Fisher

Martes Pennanti

General

The fisher (Martes pennanti,) is a medium sized member of the weasel family (Mustelidae,) native only to North America.  They are striking with their slender bodies and soft dark coats but are increasingly becoming a problem in certain geographic zones where populations are expanding into suburban areas.

Description

Male fishers tend to be larger than females, reaching a mature length of 50” to 63” and mature weight of 7.5 lbs. to 11 lbs. by one year old.  Females measure 41” to 51” and weigh between 4.5 lbs. and 5.5 lbs. by 5.5 months old.  Their long, thick, bushy tails account for approximately 1/3 their total length.  Fishers have long bodies, broad heads with short pointed muzzles, and short legs.  Round ears are located on the sides on the head.  They have five long, retractable claws on both their front and hind feet.

Fishers have soft coats that are medium to dark brown and frosted on the head, neck, and shoulders.  Their coats are accented by black on the legs and tail and white patches (that may occur on the chest, genital area, and underarms.)  Their coloration may vary due to sex and season (they tend to be darker in the winter.)

Fishers are solitary animals that are active during the day and night.  Although they spend much of their time alone, they may be found together during the mating season.  Male fishers are known to show aggression towards each other.  Fishers are shy around humans but are beginning to show more and more comfort near human populations as their ranges expand in certain geographic areas.

Fishers create dens and “resting sites”1 for year-round use in hollow logs, trees, brush, ground burrows, or crevices.  They show preference for tree nests in the spring and fall, while in the winter they tend to use ground burrows or snow dens (burrows in the snow accessed by long, narrow tunnels.)

Fishers establish home ranges that are 5.8 to 13.5 square miles in size.  Males’ ranges are typically larger than females’ ranges and tend to overlap with them; however, a male’s range will never overlap with that of another male.2  Fishers mark their territory using scent and travel within it using established trails on the ground and in the trees.3  They navigate their environments using keen senses of smell, sight, and hearing.  Although they are agile climbers and swimmers, fishers are usually found on the ground.

In the wild, fishers can live up to 10 years.

Habitat

Fishers may be found in mixed, coniferous, and deciduous forests.  They prefer habitats that offer den sites (including hollow trees,) access to prey, and high canopy enclosures.  They tend to avoid deep snow in the winter.

Within their habitats, juvenile fishers are at risk of predation by hawks and other birds of prey, bobcats, lynx, and red foxes.

Location

Fisher populations can be found across Canada and the United States (from the Sierra Nevada in California to the Appalachian Mountains in Virginia.)  They no not live in prairie habitats or the southern United States.  North America is the only continent on which fisher populations occur.

Diet

Fishers are solitary hunters whose diets consist mainly of small herbivores (such as rodents, birds, and shrews.)  Their diets may also include fruit, berries, and carrion.  Although they usually prey on animals smaller than themselves, fishers have been known to take on larger prey.  They are also one of the only predators that can effectively attack a porcupine (this is done by repeatedly attacking from the front until the porcupine tires, then flipping it on its back and attacking its unprotected stomach.)

Fishers are agile hunters in trees and are capable of elongating their bodies to hunt their prey in ground burrows and narrow spaces.

Reproduction

Fishers breed once a year between March and May.  Copulation lasts for several hours.  Once the embryos have been fertilized, they remain in a suspended state of development for the first 10 to 11 months of an 11 to 12 month gestation period.  Embryos only develop during the last 1 to 2 months of gestation.

Females choose den sites that are high off the ground in hollow trees.  The site of the den may be moved several times if the nest is disturbed.

Litters contain 1 to 6 young (on average 3,) that are born blind and naked, each weighing less than one-tenth of a pound.  The young, known as kits, are completely dependent on their mothers after birth (males provide no parental support.)  Their eyes open around 7 weeks old, and they are weaned by 8 to 10 weeks old (although, some kits continue to nurse occasionally until they are 4 months old.)  By four months old, young fishers can hunt for themselves and start to disperse by 5 months old.  Fishers establish home ranges by the time they are a year old.

Females experience a postpartum estrus and mate again shortly after giving birth.

Females reach sexual maturity by one year old and breed once a year after that.  Males reach sexual maturity by 2 years old.4

Notes of Interest

Fishers are also referred to as: 
Pekans, Fisher Cats, Black Cats, Wejacks, and American Sables.5

There has been limited success trying to breed fishers in captivity.

In the past, fisher populations were severely impacted by the fur trade.  However, the demand for their pelts has decreased and populations have been recovering (particularly in New York and southern Ontario, where populations are expanding into suburban areas.)  Due to range expansion, there have been reports of fisher attacks on domestic animals and children, attracted to human-inhabited areas by food and garbage.  Fishers are known to react aggressively toward threats or when startled and caution should be exercised in the presence of this species.

Certain fisher populations have been considered for protection under the Endangered Species Act, such as those living in southern zones of the Sierra Nevada.6

1. http://animaldiversity.ummz.umich.edu/accounts/Martes_pennanti/
2. http://animaldiversity.ummz.umich.edu/accounts/Martes_pennanti/
3. http://www.mnh.si.edu/mna/image_info.cfm?species_id=152
4. http://animaldiversity.ummz.umich.edu/accounts/Martes_pennanti/
5. http://www.mnh.si.edu/mna/image_info.cfm?species_id=152
6. http://animaldiversity.ummz.umich.edu/accounts/Martes_pennanti/

http://animaldiversity.ummz.umich.edu/accounts/Martes_pennanti/
http://www.nhptv.org/natureworks/fisher.htm  
http://www.mnh.si.edu/mna/image_info.cfm?species_id=152
http://www.fws.gov/mountain-prairie/species/mammals/fisher/  

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