Pekania pennanti

Fishers inhabit upland and lowland forests, including coniferous, mixed, and deciduous forests. They occur primarily in dense coniferous or mixed forests, including early successional forest with dense overhead cover (Thomas et al. 1993). Fishers commonly use hardwood stands in summer but prefer coniferous or mixed forests in winter. They generally avoid areas with little forest cover or significant human disturbance and conversely prefer large areas of contiguous interior forest (see USFWS 2004). Powell (1993) concluded that forest type is probably not as important to fishers as the vegetative and structural aspects that lead to abundant prey populations and reduced fisher vulnerability to predation, and that they may select forests that have low and closed canopies. Several studies have shown that fishers are associated with riparian areas (see USFWS 2004), which are in some cases protected from logging and generally more productive, thus having the dense canopy closure, large trees and general structural complexity associated with fisher habitat (Dark 1997). Riparian areas may be important to fishers because they provide important rest site elements, such as broken tops, snags, and coarse woody debris (Seglund 1995).

Fishers are regarded as habitat specialists in the western United States (Buskirk and Powell 1994), occurring only at mid- to lower elevation in mature conifer and mixed conifer/hardwood forests characterized by dense canopies and abundant large trees, snags, and logs (Powell and Zielinski 1994). In contrast, fishers in the northeastern United States and the Great Lakes region inhabit areas with a large component of deciduous hardwood forest containing American beech (Fagus grandifolia), sugar maple (Acer saccharum), and other broadleaf species (Powell and Zielinski 1994). The majority of conifer forest habitat in Canada is characterized as boreal forest, which is different from the relatively dryer environmental conditions associated with Washington, Oregon, and California. In the Rocky Mountains of north-central Idaho, certain all-conifer habitat types, which include grand fir and Engelmann spruce appear to be important to, and preferentially selected by fishers (Jones 1991).

Fishers are adapted for climbing but are primarily terrestrial. When inactive, they occupy a den in a tree hollow, under a log, or in the ground or a rocky crevice, or they rest in branches of conifer (warmer months). In Connecticut, Kilpatrick and Rego (1994) found that tree with a dbh of 32 cm or more may provide cavities for rest sites in hardwood-dominated forests.

Young are born in a den in a tree hollow (usually), or under a log or in a rocky crevice. Large snags (greater than 50 cm dbh) are important as maternal den sites (Thomas et al. 1993). Of 19 tree dens documented by Truex et al. (1998) across three study areas in California, the average diameter was 115 cm for conifers and 63 cm for hardwoods. Of 16 maternal and natal dens located on managed timberlands in northwestern California, nine were in cavities in hardwoods and seven were in conifer snags: diameters of den trees ranged from 62.5 cm to 295 cm (Simpson Resource Company 2003). See USFWS (2004) for further details on dens used by fishers in California and British Columbia.

West Coast Distinct Population Segment:

The key aspects of fisher habitat are best expressed in forest stands with late-successional characteristics. Fishers use habitat with high canopy closure, large trees and snags, large woody debris, large hardwoods, multiple canopy layers, and avoidance of areas lacking overhead canopy cover (see references in USFWS 2004). Fishers also occupy and reproduce in some managed forest landscapes and forest stands not classified as late-successional that provide some of the habitat elements important to fisher, such as relatively large trees, high canopy closure, large legacy trees, and large woody debris, in second-growth forest stands (Klug 1997, Simpson Resource Company 2003). However, intensive management for fiber production on industrial timberlands does not typically provide for retention of these elements. It is unlikely that early and mid-successional forests, especially those that have resulted from timber harvest, will provide the same prey resources, rest sites and den sites as more mature forests (see USFWS 2004). Late-successional coniferous or mixed forests provide the most suitable fisher habitat because they provide abundant potential den sites and preferred prey species (Allen 1987). Forest structure of good quality fisher habitat should provide high diversity of dense prey populations, high vulnerability of prey to fishers, and natal and maternal dens and resting sites (Powell and Zielinski 1994). Younger forests in which complex forest structural components such as large logs, snags, and tree cavities are maintained in significant numbers, and which provide a diverse prey base, may be suitable for fisher (Lewis and Stinson 1998). [from USFWS (2004), which see for further details on habitat in California]

See also Zielinski et al. (2004) for information on habitat characteristics in California.

Solitary except during the breeding season.

Home range has been estimated at 10-800 sq km by snow tracking, 7-78 sq km by telemetry using minimum convex polygon model; generally the ranges of adults of the same sex do not overlap. In Maine, home ranges of females were stable between seasons and years, but males moved extensively in late winter and early spring and their ranges shifted between years. In New Hampshire, mean annual home range was about 15-25 sq km, with daily movements usually were 1.5-3.0 km. In southern Quebec, mean home range size was 5.4 sq km for females and 9.2 sq km for males (Garant and Crete 1997). Has been recorded moving 90 km in 3 days (see Nowak 1991).

Population density in favorable habitat has been estimated at up to about 1 per 3-11 sq km in summer, 1 per 8-20 sq km in winter (Arthur et al. 1989). In southern Quebec, density was estimated at about 3 individuals per 10 sq km; the high density was atrributed to the absence of trapping (Garant and Crete 1997).

Reportedly breeds late February-April or March-May, peak in March (late March-April in Manitoba); females mate probably within days of giving birth. Gestation lasts l year, including an 11-month period before implantation. Litter averages about 3 throughout the range. Births occur primarily from March to mid-April (sometimes in February or May in some areas). Young are mobile by 8 weeks, weaned in 2.5-4 months; separation from the mother occurs in the fifth month, in late summer or early fall. In Maine, young are weaned from mid-May to early June, independent probably in late August or early September (Arthur and Krohn 1991). Sexually mature in 1-2 years; not all adult females breed in a given year. Apparently promiscuous breeding. Very few males live more than 4 years, and less than 10% of females live more than 4 years.