Rapid urbanization has become one of the most pressing environmental challenges of the 21st century, posing severe and increasingly complex threats to avian diversity across global metropolitan regions. To develop scientifically robust and practically effective conservation strategies, it is essential to systematically clarify both the direct and indirect mechanisms by which multifaceted urbanization processes affect urban avian diversity patterns and population dynamics. Guangzhou, a rapidly expanding megacity in southern China characterized by high-density urban development, was selected as a case study. An innovative methodological framework was employed, integrating advanced Structural Equation Modeling (SEM) with the Walktrap community detection algorithm. This analytical framework was used to systematically examine the complex, multi-dimensional mechanisms by which various urbanization factors influenced avian species diversity and abundance. The findings revealed: (1) Through extensive field surveys combined strategically with data mining from citizen science networks, the research documented a substantial total of 41,346 birds belonging to 174 species spanning 17 taxonomic orders. Ecological guild analysis indicated a marked dominance of Passeriformes (songbirds) within urban bird communities; specifically, Passeriformes accounted for 96 species, representing approximately 55.17% of overall species richness. This notable taxonomic bias towards small-bodied species characterized by behavioral plasticity underscored the relative rarity of apex predators and large-bodied specialist birds, reflecting clear ecological filtering processes occurring in contemporary urban habitats. (2) Advanced SEM analysis identified distinct structural variations between urbanization's ecological impact pathways classified as "linear transmission" and "network transmission." The species richness impact model revealed clearly structured transmission dynamics described as a "unidirectional-cascading multi-parallel pathway," signifying hierarchical susceptibility patterns across various avian species groups. In contrast, the abundance impact model exhibited intricate network characteristics with complex feedback mechanisms and synergistic interactions involving multiple urban stressors. (3) Within high-density urban areas, urbanization demonstrated pronounced bidirectional influences, generating multidimensional structural patterns with concurrent negative and positive pathways. Nevertheless, negative impacts predominated significantly, evidenced by the cumulative negative pathway coefficients far outweighing positive effects. This quantitatively affirmed the net adverse consequences of urbanization on avian population sustainability. (4) The investigation conclusively showed that urbanization exerted ecological impacts through various concurrent mechanisms rather than simplistic linear relationships, highlighting significant distinctions in both intensity and regulatory complexity between direct and indirect impacts. These insights guided the formulation of an innovative dual-track conservation strategy, integrating both "species diversity protection" and "population abundance maintenance," organized as a multi-level intervention approach extending from landscape-scale planning to targeted species-specific management practices. Collectively, these results provided a robust theoretical framework and methodological direction for the effective conservation of avian diversity within high-density urban landscape.