|Vampire Bat (Photo by: Ltshears, via Wikimedia Commons, CC BY-SA 3.0)|
Bats are the only mammals that can fly, and they are extremely specialized for this skill. Their bodies have an aerodynamic shape, their bones are light, and their wings are thin, flexible, and hypersensitive. In fact, their wings have almost two dozen joints, and are covered with Merkel cells, which are the touch-sensitive cells found on our fingertips.
Unfortunately, most bats' rear legs are more or less useless for anything except hanging. They are very thin and weak with fragile bones. Their knees also face backwards. If a bat ends up on the ground, he'll use his front limbs to clumsily drag his body while keeping pressure off the back legs. This can be awkward, since the front limbs are meant for flying rather than crawling.
However, out of the over 1,200 species of bat, there are two species that actually can walk - the vampire bat and the burrowing bat (also known as the lesser short-tailed bat). In fact, a laboratory study using treadmills showed that vampire bats can even sprint on all fours. They primarily use their front limbs, and can even reach speeds of 2.7 miles per hour. That may not sound very fast to a jogger or power walker, but it's definitely respectable for a small animal that's more equipped for flight.
The burrowing bat has adaptations conducive to walking - claws at the base of their toes, grooves on their feet, and elbow joints that bend sideways and allow them to use their wrists to push off. Burrowing bats take advantage of these traits to forage for food on the ground as well as in the air.