The bat house at the Creston Valley Wildlife Management Area in British Columbia, Canada, was adapted from BCI plans. It's about 10-feet (3 meters) square, sits on utility poles and can house up to 30,000 bats. That's 150 times as many bats as the "multi-chamber bat houses" BCI was exploring in the 1990s.
At the Trinity River National Wildlife Refuge in East Texas, rare Rafinesque's big-eared bats (Corynorhinus rafinesquii) are raising pups in "tower roosts" made of cinder blocks that mimic the increasingly scarce large, hollow trees these rare bats prefer. Similar artificial roosts are being used by "rafies" in six states.
The legacy of BCI's Bat House Project, which studied, designed and tested artificial bat roosts from 1993 through 2008, extends far beyond the backyard bat houses with which it began.
With BCI's active support, bat houses began appearing around the United States during the 1980s. But, among other problems, these were mostly too small and provided roosting chambers that were too large for the bat species, such as Mexican free-tailed bats (Tadarida brasiliensis), that they were intended for. Bats mostly shunned these efforts.
The North American Bat House Research Project (which became the Bat House Project) was created after BCI's first survey of bat-house success rates suggested some key criteria, especially larger houses with ¾-inch roosting chambers. The Bat House Builders Handbook reported those findings.
Over the next 10 years, the project analyzed data from a total of about 7,000 volunteer Research Associates who erected their own bat houses and reported on their design, location and success. Occupancy rates improved from about 23 percent in 1995 to more than 60 percent by 2000, with nearly 90 percent success for houses and locations that met BCI's guidelines.
Countless bats now live in BCI-style bat houses in backyards, parks and greenbelts. They're also popular at orchards, vineyards and farms that include insect-eating bats in Integrated Pest Management Plans. Longtime BCI supporter Frank Bibin installed his first bat house at his Pebble Hill Grove pecan orchard in Georgia in 1996. He now has 10 bat houses that offer summer homes to some 3,500 bats. And he consistently reports reduced damage from hickory shuckworm moths and other pests of pecans.
Bat houses built to BCI criteria are being used around much of the world. A recent experiment by Tore Christian Michaelsen and colleagues in Norway that found bat houses adapted from BCI plans were so attractive that bats often evicted themselves from private homes and moved into nearby bat houses.
BCI began exploring tower roosts in 2000 in hopes of providing homes for forest bats that are losing their natural roosts: extra-large cavities inside old-growth trees that are frequently cleared from managed forests. Initial versions of these "artificial trees" involved concrete culverts stacked two-high and capped at the top. The design attracted Rafinesque's big-eared bats and other species, but it proved too expensive and required heavy machinery to install. Studies found that the cinder-block version was at least as effective for bats and less expensive to build.
An intriguing twist on tower roosts was studied in Costa Rica by BCI Scholar Detlev Kelm. He tested very low-cost, low-maintenance artificial hollow trees designed to attract seed-dispersing fruit bats that are critical to regenerating damaged rainforests. His research demonstrated that bats moved into the artificial roosts quickly – and seed dispersal was significantly enhanced.
Sometimes a very large bat house is required, especially when bat colonies are displaced as habitat is lost to construction, agriculture or other activities. Various options have been tried over the years, but with mixed success. Then Cal Butchkoski of the Pennsylvania Game Commission designed the Pennsylvania Bat Condo in 1997 to hold as many as 10,000 bats. It proved effective for little brown myotis (Myotis lucifugus) and other bats, especially in the Northeast and Midwestern states.
The design proved less effective for southern bats, such as the Mexican freetails that often roost in large colonies, however. So in 2008, BCI worked with University of Texas architects to modify the design of the bat condo. The result is BCI's Community Bat House that can hold tens of thousands of bats.
Examples of these giant bat houses have been built from BCI plans (which are freely available) in Escambia County, Florida, as well as in British Columbia.
Although the Bat House Project is no longer an active BCI program, homeless bats across North America and the world are still finding safe refuge because of it.