Bridging conservation gaps: Spatial differentiation of urban bird diversity between citizen science and field surveys in Hangzhou, China

Biodiversity monitoring serves as the cornerstone for developing effective conservation strategies. While Citizen Science Data (CSD) has emerged as a vital source of biodiversity information, the discrepancies between CSD and Field Survey Data (FSD) in characterizing species richness and identifying priority areas remain insufficiently explored. In this study, we conducted a comparative analysis between FSD and CSD collected from 2014 to 2024 in Hangzhou, China. The results indicated that: (1) Data characteristics exhibited significant complementarity. CSD demonstrated superior species detection capability, recording 473 species (97.32%), whereas FSD achieved higher spatial coverage (76.39%) with 362 species recorded (66.60%). (2) Distinct differentiation existed in community composition. Low community similarity was observed between the two datasets (Bray-Curtis similarity = 0.171), reflecting fundamental differences in the monitored bird communities. (3) Responses of species diversity parameters to human activity drivers were inconsistent. Generalized additive models revealed that FSD robustly captured the monotonic inhibitory effects of anthropogenic disturbance on diversity (Deviance Explained 0.115–0.229, most models P < 0.001); conversely, CSD exhibited pronounced observation biases in high-disturbance areas. (4) Spatial disparities were evident in priority area zoning. Zonation assessments showed that the Tier 1 priority areas identified by CSD were concentrated in urban cores and existing protected areas, with a protection coverage of 12.0%. In contrast, only 4.3% of the core areas identified by FSD were currently protected, with a spatial overlap of only 10.8% between the two datasets. Among bird guilds, waterbirds exhibited higher overlap (29.6%), while terrestrial birds (8.3%) and sedentary species (7.5%) showed significant divergence. In conclusion, our findings suggested that CSD-driven planning was susceptible to cumulative advantage effects, which tend to favor established hotspots, whereas FSD more effectively identified conservation gaps in remote forest regions. We recommend that while leveraging the advantages of CSD in low-cost, large-scale monitoring, FSD should remain the benchmark for ecological assessment. Integrating the conservation gaps identified by FSD is essential for enhancing the scientific rigor and effectiveness of biodiversity conservation strategies.