Changes in spatio-temporal patterns of urban habitat quality and their associations with bird species diversity under China's rapid urban expansion

As a major anthropogenic pressure, urban expansion significantly alters habitat quality and biodiversity. However, the effects of urban expansion on urban habitat quality (UHQ) and their relationship with bird diversity are not comprehensively understood, especially under rapid urbanization in China. Explore the spatiotemporal changes in UHQ of 320 cities in China from 1990 to 2020, as well as the relationship between UHQ and bird species diversity, and the factors influencing bird species diversity, focusing on different climate zones and city sizes. First, based on annual land use data obtained from Landsat images using the Google Earth Engine (GEE), we detected the change in land use and UHQ. Then, structural equation modeling was used to investigate the direct and indirect effects of driving factors on bird species diversity. Our results revealed a tripling of impervious surfaces in Chinese cities over this period, mainly encroaching on croplands (92%), followed by forests (3%) and grasslands (2%). Urban natural habitat area decreased by 32.5%, particularly in subtropical monsoon climates (SMC) and medium-sized cities. The average UHQ in China declined by 35.3%, with over 90% of cities exhibiting decreasing trends, especially megacities located in the SMC zone. Urban birds were mainly directly influenced by UHQ and indirectly influenced by altitude, population, and precipitation at the national scale. The primary influencing factors and direct or indirect influencing processes (including climate factors and urbanization factors) changed across different climatic zones. These findings contribute to our understanding of the urban expansion-UHQ-bird diversity relationship, providing insights for sustainable urban development and bird species conservation.