Nowadays

The Congress Avenue Bridge, which runs over the Colorado River in the heart of Austin, is home to the largest urban bat colony in North America. More than one million Mexican free-tailed bats bats live in crevices under the bridge. Every evening at sunset, the bats emerge from their hideaway and fly out to seek food. Together, they eat up to 200,000 pounds (more than 90,000 kilos) of insects a night. No wonder Austin loves its bats.

The bats' takeoff brings hundreds of people to Congress Bridge every evening and right now is the peak of bat watching season. During the end of the summer, July and August, the bat colony is at its largest since the pups are big enough to hunt their own food.

Depending on how hot the day's been, the bats fly off sooner or later and if it's still light enough you see huge clouds of dark silhouettes against the evening sky. I went bat watching last week but wasn't very successful. (The picture above I found online). When the bats finally came out, it was too dark to see them. However, the darkness didn't hide the flapping of a million wings. Impressive. 
                                                                                                                                                
Austin, the city of music festivals, of course shows its appreciation by dedicating a festival to the bats - Batfest.