The effect of the Kameda River on the bird diversity in Hakodate City

Abstract

Avian diversity in urban areas can be strongly affected by the presence of rivers. However, to date this effect has not been quantitatively assessed. We established 16 observation points along the Kameda River, which flows through Hakodate City, Hokkaido, Japan. Half of these were set alongside the river, whereas the other half were set in residential areas, 200 m from the river. We recorded the number of bird species and individuals of each species at the observation points during summer and winter 2015. During both seasons we observed significantly higher numbers of species and individuals along the river than in the residential areas, indicating that the Kameda River provides habitats for a wide range of bird species and enhances the bird diversity in Hakodate City. We also found that the number of species recorded along the downstream section of the river decreased during summer but increased during winter. This was probably because some species breed only near the upper reaches of the river (near the mountains), during summer, while many waterfowl spend the winter along the lower reaches of the river where the flow is slower. These findings suggest that the effect of the river on the urban bird community changes not only between sections of the river, but also between seasons.