As you know, bats are the only flying mammals, and, as their bodies became increasingly specialized for flight over the course of evolution, most species lost the ability to walk. Only a couple of exceptions are known, including a species of bat that lives in New Zealand and the common vampire bat of South and Central America. While other bats can only shuffle, these bats use their wings as forelimbs, so they can walk around like any other four-legged animals.
Why is that?
Well, vampire bats, which usually feed on sleeping cattle, have to be good on the ground to avoid being stepped on by their prey. In contrast, the New Zealand bat species has no natural predators, so it lost its ability to fly. Here's something even more incredible. Scientists put both species on a treadmill, increasing the speed, and discovered that vampire bats can run, using their forelimbs to generate power the way other animals use their hind limbs. Even the New Zealand bats can't do that.