Influence of ecology and landscape on snake road mortality in a sagebrush-steppe ecosystem

Roads fragment our landscape, posing a severe threat to the persistence of wildlife populations through losses of individuals to direct mortality and decreased connectivity. Although they possess a particular suite of life history characteristics that make them especially vulnerable, snakes tend to be underrepresented in research examining vertebrate road mortality. Here, we report a statistical analysis of snake mortality along a 183-km road circuit in sagebrush-steppe habitat located in southeastern Idaho. We describe differential road mortality across snake species, season, sex and age. We also analyze both fine-scale and broad-scale habitat measurements to identify various habitat and landscape factors associated with snake road mortality. Our results show clearly that snake road mortality is influenced by interactions among demographic, ecological and temporal factors. Vagile species and life stages were particularly vulnerable to road mortality during periods of peak activity. Gophersnakes dominated our road observations, with adult male mortality peaking in spring and high casualties of neonates in the fall. Snake crossings were especially common along roadsides with high vegetative cover, in areas dominated by non-native grasses. These results suggest the potential for snake populations to become fragmented over time, and that habitat conversion and species invasions may be compounding this effect. This study suggests that conservation efforts need to account for inter- and intraspecific differences in road mortality risk and provides guidance for roadside management that may serve to minimize vertebrate mortality on roads.