Habitat configuration around spotted owl nest and roost sites In northwestern California

During each breeding season between 1988 and 1992, nests and daytime roosts were located for all territorial members of a contiguous population of northern spotted owls (Strix occidentalis caurina) in northwestern California. I used guided clustering with Landsat Thematic Mapper data to map land cover types representing seral stages of coniferous forest. I produced two maps; one had six land cover types and the other had only mature and old-growth coniferous forest. Map accuracy was estimated to be 76.4% and 83.6%, respectively, and was determined by comparing land cover map data with randomly sampled field data. Using these maps and a grid-based geographic information system, I estimated the amount of area of each land cover type, habitat heterogeneity, and the fragmentation, patch number, and patch size of mature and old-growth forest at nest, roost, and random sites. Habitat variables were measured within eight concentric circular plots of 800 - 3600 m radii. I compared the habitat variables from the 800 m plots among sample categories because this plot size approximated one-half distance between the centers of spotted owl territories. Nest and roost sites were similar, and had less herb and nonvegetated cover, slightly lower seral stage heterogeneity, and more mature and old-growth habitat which was less fragmented and arranged in fewer but larger patches than random points. Mean amounts of area of mature and old-growth habitat within 800 m radius plots were 94.1 ha, 92.0 ha, and 71.8 for nest, roost, and random sites, respectively. The area of other cover types were similar between nest, roost, and random sites. Data from all concentric circular plots were used to estimate which habitat characteristics changed non-randomly with increasing distance from owl sites. The area of herbaceous and nonvegetated, brush, hardwood, and indices of fragmentation and heterogeneity increased as distance from owl locations increased. The area of mature and old-growth forest decreased with increasing distance from owl sites. My results from the Klamath physiographic provence of California were similar to results from comparable studies in Oregon and Washington.