Why do bats sleep upside down?
Bats are the only mammals capable of flight. Mother Nature seems to have decided to give them a little of both: it endowed them with weak legs and lightweight bones.
On one hand, lightweight bones are beneficial—they enable faster flight. However, on the other hand, they struggle to support their body weight, making bats poor at standing, worse at walking, and they don't sit on branches like birds—upside down, with heads down and feet up.
Because bats have poorly developed legs, they cannot run and push off like birds. Moreover, their wings are also underdeveloped to lift their body off the ground. When a bat hangs upside down, all it needs to do is spread its fingers, and it begins to fall downwards. As it falls, it spreads its wings and takes flight.
Bats are nocturnal creatures, hunting insects and other prey at night, while sleeping during the day—upside down, when most predators sleep. Many predators hunt bats, including owls, snakes, raccoons, and even humans. Therefore, when bats prepare to sleep, they hide in places inaccessible to predators—cave ceilings, attics, bridge arches, tree hollows, and so on.
But how do they manage not to fall when they hang upside down all night? The secret lies in their unique muscular structure. For example, when a monkey hangs from a branch, it tightens its leg muscles to hold on. Bats, however, are the opposite. When they hang upside down, their muscles relax, their fingers grip tightly, and their body hangs on their bones and tendons. Their claws securely grasp the perch, preventing them from slipping.
Moreover, bats have very mobile necks—their heads can rotate 180 degrees. Their hind limbs are turned with their knees backward, which is very convenient for hanging upside down.
In this position, they enter a state of torpor (sleep). In colder climates, bats hibernate upside down throughout the winter, undisturbed until warmer weather arrives.
