HABITAT ASSOCIATIONS OF CALIFORNIA SPOTTED OWLS IN THE CENTRAL SIERRA-NEVADA

Habitat requirements of spotted owls (Strix occidentalis) are controversial, particularly with respect to private lands. Therefore, we studied the distribution and roosting and nesting habitat of California spotted owls (S. o. occidentalis) throughout a 355-km2 study area in the central Sierra Nevada, Eldorado and Placer counties, California, from May to August 1986 and 1987. Fewer (P less-than-or-equal-to 0.001) owls were detected on private land than expected from its relative land area. Slope; total canopy closure; number of possible nest trees; maximum shrub height; basal areas of old-growth, medium, pole, and live trees; percent ground cover by litter; and small and large dead or dying woody vegetation were different (P less-than-or-equal-to 0.05) between public and private land. Habitat types of mixed-conifer, large-tree successional stage, with greater-than-or-equal-to 70% total canopy closure were most abundant (38.1%) on public land; whereas mixed-conifer, pole-medium successional stage, with greater-than-or-equal-to 70% total canopy closure habitat types dominated private land (44.1%). Roost sites occurred in habitats with relatively greater total canopy closure, and basal areas of snags, medium, and old-growth trees than the abundance of habitat (Johnson 1980). Nests of owls occurred in habitats with relatively greater basal areas of live trees, snags, medium, mature, and old-growth trees; and total canopy closure than found in the abundance of habitat. Twenty-six of 29 observed roosts (89.7%) and all 11 owl nests were on public land. Our results provide forest managers with a direction towards appropriate silvicultural and logging practices for the conservation of California spotted owl roost and nest habitats. These include adequate representation of all tree size classes, especially mature and old-growth, combined with essential habitat elements (e.g., nest trees).