Watch 1.5 million bats drop down from under the Ann W. Richards Congress Avenue Bridge in Austin, Tex.CreditMerlinTuttle.org/Bat Conservation International
Every night in the summer, more than 15 million bats emerge from a hot, cavernous sinkhole just outside San Antonio. They spiral up and out of the cave’s gaping mouth like a tornado and slowly gain elevation. If you’re sitting nearby, you can feel the wind from their wings.
Once the bats reach the treetops, they form columns that flow out and over the hills like plumes of smoke that appear to never end. It’s dinner time in Texas, and in the corn and cotton fields, the hairy, winged mammals will feast on moths throughout the night.
Millions of Mexican free-tailed bats live in the caves and bridges of Texas.CreditMerlinTuttle.org/Bat Conservation International
This bat emergence at Bracken Cave, home to the world’s largest bat colony, requires an appointment, but it’s just one of many nightly shows you can catch in Central Texas in July, August and September. You can also see them at Old Tunnel State Park, just south of Fredericksburg, or for a more urban experience, you can have a picnic or cocktail and watch 1.5 million bats drop down from under the Ann W. Richards Congress Avenue Bridgein Austin and take off across the river like a school of fish.
They do this every night, but the best time to catch them is when it’s hot and dry and they’re hungry, because that’s when they’ll head out early.
“The hotter and more uncomfortable you are, the better the bat flight,” saidMylea Bayless, an ecologist for Bat Conservation International.Watching the show at Bracken Cave. Video by Bat Conservation International
As the saying goes, everything’s bigger in Texas, and the caves and bridges that these Mexican free-tailed bats call their summer home are no exception. The dome ceilings of large caverns — natural or constructed — trap heat, making them the perfect temperature for females to roost and to raise their young. Warm, stable roosts like Bracken Cave are essential because baby bats are born hairless and have only a few months to develop before migrating to Mexico and Central and South America in the fall. These bat pups spend their energy on growth, not thermoregulation. The millions of bats you see take off at once in Texas are all females and babies. The males are around, but they’re scattered about in smaller caves or parking garages.
If it’s not the big Texan caverns, it’s the migrating corn earworm moths that bring the bats here every summer. A mother bat will consume about two-thirds of her body weight in insects at night to meet her energy demands. Economists estimatethat bats save Texas more than $1 billion on pesticides annually.
The feeding frenzy can last for hours, but as day breaks, the bats return to their roosts. If you’re up for a 5 a.m. bat shower, you should head back out.Residents of Bracken Cave: Juvenile Mexican free-tailed bats Video by Bat Conservation International
“They come shooting down out of the sky like rain,” Ms. Bayless said, and they “do this crazy Olympic gymnastics type of thing” to get back into the crevices at the bridge. Using superlong toe hairs like whiskers, they find their way in the dark. The bats return to the cave in a reverse tornado and slow down by opening their wings like a rudder or sail. Ms. Bayless says it sounds like millions of people blowing on blades of grass, or a swarm of bees.