Science of Animal Slumber: Most & Least Sleepy Species
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Sleep is a way of recharging energy, and it’s something that almost every living creature on the planet does. As humans, we’re accustomed to sleeping at night and being active during the day, but where animals are concerned, sleep patterns can vary dramatically.
Do All Animals Need Sleep?
Most people assume that sleep is essential, and while this is somewhat true, it’s difficult to ascertain whether true sleep is indeed essential to survival. The reason for this is that scientists have yet been unable to properly study sleep in animals other than mammals and birds. While periods of rest and reduced activity have been noted in things like reptiles and insects, it’s not the same kind of sleep we associate with mammals.
This begs the question of whether all animals need to sleep. There is some suggestion that many creatures will sleep simply when they have nothing else to do. If my pet cat is anything to go by then I could easily get on board with this idea!
While research is limited, it is thought that some reptiles may experience REM sleep but in much shorter waves than mammals; some being just 80 seconds in length. While this may suffice for a lizard, such a short period of REM sleep would not do you or I any favors.
So, it really all comes down to the individual animal. Some may get by with much shorter periods of sleep while others require months of hibernation. There are even some animals, like the crocodile that have the ability to sleep half of the brain while the other side remains awake to be alert to threats or a potential meal.
Even animals without a brain need to sleep and this is something that a lot of people aren’t aware of since sleep is often associated with recharging the brain. But take the jellyfish as an example. These creatures are literally brainless and yet still enter into a state of rest and studies have shown that they are 30% less active at night.
Insomniac Animals: Creatures that Sleep the Least
As I have mentioned, there are some animals that don’t need quite as much sleep as others. These varying needs are what make some creatures so incredibly fascinating.
1. African Elephant
It might be easy to assume that, being so large, the African elephant needed a good amount of sleep to recharge. But the opposite is true. In fact, these huge mammals only need around two hours of sleep each day; less than any other mammal.
African elephants may sleep a little longer each day when in captivity, but this is usually no more than four to six hours. The majority of their sleep is taken at night, and they don’t even enter REM sleep every night.
What’s interesting is that, during studies of two female African elephants, it was noted that the pair slept on their feet most nights. It’s thought that this could be why they are unable to enter REM sleep as frequently. They could go three to four nights without lying down to sleep!
2. Fruit Flies
Fruit flies only live for around 45 days, but they might only ever have one sleep during their lifetime! That’s because, compared to humans, who can survive just 10 days without sleep (at the max), fruit flies can go a whopping 40 days!
But how on earth can these small insects manage that long without getting some ZZZs? Apparently, it’s all down to taurine. Taurine is a common ingredient in energy drinks that scientists have discovered in the brain of fruit flies, a massive clue into how they manage to stay awake.
All that said, while fruit flies have the ability not to sleep for long periods, for the most part, they’ll sleep for around 16 hours a day. It’s also been noted in studies that lonely fruit flies tend to spend less time sleeping.
3. Dolphins
Dolphins are known for being one of the most intelligent animals on the planet, so you’d think that they needed a lot of sleep. While they do need around 8 hours of sleep a day, dolphins do it rather differently to humans.
Instead of entering a total state of rest or inactivity, dolphins engage in what is known as unihemispheric sleep. When this happens, one side of the brain goes into rest mode while the other stays alert. This allows the dolphin to keep an eye out for predators and continue surfacing for air.
Some have argued that this is not a true type of sleep, but according to scientists, it is because dolphins seem to have developed this ability as opposed to eliminating sleep entirely.
4. Great Frigatebird
The great frigatebird can spend weeks in the air as it soars over the ocean in search of food. Of course, spending all of this time in flight uses up a good deal of energy, and the bird will need to recuperate. But with nowhere to land, these incredible birds sleep while still in the air!
This ability is once again thanks to unihemispheric sleep, which allows the birds to continue flying at the same time as taking a rest; one half of the brain at a time. They don’t sleep for long, however. During a ten-day flight, each bird might only sleep for 0.7 hours a day, according to research.
Even more interesting is that this 0.7 hours doesn’t happen all at once. In fact, each period of unihemispheric sleep may last as little as 12 seconds.
5. Giraffes
Giraffes are grazing animals which means that most of their time is spent nibbling on food. Of course, they still need to sleep, but generally, an adult giraffe will only have around 4.5 hours of sleep each day.
The tallest animal on earth doesn’t take its sleep in all one go but will split it into short naps that may only last around half an hour.
Sleeping both on their feet and recumbently, giraffes will usually take their naps between midday and 4 pm during the day and between 2 am and 4 am through the night.
6. Horses
Horses require much less REM sleep than humans. In most cases, they can manage with just 30 and 60 minutes each day. However, they can only achieve this when they sleep lying down, but if you’ve ever watched a horse resting, they’ll sometimes remain on their feet.
They do this mainly as a protective measure. If they’re taking a short nap on their feet, they are in a much better position to run away should a threat approach. What’s more, because of their size, sleeping while lying down can restrict their blood flow, so it’s generally healthier for them to remain upright.
The good news is that this isn’t uncomfortable or challenging for a horse. With specially adapted kneecaps that lock the hind legs into position, horses can sleep standing up without any issues.
7. Swifts
It would appear that unihemispheric sleep is something of a craze in the animal kingdom, with swifts having adopted this type of sleep as well. And it doesn’t come as much of a surprise that they’d have to sleep this way when you consider that they hold the record for staying in the air for the longest time; up to 10 months in a single flight!
During studies, it has been noted that some individuals won’t land for three months at a time. For this reason, swifts will not only sleep in the air but will also feed while airborne!
Flying at altitudes of up to 10,000 feet (3,048 meters), it’s thought that swifts will take short naps as they ascend and descend at dusk and dawn.
8. Sheep
For an animal that is associated with sleep (counting them to drop off), it might come as a surprise that sheep don’t actually sleep all that much. Having just 3.8 hours of sleep on average each day, sheep are very active animals. What’s more, only around 2% of that sleep is REM.
The reason for this light sleep is as a defense mechanism. Sheep are prey animals and going into a deep sleep would make them vulnerable so they tend to take light naps in short bursts. When they do sleep, they often huddle together because after all, there’s strength in numbers.
9. Bullfrog
Back in the 1960s, it was believed that bullfrogs didn’t sleep at all. However, since then, scientists have performed shock tests and discovered that there isn’t enough evidence to suggest that these animals never sleep.
What’s more, since then, scientists have better been able to understand animal sleep and realize that it doesn’t just come in one form. The bullfrog hibernates and so takes most of its deep rest during this period.
However, when they are in their active months, bullfrogs engage in short periods of rest, but during this time, the bullfrog never becomes completely unresponsive.
Sleepyhead Animals: Creatures that Sleep the Most
While some of the animals I have discussed so far don’t need much sleep at all, there are those on the other extreme end of the spectrum that require a serious amount of shut eye!
1. Koalas
Cute and cuddly koalas are the perfect teddy bear, aren’t they? But not only do they look like something a child would use for sleep, they’re pretty heavy sleepers themselves! On average, the koala will sleep anywhere between 18 and 22 hours a day!
The reason for this is that they feed on a diet that requires a serious amount of digestion and this uses much of their energy. It’s essential that they maintain a low metabolic rate, and the best way to do this is by sleeping. However, this is incredibly uncommon in herbivorous animals and is usually something only seen in carnivores, so they’re pretty unique.
During the few hours a day that they’re awake, koalas will graze and maybe mate. They don’t drink a lot of water since they get most of their moisture from the leaves that they eat.
2. Big Brown Bat
The big brown bat spends as many as 19 hours a day sleeping while suspended from trees, the roof of caves, or even on rock faces.
But what is the need for such a lengthy amount of snooze time? Well, it’s thought that sleeping for most of the day keeps the bats out of harm’s way but will also allow them to be awake at the same time as their prey, making feeding a lot easier.
For the most part, big brown bats are crepuscular which means that they are most active around dusk.
3. Python
Pythons are nocturnal animals meaning that they are most active during the night. They have special adaptations that allow them to hunt at night, such as improved vision. Just like other species of snake, however, pythons do not have eyelids so, when they sleep, their eyes remain open.
Some species of python, such as the ball python, are very popular pets and owners can sometimes have trouble telling whether the snake is awake or asleep. When sleeping, pythons will stay in the same position for long periods of time and will become less active, including stopping flicking their tongues.
What’s seriously impressive is that these snakes may sleep for up to 20 hours at a time. They usually do this after feeding as a way of digesting a large meal.
4. Giant Armadillo
On average, the giant armadillo might sleep for up to 18 hours at a time. They spend most of the day hiding in a burrow and tend to only come out at dusk and dawn to forage for food. While they’re not hugely social animals, it’s not uncommon for them to burrow in groups to stay warm in cooler weather as well as owing to the fact that these animals are unable to regulate their own body temperature very well.
When they come out to hunt, they have to make use of their sense of smell as their eyesight is not great. They are also equipped with sharp claws that allow them to dig in order to find things like insects.
5. Owl Monkey
Found in the South American nations of Brazil and Venezuela, the owl monkey, sometimes called the night monkey, can sleep for as long as 17 hours a day. This nocturnal species is the only truly nocturnal primate, with the exception of the Azara’s night monkey. Although the latter isn’t 100% nocturnal and only has occasional bursts of night time activity.
Owl monkeys form strong pair bonds but will also spend time in groups especially when the temperature is below 95°F (35°C) when they can be seen huddling during sleep.
6. Opossums
The opossum certainly doesn’t waste a moment when it comes to sleeping, and there are records of these creatures sleeping for more than 18 hours a day!
When they’re born, each opossum might weigh less than a dime and is incredibly small. What’s more, litters can contain up to 20 young, and gestation takes just 2 weeks. Scientists think that the fact these animals are born so underdeveloped could be linked to their need for lengthy sleep sessions.
During their juvenile days, the young will spend most of their days eating and sleeping. On the off chance that they reach adulthood, they’ll be better equipped to survive. But this isn’t exclusive to the opossum. In fact, scientists believe that animals that are born underdeveloped are more likely to require more REM sleep than those that are more developed at birth.
7. Sloths
When you think of a slow, sleepy animal, the sloth is one that might instantly come to mind. These animals spend up to 15 hours a day snoozing but studies have shown that, despite their reputation, they’re no lazier than the average human teen!
Moreover, while sloths might seem as though they do nothing but sleep, it’s been demonstrated that they spend less time sleeping in the wild compared to captive sloths. In the wild, they usually only sleep for 8 to 10 hours a day. Of course, they’re still incredibly slow, but there’s a good reason for this.
Sloths are slow in order to survive and it’s all to do with body temperature and metabolism. By moving slowly in all temperatures, sloths are able to keep their metabolism low without using up too much energy.
8. Cat
The term cat can refer to a wide range of creatures within the feline family. The male lion is a prime example of a cat that sleeps a lot, with most individuals snoozing for up to 20 hours per day. The female African lion isn’t too far behind and may sleep for up to 18 hours a day.
Domestic cats are well known for their ability to snooze the day away and, on average, your pet moggy might sleep for as long as 15 hours a day! They’re more likely to rest for longer periods when they’re kittens, whereas ‘teenage’ cats might be significantly more active. Of course, as they age, they’ll need to rest more and may revert back to long sleepy sessions.
But why do cats need such long periods of sleep? For starters, cats are crepuscular meaning that they are most active at dusk, and sometimes dawn. Moreover, they have an ingrained desire to rest between hunting, so they conserve energy for finding a meal. This is a trait seen in many carnivores.
Animals that Sleep Standing Up
In a lot of cases, animals will sleep standing up. Horses are a prime example of this and they do it because it makes it easier for them to get away when faced with danger. Imagine the large body of a horse having to pull itself up from recumbent sleep; it would take some time. That time could mean the difference between becoming prey and getting away.
So, while they do sometimes sleep lying down, horses will often have a light nap while still on their feet. This is achievable thanks to their stay apparatus which is a group of tendons and ligaments designed to lock the joints in the hind legs into position so the horse doesn’t fall over when sleeping on its feet.
But horses aren’t the only animals that sleep standing up. Look at the flamingo, for example; this is potentially one of the most well-known standing sleepers. Just like horses, their legs have special ligaments that lock them into place. They do this because of the environment they live in. The caustic salt flats on which they spend their days give them no place to sit or lie down, so standing is the only option.
It could be said that all birds sleep standing up as they perch on tree branches using their feet. However, this is often disputed.
Many land mammals, such as the zebra, giraffe, and elephant, will all sleep standing up. While they’re capable of sleeping on the ground, they prefer to take short naps on their feet as a protective measure against predators. While they have specially adapted bodies to remain upright when sleeping on their feet, these animals cannot experience REM sleep in this position as the muscles lose strength and prevent them from staying standing up.
Do Animals without Brains Need Sleep?
Sleeping recharges the brain and that’s why a lot of animals do it. But there are some creatures out there that don’t have brains at all so why would they need to sleep?
Knowing that the REM activity of sleep occurs in the brain, one would assume that something like a jellyfish wouldn’t even have the ability to sleep. But research has shown that this isn’t the case. When looking at the cassiopeia jellyfish, researchers found that the animal exhibited sleep-like activity.
While jellyfish might not sleep in the same way that humans do, owing to the lack of a brain, they still enter into a state of reduced activity. Studies have shown that their pulse rate slows during the night; in some cases to as little as 39 pulses a minute compared to 58 times a minute during daylight hours.
And it isn’t just jellyfish that have shocked scientists. The hydra, a tiny creature without a brain, has been demonstrated to display activity conducive with sleep. Again, it may not be the same as human sleep but it’s a period of rest.
What’s most fascinating, however, is the notion that sleep-like behavior may have developed before the brain. With this in mind, it’s less of a surprise that brainless creatures engage in sleep.
