Do green roofs support urban bird diversity? Evidence from citizen science observations in Shanghai

Green roofs hold substantial potential for supporting urban biodiversity conservation. Researchers have investigated how multidimensional characteristics of green roofs (e.g., 2D spatial and 3D structural features) influence habitat suitability for urban avifauna. Nevertheless, reliance on labor-intensive field surveys for bird observations has confined research to finite scales. Additionally, oversimplified proxies for vegetation structure (e.g., coverage and average height) overlook the structural complexity jointly formed by vegetation with divergent morphologies. To address these limitations, this study integrates citizen-science bird data with remote-sensing-derived roof metrics in Shanghai, applying Negative Binomial (NB) and Zero-inflated NB models to investigate the associations between multidimensional roof features and bird abundance and species richness at large scales across multiple buffers, while accounting for adjacent greenspace features and observation effort. Results show modest improvements in model performance when roof- and greenspace-level variables were considered jointly, suggesting that roof attributes may provide limited but complementary explanatory information beyond surrounding greenspace conditions. Roof-level associations and cross-level interactions with both avian metrics were more evident within 125 and 250 m buffers, but their direction and magnitude varied across spatial scales and surrounding landscape context, indicating scale dependence and context sensitivity. Several roof factors, including NDVI, relative land surface temperature, woody vegetation cover, and 3D vegetation structure, exhibited nonlinear or conditional associations with avian metrics. In particular, associations involving roof 3D vegetation structure varied with roof floor, roof grass coverage, and surrounding vegetation cover. Our findings advance large-scale understanding of roof-bird associations and underscore the importance of jointly considering both horizontal and vertical structural elements within a multiscale framework. The study provides evidence-based insights for designing biodiversity-friendly green roofs that consider broader urban vegetation through context-sensitive, scale-aware planning strategies.