   Excluding Bats from Homes - March 5, 2003 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County As temperatures begin to rise, bats will begin their migration northward. They move north with the changing latitudinal temperature gradient. Nectar-feeding bats follow the wave of saguaro cactus blooms. Likewise, insectivorous bats follow the emergence of flying insects. There are 28 species of bats found in Arizona. Being gardeners, the readers of this column probably already know that bats benefit many other species (including humans) and their presence should be encouraged. However, conflicts with homeowners often occur when bats roost in structures seeking protection. I often get questions from homeowners about exclusion of bats from structures where they are viewed as a nuisance pest. People have varying levels of tolerance for bats. They seldom go into our actual living space, but sometimes they get there by accident, and, believe it or not, some people just don't appreciate bats flying about inside their homes. In these cases, there are a variety of tactics that can be employed to discourage this behavior. Bats have many different reasons to roost: hibernacula, maternity (nursery) roosts, bachelor roosts, night roosts, and migratory stopovers. They identify these roost sites because they offer the optimum combination of temperature, protection, and location. Once bats locate these sites, they often return to them year after year. The most successful strategy to exclude bats is to construct a one-way "valve" that allows bats to exit the roost area but does not allow them to reenter. These should not be installed until after any young bats are able to fly. Late August is a safe time to initiate an exclusion program. In late fall most house-dwellings bats either migrate to warmer climates or enter caves or abandoned mines to hibernate. The most simple one-way "valve" is made of bird netting with openings 1/6 inch (0.4 cm) or smaller which is secured to the side of the structure on the top and both sides leaving the bottom open for bats to escape. The bottom portion should extend 18 to 24 inches below the bottom edge of the opening and should remain in place for a minimum of five to seven days to ensure all bats have exited. When bats return and try to reenter, the screen prevents them from doing so. This works best where the bats are entering through an opening in a smooth wall or louvers. Once the bats have all exited, the hole should be permanently sealed with silicon caulking, sheet metal, or hardware cloth. If bat conflicts continue, you may also want to consider installing a bat house. A more complex, but elegant exclusion method can be used where the entrance point is on an irregular surface. This method uses a 10-inch length of 2 inch PVC pipe that is fastened and sealed to the opening bats are using as an entry and exit. PVC pipe is smooth and bats cannot cling to the inner surface. To further prevent reentry, a piece of lightweight, clear plastic can be taped around the end of the tube that projects to the outside. The clear plastic collapses on itself further preventing reentry. As outlined above, the entrance points should be sealed after five to seven days to prevent reentry. For detailed descriptions and illustrations of the exclusion methods described above, visit the Bat Conservation International (BCI) web site at www.batcon.org and look under "Projects" then go to "Bats in Buildings: Exclusion Guidelines". There is also a wealth of other bat information, including plans for bat houses, at the BCI web site. Remember to exercise tolerance with bats-they are gardener's friends! The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/. |