A stable isotope approach to determine herbivory diets of wintering geese at Dongting lake, China

Abstract

East Dongting Lake Nation Nature Reserve at China is listed as a Ramsar site due to its global significance in migratory water bird conservation, especially for geese. For example, more than 90% of East Asian population of the vulnerable Lesser White-fronted Goose (Anser etythropus) (LWFG), and large numbers of Bean Goose (A. fabilis) (BG) and Greater White-fronted Goose (A. albifrons) (GWFG) overwinter here every year from October to next March. However, the habitat and food quality of the wintering geese are threatened by hydrological alternation due to the operation of the Three Gorges Dam. Understanding the diets of these geese is fundamental for their conservation.

We used stable isotopic ratios of the body tissues (feather and blood) of three predominant goose species (i.e. LWFG, BG and GWFG) and their potential diet items (six grass species), and applied SIAR mixing models to quantify the contribution of different food items to the diet of geese. The results showed that δ13C values of blood sample were significantly different from feather, and the difference was consistent for the three geese species. These results indicated clear dietary shifts from their breeding ground to wintering ground at Dongting Lake. The blood δ13C values of the three geese show no significant difference (ANOVA, p = 0.265) suggesting their diets are similar in Dongting Lake. The δ13C and δ15N values of blood were enriched predicted ways than diets. Multiple-source mixing calculation (e.g., SIAR) indicated that no single plant is contributed heavily to the diet of LWFG rather the mean contribution of plants ranging from 16% to 17% indicating that the geese had no preference for a particular plant. The findings highlight the importance of systematic approaches to manage the reserve.