Assessment of habitat supply and migratory waterbird demand under different autumn water drawdown regimes in Lake Poyang, China

• Water drawdown timing dictates slow (before 2003) or fast (after 2003) habitat succession modes. • Fast succession mode aligns better with geese overwinter rhythm in Duchang Nature Reserve. • The Theil index can clarify habitat and bird wintering “supply-demand” levels. • Integrating food availability into habitat quality is necessary for waterbird conservation. After 2003, changes in the ‘river-lake’ relationship between Lake Poyang and the Yangtze River led to rapid autumnal water drawdown, exposing mudflats and expanding grasslands. This resulted in a notable increase and concentration of the geese population, while the Grus leucogeranus (Siberian Crane) population remained stable but shifted towards artificial habitats. The study examined the interaction between hydrology, mudflats, vegetation, investigating habitat evolution through field studies and model simulations, and improving the Theil index to evaluate the dynamics between overwintering geese populations and habitat changes, using Siberian Crane as a comparative species. The results indicate that: (1) Compared to pre-2003 conditions, the area of sparse grasslands and shallow water bodies in the Duchang Nature Reserve significantly increased before early November. By early November, sparse grasslands in the Duchang Nature Reserve had peaked, increasing by almost 70 km 2 compared to the same period before 2003. (2) The Theil index effectively illustrates the supply–demand relationship between goose populations and habitat dynamics. Around 2003, the Theil index for the entire lake fluctuated between 0.05 and 0.25. However, in November before 2003, Duchang’s index surged to 0.8 (indicating a low match), attributed to changes in elevation exposure time within the 9–10 m range. Despite shallow water being suitable habitat, plant degradation led to inadequate food, prompting Siberian Crane to forage in nearby artificial habitats. (3) The normalization of drought heightens the risk of habitat supply–demand imbalance in Poyang Lake. By 2035, the conversion of mudflats to sparse grasslands and sparse grasslands to dense grasslands will accelerate. In response to river–lake changes, the optimal subsidence time for the 12 m water level should shift to around October 20, and the 9 m water level should drop in early November. Ensuring food supply in artificial habitats around the lake will become crucial.