​The Story of Austin’s South Congress Street Bridge Bat Colony

If you have driven across Austin’s South Congress bridge recently you may wonder why there are hundreds of people gathered along the eastern side of the bridge.  A little before sunset, spectators appear on the sidewalk along the bridge to watch North America’s largest urban bat colony.
 
The Mexican Free-Tailed Bats have a long history in Austin, but it wasn’t until the bridge was modified in 1980, that the bats centralized under the eaves of the South Congress Bridge.  When the bridge was widened, expansion joints were added creating the perfect nooks for the bats to call home. 
 
The bats emerge from under the South Congress bridge each night annually from March through November.  In March, the bats migrate from Mexico to Austin.  The colony that lives under the South Congress street bridge is entirely female when they migrate in March.  They reside under the bridge and emerge nightly to feed on various insects.  These females are all pregnant and they give birth to one pup each in early June.  At this time, the bat colony doubles and researchers believe the population to be between 1.5- 2 million.  Interestingly, this is approximately the same number of people who reside in Austin and the surrounding suburbs. 
 
The bats continue to leave the bridge each night around dusk from June through November.  In June and July, the mother is still nursing the pup. It is believed that they nurse the pup before and after they hunt.  Interestingly, the bats hunt alone so watching them return from hunting is not nearly as entertaining as watching the max exodus that occurs around dusk.  The pups do not stay with their mothers.  The pups are centered together and each night the mother will return to find and feed her pup before retreating to the northern side of the bridge where the mothers reside. 
 
Between Late July and October, the largest exodus of bats occurs.  This is the time that pups are learning to fly and hunt for themselves.  Hence, this is one of the best times to see Austin’s bat colony.
 
In early November, the cooler climate signals the Mexican Free-Tailed Bats that it is time to return to Mexico.  Not all the bats leave at once, but they do leave in large groups.  It is believed that the mothers will return to the South Congress bridge each year to have and raise their new pup. 
 
If you are interested in seeing the South Congress bridge colony for yourself, now is a great time of year to do it!  You can park at the Austin American Statesman building and watch from the South Congress Bridge.  Many people often gather on the hike and bike trail, just east of the bridge along Town Lake.  One of the best ways to see the South Congress Bats is from the water of Town Lake also known as Lady Bird Lake.  Companies like Capital Cruises host nightly sunset bat watching tours. Alternatively, you can rent a canoe, kayak or paddle board to view the bats in a more intimate environment.