The Mexican free-tailed bat is the most common species roosting in Texas highway structures.
Texas's bats are an essential natural resource. The Mexican free-tailed bat (Tadarida brasiliensis) consumes approximately two million pounds of insects nightly in the Texas Hill Country alone. The majority of these insects are crop pests such as the cotton bollworm moth, which is enormously costly to farmers (Kunz and Whitaker, 1995; McCracken, 1996).
Unfortunately, these and other bats are in alarming decline, with more than half of U.S. species already listed as endangered or as candidates for such status (FWS; Tuttle, 1995). For most, the single greatest cause of decline is loss of traditional roosts, especially those in caves. In Texas, at least 11 of our 33 species, including the invaluable Mexican free-tailed bat, are able to utilize highway structures as alternate havens. Although fewer than 0.01% of Texas bridges and culverts are designed in a manner that meets ideal day roost requirements for bats, minor alteration of future structures, often at little or no cost to taxpayers, could play a key role in bat conservation.
The positive potential of such modification is well documented at the Congress Avenue bridge in Austin. The bridge's 1.5 million Mexican free-tailed bats consume 10-15 tons of insects nightly and provide one of the premier wildlife spectacles in America during their evening emergences (Tuttle, 1995). The site now attracts national and international publicity and tens of thousands of tourists each summer.
The Texas Department of Transportation (TxDOT) has frequent opportunities to provide bats with much-needed roosts and also has the challenge of preventing them from roosting in locations that are
considered inappropriate. The purpose of the Texas Bats and Bridges study is to document bat roosting
preferences in highway structures and to give engineers knowledge essential for managing bats in a
manner that maximizes bats' agricultural and recreational values while minimizing problems.
