Seasonal and Regional Animal Use of Drainage Structures to Cross Under Roadways

Road drainage structures, hereafter designated culverts, are often used by wildlife and other animals to cross under roadways. However, crossings may vary by species, culvert design, different environmental factors, and land-use and land-cover (LULC) at culvert sites. We monitored 265 culverts located throughout Maryland, USA, with motion-detecting game cameras to assess seasonal and regional effects on culvert crossing rates by wildlife and other animal species considered common to the areas. Northern raccoon (Procyon lotor) and Virginia opossum (Didelphis virginiana) exhibited lower crossing rates in culverts during winter than at other times of the year. We did not detect any difference in seasonal crossings for other species, but several species exhibited similar patterns of lower crossings/culvert/day during winter. We detected more crossings/culvert/day in the Piedmont ecoregion of Maryland for several species associated with farmland and suburbia (e.g., raccoon and red fox [Vulpes vulpes]). In contrast, opossum and free-ranging domestic cat (Felis catus) crossing rates were greater in the Appalachian Mountain ecoregion. The crossing rates for the only bird species we recorded on camera traps, the great blue heron (Ardea herodias), tended to increase from west to east, with its highest crossing rate on the Eastern Shore (lower coastal plain) of Maryland, where these birds are known to be abundant in tidal marshes. Besides a myriad of LULC and structural variables known to affect wildlife and other animal crossing rates, seasonal and regional differences in animal use must also be taken into consideration for culvert design and placement or retrofitting existing culverts to enhance crossings by particular animal species