Clues to Roosting Preferences

Through BCI workshops and cooperative research projects from 1992-94, volunteers have located more than 90 natural roosts for 10 species of bats, giving us valuable information on roosting preferences.

Eight species, including both big and little brown bats (Eptesicus fuscus and Myotis lucifugus), established nursery colonies beneath the loose bark of old snags. Most of these formed groups of dozens to hundreds of individuals per roost, sometimes scattering into smaller groups in alternate roosts. All the sites found were exposed to direct solar heating, and most of the colonies seemed to prefer relatively high temperatures. The vast majority of roosts were in crevices three-quarters to one inch wide, with only the largest species accepting wider dimensions of up to two inches. Non-nursing individuals and small groups of most of the species were found in relatively cool locations.

Mexican free-tailed bats (Tadarida brasiliensis) were found roosting in large numbers in the concrete crevices of Texas bridges, either in armor joints or between box beams. They clearly preferred crevices roughly three-quarters to one inch wide, at least 12 or more inches deep, and at least 12 feet above ground. Many free-tail roosts were open at the top or sides, though this seemed to result more from a lack of alternatives than from choice. All roost temperatures were close to 90 degrees, and it was clear that the free-tails preferred slightly rough surfaces.