Case Study Sites for Prioritizing Mitigation of Road Impacts on Western Governors' Association Wildlife Corridors

These case study sites are detailed in the report accompanying this data layer. The case studies are intended to serve as examples of how some of the opportunities for diverse stakeholders to engage in the process of mitigating road impacts on wildlife that are described in the report might be applied on the ground, as well as other considerations that come into play in selecting sites for possible mitigation and designing mitigation solutions for those sites. Through these case studies, we illustrate potential opportunities for mitigation and partner engagement for each of the four alternative priority sets identified in this study.Wildlife carcasses recorded by Montana Department of Transportation, Idaho Department of Fish & Game, and U.S. Fish & Wildlife Service were aggregated to the nearest mile marker for major roads of the U.S. Northern Rockies. WGA connectivity flowlines were intersected with the road network and attributed to the nearest mile marker, along with their centrality ranking, which indicates their expected relative importance to maintaining westwide connectivity. Values for potential risk factors, including average annual daily traffic (AADT), functional class, number of lanes, road surface width, landscape condition of surrounding habitat, ruggedness of surrounding landscape, and topographic position relative to surrounding landscape, were also attributed to mile markers. Landscape condition and topographic variables were calculated based on values observed within a half-mile radius of the focal mile marker. Landscape condition, an index of the degree of human modification of the landscape, is hypothesized to affect the likelihood of animals moving through adjacent habitat and attempting to cross the road at a particular site. Ruggedness (calculated as the standard deviation of slope values within a focal area) and topographic position (defined as the elevation of the focal point minus the mean elevation within a surrounding focal area, resulting in high values attributed to peaks and low values attributed to canyon bottoms) are expected to affect driver visibility from a particular site.Note that wildlife carcass collection and reporting protocols and frequency differ between states and among maintenance sections within states. Carcass counts should therefore be used only to explore general patterns and not for statistical inference.