Minnesota bat populations are dropping at the hands of a fungal disease, heightening concern among experts for a federally-listed endangered species.
White-nose syndrome is being attributed for lower numbers in an annual bat count with the state’s Department of Natural Resources. The fungus causing the disease dwells in caves and mines, and is threatening the endangered species of northern long-eared bat.
Northern long-eared bats have been found at the Minnesota Valley National Wildlife Refuge in Carver and Scott counties.
Biologist Jill Utrup specializes in endangered species recovery with the U.S. Fish and Wildlife Service. She looks at bat populations in Minnesota and Wisconsin, and how they relate to recovery efforts nationwide.
“It’s white-nose syndrome that is the main threat to the species (northern long-eared bat),” Utrup said. “If it weren’t for that particular threat, it’s likely that species would not have to be listed under the endangered species act.”
The fungus causing white-nose syndrome is an invasive species. It entered North America in eastern New York in 2007, according to the Minnesota Department of Natural Resources. Once a location is infected, bat populations wither after two to three years, dropping by as much as 90 percent.
Among the 33 states and seven Canadian provinces it now inhabits, the fungus has killed more than six million bats.
Bats are exposed to the fungus during hibernation and become irritated. It appears as white fuzz on their noses and eats away at the delicate membrane of their wings. Bats spread the disease to one another through routine acts such as grooming.
“The fungus is attacking them when they’re at their most vulnerable,” Utrup said. “As the infection grows on their skin, they’re trying to groom and clean themselves. It irritates them and they start waking up more frequently, and each time they wake up, they’re burning up more fat. They burn up their body weight.”
Northern long-eared bats aren’t the only cave species. But their habits make them prone to the fungus.
“Typically, what they’ll do is they’ll roost deep within these caves and mines,” Utrup said. “And that’s where it’s most humid, where the fungus really thrives.”
Northern long-eared bats live in swaths across the country. They live in the northeast, in the southeast, stretching back to Oklahoma and up into North and South Dakota. They winter in caves and mines; in summer they roost in trees. The bats also have remarkable flight fidelity, she said, meaning they return to the same posts in summer and winter month.
White-nose syndrome has struck a deadly blow to the species, nearly cleaning out the East Coast population.
“Some surveyors visiting an infected cave see the floor of the cave littered with bats, or they’ll go outside and find bats that have died out in the landscape searching for water,” Utrup said. “It’s a very sad situation.”
A fellow cave species, the little brown bats, have begun to stabilize in numbers. They aren’t returning to past population numbers, but they haven’t continued to drop either.
Utrup is hopeful northern long-eared bats will do the same.
Cave bats have the potential to spread the infection regionally, but the cross-country jump in the fungus is likely due to cave visitors not properly cleaning their equipment and entering another cave several states away. Doing so has the potential to spread different strains of the fungus as well. The fungus doesn’t harm people, pets or other wildlife.
So how does this all look for bats of the southwest metro?
“Unfortunately, it’s pretty hard to get information on what’s happening locally,” said Mammal Specialist Melissa Boman with the Minnesota Department of Natural Resources. “Bats can move almost 200 miles between winter and summer sites.”
Statewide surveys help give a picture. A March 28 press release from the Minnesota DNR says white-nose syndrome is delivering a “substantial, but expected, decline.”
Bat populations have dipped as much as 94 percent in some spots in Minnesota. The culprit is white-nose syndrome, which made its first appearance in Minnesota in March of 2015 at the Soudan Underground Mine in northeastern Minnesota.
Bats save farmers millions of dollars each year by reducing the need for pesticides, Utrup said. They are critical to the ecosystem and keep certain insect populations in check.
Boman cannot share where the bats hibernate — called hibernaculum — in Hennepin, Carver and Scott counties. However, she can confirm whether or not the fungus is present. Hennepin County does contain the fungus causing white-nose syndrome. Carver and Scott county thus far are not confirmed to have the fungus.
“While there may be a rare hibernaculum in Minnesota, that hasn’t yet been impacted, WNS (white-nose syndrome) is likely to be present anywhere bats hibernate in the state,” said DNR Program Supervisor Ed Quinn in a release.