Drivers of waterbird communities and their declines on Yangtze River floodplain lakes

The seasonally flooded Yangtze Valley Floodplain wetlands of China are globally important for wintering waterbirds in the East Asian-Australasian Flyway. These birds have declined in the last 60 years, so understanding factors shaping waterbird distribution and abundance patterns is critical for their conservation. We applied linear mixed models to investigate the effects of climate, winter water area and inundation area (the difference between maximum flooded and winter dry season water area) on waterbird abundance and diversity at 72 lakes in 2005 and 2016. Neither winter water area nor climate featured in the best models, rather inundation area was the key determinant of waterbird abundance and diversity. Future water abstraction and land claim will therefore have greater impacts on waterbird abundance and diversity than likely climate change effects. Significant declines in waterbird abundance and diversity between 2005 and 2016 were not explained by modelled variables and there was no reduction in wetland inundation areas to explain these declines, confirming other factors were responsible. These potentially include declining wetland quality affecting carrying capacity (e.g. flooding phenology, disturbance, habitat loss and degradation, declining water quality caused by eutrophication and pollution) and/or factors limiting migratory waterbird populations at other stages in their life cycle elsewhere. The studied Yangtze lakes are amongst the best for wintering waterbirds and many are protected for their biodiversity, suggesting such protection cannot fully safeguard these internationally shared populations when threatened by other, currently unknown factors. This confirms the urgent need for more research to safeguard these ephemeral lake systems for their global biodiversity significance.