Testing a road mortality risk model to prioritize and design turtle eco-passages at wetland-road crossings in New Hampshire, USA

Intersections of roads and wildlife movement pathways can lead to wildlife road mortality, resulting in population-level impacts. Wetland-road crossings are vulnerable locations for freshwater turtles that conduct inter- and intra-wetland movements during their active period to mate, forage, and nest. Identifying turtle road mortality hot spots may enable managers to implement mitigation efforts, such as locating and designing eco-passages. We assessed a predictive model for turtle road mortality risk by observing eighteen wetland-road crossing sites ranked by the model. For eleven weeks during the turtles’ active period (May-July), we surveyed sites for road mortality and used cameras to observe movements across the road of four species: Blanding’s turtles ( Emydoidea blandingii ), spotted turtles ( Clemmys gutta ), snapping turtles ( Chelydra serpentina ), and eastern painted turtles ( Chrysemys picta ). We demonstrate that the predictive model identifies sites with higher rates of turtle road mortality (p < 0.01) and that road accessibility is a significant factor in road mortality rates (p = 0.02). Fewer turtles were observed on the road above wetland-road crossing structures (i.e., culverts) with larger openness ratios (p = 0.06). These findings may inform the design of road mortality mitigation structures, such as eco-passages, fencing, guide walls, and driver-awareness mechanisms. We also provide a conceptual engineering design to demonstrate how to reduce road accessibility and expand openness ratios to mitigate turtle mortality in a case study of one of our highest-risk sites.