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Fisher
(Martes pennanti Erxleben)

From: Saunders, D. A. 1988. Adirondack Mammals. State University of New York, College of Environmental Science and Forestry.  216pp.

Order: Carnivora

Family: Mustelidae

Description: The fisher resembles the marten but is larger and darker in color with white or cream (not orange or buff) colored patches on their underparts. The rather coarse fur is long, thick, slightly glossy, and dark brown to black, darkest on the tail, feet, and back. The guard hairs of the head, neck, and shoulders have white or golden brown tips, lightest and most conspicuous on older males. The cylindrical body is muscular, the legs short and stout; the feet relatively large and possessing sharp retractable claws. The head is broad with a short, narrow muzzle; small, dark eyes; and short, rounded ears. The long bushy tail tapers toward the tip, and accounts for nearly half the total length of 80-102 cm (31.5-40.2 in). Weight varies between 1.8-7.3 kg (4 -16 lb). Females are about one-half the size of males.

Range and Habitat: The former range was the forested regions of northern North America with some populations occurring in the southern Appalachians. Logging and unregulated trapping eliminated this large weasel from most parts of this range. For example, in New York the fisher occurred only in central and western regions of the Adirondacks by the mid 1930's. After complete protection was extended to the fisher by the New York State Legislature in 1937, and with only limited harvests of this valuable furbearer during some years since, the fisher is again widespread in the Adirondacks, probably occurring in most Adirondack towns. The Department of Environmental Conservation has successfully reintroduced the fisher in the Catskills. Approximately 3,000 to 4,000 fishers now inhabit the Adirondack Park.

The fisher prefers mature coniferous and mixed forests with thick overhead cover, and avoids openings such as logged areas, especially in winter. Unlike the marten, the fisher may also use deciduous forests, including dense second-growth stands. Seasonal changes in habitat use may occur, with some fishers leaving high elevations to spend the winter in conifer swamps and lowland conifer forests.

Fishers use temporary dens except when caring for their young. Maternity dens are often tree cavities 6-9 m (20-30 ft) above the ground, but may include holes in the ground or rock cavities. Hollow logs, stumps, brush piles, abandoned beaver lodges, and openings within snow banks are other places fishers rest or sleep.

Food and Feeding Behavior: The fisher is an opportunistic omnivore, eating large quantities of seeds and fruits such as beechnuts, black cherries, and mountain ash berries when seasonally abundant. However, snowshoe hares, voles, mice, red squirrels, flying squirrels, and shrews make up the bulk of the diet. The fisher hunts by running back and forth over an area, and then rushing and biting prey that it flushes.

The fisher’s reputation as a predator of white-tailed deer is exaggerated. The fisher may consume deer as carrion, e.g., road kills, but it does not kill adult deer nor is there much evidence that it preys upon fawns. The fisher kills and eats porcupines where they are abundant, perhaps in some areas even depressing Adirondack porcupine populations. Fishers, because of their size, speed, shape, and other adaptations, are the only predators that routinely kill this quill-laden rodent. Rarely, a fisher may attack a porcupine feeding in a tree, but most successful kills take place on the ground where the fisher can quickly circle and lunge at the porcupine, biting its face until the porcupine is disabled. The fisher then begins feeding upon the porcupine’s throat and belly which are unprotected by quills. Over the span of several days, the fisher consumes all but the skin, large bones, and feet. Fishers do incur injuries from impacted quills, but seem more tolerant of these wounds than other predators. One porcupine will supply the energy requirements of an adult fisher for 10-35 days, whereas a snowshoe hare will suffice for only 2.5-8 days.

Activity and Movement: The fisher is most active at twilight, but alternates periods of activity lasting 2-5 hours with bouts of resting or sleeping in temporary dens as it travels throughout a large area. In a 24 hour period, the fisher travels about 1.5-3.0 km (1-2 mi), but may cover 30 km (19 mi), for example when searching for mates. Fishers are active at all times of the year except during severe winter storms when they stay in their dens until the arrival of milder weather. In spite of the name and the fisher’s ability to swim well, most activity occurs on the ground. The fisher is adept at climbing trees, but does not travel from tree-top to tree-top, and does not often climb trees. Fishers walk on the soles of their feet, but the usual means of locomotion is by running or bounding, the tail extended above the ground much like the posture of a house cat. This is the reason for one of the fisher’s colloquial names, black cat, and also why the fisher is sometimes confused with the gray fox or other large mammals.

Reproduction: In March or April, the female bears 1-6 (average 2 or 3) young which at birth are blind and covered with fine, gray fur. The female spends most of her time with the newborn young, leaving them for no more than 2-3 hours each day. As the young mature, the female spends more time foraging, traveling directly to the boundaries of her home range to hunt. By 49 days of age, the eyes of the young open, and they are weaned by about 4 months of age. The young disperse in autumn or early winter. Females breed at one year of age; males may be sexually mature at the same age but often do not mate until their second year. The potential longevity of the fisher is at least 10 years. Adult females mate approximately 10 days after the birth of a litter, and thus the gestation period is 327-358 days. Most embryonic growth takes place during the last 30 days of the gestation period because of their delayed implantation.

Predators: Because of its size, agility, and aggressive behavior, the fisher has few predators. Coyotes, black bears, bobcats, and great horned owls may occasionally kill fishers, especially young ones.

Social Behavior:

  • Social system - The fisher, a symbol of wilderness, is well known for its solitary habits. Adults associate briefly only for the purpose of breeding, and pair bonds are temporary or nonexistent. It is uncertain if more than one mate is accepted. Each adult fisher has a large home range, a male’s 10-26 sq km (4-10 sq mi) in area, and usually larger than a female’s. Home ranges of the opposite sex overlap, but not those of the same sex. In optimum habitat, densities may reach one fisher per 2.6-7.5 sq km (1-3 sq mi).
  • Communication - Anal and other glands, e.g., on the foot pads, probably play an important role in chemical communication. Adults urinate on stumps and mounds of snow, and rub their abdomens over these objects which are likely methods of scent marking. Vocalizations include a low chuckle, growls, hisses, snarls, grunts, and a crooning sound. These occur in many contexts such as aggressive encounters and during mating, but their function is unknown.  

Additional References

Brown, M. K. and G. Will. 1979. Food habits of the fisher in northern N.Y. New York Fish and Game Journal, 26:87-92.

Clem, M. K. 1977. Food habits, weight changes and habitat selection of the fisher during winter. M.S. Thesis , Univ. Guelph. Guelph, Ontario.

Cook, D. E. and W. J. Hamilton, Jr. 1957. The forest, the fisher, and the porcupine. Journal of Forestry, 55:719-722.

Coulter, M. W. 1966. Ecology and management of fishers in Maine. Ph.D. Dissert. Syracuse Univ., Syracuse, NY.

Eadie, W. R. and W. J. Hamilton, Jr. 1958. Reproduction of the fisher in New York. New York Fish and Game Journal, 5:77-93.

Hamilton, W. J., Jr. and A. H. Cook. 1955. The biology and management of the fisher in New York. New York Fish and Game Journal, 2:13-35.

Henry, R. and K. Wallace. 1958. Return of a Catskill native. The New York State Conservationist, 40(3):16-19.

Kelly, G. M. 1977. Fisher (Martes pennanti) biology in the White Mountain National Forest and adjacent areas. Ph.D. Dissert., Univ. Mass., Amherst, Mass.

Penrod, B. 1976. Fisher in New York. The New York State Conservationist, 31(2):23.

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

Powell, R. A. 1982. The fisher: life history, ecology and behavior. Univ. of Minn. Press, Minneapolis, MN.

Schoonmaker, W. J. 1938. The fisher as a foe of the porcupine in New York State. Journal of Mammalogy, 19(3):373-374.

Wright, P. L. and M. W. Coulter. 1967. Reproduction and growth in Maine fishers. Journal of Wildlife Management, 31:70-87.


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