How do urban green space designs shape avian communities: Optimizing distribution, size and shape.

Urban biodiversity forms the foundation, objective, and means of sustainable development, with birds serving as a key indicator of urban ecological health and biodiversity changes, thus being central to urban biodiversity conservation. The urban green matrix influences bird species diversity. However, the influence mechanism of area, shape, and configuration on different bird species in the highly fragmented, heterogeneous, and insular central urban green spaces remains unclear. This study, conducted in Changchun City, China, employed the SAR shape comparison method to assess the potential small island effect (SIE) in bird species within central urban green spaces. Morphological spatial pattern analysis (MSPA) was used to evaluate green space morphology, and Fragstats was applied to calculate landscape pattern indices. The boosted regression tree (BRT) model was employed to analyze how urban birds respond to changes in urban green space patterns through variations in species abundance. The results indicate a significant nonlinear relationship between bird richness and the area, shape, and configuration of urban green spaces. Area and shape are key predictors of bird abundance, with their relative contribution exceeding that of urban green space pattern indices. Larger and more regular urban green spaces support higher bird richness. Additionally, the central urban green space exhibits a relationship between bird abundance and the area, consistent with island ecology theory. The threshold for bird richness in the central urban area was found to be 20 ha, with a core green space proportion of at least 20 %. Resident birds are primarily influenced by area, cohesion, shape index (PARA), and core area proportion, while migratory birds are more affected by urban green space connectivity, the proportion of isolated islands and edges. This research provides a scientific framework for optimizing urban green space spatial patterns to enhance urban bird diversity.