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By Lana Robinson
Field Editor
If vampires come to mind when you think of bats, you may want to consider some recent scientific data that suggests bats are actually the friend of humans, particularly farmers.
Millions of Brazilian free-tailed bats (Tadarida brasiliensis) consume enormous quantities of insects—corn earworms, cotton bollworms and tobacco budworms—on summer nights throughout the southwestern United States, including Texas. Their screechy sounds chase away numerous other pests. In Mexico, the bats cross-pollinate the agave, a cactus that produces tequila juice, which helps retain the health of the plants. But the myths and negative stereotypes associated with bats have made them a target of vandals, who have intentionally destroyed the bats' habitat. A research project launched earlier this year seeks to change that by assessing the ecological and economic impact of Brazilian free-tailed bats on agroecosystems dominated by cotton and corn.
According to Thomas Kunz, director of Boston University's Center for Ecology and Conservation Biology, the Brazilian free-tailed bat eats two-thirds of its body weight in moths each night.
"Bats are natural predators of insects that destroy economically important crops. This is a service with great economic value and makes a strong case for conserving bats in our environment," said Kunz, who is leading the $2.4 million multidisciplinary research project, funded by the National Science Foundation.
Kunz's team, made up of faculty associates and their colleagues from the University of Tennessee, the U.S.Department of Agriculture, and Texas Parks and Wildlife Department, spent much of the summer attempting to census the maternity colonies in about a dozen caves and several bridges located over 21,000 square miles of south-central Texas. The bats migrate from their winter home in Mexico to the southwestern United States beginning in February, with females returning to the caves of their birth, and males usually inhabiting different quarters, including caves, mines, bridges, and buildings. Some of the caves and fields studied were in the vicinity of Fredericksburg, Bandera, Mason, and Uvalde.
Previous studies have estimated that Brazilian free-tailed bats in Texas number around 100 million, but Kunz doubts the accuracy of that high figure.
"Having an accurate census of these bats is critical to this study," Kunz said, noting that he and his associates have developed a quantitative method to count these bats with the goal of establishing a baseline for future studies.
In order to more accurately census bats, Kunz's team used infrared thermal cameras to record and count images of bats leaving their caves at night. A complex computer program, developed by Margrit Betke, a co-investigator on the project, analyzes the images, distinguishing areas of varying heat intensity. The researchers are also interested in measuring the impact of climate change, as well as changing agriculture practices (i.e. genetically-altered corn), on the bat population. Kunz is also working with mathematicians, meteorologists, and entomologists from the University of Tennessee and the USDA Agricultural Research Service to quantify the bats' impact on factors such as crop productivity and use of pesticides. By using DNA tests on bat feces, the scientists can calculate how much of the bats' diet consists of moths that have metamorphosed from corn earworms, cotton bollworms and tobacco budworms. By combining field data on bats with data mined from state records of crop types, crop yields, and pesticides used, Kunz's team will build a complete picture of the role of the Brazilian free-tailed bat in the natural ecology and the economy of south-central Texas.
Additionally, the scientists are exploring how the feeding sounds of Brazilian bats affect the moths.
"In the future, farmers in South Texas may be able to broadcast an imitation of that sound to intimidate moths and keep them from laying eggs on cotton crops," said Kunz.
While the research is underway, the Texas Parks and Wildlife Department plans to start a campaign with videos and children's books to teach the public about the benefits Brazilian free-tailed bats provide to the ecosystem.
The role of Patricia Morton, program leader for education at the park department's Wildlife Diversity Branch, is to videotape and write articles about the research so people will stop disturbing the bats' habitat. According to Morton, vandalism of bat caves isn't as much of a problem in Texas as it is in Mexico, where the bats spend their winters.
"Damage to one cave can seriously hurt the bat population because they huddle in colonies of millions," Morton said.
Superstition is often the cause of the vandalism, she said. The videos and the literature will be distributed throughout Mexico and Texas in both English and Spanish. Texas Parks and Wildlife Department is working with the research team to create bilingual video programs and a children's book that feature the importance of bats to Texas agroecosystems. These education items will highlight project research activities and the natural history of the Brazilian free-tailed bats and are expected to be available in 2006.
For more information about this project , visit the Texas Parks and Wildlife Department website: www.tpwd.state.tx.us/nature/wild/mammals/bats/intro.htm; or contact Morton at 512/912-7011 or email: pat.morton@tpwd.state.tx.us.
