In an effort to photograph the greatest concentrations of critters around, I spent a month in Texas working on bats. Just north of San Antonio, is a cave called Bracken Cave where 20-30 million Mexican Free-tailed bats come, making it the greatest concentration of mammals on the earth. All the caves in Texas/New Mexico of Mexican Free-tail bats are places where the females come to give birth to a single pup (males stay in Mexico). Prior to oil, bat guano was one of the largest exports from Texas. The bridge in Austin is famous for having the largest urban colony of Mexican Free-tail bats (1-1.5 Million). People line up on the bridge to watch the daily emergence. The bats feed on migratory insects, most of which are agricultural pests (beetles and moths). The bats are very fast flyers (up to 60 MPH) and will venture out as much as 100 miles from the cave to feed, feeding at altitudes up to 10,000 feet.