The United States is known to have 15 genera, totaling 44 species of bats. Bats are unique in the animal kingdom because they are the only mammals to have evolved true flight. There are numerous species of bats throughout North America. Those that inhabit the southwestern deserts comprise 11 genera and more than 18 species. Free-tailed bats also known as Mastiff Bats, or Bulldog, Bats because of their facial resemblance to dogs, comprise about 90 species of bats in the family Molossidae.
Most species live in groups.
A US population of more than 100 million also makes it one of the most numerous of all mammals. Most individuals from this region migrate to Mexico for the winter, usually toward the end of October, and return in March to mate. Throughout all 4 deserts of the American Southwest.and along the Pacific coast. Extreme southern Sonoran and Chihuahuan deserts. A subspecies of the Brazilian Free-tailed Bat, forms colonies of several million individuals.