Ann W. Richards Congress Avenue Bridge is home to the world's largest urban bat colony, which is composed of Mexican free-tailed bats. The bats reside beneath the road deck in gaps between the concrete component structures. They are migratory, spending their summers in Austin and the winters in Mexico. According to Bat Conservation International, between 750,000 and 1.5 million bats reside underneath the bridge each summer.
The nightly emergence of the bats from underneath the bridge at dusk, and their flight across Lady Bird Lake primarily to the east, to feed themselves, attract as many as 100,000 tourists annually. Tourists can see the bats from the bridge, from the sides of the river and from boats.
