At night, bats fly all over, snatching up hundreds of insects and other small animals. During the day however, they hardly move at all. Instead, bats spend the day hanging upside down in secluded spaces.
There are two main reasons why bats hang upside down during the day when they are usually sleeping and not active hunting for food:
The ideal position for takeoff
Unlike birds, bats can’t launch themselves into the air from the ground. Their wings don’t produce enough lift to take off from a dead stop, and their hind legs are so small and underdeveloped that they can’t run to build up the necessary takeoff speed. Instead, they use their front claws to climb to a high spot, and then fall into flight. By sleeping upside down in a high location, they are all set to launch if they need to escape
A great way to hide from danger
During the hours when most predators are active (particularly birds of prey), bats congregate where few animals would think to look and most can’t reach. This allows them to disappear from the world until night comes again. There’s also little competition for these hanging spots, as other flying animals don’t have the ability to hang upside down.
But how can bats so effortlessly hang upside-down while they are sleeping?
A bat doesn’t have to do anything to hang upside down thanks to a certain psychological adaptation that lets them hang around this way without exerting any energy.
If you want to clench your fist around an object, you must contract several muscles in your arm, which are connected to your fingers by tendons. As one muscle contracts, it pulls a tendon, which pulls one of your fingers closed. A bat’s talons close in the same way, except that their tendons are connected only to the upper body, not to a muscle. To hang upside down, a bat flies into position, pulls its claws open with other muscles and finds a surface to grip. To get the talons to grab hold of the surface, the bat simply lets its body relax. The weight of the upper body pulls down on the tendons connected to the talons, causing them to clench. The talon joints lock into position, and the bat’s weight keeps them closed.
Considering that the talons remain closed when the bat is relaxed, even if the bat dies while hanging upside-down, it will remain so unless wind or some other animal pulls it down.
