From the January/February 2012 issue of Iowa Outdoors magazine
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Unlike birds, bats have trouble with takeoffs from the ground. Their wings are not as strong as those of birds and they cannot run fast enough to build up flight speed. Bats have an easier time flying when they start already in the air. They use their front claws on their wings to climb to a high spot and launch themselves to achieve flight.
Another reason they hang upside down is because a bat’s talons or back claws work opposite of most muscles. In fact, their knees face backwards. When they relax, special tendons lock the toes and talons in place, so they do not exert energy while hanging. Once their toes and legs are locked in place, their body weight and gravity keep them hanging. By flexing leg muscles, the toes and talons release and flight begins.
Humans cannot hang upside down as blood rushes to the head and tends to pool or collect. But the bat’s compact, small size allows their heart to easily distribute the small volume of blood even when upside down.
Because of their unique physical abilities, bats can safely roost in places where predators cannot get them. To sleep, bats hang themselves upside down in a cave or hollow tree, with their wings draped around their bodies like cloaks. They hang upside down to hibernate and even upon death.