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Holy hibernacula, Batman!
UW-Madison Has Its Very Own Sleuth Of The Night

October 21, 2002
Emily Carlson, 608-262-9772 emilycarlson@wisc.edu

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Bat hibernate
MADISON -- Dave Redell lives in Madison - not Gotham City. He drives a Honda Civic - not the Batmobile. He wears jeans and plaid shirts - not a cape and mask. Yet, many people think he's the Hollywood superhero.

"I'll show up at a farm with my assistant," he says, "and the landowner will automatically call us Batman and Robin."

The reason's simple: Redell, a researcher in the wildlife ecology department at the University of Wisconsin-Madison, studies bats. During the summer months, he spends his nights - just like Batman - patrolling dark streets, parking lots and mine entrances in search of these flying, nighttime predators.

As you'd expect, Redell knows all the trivia: There are about 1,000 species of bats, accounting for 20 percent of all mammal species, and they live throughout the world, with the exception of high altitudes and the Arctic. About 700 species feast solely on insects, and each of these insectivores can gobble up as many as 600 mosquito-sized critters per hour. In Wisconsin, seven types of bats glide through the night skies. No need to worry about the blood-sucking vampire bats here, or nearly anywhere, because only three species of them exist.

Despite all this knowledge, Redell says, "There's so much to be learned about bats."

One important question he wants to answer is how many bats spend the winter months roosting in the cracks and fissures of the Neda Mine, one of the largest bat hibernacula in the Midwest? Redell says that knowing this number could help conservationists and developers recognize the importance of protecting this area as a bat habitat.

With its four miles of tortuous tunnels, the Neda Mine - an old iron-ore mine north of Madison that was abandoned in 1914 - is a hibernating haven for several species of Wisconsin's bats. From as early as August, the bats enter the mine, find the perfect spot and just hang out (upside down, of course). Come spring, they make their exit.

During the night, they swoop under tree limbs and above bushes to feed on insects. "Some nights there are so many bats, you can feel their wings against your face," says Redell. Just before sunrise, many return to the mine.

Counting these bats, though, isn't exactly like counting sheep. Besides putting many diurnal mammals like us to sleep, it's virtually impossible. First, previous estimates have placed the hibernating population of bats between 300,000 and 500,000. Second, the bats are tiny, making some heads hard to count. And, perhaps the biggest caveat: all the entryways are sealed with metal grates that admit bats, but not people.

With the aid of technology, some of which he has helped develop, Redell can track the number of bats that leave the mine during the spring.

At each of the four remaining mine entrances, Redell has mounted detectors that shine two beams of invisible, infrared light across the entrance to two corresponding photocells. Based on the way a flying bat breaks the light beams, the photocells can tell whether a bat is coming or going. The detectors run year round, 24 hours a day. "This way, you don't have to have someone sitting outside all night counting," says Redell.

By comparing the detectors' data with what he calls "painful frame-by-frame images from an infrared video camera," Redell can check the accuracy of the recorded number.

Preliminary measurements from last year indicate that about 150,000 to 200,000 bats used the mine, but Redell thinks that combining data from 2001 and 2002 will give more reliable estimates.

Even with the detectors and their downloadable data, Redell spends many of his spring and summer nights up at the mine. He usually arrives just before sunset, sets up and then works five to six hours in the field - in complete darkness. Many times, he strolls the land around the mine with an ultrasound sensor that translates the bats' high-frequency sounds into noises humans can hear. This information lets him chart where the bats head and why. "From the sounds they make, you can tell whether they're feeding in the area or just cruising by," he says.

A few hours before sunrise, Redell packs up and heads home: "I usually leave right before the bird crew shows up."

There are many things Redell likes about studying bats, even though he jokingly says, "I think I was drawn to them because I've always been a night person." But, most of all, he recognizes the important role bats - especially the insectivores - play in the ecosystem. "By knowing the number that live in Neda Mine and by understanding more about their behavior," he says, "we can assess from year to year if the population is doing all right."

For more information, contact David Redell, 608-263-7595; dnredell@students.wisc.edu.

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