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Large animals including waterbirds are traditionally considered passengers in wetland ecosystems and used as indicator, flagship or umbrella species in wetland conservation, but whether they are drivers of wetland ecosystem patterns and dynamics is poorly understood. Combining a field experiment in a tidal flat in the Yangtze estuary and a global meta-analysis, we tested the hypothesis that waterbirds exert top-down control on wetland macrofauna. Waterbird exclusion more than doubled the abundance of grazing crabs in our field experiment but did not affect other macrofauna. Conversely, excluding grazing crabs to simulate above-current levels of waterbird predation increased macrofauna abundance and biomass and decreased their diversity, ostensibly by allowing the establishment of habitat-engineering plants otherwise eliminated by crab grazing. Meta-analysis of 135 tests revealed that waterbirds had negative, positive, or neutral effects on macrofauna, with an overall significantly negative effect. This finding was evident across different seasons, wetland types and macrofauna classes and was largely based on tests from coastal rather than inland wetlands in Europe and Americas and none in Asia and Australasia. Our results suggest that the roles of waterbirds in wetlands are more diverse and profound than currently recognized and that their driver roles in shaping wetland ecosystems warrant incorporation into conservation decisions. [ABSTRACT FROM AUTHOR]

Exposure to pollutants is a potentially crucial but overlooked driver of population declines in shorebirds along the East Asian-Australasian Flyway. We combined knowledge of moult strategy and life history with a standardised sampling protocol to assess mercury (Hg) contamination in 984 individuals across 33 migratory shorebird species on an intercontinental scale. Over one-third of the samples exceeded toxicity benchmarks. Feather Hg was best explained by moulting region, while habitat preference (coastal obligate vs. non-coastal obligate), the proportion of invertebrates in the diet and foraging stratum (foraging mostly on the surface vs. at depth) also contributed, but were less pronounced. Feather Hg was substantially higher in South China (Mai Po and Leizhou), Australia and the Yellow Sea than in temperate and Arctic breeding ranges. Non-coastal obligate species (Tringa genus) frequently encountered in freshwater habitats were at the highest risk. It is important to continue and expand biomonitoring research to assess how other pollutants might impact shorebirds., (© 2024. The Author(s).)