The Congress Avenue Bridge, which spans Lady Bird Lake, formally Town Lake, in downtown Austin, is home to the largest urban bat colony in North America.
The colony is estimated at 1.5 million Mexican free-tail bats. Each night from mid-March to November, the bats emerge from under the bridge at dusk to blanket the sky as they head out to forage for food. This event has become one of the most spectacular and unusual tourist attractions in Texas.
The most impressive bat flights happen on hot, dry August nights, when multiple columns of bats emerge. There are several points from which to view these events, and an information kiosk is located on the north bank of the river, just east of the bridge.