Conservation planning for the federally threatened northern spotted owl (Strix occidentalis caurina) requires an ability to predict their responses to existing and future habitat conditions. To inform such planning we modeled habitat selection by northern spotted owls based upon fine-scale (approx. 1.0 ha) characteristics within stands comprised primarily of mixed-aged, mixed coniferous forests of southwestern Oregon and north-central California. We sampled nocturnal (i.e., primarily foraging) habitat use by 71 radio-tagged spotted owls over 5 yr in 3 study areas and sampled vegetative and physical environmental conditions at inventory plots within 95% utilization distributions of each bird. We compared conditions at available forest patches, represented by the inventory plots, with those at patches used by owls using discretechoice regressions, the coefficients from which were used to construct exponential resource selection functions (RSFs) for each study area and for all 3 areas combined. Cross-validation testing indicated that the combined RSF was reasonably robust to local variation in habitat availability. The relative probability that a fine-scale patch was selected decreased nonlinearly with distances from nests and streams; varied unimodally with increasing average diameter of coniferous trees and also with increasing basal area of Douglas-fir (Pseudotsuga menziesii) trees; increased linearly with increasing basal areas of sugar pine (Pinus lambertiana) and hardwood trees and with increasing density of understory shrubs. Large-diameter trees (>66 cm) appeared important <400 m from nest sites. The RSF can support comparative risk assessments of the short-versus long-term effects of silvicultural alternatives designed to integrate forest ecosystem restoration and habitat improvement for northern spotted owls. Results suggest fine-scale factors may influence population fitness among spotted owls. ß 2011 The Wildlife Society.

The northern spotted owl (Strix occidentalis caurina (Merriam, 1898)) is listed as threatened in both Canada and the United States. As part of a 1998–2004 study of habitat usage, we attached radio tags to 197 northern spotted owls. Owls that died or emigrated from the study areas could be identified with high certainty. The long-term data we obtained enabled us to estimate survivorship using multiple statistical methods. Using a pooled data set, we estimated annual survivorship at 0.927. Using a year-by-year analysis, we obtained some variation in survival by year, but the same overall mean. Using a staggered-entry cohort approach, we obtained an estimate of 0.934. Mean annual survival estimated by program MARK was 0.927. These estimates are outside the confidence intervals of prior studies that used capture–recapture methods. Capture–recapture methods are based on the assumption that birds remain within a demographic study area, but our data suggest that owls may disperse or remain undetected within a study area often enough that capture–recapture methods may overestimate mortality. Our results imply that the true finite population growth rate, λ, may be higher than estimated in prior studies that used capture–recapture methods.

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The invasion of the Pacific Northwest, USA by northern barred owls (Strix varia) is a conservation conundrum because it contributes to lingering declines in populations of northern spotted owls (Strix occidentalis caurina). We evaluated factors influencing nocturnal (i.e., foraging) habitat selection by northern barred owls using a repeated-studies design and information-theoretic methods across 3 Pacific Northwest study areas, each containing a broad range of forest and environmental conditions. We constructed discrete-choice resource selection functions (RSF) based upon telemetry points linked to forest inventory plots and map-based physical environmental metrics within home ranges of radio-tagged barred owls at Chehalis, Washington (n ¼ 16), Springfield, Oregon (n ¼ 22), and Arcata, California (n ¼ 15). A general RSF based upon pooling data across study areas suggested barred owls selectively hunted for prey in lower-slope positions on southerly aspects often near streams at low elevations, and often within red alder (Alnus rubra) dominated stands or in moderately dense patches of medium-and large-diameter coniferous trees close to patches containing nests. The relative probability of use decreased with increasing densities of small-diameter trees, suggesting barred owls avoided clearcuts and young plantations. These general patterns were modified by study-area variation in tree species composition and density. Study-area-specific factors that were associated positively with barred owl habitat selection included increasing basal area of western redcedar (Thuja plicata) and red alder at Chehalis and increasing densities of western redcedar and basal area of bigleaf maple (Acer macrophyllum) and western hemlock (Tsuga heterophylla) at Springfield. At Arcata, high densities of Douglas-fir (Pseudotsuga menziesii) trees and increasing basal area of tanoak (Notholithocarpus densiflorus) were negatively associated with barred owl habitat selection. Seasonal patterns of habitat selection did not differ dramatically although model coefficients suggested selection for specific tree species was weaker in the non-breeding season and barred owls did not seek topographic situations that provided thermoregulatory benefits. The information may help inform conservation strategies for reducing competition between barred owls and northern spotted owls or perhaps in predicting colonization of new areas by barred owls. Ó 2017 The Wildlife Society.

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