Nest site selection, nest characteristics, and breeding ecology of the Eurasian tree sparrow, Passer montanus, living in an urban area

Urbanization has resulted in changes in bird life histories, and some species have successfully adapted to urban environments, resulting in synurbization. Nest site selection in urban areas challenges cavity nesters because natural nest sites are often replaced by artificial holes. This study was conducted to identify the nest site selection and nest characteristics of the Eurasian tree sparrow (Passer montanus) living in an urban environment. This species inhabits artificial structures and tree holes around human settlements. We surveyed nests of tree sparrows on the Chonnam National University campus, located in Gwangju, Republic of Korea, during the first clutch from March to May 2020. We categorized nest types into natural and artificial nest sites. The tree sparrows selected natural nest sites such as woodpecker's holes and cracks in trees, and selected artificial nest sites which included holes in concrete buildings, under roofs, and in steel frames and nesting boxes. No significant differences were found in breeding schedules and reproductive success between birds nesting in artificial and natural holes. The results suggest that tree sparrows can successfully adapt to an urban environment by selecting nest sites regardless of nest hole type, and can reproduce successfully when nesting in both natural and artificial holes.