An investigation into the use of road drainage structures by wildlife in Maryland, USA

Culverts have been installed beneath roadways for drainage or to contain existing streams; however, most of them have not been installed to facilitate the passage of wildlife. Prior studies of existing drainage structures used by wildlife have been narrow in scope, targeting a restricted number of culverts, time periods, or locales. Use of culverts by wildlife has been postulated to promote connectivity of fragmented populations and their habitats and to reduce roadkills. We monitored 265 culverts located throughout Maryland, USA, with game cameras in all seasons and in every physiographic province. Our objectives were to identify those species using culverts and their relative occurrence and to determine how culvert and land-use and land-cover (LULC) characteristics affect use. We documented culvert use by 57 wildlife species. We analyzed species affiliation with culvert and LULC variables for 12 species that occurred in ≥30 culverts. Different factors affected culvert use by these species. White-tailed deer (Odocoileus virginanus), in particular, used culverts that were wider, taller, and longer than unused culverts, with higher use occurring in the Piedmont physiographic province of Maryland. Our results can be used to make informed decisions on retrofitting existing culverts or designing cost-effective underpasses that provide basic wildlife needs and promote wildlife passage across roadways