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Martes pennanti

What do they look like?

Male fishers are, on average, larger than females, with a body length of 900 to 1200 mm and a body weight of 3500 to 5000 grams. Females range from 750 to 950 mm in length and 2000 to 2500 grams in weight. Tail length of males is between 370 and 410 mm and tail length of females is between 310 and 360 mm. Their coats range from medium to dark brown, with gold to silver hair tips on their head and shoulders, and with black legs and tail. They may also have a cream chest patch of variable size and shape. Fur color and pattern varies among individuals, sexes and seasons. Fishers have five toes on their feet, and their claws can be drawn up into the paws, like a cat's.

  • Sexual Dimorphism
  • male larger
  • Range mass
    2000 to 5000 g
    70.48 to 176.21 oz
  • Range length
    750 to 1200 mm
    29.53 to 47.24 in

Where do they live?

Fishers are found only in North America, from the Sierra Nevada of California to the Appalachians of West Virginia and Virginia. They range along the Sierra Nevada to their southernmost extent and south along the Appalachian mountain chain. They do not occur in the prairie or southern regions of the United States. Populations have declined in the southern parts of their range in recent history.

What kind of habitat do they need?

Fishers prefer coniferous forests, but they are also found in mixed and deciduous forests. They prefer habitats with thick canopies. They also prefer habitats with many hollow trees for dens. Trees typically found in fisher habitats include spruce, fir, white cedar and some hardwoods. Also, as would be expected, their habitat preference reflects that of their favored prey species.

How do they reproduce?

No information is available on the mating system of these mammals.

The breeding season is late winter and early spring, from March to May. After fertilization, the embryos stop developing for 10 to 11 months, and start developing again late in the winter following mating. Overall, pregnancy lasts almost a full year, 11 to 12 months. The average number of young in a litter is 3, ranging from 1 to 6. Shortly after giving birth, females mate again. Healthy females first breed at age 1, produce their first litter at age 2, and probably breed every year after that. So females essentially spend almost all of their adult life either pregnant or nursing young. Males breed for the first time when they are two years old.

  • How often does reproduction occur?
    Fishers breed once per year.
  • Breeding season
    Fishers breed in the late winter to early spring, from March to May. Breeding times vary with location.
  • Range number of offspring
    1 to 6
  • Average number of offspring
  • Average number of offspring
  • Range gestation period
    11 to 12 months
  • Range weaning age
    8 to 16 weeks
  • Range time to independence
    5 (low) months
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    365 days
  • Average age at sexual or reproductive maturity (male)
    2 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    365 days

Young fishers are born blind and nearly naked. Each weighs about 40 grams at birth. The eyes open after about 53 days. Young begin to be weaned at 8 to 10 weeks, but may nurse occasionally for up to 4 months after birth. By the time they are four months old, the young are able to hunt for themselves, and they leave their mother at least one month later. Most dens in which young fishers are raised are high up in hollow trees, and females may choose to move their young up to several times if the litter is at all disturbed. Male fishers do not help raise their young.

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

How long do they live?

Fishers can live up to ten years in the wild.

  • Range lifespan
    Status: wild
    10 (high) years

How do they behave?

Fishers are agile and speedy tree climbers, but they usually move on the ground. They are quite solitary; there is little evidence that they ever travel together, except possibly during the mating season. There has been some aggression seen between males, which supports the idea that they are solitary.

Fishers use "resting sites", such as logs, hollow trees, stumps, holes in the ground, brush piles and nests of branches, during all times of the year. Ground burrows are most commonly used in the winter, and tree nests are used all year, but mainly in the spring and fall. During the winter, fishers use snow dens, which are burrows under the snow with long and narrow tunnels leading to them.

Fishers are active during the day and night and may be agile swimmers.

  • Range territory size
    4 to 50 km^2
  • Average territory size
    25 km^2

Home Range

Home range size varies from 15 to 35 square kilometers in area, averaging about 25 square kilometers. Home ranges of males are larger than those of females and may overlap with them, but they usually do not overlap with the home ranges of other males.

How do they communicate with each other?

Fishers have good senses of smell, hearing and sight. They communicate with each other by scent marking.

What do they eat?

Fishers are predators, and most of their prey are plant-eating mammals. Fishers eat mice, porcupines, squirrels, snowshoe hares, birds, and shrews, and sometimes, other carnivores. They may also feed on fruits and berries, such as beechnuts and apples.

They have also been seen to eat white-tailed deer, though they are most likely scavenging a deer carcass.

Fishers and American martens are the only medium-sized predators agile in trees that also have the ability to stretch themselves to look for prey in holes in the ground, hollow trees and other small areas. Fishers are hunt alone, and look for prey that is their own size or smaller, although they are capable of taking on prey larger than themselves.

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • Plant Foods
  • fruit

What eats them and how do they avoid being eaten?

Young fishers fall prey to hawks, red foxes, lynx and bobcats. Adult fishers are generally safe from predation.

What roles do they have in the ecosystem?

Fishers are important predators in their ecosystems. They are often in competition for food with foxes, bobcats, lynx, coyotes, wolverines, American martens and weasels. Fishers rarely get diseases.

Do they cause problems?

In recent years fisher populations in some areas, particularly southern Ontario and New York, have been recovering. In these areas they may be becoming used to humans and venturing into suburban areas. There have been many reports of fisher attacks on domestic animals and even children. It is important to recognize that fishers are simply trying to find food and protect themselves. It is important to not allow them access to garbage, pet foods, pets, and domestic fowl. When startled, fishers may react aggressively to what they see as a threat. Diseased animals may react unpredictably.

  • Ways that these animals might be a problem for humans
  • injures humans
    • bites or stings

How do they interact with us?

Fishers are trapped and killed for their pelts. Trapping, in the past, had a large effect on fisher populations, but the problem is not as severe now. Fishers hunt porcupines, and can effectively control porcupine populations (porcupines are known to damage timber crops by eating the bark and killing trees).

  • Ways that people benefit from these animals:
  • body parts are source of valuable material

Are they endangered?

Logging of forests greatly affects fishers and fisher populations by destroying their preferred habitat--continuous or nearly continuous coniferous forests.

Zoos have had a hard time breeding fishers in captivity, but there has been some success. Because there are many thriving and healthy fisher populations, there has been little desire to develop fisher breeding programs in captivity.

In some areas of North America, such as Michigan, Ontario, New York, and some areas of New England, fisher populations seem to have rebounded in recent years.

Fisher populations in the southern Sierra Nevada have been said to need protection under the Endangered Species Act.

Some more information...

Fishers are generally thought of as shy and rarely observed. This may be changing in parts of their range as populations re-expand and become used to human presence.


Tanya Dewey (editor), Animal Diversity Web.

Allison Poor (editor), University of Michigan-Ann Arbor.

Cynthia Rhines (author), University of Michigan-Ann Arbor.


Macdonald, David. (editor) The Enclopedia of Mammals. Facts on File Publications, NY. 1984

Powell, Roger A. The FIsher: Life History, Ecology, and Behavior. University of Minnesota Press, MN. 1993.

Johnson and Todd. Fisher, Behavior in Proximity to Human Activity. Canadian Field Naturalist 99 (3) 1985.

Arthur, Krohn and Gilbert. Habitat Use and Diet of Fishers. Journal of Wildlife Management 53 (3) 1989.

Kurta, A. 1995. Mammals of the Great Lakes Region. Ann Arbor: University of Michigan Press.

Powell, R. 1981. Martes pennanti. Mammalian Species, 156: 1-6.

University of Michigan Museum of ZoologyNational Science Foundation

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Rhines, C. 2003. "Martes pennanti" (On-line), Animal Diversity Web. Accessed May 20, 2024 at http://localhost:2015/accounts/Martes_pennanti/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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