Is That Some Weird Storm On The Radar? Nope, It's Bats.

Aug 17, 2017

Take a look at this radar image of Central Texas. What do you see?

Do you see what look like green explosions? You can see the circles radiating from single points.

But that’s not rain — it’s bats.

“There’s different types of animals — and even insects — that the radar can pick up,” says Nick Hampshire, a meteorologist at the National Weather Service in New Braunfels.

It’s called “bioscatter.”

Every night around sundown between March and October, you see these little guys flying out of their caves and from under bridges to hunt for insects to eat. But there’s something about seeing them on radar that really gives you a sense of their sheer numbers that watching them in person just can’t.

During the warmer months, a colony of 15 million bats emerges each night from the Bracken Cave, north of San Antonio, for instance.

“The weather usually blows through from one direction or another,” says Lee Mackenzie, co-founder of the nonprofit Austin Bat Refuge. “But the bats and the bioscatter tend to emerge from single-point sources … and go out in concentric circles.”

The images don’t just look cool. Bat conservationists, like Mackenzie, use the data to track bat populations and keep an eye on any changes in their behavior that might signal a problem.

“We’re able to keep our finger on the pulse of what’s going on with all these bat colonies in the Hill Country and all around the area,” Mackenzie says. Their emergence “changes seasonally and according to how severe a drought we’re going into. We’re looking for correlations to see how the bats are being affected by various things — how they act seasonally and how the drought might be affecting them.”

In dry times, like the end of the summer, bats tend to emerge earlier because it takes longer for them to find food, he says. “So that’s what makes viewing so great for us at this time of year.”

Each night around sundown between March and October, millions of Mexican free-tailed bats emerge from the Congress Avenue bridge in downtown Austin.
Credit Mose Buchele / KUT

And when cold fronts come through, things get even more interesting.

“The thin line that marks the edge of the cold front a lot of times can be insects or other small particles that are picked up by the wind,” Hampshire says.

And sometimes you can see the bats on radar taking advantage of that — following the line of the cold front and feasting on the insects piling up along it.

“It’s fun to watch. You can let your imagination soar — they look almost like they’re surfing on that front,” Mackenzie says. “So, it’s kind of fun … we just kind of imagine ourselves up there with them.”