the coming cold. They can experience up to six hours of REM sleep, more than most mammals.
12. 12. Platypus: These nocturnal carnivores spend most of their sleeping time in the REM phase—about six to eight hours a day, more than any other mammal. Scientists believe that this extended REM phase may be a holdover from their pre-mammalian reptilian ancestors.
13. 13. Seals: Studies show that seals only engage in REM sleep on land; in the water, they appear to use slow-wave sleep (stage N3 of NREM sleep) exclusively. While most seals only spend about 80 minutes in REM sleep, fur seals can suppress REM sleep for weeks at a time. Seals are also capable of unihemispheric sleep so that they can stay alert for survival.
14. 14. Sloths: Wild sloths usually get around 10 hours of sleep per day, while captive sloths can sleep about 15 to 20 hours. Sloths can sleep curled up in a ball, high in a tree, or snooze while hanging from a branch by their claws.
15. 15. Sperm whales: Sperm whales can sleep fully and deeply while drifting on the water, taking power naps that last about 10 to 15 minutes. During this time, they appear entirely unresponsive. Sperm whales sleep the least out of all the whale species.
16. 16. Walruses: Walruses are among the most adaptable sleepers, capable of resting above and below the water’s surface. These marine mammals can hold their breath for at least five minutes, allowing them to nap underwater. They can also inflate their pharyngeal pouches, allowing them to store up to 13 gallons of air, which helps them stay afloat while they rest on the water. Walruses can sleep up to 19 hours a day but don’t need to sleep everyday like most mammals. Walruses will also hook their tusks into ice or move onto land for a deeper sleep.
17. 17. Zebrafish: Zebrafish have a non-REM and REM phase. During NREM, they are motionless and have a slower heart rate. In the REM phase, they exhibit the characteristics of REM sleep in other mammals, minus rapid eye movement.

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