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How to help hibernating bats defeat fungal disease?

Andrew Herberg, mammalogist, sets up a net during a bat survey on June 28 at Beaver Creek Valley State Park near Caledonia.
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Researchers will be keeping an eye on Southeast Minnesota caves this winter.

Bat populations that are being ravaged by a fungal disease spend much of the winter hibernating in area caves. The disease, called white nose syndrome, has killed hundreds, likely thousands, of Minnesota bats.

Bats hibernate at Forestville/Mystery Cave State Park and Crystal Cave in Spring Valley. The number of bats that hibernated at Mystery Cave was down 70 percent last winter, said Andrew Herberg, a mammalogist with the Minnesota Department of Natural Resources. At Crystal Cave last winter, an estimated 200 bats hibernated there — down from more than 800 the year before.

Various species use the caves as hibernaculum. Little brown bats, northern long-eared bats and tricolor bats share the space. However, the deadly fungus is equally inclusive in which species it affects.

Over the winter, the caves offer a snapshot at how the disease is progressing and signs have not been good the last few years, MnDNR officials said. It is also a chance to do research including possible treatments to fight the disease. Having the populations in one place is helping naturalists and scientists understand how the fungus spreads and is offering opportunities to test treatments.


The white nose fungus was first confirmed in Minnesota bat populations at Lake Vermillion in the winter of 2015-2016. Since then, the colony that hibernates at Soudan Underground Mine has declined by an estimated 90 percent.

The fungus usually takes hold in the winter. It causes bats to rouse too frequently when they should be hibernating, causing them use their energy and starving to death because food isn’t available.

Researchers from the Wisconsin Department of Natural Resources and the University of California, Santa Cruz brushed bats with fluorescent dust right before they retired to hibernation. In spring, after the bats left their hibernaculum, researchers explored the cave with ultraviolet lights to see what had happened.

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

Crystal Cave is an ideal spot for research, including private ownership, multiple caves on the 100-acre site and consistent oversight from Eric McMaster, Crystal Cave’s executive director, who protects the bats from human activity while they’re hibernating.

Some possible treatments including ultraviolet light exposure have been tried.

"There’s really been no silver bullet yet," Herberg said.

Crystal Cave can offer researchers a place to test such treatments — if the bat populations there don’t disappear entirely.


It’s the time of year where Minnesota’s caves can be warmer than the temperature outside.

Quarry Hill Nature Center in Rochester holds tours of the park’s historic caves every other week. The park was once the site of the Rochester State Hospital. Storage caves for the hospital were carved into sandstone on the grounds in 1882.

Tour dates:

Nov. 11; Nov. 25; Dec. 9; Dec. 23.

Tours begin at 1:30 p.m.

$2 for adults, $1 for children. Quarry Hill Nature Center members are free.

The caves are a short hike from the nature center building. All ages are welcome on the event but parts of the hike are not stroller or wheelchair accessible.


Two brown bats cling to the wall just inside the entrance to Mystery Cave in Forestville State Park. A fungus linked to white-nose syndrome was found in the park in 2015. The syndrome killed hundreds of bats at Lake Vermilion-Soudan Underground Mine State Park.

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