Winter Resting Site Ecology of Marten in the Central Rocky Mountains

Abstract

We investigated the resting site ecology of American marten (Martes americana) in the central Rocky Mountains during 2 winters, 1985-86 and 1986-87. We found 8 marten used 57 resting sites on 141 occasions. Marten rested primarily in subnivean sites associated with coarse woody debris, including logs and stumps. Use of spruce (Picea spp.)-fir (Abies lasiocarpa) stands by adults was greater than expected and use of lodgepole pine (Pinus contorta) stands was less than expected on the basis of spatial availability. Juveniles used stand types in proportion to spatial availability. Fidelity to individual resting sites and to subnivean sites associated with coarse woody debris was highest among adults. Type of resting site used depended on air temperature at the time of resting; above-snow sites were used during the warmest weather, and subnivean sites associated with coarse woody debris were used during the coldest weather. Marten rested for longer periods where coarse woody debris formed all or part of the resting site than they did at other sites. Log densities were higher and mean log diameters greater in spruce-fir stands than in lodgepole pine stands. Resting sites associated with coarse woody debris occurred primarily in spruce-fir stands, whereas other resting sites occurred in other stand types. Resting sites were closer to streams and lakes than expected. The importance of resting where coarse woody debris is available to provide thermal cover may explain the apparent dependence of marten on old-growth forest in the central Rocky Mountains in winter. J. WILDL. MANAGE. 53(1):191-196 Resting sites used by American marten have been described for a wide range of geographic locations and include a variety of natural and man-made microhabitats (Campbell 1979, Steventon and Major 1982, Martin and Barrett 1983, Buskirk 1984). Locations of resting sites range from the forest canopy to beneath the soil surface. Winter resting sites are often associated with coarse woody debris (CWD), including logs, stumps, and snags (Steventon and Major 1982, Martin and Barrett 1983, Spencer 1987). In summer, marten generally rest in sites above the ground, often in the canopy layer (Masters 1980, Burnett 1981, Martin and Barrett 1983). Temporal differences in resting site preferences could be explained by thermoregulatory needs of marten, or by other factors such as vulnerability to predation. Marten live where above-snow air temperatures (Ta) in winter are lower than their lower critical temperature (T,c = the temp at which an animal must increase its metabolic rate above resting levels to offset thermal losses [16 C]) (Buskirk et al. 1988) by ?50 C. Thus they would appear to pay high energetic costs to rest at or near To in winter. Marten are associated with late successional stands of conifer-dominated forest over a wide geographic area (Francis and Stephenson 1972, Koehler and Hornocker 1977, Simon 1980, Bateman 1986) and have a close and seemingly obligatory association with old-growth stands in the Rocky Mountains in winter (Campbell 1979). However, a clear understanding of why marten are associated with old-growth is lacking. Patte ns of use of resting sites may provide a better understanding of the apparently obligatory nature of this association. We report on characteristics of resting sites used by marten in the Medicine Bow Mountains, Wyoming during 2 winter field seasons. We identify environmental and behavioral correlates of resting site use and draw inferences about the importance of resting site types for thermoregulation. We also discuss the importance of CWD as a resting site component in understanding the old-growth dependency of marten during winter. L. R. Forrest provided invaluable assistance during the winter field studies. We appreciate the cooperation of R. H. Abell, for allowing use of a portion of his trapline for field work. This research was supported by the Committee for Research and Exploration, National Geographic Society, the U.S. Forest Service (USFS), Rocky Mountain Forest and Range Experiment Station, and the Office of Research, University of Wyoming. We thank the Wyoming Game and