I've been watching the iPad app 'Radarscope' quite a bit, hoping for a thunderstorm to come my way. It's been dry so long here. But I've been noticing some activity about sunset every day and I finally realized what I was seeing. In several locations here in Central Texas, the Mexican free-tail bat hides out in colonies of millions under bridges and in caves and tunnels. When the mood strikes, at about sunset, they stream out and go foraging for the night.
Taking screenshots and combining them with Keynote, I made a 2 minute slide show of the display, with three different zoom factors.
The bats are fascinating to watch, on radar, and in person. The Congress Avenue Bridge colony is famous, as well as the McNeil Bridge in Round Rock, but you can see many colonies all over the state.