Anthropogenic nesting materials and reproductive performance of Chinese Bulbuls (Pycnonotus sinensis) along the urbanization gradient in Hangzhou, China

Urbanization induced by human activities presents both challenges and adaptive opportunities for wildlife. One notable impact of urban sprawl is the vast amount of waste it produces, which has discernible effects on wildlife. Interestingly, an emerging trend has been observed that birds are incorporating anthropogenic materials into their nests. However, the relationship between anthropogenic nesting materials (ANMs) and the reproductive performance of urban birds is unclear. In this study, we investigated the relationship between the incorporation of ANMs into nests and the reproductive performance of Chinese Bulbuls (Pycnonotus sinensis) by monitoring and collecting data on 136 breeding nests in Hangzhou, China. We gathered data on seven reproductive traits of Chinese Bulbuls, including laying date, incubation period, nestling period, clutch size, egg volume, hatching success rate, and fledging success rate. We then calculated the urbanization synthetic index as a measure of the level of urbanization and examined its relationship with the proportion and weight of ANMs. Through examination of nest components, we observed significant increase in the proportion and weight of ANMs with the urbanization synthetic index. Notably, we found a higher hatching success rate of Chinese Bulbuls with an increasing proportion of ANMs. However, the inclusion of ANMs in nests was not correlated with other reproductive traits of Chinese Bulbuls. Overall, the use of ANMs by Chinese Bulbuls is consistent with the adaptive hypothesis and the availability hypothesis. Further studies should use controlled experiments to investigate the impact of ANMs on avian reproductive success.