page_title: Mexican free-tailed bat
section_title: Migration
hierarchical_section_title: Mexican free-tailed bat / Range and ecology / Migration
caption_attribution_description: English: Mexican (or Brazilian) Free-Tailed Bats, Tadarida brasiliensis, emerging from Carlsbad Caverns, Carlsbad Caverns National Park, New Mexico.
context_page_description: The Mexican free-tailed bat or Brazilian free-tailed bat is a medium-sized bat native to the Americas, regarded as one of the most abundant mammals in North America. Its proclivity towards roosting in huge numbers at relatively few locations makes it vulnerable to habitat destruction in spite of its abundance. The bat is considered a species of special concern in California as a result of declining populations. It has been claimed to have the fastest horizontal speed of any animal, reaching top ground speeds over 100 mph; its actual air speed has not been measured. The Texas Legislature designated the Mexican free-tailed bat the state mammal in 1995.
context_section_description: Mexican free-tailed bats in southeastern Nevada, southwestern Utah, western Arizona, and southeastern California come together to migrate southwest to southern California and Baja California. Bats in southeastern Utah, southwestern Colorado, western New Mexico, and eastern Arizona travel through the western edge of the Sierra Madre Oriental into Jalisco, Sinaloa, and Sonora. Some bats that summer in Kansas, Oklahoma, eastern New Mexico, and Texas  migrate southward to South Texas and Mexico.  Some bat populations in other areas of North America do not migrate, but are residents and may make seasonal changes in roost sites. While this migration is extremely extensive,  a way must exist for these bats to continuously congregate in the same roosts every year. T. brasiliensis bats have copious numbers of sebaceous glands covering their entire bodies. These glands leave a trace of a lasting scent to which other bats are sensitive. This odor is crucial to marking habitual roosts.
  In Austin, Texas, a colony of Mexican free-tailed bats summers (they winter in Mexico) under the Congress Avenue Bridge 10 blocks south of the Texas State Capitol. It is the largest urban colony in North America, with an estimated 1,500,000 bats. Each night they eat 10,000 to 30,000 lb (4,500 to 13,600 kg) of insects. Each year, they attract 100,000 tourists who come to watch them. In Houston, Texas, a colony is living under the Waugh Street Bridge over Buffalo Bayou. It is the home to 250,000 bats and also attracts viewers. The Mexican free-tailed bat is the official flying mammal of the state of Texas.
  Bats ranging eastward from East Texas do not migrate, but local shifts in roost usage often occur seasonally. Also, a regional population that ranges from Oregon to California, has a year-round residence.
caption: Mexican free-tailed bats, emerging from Carlsbad Caverns, Carlsbad Caverns National Park, New Mexico
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