SPRING VALLEY — This winter, about 200 bats spent their hibernation nestled into corners and cracks seven stories below ground at Crystal Cave in Spring Valley. The year before, there were 800 of them.

The nocturnal, furry creatures that play a large part in the state’s pest control have been hit by white-nose syndrome, said Crystal Cave’s executive director, Eric McMaster.

“They end up starving to death, really,” McMaster said of the fungal disease. “It’s really decimating the bat population.”

The syndrome that fells bats by causing them to wake up too often during hibernation first appeared in the U.S. in 2006 on the East Coast and has slowly been traveling west. It was found in Wisconsin in 2014.

While the bats at Crystal Cave are no exception to the disease’s destruction, they are contributing to scientific understanding of how it spreads and affects them during hibernation. The bats have been recent research project subjects for both a team from the University of California, Santa Cruz — which McMaster refers to as a premier bat research university — and the Wisconsin Department of Natural Resources.

J. Paul White, mammal ecologist with the Bureau of Natural Heritage Conservation at the state DNR, said one such project tested how the disease moves from bat to bat.

“We were definitely very interested in knowing if bats might be more vulnerable to the disease based on their social behavior,” White said. “That was something that was really groundbreaking.”

To accomplish that, UC Santa Cruz researchers brushed seven different bats with fluorescent dust right before they retired to hibernation. In spring, when the bats emerged from hibernation, researchers explored the cave with ultraviolet lights to see what had happened.

They discovered the marked bats had transferred their flourescent dust to others in the cave during the hibernation period.

“The idea, of course, is the fluorescent dust is a surrogate for the fungal white-nose,” McMaster said. “It really shows how you can have just a few bats in the hibernaculum, and it can spread extremely quickly.”

That project has yet to complete the peer review process, White said.

Other research projects at the cave involved marking the bats with tiny transmitters — similar to key fob for building access — that allowed researchers to track how often bats come and go, McMaster said.

Another project aimed at quantifying how often bats wake up during hibernation, and for how long. White-nose syndrome causes an itchy, irritating sensation in bats, thus waking them up when they’re supposed to be asleep, McMaster said. Though bats naturally wake up occasionally during hibernation, if they do it too often, they’ll use up too much of their fat reserves and starve.

According to whitenosesyndrome.org, the disease is caused by a fungus that thrives in the cold environments where bats hibernate. Bats with white-nose syndrome often display a white fungus on their noses and on other hairless parts of their bodies, including their wings. The fungus isn’t always easily visible, however.

The bats at Crystal Cave were popular research subjects before the disease manifested, White said. He pointed to a team from Minnesota that used the caves as a site for research in the 1990s, before the DNR had a bat program established.

White said there are numerous reasons Crystal Cave is an ideal spot for research, including private ownership, multiple caves on the 100-acre site and consistent oversight from McMaster that protects the bats from human activity while they’re hibernating.

“They’re always consistently monitored, so that helps,” he said, “as opposed to a site in the middle of a forest, where it’s hard to understand if human presence is interfering with the research.”

Despite ongoing research, McMaster warned the bat population is going to continue to drop, a trend at all bat sites across Wisconsin.

“If you had a disease that was killing all your songbirds, can you imagine the uproar from the general public?” McMaster said. “But you don’t see that for bats. That frustrates me.”

Contact: 715-830-5828, lauren.french@ecpc.com, @LaurenKFrench on Twitter