Not every field trip in Austin is related to state history and government. The colony of Mexican Free-tailed bats who have taken up residence beneath the Congress Avenue bridge could not care less who has “bats in the belfry” at the other end of Congress Avenue. Viewing is usually best May-October when there are more insects for feeding. (Great for the bats; not so much for you, maybe).
You can watch them for free, of course, but if you’re in the mood for something extra-special, you might be interested in taking a bat-watching cruise on the Colorado River at sunset.