Why do bats sleep upside down?

Unlike birds, bats cannot launch their bodies into the air from the ground, because their wings don't produce enough lift to take off like a helicopter. ... If sleeping bats need to escape quickly, hanging upside-down means they are already in the perfect position to spread their wings and fly away. read more

Bats roost, or perch, upside-down for several reasons. Unlike birds, bats cannot launch their bodies into the air from the ground, because their wings don't produce enough lift to take off like a helicopter. A running start would help, but bats' hind legs are too tiny to gain enough speed for lift-off. read more

Not all bats are the same, but there are a few reasons why so many of them sleep hanging down from tree branches. One reason has to do with flying. Most bats aren’t able to fly if they start off on the ground; instead, to get the momentum (speed) that they need to fly, they have to start by dropping into the air from a tall perch. read more