Urbanization made rivers as important movement corridors for waterbird species, Black-headed Gulls

Abstract Understanding the geographic characteristics of animal movement corridors can help landscape management for animal access to critical habitats. However, corridors for waterbirds are a classic those estimated with inappropriate methods ignoring actual individual movements, and it is not even clear whether their movement space is limited by urbanization. In this study, we tracked waterbirds to examine the impact of urbanization on movement routes by focusing on the importance of rivers as movement corridors for them. Black-headed Gulls ( Chroicocephalus ridibundus ), a typical wintering waterbird that depends on rivers as movement corridors in the city center, were captured and their movements were tracked in Kanto, Japan. Using the GPS locations of tracked gulls recorded during the three wintering seasons from 2021 to 2023, the urban–rural gradients along the movement trajectories was evaluated based on the percentage of urbanized land use along trajectories. The relationship between the degree to which movement trajectories follow rivers and urban–rural gradients was analyzed by fitting a generalized linear mixed model. We revealed that the more urbanized the area, the more gull movement trajectories tend to be along the rivers. Even waterbirds, which are considered to have a highly mobile capacity, were shown to be limited in their movement routes by urban land use. Even if a river has little value as a foraging or roosting habitat, it should be conserved as a movement corridor in urban areas. We emphasized that movement corridors cannot be effectively conserved unless they are estimated based on actual movement routes of animals.