This spring, DNR's Heather Kaarakka helped Girl Scouts from Troop 2330 assemble, caulk and stain two bat houses. The troop donated one bat house to the Friends of Indian Lake and the other bat house to Prairie Elementary School in Waunakee.
Building a better life for bats
How a housing project can help.
Story by Laura Lane and photos by Becky Hunter
The bad news for Wisconsin bats came last spring when DNR biologists found the deadly white–nose syndrome (WNS) in Grant County. WNS is a fungal disease that kills insect–eating bats when they are hibernating in caves and mines. Over 6 million bats and counting have been killed by WNS and it's spreading across the central United States.
The microscopic fungus spores thrive in cold temperatures and attack bats when their immune systems have shut down during hibernation. The disease passes from bat to bat, and the fungus particles may also attach to people's clothing or shoes and can be transported to different areas.
The benefits of bats
Bats play a critical role in keeping insect populations in balance. Insectivorous bats will eat mosquitoes, moths, beetles, flies, termites and spiders. They also eat agricultural pests such as corn borers, cutworm moths, potato beetles and grasshoppers.
"They eat massive quantities of insects. One single big brown bat that is nursing will eat 110 percent of its body weight in insects every night," says DeeAnn Reeder, associate professor of biology at Bucknell University. "It would be like me eating 500 hamburgers every night."
While bats are often overlooked, they are among the most economically important, non–domesticated animals in North America, according to a recent study in the journal Science. Pest–control services provided by insect–eating bats in the United States likely save the U.S. agricultural industry at least $3 billion a year, the study reported.
"In the context of white–nose syndrome, every single bat we have left is precious," Reeder says.
Safe havens for bats
While scientists across the country race to discover ways to save bats from the deadly fungus, there are things you can do to help bats. One of the best ways is to leave them alone.
"It's really important not to disturb bats that are hibernating," Reeder says.
Building a bat house is also a great way to give bats a safe place to roost in the summer. Mother bats give birth in bat houses and can raise their pups there.
"When built and placed correctly, bat houses offer safe, warm habitat for maternity colonies," says Heather Kaarakka, a conservation biologist with DNR's Bureau of Natural Heritage Conservation. "Mother bats leave the roost nightly to feed while the pups remain in the roost, and bat houses act as shelter for the pups that are not able to fly yet."
Wisconsin's four bat species that might roost in bat houses include: little brown bats, big brown bats, eastern pipistrellle bats and northern long–eared bats. The little brown and big brown bats are the most likely of the four species to take up residence in bat houses. A bat nursery house can provide shelter for 100 to 300 little brown bats.
Building a bat nursery house
The DNR's Building a Bat House Handbook recommends using naturally decay– resistant materials such as rough–sawed black locust, white oak, cedar or old barn wood to build your bat house. Also make sure the wood is not treated because the chemicals can be toxic to bats.
Painting the bat house dark brown or black helps the house heat up and stay warm through the night.
"Bats like it warm, because it helps the baby bats mature," Kaarakka says.
Avoid Kilz brand primer or paint as bats tend to avoid it, she adds.
As you follow the step–by–step instructions, remember to seal all the joints with caulk, because it protects the wood from decay and also prevents the house from becoming too drafty.
Mounting your bat house
Kaarakka says bat houses should be mounted 10 to 15 feet in the air on a pole or a building (not a tree as it provides too much shade), be located within one quarter mile of water and be protected from wind, but still exposed to southern or eastern sun.
"The first thing a bat thinks about when it emerges in the evening is getting a drink of water. The closer the bat house is to water, the more likely bats are to use it because it reduces commuting costs," Kaarakka says. "Little brown bats especially, also like to forage over water consuming small, soft–bodied aquatic insects like midges and mosquitoes."
Because predators such as owls can attack bats when they emerge, place your house 10 to 15 feet away from trees, but keep it sheltered from winds. Trim back tall shrubs and bushes below the base of your bat house.
"If there is a colony within a mile or so, the bat house may get used within a couple of months, especially in the late summer and fall as juvenile bats are exploring and learning to forage," Kaarakka says. "If there is no established roost in the area, it can sometimes take several years for bats to find and inhabit the bat house."
Monitoring your bat house
Once bats take up residence in your bat house, do not shine lights up into the house. If the bats are disturbed, they will abandon the roost and the pups might die. The best way to monitor whether bats are using your bat house is to look for guano under the house or sit outside in the evening and watch for bats to emerge.
Once your bat house is inhabited, join the DNR's roost monitoring project and share what types of bats are in your bat house, how many bats you have and the best methods you've found for encouraging bats to roost in your house.
Laura Lane writes from Madison, Wis.