Monika Maeckle

By Monika Maeckle

Every night this summer, a bachelor boys’-night-out unfolds around dusk as an estimated 20,000 male bats leave their roost at the IH-35 bridge near Camden and Newell along the San Antonio River’s Museum Reach.  The summer colony flies into the night from the eaves of the bridge to feast on insects.   Interested observers can witness the nightly nature phenom from the banks of the San Antonio River.

San Antonio River Bats
20,000 male Mexican free-tailed bats emerge at dusk from the I-35 bridge at Camden Street. (Photo courtesy SARA.)

On a recent balmy Tuesday evening, about 250 bat fans lined the riverbanks, awaiting the bats’ emergence.  Grandparents with grandkids, families and children, couples walking dogs–even the occasional cyclist–paused to take in the spectacle.  Representatives from the San Antonio River Authority staged an informal “Bat Talk,” an educational chat to enlighten the crowd.

“This colony makes a small dent in the insect population,” explained Matthew Driffill, a SARA education specialist assigned to Bat Talk duty.  SARA stages the Bat Talks each Tuesday evening in July and August at 7:30 PM.  The bats emerge around 8 or 8:30, depending on conditions.

YouTube video

Driffill shared interesting bat facts:  the all-male colony of Mexican free-tailed bats arrives in March and departs in October.  The nocturnal mammals  navigate using echolocation.   The bat density in the eaves of the bridge is about 200 bats per square foot.   Bats like it hot, somewhere between 98 and 106 degrees. They assist mightily with insect control and pollination chores, and despite their creepy reputation, bats are pretty much harmless.

Bat Talks
Bat Talks every Tuesday in July and August on the San Antonio River, 7:30 PM

“You’re more likely to get rabies from a dog than a bat,” said Driffill in answer to a question from the crowd.

Because of our relatively rainy year, the bats have emerged later in the evening, causing a less dramatic show for the crowds.  But as the summer wears on and rain and moisture run scarce, they emerge earlier in the evening in order to locate and consume enough insects to fuel their activities. When moisture prevails, the bats leave later, in the dark, since they don’t have to fly as far for food.  Bats prefer the cover of night, which protects them from hawks, owls and other birds of prey.

Matthew Reidy, urban biologist for Texas Parks and Wildlife, told the Rivard Report earlier this year that San Antonio’s urban bat colony went relatively unnoticed for years. “Nobody really noticed them until the the Museum Reach project opened in May of 2009, but people had always seen stuff fly out,” he said.   The Museum Reach has brought the bats’ presence “to light” said Reidy.

Matt Driffill of SARA at Bat Talks
Matt Driffill of SARA provides interesting bat facts at weekly Bat Talks.

Central and South Texas are well-known for their welcoming bat habitats.  The maternal colony living under the Congress Avenue Bridge in Austin hosts about 1.5 millions of the creatures.   Bracken Cave, in Comal County, is home to the largest Mexican free-tailed bat colony on the planet with 20 million bats, and other locales, like Mason’s Eckert James River Bat Cave, a Nature Conservancy preserve, and even the parking garage at North Star Mall, have transient bat colonies–some male and some maternal.  Collectively, Texas’ seasonal bat population consumes 1,000 tons of insects each evening, according to Bat Conservation International.  Hard to visualize, but…imagine what the mosquitoes would be like if they weren’t around.

The bachelor bats will continue their  boys’-night-out insect feast every evening until mid October.  Then, as the weather cools, one night the bats will continue flying south to Mexico where they will hook up with their female counterparts for some winter mating.   The bats will return in the spring and the females will give birth in Austin and the other maternal colonies.

Only three more Bat Talks remain for this season.  As soon as school starts, SARA ceases the weekly educational chats.

Bat Talks on the San Antonio River Camden and I-35
Bat Talks on the San Antonio River Camden and I-35. (Map by Google.)

Bat Talks on the San Antonio River

Where: River level near the intersection of Camden and Newell

When:  Tuesdays  August 14, 21, and 28  7:30 pm – 9:00 pm

Park at the Pearl and walk five minutes south along the river;  or, park at Newell and Camden and follow the ramp down to the river.

For more information contact Matthew Driffill at 210.302.3222 or

Monika Maeckle writes about gardening, butterflies, conservation and the Monarch butterfly migration at the Texas Butterfly Ranch.  She covers nature in the urban environment for this website.  You can reach her at or follow her on Twitter @monikam.

San Antonio Report co-founder Monika Maeckle writes about pollinators, native plants, and the ecosystems that sustain them at the Texas Butterfly Ranch website. She is also the founder and director of...