Importance of farmland in urbanized areas as a landscape component for barn swallows (Hirundo rustica) nesting on concrete buildings.

Urbanization is one of the key factors in the population declines of many species. Conversely, some species may favor urbanized areas. The barn swallow Hirundo rustica is well known to breed in urban areas of Japan, and uses both urban and farmland areas as habitat during the breeding season. Specifically, this species often nests on concrete buildings and feeds in surrounding farmland. Therefore, it was hypothesized that H. rustica is not strongly influenced by heavy urbanization and benefits from farmland areas, even if they are not near its nests. In this study, I evaluated the landscape components around H. rustica nests situated on concrete buildings, focusing on both urbanized and farmland areas. In particular, I explored the occurrence of H. rustica nests at train stations in the Kinki region of Japan. Assisted by 124 citizen scientists, I analyzed the landscape components around the train stations at multiple spatial scales. Results showed that the occurrence of H. rustica nests was negatively influenced by both urbanized land area and road density, whereas nest occurrence was positively influenced by farmland area and river density. These results suggest that H. rustica does not prefer urbanized areas overall, but can rather utilize urbanized areas primarily as nesting spots. Therefore, H. rustica cannot breed in heavily urbanized areas without feeding sites such as farmland or riparian areas.