| Summary: | Fishers (Martes pennanti) and American martens (Martes americana) reportedly use mature and older-growth coniferous forests to meet their life history needs. Regional differences in forest species composition, age, and disturbance regimes across fisher and marten ranges suggest that additional factors, beyond cover type, may be influencing their use patterns. Dead woody materials (DWM) are important components of mature or disturbed forests and are reportedly used in winter by fishers and martens for thermal and overhead cover, forage sites, and air spaces for subnivean access. While DWM use has been studied at site specific scales ( e.g. subnivean access points), its influence on habitat use at larger scales has not been studied. We monitored fishers and martens during winters in northern Wisconsin to determine if DWM influenced their habitat use at the home range scale. Eighteen fishers and 24 martens were monitored during the winters 1990-1995 yielding > 3,300 telemetry locations. Fisher winter home ranges were significantly larger than marten winter home ranges. Male fisher and marten winter home ranges were similar in size to their conspecific females. Cover type composition in fisher and marten home ranges did not differ significantly between sexes or with the study area composition. Stand diameter class (aggregations of tree bole diameter classes regardless of stocking density or species) composition in fisher and marten home ranges did not differ significantly between sexes or with the study area. Fishers did not select for habitats based on cover type or stand diameter class, nor did selection differ significantly between sexes. Male martens selectively used some cover types while avoiding others. Mixed hardwood and red pine (Pinus resinosa) cover types were used significantly more than expected, while aspen (Populus spp.), swamp conifer, and nonforested cover types were avoided. Female martens selected for mixed hardwoods, while red pine, aspen, swamp conifer and nonforested cover types were avoided. Dead woody material characteristics were measured in more than 1,000 circular plots (0.02 ha) randomly within cover types (n = 625) and randomly within animal activity centers (n = 386). Fisher and marten activity centers had greater numbers, heights and volumes of fine (<0.6cm) down DWM. Additionally, they had greater numbers of stumps and root tip-ups. These results suggest that fine as well as coarse DWM's are important fisher and marten habitat components. Further, it appears that DWM is important in determining use beyond site specific scales.
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