Population biology of the California spotted owl in the central Sierra Nevada

Individual reproductive output and survival are two key population vital rates that influence a species' population growth (λ). There is great uncertainty regarding the factors that influence these vital rates in California spotted owl (Strix occidentalis occidentalis) populations. Therefore, I estimated sources of variability in population vital rates for a marked sample of California spotted owls in the central Sierra Nevada from 1990 to 2004. I first reviewed the use of random effects analysis to estimate variability in vital rates and assessed the effect that field methods had on estimates of reproductive output. I then estimated temporal and spatial sources of variability in population vital rates within the contexts of life history theory and habitat selection theory.;I treated general predictions from life history theory as hypotheses that I tested with my data. Temporal variability in the environment appeared to affect the number of young fledged (R) by owls much more than it affected their survival probability (ϕ); ϕ exhibited much less temporal variability ( CV&d4; = 0.04) than R ( CV&d4; = 0.83). This suggested ϕ was under greater selective pressure. Weather covariates explained 84% and 60% of the temporal variability in R and ϕ, respectively. Although λ was most sensitive to ϕ, R contributed relatively more to annual variability in λ.;Overall, habitat composition around 400 ha of territory centers was a relatively good predictor of ϕ but a poor predictor of R. Territory colonization and ϕ were positively related to the area of forest with high canopy cover (≥70%) dominated by medium (30.4-60.9 cm dbh) and large (≥61 cm dbh) trees. Habitat composition explained 93% and 36% of the total spatial variability in ϕ ( CV&d4; = 0.34) and R ( CV&d4; = 0.19), respectively. Much of the variability in λ may be beyond the control of managers because R appeared to be highly correlated with weather and was responsible for much of the annual variability in λ. Never the less, because λ was most sensitive to ϕ, I concluded that maintaining forests with high canopy cover dominated by medium and large trees is essential for sustaining this population.