Ecology and Conservation of the Western Gray Squirrel (Sciurus griseus) in the North Cascades
Stuart, Kathryn Diane
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University of Washington Abstract Ecology and Conservation of the Western Gray Squirrel in the North Cascades Kathryn Diane Stuart Chair of the Supervisory Committee: Associate Director and Professor Stephen D. West School of Environmental and Forest Sciences The western gray squirrel (Sciurus griseus) was classified as a Washington State threatened species by the Washington Department of Fish and Wildlife in 1993 due to a decline in range and number. The North Cascades population is geographically and genetically isolated from others in Washington, Oregon, and California, and may be ecologically unique as it exists in a mixed-conifer forest habitat that lacks oak (Quercus spp.): a source of forage and maternal nests in most other portions of the range. The North Cascades are also distinguished by high average annual snowfall and cold temperatures, frequent wildfire and dynamic forest management. Land management agencies have initiated fire fuel reduction plans that may have potentially adverse effects on western gray squirrels. Local populations in Stehekin and the Methow Valley are likely small, making them susceptible to stochastic threats including genetic drift and inbreeding, which reduce evolutionary fitness and increase extinction risk. We studied distribution, life history, and response of squirrels to fire fuel treatments in the North Cascades from 2008-2011 using live trapping, radiotelemetry, and genetic and fecal sampling. Scientific communication between researchers and the general public was evaluated with interviews and an experimental study on the effectiveness of alternate communication methods. Squirrels used fire fuel treated areas disproportionately within their home ranges indicating that recent treatments and wildfires have not negatively affected western gray squirrel habitat at the home range scale. We also found no evidence that treatments and wildfire have negatively affected western gray squirrel diet. Areas used for nesting were characterized by large, tall trees, high levels of dwarf mistletoe infection, high canopy cover and connectivity; all characteristics that can decrease with fire fuel reduction treatments. Future treatments can focus on retaining patches of large trees with some mistletoe infection, and moderate levels of canopy cover and connectivity to conserve western gray squirrel nesting habitat in the North Cascades. Average home range size, degree of overlap, and effective population size indicate that the North Cascades may support a larger population of western gray squirrels than previously thought. Understanding and support for wildlife research increased significantly through science communication.
- Forestry