Graduation Date

Spring 2019

Document Type



Master of Science degree with a major in Natural Resources, option Wildlife

Committee Chair Name

Dr. Micaela Szykman Gunther

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Sean Matthews

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Dr. Aaron Facka

Third Committee Member Affiliation

Community Member or Outside Professional

Fourth Committee Member Name

Dr. Barbara Clucas

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories



In western North America, tree squirrels such as western gray (Sciurus griseus) and Douglas squirrels (Tamiasciurus douglasii) are potentially important prey for fishers (Pekania pennanti). Western gray squirrels in particular may be highly ranked due to their large body size. Masting trees including black oak (Quercus kelloggii) and tanoak (Notholithocarpus densiflorus) produce an important food source for tree squirrels; therefore, forest stands containing these trees may be useful to foraging fishers. I hypothesized that; 1) the abundance of western gray and Douglas squirrels in a stand is influenced by the mast production capacity of that stand, and 2) fisher stand use is influenced by the tree squirrel abundance in a stand. I deployed remote cameras for 44 weeks in 2017 in 85 forest stands dominated by compositions of conifer, or co-dominant with conifers and tanoak or black oak in the northern Sierra Nevada Mountains of California. I predicted that; 1) forest stands with the greatest capacity for mast production would have the highest probability of occupancy and detection of tree squirrels; 2) stands with the highest occupancy and detection of tree squirrels would have the highest probability of fisher occupancy and detection, and 3) fisher stand use and detection would be conditional on the western gray squirrel occupancy status of that stand. I tested the effects of stand type and other covariates on tree squirrel and fisher occupancy and detection using single-species occupancy models, and tested the effect of gray squirrel presence on fisher occupancy and detection probability using two-species co-occurrence models. Douglas squirrels occupied most sites (psi = 0.96-1.0) irrespective of stand type. Gray squirrels and fishers had highest rates of occupancy (psi = 0.86, Ψ = 0.93) and detection (p = 0.28, p = 0.13) in tanoak co-dominant stands. Fisher stand use patterns suggested both conditional and unconditional occupancy with western gray squirrels, and model-averaged occupancy estimates were highest in tanoak co-dominant stands regardless of whether gray squirrels were present (psi = 0.95) or absent (psi = 0.97). The results of this study indicate that habitats containing masting trees such tanoak may support greater numbers of western gray squirrels than other habitats, and retention of these trees across the landscape may improve foraging habitat for fishers.

Citation Style

Journal of Wildlife Management


Thesis/Project Location