LANDSCAPE ANALYSIS OF NORTHERN GOSHAWK BREEDING HOME RANGE IN NORTHERN JAPAN

Abstract

Large raptors such as northern goshawks (Accipiter gentilis) frequently have been the focus of conservation efforts because of their large area requirements and habitat sensitivity. We examined landscape-scale habitat selection of breeding goshawks and created a habitat model of goshawk landscape use in an area (1,600 km2) that contained forested, agricultural, and urban landscapes in northern Japan. From a systematic nest survey and extensive radio telemetry, we delineated 36 male home ranges (18 of them were approximated with similar-sized plots around nests) and 44 similar-sized unoccupied plots over the study area. The proportions of forest cover in each home range varied widely (between 2 and 88%). Despite this variation, goshawk landscape use was estimated accurately (classification accuracy = 84%) with a stepwise logistic regression model; the probability of occupancy was positively associated with the proportion of forest interior (>200 m from the forest edge) and that of open land <200 m from the forest edge, but it was negatively associated with the proportion of water and the mode of the slope. In home ranges, the proportions of forest interior and open land <200 m from forest edge complemented each other with the change in forest cover in such a way that the sum of the 2 variables always occupied >30% of the home ranges. These results suggest that a preference for the 2 different habitats, both of which may have a high prey availability, enables goshawks to nest in landscapes with a wide variety of forest fragmentation. The adverse effect of water on goshawk occupancy was due to the tendency of goshawks not to include a large river (>800 m wide) in their home ranges. This suggests that goshawks need connectivity between forest patches in their home ranges. The proportion of urban land was 19% lower in home ranges than in unoccupied plots. These results indicate that management efforts should focus on maintaining landscapes with high prey availability and connectivity between forest patches and on preventing urbanization over entire home ranges.