Fishers are opportunistic predators that eat a wide range of animals, from snowshoe hares and squirrels to porcupines, birds, insects, and seasonal fruits. Despite their common nickname “fisher cat,” they are neither cats nor particularly fond of fish. These muscular members of the weasel family rank among the most versatile forest carnivores in North America, shifting their diet with the seasons, the landscape, and whatever prey happens to be available. Their reputation, though, rests heavily on one skill that almost no other predator has mastered: killing porcupines.
Primary Prey Items
Fishers eat what the forest provides, and in most of their range that means small to mid-sized mammals form the backbone of their diet. Snowshoe hares are a staple across much of northern and eastern North America, and in many study areas they show up in fisher stomach contents and scat more than any other single prey species. Squirrels, both red and grey, are another consistent food source. Mice, voles, and shrews round out the small-mammal portion of the diet and tend to show up frequently in scat studies, though individually each one provides much less energy than a hare.
Beyond mammals, fishers eat birds and their eggs, particularly ground-nesting species and grouse. Research on fisher populations in western Canada found that Columbian fishers consumed grouse and squirrels more frequently than their boreal counterparts, who relied more on ungulate remains and small mammals.1The Stacks. Differentiation and adaptation among fishers in Western Canada: Evidence for validity of Pekania pennanti columbiana subspecies Insects, particularly beetles and other larger species, appear in warm-weather diets, along with berries, apples, beechnuts, and other fruit. Fishers are not strict carnivores; they eat plant matter when it is abundant and accessible.
Carrion is another important food source, especially in winter. Deer carcasses left by hunters, vehicles, or other predators provide critical calories during months when live prey is harder to find and energetic demands are highest. A fisher will readily scavenge from a frozen deer carcass over the course of days or even weeks, returning repeatedly to the same kill site.
How Fishers Kill Porcupines
The fisher’s most famous dietary habit is its ability to prey on North American porcupines, an animal most predators avoid entirely. Porcupines carry roughly 30,000 barbed quills on their back and tail, and a single defensive swipe can embed dozens of painful, infection-prone quills in an attacker’s face. Most carnivores have learned to leave them alone. Fishers have not, and that is part of what makes them ecologically significant.
The hunting technique relies on speed, persistence, and targeting the one part of the porcupine that lacks quills: its face. A fisher circles the porcupine on the ground, darting in to bite at the face and then retreating before the porcupine can turn and present its quilled back or tail. This process can take half an hour or more, with the fisher landing repeated bites to the nose, eyes, and mouth. Eventually the porcupine weakens from blood loss and shock, at which point the fisher flips it over and feeds from the unprotected belly. Fisher skulls recovered in the wild sometimes show embedded quill fragments healed over with bone, evidence that the technique is not always clean.
The relationship between fishers and porcupines has attracted attention from forest managers for decades. Porcupines can cause significant damage to trees by gnawing bark, and in areas where porcupine populations grow unchecked, timber losses can be substantial. The classic ecological argument, articulated as far back as the mid-twentieth century, is that fishers serve as a natural check on porcupine numbers.2Oxford Academic / Journal of Forestry. The Forest, the Fisher, and the Porcupine Several states and provinces that reintroduced fishers in the latter half of the 1900s did so partly with timber protection in mind, and porcupine populations did decline in some of those areas afterward.
Why Males and Females Hunt Differently
Fishers are strongly sexually dimorphic: adult males typically weigh about twice as much as females. A large male can reach 5 to 6 kilograms, while females often weigh around 2 to 3 kilograms. That size gap directly shapes what each sex tends to eat. Larger males can tackle bigger prey, including porcupines and hares, while smaller females lean more toward squirrels, mice, voles, and birds.
This is not just an anecdotal observation. Researchers in New Hampshire examined how prey selection tracked with the size difference between male and female fishers and found meaningful dietary divergence tied to body size.3Journal of Mammalogy. Prey Selection in Relation to Sexual Dimorphism of Fishers (Martes pennanti) in New Hampshire From an ecological standpoint, this makes sense: if males and females were eating the exact same prey at the same rates, they would be competing with each other more intensely for food. By partitioning their diets somewhat, the two sexes reduce intraspecific competition, which can help sustain denser fisher populations in a given patch of forest.
The size difference also affects hunting technique. Males are powerful enough to wrestle a porcupine through the sustained face-biting attack described above, while females, being lighter and more agile, may rely more on ambush and pursuit of fast, small prey. Female fishers are excellent climbers and often chase red squirrels through the canopy, a pursuit that demands acrobatic skill more than brute strength.
Seasonal and Regional Shifts
Fisher diets are not fixed menus. They shift with the seasons in ways that reflect prey availability and energetic need. In winter, when deep snow limits mobility for both predator and prey, fishers tend to focus on larger items that offer a bigger caloric payoff per catch: snowshoe hares, porcupines, and carrion from ungulate carcasses. Scavenging becomes more important during this period because hunting in deep snow is expensive, and a dead deer provides thousands of calories for the effort of locating it.
In spring and summer, the diet broadens considerably. Insects become available, fruit ripens, and small mammals are more active and easier to find. Fishers eat berries, cherries, and beechnuts when they can find them, and nursing females in particular may need the easily digestible sugars that fruit provides. Nesting birds and their eggs are another warm-weather food source that essentially disappears in winter.
Regional variation is just as pronounced. Fishers living in boreal forests across Canada face a very different prey landscape than fishers in the mixed hardwood-conifer forests of the northeastern United States or the montane forests of the Pacific Northwest. The western Canada research mentioned earlier showed clear dietary differences between Columbian and boreal populations, with the Columbian fishers eating more mid-sized mammals, grouse, and squirrels while boreal fishers ate more ungulate remains and small mammals.1The Stacks. Differentiation and adaptation among fishers in Western Canada: Evidence for validity of Pekania pennanti columbiana subspecies Studies of fisher diets in the Cascade Range of southern Oregon and in Pennsylvania have added to the picture of how geography shapes what fishers eat, reinforcing that no single prey list applies everywhere.4Northwestern Naturalist. The Food Habits of Fishers (Pekania pennanti) in the Cascade Range of Southern Oregon5The American Midland Naturalist. Diets of Fishers (Pekania pennanti) and Evidence of Intraspecific Consumption in Pennsylvania
Competing With Other Predators
Fishers do not exist in a vacuum. They share forest habitat with coyotes, bobcats, martens, foxes, and in some areas, lynx. All of these animals eat some of the same prey, so the question of how much their diets overlap matters for understanding whether fisher populations can thrive after reintroduction or in areas with high predator diversity.
A study of reintroduced fishers in Washington’s North Cascades used DNA analysis of scat to compare the diets of fishers, coyotes, bobcats, and Pacific martens living in the same area. Dietary overlap was moderate overall, with fishers showing the greatest similarity to bobcats. Overlap increased as the body-size difference between two species decreased, meaning similarly sized carnivores tended to compete more for the same food. Still, despite sharing common prey items, the four species showed strong compositional differences in their overall diets, suggesting they partition the prey base enough to coexist.6Animal Conservation. Prey Partitioning in a Diverse Carnivore Community: Implications for Reintroduced Fishers in Washington
This is good news for fisher conservation. It means fishers can carve out a dietary niche even when dropped into a landscape already full of other mesocarnivores. Their versatility, the ability to climb trees, kill porcupines, eat fruit, and scavenge carrion, gives them options that more specialized predators lack. But it also means that in areas with very high coyote or bobcat densities, fishers may face pressure on their most important prey. Snowshoe hares, for instance, are eaten by nearly every predator in the northern forest.
Fishers also face risks from larger predators. They can be killed by coyotes, bobcats, and occasionally great horned owls, especially juveniles and smaller females. These intraguild predation events are not frequent enough to be a primary mortality source in most populations, but they add to the pressures fishers face alongside trapping, vehicle strikes, and habitat loss.
Hunting Style and Physical Adaptations
Fishers hunt primarily by active searching rather than ambush. They travel through their home range along somewhat predictable routes, investigating hollow logs, rock crevices, burrow entrances, and the bases of trees. When they detect prey, they switch to a burst of speed or, in the case of arboreal prey like squirrels, a rapid climb. Fishers have semi-retractable claws and ankle joints that can rotate nearly 180 degrees, allowing them to descend trees headfirst the way a squirrel does. This adaptation is unusual among carnivores and gives fishers a significant advantage in pursuing prey through the canopy.
On the ground, fishers are fast and agile for their size but not built for long chases. Their hunting strategy favors short, explosive pursuits or the patient circling approach used against porcupines. They have a well-developed sense of smell and hearing, and they investigate potential prey refugia systematically. In snow, their relatively large feet for their body weight help distribute their mass, but deep powder still slows them considerably, which is one reason carrion and sedentary prey like porcupines become more important in winter.
Fishers are largely solitary and mostly active during dawn, dusk, and nighttime hours, though they can be active at any time. Their activity patterns sometimes shift in response to what they are hunting; for example, squirrel-hunting fishers tend to be more active during daylight when squirrels are out foraging. This flexibility in activity timing is another aspect of the generalist strategy that makes fishers successful across a wide range of habitats.
Do Fishers Actually Eat Fish?
Almost never. Despite the name, fishers have very little to do with fishing. The name likely derives from early European colonial usage, possibly a corruption of the French word “fichet” or “fiche,” which referred to the European polecat, a related mustelid. Another theory ties it to the Dutch word “fisse” or “visse.” Either way, the name stuck even though it has nothing to do with the animal’s actual diet.
Fish do appear in fisher scat on rare occasions, but when they do, researchers generally attribute it to scavenging rather than active fishing. A fisher might eat a dead fish found along a stream bank, but it is not wading into water to catch trout. Fishers are competent swimmers if they need to cross a stream, but they are not aquatic hunters. Their body plan, dense fur, climbing adaptations, and hunting style are all oriented toward the forest floor and canopy, not waterways.
This is worth emphasizing because the name generates real confusion. People encountering the term “fisher cat” for the first time often imagine either a cat that catches fish or some kind of aquatic feline. The animal is neither. It is a weasel-family carnivore, more closely related to martens, mink, and wolverines than to any cat. The “cat” part of the common name is a folk addition, possibly inspired by the fisher’s somewhat catlike face or its agility in trees. No scientific or wildlife management authority uses “fisher cat” as the formal common name; the correct common name is simply “fisher.”
Fishers Near People and Pets
As fisher populations have recovered across the northeastern United States and parts of the Pacific Northwest, encounters with humans have become more common. Fishers are increasingly spotted in suburban and even semi-urban areas where forest patches abut neighborhoods. This has raised concerns about pets, particularly outdoor house cats and small dogs.
Fishers can and do kill domestic cats, though how often this happens is debated. In areas with established fisher populations, there are anecdotal reports of cats disappearing, and necropsies occasionally confirm fisher predation. But fishers are not specialized cat-killers, and the frequency of cat predation is probably lower than many homeowners fear. Fishers in suburban settings are more likely to be attracted by easy food sources: garbage, bird feeders that attract squirrels, compost piles, and the general abundance of prey that suburban habitat supports, including rabbits, chipmunks, and rats.
Small chickens and other backyard poultry are a more realistic concern. Fishers are strong enough to break into poorly secured coops, and once inside, they can kill multiple birds in a single visit. If you keep poultry in fisher country, hardware cloth (not chicken wire, which fishers can pull apart) and secure latches are essential. Fishers are dexterous and persistent, so flimsy barriers are rarely enough.
Fishers are not a threat to people. They are shy, avoid confrontation, and will almost always retreat when they encounter a human. The rare exceptions involve animals that are sick, cornered, or habituated to food sources near human dwellings. The screaming sounds sometimes attributed to fishers at night are more often red foxes or other animals; fishers are relatively quiet, and the “screaming fisher” is one of the more durable pieces of wildlife folklore that does not hold up well to scrutiny.
Intraspecific Consumption
One of the more surprising findings from fisher dietary research is that fishers occasionally eat other fishers. Intraspecific consumption, where an animal eats a member of its own species, has been documented in Pennsylvania through scat analysis.5The American Midland Naturalist. Diets of Fishers (Pekania pennanti) and Evidence of Intraspecific Consumption in Pennsylvania This likely reflects scavenging from dead fishers rather than active predation on healthy adults, though territorial aggression between males can be intense and could plausibly result in a kill followed by feeding.
Cannibalism or quasi-cannibalism is not unique to fishers; it has been documented in many carnivore species. But its occurrence in fishers is a reminder of how thoroughly opportunistic these animals are. If a dead fisher represents available calories, another fisher will eat it. That kind of dietary flexibility, uncomfortable as it may be to contemplate, is part of what makes fishers resilient in landscapes where food availability is unpredictable and harsh winters can push energy budgets to their limits.