The Congress Bridge Bats

When the state highway department rebuilt the Congress Avenue Bridge in 1980, its engineers set the deck on concrete box beams and left narrow gaps between them, roughly three quarters of an inch to an inch and a half wide and sixteen to eighteen inches deep. Nobody planned it, but that is almost exactly the roost a Mexican free-tailed bat wants. Within a few years those gaps held the largest urban bat colony in North America, now put at about one and a half million animals, and mothers raise something like three quarters of a million pups under the traffic each summer. Austin did not take the news well. Newspapers ran headlines about bats sinking their teeth into the city, and residents circulated petitions asking that the colony be destroyed. Bat Conservation International, which moved its headquarters to Austin in the 1980s, spent years making the opposite case: that these are insect eaters taking tons of moths and beetles off the surrounding farmland every night, and that disease in the colony was vanishingly rare. The argument was won so completely that the nightly emergence is now one of the reasons people come here. The bats arrive from Mexico in March and are gone by early fall. They pour out from under the deck in a long column around sunset, and the bridge carries Congress Avenue straight at the Capitol dome, so it is an easy crossing to make without knowing what is underneath it.