NATURAL HISTORY

PACIFIC FISHER } Martes 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.

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.

POPULATION TREND: Only three small, isolated populations of the Pacific fisher remain; one of those is the result of reintroduction efforts.