Fishers (Pekania pennanti) are medium-sized carnivores that have the long thin body characteristic of the weasel family. Their fur is deep brown to black with lighter hairs around the face, neck, and shoulders. Female fishers weigh 2-3 kg and measure 75-95 cm in length whereas males weigh 4-6 kg and measure 90-120 cm in length.
Fishers are found only in North America with most of their range located in Canada. They are often associated with riparian forest and have an affinity for deciduous stands in western North America, although coniferous forests dominate most home ranges in B.C.
Fishers require very specific habitats for several life requisites at a variety of spatial scales [download scale figure (PDF, 0.3MB)].
Fishers are solitary animals that only interact with other fishers during mating, territorial defense, or when raising young. Fisher home ranges typically overlap little with others of the same sex, but male home ranges will usually overlap more than one female home range. Depending upon forest type, the average size of a female home range in B.C. varies from 30-50 km2 while male home ranges can cover 100-200 km2.
Fishers require movement habitat to safely travel between important habitats within their home range, and to access new areas when dispersing. Movement habitat can be supplied by tree cover, which provides protection from above and vertical escape opportunities, and dense shrub cover that provides horizontal and vertical screening. Movement habitat is found in those stands where the total cover (tree + shrub) is greater than 50%. This cover does not need to be continuous, but openings more than 50 m wide likely create an increased risk to fishers. Highly fragmented landscapes appear to limit fishers ability to disperse. The amount of movement habitat needed within an individual home range varies by Fisher Habitat Implementation Zone (Table 1).
Table 1. Minimum landscape targets for movement habitat (i.e., greater than 50% total cover; tree and shrub combined)
|Boreal Forests||56.3% of “home range” (16.9 km² in 30 km²)|
41.7% of “home range” (20.8 km² in 50 km²) in moist/wet subzones
26.2% of “home range” (656 ha in 25 km²) in dry subzones
|Dry Forests||49.2% of “home range” (14.8 km² in 30 km²)|
Foraging habitat for fishers can be found in a variety of forest stands including young forests as long as there is sufficient security cover present. Fishers are opportunistic predators that feed primarily on small to mid-sized prey such as snowshoe hares, red squirrels, small rodents, and grouse, but their diet can include other birds, ungulate carrion, reptiles and amphibians, insects, and plant material. Foraging habitat for fishers depends on the species of prey; however, this habitat typically includes sufficient forest cover to provide security from their predators. That is, good foraging habitats will provide opportunities to capture and consume prey while remaining safe from their own predators. For example, fishers will hunt snowshoe hares in young stands with dense canopy cover and scattered larger trees or complex woody debris (e.g., sites to escape larger predators). Known predators of fishers include cougar, lynx, bobcat, coyote, wolverine, other fisher, and golden eagle.
Structural attributes of old forest, such as large diameter trees, complex forest structure, and elevated large woody debris are important in meeting life requisites, such as denning and resting habitat.
In B.C., the normal lifespan of wild fishers is usually less than 8 years, and females produce 3-4 litters of kits over their lifetime. Fishers give birth to 2-3 kits in late March to early April and natal dens are always found in cavities of standing trees. At birth, fishers are blind, deaf, and have only a sparse covering of fine hair. Fisher young stay in the den for the first 8 weeks of their life, during which their eyes and ears open and they begin to eat solid food.
Fishers need large, standing trees with heart rot cavities for their reproductive (birthing and denning) dens. Access holes (5-10 cm wide by 7-15 cm tall) to the cavity are generally located in the tree more than 1.5 m above the ground to almost at the top. High quality denning stands are typically dense (large diameter trees located close together), complex (many tree species, many age layers, logs, etc), and old (greater than 80 years).
Another important type of habitat, resting habitat, offers fishers protection from predators, thermal cover, and opportunities for prey detection while resting. Fishers rest primarily in trees and most rest trees are old, decayed and display abnormal growths. Rust brooms in spruce are the structures most often used for resting by fishers in B.C., but they also rest on large limbs and in cavities of black cottonwood, trembling aspen and other tree species.
Ground-based rest sites are usually associated with complex piles of large woody debris (>30 cm diameter) but can also be found in animal burrows. Ground-based rest sites are used more in winter when temperatures are very cold (less than -10˚ C) and deep snow provides an insulating layer.
For more photos and description of denning and resting habitat take a look at the Pictorial Guide of Important Fisher Habitat Structures in British Columbia (Download pictorial guide [PDF, 3 MB])