Effects of high water levels on waterbird diversity at Wuchang Lake, a gate-controlled lake in the middle and lower Yangtze River floodplain, China

The natural hydrological rhythms of lakes play a crucial role in the aggregation of waterbirds. However, artificial controls of gate-controlled lakes alter water level fluctuations in the natural lakes and affect the diversity of waterbird communities. Wuchang Lake, a gated-controlled lake in the middle and lower Yangtze River floodplain, is an important wintering site for waterbirds on the East Asian–Australasian Flyway. Lake water level control during the wintering period in 2021–2022 was different than that in 2022–2023. We collected waterbird data from two wintering periods, based on functional alpha and beta diversity and waterbird functional groups, we analyzed the impact of water level regulation on wintering waterbird communities. By remote sensing data of foraging habitats we further analyzed the effects of changes in habitat structure to waterbird communities at different water levels. The results showed that during high lake water level, the numbers of deep water swimmers feeding on fish (G3) and swimmers feeding on seeds (G7) increased significantly, the number of large wading birds feeding on fish (G2) decreased significantly. And high lake water level decreased functional richness indices (FRic), functional evenness indices (FEve) and functional divergence indices (FDiv). Among them, in January and February 2023, the functional divergence indices significantly decreased. Functional beta diversity analysis showed that the total dissimilarity among communities decreased significantly in 2022–2023, with the functional nestedness component increasing significantly in October and February and the functional turnover component decreasing significantly in October, December, and February. Generalised linear mixed models (GLMM) showed that high lake level expanded the water area and favored the habitat of swimming birds, while decreased mudflat area, limiting the habitat space for wading birds. In contrast, lake water level decreased to increase the mudflat area and promoted the differences among communities. This study analysis a coupling relationship among water levels, habitats, and waterbirds, the results show that appropriate lake level regulation is an effective method to protect waterbirds. It provides scientific information for the lake wetland management and waterbird conservation.