The study investigates the impact of urban green space design on avian communities, focusing on the area-heterogeneity trade-off. The authors examined six European cities with varying climates to understand how land cover heterogeneity and patch size affect bird species richness. They found a significant area-heterogeneity trade-off, where increasing heterogeneity reduces patch size. However, land cover heterogeneity did not significantly affect total avian richness within green areas. Instead, both heterogeneity and patch size positively influenced the richness of urban avoider species, which are more sensitive to urban environments. The study also highlighted the importance of maintaining large, diverse green spaces and heterogeneity in the urban matrix to conserve avian richness. The findings suggest that urban planners should prioritize large, heterogeneous green areas to protect bird species, especially those with high urban avoidance traits.The study investigates the impact of urban green space design on avian communities, focusing on the area-heterogeneity trade-off. The authors examined six European cities with varying climates to understand how land cover heterogeneity and patch size affect bird species richness. They found a significant area-heterogeneity trade-off, where increasing heterogeneity reduces patch size. However, land cover heterogeneity did not significantly affect total avian richness within green areas. Instead, both heterogeneity and patch size positively influenced the richness of urban avoider species, which are more sensitive to urban environments. The study also highlighted the importance of maintaining large, diverse green spaces and heterogeneity in the urban matrix to conserve avian richness. The findings suggest that urban planners should prioritize large, heterogeneous green areas to protect bird species, especially those with high urban avoidance traits.