Updated at: 30-12-2021 - By: Jane Brody

What do animals do when they’re not snoozing Absolutely! Almost all animals, like humans, require some type of rest or sleep to function properly. An intrinsic biological 24-hour clock governs sleep and wakefulness for most animals in the wild.

Slumber is a necessity for human health. Humans can recharge, consolidate their memories, and restore their bodies when they sleep. Children, like adults, require adequate rest in order to grow properly. Despite the fact that napping exposes animals to danger, they do it regardless, according to experts.1 The advantages of sleep outweigh the risks.

How Mammals Sleep

Animals sleep in order to conserve energy and recharge their bodies and minds. A mammal’s sleep requirements are influenced by a wide range of characteristics, including its age, size, environment, nutrition, and the safety of its sleeping area, among others. How much sleep a mammal need can also be affected by where it lives.

Non-REM sleep and REM sleep last varying periods of time depending on the species. All mammals investigated thus far show indications of REM sleep, which suggests that mammals dream exactly like humans.

It is common to classify mammalian sleep as either monophasic or polyphasic.

The term “monophasic sleep” refers to an animal’s tendency to sleep in a single, focused period of time. Monophasic sleepers, such as humans, are common. When it comes to sleep and alertness, our circadian cycles are in sync with each other.

On the other hand, those who have a polyphasic sleeping pattern do so during a 24-hour period. Many animals need to keep an eye out for predators, which is why polyphasic sleep is more common. Animals, on the other hand, can benefit from monophasic sleep if dangers are kept to a minimum. Sleeping in trees with their family helps marmosets feel more secure and sleep in a monophasic pattern.


Land Mammals and Sleep

Land mammal species differ greatly in the quantity of sleep they require. Giraffes require only a few hours of sleep a night. Every day, the average giraffe sleeps for 4.6 hours. Giraffes spend the majority of their time sleeping at night, however they are known to take short naps during the day. Sleeping on their side or on their back is just as comfortable for giraffes, and their cycles are only 35 minutes or less.

Also, elephants do not get much rest. Only two hours of sleep each day has been reported by some researchers6. When elephants are sleeping, their trunks cease moving, which is how scientists know they’re asleep. In order for elephants, giraffes, and other large herbivores to survive, they must eat frequently. Because of how far they’ll walk when awake, predation risk could potentially have a part in how little sleep they get. Research shows that elephants are capable of trekking for nearly two days straight with no rest.

Horses, like giraffes and elephants, don’t sleep much and, when they do, they can do so while still standing up in their stables. The REM sleep stage is characterized by lying down7.

Dogs, on the other hand, sleep for more than a third of the day.8. Another 21% of their waking hours are spent in a condition of calm lethargy, ready to fall asleep at any moment. Overnight sleep duration for little brown bats is much greater, at around 20 hours9! Torpor, often known as hibernation, takes up some of that time.

What Is Hibernation?

Many mammals and several other types of animals go into hibernation, which is a sleep-like state. Many animals go into hibernation for long periods of time and are only awake for short periods of time at a time.

A popular misperception about hibernation is that it’s an extended period of sleep, but that’s not quite accurate. To put it another way, hibernation is a condition of torpor. The metabolic rate, heart rate, body temperature, and respiratory rate of animals are all reduced during torpor. During hibernation, these effects are more apparent than they are during normal sleep.

During extreme climate fluctuations or when food is scarce, animals go into hibernation to conserve energy. During the winter months, bats, for example, must determine whether to hibernate or migrate in order to replenish their food source of insects. Even if it’s cold outside, some bats will hibernate or go into torpor to conserve energy until the insects return in the spring.

People often associate hibernation with bears, despite the fact that bears’ hibernation is distinct from that of humans12. For up to seven months, a bear’s body temperature remains practically constant while it refuses to eat, drink, urinate, or defecate. The Madagascan fat-tailed dwarf lemur13, European hedgehogs14, ground squirrels, and pygmy possums15 are examples of animals that hibernate.


Marine Mammals and Sleep

Walruses sleep between 19.4 and 20.5 hours16 a day. In water, they can sleep for longer lengths of time, while on land, they sleep longer durations of time (17). walruses sleep in the water by lying on the bottom, floating, or leaning against something while upright. They’ve been known to sleep with their tusks hooked into an ice floe. Walruses, like elephants, can go without sleep for days at a time. These fish may stay in the water for up to 84 hours before they need to be refilled with fresh water.

It’s not just walruses who have distinctive sleeping positions; sperm whales do, too. Actually, they sleep on their backs18. Because they didn’t respond to a ship going by until it bumped into them, scientists were able to determine that they were asleep!

They are all marine mammals that sleep unihemispherically19: dolphins, seals, and manatees. In unihemispheric sleep, only one hemisphere of the brain shuts down, allowing these animals to benefit from sleep’s rejuvenating effects while also keeping an eye out for danger.

How Birds Sleep

With one side of their brains unconscious, birds can also sleep unihemispherically. Their sleeping hemisphere’s eye is closed solely when they are asleep.

Birds use unihemispheric sleep as a defense against predators. Several mallard ducks can sleep together in a row, for example. Unihemispherically sleeping ducks are more likely to keep their exterior eye open, while bihemispherically sleeping ducks close both eyes.

Migratory birds’ extended flights are made possible by unihemispheric sleep. When they’re gliding and their wings aren’t flapping as much, they might go off and sleep. In the Alpine Alps, records of nonstop flight for 200 days20 have been achieved.

Migrating birds, on the other hand, do not sleep as much as they normally would while on their journeys. While migrating, white-crowned sparrows, for example, sleep at a fraction of their normal rate. When they’re perched, they’ll be able to catch up on sleep with micro-naps during the day. When they perch, the tendons in their feet lock into place, making it possible for them to sleep with no effort. Bats, like humans, have a locking mechanism that allows them to sleep in an upright position.

How Reptiles and Amphibians Sleep

When it comes to sleep, reptiles and amphibians are among the least researched creatures. REM and slow-wave sleep have long been assumed to be unique to animals and birds, respectively. Even in sleep cycles as short as 80 seconds, new research suggests that reptiles such as lizards may experience these sleep stages.23

Lizards, like other animals, seek sleeping spots that are safest for them. They may sleep on leaves with their heads pointing towards the direction of a predator’s approach24. Crocodiles25, for example, sleep unihemispherically so that they can keep an eye out for any threats and prey they can consume while they sleep.

In contrast to crocodiles, snakes sleep with both eyes open26 — in fact, since they lack eyelids, this is necessary. Snakes can go days without moving as they digest their food.

Western fence lizards and cottonmouth snake brumate. Like hibernation, the brumation of reptiles occurs in reaction to cooler temperatures and a lack of adequate food. ‘Brumation’ Every 100 days or so, Salamanders will go into brumation.

Amphibians, too, have the ability to go into a slumber-like state in order to survive in dry environments. Estimation28 is the name given to this condition. Green-striped burrowing frogs hibernate underground for months at a time during estivation.

How Fish Sleep

What happens to fish when they go to sleep? There is some truth to this, although it’s probably better to describe what fish do “resting.” When fish rest, they reduce their activity and metabolism29, but they don’t lose their alertness or ability to defend themselves. They rest in the mud, sand, or coral, or they float like zebrafish30. They don’t eat. A cocoon of mucus forms around parrotfish as they sleep to keep them safe.

In order for a shark to sleep, it must be able to breathe properly.

It is possible for a buccal pumping shark to remain immobile in an underwater cave or on the sea floor since they breathe via their cheeks. They appear lethargic and inert in this sleep-like state that has been observed in nurse sharks, the type of buccal pumping shark. They’re lying on a rock with their eyes half-closed, propped up by their pectoral and tail fins.

The gills of fish and sharks are ventilated by keeping their mouths open while swimming, which is known as ram ventilation32. They have to come up with inventive ways to sleep because they have to swim nonstop. Ram ventilating fishes may be able to take use of currents, allowing water to be pushed over their gills and allowing them to breathe, according to scientists. Rather than unihemispherically sleeping, it’s more likely that they doze off with one eye open, keeping a watchful check on the surrounding environment.

The study of animal sleep is a fascinating one, and new discoveries are being made all the time.


How Long Do Other Animals Sleep Compared to Humans?

There is a wide range in the amount of sleep that animals require. During a 24-hour period, neonates need up to 17 hours of sleep, whereas adults need 7–9 hours of nightly sleep2.

The amount of sleep many animals require is far more than that required by humans. Three-toed sloths and two-toed sloths both require more than 16 hours of sleep every day to function properly. Other long sleepers include the small brown bat (19.9 hours), the North American opossum (19.4 hours), and the enormous armadillo (19.9 hours) (18.1 hours).

Large land mammals, on the other hand, may sleep only a few hours a night. Three to four hours a day, cows and horses sleep for an average of three to four hours a day.4

For one thing, animals’ sleep cycles differ from ours in terms of duration and division. People’s sleep patterns change beyond the early years of childhood and tend to be either monophasic or biphasic, lasting for only part of the 24 hours in a day, maybe with a short nap in the middle. It is not uncommon for animals to sleep many times during the course of a 24-hour period, which is known as polyphasic sleep. As an example, dogs sleep between 9 and 14 hours a day on average yet only sleep for a total of 45 minutes at a time. There are 78-minute intervals of sleep in a cat’s day.

How Does Human Sleep Compare With the Sleep of Other Animals?

Humans and other animals don’t just have different sleep needs. Additionally, sleep cycles and the processes that take place when one is asleep may be different. Many factors, including brain size, food, body mass index (BMI), and social hierarchy7, play a role in these disparities in sleep patterns and demands. Most predators’ sleeping patterns are either diurnal — occurring largely at night, like in humans — or nocturnal, like tigers, which occurs primarily during the day.

REM Sleep in Humans and Animals

As humans drift off to dreamland, what exactly is going on? Our bodies go through a four-stage cycle while we sleep. At each stage, the body undergoes physical changes, such as a drop in temperature and heartbeat. Rapid-eye movement (REM) sleep is the most active stage of sleep, with different types of brain activity occurring at each stage. Muscle twitching and waking-like electrical brain patterns are also common in this stage of sleep, along with the fluttering of the eyes behind the eyelids (electroencephalogram or EEG8). Humans can dream at any stage of sleep, although REM sleep is the most common time for this to happen.

Is REM sleep common to all animals? REM sleep is experienced by many terrestrial animals, including primates, as well as several birds, reptiles, and aquatic invertebrates. The length of time spent in rapid eye movement (REM) sleep varies greatly among animals. Elephants don’t get enough REM sleep since they sleep so little. The REM sleep time of a domestic cat, on the other hand, can reach up to eight hours daily.

In certain creatures, such as dolphins and whales, REM sleep does not manifest itself in normal ways. However, whales show some jerking of their muscles that could be a sign of REM sleep.

REM sleep cycles are also unique to each species. REM sleep occurs every 90–120 minutes in humans, whereas it occurs every 10–15 minutes in mice.

The Brain During Sleep in Humans and Animals

A wide variety of methods are used by animals to get the sleep and rest they need. Some animals only sleep in one hemisphere of the brain at a time, unlike humans, who sleep in both hemispheres. So, for instance, in dolphins, it appears that only one half of the brain exhibits sleep features, while the other half exhibits wakeful characteristics. The water’s surface provides them with a source of oxygen as they sleep.

Lack of Sleep in Humans and Animals

Humans are vulnerable to mood swings, memory loss, disease, and even death if they don’t get enough sleep. Many other animals, such as rats, face similar dangers. Rats that aren’t getting enough sleep lose weight and become sick. Rats die after just a few weeks of going without adequate sleep.

How Does Human Sleep Compare To Other Primate Sleep?

Humans slept the least out of 30 different species of primates in a 24-hour period9, according to the research. Some scientists believe that humans’ reduced sleep habits can be traced back to a time when they were subjected to greater threats to their survival, such as being preyed upon10, and the advantages of social engagement. They may have had an effect on present sleep habits. Humans now have shorter, deeper sleep with more REM cycles than any other primate in the animal kingdom. According to this theory, human sleep is more “efficient” than that of monkeys.

Primate nest-making, or bed-making, is a commonality among all primates. Great ape species11 engage in nest building, while the types, sizes, and placements of nests differ. It is speculated that the last common ancestor of humans and other primates was a nest builder because of the ubiquity of nest building. As a place of rest and better sleep, primate nests changed from being feeding stations for primates. According to this theory, human ancestors had to shorten their sleeping hours because ground sleeping rendered them more vulnerable.


What Are Some Sleep Disorders That Are Also Present In Animals?

Human sleep is often compared to that of other animals including mice, rats, cats, and dogs in studies like these. Multiple species of animals have been found to be susceptible to sleep disorders or to mimic the symptoms of human sleep disorders, according to this study.

  • Narcolepsy. When researchers studied both dogs and mice, they discovered a genetic abnormality that caused both animals to suffer from narcolepsy12. It is hypocretin, which regulates wakefulness, that is damaged in the mutation. Because of this discovery, scientists are working to create medications that imitate hypocretin in order to treat narcolepsy and other sleep disorders.
  • Apnea (a.k.a. sleep breathing when asleep). Sleep apnea has been studied in mice to better understand the role that aging, obesity, and lack of conscious muscle control play in the condition. Snoring, irregular breathing, and frequent interruptions in sleep are all common symptoms of sleep apnea in English bulldogs. It has been determined that pharmaceutical treatment for sleep apnea can be achieved with these dogs. Obese Yucatan minipigs have also been utilized as a model for obesity-related sleep apnea.
  • Insomnia. Stressed-out rats show insomnia-like symptoms in humans who are exposed to the same conditions. Also, sleeplessness may be modeled in rats by administering caffeine to the animals. When looking for animal models of insomnia, it is difficult to identify if an animal is sleeping on purpose or if they are attempting to sleep but failing.
  • Anxiety-Induced Diarrhea (Rls). Dopamine- and iron-deficient mice are able to imitate the sleep disturbances experienced by RLS sufferers. Researching RLS in animals presents a problem due to the difficulty in verifying the animal’s perception of pain.

In addition, studies on monkeys’ circadian rhythms may yield significant knowledge for humans. More and more studies are pointing to the fact that the circadian system develops neonatally13 before an infant is born. In the early stages of life, baby primates have responded to light. Exposure to low light may help regulate the growing system, according to this theory. Humans may benefit from this research because many sleep and overall health issues are caused by a disruption in circadian rhythms.

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