Summer Habitat Ecology of Northern Spotted Owls in Northwestern California

Abstract

We studied the summer habitat ecology of 12 Northern Spotted Owls (Strix occidentalis caurina) in two areas of northwestern California. Spotted Owls used mature or old-growth conifer forests significantly more than expected relative to their availability within their home ranges. In contrast, Spotted Owls used forests of intermediate and young age significantly less than expected relative to their availability within their home ranges. Eighty four percent of 616 Spotted Owl radiotelemetry locations were recorded in mature or old-growth forests. Spotted Owls used forests of complex structure and old age. There were significant differences in habitat structure (e.g., canopy closure, shrub cover, herb cover, old-growth conifer basal area, and hardwood tree density) among habitats used for frequent foraging, infrequent foraging, and roosting. In addition, male and female owls appeared to select habitats with different structure for foraging. Male owls which are smaller than female owls foraged in habitats which had higher tree density than female owls. The mean summer home-range size was 413 ha (SD = ?+196 ha) with males having smaller mean home-range size than females (338 ha and 538 ha, respectively).