Spatial Patterns of Avian Stable Isotopes Reveal Ecological Impacts of Climate and Land-Use Change

Stable isotope analysis provides an integrated approach to tracing animal dietary sources and trophic structures while being sensitive to environmental and land-use changes. It therefore serves as a powerful tool for evaluating the interactions between animal resource use and environmental variation. However, spatial isotopic patterns across large numbers of species and their responses to climate change and anthropogenic activities remain poorly understood. Here, we applied a Bayesian mixed-effects modeling framework and isotopic niche analyses using feather samples from 766 individuals of 200 bird species in southwestern China (1958-2007) to assess how ecological, climatic, and anthropogenic factors jointly shaped the spatial patterns of feather carbon (δ^{1 3}C) and nitrogen (δ^{1 5}N) isotopes across taxa. The results revealed that the δ^{1 3}C and δ^{1 5}N values differed markedly across dietary and migratory guilds, highlighting distinct strategies of resource use and trophic organization among species. The feather δ^{1 5}N values increased with increasing pasture coverage, suggesting a potential elevation of the baseline δ^{1 5}N in grazing landscapes. δ^{1 5}N also showed a positive trend with precipitation, indicating that wetter environments may be associated with elevated nitrogen isotopic baselines. Furthermore, isotopic niche analyses revealed that farmland habitats exhibited broader isotopic niches than forest habitats, especially for herbivores, highlighting the influence of agricultural expansion on resource use. Overall, this study demonstrates how ecological traits, climatic factors, and human disturbances jointly shape avian trophic patterns across taxa and scales, providing new insights into trophic structure and the consequences of land use change for ecosystem function across diverse ecosystems.