The Connection Between Animal and Human Sleep Update 09/2022

What time of day do animals go to sleep? Absolutely! Animals, like people, necessitate rest and sleep in the same way. In most animals, sleep and wakefulness are regulated by an internal 24-hour clock known as a circadian rhythm or biological 24-hour clock.

Slumber is a necessity for human health. Humans can recharge, consolidate their memories, and restore their bodies when they sleep. Sleep is also essential for the proper development of children and infants. Animals sleep despite the fact that it puts them at risk, according to experts1, leading them to assume that humans do as well. The advantages of getting enough shut-eye outweigh the disadvantages.

How Mammals Sleep

In order to conserve energy and replenish mental and physical strength, mammals sleep. Age, body size, environment, nutrition, and the safety of the sleep place all play a role in how much sleep an animal needs. The amount of sleep a mammal requires may differ depending on whether it is a land animal or an aquatic one.

Each mammal’s REM and non-REM sleep cycles are unique, as are the amounts of time spent in each. Mammals, like humans, show indications of REM sleep, which suggests they have the ability to dream3.

Sleep in mammals is frequently divided into two types: monophasic and polyphasic. Monophasic sleep4 refers to animals that sleep for a short period of time at a time. A good illustration of a monophasic sleeper is a human being. 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. A greater number of animals are polyphasic sleepers because they need to keep an eye out for predators at all times. Even if dangers are avoided, animals can rest peacefully in a single phase. When marmosets sleep in the trees with their family, they are able to achieve monophasic sleep because they feel safe.

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. Giraffes sleep for an average of 4.6 hours each day5. Even though they sleep a lot during the day, giraffes spend most of their time sleeping at night. The sleep cycles of giraffes are short, lasting no more than 35 minutes, and they are able to sleep both standing and laying down.

Also, elephants do not get enough rest throughout their long lives. In certain cases, researchers have reported a total sleep time of barely two hours each day6. When an elephant’s trunk stops moving, scientists know it’s time to sleep. As with giraffes, elephants, because of their enormous size and frequent need to graze, may only get a few hours of sleep each day. There’s also a possibility that the amount of time they spend awake increases their vulnerability to predation, which could explain why they sleep so little. Research shows that elephants are capable of trekking for nearly two days straight with no rest.

A horse’s sleeping habits are similar to those of a giraffe or an elephant. However, as soon as they enter REM sleep, they fall to the ground7.

Dogs, on the other hand, spend more than a third of their waking hours asleep9. At the same time, another 21 percent of their day is spent in an uneasy state of sleepy alertness. 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?

Mammals and some other species go into hibernation during the winter months. For months at a time during hibernation an animal consumes very infrequently, moves very infrequently, and excretes waste only during brief episodes of mild wakefulness.

A widespread misperception about hibernation is that it’s an extended period of sleep. A state of torpor is a more accurate description of hibernation. In torpor, animals’ metabolism, heart rate, core body temperature, and respiration rate are all reduced10. During hibernation, these effects are more apparent than they are during normal sleep.

In times of extreme weather or scarcity, 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. To conserve energy, some bats may remain in the area and enter torpor for a few hours on a cold day or hibernate for six months until the insects return in the spring.

Bears are often associated with hibernation, however bears’ hibernation is distinct from the conventional hibernation13. Bears can go up to seven months without eating, drinking, urinating, or defecating when in torpor, although their body temperature remains practically constant during this time. Hibernating animals include the Madagascan fat-tailed dwarf lemur13; European hedgehogs14; ground squirrels15; and pygmy possums16.

Marine Mammals and Sleep

Widowed walrus is like a bat on land when it comes to sleeping time. They can sleep in water and on land, but they prefer to sleep on land for longer stretches of time17. When walruses go to sleep in the water, they either rest on the bottom, float on the surface, or lean against a surface while standing. Tusks can even be used to sleep on an ice floe. Elephants can go days without sleeping, and so can walruses. Recharging isn’t necessary for up to 84 hours of swimming.

Sperm whales, like walruses, have unusual sleeping arrangements. They are actually able to sleep in a more upright position than they are used to. It took a passing ship bumping against them to wake up the scientists, who had been keeping a close eye on them.

All marine mammals, including dolphins, eared seals, and manatees, sleep unihemispherically19. Due to the fact that only one side of their brains shuts down during unihemispheric sleep, these animals are able to get the rest they need while also keeping an eye out for danger.

How Birds Sleep

One part of a bird’s brain goes to sleep while the other remains awake. A person’s sleeping hemisphere-associated eye is the only one that is closed during sleep.

Unihemispheric sleep protects birds from predators by allowing them to fall asleep in one hemisphere. Mallard ducks, for example, can sleep in a row. They will be most likely to sleep unihemispherically, with their outward eye still open, whilst the ducks in the centre will sleep with their eyes shut.

Migratory birds’ extended flights are made possible by unihemispheric sleep. Even when gliding, they may be able to get some shut-eye. These birds have been reported flying non-stop for 200 days20.

Migrating birds, on the other hand, sleep less than non-migrating birds. While migrating, white-crowned sparrows, for example, sleep only one-third as much as they do when they are not. They’ll make up for lost sleep by taking micro-naps throughout the day and by perching. Tendons in their feet lock into place21 when they perch, allowing them to sleep with little effort. It is possible for bats to sleep on their backs because they have a locking mechanism.

How Reptiles and Amphibians Sleep

When it comes to sleep, reptiles and amphibians are among the least researched animals22. 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 seconds23, new evidence suggests that reptiles like lizards may also go through these stages of sleep.

Lizards, like other creatures, pick sleeping spots where they’ll be safest. With their heads turned toward the route of an approaching predator, they may sleep on leaves. Crocodiles25, for example, sleep unihemispherically so that they can keep an eye out for any threats and prey they can consume while they sleep.

One eye is open in a crocodiles while the other is closed in a snake since snakes have no eyelids. In order to digest its food, snakes may sleep for days at a time.

Western fence lizards and cottonmouth snake brumate. Like hibernation, the brumation of reptiles occurs in reaction to cooler temperatures and decreased food availability. A salamander’s brumation period can last up to 100 days27.

The ability to enter a state of torpor in arid regions is also an option for amphibians to survive. Estimation28 is the name given to this condition. In estivation, green-striped burrowing frogs go into hibernation and stop moving and eating for months.

How Fish Sleep

What about fish? But it’s definitely more acceptable to label what fish do “rest” instead. When fish are resting, their activity level and metabolism fall down, but they are still aware enough to protect themselves from harm. They rest in the mud, sand, or coral, or they float like zebrafish30. They don’t eat. To ensure their safety at night, parrotfish create a mucus cocoon around their bodies.

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.

Fish and sharks, on the other hand, use a technique called ram ventilation32 to keep their mouths open while swimming in order to breathe their gills. They have to come up with unique ways to get some shut-eye 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. It seems more likely, however, that they sleep unihemispherically, allowing one eye to remain open and keep a watch on their surroundings while they sleep.

There is a lot to discover about how animals sleep, 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, a human infant requires up to 17 hours of sleep, while an adult need 7–9 hours of sleep per night2.

Many animals, on the other hand, need a lot more shut-eye. 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).

Some huge land mammals, on the other hand, require hardly no sleep at all. Elephants in Africa sleep an average of two hours per day, while cows and horses sleep between three and four hours each day6.

Animals not only sleep for longer periods of time than humans, but they also sleep in different patterns. After adolescence, human sleep tends to become monophasic or biphasic, lasting for only part of the 24 hours in a day, with the occasional afternoon nap. Sleep in animals, on the other hand, is commonly separated into multiple periods of time throughout the course of a 24-hour day. Dogs, for example, sleep between 9 and 14 hours per day, but only sleep for 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?

People and other animals differ in the quantity of sleep they need. The processes that occur in the brain while you sleep, as well as your sleep cycle, can vary. Some of the reasons for these variations in sleep patterns are related to our individual variances in brain size, diet, BMI, and socioeconomic class7. Predatory animals, such as tigers, sleep for extended periods of time, whether they are nocturnal (mainly at night) or diurnal (mostly during the day).

REM Sleep in Humans and Animals

Sleeping individuals have a lot of time to think. Our bodies go through four stages of sleep during the course of a night’s rest. At each stage, the body undergoes physical changes, such as a drop in temperature and heart rate. Each stage of sleep has a different sort of brain activity, with the most activity occurring in the fourth stage, known as rapid-eye movement (REM) sleep. Muscle twitching and waking-like electrical brain patterns are also present during this stage of sleep, in addition to the fluttering of the eyes behind the lids (electroencephalogram or EEG8). People are more likely to have vivid dreams during REM sleep than any other stage of the sleep cycle.

Is REM sleep the same for all animals? REM sleep is common in a wide variety of animals, including primates, reptiles, birds, and aquatic invertebrates. The quantity of REM sleep that a species gets differs greatly from one another. Elephants don’t get enough REM sleep since they sleep so little. House cats, on the other hand, can sleep in REM for up to eight hours every day.

Dolphins and whales, for example, don’t exhibit the standard sleep-related behaviors. The jerking of whales’ muscles, however, may be a sign of REM sleep.

REM sleep cycles are unique to each species, as well. Mouse REM sleep occurs every 10–15 minutes, but humans get REM sleep every 90–120 minutes or so while sleeping.

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’ brains only sleep in one hemisphere at a time, unlike humans. For instance, in dolphins, only one half of the brain appears to exhibit sleep features while the other half exhibits wakeful qualities. As a result, they are able to sleep by swimming to the water’s surface and taking a breath.

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 only a few weeks of not getting enough sleep.

How Does Human Sleep Compare To Other Primate Sleep?

Humans slept the least in a survey of 30 primates over a 24-hour period9. Why humans sleep less than other primates has been hypothesized as a result of heightened survival pressures, predatory hazards, and the positive social effects of human connection. Current sleep habits are most likely the result of these events. Compared to other primates, humans’ sleep cycles are longer, deeper, and include more rapid eye movement (REM). Sleep in humans is said to be “more efficient” than in primates.

Humans and other primates have one thing in common: they build nests or beds. Great ape species all create nests, although the shape, size, and location of each nest varies. It is speculated that the last common ancestor of humans and other primates was a nest builder because of the ubiquity of nest building. Even though primate nests used to be for feeding, they have developed into places of rest and relaxation that aid in sleep. Because ground sleeping rendered our ancestors more susceptible, sleep durations had to shorten as a result, according to this theory.

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

Mice, rats, cats, and dogs are widely used in studies comparing the quality of human sleep. Animals can suffer from sleep problems or exhibit symptoms similar to those of human sleep disorders, according to this study.

  • Narcolepsy. Narcolepsy has been linked to a genetic abnormality in both dogs and mice, thanks to studies conducted on both species12. The neurons that create hypocretin, the hormone that regulates wakefulness, are wiped out by 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. snoring) during sleep Mice have helped researchers better understand how sleep apnea is affected by factors such as age, weight, and the ability to operate muscles without conscious effort. Snoring, breathing problems, and frequent awakenings are all symptoms of sleep apnea in English bulldogs. Sleep apnea is a condition that can be treated with medication. The sleep apnea caused by obesity has also been studied in Yucatan minipigs.
  • Insomnia. When rats are placed in a stressful setting, they display sleep-related symptoms. Caffeine-induced sleeplessness is also modeled in rats. 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.
  • Syndrome of the Squirmy Legs (Rls). Both dopamine-deficient and iron-deficient animals are able to simulate the sleep disturbances experienced by persons with RLS. Researching RLS in animals has the disadvantage of relying on patient reports of discomfort, which makes it difficult to corroborate in animals.

Additionally, studies on monkeys’ circadian rhythms may yield helpful knowledge for humans. It’s becoming more and more clear that a baby’s circadian rhythm begins to take shape even before he or she is born. In the early stages of life, baby primates have responded to light. Exposure to low light is thought to have a regulating effect on the growing system. The findings of this study may be useful in human infant care in the future because circadian rhythm disturbances are at the root of many sleep and health issues.

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