Thinking outside the box: A review of artificial roosts for bats

Artificial roosts designed to attract bats have been used to increase populations, aid seed dispersal, and control insects. More important from a conservation perspective, artificial roosts provide habitat where natural roosts have been lost. Although artificial roosts have been widely used, much of the information on species that use artificial roosts, roost design, and placement is anecdotal and poorly reported. We reviewed the existing literature on artificial roosts to summarize current research and inform research and management decisions. From 47 publications and reports, we identified 48 types of structures used by 59 species. Roosts were constructed from wood (66.7%), concrete (8.3%), or other materials (25.0%) and varied in size and shape from small-volume wood boxes (0.002 m³) to large (6 m tall) free-standing structures. Variables most often considered in the context of attracting bats were aspect, substrate, and mount location; few studies measured height or microclimate. Colonization rates ranged from 7% to 100%. Bats commonly used structures as solitary (21 species) or social (breeding or maternity; 21 species) roosts. Most species documented to use artificial roosts are vespertilionids (73%), have the International Union for Conservation of Nature's designation of least concern (93%), and roost in tree cavities or buildings. Three species are designated as endangered (Myotis sodalis) or near threatened (M. bechsteinii, M. dasycneme). Artificial roosts should be constructed and installed to mimic natural roosts, emphasize requirements of target species, and exclude non-target species. Monitoring species composition and identifying effects of roost density will help determine conservation impacts of artificial roosts.