Photo by John Jacobsen
The fisher (Martes pennanti) is a medium-sized mammal native to North America. It is classified in the order Carnivora, family Mustelidae – a family that also includes weasels, mink, martens, and otters.
Adult fishers are light brown to dark blackish-brown, with the face, neck, and shoulders sometimes being slightly gray. The chest and underside often have irregular white patches. The fisher has a long body with short legs and a long bushy tail. Males range in length from 90 to 120 centimeters (35 to 47 inches), and weigh 3 to 6 kilograms (6.6 to 13.2 lbs). Females range from 75 to 95 cm (29 to 37 in) in length and weigh 1.5 to 2.5 kilograms (3.3 to 5.5 lbs).
Fishers are found across Canada and in four areas of the United States – New England, Great Lakes, Northern Rocky Mountains, and the Pacific Northwest. In the Northern Rocky Mountains, fishers are distributed in northwest and west-central Montana and northern and north-central Idaho with rare detection in southwestern Idaho. Snowtrack surveys have documented fisher in Glacier National Park in the 1980s and the Greater Yellowstone area in the late 1990s, but more verified records are needed to confirm the presence of fisher in these areas.
Fishers live in coniferous and mixed conifer and hardwood forests and are found commonly in mature forest cover. Riparian forests and habitat close to open water such as streams are important to fishers in northern California and the Rocky Mountains of Idaho. In the Rocky Mountains, fishers avoid areas of deep, fluffy snow and select riparian areas with relatively gentle slopes and dense canopy cover that may provide protection from snow during winter. Cavities and branches in trees, snags, stumps, rock piles, and downed timber are used as resting sites, and large diameter live or dead trees are selected for natal and maternal dens.
Fishers are opportunistic predators primarily of snowshoe hares, squirrels, mice, and birds. Carrion and plant material (e.g., berries) also are consumed. The fisher is one of the few predators that kills porcupines, and porcupine remains have been found more often in the gastrointestinal tract and scat of fisher than any other predator. As dietary generalists, fishers tend to forage in areas where prey is both abundant and vulnerable to capture. The physical structure of the forest and prey associated with forest structures are thought to be the critical features that explain fisher habitat use, rather than specific forest types.
Fishers are solitary except during the breeding season, which is generally from late February to the middle of May. Litter sizes for fishers range from one to six with a mean of two to three kits. New born kits are entirely dependent and may nurse for 10 weeks or more after birth. Kits develop their own home ranges by one year of age. Populations of fisher fluctuate in size, and reproductive rates may vary widely from year to year in response to the availability of prey.
Recent Actions: June 2011: The Fish and Wildlife Service completed a status review of the fisher in the U.S. Northern Rocky Mountains, and concluded it does not warrant protection under the Endangered Species Act in Idaho, Montana, or Wyoming.
We analyzed potential factors that may affect the habitat and range of the fisher in the U.S. Northern Rocky Mountains including timber harvest and management, climate change, fire, forest disease, furbearer trapping, disease and predator relationships, inadequacy of existing regulatory mechanisms, and the effects of small population size. We concluded that these potential factors do not significantly impact the species.
Even though the species will not be protected under the Endangered Species Act, we recognize that the fisher in the Northern Rockies may benefit from increased management emphasis due to its need for forest cover and its susceptibility to capture and mortality from furbearer harvest. We recommend and encourage additional research to improve the understanding of the species and precautionary measures to protect the species.
To assist in monitoring the fisher in the U.S. Northern Rockies, we ask the public to submit any new information on the fisher’s status or impacts. Please submit your comments to the U.S. Fish and Wildlife Service, Montana Ecological Services Field Office, 585 Shepard Way, Helena, MT 59601.
- Federal Register Notice: June 29, 2011 12-Month Finding on a Petition to List a Distinct Population Segment of the Fisher in Its United States Northern Rocky Mountain Range as Endangered or Threatened with Critical Habitat
- Press Release: June 29, 2011 U.S. Fish and Wildlife Service Determines Fisher In The Northern Rocky Mountains Does Not Warrant Protection Under The Endangered Species Act
- Questions and Answers
The U.S. Fish and Wildlife Service recently determined that the Northern Rocky Mountain distinct population of the fisher may warrant federal protection as a threatened or endangered species. The Northern Rocky Mountain population area includes portions of northern Idaho, western Montana, and northwestern Wyoming.
The Service will undertake a more thorough review of the fisher to determine if adding the species in the Northern Rocky Mountains to the federal list of threatened and endangered wildlife and plants is warranted.
- Federal Register Notice: April 15, 2010 90-Day Finding on a Petition to List a Distinct Population Segment of the Fisher in Its United States Northern Rocky Mountain Range as Endangered or Threatened with Critical Habitat
- Press Release: April 15, 2010 Fish and Wildlife Service to Conduct Status Review of the Northern Rocky Mountain Population of Fisher