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$2.4 million NSF grant for software design
Bat study translates into dollars and census
By David J. Craig
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Brazilian free-tailed bats emerge from caves by the millions on summer evenings in south-central Texas, eating crop-destroying insects and thereby providing a vital service to agriculture. Photo by Thomas Kunz |
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From a distance, the millions of Brazilian free-tailed bats pouring out of south-central Texas caves and spreading out against the deep blue summer evening sky look like huge plumes of smoke. With a sound like sheets snapping in the wind, the bats emerge from their daytime resting places in seemingly endless dark swaths — their exodus from a large cave can take as long as four hours. Like the locals who pile onto specially built grandstands to watch the spectacle, Thomas Kunz is awestruck before what he calls one of “the great wonders of the world.”
But Kunz, a CAS biology professor and director of BU's Center for Ecology and Conservation Biology, wants the bats to be appreciated on a more material level. Since 1999, he has directed an effort to census the region's bat population — which he says protects local corn and cotton crops by eating pest insects — so that its fluctuations can be measured and its economic impact assessed. The multidisciplinary research project was expanded recently with a five-year $2.4 million National Science Foundation grant, which funds the development of computer software that will help count the bats, as well as related studies on the bats' diet and foraging patterns. Also involved in the project are Cutler Cleveland, a CAS geography professor and director of the Center for Energy and Environmental Studies, Margrit Betke, a CAS computer science assistant professor, and Stan Sclaroff, a CAS computer science associate professor.
“Having an accurate census of these bats is critical,” says Kunz, who speculates that 100 million Brazilian free-tailed bats live in the area targeted by the study. “Ultimately, we want to be able to translate the value of these bats into dollars, because that's what will allow us to communicate the importance of preserving them.”
Cheap help
Because they can eat two-thirds of their body weight daily in corn earworms, cotton bullworms, and other insects, Kunz says, Brazilian free-tailed bats “essentially provide a shield that protects crops” not just in Texas but across the Midwestern cornbelt, through which the insects travel northward each year. The bats themselves migrate from their winter home in Mexico to the southwestern United States beginning in February every year, with females returning to the caves of their birth, and males inhabiting different caves. Kunz's research team is attempting to census the matrilineal colonies in about a dozen caves in a region of Texas twice the size of Massachusetts.
Some caves in the area west and north of San Antonio have been estimated to contain as many as 20 million bats, but Kunz says no reliable method exists for counting them. Studies have suggested, however, that Brazilian free-tailed bat populations in Arizona have been decimated by pesticides over the last few decades. And in south-central Texas, “there has been a concern about depletion of the bat population, although estimates about numbers are not scientific,” he says. “We want to develop a quantitative method for counting these bats so we see if the population is dropping, and in order to have a baseline for future comparisons. We'd like to be able to measure the impact on the bat population of climate change, for example, and of changes in agriculture practices, such as the use of genetically engineered corn that is resistant to insects.”
To count the bats, Kunz's research team uses infrared thermal cameras to record images of bats leaving their caves at night. A complex computer program created by Betke and several of her graduate students then analyzes the images, distinguishing areas of varying heat intensity. “A challenge is designing algorithms that can tell the difference between a bat and parts of an image that may have a similar thermal intensity, such as vegetation in the background, or a cloud,” says Betke. “One trick we use to identify the bats is their fast movement. Another is the fact that they're warmer in the center of their body, whereas vegetation tends to be uniformly warm.”
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Thomas Kunz, a CAS biology professor and director of BU's Center for Ecology and Conservation Biology, and Margrit Betke, a CAS computer science assistant professor, are developing cutting-edge methods of computer analyses for censusing Brazilian free-tailed bats in Texas. Photo by Vernon Doucette |
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Attaching a figure
Over the next five years, Betke plans to fine-tune those algorithms, and to develop a method by which two infrared cameras will be used to track bat movements, creating a binocular effect that will perceive the bats in three dimensions, much like a pair of eyes. Currently, Jason Horn (GRS'02,'04), a Ph.D. student working under Kunz, is analyzing data collected during the first three years of the project with Doppler radar, which is often used by meteorologists to track clouds, to better understand their movement patterns.
Also as part of the NSF study, Kunz has assembled mathematicians, meteorologists, entomologists, and economists from the University of Tennessee and the USDA Agricultural Research Service to measure a variety of benefits the bats provide their ecosystem, such as increased crop productivity and reduced pesticide costs. By combining data that the BU-led researchers gather in the field with data mined from state records of crop types, crop yields, and pesticides used, Kunz's team intends to build a complete picture of the role of the Brazilian free-tailed bat in the natural ecology and the economy of south-central Texas.
“We'll start by determining the economic impact of the bats at the local level,” he says, “and from there we'll extrapolate to cover about 14 states, all the way up to Minnesota.” The researchers also are working with Texas Parks and Wildlife to create and distribute educational material about bats.
The project, Kunz adds, should have repercussions in many disciplines because of its innovative combination of biology and computer science research techniques. “Because we're using infrared thermal imaging cameras, we don't need light sources to record video images of bats as they leave their caves for nightly feeding,” he says. “Our use of computer-vision software to count individual bats in these clouds of thousands brings a new dimension to this research and to computer vision itself, improving it as a tool for counting anything that moves, whether for conservation biology or homeland security.”
9
January 2004
Boston University
Office of University Relations