Mechanisms driving variation in American marten winter rest site use across the Western Great Lakes Region

Abstract At high latitudes, the thermal protection of snowpack is important for many small-bodied mammal species during the winter. As depth and persistence of snow changes due to climate change, species that rely on snowpack’s insulation must increasingly depend on alternative thermal refuges. For the American marten ( Martes americana ), winter rest sites are predominantly in ground microsites. In some regions, however, martens primarily use tree cavities. Differences are hypothesized to be driven in part by regional differences in climate, which can be tested by comparing the use of different rest site types in areas with varying winter conditions. Here, we evaluated the roles of ambient temperature, snowpack, tree cavity temperature, and ground temperature on marten winter rest site use in two contrasting areas in the Western Great Lakes Region. Use of tree cavities in the lower peninsula of Michigan, USA appears to largely be linked to the area’s shallow snow depths and relatively warm ambient temperatures. Conversely, the use of ground microsites in northern Minnesota, USA was linked to deep snow depths and cold ambient temperatures. However, factors like microsite availability are also likely driving microsite use in both populations. Our results suggest that with rapid changes in snowpack and ambient temperature, tree cavities and subterranean burrows may become increasingly important alternatives to ground microsites that were historically covered by snow. Consequently, rapid and effective strategies will be needed to maintain or increase the availability of these alternatives.