Bats are an important part of almost every ecosystem on the planet. They participate in pollination, seed dispersal and pest control. In Wisconsin, bats play an important role in the agricultural industry as well.

Also helpful with insect control, a single little brown bat can consume up to 1,000 mosquito-sized insects in one hour.

In recent years, many bat species in North America, including several in Wisconsin, came under threat of extinction due to an invasive fungal disease called white-nose syndrome (WNS). To help combat the threat, the Wisconsin Bat Program (WBP) began efforts to monitor bat populations in order to establish baseline information about where bats are, the type of roosts they use and how many bats live in the roost over the summer.

In 2006, WNS, which affects cave-hibernating bats, was found in a cave in New York. Since its arrival, WNS has spread to 38 states and eight Canadian provinces, according to the 2021 Roost Monitoring Report.

WNS was first discovered in Wisconsin in 2014 with reports of 25 counties infected as of fall 2021, and it is reported that millions of bats in North America have died from WNS since it was first discovered.

Results from 2016 bat roost monitoring showed the average size of a little brown bat summer colony was 300 to 600 bats. In the years following WNS, summer colony sizes reduced dramatically or in some cases simply vanished. However, in 2021 some colonies reported signs of stabilization or even modest increases in colony size.

Landowners and volunteers have helped locate and monitor bats since 2007. Two such volunteers, Sue Holloway and Bonnie Mosbrucker, are citizen-scientists in the Conover area. Quita Sheehan, conservation specialist with Vilas County Land and Water Conservation Department, assists the volunteers with data collection.

“Vilas County has been monitoring bat populations since 2012 when Trees For Tomorrow collected the data,” said Sheehan.

A monitoring device called a walkabout bat detector collects data on colonies that is then uploaded to the Wisconsin Department of Natural Resources (DNR) to produce maps and charts of current bat populations. The walkabout is a portable device about the size of a large cellular phone that records in real time.

A built-in GPS and mapping system allow you to collect data and log your path as you go. Sheehan said the walkabout can be checked out from the land and water department located at 330 Court St. in Eagle River by calling 715-479-3721.

Sheehan and volunteers Holloway and Mosbrucker, along with others in Vilas County use the walkabout to monitor bat populations on area waterways and paths.

“As long as the daytime temperatures are above 50 and it isn’t raining or too windy, the bats should be flying because they are out hunting bugs,” Sheehan said.

According to Sheehan, it is important to collect data in May and June in Vilas County before baby bats (pups) are able to fly. Additional data should be collected when the pups are mature so they may be included in the population count.

Sheehan said data collection should be completed a half-hour after sunset and is more accurate when volunteers do a loop pattern on waterways and walking paths. Data may be more difficult to interpret when you go out and come back on the same pathway.

Sheehan said there is the bat roost monitoring program where volunteers sit by the roost and count the bats that come out at dusk as they see them. (No Walkabout used). The counts are conducted two times a year — in the end of May or early June, and then again in end of July. This monitoring program show the number of pups that are fledged each year.

According to the DNR, two out of the eight species of bats that are found in Wisconsin live in large size colonies. These bats, the big brown bat, and the little brown bat are easier to monitor by WBP volunteers because they are more likely to use a bat house (roost) or man-made structure, like barns, outbuildings or attics.

The other six species are solitary or form smaller colonies and therefore are harder to find and monitor. Little brown bats hibernate in caves and mines from October through April, and mating occurs in the fall. Usually, one pup is born in early June and matures in four to six weeks. Big brown bats are found in various habitats including mixed landscapes of deciduous woodlands, farmlands, edges near water and urban areas, DNR data shows.

Females may form large colonies in bat houses and buildings over the summer. During the winter months, they are found in natural and manmade structures such as caves, mines, and sometimes human dwellings. Like the little brown bat, mating also occurs in the fall and one to two pups are born in early June and mature after four to six weeks.

Holloway and Mosbrucker are active citizen scientists in bat monitoring. Citizen scientists are members of the public who collect and analyze data relating to the natural world, typically as part of a collaborative project with professional scientists.

“No data could be collected without the dedication of the citizen scientists,” Sheehan said. “And that would be bad for the bats.”

In addition to bats, citizen-scientists programs in Vilas County and throughout Wisconsin include data collection about rare plants, frogs and toads, birds, bees, dragonflies, butterflies, turtles, streams, lakes and wetlands.

For more information on citizen-scientist or citizen-based monitoring programs, visit or