Austin boasts the world's largest urban bat colony, and in the summer, you can watch 1.5 million-ish of the little beasts fly out from under Congress Avenue Bridge and consume what would otherwise be a hellish mosquito population. They're Mexican free-tails, and they migrate south o' the border for winter.
This is Congress Avenue Bridge (aka Ann W. Richards Congress Avenue Bridge). The original picture is much clearer than this, but I typically destroy pleasant things, and this is no exception. Besides, I didn't want give the capitol building away yet. I'm a jealous resident.