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Serving Northern St. Louis County, Minnesota

More bat deaths at Soudan

Unusual bat activity in the area a sign of white-nose syndrome infection

Marshall Helmberger
Posted 1/25/17

SOUDAN UNDERGROUND MINE— Last year, state park officials here saw the first evidence of bat deaths associated with the fungal pathogen that causes white-nose syndrome. This year, the evidence …

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More bat deaths at Soudan

Unusual bat activity in the area a sign of white-nose syndrome infection

Posted

SOUDAN UNDERGROUND MINE— Last year, state park officials here saw the first evidence of bat deaths associated with the fungal pathogen that causes white-nose syndrome. This year, the evidence points to a worsening situation, although park officials won’t know for sure until they conduct a thorough bat survey in late February.

Last year, according to Jim Essig, who manages the Lake Vermilion Soudan Underground Mine State Park, park officials first began finding dead bats on the surface in mid-January. This year, he said, they began showing up during a cold snap in December, and in larger numbers than in the past.

“I’ve picked up probably 300-400 so far this winter,” said Essig, including about 80 in a single morning last week. The fungus that causes the syndrome doesn’t kill the bats directly. Instead, it irritates their skin and causes them to wake from hibernation too early. As irritated bats have left the relative warmth of the mine in recent weeks, they have frequently encountered temperatures that are deadly within a matter of minutes.

“We’re definitely seeing a die-back,” said Essig. “Though I’m hoping it may not be as extreme as I was fearing.”

In recent days, with the warmer weather that set in, Essig said the bats are starting to show up across a wider area. He said he’s gotten reports of active bats in both Ely and Tower-Soudan, although he said they can’t know for sure whether those are bats from the Soudan Mine. Essig said the DNR is looking for the public’s help in tracking bat movements and have set up an online bat observation reporting page that allows the public to report unusual bat activity, winter and summer roost locations, and other information. You’ll find the reporting page at dnr.state.mn.us/reportbats/index.html.

Park officials hope to get a much better idea of the condition of the mine’s bats in late February, when park staff and bat researchers from the University of Minnesota conduct an extensive survey of the bat population in the mine. While the park conducts an annual bat census on three of the mine’s levels, they do a more extensive survey every five years. It’s been three years since the last extensive survey, but Essig said the park is opting to take the more in-depth look this year, rather than wait another year.

Essig said he’s most interested to see how bats are faring on the mine’s tenth level, which is known to house the largest number of hibernating bats. That level also happens to be one of the cooler and damper levels, and Essig is hopeful that the conditions there might discourage the growth of the fungus, known as Pseudogymnoascus destructans, that causes white-nose syndrome.

The fungal disease, first identified in the U.S. in 2007, has decimated bat populations in eastern North America over the past decade. The disease is named for the fuzzy white growth of fungus observed on infected bats. Bat researchers first documented the presence of the pathogen in the Soudan Mine in 2013, but researchers didn’t find evidence of a significant number of bat deaths until last year. The Soudan Mine is the state’s largest known hiberaculum, home to an estimated 10,000-15,000 bats.

In conversations with managers of parks containing bat hibernacula in the other parts of the U.S., Essig said there is some evidence that some bats may be avoiding areas where the fungus grows most readily. That is confirmed, as well, by Dr. Jeremy Coleman, the national white-nose syndrome coordinator with the U.S. Fish and Wildlife Center. The fungus thrives under certain conditions, with the right humidity and temperature, and Coleman said it appears that bats are now favoring locations within hibernacula that are less favorable to the fungus.

Bats can recover from the disease if they survive the winter, and biologists are studying why some bats in affected caves are surviving multiple years.

Essig said that was encouraging news, since the Soudan Mine offers a substantial range of temperature and humidity for bats.

“We have about a ten degree difference in the mine,” noted Essig, who noted that temperatures get cooler nearer to the surface. “It’s possible that the bats at the upper levels are seeing fewer effects,” he said. “Then again, it could be really bad.”