What landscape elements are correlated with the distribution of wintering Grey-faced Buzzards Butastur indicus in the Sakishima Islands, southwestern Japan?

Abstract

The Grey-faced Buzzard (Butastur indicus) is a typical migratory raptor species in East Asia, and has suffered a population decline recently. In southern Japan, the wintering buzzards are widely distributed to the Sakishima Islands. The mainly human activity on these islands is agriculture, and the natural environments are fragmented by such exploitative land-use that produces a characteristic landscape pattern. In this study, we describe the distribution pattern and habitat selection of the buzzards wintering in the Sakishima Islands, and focus on landscape elements in order to give a basic reference for further conservation study. Ten islands were investigated during January to March 2005. We used the generalized linear mixed model (GLMM) on a set of landscape elements to model buzzard distribution in the 1×1 km grid cell within each island, and studied the relationships between the numbers of buzzard and landscape elements among islands by using the generalized linear model (GLM). The results were similar on two spatial scales, and they both suggested that the area of farmlands (sugar cane, pasture, and rice paddy), and the perimeter of forests have significant correlation with the distribution and the numbers of the wintering buzzards. Different from breeding sites where distribution was limited by critical nest resource, distribution of Grey-faced Buzzards in wintering sites was simply related to foraging habitats. We suggest that further study should focus on measuring quantitatively the relationships of different farmland types with buzzard distributions in order to make more realistic predictions about distribution when habitat is lost or shifted from one category to another.