At dusk nearly every night in summer, the hot muggy air encompassing downtown Austin suddenly fills with 1.5 million Mexican free-tailed bats—forming what resembles a torrential hurricane as they pour out from under the Ann W. Richards Congress Avenue Bridge and take off across the river. Tourists line up daily on and around the bridge—some setting up picnics, some in canoes or balancing on stand-up paddleboards on the water—to catch a glimpse of the colony as it takes flight. And on August 19, the city aims to celebrate its winged residents with Bat Fest, an annual festival on the bridge. The family-friendly event offers children’s activities, a batty costume contest, and live music from Blue October, American Authors, Warren G, Puddle of Mudd, and others. While the day’s activities are well planned, the timing of the bats’ flight is not (they’re wild animals, after all). Experts predict their emergence to occur sometime between 7 and 8:45 p.m. and last for half an hour.