Congress Avenue Bridge Mexican free-tailed bat colony

An estimated colony of Mexican free-tailed bats (Tadarida brasiliensis) roosts beneath the Ann W. Richards Congress Avenue Bridge in downtown Austin; the colony is considered the largest urban bat colony in North America. The bats emerge at dusk from roughly March/April through October in huge, twisting streams that are best seen from the bridge or nearby viewing spots. Because they roost under the bridge structure and are most visible only at dusk, observing the emergence can be hard to time unless you know the seasonal schedule.