Habitat characteristics of the hoary marmot: assessing distribution limitations in Montana

Abstract

Species that live in ecosystems with extremely different seasonal conditions must balance the constraints of each season to survive. Alpine species that do not migrate seasonally are especially adept at balancing the constraints created by short growing seasons and long, harsh winters. We investigated the habitat characteristics of hoary marmots in western Montana to provide a better understanding about habitat selection at the southern extent of this species' distribution. Hoary marmots are an alpine obligate of special concern in western Montana; given that climate change is impacting alpine ecosystems at a rapid rate, this species may be especially vulnerable at the southern edge of their range. We conducted occupancy surveys in three study areas along a latitudinal gradient in 2014 and 2015 to assess the importance of specific habitat characteristics to their presence on the landscape. Slope, aspect, and presence of shrubs were all important habitat characteristics. Marmots preferred shallow slopes and southern aspects, similar to findings from other studies on hoary marmots and other marmot species. Our results provide evidence that marmots may strike a balance between the environmental conditions they require during summer and winter. Shallow slopes typically accumulate deeper snow in winter that provide the best insulating snowpack. However, a preference for southern aspects allows for more snow-free areas in spring, providing a slightly longer growing season than northern aspects. Hoary marmots may be selecting areas with shrubs because shrubs can accumulate deeper snow and the additional insulation can increase subnivian temperatures. Other studies suggest that marmot survival is influenced by snowpack, indicating that marmot distribution may be more closely tied to winter conditions rather than summer conditions. This highlights the difficulty of working on marmots and other alpine obligates, as most studies occur only during the short growing season. Given the current and projected increases in temperature and reduction in snowpack in Montana, areas that provide the winter conditions hoary marmots require may become more limited. Effectively conserving, monitoring, and managing alpine obligates under an uncertain climate future will require a closer look at how winter conditions drive habitat selection and distributions on the landscape.