Common construction materials do not deter turtles from nesting in roadside habitat

Roads are pervasive linear features that bisect landscapes, altering how female turtles use and move between critical habitats during nesting migrations. We evaluated a new mitigation strategy aimed at deterring females from nesting along road shoulders at wetland crossings in eastern Georgian Bay, Ontario, Canada. The mitigation strategy was designed to reduce roadside nesting habitat by covering gravel on road embankments near wetlands with rock rip‐rap (large angular rocks; in ~100‐m‐long sections) paired with paved road shoulders (paved using tar‐and‐chip; in ~300‐m‐long sections). We evaluated the mitigation strategy using a mark‐recapture study and a before‐during‐after comparison of nest observations at mitigated and unmitigated sites and nesting hot spots on the road. We found a significant reduction in the number of females nesting at mitigated sites in the after period, and no females of any species nested in the rip‐rap on road embankments. However, females continued to nest in the nearest available roadside habitat in unmitigated and mitigated road sections (including in the semi‐compact tar‐and‐chip shoulders). Notably, we found a high proportion of the local populations of Blanding's turtles ( Emydoidea blandingii ; 45% [36/80]) and snapping turtles ( Chelydra serpentina ; 52% [91/172]) nesting on the road in the during and after periods. Our findings suggest that the mitigation strategy was unsuccessful at deterring female turtles from nesting on roads and indicate that the application of rip‐rap and paved road shoulders as a mitigation strategy to reduce roadside nesting should not be applied without further research. Females will likely continue to nest in the roadside habitat if a barrier (e.g., exclusion fencing) is not deployed. Our study elucidates the importance of incorporating species‐specific behavior and movements into all aspects of road planning and highlights that new road‐effect mitigation strategies should be empirically tested before widespread adoption.