urbpan | 365 Urban Species. #253: Mexican Free-tailed Bat (Reply)

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urbpan. Location: Congress Ave. Bridge, Austin.
The bat on the far left shows the "free tail," protruding past the membrane between the back legs.

Urban species #253: Mexican free-tailed bat Tadarida brasilensis

According to Bat Conservation International, one and a half million Mexican free-tailed bats emerge from Austin's Congress Avenue Bridge each night, between March and November. These mammals are migratory, and spend winter in Mexico. When I learned about the Congress Avenue Bridge, I assumed it was a highway bridge at the margin of settled Austin, on a remote piece of desert. Visiting it in person, I was amazed to find myself on the main street of downtown Austin, a few blocks from the Texas Capitol building, surrounded by skyscrapers. The bridge is one of several that cross the Colorado River, which winds through the city (this section of the river is dammed, and is known as Town Lake). When the bridge was renovated in 1980, changes in the structure proved to be attractive to roosting bats, and the most remarkable urban nature attraction in the country was born. I was thrilled to see, not just the swirling mass of flying mammals, but the huge crowds of people gathered for the experience. It's similar to the regular eruptions of a geyser in a National Park, only this is an artificial serendipity. Every human activity potentially creates habitat: skyscraper ledges provide nest space for pigeons, subways shelter mice, garbage provides a year-round food for skunks and many other animals. But this was one of the only places I've seen where the fact that the construction accidentally created wildlife habitat was celebrated. Future engineers should study this example, to encourage the wildlife that we, collectively, want to share our city with.

Mexican free-tailed bats are welcomed, in large part, because they eat insects. While many people like to think that bats control mosquito populations, the truth is that mosquitoes are paltry sustenance. While some mosquitoes are probably eaten by bats, the greater bulk of their food consists of beetles and moths. The larvae of many moths are serious pests of the vast Texan agricultural fields surrounding the city. Migrating bats stopover in open buildings, abandoned mines, and in tunnels and bridges. Before there were man-made structures in the bats' range, they roosted entirely in caves. These bats are encountered more frequently than any other species in Texas, and are often seen hunting insects attracted to streetlights.