Why do birds not fall out of trees when they sleep?

Question

Why do birds not fall out of trees when they sleep?

Answer 1

Birds that roost in trees have different feet than other birds, like ducks that swim or gulls that roost on beaches or rocky shores.

"To hold onto a twig, a bird needs feet with opposing toes that wrap around the branch. Why don't perching birds fall off when they sleep? When perching birds sit, their feet automatically lock on the limb. With feet locked, sleeping birds don't fall. As the bird stands up its feet release." http://www.nhm.org/birds/guide/pg010.html

"When a perching bird (passerine) lands and its legs flex, its flexor tendons automatically tighten. This causes the toes to close around a branch. The taut tendons lock the toes. The tendons stay tight until the legs straighten. Then the tendons relax, releasing the toes’ grip. That’s why birds can sleep without falling off — their toes fasten them to their perches.

The flexor tendons are narrow strips of gristle that extend from the leg muscles down the back of the tarsus bone and attach to the toes. The tarsus bone looks like part of the bird’s lower leg but actually corresponds to the five bones running from ankle to toes on a human’s foot.

Woodpeckers also hook their feet into the bark of a tree while they sleep, appearing frozen in a climb."
http://www.wonderquest.com/sleeping-birds-gas-nozzles-cold-hospitals.htm

Answer 2

Most birds snooze with the head turned and resting on the shoulder and the bill tucked among fluffed up back plumage. Fluffing out feathers improves insulation by trapping air against the warmth of the bird's body. Depending on the species, birds sleep while standing or sitting with feet locked on perches, or cling by toenails to tree-trunks.


They are light sleepers alert to threats from predators. Flocking birds have members of the flock keeping watch. They also have to try and keep warm. They therefore don't have heavy sleep which would lead to them falling off the tree or being caught sleeping by a predator.

The tendons in perching birds legs and feet are set up so that when they relax, the toes tighten down. So when a perching bird sits on a branch, its toes automatically tighten and grip the branch.
They have to flex their toes to let go

Answer 3

Birds don't fall while sleeping because of their claws that holds the twig fully by nature.

Answer 4

there is something about them being able to lock up their tendons or something in their feet or legs.