We All Need Rest But… Do ALL Animals Really Sleep?

Animal Sleep
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While there is no definite answer as to whether all animals sleep as the entire animal kingdom is full of mystery and wonders and has still species yet to be discovered, it is proven that not all animals sleep in the same way. Sleep is an important part of most creatures and serves an evolutionary purpose for most creatures. Sleep patterns differ among animals due to the differences in environment, protection mechanism, and food supply.

Significance of sleep in animals

Energy conservation

Some species sleep during certain seasons, in winter it is called hibernation, and in summer it is called aestivation. This is to conserve energy as a survival strategy when food is scarce for the next season. Animals in hibernation or aestivation go without eating, defecating, or urinating. Before hibernating, the creature’s body changes such as dropping body temperature, blood circulation, brain action, and heart rate.

Learning and growth

Sleep helps animals learn and consolidate memories. Animals with bigger brains need more REM sleep. On the other hand, it has been observed that greater REM sleep leads to cognitive growth in animals.

How do animals sleep?

Different animals vary in their sleeping patterns and positions this is due to many factors, one of which is their body structure and environment. Different animals developed their sleeping habits as a means to protect themselves from predators while they sleep. It is no wonder that some animals sleep while standing as it will be easier to run away when there is danger.


Mammals experience sleeping with different types, light sleep, deep sleep, and REM sleep. Mammals differ in sleep lengths but they can sleep several times every day or polyphasic sleeping. Generally, sleep comes more at nighttime.

Marine mammals

Whales, dolphins, and seals are marine mammals that have a different type of sleeping method and pattern. They have the ability to maneuver in 1 brain hemisphere at a time. It means that they can sleep while still floating and in some cases navigating through waters.


Migration is part of the life of birds this entails constant flying without stopping. Migratory birds have unihemispheric sleep that assists them to sleep while flying.

Some birds sleep uni hemispherically for protection. For example, ducks sleep lined up in a row. Ducks on either side sleep with one eye while the studs at the center sleep with both eyes closed.


Reptiles do not have cerebrums like mammal brains that is why they sleep differently. Lizards for example have a different sleep cycle of 80 minutes each of their 350 cycles each night.
Also, reptiles like snakes do not need to close their eyes to sleep. For humans closing our eyelids guards our eyes while we sleep and keep it moist. With reptiles, they have transparent scales that serve as their eyelids and shed them like the rest of their skin.


Fish generally appear motionless when hovering close to the bottom of the water when they are sleeping. Their sleep pattern depends on their environment and adapts their sleep on the interior lighting of the surroundings.

Sharks sleep differently because they need to keep swimming to continuously vent their gills. So they do not shut their eyes when they sleep.

Animals that do not sleep much


Giraffes do not sleep that much they may lie down or stay standing while sleeping. Older giraffes commonly sleep standing. Scientists call their sleeping the paradoxical sleep because while giraffes are resting there is rapid eye movement as well as reduced muscle activity.


Elephants are vegetarians which is the main reason why they sleep so little. Vegetation provides little energy that is why elephants need to spend more hours eating than sleeping to provide enough energy for their big build.

Alpine Swifts

Alpine swifts are birds that live in southern Europe all the way to the Himalayas. These birds spend most of their time migrating and sleep little along the way.


Deer do not sleep that much due to the presence of several predators. They have to be careful even while sleeping so they sleep on times where the predators are also asleep.


Ostriches sleep while standing up and with both eyes open to be alert for predators.


Horses sleep in short bursts of 15 minutes each cycle that totals to only two hours a day. This is to protect themselves from predators and care for young horses.

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