Distributional and behavioral responses of the wintering Oriental Storks to drought in China's largest freshwater lake

Extreme droughts are increasing in frequency and severity globally as a result of climate change. Developing understanding of species' responses to drought is crucial for their conservation, especially in regions experiencing increased aridity. Although numerous studies have investigated birds' responses to drought, the emphasis has primarily been on landbirds. Drought can significantly alter the wetland environments that waterbirds inhabit, but the response of waterbirds to drought remains understudied. In this study, we surveyed the distribution and behavior of Oriental Storks (Ciconia boyciana) in Poyang Lake, which is the largest freshwater lake in China. Results indicate that drought-induced catchment areas at the lowest water level limited the total population size of Oriental Storks in the sub-lakes. Sub-lakes with large catchment areas at the lowest water level demonstrated a capacity to support a larger population of wintering Oriental Storks. Over time, Oriental Storks exhibited a gradual concentration in Changhu Lake, characterized by larger catchments, after resource depletion in sub-lakes with smaller catchments. Additionally, the duration of Oriental Storks' vigilance and moving behaviors decreased significantly compared with that observed before the drought. After the drought, Oriental Storks increased their foraging efforts, as evidenced by increased presence in deeper water and reaching their heads and necks into deeper water to forage, higher search rates, but lower foraging rates. In accordance with area-restricted search theory, reductions in habitat quality resulting from drought, including extensive fish die-offs, forced Oriental Storks to increase their foraging efforts. Sustaining a specific water area in sub-lakes during droughts can preserve resource availability, which is crucial for the conservation of Oriental Storks. Implementing measures such as water level control and micro-modification of lake bottoms in sub-lakes might mitigate the impact of drought on the piscivorous Oriental Storks.