Well-placed bat houses can attract bats to Central Valley farms

In an 8-year study from 1997 to 2004, we evaluated the use of 186 bat houses in rural areas of California's Central Valley. We considered the bat houses' size, color, height and location, and found that location was the main factor affecting bat use. Colonies of bats (generally mothers and their young) preferred houses mounted on structures such as buildings, shaded or exposed only to morning sun, and within one-quarter mile of water. In contrast, individual bats (generally males and nonreproductive females) were less selective in where they roosted. The overall occupancy rate for bat houses in our study was 48% for colonies and 28% for individual bats. Mexican free-tailed and Myotis bats were the main species using the houses, with occasional sightings of pallid and big brown bats. Bats occupied most houses within the first 2 years of placement.