UNIVERSITY PARK, Pa. -- As they awaken from their long winter's nap, bats may be coming to your home to roost. So now's the time to seal the chinks in your attic, say two wildlife biologists in Penn State's College of Agricultural Sciences.
"Late winter -- while bats are hibernating in caves -- is a good time to bat-proof your house," says Gary San Julian, professor of wildlife resources. "Soon they will be waking and looking for a warm place to raise their new pups."
"When bat-proofing, timing is crucial," adds Margaret Brittingham, associate professor of wildlife resources. "Never seal holes in your attic during May through July, because you can trap females and their pups inside."
Late fall -- after bats return to their caves -- also is a good time to bat-proof.
The bats that live in houses, the little brown bat and big brown bat, once roosted in hollow trees. But now, these "house bats" have moved their roosts into hot attics, which act as incubators for their growing pups.
Although people often aren't thrilled about sharing their living quarters with bats, bats make good neighbors. One little brown bat can eat 600 mosquitoes per hour, and big brown bats eat many agricultural pests.
"If you see bats flying around your neighborhood at night, they're doing you a great service," says Brittingham. "They're catching a lot more insects than that bug zapper you have out back. They also help us to reduce our use of insecticides."
If you're not sure if bats are sharing your domain, San Julian suggests looking for bat droppings in your attic. Bats leave dry, black droppings the size of rice grains, filled with shiny insect wings. If you find large accumulations of bat droppings, you probably house a summer maternity colony -- a roost where female bats gather to raise their pups.
Because house bats have only one or two pups each year, protection of maternity colonies is important for their survival, says Brittingham. Destroying just one maternity colony can have a long-term impact on the populations of both bats and insects in a local area.
So what should you do if you find evidence of these guests? First, look for areas in your attic where bats can get through, says Brittingham. Bats enter through spaces where joined materials have pulled away. They often get through louvered vents with loose screening, roof peaks, dormer windows or areas where flashing has pulled away from the roof or siding. "Bats can crawl through holes the size of a quarter," she says.
To cover louvered vents or large gaps and cracks, use window screening or hardware cloth. Fill smaller cracks with expanding foam insulation or caulking compound.
After sealing your attic, Brittingham suggests providing a bat box near your house as an alternative roost. "Bats are very site-faithful," she says. "They tend to come back to the same place year after year. With a bat box, the bats still have a safe place to raise their pups, and you get the bats out of your house -- while still benefiting from their insect control."
The small bat boxes available at garden centers serve mostly as bat motels. "During the summer, while females are gathered together in maternity colonies, males are basically single, flying around," Brittingham explains. "When you put up a small bat box, often you'll get a male bat using it for a night or two, then moving on."
To provide housing for maternity colonies, homeowners can build their own bat boxes that are larger, holding from 100 to 300 bats. The interior should be divided into multiple roosting crevices, and the design should allow for proper incubation temperatures. "Siting also is important," says Brittingham. "The most successful bat boxes get at least seven hours of sunlight each day."
For more information about bats and bat-proofing, as well as detailed instructions on building bat boxes, see the Penn State College of Agricultural Sciences publication, "A Homeowner's Guide to Northeastern Bats and Bat Problems." Single copies are available free of charge from your county Penn State Cooperative Extension office, or from the College of Agricultural Sciences Publications Distribution Center at 814-865-6713.
The 23-minute video, "Bat-free Belfries: A Guide to Bat-Proofing," also demonstrates how to deal with a single bat or colony of bats in a building, and explores the role of bats in northeastern ecosystems. You can borrow the video from your local county extension office. To purchase the video, contact Information and Communication Technologies -- Video Unit, 119 Ag Administration Building, University Park, PA, 16802; phone 814-865-6309; FAX 814-863-9877. The price is $35. Allow three weeks for delivery. Make checks payable to Penn State or include a purchase order.
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EDITORS: For more information, contact Gary San Julian at 814-863-0401. To contact Margaret Brittingham, call 814-863-8442.
Contacts: Kim Dionis KDionis@psu.edu 814-863-2703 814-865-1068 fax