Urban forests are key habitats for maintaining urban biodiversity, and the vocal dynamics of their avian communities are infl uenced by both seasonal variation and urbanization disturbances. However, the cross-seasonal relationships between the acoustic characteristics of avian communities, urban forest phenology, and surrounding environments remain poorly understood. To address this, passive acoustic monitoring technology was employed to collect continuous data over a 10-month period in four typical urban forests in Shenzhen. By calculating the Acoustic Complexity Index (ACI) and the Normalized Diff erence Soundscape Index (NDSI) to quantify avian sound diversity, this study investigated dynamic changes in this diversity across seasons and dietary guilds, while assessing the infl uence of multi-scale environmental factors, including urban forest vegetation phenology and surrounding urbanization intensity. The results reveal signifi cant seasonal variation and dietary diff erences in avian soundscapes within the urban forest. Omnivorous birds exhibited signifi cant seasonal variation, with their ACI peaking in summer; insectivorous birds maintained high levels of vocal complexity throughout the year, whereas the acoustic contribution of carnivorous birds remained consistently low. Peak timing of the NDSI diff ered among dietary guilds: omnivorous and insectivorous birds dominated the soundscape in the spring, whereas carnivore-insectivore birds exhibited an inverse pattern, with peak acoustic activity occurring in the summer. Interaction eff ects confi rmed that the infl uence of season on avian sound diversity varied by dietary guild. Analysis using Generalized Linear Mixed Models (GLMMs) further clarifi ed the environmental drivers. Specifi cally, night light intensity (average radiance) signifi cantly increased the ACI, while the fl owering index (bloom) signifi cantly reduced the ACI. Meanwhile, the Normalized Diff erence Vegetation Index (NDVI) showed a marginally signifi cant negative trend on the NDSI. Furthermore, seasonal eff ects were evident: summer signifi cantly increased the ACI, whereas winter signifi cantly decreased the NDSI. Dietary eff ects indicated that avian diets diff ered markedly in their acoustic contributions: compared with insectivorous birds, the ACI of carnivorous and carnivore-insectivore birds was signifi cantly lower, whereas carnivorous and nectarivorous birds exhibited highly signifi cant positive contributions to the NDSI. The results provide a scientifi c basis for the ecological management of avian sounds in urban forests, emphasizing that maintaining and restoring functional food webs and optimizing the internal structure of urban forests are central to future urban biodiversity conservation planning.