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NATURAL HISTORY

FISHER } Pekania pennanti
FAMILY: Mustelidae

DESCRIPTION: The fisher has a slender body, a long, bushy tail, short legs, and a triangular head with a sharp, pronounced muzzle and large, rounded ears. Its body is mostly brown; males range in length from 35 to 47 inches, while females range from 29 to 37 inches.

HABITAT: The fisher is closely associated with large, contiguous blocks of mature and old-growth forests. It dens in rotting logs, hollow trees, rocky crevices, and the “witch’s brooms” of tree branches.

RANGE: The Pacific fisher once ranged from British Columbia through Northern California and the Sierra Nevada, but only two native populations remain today — one around the western California/Oregon border, and one in the southern Sierra Nevada Mountains. The Northern Rockies fisher once ranged from eastern British Columbia and southwestern Alberta through northeastern Washington, Idaho, Montana, northwest Wyoming and north-central Utah. Today it survives only along the border of Montana and northern Idaho.

MIGRATION: Fishers do not migrate seasonally. Dispersal is the primary method for spreading a population. A study of fishers in the southern Cascades found evidence of male-biased juvenile dispersal and female philopatry (the tendency to return to or stay within the home range), which may be a function of the species’ ability (or lack of it) to colonize formerly occupied areas.

BREEDING: The fisher’s breeding season is generally from late February to late April. Birth occurs nearly a year after copulation, due to a delayed implantation period in which the embryos’ development is arrested for about 10 months. Fishers have a low annual reproductive capacity, and reproductive rates may fluctuate widely from year to year.

LIFE CYCLE: Raised entirely by the female, kits are completely dependent at birth and weaned by 10 weeks of age. After a year, kits will have developed their own home ranges. Fishers are estimated to live up to 10 years.

FEEDING: Fishers have a diverse diet, including small mammals, snowshoe hares, porcupines, birds, carrion, fruit and truffles.

THREATS: Fishers are threatened by habitat loss and fragmentation due to logging and development. They are also threatened by trapping, poisoning and disease.

POPULATION TREND: Only three small, isolated populations of the Pacific fisher remain; one of those is the result of reintroduction efforts. The Northern Rockies fisher survives as small, low-density populations along the border of Montana and northern Idaho.

Photo courtesy of Washington Dept. of Fish and Wildlife