Patterns and drivers of amphibian and reptile road mortality vary among species and across scales: Evidence from eastern Ontario, Canada

The mortality of wildlife on roadways is a major conservation concern worldwide. Amphibians and reptiles are especially vulnerable to vehicular collisions, and this is of particular concern in the Frontenac Arch Biosphere Reserve (Ontario, Canada) where several species are near their geographic limits of distribution and designated as species-at-risk. We completed regular surveys (n = 270) of two major highways in the Reserve, each slightly less than 40 km in length. All observations of wildlife-vehicle collisions were documented for two years on each road, including 18,278 frogs, turtles, and snakes. We used kernel density estimation to map relative magnitude of this mortality and built a suite of regression tree models to assess the influence of landcover and other habitat factors on roadkill at two scales (1 ha and 20 ha). Sample size was large enough to conduct species-level analyses for Chrysemys picta marginata (midland painted turtle) and Nerodia sipedon (northern watersnake). Spatial clustering of roadkill was evident on both roads and for all taxa. However, the extent of clustering varied between the two roadways due to differences in landcover pattern and clustering was more discrete for frogs and turtles than for snakes. For frogs, turtles, and northern watersnakes we found that elevated levels of mortality were positively associated with the amount of wetland and open water in adjacent areas as well as the proximity of water features. However, mortality locations for other species of snakes were more closely associated with upland habitat types. While some generalities emerge from our study, the variation also suggests that caution be exercised when attempting to extend results to different taxa and roadways, especially since these results may vary with scale. Nonetheless, scale-related differences can be informative for identifying the location of roadkill mitigation efforts and we illustrate how such an approach could be implemented for snakes that exhibit less discrete clustering of mortality.