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Survey Nets Bats

Between May 15th and August 15th, scientists from the Illinois Natural History Survey are conducting a bat survey throughout northeastern Illinois in hopes of confirming the return of the Indiana bat to the Chicago area. Although this federally endangered bat has not been recorded in the region since 1928 when it was discovered outside The Field Museum, a confirmed sighting in Newton County in northwestern Indiana has prompted a cooperative effort amongst government agencies to survey sites within Cook, DuPage, Kane, Lake, McHenry, Kankakee, and Will Counties.

To conduct these surveys, scientists prowl older forests for wooded areas with large, dead trees, and a nearby water source. “The female Indiana bats like to spend most of the day hiding behind loose bark,” explains Joyce Hofmann, senior research scientist for the Natural History Survey. What about the males? “They’re not as picky,” she says. Once scientists find a survey site, they erect 20-foot-high poles and return that evening to raise mist nets and begin observations. “We spend two nights at each site, checking the nets every ten minutes for five hours,” says Hofmann. “The bats are most active for the first couple of hours after the sun goes down, so after five hours you don’t see much activity.”

Because the mist nets can reach 20 feet by 40 feet, they are large enough to capture bats that fly on the treeline as well as foragers that fly lower to the ground. Although no Indiana bats were netted during the 2006 sampling season, researchers did observe four main bat species: big brown bat, hoary bat, northern bat, and eastern red bat.

The red bat is the only mammal in Illinois in which the sexes are of different colors (the male is rusty red, while the female is chestnut brown). This bat also never enters caves. The female gives birth to five babies at once, and is often so burdened by the weight of her clinging offspring that she can fall right off the tree.

The Northeastern Illinois bat survey is funded by the Illinois Department of Transportation and the Illinois Tollway. The reason is quite practical — when building new roadways, the department is required to do environmental surveys in areas where there may be federally endangered species. Hopefully the result will be confirmation that the Indiana bat is back. “There has not been a lot of survey work done in this area,” Hofmann says. “It’s time to take a close look into northeastern Illinois!”

—Jennifer Tang

Related Articles:

2006 Bat Survey Results on Illinois Department of Transportation Web site