Soudan Mine Bat Population Seems to Continue Declining

Baihly Warfield
March 30, 2017 07:20 PM

After a count of bats on all levels of Soudan Underground Mine State Park, a Minnesota DNR official says they "definitely saw a decrease," possibly because of spreading white-nose syndrome. 

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White-nose syndrome is a fungal disease that can kill hibernating bats. 

"It's an irritant for the bat. And ... during hibernation, causes them to wake up," James Pointer with the Minnesota DNR said, "which for a hibernating bat is not a good thing because they end up using a lot of their fat reserves."

To try to replenish those, the bats leave their belowground hibernation. 

"The minute they come up on a cold, winter day in Minnesota, they're going to die of exposure," Pointer said. 

White-nose syndrome was confirmed in Soudan last March. It was the first place with verified cases in Minnesota. Since then, it's also been found in Becker, Dakota, Fillmore, Goodhue and Washington counties.

It can be hard to tell which bats have the disease while they're curled up and hanging on the former mine's walls. 

"Typically what we've found here when we have the bats with white-nose is right on the nostrils is where you start to see the white," Pointer explained. "It will eventually spread to his whole muzzle area and then onto his wings."

The DNR staff at Soudan Underground Mine State Park counts bats on three levels of the mine every year. But this year, they decided to do a full-level count and try to get an idea of the effect of white-nose syndrome. 

"In a typical year, when we do a full level count, we would have seen over 5,000 bats," Pointer said. "It was definitely down this year."

Scientists have estimated between 8,000-12,000 bats take up residence in Soudan Mine during the winter. So they know even in normal years, they don't see all the creatures. And they can't be sure if the 2016-2017 winter decline was because of white-nose syndrome. 

"What we don't know is does that mean that the bats have all died or have they just moved locations within the mine because we can't get to every single spot in the mine," Pointer explained. 

Some species of bats migrate, and those ones are not affected by white-nose syndrome. Little brown bats, or little brown myotis, are most common at Soudan. 

It mostly spreads from bat-to-bat, but humans may play a role. Spores of fungus can get on clothes, shoes and gear and may travel with us and contaminate other areas. 

"I've worked here almost 13 years, and I've been on the bat counts every year. I do bat programs, and it's a great mammal to have here. It's a great addition to our mine," Pointer said. "It was hard this year to see them dying off."

So far, there is no way to treat white-nose syndrome, but Pointer said researchers are working on options for prevention and treatment. 


Baihly Warfield

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