Eagle River Chain of Lakes Bat Monitoring Update

NPS photo by Neal Herbert

A group of volunteers continue to monitor the native bat population with an acoustic monitoring device for the WDNR on a handful of lakes on the Eagle River Chain. The lakes that were monitored this Summer included Duck (5), Otter (1), Cranberry (8 parts of the lake), and the Wisconsin River just off of Watersmeet (3).

As mentioned in the 2023 Fall Newsletter, starting in 2006 and confirmed in Wisconsin in 2014, an invasive fungus from Europe called White Nose Syndrome (WNS) has negatively affected our local hibernating bat populations, especially Little Brown Bats.

However, all news on our endemic bat populations is not negative. Bat numbers have been slowly creeping up. The Summer monitored sites have started to increase slightly. For example, individuals who have been monitoring bat houses may have seen populations go from 200 bats to 30 bats in one year and now it is slowly approaching 100 bats.

Bats are long-lived, up to 30 years of age. They generally only have one pup a year, that makes a disease like WNS able to almost wipe out colonies. It is very difficult and long process for them to rebound.

WNS is now considered endemic in Wisconsin. With bat numbers greatly reduced or non-existent at most underground hibernation sites. The site visits are being put on rotation of two, five or ten-year schedules, depending on their original population size, level of disturbance and species.

There are important ways landowners can help bats on their property. Some species of bats roost in dead trees that have peeling bark or cavities in them. Keeping those dead trees (snags) that are not a human safety hazard will provide habitat. Another way is to keep areas around creeks and rivers clear. These are both important migratory corridors and foraging areas. For folks who don’t have woods but are close to water, consider putting up one or more bat houses. Little brown and big brown bats in particular are known to use artificial structures.

Bats also have high site fidelity, returning to the same locations every year. Once you have an established colony of little brown bats in a bat house, for example, the same bats will return repeatedly. Females give birth to pups in early to mid-June. The pups are flightless for the first few weeks until they learn how to fly. In mid-July they begin to disperse, but the females will return to the maternal roost and share the same bat house with several generations. Information courtesy of H. Kaarakka, WDNR.

Vilas County is fortunate to have one of the most active bat monitoring programs in the country, thanks to many volunteers, including local ERCLA members. Currently, Cranberry Lake (Steve Skora), Duck Lake (Marc Groth), Watersmeet Lake (Ed Bonack) and Otter Lake (Jody Voight) have been active monitor participants joining hundreds of volunteers across the state.

If you have questions or would like to get involved as a volunteer, please feel free to contact Mariquita (Quita) Sheehan, Conservation Specialist, Vilas County Land and Water at 715-479-3721. It is Quita’s dedication to these activities that have made the Vilas County Program so successful and impactful.