The Congress Avenue Bridge

Last updated on August 22, 1999

From March through October the largest urban population of bats in North America roosts under the Congress Avenue Bridge in Austin, Texas. During the summer months as many as 1.5 million Mexican free-tailed bats take shelter there over the waters of Town Lake.

When workers renovated the bridge in 1980 they unintentionally made it a perfect habitat for small bats. People in the community were very surprised and concerned about the bats when huge numbers of them were first discovered there. When the city was considering plans to get rid of the bats, the Austin-based non-profit organization Bat Conservation International (BCI) stepped in and explained how helpful the bats are to the local ecosystem.

After the people of Austin learned that on a given night, the Congress Avenue bats together consume between 5 and 15 tons of pesky insects, the controversy died down. Austin is now proud of of its bats and the attention (and business) they draw.

The Austin American-Statesman, a newspaper whose office is right next to the Congress Avenue Bridge, allows visitors to park there to watch the nightly emergence of Mexican Free-tailed bats. Local artist Dale Whistler designed a stylized bat sculpture which stands across the street from the American-Statesman office and serves as a landmark to visitors.

[This photo and the next one seem to have suffered processing problems, unfortunately.]

The dark patches in the shady upper portions of each of the bridge supports are actually teeming clusters of bats. There are a few hundred in each cluster. But that's not all- the numerous vents that span the length of the bridge (the dark stains on the first support point up to the vents) are jam-packed with bats. You can hear them chirping away long before the emergence begins.

The 750 thousand adult bats who flock to the bridge each March are mostly pregnant females. (Males stay elsewhere, in smaller groups.) The pregnant mothers will each give birth to one pink little naked pup, doubling the population to 1.5 million by the end of Summer. When their mothers are out catching bugs for the night, the pups all scoot together to keep warm. In the morning when the mothers return they are able to find their own babies by recognizing their scent and the sound of their voice.

This was taken from on top of the bridge. Many cars slow down (and some even stop) during the emergence. When you're standing on the bridge you can look down over the rail and see bats flying out right under your feet.

Mexican free-tailed bats (Scientific name: Tadarida brasiliensis) migrate north from Mexico during Summer just like North American birds migrate south during Winter.

 Want to see the bats for yourself?

From mid-March through October you can watch the bats emerge from almost any location on or around the Congress Avenue Bridge. The later months (August-October) are better, because by that time the babies are big enough to fly, so you'll see twice as many bats as you would earlier.

There is no fixed time for when the bats emerge; it changes with the season. But according to a flier that we picked up outside the American-Statesman, there are two ways that you can find out when the estimated emergence time is on a given day: