Martes pennanti

Order: Carnivora
Order Description: Carnivores
Family: Mustelidae
Family Description: Weasels, Skunks and Others

Fishers are rare in Idaho, but if you should observe one, it looks larger than a marten, almost the size of a small fox, and it has no throat patch. Its longer fur is very dark, black to dark brownish, and often with a grizzled appearance on the face, neck and shoulders. Their legs and feet appear black. They appear stouter than a marten or a weasel. Total length is 31 to 41 inches (790-1033 mm), tail length is 11 ¾ to 16 5/8 inches (300-422 mm), and they weigh 3 to 18 pounds (1.4-8.2 kg).

They occur throughout much of Canada, and south through the Rockies, and in the northern Great Lakes Region and New England. Fishers were extirpated from Idaho, and re-introduced to three, north-central Idaho sites in the early 1960's. They are rare in other parts of Idaho, but little is known about their distribution.

They are found in upland and lowland mixed, deciduousClick word for definition, or coniferousClick word for definition forests, but they prefer mixed or coniferous forests. In Idaho, they prefer mature or old-growth coniferous forests with a dense canopy. They seem to favor forested riparianClick word for definition habitats in spring, summer, and fall, and younger-aged forests in the winter.

They mainly prey on other mammals such as small rodents, shrews, squirrels, hares, muskrat, beaver, porcupine, and raccoons. They also feed on deer carrionClick word for definition, but will also eat birds and fruits. They have a reputation of being predator specialists on porcupines.

Trapping and habitat loss due to logging extirpatedClick word for definition them from their range by the early 1900's. However, reintroduction has established their populations in certain areas. They are active both day and night, but seem more nocturnal in summer and diurnal in winter. In a study in Maine, they were mostly active shortly before sunrise and after sunset; and activity was reduced in winter. When inactive, they occupy dens in tree hollows, under logs, or rocky crevices, or in warmer months they rest in branches of conifer trees. Their home range has been estimated at 10 to 800 km2 by snow tracking, and 2 to 75 km2 by telemetry. An Idaho study found their home range to vary from 6 to 120 km2. Generally, the ranges of adults of 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. population densityClick word for definition in New England and the Great Lakes area has been estimated at up to about 1 per 3 to 11 km2 in summer, and 1 per 8 to 20 km2 in winter. Densities are lower in the western U.S. due to lower habitat quality.

They breeds from late February to April; the peak occurs in March. After fertilizationClick word for definition of the egg, the embryoClick word for definition becomes dormant for 10 to 11 months (delayed implantationClick word for definition). Young are born from March to early April. LitterClick word for definition size averages about 3 young. Young are weanedClick word for definition mid-May to early June, and become independent probably by late August to early September when they can kill on their own at about 4 months of age. They sexually mature in 1-2 yr; not all adult females breed in a given year. Apparently, breeding is promiscuousClick word for definition.

Status: Protected nongame species
Global Rank: G5
State Rank: S1

Important State References:
Jones, J.L. 1991. Habitat use of fisher in north-central Idaho. M.S. Thesis, Univ. Idaho, Moscow. 147pp.

Information written by Donald Streubel,© 2000
Map image provided by
Stephen Burton,© 2000
Design by Ean Harker©1999, 2000.