A lethal fungus decimating the country's bat population has taken hold in Minnesota and has now entered the Twin Cities metro area.
State wildlife officials on Thursday confirmed white-nose syndrome affecting bats in six counties — St. Louis, Becker, Dakota, Fillmore, Goodhue and Washington — and said it's suspected to be in four more: Lake, Pine, Ramsey and Hennepin.
The pace of the spread is typical, officials said. But while there are early signs that white nose syndrome could be bottoming out in other parts of the United States, the scourge is just taking hold in Minnesota, where it first appeared in 2013.
Separately, federal wildlife officials on Thursday confirmed that the bat-killing fungus has been detected in Texas for the first time and has spread to two more species of bats.
At Lake Vermilion-Soudan Underground Mine State Park, ground zero for the epidemic in Minnesota, the bat population plunged by 73 percent from February 2013 to December 2016, and it now stands at less than 3,000 bats, said Gerda Nordquist, a bat specialist with the state Department of Natural Resources (DNR). Nordquist does direct counts in caves with a clicker; staff just finished the annual bat survey Wednesday.
Die-offs are expected to get far worse, officials said. Recovery will be slow because the most common bat species give birth to only one pup, and it's not known whether bats that survive the syndrome pass their resistance to their young.
The scourge worries naturalists because bats are a critical part of the ecosystem, pollinating plants and eating huge quantities of insects. "A healthy bat eats its weight in insects every night," said Rich Baker, endangered species coordinator for the Minnesota DNR. "Five grams of insects is a lot of insects."
In the Twin Cities area, bats hang out in the many man-made caves along the Mississippi River, but wildlife officials would not reveal specific locations because they are vulnerable to human disturbance.
The disease is called white-nose syndrome for the white powdery fungus that can form on the muzzle, tail and wings of infected bats. Scientists suspect the fungus irritates the bats, rousing them out of hibernation too early and leading them to fly off, perhaps out of thirst, and die of exposure or starvation.
At the Lake Vermilion-Soudan cave, park staff counted nearly 3,000 dead bats outside the mine over a recent 12-to-14 day period, said Ed Quinn, a DNR supervisor. The mine is home to three bat species: the northern long-eared bat, the little brown bat and, rarely, the tri-colored bat.
That count is probably conservative, he said, because many bats fly off and die elsewhere, and because weak and dead bats are snatched for dinner. "The ravens and other scavengers are pretty quick to get on those," Quinn said.
The disease doesn't affect humans or species that eat bats.
Erratic grooming behavior
Declines in bat populations have been as high as 98 percent to 100 percent at other sites in the state. At Forestville/Mystery Cave State Park in southeastern Minnesota, where the disease was also first spotted in 2013, bats haven't yet started dying off, Nordquist said. But the majority of the bats show signs of the disease and are roosting in areas they normally don't, Nordquist said.
Nordquist said she sees bats in winter "eagerly grooming themselves" to try to remove the fungus. "Bats are supposed to be hibernating, not wide-awake grooming themselves," she said. "That's costing valuable energy and eventually it runs out."
Nordquist said a recent influx of citizen reports on unusual bat behavior is very useful. She encouraged people to continue using the DNR's online reporting site to report such things as bats flying in daytime: www.mndnr.gov/reportbats
The U.S. Fish & Wildlife Service said an updated map showing the spread of the disease will be available Thursday at whitenosesyndrome.org
Jennifer Bjorhus • 612-673-4683