Martes pennanti
fisher

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.

Fishers prefer coniferous forests, but they are also found in mixed and deciduous forests. They prefer habitats with high canopy closure. 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.

Males 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 hoariness 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 are retractable.

Little is known about mating in fishers. Copulation may last up to seven hours. (Powell, 1981)

The breeding season is late winter and early spring, from March to May. After fertilization, the embryos sit in suspended development for 10 to 11 months, and resume developing late in the winter following mating. Overall, gestation 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 experience a postpartum estrus and 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 in a state of pregnancy or lactation. Males breed for the first time when they are two years old. Females reach adult weights at 5.5 months, whereas males reach adult weights after 1 year old. (Kurta, 1995; Powell, 1981)

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 disperse 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 disturbed. Male fishers do not help raise their young. (Kurta, 1995; Powell, 1981)

Fishers can live up to ten years in the wild. (Kurta, 1995)

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 observed aggression between males, which supports the notion 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.

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. (Kurta, 1995)

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

Fishers are predators, and most of their prey are herbivores. 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 possess the ability to elongate themselves to seek prey in holes in the ground, hollow trees and other small areas. Fishers are solitary hunters, and seek prey that is their own size or smaller, although they are capable of taking on prey larger than themselves.

Young fishers fall prey to hawks, red foxes, lynx and bobcats. Adult fishers are generally safe from predation. (Kurta, 1995)

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 have a low incidence of diseases.

Fishers are trapped and killed for their pelts. Trapping, in the past, had a significant 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 debarking and killing trees).

In recent years fisher populations in some areas, particularly southern Ontario and New York, have been recovering. In these areas they may be becoming habituated to human presence and venturing into suburban areas. There have been numerous 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 restrict access to garbage, pet foods, pets, and domestic fowl. When startled, fishers may react aggressively to the perceived threat. Diseased individuals may react unpredictably.

Logging of forests greatly impacts 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 numerous thriving and healthy fisher populations, there has been little pressure or initiative to develop fisher breeding or maintaining 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 proposed as candidates for protection under the Endangered Species Act.

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