The most famous characteristics of a bat is its behaviour of hanging upside down. This strange behaviour actually greatly benefits a bat’s survival. Because a bat’s wing is structurally different to a bird’s, it cannot generate enough flight to lift a bat off the ground directly. Therefore, bats leap off a high location to fly, so hanging from a high place allows them to fly off at any given moment. Also, living in a high place provides protection from predators.
A bat’s anatomy has heavily adapted to accommodate this behaviour. Thanks to its unique anatomical structure, a bat expends no energy while hanging. This is because they have talons that are designed to clench naturally when pulled by gravity, as the tendons tense. Thus, when hanging upside down, a bat can rest peacefully, and can even sleep in that posture as it requires no muscle action (all muscles relax in REM sleep).
As it is the norm to live upside down, a bat does everything in that manner. As stated above, a bat sleeps upside down, eats upside down, mate upside down, and even stay like that after death. There is only one time a bat stands upright: when it excretes waste. Even behaviour cannot overcome the power of gravity.