Spotted Owl Roost and Nest Site Selection in Northwestern California

We directly observed roost and nest site selection in a population of northern spotted owls (Strix occidentalis caurina) in northwestern California during 1985-89. Because of potential biases caused by use of radio telemetry in previous studies, we examined habitat use relative to habitat availability at a level not previously reported for spotted owls. Spotted owls selected coniferous forest characterized by trees >53.3 cm in diameter more often (P < 0.05) than it was available. Hardwood stands and coniferous forest dominated by smaller trees were used less than (P < 0.05), or in proportion to, their availability. The owls selected forests at 300-900 m elevations for roosting (P < 0.05), selected the lower third of slopes within a specific drainage (P < 0.05), and avoided the upper third for both roosting and nesting (P < 0.05). These observations support the findings of earlier workers who used radio telemetry to assess habitat selection in the northern spotted owl.