Effects of river-crossing structures in small and medium-sized urban rivers on urban waterfowl population and diversity

Abstract

 The present study aimed to examine the relationship among urban waterfowl numbers, diversity indices, and river-crossing structures in the Nogawa, Sengawa, Zenpukuji, and Kandagawa Rivers, which are typical urban rivers flowing through Musashino Plateau in Tokyo. In this study, we conducted surveys of over 20 species of bird by using the line census method from May 2016 to January 2017. We also measured parameters such as river width, waterway width, land width, and height from the waterway to the bank crest and analyzed these with respect to the bird survey results. The analysis by generalized linear model revealed that members of the family Ardeidae and Anas crecca tended to use narrow habitats, whereas Anas acuta and Anas platyrhynchos tended to use spacious habitats. From this, it was thought that the narrow structure of the urban river was effective in covering pressure of human for some birds. Additionally, the analysis by multiple regression revealed that larger river-crossing structures were positively associated with diversity indices. The results suggest that the river-crossing structures affect both waterfowl amount and diversity.