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 < O.O5), or in proportion to, their availability. The owls selected forests at 300-900 m elevations for roosting (P < O.O5), 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. J. WILDL. MANAGE. 56(2):388-392 Johnson (1980) described habitat selection by umented a strong selection by individuals for an organism in terms of 4 hierarchical classifiold-growth coniferous forest. This habitat seleccations: first-order selection of the geographical tion pattern has led to a major controversy bedistribution of a species; second-order selection cause of its potential impact on the timber inof home ranges, or sites, within the geographical dustry in the Pacific Northwest (Dixon and distribution; third-order selection of habitat Juelson 1987, Simberloff 1987). However, comcomponents within home ranges; and fourthparisons of habitat use and availability within order selection of, for example, food items within a feeding site. Studies of the northern spotted owl have documented first-order selection of home ranges may be misleading when viewed from outside the context of second-order selection. All home range studies of northern spotted major coniferous forest types in the Pacific owls used radio-telemetry to document owl Northwest (Forsman 1976, Forsman et al. 1984, movements from which to infer habitat selecGould 1977, Garcia 1979); third-order selection tion patterns. Potential sources of bias in owl for mature and old-growth forests within home ranges (Forsman et al. 1984, Carey et al 1990, radio-telemetry st udi the home ranges in es mav which have included: (1)