Broad-scale models of a foundational alpine insect: Implications for grizzly bear ecology and conservation

Alpine regions provide temporary habitats for many species and support complex food webs. These ecosystems are poorly described and threatened by anthropogenic stressors. Thus, there is a need to better characterize the populations and interactions of species that use alpine environments. The army cutworm moth (ACM) migrates great distances to reside within alpine talus slopes of the Rocky Mountains, where they aggregate in large numbers. Their high energy content is attractive to grizzly bears, which ascend mountains to consume them. However, the full nature and extent of the ACM-grizzly relationship remains unclear. We implemented two survey techniques to elucidate grizzly bear-ACM interactions across 40 peaks in Glacier National Park, Montana. We used field surveys of alpine talus slopes to determine environmental drivers of ACM distribution and create broad-scale models of ACM occurrence. We then executed helicopter surveys of talus slopes to document grizzly bear presence and create models of grizzly bear foraging. ACM occurrence was influenced by the physical characteristics of talus slopes that provided stable, cool microclimates. These environments are rare, with ACM occurrence confined to 0.3% of the national park. ACM probability of occurrence was the most influential predictor of grizzly bear foraging on talus slopes. Given the importance of physical talus characteristics for ACM occurrence, better tools are needed to finely characterize and map the talus habitat for this foundational alpine species. Our models can help park managers develop access management strategies to limit impacts to grizzly bears and other species that consume this energy-rich food resource.