Bat Colony Occupies North Austin Overpass

Come see for yourself, and bring a hat...

Dusk at the McNeil and I-35 Overpass bridge, July 17, 2013. Rebecca Bennett.

Something’s stirring under the McNeil and I-35 Overpass in Round Rock.

At around dusk on most evenings between March and November, teeming black clouds spawn from crevices beneath the bridge and lurch across the sky in narrow columns. Hat-clad and sometimes umbrella-carrying spectators come in twos and threes to see the sight and dodge falling guano.

Apparently, the Congress Bridge isn’t the only place to watch bats around Austin.

The bats of Round Rock begin their nightly feast, July 17, 2013. Rebecca Bennett.

While South Congress’ colony of 1.5 million bats is a popular tourist attraction, few know about the smaller (but no less dynamic) bat colony beneath Round Rock’s McNeil and I-35 Overpass. Like their Congress counterpart, the bats of Round Rock are female Mexican free-tailed bats, which migrate to raise their young in Texas’ relentless summer heat.

At least someone here loves the humidity!

A downed bat crawls through guano to higher ground, July 17, 2013. Rebecca Bennett.

Mexican free-tails may be common bats, but they do boast some impressive stats; not only are they capable of traveling up to 100 miles per evening to catch food, but also their small, streamlined build allows them to fly up to 60 miles per hour.

To a bat, the sky is an all-you-can-eat insect buffet, and each bat can eat up to two-thirds of its body weight every night. This means that the Round Rock colony eats an estimated 20-30 thousand pounds of bugs per evening!

Maybe pigs really do fly.

The bats of Round Rock spiral through the sky, July 11, 2013. Rebecca Bennett. 

While bats are a horror to many—guano and rabies and vampires, oh my!—local farmers are grateful, as the bats’ bug-eating frenzies can save farmers millions in pesticides. Oh, and are you enjoying that shot of tequila? You can thank the bats for that too, since Mexican-free tails pollinate agave plants.

The Round Rock bats’ aerial displays are always impressive, but the best time to watch is during August when the pups begin flying and the colony’s size doubles.

Spectators gathers to see a downed bat, July 17, 2013. Rebecca Bennett.

For the ideal experience, twiddle your thumbs until just before dusk, and then drive to the NAPA Auto Parts store at 601 N I-35 Frontage Rd, where you can park. You won’t need directions after that—the smell of guano and the high-pitched drone of thousands of screeching bats will lead the way. You could watch the show from NAPA’s front porch at a safe distance, but those seeking a more interactive experience should put on a hat and cross the street for a closer look. 

If you’d like to pretend that you’re Batman and become one with our state flying mammal, you can venture under the bridge, but be warned—all of that “mud” beneath your feet is not mud.

For more information about the Round Rock bats, visit or read this article by Texas Parks & Wildlife. Do not handle downed bats, as they can carry harmful diseases, including rabies.

McNeil / I-35 Overpass Bridge

601 N Interstate 35 Frontage Road
Round Rock, TX Map


Tags: bats, Round Rock

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