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Yellowstone National Park Report

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American marten (Martes americana) use primarily old growth coniferous habitat (Bateman 1986, Raine 1983, Soutiere 1979, Steventon and Major 1982). However, their use of habitat may vary by season (Steventon and Major 1982, Koehler and Hornocker 1977, Wynne and Sherburne 1984). In summer, marten use of non-forested areas to forage for fruits and berries has been documented (Soutiere 1979, Steventon and Major 1982). While there is some seasonal variation in habitat use, all authors agree that old growth is the core habitat required by marten. During winter, marten tend to remain in mature coniferous forests and will seldom cross open areas greater than 100m wide (Steventon and Major 1982, Soutiere 1979). Winter appears to be the most critical period for marten survival (Zielinski et al. 1983, Buskirk 1984). In winter, marten seem to require subnivean access for three major reasons: food, escape cover, and homeothermy. The use of subnivean access points has been well documented (Pullianen 1981, Buskirk 1984, Buskirk et al. 1989), but the mechanisms that determine the use of some access points and not others are not well understood. Certainly there is a relationship between the use of access points and coarse woody debris (CWD). Buskirk et al. (1989) found that 49% of marten resting sites and 63% of resting episodes were associated with CWD. CWD provides structure that breaks the snow surface, providing access to the subnivean zone where marten may escape low ambient temperatures, find prey or escape from predators. Buskirk (1989) has suggested that marten use subnivean access points to reach CWD that provides insulation from the cold. Marten in Wyoming (Buskirk et al. 1989) were found to use resting (access) sites associated with CWD when ambient temperatures were coldest; therefore, use of access points can decrease the metabolic demand for maintenance of body temperature. Studies of marten activity patterns, however, have shown that marten are most active at night during the winter (Zielinski 1981, Zeilinski et al. 1983, Lensink et al. 1955) when temperatures are coldest. This strategy is not energetically beneficial from a thermoregulatory standpoint and implies that other mechanisms may contribute to access point use. Microtines are the major food item in marten diets. Additionally, marten tend to hunt on a daily basis and their activity patterns in winter tend to be nocturnal. Zielinski et al. (1983) showed a correlation between marten activity and the activity of their principle prey in California. These aspects of their natural history suggest a relationship between the use of subnivean access points and prey densities. The primary goal of this study is to determine if this relationship occurs.