Northern goshawk (Accipiter gentilis) nesting habitat in northwestern California : an examination of three spatial scales: the nest area, the post-fledging area, and the home range

The northern goshawk (Accipiter gentilis) is a large, forest dwelling raptor that uses a wide variety of habitat types for both nesting and foraging. Due to fire suppression and extensive harvest of mature trees in northwestern California, goshawk nesting habitat has decreased in the region. In addition to forty-nine historic goshawk nest sites, other mature forest patches on several land use types in the coastal region of northwestern California were surveyed. No evidence of breeding goshawks was found within 33 km of the coast. Habitat and topography at goshawk nests found further inland was analyzed at three spatial scales important to breeding goshawks: the nest area (21.5 ha), the post-fledging area (170 ha) and the home range (2110 ha). At the smallest scale, the distance of nests to streams, canopy depth, and Douglas-fir (Pseudotsuga menzeesii) trees in the largest size class created the best model to describe nest areas. Using a Geographic Information System to calculate habitat variables at landscape scales, I found that the post-fledging area contained a lower percentage area of Douglas-fir (Pseudotsuga menzeesii) in the pole seral stage, a lower percentage area of medium sized Quercus sp. overstory, and a greater percentage area of early mature Douglas-fir than at paired random plots. Home ranges contained a greater percentage area of late mature Abies sp./Douglas-fir forest and a lower percentage area of medium sized Douglas-fir overstory than random plots. As the level of spatial scale increased, the number of significant variables decreased and habitat heterogeneity increased, suggesting that goshawks used nest sites based on smaller scale habitat attributes.