Seasonal shifts in foraging site and prey of Grey-faced Buzzards (Butastur indicus), breeding in Satoyama habitat of central Japan

抄録

The Grey-faced Buzzard (Butastur indicus) is a migratory raptor breeding in Japan. It has a high breeding density in what is known as “Satoyama”, a traditional mosaic landscape of paddy fields, woodland, grassland, and streams. We studied the foraging behavior of five buzzard pairs in Satoyama of Tochigi Prefecture, central Japan, for two years. Seasonal changes in foraging sites and differences in the amount of prey captured at each foraging site were analyzed by Bayesian inference using a Markov Chain Monte Carlo (MCMC) algorithm. The main vegetation types which characterized the foraging areas of the buzzards varied over the course of the breeding season from paddy fields to levees and grass-arable fields, and eventually to wooded areas. Along with this shift, the main prey of the buzzards changed from frogs to insects. In paddy fields, frogs and small mammals were frequently captured. A variety of prey including frogs, small mammals, lizards, snakes, and insects were taken at levees and grass-arable fields. Insects and frogs were captured in woodland areas. Since the buzzards utilized almost all vegetation types found in Satoyama when foraging, spatial distribution of these foraging sites and the prey biomass therein need to be considered when planning the conservation of breeding habitat for this species.