Horses, zebras and elephants sleep standing up.
The first thing is that it is one of the mistakes lots of people make about horses. It’s true they do have an amazing ability to sleep standing up. But they do also sleep lying down.
Why Should Horses be Able to Sleep Standing Up?
Horses first evolved in open plains. As a prey species, they needed to be able to see quickly if another predator that might attack them was nearby.
Being able to rest or sleep standing up meant they could get their rest, but if they saw a predator, they could quickly run away. That’s one of the reasons horses run so fast – to get away. The early horses that ran the fastest were more likely to survive.
How are Horses Able to Sleep While Standing?
Three legs on, one leg off
The most interesting part of horses resting standing up is how they do it. In horses there is a special arrangement of muscles and the parts that connect muscles and bones together (ligaments and tendons). This is called the stay apparatus.
The stay apparatus means that horses can stand on three legs and rest the other leg. They can change the leg they rest so all of their legs get a chance to have a break.
A horse can weigh more than 500kg so their legs need a rest!
Even though they can sleep standing up, scientists think horses still need to lie down and sleep each day. Horses go through different stages of lighter and deeper sleep.
The deeper stages of sleep are only seen in horses lying down. Horses need to go through deeper stages of sleep for their brains to work properly.