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Highway infrastructure represents one of the most consequential anthropogenic impacts on natural ecosystems. However, infrastructure (i.e., bridges, culverts) can establish otherwise esoteric microhabitats and desirable resources for microchiropteran species worldwide. Throughout North America, bats benefit from these anthropogenic structures, which function as alternative roosts (i.e., diurnal roosts, nocturnal roosts, maternity roosts, bachelor roosts) and stepping-stone refugia (i.e., transitory “stop-over” roosts) for migratory populations.
Despite abundant documentation of bridge occupancy, publications characterizing culvert use are relatively uncommon, predominantly anecdotal and/or comprise small sample sizes. Consequently, culverts are critically undervalued as roost habitat. This undervaluation, coupled with an oversimplification of “suitability,” unquestionably causes oversights with respect to occupancy. While composing the document, Best Management Practices for Bat Species Inhabiting Transportation Infrastructure, three enduring misconceptions were evident; steel culverts are unsuitable, small culverts are unsuitable, and culverts are not amenable to hibernation. These misbeliefs underlie statements such as “…we excluded culverts because we considered them unsuitable for roosting due to a lack of crevices or perching substrate” and “culverts had much shorter lengths than previously published dimensions of occupied culverts and would typically be overlooked…”
An opportunistic examination of culverts within Socorro County, New Mexico suggests high occupancy rates (71.4-100%), comparable to similar preliminary studies, which document occupancy rates of 53.3% to 85%. Corynorhinus townsendii, a State of New Mexico Species of Greatest Conservation Need (SGCN) was commonly present, exhibiting occupancy rates of 77.7%. Multiple species, including C. townsendii, were present October-January and across the United States, several publications document culvert use November – March. Furthermore, bats consistently exploited culverts with characteristics that controvert existing measures of “suitably.”
The emergence of broadscale threats to bat populations (e.g., white-nose syndrome, habitat destruction and modification, climate change) underscores the importance of illuminating a habitually overlooked, but crucial aspect of modern bat ecology – anthropogenic roosts. Roost availability and abundance are critical elements limiting populations; thus, the successful management (i.e., identification, evaluation, mitigation) of these amenable substitutes becomes increasingly important. Educating conservation and transportation authorities can ensure positive outcomes, for both DOTs and endemic bat populations. Our presentation will elucidate culvert microhabitats, address common misconceptions and identify best management practices. Additionally, we will introduce bati.institute, an e-learning site providing comprehensive information on evaluative surveys, appropriate time schedules, and mitigation measures; online courses; informative case studies; interactive imagery; and an e-forum to communicate, and exchange valuable information. These resources will further enhance bat conservation and stewardship practices.