How do birds with different traits respond to Urbanization? A phylogenetically controlled analysis based on citizen science data and a diverse urbanization measurement

Abstract

The acceleration of urbanization has globally threatened bird diversity. Understanding how birds respond to the urban environment, and what, if any, traits predict this response to urban environments, is crucial in mitigating these declines. However, existing research often focuses on local or regional scales, utilizes restricted measures of urban tolerance, and does not always consider the interaction between evolutionary relatedness and traits, resulting in an unsettled relationship between some traits and urban tolerance. Our analyses aimed to test whether there is generalizability in previous results with that of the results in China, integrating 947,030 citizen science observations of birds with a continuous measure of urbanization. We synthesized an urbanization index for 874 species, representing their tolerance to urbanization by accounting for stressors such as built-up land, population density, and night-light intensity. First, we aimed to quantify which traits were positively and negatively associated with urban tolerance in Chinese birds, when considering all possible ecological and life history traits. Second, we tested specific hypotheses, based on a priori literature. Third, we tested whether the results from above change when phylogenetic relatedness is included in the models. The findings reveal that passage migrants or species with multiple main migration types with larger clutch sizes and more generalist diets are the most common in urban environments. Moreover, the evolutionary relationship between species conceals the expression of several traits in urban tolerance that omnivorous species that nest on architectural buildings or cliffs showed higher urban tolerance within clades. Our findings highlight the challenges in identifying consistent patterns in the relationships between species traits and their tolerance of urban environments. To optimize urban design and reduce the negative influence on birds from rapid urbanization, protecting existing trees and buildings where birds nest, increasing the proportion of shrubs to compensate for sources of ground-dwelling birds, and controlling the predation risk of the ground nests are beneficial.