Millions of Brazilian free-tailed bats spend their summers in the southwestern United States. Gigantic colonies summer in Bracken Cave, Texas; Carlsbad Caverns, New Mexico; and even within the city of Austin, Texas, under the Congress Avenue Bridge. They are a spectacular sight spiraling out of their day roosts like great, dark, swirling clouds when they emerge in the evening to forage. The bats eat untold numbers of insects each night, sometimes catching their prey at altitudes of a mile or more. They typically migrate to central and southern Mexico in the winter, where they live in smaller colonies. They mate there, and fly north again - as far as 1,300 km - between February and April. Females give birth to a single pup, in June, and nurse it for about six weeks. Although they number in the millions, conservation is a concern, because they raise their young in a limited number of caves, and because pesticides can accumulate in their body tissues.

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account