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Bat-o-nomics

In a new study, scientists hope to quantify the value of bats in Texas.

By Sheryl Smith-Rodgers

It’s dusk in the Hill Country, and a bat flits out of Bracken Cave in northwestern Comal County. Another follows, then a few more. Soon, a cloud of Brazilian free-tailed bats spirals from the cave and disappears into the darkening sky.

“It’s one of the great wonders of the world,” says Dr. Thomas Kunz, the director of Boston University’s Center for Ecology and Conservation Biology. “Watching bats emerge is like watching flames of a fire — it’s mesmerizing.”

An estimated 100 million Brazilian free-tailed bats (Tadarida brasiliensis) roost in caves, under bridges and within buildings across Central Texas. During their nightly forays, they consume enormous amounts of insects, including pests that wreak havoc on area crops. Researchers like Kunz want to know more precisely their significance to agroecosystems in Texas.

A five-year, $2.4 million project — funded by the National Science Foundation — is underway to assess the bats’ ecological and economic value.

Kunz leads a team that includes mathematicians, meteorologists, climatologists, economists and entomologists from the University of Tennessee, the U.S. Depart-ment of Agriculture and TPWD.

A major goal will be to count the bats. Using infrared thermal video cameras and a specialized computer program, researchers take images of bats at night as they leave 12 selected caves and several key bridges. “They fly out at 600 - 1,000 bats per second,” Kunz says. “No one could stand there and count them one at a time.”

Having a more accurate handle on bat numbers will better equip scientists to estimate how much they’re eating on the fly at night. Plus, DNA tests on bat feces will reveal exactly what they’re devouring — likely thousands of destructive corn earworm moths that migrate north from Mexico in June.

According to Kunz, biologists already know that a nursing mother bat weighing 12 grams can consume up to two-thirds her body weight in insects every night. A million nursing bats eat up to 21.5 tons nightly, so the bats’ appetite translates to less need for pesticides to treat corn and cotton.

“Which reduces costs for farmers,” Kunz adds, “and also costs beyond purchase, because pesticides tend to accumulate in the environment.”

Part of the research project includes developing educational materials that will teach people how bats benefit the environment. “Historically, bats have been portrayed as evil,” Kunz says. “They’re considered to be bad because they come out at night and are shrouded in myth and superstition. It’s just a matter of putting bats in perspective. They do have many valuable traits.”

Patricia Morton, program leader for conservation outreach in TPWD’s Wildlife Division, will produce two videos and a bilingual children’s book on the importance of bats to agriculture.

“We share the species with Mexico, so it makes sense to produce materials in English and Spanish,” Morton explains. “If the bats are not protected in Mexico, where they overwinter, then they won’t be as effective in consuming agricultural pests here in the U.S.”

“In Mexico, the bats roost in such large numbers in caves that if someone started a fire, they could kill a huge number of bats,” Morton says. “Bats roosting in large numbers are always vulnerable to human disturbance,” Morton adds. “Education on both sides of the border is essential to maintaining healthy populations of these highly beneficial animals.”

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