| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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| Wild Lives Fishers Prefer Porcupines In the mid-elevations of the Sierra Nevada and northern Coast Ranges lives a small, rarely seen forest carnivore called a fisher. Much about this animal is a mystery, including its name, since fishers do not fish. Roger Powell, in his book The Fisher, suggests that early European settlers to North America may have named the animal for its similarity to the European polecat, which was also known as a ferret, or fisher, words derived from the Dutch root visse, meaning "nasty." This linguistic accident could be partly responsible for the fisher's reputation for meanness, though another explanation is the ferocious displays of fishers caught in traps, not the best circumstance for judging anyone's disposition. They have been called "black cats" and "fisher cats," and although fishers do have somewhat feline-like, long, low-slung bodies and are about the size of large house cats, they belong to the mustelid family, which includes weasels, ermines, ferrets, badgers, minks, wolverines, otters, and even the common striped skunk. Another mustelid with which the fisher is often confused is the marten, similar in appearance but much smaller-just a pound and a half compared to the 10- to 15-pound adult male fisher. Fishers have triangular heads with mid-sized, close-set ears and pointed snouts. Individuals have cream-colored patches on their chests and around their genitals by which they are sometimes identified. Like all mustelids, fishers have anal glands that can release a musky odor when the animals are agitated or frightened. On the central pads of their hind paws fishers also have small circular patches of coarse hair, which are associated with plantar glands and have a distinctive odor. These patches enlarge in the breeding season and may be a reproductive signal. Fishers usually breed during March and April. Although males are thought to be polygamous, much of what is known about fisher mating behavior is based on observations on fur farms and is hardly conclusive. Females raise their young in protected dens, most often in tree hollows, without help from their mates. An average litter consists of three young kits, born helpless, with eyes and ears tightly closed. Within ten weeks the kits stop suckling and begin to walk and climb on their own. At about four months, they can kill their own prey but will remain with their mothers well into their first winter. By the time they are a year old, most have established their own territories. Fishers are solitary animals and are active primarily at night, although they have occasionally been seen at sunrise and sunset, traveling on trails or fallen logs, or moving from tree branch to branch. Occupying the top link of their food chain, adult fishers have little to fear. Humans are their only major predator. Eagles, hawks, foxes, bobcats, and black bears, however, all sometimes hunt young fishers. Fishers will eat any animals they can catch, including squirrels, mice, voles, moles, lizards, birds, and insects. But with their low, agile bodies and arboreal abilities, fishers are perhaps best adapted for hunting porcupines. A fisher usually attacks a porcupine on the ground, circling it and biting at its face until it can inflict a lethal bite-a relentless process that can last half an hour. To wear out a porcupine, a fisher occasionally pursues it up a tree and chases it off the end of a branch. Fishers are quilled during these jousts, but the meal is apparently worth the injuries. Fishers once ranged throughout the northern forests of North America and south along the Appalachian and Rocky mountains, and the Pacific Coast. But their glossy, dark brown fur-particularly that of the females-was their downfall. Between 1800 and 1940, trapping and habitat destruction caused fishers to be extirpated throughout most of the United States and much of Canada. As fisher numbers plummeted, porcupine populations skyrocketed, prompting many states to reintroduce fishers in the 1950s and 1960s to control porcupines, which were blamed for damaging timber. In the East, fishers have since recolonized parts of their original range, particularly where farmland has returned to forest. In the West, fishers were thought to have once been distributed continuously from British Columbia through the southern Sierra Nevada. William Zielinski, with the U.S. Forest Service's Pacific Southwest Research Station in Arcata, has been studying California fishers since 1992. His surveys show that no more than 400 fishers remain in the southern Sierra, and they are probably isolated from fishers in the northwest part of the state. Such isolation could lead to inbreeding and, for the small, southern population, possibly even extinction, says Zielinski. He attributes their isolation and small numbers mostly to habitat loss due to timber harvesting, encroaching residential communities, and road building-especially trans-Sierran highways, which reduce north-south movement and are death traps for fishers. Also, although trapping fishers in California was outlawed in the mid-1900s, they may have been overtrapped before that time. Even now, fishers are often accidentally caught in traps set for other animals. Zielinski's team is surveying the southern population to get a better idea of its habitat requirements. So far, the team has determined that fishers seem to prefer mature, complex forests with a few gaps in the canopy that let the understory grow. Ric Schlexer, one of the team's biologists, says radio-collared fishers frequently lead him to tree cavities, where he sometimes hears the chuckling sound of a happy or distressed fisher. Fishers also use abandoned squirrel nests or "witches' brooms" (tangles of branches) to rest in, and Schlexer sometimes sees them draped over a large branch, catlike, their legs dangling loosely. Schlexer, who spends long hours walking in the woods, says that encounters with wild, uncollared fishers are rare. One day, he recalls, "I saw a fisher coming down the bank. It ran across the road and stopped right at my feet. It was an older male with the beautiful frosted or grizzled patterning they get on their necks and shoulders." Schlexer waited, motionless. "He looked at me, and I looked back at him. We must have stared at each other for five to ten seconds. I wasn't sure what to do, so I just said 'Hi.' That startled him, and he jumped over the bank and ran off." While radio collaring fishers, Schlexer has had other close encounters that belie their reputation for meanness. Despite being handled, he says, fishers have never tried to bite him, even when they could easily have done so. "Handling a fisher is completely different than handling a marten," says Schlexer. "There seems to be an inverse relationship between size and disposition with these animals. Some of the smaller weasels are more ferocious than the fishers, which are not quite the monsters they're made out to be." Unless, of course, you are a porcupine. Lisa Owens-Viani is a freelance writer specializing in science and the environment. |
Spring 2000
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