HABITAT CONFIGURATION AROUND SPOTTED OWL SITES IN NORTHWESTERN CALIFORNIA

During each breeding season between 1988 and 1992, nests and daytime r oosts were located for most territorial members of a contiguous popula tion of Northern Spotted Owls (Strix occidentalis caurina) in northwes tern California. Using Landsat imagery, we compared the amount of five land cover types, mature and old-growth forest fragmentation, and ser al stage heterogeneity within 800 m (200 ha) circular plots around nes t, roost, and random sites. This plot size was based on the observed s patial distribution of owl sites (one-half the average nearest-neighbo r distance between territory centers) within the study area. Nest and roost sites were characterized by lower amounts of nonvegetated and he rbaceous land cover, and greater amounts of mature and old-growth coni ferous forest which was less fragmented than random sites. Mean amount s of mature and old-growth forest within 200 ha radius plots were 94.1 ha, 92.0 ha, and 71.8 for nest, roost, and random sites, respectively . The area of other land cover types was similar between owl and rando m sites. All habitat variables were similar at nest and roost sites. T o evaluate the influence of spatial scale, habitat variables around ne st and random sites also were estimated within eight concentric circul ar plots ranging from 800 to 3,600 m radii. Differences between nest a nd random sites in the amount and fragmentation of mature and old-grow th forest were significant (P < 0.01) out to 1,200 m. Differences in t he amount of nonvegetated and herbaceous, and semi stage heterogeneity were significant (P < 0.05) out to 1,200 m and 800 m, respectively. T hese results indicate that spatial scale of sampling is important and will affect analytical results. Our findings from the Klamath Physiogr aphic Province of California were similar to results from comparable s tudies in Oregon and Washington.