Population Trends of Grassland Birds in Hokkaido, Focussing on the Drastic Decline of the Yellow-breasted Bunting

Abstract

To examine the population trends of grassland and shrub birds in Hokkaido, we conducted line transect censuses in 2002 and 2003, in area where avifaunal studies had been performed in the 1970s and 1980s. To document the decline in the Yellow-breasted Bunting Emberiza aureola, birdwatching data were also analysed. The Yellow-breasted Bunting population has decreased drastically both in density and in distribution over the intervening thirty years. The decline in occupied breeding sites and in the population is continuing. Densities of Eurasian Skylark Alauda arvensis and Lanceolated Grasshopper Warbler Locustella lanceolata have also declined, although their range contractions are not yet severe. The ranges of Brown Shrike Lanius cristatus and Chestnut-eared Bunting E. fucata appear to have contracted. In contrast, data analysis revealed that the breeding range of Yellow Wagtail Motacilla flava has expanded in northern Hokkaido, but it is possible that the range had expanded in the past but had been overlooked. The present study suggests that the ranges of Bull-headed Shrike L. bucephalus and Gray's Grasshopper Warbler L. fasciolata had expanded, although some previous studies do not support this trend. In this study we were not able to clarify the reason why the population trends of these species have changed. Further research is necessary focussing on: breeding habitat analysis, breeding biology in relation to population trends, population trends in wintering and migration areas and clarification of migration routes. The population decline in the Yellow-breasted Bunting is both dramatic and very severe. This migratory species in particular requires immediate international conservation measures to avoid national and regional extinction.