Talk Carcass Removal and Detectability: Reducing the Uncertainty Surrounding WildlifeVehicle Collision Surveys

Wildlife-vehicle collisions (WVC) are recognized as an important source of non-natural animal mortality. To accurately quantify this impact, two main sources of uncertainty have to be accounted for: carcass persistence time and carcass detectability. In this study, we evaluate the influence of these uncertainties on roadkill surveys. We expect the size of the carcass, road type and traffic, the probability of occurrence of scavengers in the roads’ vicinity, and weather conditions to be the main drivers of carcass removal, but their relative importance was unknown.  To estimate carcass persistence time, we conducted road surveys on a monthly basis, for two years. Each survey consisted of five consecutive days, during which three observers searched for WVC by car. To estimate carcass detectability, we randomly selected stretches of 500 m to be additionally surveyed on foot by two other observers (total 292 walked stretches). Overall, we recorded low persistence times (median one day) and low detectability (<10%) for all vertebrates. The results suggest that body size and probability of scavenger occurrence are the major drivers of carcass removal. We estimated that our recorded mortality rates underestimated actual values 3-10 fold. Although persistence times were similar to previous studies, the detectability rates described here and those of previous studies were very dissimilar. We suggest that detectability is the main source of bias across WVC studies and, therefore, more than persistence times, studies should carefully account for differing detectability when comparing WVC studies. This study is of interest for road managers and researchers aiming to better understand the impacts of WVC on biodiversity.

Carcass Removal, Detectability, Wildlife-Vehicle