Hi-Tech Bat Detector Sheds Light on Shadowy Species

Sharon Guynup
National Geographic Today
March 13, 2002

As evening falls in northwestern Belize, Bruce Miller stands in the forest, waving a small white box through the air. When a bat swoops overhead, Miller's laptop beeps and clicks, and corresponding lines and squiggles appear on the screen. He points to a succession of slashes. This one's a mastiff bat," says Miller, a zoologist with the Wildlife Conservation Society.

The white box is an electronic "ear" called the AnaBat. Hooked to a computer, it enables scientists to "hear" the inaudible calls of bats and determine the species of the "speaker." The device allows scientists to survey bat populations with unprecedented accuracy. These surveys, in turn, are helping conservationists determine which species are truly threatened and where protection is most needed.

Bats in Peril

"Bats are exceptionally vulnerable to extinction, in part because they are the slowest reproducing mammals on earth for their size, most producing only one pup annually," says Bob Benson, a spokesperson for Bat Conservation International. "More than half of the United States' 45 species are now either endangered or in severe decline. Losses are occurring at alarming rates worldwide."

William Gannon, a biologist at the University of New Mexico, adds, "In the U.S. and around the world, bats face serious threats, from habitat loss and pesticide poisoning to widespread extermination." He continues, "One of the big problems is that not enough is known about bat behavior because they're nocturnal and they fly."

Miller and Gannon are among those who combine acoustic technology with traditional study methods—netting, trapping, and hand-examining bats to fill these knowledge gaps.

In order to protect these elusive mammals, scientists must determine which species are where and which are in trouble. They also must locate critical roosting and feeding areas.

Identifying Bats by Voice

Recent advances have transformed bat detectors from mere listening devices into "voice recognition" systems for echolocation calls. These cries, which are beyond the range of human hearing, bounce off objects and echo back, guiding bats as they hunt and fly.

Each bat species has a distinct vocal signature, which AnaBat translates into a unique shape and pattern on a computer screen.

Miller first tried out the AnaBat on his front porch in Belize six years ago. Within five minutes he identified four different species buzzing the house. "Then it became a question of capturing the bats to see who they were. It became a biological detective story," he remembers.

Miller and his biologist wife, Carolyn, began cataloging calls in the field. At the same time they trapped bats and used AnaBat to definitively match species to voices. "Once you have reference calls in an acoustic archive, then you can just ID them by voice in the field," says Miller.

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