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From "The Wild Bunch"
The Fisher
A fisher is a bigger, stronger, darker, and browner version of its cousin, the marten. The fisher has the same general long and low–slung weasel-like body shape as the marten, but it’s larger and stockier, with thicker fur and a flatter face.
Why it’s called the fisher isn’t certain – but as a description, the name doesn’t make much sense. Fishers do seem to prefer riparian, or streamside, zones in the forest, but fish actually make up a very tiny percentage of their diet!
Although very different from each other, the marten and the fisher share some similarities. First, fishers and martens both need home ranges that are very large for carnivores of their size. (An animal’s "home range" is the total amount of habitat it requires in order to meet all of its needs – for food, water, shelter, and denning.) Fishers have home ranges that are about 50 times greater than would be expected for an animal of their body weight!
Second, fishers, like martens, are very dependent on old growth forests. A study of 68 mammals in the Pacific Northwest found that marten and fisher ranked one and two in their dependence on mature forests.
Because of their larger size, fishers have an easier time than martens staying warm in the winter. On the other hand, because of their larger size and weight, they have more trouble staying on top of the snow. As a result, although fishers and martens can be found in the same habitat, fishers tend to use lower elevation forested areas that have less of the deep, soft snow that is hard to travel through.
While fishers eat the same range of items that are in a marten’s diet, they tend to eat more of the larger animals, such as ruffed grouse and snowshoe hare. Snowshoe hare are to the fisher what voles are to the marten – the backbone of a diverse diet. Fishers also kill a few animals that marten never do – the porcupine, the raccoon, and even the marten itself!
The fisher is a premier example of a generalized predator – one that eats any animal it is able to catch and overpower with its speed, agility, and strength. Perhaps the most impressive display of the fisher’s prowess as a hunter is its ability to regularly kill porcupines, something that few other animals are able to do.
When a fisher catches a porcupine out in the open, away from the safety of a tree or its den, it begins a circling attack. As the porcupine tries to waddle to safety, the fisher heads it off, darting in to claw at the unprotected face. In this situation, the fisher’s weasel shape – long and low to the ground – gives it the clear advantage over the porcupine, whose quills guarding its face from above are useless against the fisher attacking from below. After about half an hour, the porcupine collapses, and the fisher settles down to a spiny, but nutritious, 10 or 15-pound meal.
The fisher is affected by the same human activities as is the marten. In the past, trapping pressure, along with logging, was great enough to eliminate fishers from large parts of their range. Although reintroductions in the East have been successful, most fisher populations in the United States have never recovered, and trapping for fishers is now banned in most states. Sadly, fishers still die when they explore traps legally set for other animals.
In the West, a half century after most trapping ended, logging of their habitat is now the main threat to fishers, as is demonstrated in the coastal forests, where the fisher is at dangerously low numbers and may still be declining.
Although we don’t know exactly why fishers need old growth, we know that they do. Biologists have found that fishers are intolerant of open areas, and will go out of their way to find the narrowest gap in a forest opening, and cross it quickly in a straight line. Maybe the thick growth in the upper reaches of the old growth canopy catches and holds enough snow that it’s easier for fishers to travel in old growth than in areas where the trees are smaller and the drifts of snow deeper. Perhaps fishers need old growth forest because it is easier for them to catch their prey or find better dens when there is a lot of dead wood and complexity on the forest floor.
One thing we do know – because they rely on a particular type of forest to survive, fishers are highly sensitive to the destruction of their forest home from from logging and road building.
Conserving the fisher is a matter of limiting our appetite for its old growth habitat, and leaving as much as possible for the fisher and the other creatures that need mature forests in order to survive.
From our experience in the northeast, where reintroduced fishers are making a comeback, we know that fishers can recover – if only we save them a place to live.
fisher| forest | slideshows
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