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Minnesota bats devastated by white-nose syndrome

A group of little brown bats with white nose syndrome, a deadly fungus now blamed for cutting bat numbers by 90 percent in the Soudan underground mine near Lake Vermilion. U.S.D.A photo.

Minnesota's bat population continues to be devastated by white-nose syndrome, with now a 90 percent decline in bats at the Soudan Underground Mine near Lake Vermilion and a 94 percent drop at Mystery Cave in southern Minnesota.

The Minnesota Department of Natural Resources on Thursday, March 28, reported the continued bat decline, saying it was expected but not welcome.

Despite years of research and tracking, no cure has been found for the European fungus that has spread from a single cave in New York in 2007 to 33 states and seven Canadian provinces killing more than 6 million bats so far as it spreads west. Fish and Wildlife Service officials have called it the most catastrophic wildlife disease in U.S. history.

In Minnesota, the decline has been as rapid as it has been broad. The fungus that causes white-nose syndrome was first discovered at the Soudan mine in 2013. Bats were found dying by the hundreds outside the mine in winter 2016. By 2017, their numbers had plummeted 70 percent from historic levels. This winter, their numbers dropped 90 percent below pre-disease levels.

Bats spread out during nesting months in summer when they consume huge amounts of insects. Four of Minnesota’s eight bat species migrate south in winter, but the other four — little brown bats, northern long-eared bats, tri-colored bats and big brown bats — group up in colder months in warmer areas like caves and underground mines. That grouping makes perfect breeding grounds for the deadly fungus to spread.

“While there may be a rare hibernaculum in Minnesota that hasn’t yet been impacted, (white-nose syndrome) is likely to be present anywhere bats hibernate in the state,” said Ed Quinn, DNR natural resource program supervisor.

The news has been just as bad in Wisconsin, with wildlife officials there reporting last year a 92 percent decline in bats from historic numbers, and white-nose syndrome confirmed in 25 of the 28 counties that have bat wintering areas, called hibernacula.

White-nose syndrome is named for the white fungal growth observed on infected bats. It is believed to come from Europe, where it’s common but where most bats don’t die from it. It is not known to pose a threat to humans, pets, livestock or other wildlife. Although the disease is transmitted primarily from bat to bat, people can inadvertently carry fungal spores on clothing and caving gear.

Bats that develop the fungus eventually begin to waste away. Infected bats show unusual behavior, such as flying during the day in summer or leaving caves during their usual winter hibernation when no bugs are present for them to eat. A wildlife veterinarian at the University of Wisconsin confirmed the disease kills bats by causing their bodies to overheat, burning energy too quickly and at a time — in winter — when no insects are present to replace the lost calories and it's far too cold for the mammals to survive outside.

DNR mammalogist Gerda Nordquist said they are already hearing from Minnesota residents who are seeing few if any bats at the same time there has been a big increase in mosquitoes and moths. A single bat can eat more than 1,000 mosquitoes in a single night.

There’s been some hope raised in recent years with success using UV light and fungicides to kill the fungus. Other scientists are hoping some bat species may develop resistance to the disease with enough survivors to rebuild the population. That appears to have happened in low numbers in some eastern U.S. bat colonies that have hung on at low levels.

Bats can live for 30 years but reproduce slowly, with generally one pup per year, so if a cure is found it will take decades to rebuild the population, if that’s even possible.

Bats are considered important for ecosystems because they eat so many insects and some species pollinate fruits and flowers. One Minnesota bat impacted by white-nose syndrome, the northern long-eared bat, was given federal Endangered Species Act protection in 2015.

To learn more about white-nose syndrome and Minnesota’s bats, or to submit a report if you find a dead bat and suspect white-nose syndrome, go to mndnr.gov/wns.

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