Masters Thesis

Northern spotted owl nesting habitat on private timber lands in northwest California

I evaluated nesting habitat relationships of northern spotted owls (Strix occidentalis caurina) on private lands in coastal northwestern California by comparing habitat metrics (nesting, roosting, foraging, and shrub habitats, amount of core area and linear distance of edge between vegetation types) at used and random sites at four spatial scales. I developed ten a priori models with three functional forms using logistic regression in an information theoretical framework to examine the strength of habitat covariates to predict owl habitat use for nesting. The best-fitting model predicting the probability of site use for nesting by northern spotted owls had a positive non-linear quadratic relationship between nesting and the nesting/roosting and foraging/shrub covariates at the 398 ha scale. These same covariates also ranked high consistently across all scales. Core area parameters were mostly positive, and edge mostly negative in their relationship with the probability of nesting at all scales although they were not represented in the highest ranking models. Shrub habitat was positively related to the probability of nesting at all scales except the 29 ha scale where nest sites are generally dominated by forested habitats. My results indicate spotted owls selected habitat differentially (i.e., some degree of habitat specialization), selecting habitats with more complex attributes at increasing distances from the nest.

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