Ann W. Richards Congress Avenue Bridge

Built in 1910 and rehabilitated in 1980, the Ann W. Richards Congress Avenue Bridge spans 910 feet atop a series of concrete arches over Lady Bird Lake. Prior to the present-day concrete structure, the same location was crossed by a number of bridges made of pontoons, wood, and iron. Today, the bridge is home to the world’s largest urban bat colony, composed of up to 1.5 million Mexican free-tailed bats.

The Congress Avenue Bridge exemplifies how structures can be imbued with meaning far beyond what their creators intended or imagined. Viewed from street level, the bridge is a fairly unremarkable structure: a flat roadway, two sidewalks, and metal guardrails. The picture improves from the lakeshore, where the open web of thin vertical ribs that support the roadway contrasts the robust concrete pylons. But what makes this structure so remarkable is actually invisible most of the time: a thriving colony of Mexican free-tailed bats that resides within the structure.

The bats below the bridge have become synonymous with Austin; hundreds of visitors line the railings at sunset from spring until fall to watch the world’s largest urban bat colony take to the skies. The bats have been around since the bridge’s construction, but their population skyrocketed after the bridge was rehabilitated in 1980, when a series of 17-inch-deep by one-inch-wide joints were introduced into the structure. Unbeknownst to the engineers, the narrow but deep slots provided the perfect hidey-holes for the city-dwelling Chiroptera, which measure about 3½ inches long.

Despite their small stature, Austin’s beloved bats have an outsize economic impact to the tune of 100,000 visitors and over $10 million annually. The nocturnal residents even have their own festival—Bat Fest—that takes place on the bridge every summer and features live music, arts and crafts, and a bat-themed costume contest. The bats earn their keep, devouring over 30,000 pounds of pest insects every night.

With over half of bat species in the U.S. facing endangerment or declining populations, the bridge’s bat colony provides an important example for how human and animal populations can coexist. To learn how you can help the bats—and even adopt a bat for yourself—visit Bat Conservation International. – Bud Franck