Nesting locations of gray-faced buzzard eagles were studied in two areas of about 348 in Tochigi prefecture. Their food items were also monitored. From the nesting data, a multiple regression model ...was constructed to predict the number of nesting locations within a 2x2 mesh grid from several environmental factors such as vegetation and human population size. The resulted model could explain about 70% of the variation in the number of nests (r2×0.71). Factors used in the model were length of forest edge facing paddy fields in a mesh grid and in surrounding eight meshes grids (positive factor), and population (negative factor). In the study area gray-faced buzzard eagles were feeding mainly on frogs, and the birds were observed to perch on the tree top in the forest-paddy field edge waiting for frogs to appear. The preference on forest-paddy field edge shown by the model might reflect the importance of such habitat as the species' hunting area. In our study area, the gray-faced buzzard eagles were especially abundant in continuous 'Yatsu' area, a landscape in which a low tableland is eroded by rivers to create a fractal shaped network of valleys. Our results, along with other published data, indicate that the Yatsu landscape is an important breeding habitat for this species.
Nesting locations of gray-faced buzzard eagles were studied in two areas of about 348 in Tochigi prefecture. Their food items were also monitored. From the nesting data, a multiple regression model ...was constructed to predict the number of nesting locations within a 2x2 mesh grid from several environmental factors such as vegetation and human population size. The resulted model could explain about 70% of the variation in the number of nests (r2×0.71). Factors used in the model were length of forest edge facing paddy fields in a mesh grid and in surrounding eight meshes grids (positive factor), and population (negative factor). In the study area gray-faced buzzard eagles were feeding mainly on frogs, and the birds were observed to perch on the tree top in the forest-paddy field edge waiting for frogs to appear. The preference on forest-paddy field edge shown by the model might reflect the importance of such habitat as the species' hunting area. In our study area, the gray-faced buzzard eagles were especially abundant in continuous 'Yatsu' area, a landscape in which a low tableland is eroded by rivers to create a fractal shaped network of valleys. Our results, along with other published data, indicate that the Yatsu landscape is an important breeding habitat for this species.
Nesting locations of the Northern Goshawks (Accipiter gentilis) were investigated in two areas of about 390 km(2) in Tochigi prefecture, about 50km north of Tokyo. A total of 22 nesting locations ...were found in the area. Their food items were also monitored. A multiple regression model was constructed to predict the breeding density (measured as the total area covered by l.8 km buffers generated from the location of each nests within a 3 x 3 km grid) from several environmental factors such as vegetation and human population size. The resulted model could explain about 63% of the variation in the breeding density (r =0.63). Factors used in the model were: length of forest edge facing grassland (positive factor), area of bare land, construction sites etc. and human population size within each grid (negative factors). In this area, Goshawks were feeding mainly on small or medium sized birds, but the abundance, or biomass, of the birds was not an important factor that affected the breeding density of the Goshawks. The reason for this might be either that the food (amount of birds) is generally abundant in the area and therefore not an important limiting factor, or that availability of the suitable hunting area such as the forest edge facing the grassland is more important than the availability of the food itself.
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