Daily records of bird observations were obtained from the Wild Bird Society of Japan bird sanctuary at Lake Utonai, Hokkaido, from 1982 to 2002. We analysed the daily records of four species thought to be experiencing declines: Brown Shrike Lanius cristatus, Black-browed Reed Warbler Acrocephalus bistrigiceps, Chestnut-eared Bunting Emberiza fucata and Yellow-breasted Bunting E. aureola. The detection rates of Brown Shrike and Yellow-breasted Bunting declined drastically during the two decades, whereas the detection rates of Black-browed Reed Warbler and Chestnut-eared Bunting remained stable. In 2002 and 2003 we conducted line transect censuses, and detected very few Yellow-breasted Buntings and no Brown Shrikes, both of which had been abundant as recently as 1977. The accumulated data from annual bird watching surveys showed similar declines in the same two species. These observations suggest that whereas the Brown Shrike had been common prior to the early 1980s, it declined drastically in 1986. The Yellow-breasted Bunting remained common until 1997, but declined seriously thereafter. There were no clear trends for Black-browed Reed Warbler or Chestnut-eared Bunting from 1982 to 2002, although the latter appeared to decline from 2011 onwards. Large-scale habitat destruction is unlikely in the study area, since the lake and its surrounding area have been a designated a wildlife protection area since before the study began. We discuss potential causes, together with previous studies.
2017 The Ornithological Society of Japan