Potential future mitigation measures for wildlife and people along I-90 and other major highways in western Montana, USA

Abstract

We explore the opportunities for potential future mitigation measures for wildlife and people along I-90 and other major highways across the Y2Y (the Yellowstone to Yukon Conservation Initiative) region in western Montana. We identified highway sections that had the highest concentration of collisions with large wild animals based on crash data and carcass removal data. We also conducted cost-benefit analyses for the implementation of wildlife fences in combination with wildlife crossing structures (underpasses and overpasses) along the highways in the study area. Then we compiled existing data on habitat and corridors for species of special conservation concern (grizzly bear, Canada lynx and wolverine) and obtained existing range distribution maps for other large wild mammals (white-tailed deer, mule deer elk, moose, pronghorn, bighorn sheep, bison, mountain lion and gray wolf). We conducted further analyses on grizzly bear road mortality and grizzly bear connectivity pathways. Our analysis of the barrier effect of the highways (based on hourly traffic volume counts) that cut through grizzly bear connectivity pathways centered around two conservation objectives. The first objective was to establish robust and functional connectivity between the Northern Continental Divide Ecosystem (NCDE) grizzly bear population and the Greater Yellowstone Ecosystem (GYE) grizzly bear population. The second objective was to facilitate recolonization by grizzly bears of the Bitterroot Ecosystem (BE). Depending on the objective, different highway sections were identified as barriers to grizzly bears. The road sections that were identified based on the two connectivity objectives were different from the road sections where most grizzly bears are killed by vehicles. The road sections that were identified based on the two connectivity objectives would need to be mitigated in a spatially coherent manner to reach the objectives, illustrating a strategic anticipatory approach to conservation rather than a reactionary approach to either conservation or human safety. An analysis of the 360-mile-long section of I-90 through the Y2Y area in Montana showed that 124 miles (34.4%) is important for grizzly bear connectivity and that 152 miles has major human safety concerns because of collisions with large wild mammals (mostly ungulates). While there is some overlap between the road sections that are important for grizzly bear connectivity and the road sections that have a relatively high concentration of collisions with large wild mammals, only 41.9% of the length of the road sections along I-90 that are important to grizzly bear connectivity are also important because of collisions, and only 34.2% of the length of the road sections along I-90 that are important because of collisions are also important to grizzly bear connectivity. This illustrates the need for a two-track system for the policy, funding and implementation of mitigation measures; one that is based on human safety, and one that is based on conservation. Furthermore, measures for human safety can relate to individual road sections, whereas measures for conservation must be spatially coherent at a landscape level.