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Spring 2008 Table of Contents

In the Field with BU's Bat Man

Infrared cameras and algorithms count mammals flying in dark

| From Commonwealth | By Edward A. Brown

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A thermal infrared image of Brazilian free-tail bats foraging at night. Image courtesy of Margrit Betke and Thomas Kunz

Although they maintain a dignified silence, at least to human ears, bats get a raw deal: they are swatted at with brooms and tennis rackets and vilified in folklore.

In fact, bats are hardworking and beneficial creatures that rarely pose any real threat to people and only occasionally carry bacteria and viruses that cause disease. There are more than 1,100 species of bats in the world, of which only 3 feed on blood. Few, if any, bite humans without provocation. Many species do, however, love to chow down on insect pests that otherwise wreak havoc for farmers.

And they are voracious. They eat about two-thirds of their own body weight each night, making a significant contribution to the health of an ecosystem by suppressing insect populations, which in turn reduces the environmental and economic costs of pesticide use. To better understand just how beneficial bats are as a natural pesticide, Thomas Kunz, a College of Arts and Sciences professor of biology and an expert on these flying mammals, has spent the past two decades devising ways of assessing their impact on natural and agricultural ecosystems. Most recently, he's been working at a dozen caves in the corn- and cotton-producing Hill Country of south-central Texas. Depending on the time of year, he says, about 1.2 million to 1.4 million Brazilian free-tail bats inhabit a single cave.

In order for Kunz and his colleagues to assess the bats' ecological and economic value, they must first determine how many bats are present in the regions they're studying. Getting an accurate count isn't easy; bats roost in dark places during the day and fly at night. The challenge, Kunz says, "is to observe in the dark and to minimize disturbance to them."

He and his team use advanced thermal infrared cameras, which detect the heat produced by bats, and sophisticated computer algorithms developed by colleagues in the University's computer science department to count the bats as they emerge nightly from the caves. Even though they stream out in dense columns, Kunz says, the technology makes it possible to "actually count just about every bat that passes through the camera's field of view."

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