Grizzly bears and humans at two moth aggregation sites in Wyoming

Abstract

Human interactions with grizzly bears at moth sites is an important management issue because of the potential for displacing bears and the implications for human safety. The objective of our study was to quantify human and bear use overlap and interactions associated with two of the most human-accessible moth sites in the Greater Yellowstone Ecosystem. Our field work was conducted during the summers of 2017 and 2018. We conducted systematic bear surveys and analyzed the data using a resource selection function. Human use was quantified through trailhead monitoring, peak log entries, and opportunistic documentation. Hiking route data were collected using GPS tracking units distributed at trailheads. Human-bear overlap was assessed by comparing human and bear use and validated against interaction location data. We conducted 293 surveys and documented 266 bear locations. Landscape covariates describing temperature, moisture, terrain, and landcover were important to grizzly bear use. We recorded very different human use levels between the two study sites (North site: 3 groups/year; South site: 35 groups/year). Human use at the North site was dispersed and associated with hunting and use at the South site was most often associated with peak climbing and/or bear viewing and was concentrated along one primary route to the peak. We documented a total of 43 interactions (at the South site only) and obtained location data for 29 of those interactions. During human-bear interactions, bears strongly avoided human presence 80% of the time and had no apparent reaction 20% of the time. Most interactions occurred immediately around the South site peak (14/29) or along the primary route (12/29), areas that we identified to have high human and bear use overlap. We confirmed significant human safety and bear disturbance management concerns. Human safety concerns were most apparent in uneducated, and consequently unprepared, mountain climbing groups with small groups sizes (<4 people, n=64/70). Bear disturbance concerns were apparent from numerous interactions that resulted in bear displacement. Overall, we suggest that the concern expressed by managers over human and bear use overlap at the South site is warranted. Mitigation efforts should be explained in a management plan.