The fisher (Pekania pennanti) is a medium-sized, solitary carnivore native to North America’s forested regions and is a member of the weasel family, Mustelidae. Although sometimes mistakenly called a “fisher cat,” it is not a feline but a fierce predator known for its agility and ability to hunt porcupines. Despite its reputation, the fisher is not at the top of the food chain and constantly faces threats to its survival from other animals and environmental factors. Understanding which animals successfully prey on this agile mammal is important to understanding its ecology.
Identifying the Fisher’s Primary Natural Predators
Predation is consistently identified as the leading cause of death for fishers in many populations, accounting for a majority of documented mortalities. The animals that successfully prey upon fishers are generally larger carnivores and formidable raptors. Key terrestrial predators include the bobcat, the coyote, and the mountain lion.
Bobcats are a significant threat, and their predation on fishers is sometimes viewed as a form of competition, as both species hunt similar prey. Coyotes and mountain lions are substantially larger than the fisher and use their size advantage to overwhelm adult fishers. While fishers are fierce, young kits or weakened, injured, or diseased adults are particularly vulnerable to these larger hunters.
Large raptors also pose a danger to fishers above the forest floor. Great Horned Owls and Golden Eagles are powerful avian predators known to attack fishers, especially when they are exposed in the canopy or moving on the ground. Other potential predators include the Canada lynx, wolverines, and occasionally other fishers, which may kill one another in territorial disputes.
The Role of Habitat and Size in Predation Success
The fisher’s relative size is a primary factor determining its vulnerability to larger predators. Males can weigh up to 6 kilograms, while females are significantly smaller at 2 to 3 kilograms. This size places them squarely within the prey range of animals like the coyote and mountain lion.
Their habitat use, which balances terrestrial movement with arboreal resting, dictates the type of predator that poses the greatest risk. Fishers are competent climbers but spend most of their time foraging on the forest floor, making them susceptible to attack by terrestrial carnivores. Dense forest cover is sought out by fishers because it provides security from attack from both the ground and the air.
When a fisher climbs to rest or den, it seeks out large trees with cavities or dense overhead canopy cover, which provides security against aerial predators. However, this strategy does not fully protect them, as large owls and eagles can still successfully attack from above if the canopy is fragmented. Security cover is especially important for females raising young, as a scarcity of suitable den sites can increase vulnerability for the mother and her kits.
Non-Predatory Threats to Fisher Survival
While predation is the most frequent cause of death, human-related and environmental factors present significant, ongoing threats to fisher populations. In some eastern populations, legal harvest or trapping has historically been a dominant cause of mortality. In western populations, other human-caused factors are more pronounced.
The loss and fragmentation of forest habitat due to logging and human development reduce the protective cover fishers rely on, which indirectly increases their risk of predation. Direct mortality from humans also includes vehicle strikes, which occur when fishers cross roads in search of resources or mates.
The use of toxic chemicals, such as rodenticides and pesticides, is a growing problem, particularly in western states where fishers may consume poisoned prey. This poisoning can be lethal or weaken the animal, making it more susceptible to other causes of death like disease or predation. Natural disease and starvation also contribute to mortality in monitored populations.
Factors like disease, poisoning, and habitat loss can work together, making isolated or small populations of fishers highly vulnerable. The frequency and severity of wildfires, exacerbated by climate change, further destroy the mature forest habitat fishers depend on for denning and resting.