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Conservation biologists radio-track bat to reveal summer habitat secrets

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HUDSON, Wis. -- Somewhere in a Pierce County cave, one of the state's smallest bats is getting a well-earned rest from its 35-mile flight into conservation history.

The bat, an eastern pipistrelle weighing less than a nickel, led state conservation biologists on a historic chase last spring.

"Nobody had ever really done this before with this particular species in North America," says Heather Kaarakka, the Department of Natural Resources conservation biologist leading the eastern pipistrelle radio-tracking.

"We had tried the same thing the previous year and it didn't work. So to be able to track a bat this year from its hibernation site to its presumed summer roost was super exciting."

The biologists radio-tracked the bat as part of research to better understand the connection between habitats of bats that hibernate in caves or mines in the winter and spend their summers in the forests.

Such understanding is particularly important as eastern pipistrelles in Wisconsin and other states die from white-nose syndrome, a deadly bat disease that strikes while they hibernate. Study results will funnel into a habitat conservation plan for cave bats that roost in forests, including eastern pipistrelles and northern long-eared bats, Kaarakka says.

So in early May, she and other DNR biologists and volunteers placed fine-mesh nets over the entrances of a Pierce County cave and waited. They captured two female eastern pipistrelles, weighed them, and outfitted them with radio transmitters.

They released the bats around 11 p.m., and in a flash, the bats were gone. The bats headed due west and their human trackers did too. A few teams heard signals periodically as they headed west toward the Mississippi River following the bats, but by 12:15 a.m., all of the teams had lost the bat signals. "It was heartbreaking," Kaarakka says.

More than an hour later, Conservation Biologist Katie Luukkonen, who had been driving westward hoping to pick up the signal, heard a beep.

"I think I lucked out on that," she says. "Finding that signal again was one of the most exciting things I've done in conservation biology."

The other teams crossed the river to parallel her and they all spent the next two hours tracking the bat back and forth across the Mississippi River until it settled on a birch tree north of Hudson.

It was 3:30 a.m. Kaarakka and Luukkonen stayed until dawn to make sure the bat didn't move. They returned the next few nights to watch its movements.

"Katie saved the day," Kaarakka says. "There was a lot of hugging. It was pretty incredible to finally see some results."

The bat had traveled roughly 35 miles in 3.3 hours, at a rate of about 10.6 miles per hour, in a straight line from the hibernation site to the river as the bat flies. The telemetry results for this bat also suggest this species may move its greatest distances from hibernation sites during the first night of emergence.

"This is just one bat, so you can't draw too many conclusions from its behavior, but it's 100 percent more than what we knew before," Kaarakka says. "There is still so much to learn about eastern pipistrelles, but this is one piece of the complex puzzle of how we conserve them in the future."

To learn more about Wisconsin bats and efforts to protect them, search the DNR website, dnr.wi.gov, for keyword "bats."

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