Birds that nap while flying, the surprising ways in which animals sleep

Many ways of sleeping
Monophasic sleep in humans and great apes
Sleep cycles vary from one animal species to another
Dogs
Dogs sleep around 12 hours a day
Giraffes
Horses
Elephants
Koalas
Bats
A way to escape their predators
Hedgehogs
Hedgehogs hibernate for almost four months
Dolphins
Dolphins switch sleep between brain hemispheres
Sea lions
How do birds sleep?
Birds can lock their claws like a handbrake
One-sided hemispherical sleep
Migratory birds
Napping while flying
Fish sleep with their eyes open
Some fish camouflage themselves while they sleep
Many ways of sleeping

Sleeping is a necessity for humans and for most animals. From duration, depth of sleep, position and brain activity, animals sleep in ways that are about as varied as the animal kingdom itself. Take a look at the many different ways in which animals sleep!

Monophasic sleep in humans and great apes

Like all other great apes, humans have so-called "monophasic" sleep, that is, we sleep for a long interval over a 24-hour period. Humans have, on average, a cycle of eight hours of sleep per day, just like orangutans.

Sleep cycles vary from one animal species to another

But sleep cycles vary completely from animal to animal, both in duration and depth.

Dogs

Most mammals have polyphasic sleep: their sleep time is divided into several phases, and they alternate between activity and rest throughout the day. This is the case of the adult dog.

Dogs sleep around 12 hours a day

Dogs sleep about twelve hours, spread over the day, and alternate between phases of deep sleep and paradoxical sleep (phase in which they dream).

Giraffes

Giraffes have the ability to doze off while standing up. However, they just need about 4-5 hours of sleep daily. Its cycle consists of both three to four hours of deep sleep, and naps of 20 minutes maximum.

Horses

On average, horses sleep 3 to 5 hours a day. They take several naps in a standing position throughout the day, but lie down on the floor when they enter REM sleep. Their sleep cycle is divided into fairly short intervals, which last about twenty minutes.

Elephants

The bigger and taller an animal is, the less sleep they require, as they feel more satiety, which keeps them awake. Wild African elephants sleep an average of two hours a day. Most of the time they sleep standing up, but lie down to sleep every three or four days.

Koalas

Koalas are nocturnal animals that sleep during the day and are awake at night. They are heavy sleepers, and even sleep for part of the night too. On average, koalas sleep between 18 and 20 hours a day, on a tree branch.

Bats

Bats have a peculiar way of sleeping: upside down. This is an ideal posture for this small flying mammal, because its legs are too weak to hold it upright, and it does not expend any energy hanging on, thanks to a tendon located in its claws.

A way to escape their predators

Hanging upside down from trees also allows them to escape their predators on the ground, such as cats or snakes. It is in this position that bats sleep about 20 hours a day.

Photo: Riiz/Unsplash

Hedgehogs

This semi-nocturnal animals sleep for most of the day and hunt at night for food. But they are unique in that they hibernate for several months of the year.

Hedgehogs hibernate for almost four months

In October, hedgehogs store up to 40% of their body mass and build a small cozy nest, sheltered from the cold winter. Its physiological needs decrease, its breathing slows down and they enter a phase of hibernation which lasts almost four months.

Photo: Tadeusz Lakota/Unsplash

Dolphins

All cetaceans sleep with one eye open, including dolphins who must remain active to go to the surface to be able to breathe. This is why, as strange as it may seem, when the dolphin is resting, only half of its brain is asleep.

Dolphins switch sleep between brain hemispheres

According to researchers, dolphins sleep in episodes of less than an hour, repeated ten times a day. That is five episodes per day for each brain hemisphere.

Sea lions

Like dolphins, sea lions only sleep on one cerebral hemisphere at a time while they’re swimming. However, when they are on dry land and they sleep, both their brain hemispheres will rest.

How do birds sleep?

Contrary to what one might think, birds do not sleep inside a nest; its purpose is only to protect their eggs. The majority of birds sleep in hollow walls or by remaining perched on a branch or an electric wire.

Birds can lock their claws like a handbrake

Even though this posture does not seem comfortable, it is in fact ideal for birds, which have flexor tendons on their legs that lock their claws, like a handbrake. The tendon unblocks when the bird wakes up.

One-sided hemispherical sleep

Generally, birds keep one eye open when they sleep because only part of their brain is asleep. This allows them to stay alert if a predator gets a little too close. Logically, nocturnal birds sleep during the day, and diurnal ones at night.

Migratory birds

Some migratory birds make stops to rest and eat during their journey. But some species travel thousands of kilometers without ever landing. This is the case, for example, for the black swift, which flies for ten months in a row, without stopping.

Napping while flying

But then, how do they rest? According to researchers, the black swift rises very high in elevation at dawn and dusk, and then slowly descends. It is during this phase of descent, while gliding, that the black swift sleeps.

Fish sleep with their eyes open

Fish sleep with their eyes open for the simple reason that they generally don't have eyelids. Fish have periods of inactivity of a few minutes rather than phases of sleep. Their breath and heartbeat slow down but they remain on the lookout for predators.

Some fish camouflage themselves while they sleep

Some species of fish change color while they sleep, to camouflage themselves and go unnoticed by their predators. This is the case, for example, with the cuttlefish, which blends into its environment to avoid sharks.

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