House bats and bat houses . . . five problems and solutions

FOR MOST PEOPLE, bats are unwelcome house guests. They can, however, be good neighbors. They eat a lot of night-flying insects and try to stay out of your way. If bats have made their way into your home, here's some tips on how to get them out and into a safe house of their own.

Bat houses are for maternity colonies, primarily female little brown and big brown bats and their young. Bat houses are not for adult males or species that prefer trees to houses. Those generally solitary bats have no trouble finding housing in Penn's Woods, which is why we don't recommend purchasing or building a birdhouse-size bat box. They're rarely used and not needed.

In April or May, female house bats will return to your neighborhood after spending the winter hibernating in a cave or mine. In spring and summer, they are attracted to the hotter parts of buildings -usually an attic or the under-roof of an outbuilding - to birth and nurse their young. Each year a female little brown bat will give birth to a single pup, while big browns have two. Pups are born in June and ready to fly by mid to late July. Females and juveniles begin to leave their summer quarters in August and September, and by October or November they're swarming around caves and mines, getting ready to hibernate.

House bats may use multiple day-roosts (buildings). If a preferred roost is disturbed, destroyed or remodeled, they'll find other, secondary roosts in nearby buildings. Population build-up occurs for two main reasons: bats are capable of living in excess of 20 or even 30 years and are faithful to a neighborhood; and when buildings with bats are remodeled or destroyed, bats become more concentrated in the roosts that remain. A stable day roost will eventually house a large number of female bats and their young. While maternity colonies of big brown bats are small, with fewer than a hundred bats, some old buildings in Pennsylvania house thousands of little browns.

At some point in buildings bats are using, their numbers will become so great that they'll be noticed; and at that point, homeowners want them evicted.

Killing bats. Killing these important species should not be an option. It will not solve the problem, which is the attractiveness of your building, and within a year, other bats from nearby colonies will start to filter in. The permanent solution, good for you, the bats, conservation and your neighbors, is to seal the bats out of your building and provide them with their own bat house.

Impatience. Wait until fall and the bats will leave your house for free. Meanwhile, observe where they fly out of your house, then in late fall and winter seal those holes and cracks so the bats cannot get back in the spring. Unlike mice, bats can't chew their way into your house, so even soft materials like Styrofoam will keep them out. There are companies that will help you solve your problem right now - for a price. But if "right now" is summertime, there's always the danger that hidden, newborn bats incapable of flight will be trapped and die in your home.

Eviction. By excluding the bats from your house, you've created a problem for the bats and your neighbors. In the spring, the returning but now displaced colony will attempt to find another way into your house or move into other nearby buildings. The best solution is to provide them with a bat box meeting the specifications provided by the Game Commission, Bat Conservation International, or Bat Conservation and Management, a Pennsylvania based wildlife consulting company. While small, store-bought boxes may seem like a quick fix, they are incapable of providing the range of temperatures or space needed by colonial house bats.

Location, location, location. Don't put bat boxes on trees, in too much shade, or with their bottoms less than eight feet from the ground. In Pennsylvania, bat boxes should receive at least six (preferably more) hours of direct sunlight every day, and the largest surface of the box should be angled mainly toward the south. Bats are quicker to move into a bat box if it was part of their summer neighborhood and installed before they left to hibernate.

Bouncing bat syndrome, a community problem. Older communities, especially those along rivers and large streams, often house thousands of bats in multiple old buildings. As these old buildings are destroyed or remodeled, surviving bats access the remaining day-roosts in other buildings. Fewer day-roosts with more bats spells trouble for homeowners and for bats. The Game Commission is recommending a proactive solution to this unwanted scenario. Engage in community bat management by installing a huge bat house called the Condo. Finished, it's 8'x8'x8' and capable of housing 5,000 bats.

The town of Newport, in Perry County, installed a Condo at its water treatment plant as a community project spearheaded by the high school's conservation club. Other communities are encouraged to follow suit. For information on how to build and install the Bat Condo 5000, contact Bat Condo, PA Game Commission, Bureau of Wildlife Management, 2001 Elmerton Avenue, Harrisburg PA 17110-9797 or phone 717-787-5529.

Bat conservation includes, above everything else, debunking the myths and learning the facts about bats. Once you've started down this path, you can't help but admire them. Bats are just trying to survive our ignorance. Help them out by building and installing a safe home for bats.

- Jerry Hassinger, Retired PGC Biologist









Pennsylvania Game Commission, 2001 Elmerton Ave, Harrisburg Pennsylvania 17110-9797