Staying in Austin for work, I walked to dinner from my hotel. While at dinner I asked the waitress why everyone was hanging out on a nearby bridge. Her response was that there was a congregation of bats living under the bridge and everyone was waiting from them to fly at from their home at dusk.
Upon finishing dinner I began to walk across the bridge to return to my hotel. I stopped every so often to look over the edge of the bridge to see if any bats were flying about. At first I didn't see any. Then a few started to come out. They started to circle the supports of the bridge. Then it seemed as if there were thousands of them. It was a torrent of bats constantly circling the supports of the bridge. People were taking flash photos that illuminated many more bats.
It was an awesome sight.