Congress Avenue Bridge

Mexican free-tailed bats emerge from under the Congress Avenue bridge in 2012.
Gabriel C. Pérez / KUT

Every night beginning in late March and into early September, nearly 1.5 million Mexican free-tailed bats emerge from the Congress Avenue bridge in Austin. The bats aren’t the only thing making a nightly exit, though: Bat guano, otherwise known as poop, makes its exit as well.