Factors Affecting the Number of Breeding Grey-faced Buzzard-Eagles Butastur indicus

Abstract

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.