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Contact: Heather Kaarakka, DNR Conservation Biologist or 608-266-2576;
J. Paul White, DNR Mammal Ecologist or 608-267-0813

Safely And Humanely Evict Bats From Buildings Through May 31

Two little brown bats roosting in an attic. Little brown bats (pictured) and big brown bats, along with northern long-eared bats and eastern pipistrelles (also known as tricolored bats), are all threatened species in Wisconsin. Photo credit: Wisconsin DNR

MADISON, Wis. – With bats soon leaving their summer roosts to return to their winter hibernation sites, the Wisconsin Department of Natural Resources (DNR) reminds Wisconsinites that fall is a good time to safely and humanely evict bats from homes and buildings.

Now through May 31, before the nursing and baby bat protection period begins, you can keep bats out of homes and buildings by following best practices. 

The DNR provides do-it-yourself instructions and information on hiring a professional to get bats out of buildings humanely through a process called exclusion. Exclusion includes sealing a building except for primary exits, outfitted with one-way doors that let bats exit and prevent re-entry.

“While the goal of the DNR’s bat program is to protect bats and bat habitat, we understand that bats don’t need to share living spaces with humans,” said Heather Kaarakka, DNR Conservation Biologist. “Our online resources help people effectively and safely exclude bats or hire a wildlife control operator.”

Exclusions are prohibited June 1 through Aug. 15 to protect Wisconsin’s little brown and big brown bats during their maternity seasons. Exclusions occurring during this period will separate mothers from their flightless pups, leaving the pups to die of starvation and potentially exacerbating the homeowners’ bat problem as frantic bat mothers search for an opening to reach their pups.

Effective exclusion efforts should target time periods in the fall and spring where temperatures are consistently above 50°F as bats are generally active at temperatures above that level.

To permanently and humanely evict bats from structures, one-way venting devices should be installed at the primary entries/exits for 7-10 days in addition to sealing up secondary holes, cracks and crevices that may allow entry into a structure. Primary entries should be closed after a one-way venting device has been in place for 7-10 days and bats are out of the building.

Protections For Bat Populations Decimated By White-Nose Syndrome

Little brown bats and big brown bats, along with northern long-eared bats and eastern pipistrelles (also known as tricolored bats), are all threatened species in Wisconsin and receive legal protection, including the ban on exclusions during maternity seasons. These four bat species hibernate in caves and mines in the winter and have been decimated by the deadly bat disease white-nose syndrome.

White-nose syndrome does not affect humans but causes a fungus to grow on bats’ noses and skin, disrupting normal hibernation patterns and burning up the energy needed to get them through long Wisconsin winters.

Although bat roosts are protected during the maternity period (June 1-Aug 15), exclusions may be completed if the landowner feels the bats pose a health or safety risk to humans and a health exemption form is submitted. Exclusions are allowed during the maternity season in hospitals, medical clinics, daycare centers, nursing homes, assisted living facilities and restaurants without a health exemption form.

Build A Bat House To Provide An Alternate Roost

Bats can reduce pesky mosquitoes and night-flying insects around your home and garden. Help keep these valuable mammals in your area by building a house for roosting and to raise their young.

Late winter/early spring is a good time to provide an alternative roost – a bat house – in the general vicinity of where bats enter the building. Find a supply list, instructions and how-to videos on the DNR’s Build A Bat House webpage.

“By installing a bat house before you exclude bats, you increase the odds of maintaining the beneficial insect-eating service the bats provide in your backyard,” said J. Paul White, DNR Bat Team Lead.

A single bat can eat up to 1,000 mosquito-sized insects an hour and the equivalent of its bodyweight every night. University of Wisconsin-Madison research analyzing bat guano (manure) collected at sites across Wisconsin confirms that bats consumed 17 distinct types of mosquitoes, including nine species known to carry West Nile virus.

Learn more about Wisconsin bats and how to help them on the Wisconsin DNR’s Saving Wisconsin’s Bats webpage.