Mexican Free-tailed Bat

The Mexican free-tailed bat ranges from the southern half of the continental United States through most of Mexico, and through most of Central America into South America. Their range in South America is less understood where they live in the eastern Brazilian highlands and coast, the northeastern Andes, the coast of Peru and northern Chile, and the center of Argentina. They are absent in much of the Amazon rainforest. They are also found in the Caribbean, and are native to all of the Greater Antilles and 11 of the Lesser Antilles. The largest known colony is found at Bracken Cave, north of San Antonio, Texas, with nearly 20 million bats; the bats from this colony congregate in huge numbers at altitudes between 180 and 1,000 m (590 and 3,280 ft), and even as high as 3,000 m (9,800 ft).

Habitat. Mexican free-tailed bats roost primarily in caves. However, they also roost in buildings of any type as long as they have access to openings and dark recesses in ceilings or walls. The bats can make roosting sites of buildings regardless of "age, height, architecture, construction materials, occupancy by humans and compass orientation". Caves, though, need to have enough wall and ceiling space to fit millions of bats. …

Mexican free-tailed bats are nocturnal foragers and begin feeding after dusk. They travel 50 km in a quick, direct flight pattern to feed. This species flies the highest among bats, at altitudes around 3,300 m (10,800 ft). Bats appear to be most active in late morning and afternoon between June and September. Free-tailed bats are more active in warm weather. The species has been measured at a ground speed of 160 km/h (99 mph), measured by an aircraft tracking device. The measurement methodology did not simultaneously record wind speed and ground speed, so the observations could have been affected by strong local gusts, and the bat's maximum air speed remains uncertain.

Guano and ammonia. Among bats that roost in great, concentrated numbers, T. brasiliensis roosts produce large quantities of urine and guano; from 22 to 99 metric tons per cave and over 18,700 metric tons are produced annually. The concentrated waste generates high levels of toxic ammonia in the air of a cave. T. brasiliensis individuals have genetic adaptation for withstanding or countering these high levels of ammonia. The bats' content of CO2 and protein in respiratory mucus and CO2 dissolved in blood plasma increase with increasing levels of dissolved ammonia, providing the bats with a buffer against pH change. …