Beyond the concrete jungle: The value of urban biodiversity for regional conservation efforts.

Urbanization deletes and degrades natural ecosystems, contributing to the ongoing biodiversity crisis. Yet, on the local scale, well-managed cities can host significant biodiversity, including endemic and threatened species. Understanding the trade-off between local and regional biodiversity outcomes is limited, primarily due to the lack of comprehensive sampling across heterogeneous urban areas and adjacent regions. To address this knowledge gap and assess urban areas' value for conserving the regional species pool, we conducted an extensive bird survey across an urbanized metropolitan area and its surrounding region (>300 km²). The survey included 11 cities, 24 rural settlements, agricultural areas, and natural habitats, employing high-resolution geographic data (e.g., 3D vegetation layer) to examine land cover effects on α- and β-diversity metrics. Our findings reveal that urban avian diversity can surpass adjacent non-urban areas, with urban green spaces among the most species-rich habitats. Most regional bird species did not avoid urban areas, indicating their significant potential for regional conservation, particularly in human-dominated areas. Across the region, avian communities were highly heterogeneous, driven by species turnover rather than loss, highlighting urban biodiversity complexity. However, factors associated with urbanization negatively affected both α- and β-diversity, with synanthropic species most prevalent in urban habitats. Our findings suggest that strategic urban planning, focusing on compact development and accommodating non-synanthropic species in green spaces, can significantly contribute to regional conservation efforts.