Fisher (Pekania pennanti)
This denizen of the forest isn’t inclined to swim and does not catch or eat fish.
Appearance. Like all members of the weasel family, fishers have long, tube-shaped bodies, short legs, rounded ears, and large, dark eyes with a pointy snout. Fishers are a medium-sized predator—females weigh 6 to 8 pounds, and males can reach up to 18 pounds. Unlike the short-tailed, long-tailed, and least weasels, fishers don’t turn white in winter. Their grizzled brown and black fur helps them blend into the trees, where they spend much of their time. They may also have a white or cream-colored patch on their chest. They have five toes with retractable claws and a bushy tail they can use as a wrap to help conserve body heat when resting. Despite a name that implies angling, this denizen of the forest isn’t inclined to swim and does not catch or eat fish.
Range. Found only in North America, fishers range across Canada and parts of the northern United States from the Sierra Nevada Mountains of California to the Appalachians of West Virginia and Virginia, the southernmost extent of their range. Fishers once populated mainly northern and central Minnesota but recently have been expanding their range southward. Sightings now are common in Otter Tail and Washington counties, with a number of sightings in the hardwood forests of southeastern Minnesota. Similar range expansions have been reported in other states. Biologists aren’t sure why this is occurring, but many speculate the warming climate and competition with other species, such as bobcats, might be the cause.
Behavior. Although their tube shape makes for fast, efficient hunting, the high surface area to weight ratio causes fishers to quickly lose body heat. Staying warm means voracious feeding on snowshoe hares, rodents like mice and voles, squirrels, and other small prey. If fresh prey isn’t available, they will scavenge deer carcasses or feed on berries and nuts. They are one of the few species known to kill and eat porcupines. Hunting alone, they elongate their bodies to seek prey in holes in the ground, hollow trees, and other small areas.
Reproduction. Females get pregnant in spring, usually days after giving birth. For several months, the young exist as tiny embryos, developing into fetuses two months before birth the following spring. One to five young fishers are born in a hollow tree or log or in a rock cavity. This type of pregnancy, known as delayed implantation, is common in the weasel family. Young fishers stay with their mothers for just a few months, leaving in early fall to find their own home territory.
Population management. Minnesota’s fisher population was very low in the early 1900s but has grown steadily. Today’s population, estimated at just under 10,000, is lower than in recent years but stable. A small number of fishers are harvested during a nine-day trapping season held in late December north of Interstate 94.