Everyone knows the unique traits of horses, characterized by their slender bodies and sturdy legs. However, horses have a characteristic that sets them apart from other animals: they prefer to sleep standing up at night. No matter when you visit them at night, they are always standing with their eyes closed, seemingly asleep.
Horses are mammals belonging to the Equidae family and the Perissodactyla order (odd-toed ungulates). They are one of the eight subspecies of the Equidae family that still exist today. They have undergone an evolutionary process over 45 to 55 million years to evolve from small, multi-toed creatures into the large, single-toed animals we see today.
Humans began domesticating horses around 4,000 to 4,500 years ago. This species became widespread in Europe around 2,000 to 3,000 years ago. They were extensively used in ancient wars. The average lifespan of a horse is about 25 to 30 years, depending on the breed, environmental factors, and care.
Despite having been companions to humans for a long time, there is much about horses that not everyone knows, such as the reason behind their ability to sleep standing up.
Horses sleep standing due to their wild behavior patterns. Wild horses live in vast grasslands and deserts. In ancient times, horses were both prey for humans and a tasty meal for predators like wolves. Unlike cattle or goats, which can use their horns to defend themselves, horses have only one option: to escape swiftly from their enemies. Predators like wolves hunt at night, resting during the day in tall grass or caves, and only venture out to hunt at night.
Even during the day, horses must stand to maintain high alertness, prepared for any danger.
Wild horses cannot afford to sleep soundly at night, as they need to be ready to flee from predators. Even during the day, they remain standing, alert to any potential threats. Although domestic horses do not face the same predatory dangers as their wild counterparts, they are descendants of wild horses, and this instinct to sleep standing has been preserved.
In stables, while horses may not face many threats from predators, they still tend to sleep standing during the day.
Among various animal species, donkeys also share the trait of sleeping standing, owing to the similar living conditions of their ancestors compared to wild horses.
According to experts, the reason horses can do this is that they possess what is called a “locking mechanism”, which includes a system of ligaments and tendons that allows them to lock their leg joints when they sleep, maintaining an upright position.
When a horse begins to take a quick nap, they activate this resting mechanism by bending one of their legs, typically a hind leg, and “locking” it at the knee. The remaining three legs support the horse’s weight. After a while, the horse will shift its weight to another leg to prevent fatigue.
Beyond self-defense, the standing sleeping position provides additional benefits for horses. Lying down for extended periods can put pressure on their heart, lungs, and internal organs, especially for larger horses. Sleeping while standing helps maintain better health and reduces stress on the heart and internal organs.
Interestingly, horses do not always sleep standing. In situations where they need to achieve deep sleep for recovery, they will lie down like most other animals. During this time, the herd employs a teamwork strategy, where one horse takes on the role of a lookout while the rest of the group dozes off.
Horses are not the only animals in the animal kingdom that can “nap” and sleep in an upright position. They belong to a small group of animals capable of sleeping standing. Other mammals such as giraffes, elephants, and camels also have the anatomical structures that allow them to sleep while standing. Many bird species also sleep upright and on one leg. The most common example is the flamingo, but many other birds use unique perching mechanisms to sleep on branches without falling.
