[Objectives] Investigating the dietary information and trophic niche of animals has great significance for assessing individual quality and formulating conservation and management strategies. The Crested Ibis (Nipponia nippon) is an endangered species. Since 10 individuals were reintroduced to Deqing, Zhejiang in 2008, the Deqing captive-bred population has grown to 382 individuals and has now become an important source base for the Crested Ibis reintroduction program in southern China. However, due to the lack of effective technical methods and evaluation indicators, the trophic status of the captive-bred population in Deqing has not been assessed. Consequently, the formulation of conservation management measures lacks a scientific basis. The isotopic niche, based on stable isotope analysis, provides a novel approach for quantifying animal diets and trophic levels. [Methods] In this study, feather samples were collected from captive-bred Crested Ibis populations in both Deqing and Yangxian (10 samples per site) in 2022 and 2023. By measuring the δ¹³C and δ¹⁵N values in the feather samples, we quantitatively evaluated the trophic niches and their differences between the captive-bred populations in Deqing and Yangxian. [Results] The Deqing population exhibited a similar range of δ¹³C values, a significantly higher mean δ¹³C value (t = 12.94, df = 17.72, P < 0.001), and slightly lower range and mean of δ¹⁵N values (W = 0.94, P > 0.05) in comparison with the Yangxian population (Fig. 1). Furthermore, the Bayesian standard ellipse area (SEA_B) of the Deqing population was smaller (1.19‰² vs. 1.77‰²), and the isotopic niches of the two populations were significantly separated without overlap (Table 1, Fig. 2). These findings indicated that the captive-bred population in Deqing occupied a lower trophic level in their diet, which may contribute to the poorer physical condition. Furthermore, we found that the trophic niche of captive-bred populations was significantly lower than that of wild populations. This suggests that increasing dietary diversity during acclimation may improve reintroduction outcomes. We recommend enhancing environmental enrichment and management within the acclimation cage, optimizing feed formulations and loach variety selection to diversify food sources, thereby improving the overall quality of captive-bred populations. [Conclusion] Overall, this study demonstrates that δ¹³C and δ¹⁵N values for feathers, along with isotopic niche, can serve as quantitative indicators for assessing the dietary information of captive-bred Crested Ibis populations, thereby providing a scientific basis for informing conservation and management strategies.