Why don't birds fall out of trees while sleeping? The unusual science behind the phenomenon

Most small birds that regularly sit on branches belong to a group known as perching birds (passerine). Have you ever seen a bird sleeping on a thin tree branch and wondered why it does not fall? While humans may lose their grip when their muscles relax during sleep, many birds can remain safely perched for hours. The answer lies in the structure of their legs, feet and tendons. But the explanation is not exactly the same for every bird.How birds hold on to branches while sleepingMost small birds that regularly sit on branches belong to a group known as perching birds (passerine). These birds have feet adapted for gripping branches, with three toes pointing forward and one toe pointing backwards. The backward-facing toe is called the hallux. Together, the toes help the bird hold a branch from different sides. When a perching bird lands on a branch, its legs bend at the knee and ankle. This stretches the tendons running down the back of the leg and into the toes. The movement causes the toes to curl around the branch, helping the bird maintain its grip without having to consciously hold on.The Cornell Lab of Ornithology explains that when a bird places weight on its feet, the leg mus...