Modeling road mortality of prairie rattlesnakes and bullsnakes in Alberta

Abstract

The grasslands of the Northern Great Plains have experienced significant change, first from crop agriculture during the settlement period, then with expansion of the transportation network, and in recent decades for hydrocarbon extraction. Roads with vehicles can have significant ecological effects including wildlife road mortality. Road density and vehicle access pose unquantified threats to snake populations in Alberta's Mixedgrasslands Natural Subregion, where development has been accompanied by increased road density and vehicular traffic. I studied the movement behaviour of prairie rattlesnakes (Crotalus v. viridis) and bullsnakes (Pituophis catenifer say i) and developed models of their risk of road mortality. I found that temperature was a good predictor of snake movement and influenced road mortality rate. Traffic density also significantly influenced the number of snakes killed on roads. Additional factors that influence mortality risk were incorporated into a system dynamics model that I used to evaluate the sensitivity of parameter value changes. Model results indicated that road density and traffic density were the most influential factors for snake road mortality risk; while vehicle speed had a moderate effect and the influence of driver awareness was negligible. I propose that wildlife managers can use these models as planning tools for mitigating the impacts of road mortality on prairie rattlesnake and bullsnake populations.