Effects of forest management, prey, and predators on the habitat selection of fishers in the South Cascades of Washington.
Parsons, Mitchell Alan
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One of the most common reasons for failure of wildlife reintroductions is releasing animals into low quality habitat that does not meet resource needs. Food availability and the presence of potential predators or competitors in the reintroduction area are integral aspects of habitat quality that are rarely assessed prior to reintroductions. The fisher (Pekania pennanti) is a commonly reintroduced species that requires complex forest structure for reproduction, relies on a variety of prey, and interacts with a number of other carnivore species. In this thesis, I assessed prey availability for a reintroduced population of fishers and modeled their habitat selection based on forest structure, prey, and predators to better understand what factors could influence reintroduction success of fishers. In the first chapter, I evaluated the relationship between forest management and prey availability for fishers. I conducted habitat surveys, live trapping, and sign surveys for mammalian prey in forests that differed in management history. I then assessed how forest management and habitat influenced prey diversity and community structure. I found equally diverse but distinct prey communities in forests with different management histories. The prey community in old stands consisted of abundant small rodent species, while younger stands had higher abundance of snowshoe hares (Lepus americanus) and mountain beavers (Aplodontia rufa). I identified a potential disconnect between preferred habitats of fishers and two common prey species, mountain beavers and snowshoe hares. In the second chapter, I examined the relative importance of landscape features and species interactions in determining habitat selection of fishers. I used species detections at 134 remote cameras stations, remotely sensed forest structure data, and telemetry locations of fishers to construct a resource selection function assessing the relative importance of prey, predators, and forest structure in habitat selection by fishers. I found that the probability of fisher use increased in older forests, in close proximity to recently disturbed stands, and in areas with moderate snowshoe hare abundance. Additionally, I documented a potential food-safety tradeoff for fishers between bobcats (Lynx rufus) and snowshoe hares, which fishers may mediate through temporal avoidance of bobcats. Selection for old forests close to recently disturbed stands and the preference of important prey for young stands suggests that habitat mosaics of these forests are valuable for fishers in the Pacific Northwest. Managers should seek to create heterogeneous forest habitats where young stands are intermixed in a matrix of old forest to provide for all habitat needs of recovering fishers. I documented complex relationships between forest structure, prey, predators, and fisher habitat selection, highlighting the importance of addressing species interactions prior to reintroductions.
- Forestry