A fisher runs over a creek bed after being released in the Gifford Pinchot National Forest near the Cispus Learning Center in December 2015.
A unique research approach by inquiring minds at Oregon State University has led to findings that are expected to result in improved recovery results for the long-imperiled fisher.
The OSU study sought to find a better understanding of how three similarly sized carnivores — ringtails, foxes and fishers — impact the population numbers and colonization behavior of the other species when in near proximity to each other. Their findings have been published in the Journal of Animal Ecology.
Wiped out from most of the Pacific Northwest by the early 1900s due to trapping and habitat loss, efforts have been underway in recent years to reintroduce the midsize forest predator to the Olympic and Cascade mountain ranges.
“They’re larger than people realize,” said corresponding author David Green, in a press release. “They can be the size of a large house cat, and they’re really interesting critters.”
Fishers are able to climb trees like a cat, but thanks to nimble hind feet, they are also able to rotate 180-degrees and climb down head first. That ability allows fishers to hunt dangerous porcupines from above by attacking their heads and avoiding their quills.
Fishers earned their name because early North American settlers believed they resembled the European polecat, which was also called a fitch, fitchet or fitchew. Wild fishers are found only in Canada and the northern United States. They are related to wolverines, badgers, otters and minks as a member of the Mustelidae family.
Green and his colleagues spent eight years studying fishers and other predators in a 179-square-mile region along the Oregon-California border. The main objective of the study was to find out how the translocation of fishers affected their numbers and the populations of similarly sized forest predators. Translocation is essential to the fisher recovery effort. For the OSU study, fishers were moved from Oregon to the northern Sierra Nevada mountains.
“There’s been quite a bit of research that shows how larger carnivores have negative effects on fishers, but this is some of (the) first research to look at their interactions with carnivores of about their same size,” said Green, whose group also included researchers from North Carolina State University, the U.S. Forest Service, the U.S. Fish and Wildlife Service and the California Department of Fish and Wildlife.
Green added that, “Throughout the world, numbers of grey foxes, fishers and other midsized predators are actually increasing, and usually that happens because the bigger animals that are limiting them are decreasing. But we thought we might also see changes in midsized predator numbers because of some kind of hierarchy among them.
The idea that they could be interacting with other carnivores their same size in ways that might affect their distribution was new, novel and important to pursue.”
For the study, nine fishers were relocated from Oregon to California where they joined a forest also populated by ringtails and grey foxes. Those nine fishers represented about 20 percent of the overall population in the study area.
“The foxes likely compete with fishers due to their similar sizes and dietary overlap,” Green noted in the release. “And ringtails are similar to fishers in that both are semi-arboreal and of conservation concern. Determining how all of those types of animals coexist is critical for understanding functional diversity, niche partitioning and interspecific interactions.”
The study found that following the removal of the study animals the fisher population density remained unchanged, although they occupied fewer places and certain home ranges became vacant.
“We sampled the animals using non-invasive means — capturing hair as they visited our baited sampling sites — and we used genetic techniques to identify the animals that visited our sites down to the individual fisher,” explained Green. “We found a complicated hierarchy among fishers, foxes and ringtails. In summary, fishers were the dominant small carnivore where present, and they negatively affected foxes directly and ringtails indirectly.”
According to Green, the study provided findings that are encouraging for fishers, and just generally fascinating.
“I think of this as a beginning step to understand how fishers interact with other species in their environment,” Green said. “But the big picture right now is funding for research like this is declining rapidly given the current state of government agencies, and it’s important for research like this to continue to move forward so we can better understand one of the important and charismatic species in the Northwest and the nation.”
Th research project was supported by the National Council for Air and Stream Improvement, the U.S. Fish and Wildlife Service, the California Department of Fish and Wildlife, the U.S. Forest Service Rocky Mountain Research Station, North Carolina State University, Fruit Growers Supply Company, Timber Products Company, and Sierra Pacific Industries.
