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Biologists track disease-threatened bats

Mammalogists Andrew Herberg, left, and Melissa Boman set up an acoustic detector by the nets to hear the bats in the area during a bat survey Wednesday, June 28, 2018, night at Beaver Creek Valley State Park near Caledonia.
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CALEDONIA — Minnesota wildlife biologists want to learn where northern long-eared bats raise their young.

For that, they need to catch specimens of the federally threatened species.

The bat has seen a steep decline in number in Minnesota due to white-nose syndrome — a fungus that is spreading among bats throughout the U.S.

The past couple weeks, biologists and staff from the Minnesota Department of Natural Resources have set up nets at dusk in multiple wildlife areas in hopes to catch bats and place radio trackers on the females to track where they roost.

So far this year, they’ve met with limited success.


The decline in the bats’ population due to the fungus is likely the main reason biologists have had difficulty catching them them. The bats’ agility might be another.

"We’ve had quite a few avoid our nets at the last minute," said Andrew Herberg, a mammalogist with the DNR.

Learning where bats roost for the summer can help conservation officials identify areas that need to be protected to help try to slow the specie’s decline.

Herberg and other DNR staff were at Beaver Creek State Park in Houston County this week setting up nets in hopes of snagging female long-eared bats.

Their presence and equipment — 10-foot poles, arrays of carabiners used to deploy nets, a turkey fryer to sterilize equipment and a camping canopy that serves as a bat examination station — nets some attention at the campgrounds where they stay.

"We get some funny looks," Herberg said.

At dusk Wednesday night, crews set up poles to raise nets more than 29 feet into the air at three locations in the park. They set up two smaller nets about 10 feet high in other areas. Shortly after the nets were set, bats could be seen in the sky.

"We try to set up areas that provide natural channels for the bats to fly," Herberg said.


The team checked the five locations for bats caught in the nets every 20 minutes or so. None were found that night. The night before, one bat was snagged in one of three nets that were set up. The crew started this year’s collection effort last month near Chaska.

This is the fourth year of a study on the bats roosting locations. The study is being funded by the Minnesota DNR, University of Minnesota Duluth and the U.S. Forest Service.

"As our study has progressed, it’s gotten harder and harder to find bats," Herberg said.

"Some of the other groups went nights and nights without catching any bats," said Melissa Boman, DNR mammalogist.

The trackers last for several weeks. However bats will groom them off their fur in a matter of days. As soon as females are tagged, crew members immediately spend the next few days tracking their location.

‘That ‘zzt’ you heard’

The white nose fungus was first confirmed in Minnesota bat populations at Lake Vermillion in winter 2015-2016. Since then, the colony that hibernates at Soudan Underground Mine has declined by an estimated 90 percent. The colony that hibernates at Mystery Cave has lost an estimated 70 percent of its population, according to the DNR.

Boman said population decline from the fungus usually plateaus the third year after cases of white nose fungus are confirmed.


Although no bats were netted, they could be seen flying during the evening hours. An audio tracker that detect the high frequency sounds bats use to echolocate insects buzzed with activity. The device translates the high frequency noises bats use to locate food and objects into frequencies detectable by the human ear.

"That ‘zzt’ you heard, that’s them right at the moment they zero in on something," Herberg said.

The activity was encouraging, but not unexpected. Crews placed audio detectors at the park the week before to scout the location and recorded several bats each evening.

While the crew was also looking for and documenting signs of the fungus, there is little they could do for a bat that is infected.

"There’s really been no silver bullet yet," Herberg said

They work to keep equipment that touches bats sterilized. In between netting sessions, they boil the nets in a turkey fryer at the campground.

Bats important to ecosystem

The fungus usually infects bats in the winter. It causes them to to rouse too frequently during the winter when they should be hibernating. The bats then use their energy stores up before spring when they’re able to forage for food and don’t survive the winter.

Collecting data on bat behavior will help bat conservation efforts. While they might make some people feel squeamish, bats are an important part of the ecosystem, Herberg and Boman said. A single colony can devour more than 30 pounds of insects in a day.

"Somebody’s got to speak up for them," Boman said.

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