Steven C. Forrest

Winter Resting Site Ecology of Marten in the Central Rocky Mountains

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

Population attributes for the black-footed ferret (Mustela nigripes) at Meeteetse, Wyoming, 1981-1985

Numbers of adults and juveniles in the single known free-ranging population of the endangered black-footed ferret ( Mustela nigripes ) at Meeteetse, Wyoming were estimated annually in July from spotlighting as 88 (1983), 129 (1984), and 58 (1985). Population sizes in September, determined from mark-recapture studies, were 128 ± 25 (1984) and 31 ± 8 (1985). Lower population estimates in 1985 reflected, at least in part, an ongoing epizootic of canine distemper in ferrets that decimated the population through November 1985, reducing it to ca. 6 individuals. From 1982 to 1985, adult sex ratio was 1 male: 2.2 females; juvenile sex ratio (1 male: 0.80 females) did not differ significantly from 1:1. The ratio of young to adults averaged 1.95:1 from 1982 to 1984 and 1.2:1 in 1985. At least 224 young were produced in 68 litters from 1982–1985, with a mean litter size at emergence of young of 3.3. Juvenile ferrets reached adult weight by September. Only one female tagged as a juvenile was recaught at 1 year of age, and she reproduced. Intercolony movements were primarily by juvenile males and occurred from September to October. Adults maintained geographic fidelity between years. Disappearance (mortality and emigration) rates ranged from 53 to 86% annually and were highest for juveniles. Observed ferret mortality in the absence of disease was primarily from predation. Reduction of the population during the epizootic suggests persistence of this population in the wild is unlikely.

Black-footed ferret Mustela nigripes energy expenditure and prey requirements

Abstract Black-footed ferrets Mustela nigripes are exceedingly rare and only a single extant population in Wyoming is known. Tracks in the snow and direct observations have provided data on activity and show that a ferret can travel from 0 to 7 km and may move up to 50 litres of soil from prairie dog Cynomys spp. burrows in a night. We constructed an additive model to estimate ferret energy expenditure, including energy for running, digging, investigating burrows, and thermoregulation. From field data, we estimate that ferrets expended an average of 130 kcal day−1 during winter. We used the Siberian polecat M. eversmanni as a biological model for the endangered ferret to estimate energy and nutrient aquisition from two ferret prey species. Gross energy content, proximate analyses and utilisation by the polecats of the two prey did not differ and were comparable to results for other carnivores. The polecats consumed an average of 125 kcal day−1 during trials, which is equivalent to 104 metabolisable kcal day−1. At least 20 prairie dogs must be eaten by a ferret during the four winter months (December–March) to meet these requirements. During summer months lactating female ferrets might need to eat prairie dogs at up six times this rate. Our results have conservation implications, including expected ferret densities in prairie dog towns.