Can you imagine getting to the end of a long day of work, tired and ready for your bed. Then imagine that rather than curling up under covers at night, that ‘bed’ actually means falling asleep, horizontally on your feet, standing up.
Its something that is quite hard to actually imagine as a human. You would expect to instantly fall to the ground, to collapse as soon as you doze off, then wake yourself with a clatter in a heap on the ground. Yet for many animals, it is the norm. As alien as it sounds, there are many animals that sleep while standing up.
We take a look at which animals and birds sleep standing up, as well as why, in what capacity and how they are able to do this.
Animals That Sleep While Standing Up
- Bison – Conflicting sources as to whether Bison actually have the stay apparatus or not. Either way, they sleep in herds where some stay awake and some sleep, rotationally.
- Buffalo – Sleep for as little as one hour per day.
- Camel – Very stubborn sleepers, known to doze off when they feel like it, without warning.
- Cows – Cows sleep for about 4 hours per day, of which around a quarter is REM sleep laying down. They will take small dozes or slow-wave sleep standing up, several times in a day. Most sleep will be laying down at night.
- Deer – While deer (including reindeer) can doze standing, they usually sleep laying down with their limbs tucked in. They can alternate between dozing and deeper sleep frequently and can even be asleep with their eyes open.
- Donkeys – Donkeys will spend around 3 hours asleep at night, including laying down for REM sleep, but spend most of their resting time through the day standing up snoozing.
- Elephants – Can survive on as little as 2 hours sleep per day. They stand to sleep more and sleep for less time in the wild than in captivity.
- Gazelle – Gazelle only sleep for around 5 minutes at any time, and for around 1 hour across a whole day. Their ‘flighty’ sleep is well suited to the stand apparatus that they master.
- Giraffes – Sleep usually for one to two hours per day, but in very short standing nap cycles. They can survive on very little sleep. They may rest their heads on their rumps and spend little time at all laying down.
- Horses – Sleep for around 3 hours per day, mostly in short standing naps. Longer REM sleeps require laying down.
- Moose – Moose can sleep both standing and laying down. When snoozing on their feet, their ears are still very active, on the lookout for potential threats.
- Rhinos – At deep sleep, Rhinos will lay down and tuck their legs in. They are often found dozing on their feet in the shade through the hot days though, and can sleep for up to 8 hours a day.
- Wildebeest – Wildebeest, in one study by science direct, slept for about 4.5 hours a day in slow-wave sleep (which they can achieve standing), and around 30 minutes of REM sleep for which they will lay down.
- Zebras – Much like horses, Zebras can doze on their feet and do most of their resting this way. For REM sleep they need to lay down but will only do this when they feel secure in a group.
Birds That Sleep While Standing Up
- Canary – The only time a Canary has it’s eyes closed is when it is sleeping. It will sleep gripping with its flexor tendons onto branches or twigs.
- Cranes – Cranes will sleep or rest on one leg often. They lose heat quicker than humans, and the one legged sleep helps them reduce this heat loss.
- Crows – Can sleep standing up with their flexor tendons longer than most large herbivores can with their stay apparatus. Very intelligent birds.
- Ducks – Often found sleeping around the edge of water on one leg, and with their beak tucked into their plump feathers.
- Flamingos – Masters of the one-legged sleep, and can maintain the position for long periods of time.
- Geese – Like other aquatic birds, Geese will often sleep on one leg.
- Hawks – It is mostly aquatic birds that use the one legged sleep technique, but the hawk also uses this. It is thought the branches of trees that get very cold may cause heat dissipation and that hawks reduce this by alternating their resting foot.
- Hens – Hens are another non-aquatic bird that often rest on one leg to reduce heat loss. They spend most of the day on their feet, and when resting outside their coop they often do this perched on one leg.
- Pigeons – Pigeons, (including doves) are often found sleeping standing up with their heads tucked in, on ledges, branches and rooftops.
- Quail – Often found on one leg to reduce the heat lost through exposed, featherless legs. Particularly when sleeping or in shallow water.
- Seagulls – These aquatic birds lose a lot of heat in their exposed limbs and are another that will rotationally tuck their legs in while at rest to preserve heat.
- Songbirds – These birds like to sleep in bushes and under cover from predators, and they do this while gripped onto twigs and thin branches using their flexor tendons.
- Sparrows – Much like songbirds, sparrows often sleep in the cover of bushes and shrubberies, using their flexor tendons to remain vertical and ready to move if alerted.
- Storks – In Colder climates, Storks will sleep and rest on one leg, and are commonly observed sleeping like this.
- Swifts – Can perform Unihemispheric slow-wave sleep, allowing them to remain in a state of sleep and flight at the same time. In this type of sleep, one side of the brain is alert while the other is at rest.
How Do Animals Sleep Standing Up?
Believe it or not, the majority of large land dwelling herbivores are able to snooze on their feet. In most cases this is not a deep sleep, but rather a state of slow-wave sleep, or deep relaxation.
While these animals can sleep to some degree standing up, that’s not to say that they don’t sleep lying down too. In order to achieve deep sleep, many animals still need to lay down to achieve this.
From the human experience, such a task seems virtually impossible, without being tied tight to a wall or apparatus. So how exactly are some animals able to do this?
Well for animals that can sleep while standing, they do so through a variety of evolutionary characteristics that enable this. It differs from species to species, but here are the main features that enable animals to sleep on their feet.
The Stay Apparatus – Land Animals
The ‘Stay Apparatus’ refers to an evolutionary feature in the limbs of large herbivores. In their limbs are a series of tendons and ligaments that allow the animal to remain standing with very minimal effort. They do this by allowing the joints to lock and their muscles to relax to reduce load. This allows the animal to enter a light state of sleep without collapsing.
Slow-Wave Sleep (SWS)
Slow-Wave Sleep (SWS) is the state of deep rest that includes what we consider to be ‘Stage 3 deep sleep’ in humans. This is the state that land animals such as horses can enter when they are standing. In SWS, the body rather than the brain is the major beneficiary of the rest.
For deeper REM sleep, where the brain undergoes deep rest but also deep activity (such as dreaming) animals still need to be at rest, sitting or laying down. This is because REM sleep causes atonia (muscle paralysis) and the body needs to be safely at rest for this.
One variation of SWS, is Unihemispheric slow-wave sleep or USWS. This is a remarkable feature, which is seen in several species of animals in the sea, land and air. It is the ability to enter this state of sleep that allows the Swift to sleep on the wing (in flight), or the dolphin to surface for air while resting.
Flexor Tendons – Birds
Some birds have tendons in their legs that allow for an involuntarily reflex that with the aid of bodyweight, causes the feet to clasp. These are called flexor tendons (Flexor Digitorum Longus and Flexor Hallucis Longus), and there are two of these that stretch down a birds legs to the feet. While sleeping, with relaxed limbs, these tendons provide a pressured grip to branches and twigs. This grip releases when the birds awaken and straighten their legs.
Masters Of Balance – Birds
Many birds have the ability to rest and sleep on one leg. They do this for a variety of reasons, mostly to insulate areas of the body from the cold that are not well covered with feathers. It is quite an exceptional skill.
To sleep on one leg, they adjust their balance so that their lowered leg is directly under their center of gravity. By localizing the gravitational pressure they can lock their ankle joint and this keeps them vertical. By resting or sleeping on one leg, they can raise the other into their feathers to protect it from the cold. While resting, they will often alternate legs and may also tuck their heads round into their back feathers too.
It’s common to see aquatic birds do this both in the water and on land to lower heat dissipation.
Why Do Animals Sleep Standing Up?
There are a few different reasons that animals sleep while standing up. Here are some of the most common:
- Herd Protection – In a heard, some animals may sleep while others stand guard. Those that are sleeping may be horizontal or vertical, depending on the type of sleep state they are in. From a distance it would be hard for predators to see which animals are awake and which are sleeping and more vulnerable.
- Protection From The Cold – Standing in a group can help a heard to maintain a level of heat, particularly useful in the colder months. Birds standing on one leg can protect their featherless limbs from the cold also, by tucking one leg into their feathers and reducing the impact of the cold.
- State Of Readiness – Animals in a state of drowziness or slow-wave sleep can ‘switch on’ quicker than animals lying down in REM sleep. So in cases where a doze is enough, they can maintain a state of readiness to run or react from any threats. Some aquatic and flight animals that are lucky enough to have the ability of Unihemispheric slow-wave sleep (USWS) can actually rest one half of the brain at a time, allowing them to still function to some degree, like in flight, while still sleeping.
Animal Sleep Facts
- Giraffes can survive on as little as 5 minutes of sleep in a day!
- Some animals, such as Bison will often take it in turns to sleep. Some will stand awake like sentries, while others sleep and they will rotate this frequently.
- Swifts can spend most if not all of their lives in the air, not even stopping to sleep or eat. They will catch flies as they are in motion, and sleep using USWS sleep.
- An octopus changes color when in REM sleep.
- Flamingos sleep standing up because they live in salt flats which are caustic and can burn their feet over long periods of contact.