Tips and Guidelines
Bats have to find new roosts on their own. Existing evidence strongly suggests that lures or attractants (including bat guano) will NOT attract bats to a bat house. Bats investigate new roosting opportunities while foraging at night, and they are expert at detecting crevices, cracks, nooks and crannies that offer shelter from the elements and predators. Bat houses installed on buildings or poles are easier for bats to locate, have greater occupancy rates and are occupied two and a half times faster than those mounted on trees.
Unlike domestic animals, bats are wild and free-ranging. It is usually illegal to buy or sell them, and permits to capture and possess bats are generally limited to researchers, zoos, wildlife rehabilitators and educational organizations. Catching and relocating bats to new areas is, in any case, highly unlikely to succeed. Bats have strong homing instincts, and once released into a bat house, will attempt to return to their former home area. Consequently, placing bats in a bat house is usually futile and is not recommended. If a bat house remains unoccupied after two full years, consider repositioning of modifying the house.
The odds of attracting bats are very good for well-designed, well-built bat houses mounted according to recommendations developed by the Bat House Project during 12 years of bat house research by BCI and its volunteer Research Associates across the U.S., Canada and the Caribbean. This project found:
- Bats inhabited an average of 60 percent of all reported bat houses (both good and bad houses and installations) in BCI's 1999 to 2001 annual surveys.
- Occupancy in rural areas was 61 percent, compared to 50 percent for urban and suburban areas.
- 90 percent of occupied bat houses were used within two years (with 50 percent occupancy in the first year). The rest needed three to five years for bats to move in.
- Tall designs like the multi-chamber (nursery) and rocket-style houses performed best in our surveys. For example, 80 percent of 123 houses with chambers at least 25 inches tall were occupied in 2000.
Maintaining proper roost temperatures is probably the single most important factor for a successful bat house. Interior temperatures should be warm and as stable as possible (ideally 80º F to 100º F in summer) for mother bats to raise their young. Some species, such as the big brown bat, prefer temperatures below 95º F, while others, such as the little brown bat, tolerate temperatures in excess of 100º F. Bachelor bats are less picky and may use houses with cooler temperatures. The sides of wooden or masonry structure are the best mounting sites, especially in colder climates, because temperatures are more stable than for houses attached to poles.
Bat house temperatures are influenced directly by the exterior color, compass orientation (east-, southeast-, or south-facing are generally good bets for single houses in most climates), the amount of sun exposure, how well the house is caulked and vented, and the mounting and construction materials. You may have to experiment to get the right placement and temperature range. You can always use a thermometer taped to a pole to see if temperatures are suitable inside the bat house (check the chambers high and low, and front and back).
Pick installation sites with care so you don’t have to move it after it is occupied. Most bat houses have open bottoms, which keeps guano from accumulating inside. Guano will, however, end up on the ground underneath, so avoid placing bat houses directly above windows, doors, decks or walkways. Bat urine may stain some finishes. Two- or four-inch spacers between a bat house and the wall, a large backboard or a longer landing area below a bat house may reduce guano deposits on the wall. A potted plant or a shallow tray or plant saucer can be placed underneath a bat house to collect bat guano for use as fertilizer in flower beds or gardens. Do not use a bucket or deep container (unless 1⁄4-inch or smaller mesh covers the entire top of the container), as any baby bats that fall from the bat house could become trapped inside. For more installation advice visit our Install page.
Maintaining you bat house
Once you have attracted bats, you must maintain the bat houses to keep bats coming back year after year. Wasp and mud dauber nests should be cleaned out each winter after bats and wasps have departed. New caulk and paint or stain may be required after three to five years to guard against leaks and drafts. Bat houses should be monitored at least once a month (preferably more often) to detect potential problems such as predators, overheating, wood deterioration, etc. Any repairs or cleaning should be performed when bats are not present.
Getting rid of wasps
As the bats’ landlord, it is your duty to make sure the bat house is in good shape and is habitable. This means doing routine maintenance on the house and taking care of unwanted guests. Some of the most common non-bat visitors to bat houses are wasps. Wasps can be a problem before bats fully occupy a house. Use of 3/4-inch roosting spaces reduces the risk of wasps. If nests accumulate, they should be removed in late winter or early spring before either wasps or bats return. Open-bottom houses greatly reduce problems with birds, mice, squirrels or parasites, and guano does not accumulate inside.
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