Bat City USA delves into Austin's complicated relationship with a colony of Mexican free-tailed bats under the downtown Congress Avenue Bridge. Each year, thousands of people get a fascinating, close-up glimpse of the world's largest urban bat colony amid the colorful downtown Austin, Texas setting. The film reveals how the bats moved into the bridge and survived eradication plans by hostile residents. Viewers discover how the bats eventually became a beloved part of what makes Austin unique and weird, mainly through the efforts of Merlin Tuttle, founder of Bat Conservation International, who convinced residents of the benefits of the bats.