Written By: Lana Adler
Updated March 26, 2021
Most people are used to seeing animals like dogs and cats sleep. Although they occasionally rest in positions that look uncomfortable to us, they generally sleep like we do: lying down. While many animals rest horizontally, other animals sleep standing up.
Though it may seem a little strange, sleeping while standing is advantageous for certain animals. We take a closer look at why some animals sleep standing up, how long they can remain asleep in a standing position, and how sleeping while standing works.
How Do Certain Animals Sleep Standing Up?
Animals that sleep standing up have special body mechanics that support their ability to doze off without lying down. Although animals that sleep in an upright position differ from each other in terms of muscle and bone structures, they have each evolved (1) to be able to rest while standing.
Horses can sleep standing up because of a stay apparatus (2), which is a unique body mechanism that essentially locks their knees in place. The stay apparatus stabilizes the muscles and tendons in horses’ legs to prevent their knees from flexing.
The stay apparatus helps horses conserve energy and retain muscle. It also prevents them from falling down while they sleep. Additionally, the stay apparatus lets horses sleep while standing on just three legs, which means they can trade off to give each leg a rest.
Flamingos also sleep upright. Similar to horses, flamingos are able to remain standing without actively using their muscles. Instead, flamingos use gravity strategically (3) while they rest standing up.
When they lift one of their legs, flamingos shift their center of gravity slightly forward. This change in weight distribution keeps them from falling over and allows them to exert less energy than they would spend while using both legs.
Do Animals That Sleep Standing Up Ever Lie Down?
Like humans, animals cycle through different sleep phases. The rapid eye movement (REM) sleep phase can cause muscle atonia, a type of temporary muscle paralysis (4), in both humans and animals. Some animals that can sleep standing up, such as horses, cows, and elephants, lie down during REM sleep to avoid collapsing when they experience muscle atonia.
Which Animals Sleep Standing Up?
Generally speaking, the animals that sleep standing up are those that would have the hardest time getting off the ground to escape a predator. Large animals like elephants, bison, cows, and giraffes likely evolved to sleep standing up at times because they can’t spring to their feet quickly enough to get away from danger.
How Long Do Animals Sleep While They’re Standing Up?
While some animals rest for such short amounts of time that it may seem like they aren’t sleeping at all, scientists believe that all animals do sleep. Although it's sometimes difficult to tell if a standing animal is sleeping, research indicates the following trends:
- Giraffes: Giraffes sleep about 4.6 hours per day (5) on average, but not all of that time is spent standing up. These long-necked animals tend to sleep in shorter blocks of time throughout the day and night, with many sleep periods lasting only 11 minutes. Multiple factors affect whether a giraffe stands or lies down to sleep, including their age, how often they're napping, and whether they're in an enclosure or outdoors.
- Elephants: Elephants sleep for an average of two hours each day (6). In fact, elephants can go as long as 46 hours without sleep. Most of the sleep elephants do receive happens while they're on their feet. These animals tend to only lie down for sleep every third or fourth day.
- Cows: Cows may be one of the more well-known animals that sleep standing up, even though they spend many hours lying down each day. Much of this time is spent resting and conserving energy rather than truly sleeping. Cows actually only sleep about four hours (7) a day, and they are usually standing up during non-REM sleep.
- Horses: Horses sleep in small increments spread throughout the day. On average, they spend about five to seven (8) hours sleeping, and only need about 30 minutes of REM sleep. Although horses often catch daytime sleep while standing, they generally lie down to sleep at night.
Can Humans Sleep Standing Up?
With knees that don’t fully lock and a place at the top of the food chain, humans haven't evolved to need to sleep while standing. Chances are high that humans will be able to continue sleeping while lying down for years to come.
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