Influence of interspecific competition on nest site selection among Chestnut-cheeked and White-cheeked Starlings in the Northern Tohoku Region

Abstract

Nest sites of both Chestnut-cheeked Starling Agropsar philippensis and White-cheeked Starling Spodiopsar cineraceus were compared in Morioka City, a core city in the Tohoku region of Japan. Surveys were conducted in June 2023 and from April to June 2024; these involved walking along all roads within 500 m square grids to locate nests of both species. Nests were classified based on their location, and the following variables were measured: nest height, structure height, entrance orientation, and entrance angle. Totals of 51 Chestnut-cheeked Starling and 47 White-cheeked Starling nests were observed across 32 survey sessions. When comparing nest location categories based on land use, significant differences were observed in the nest site selection of Chestnut-cheeked Starling breeding in urban areas compared with those in agricultural areas and with White-cheeked Starling breeding in urban areas. The nests of Chestnut-cheeked Starling breeding in agricultural areas were significantly lower than of those breeding in urban areas or of White-cheeked Starling breeding in agricultural areas. Whereas some of the Chestnut-cheeked Starling nests had upward-facing entrances, those of the White-cheeked Starling had more downward-facing entrances. These findings suggest that, to avoid competition with White-cheeked Starling, Chestnut-cheeked Starling may alter its nesting locations in urban areas and and nesting heights in agricultural areas, and this might be disadvantageous for its breeding strategy.