National Checklist Time Series Reveal Structured Distributional Knowledge Accumulation in Chinese Birds

Aim Newly documented records are widely used as historical evidence for species redistribution, especially where continuous monitoring is unavailable. However, they are often summarized as range expansion or directional shifts, without testing whether they deviate from random additions to incomplete biodiversity baselines. Here, we ask whether newly documented bird records reveal structured distributional knowledge accumulation, shaped by prior distributions, species traits and habitat context. Location China. Taxon Birds. Methods We compiled seven national bird checklists spanning 1955 to 2023 and analysed 2258 newly documented subregional records. Using nullmodel‐based metrics, we compared the proximity and northward displacement of new records with random expectations. We then related these spatial patterns to species traits and tested whether new records occurred in land‐cover contexts matching species' primary habitat preferences. Results New records accumulated unevenly across taxa, time and zoogeographical regions. They occurred significantly closer to prior distributions than expected, and this proximity was stronger in species with restricted distributions and narrower habitat breadths. Migratory species were distributed farther north than expected under the null model during most of the study period, especially among species with broader distributions and greater ecological flexibility. While resident species were generally distributed farther south than expected. Habitat analyses further showed that new records were more often located in land‐cover contexts matching species' primary habitats, both in current landcover composition and temporal land‐cover change. Main Conclusions Long‐term changes in documented bird distributions in China cannot be reduced to simple range expansion or poleward displacement. Repeated national checklists reveal spatial, trait and habitat patterns in new records, highlighting a structured process of distributional knowledge accumulation in an incomplete biodiversity baseline. Our framework helps distinguish random additions to incomplete biodiversity baselines from structured distributional knowledge accumulation, especially where continuous standardised monitoring is limited.