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Many of the world’s lagoons and estuaries, representing the most important habitat for shorebirds, are increasingly degraded, often associated with dramatic declines in shorebirds, particularly in Asia. We investigated effects of hydrology on shorebird communities of two coastal lagoons of a Ramsar site in south-east Sri Lanka. One of the lagoons (Bundala) experienced natural water level fluctuations, while the other (Embilikala) had high stable water levels (>10 cm), maintained by inflows from irrigated agriculture. These inflows dramatically affected composition and abundance of shorebird communities and their prey. Tactile and visual foraging shorebirds were consistently more abundant on Bundala than Embilikala lagoon. Their feeding efficiency was significantly (50%) higher on Bundala, where large (500 μm) benthic prey were more abundant than on Embilikala. Contrastingly, small (60 μm) planktonic prey dominated the hydrologically stable Embilikala lagoon where pelagic foraging shorebird species dominated the shorebird community. On both lagoons, visual and tactile species foraged predominantly in shallow water (1–10 cm). Pelagic shorebirds also foraged in water depths >10 cm but 20% less efficiently than in shallower water. Effective shorebird conservation depends on reducing anthropogenic impacts that detrimentally affect functional processes and habitat value. The detrimental effect of altered hydrology on Embilikala lagoon could be reversed by diverting drainage water. Re-establishing a natural hydroperiod, would increase the productivity of the lagoon for foraging shorebirds. Restoration of shorebird habitat on this Ramsar site could also improve other ecosystem services such as fisheries and tourism. Changes to the hydrology of coastal lagoons elsewhere may be similarly affected.

As natural wetlands have disappeared around the world, artificial wetlands have increased. We found interesting differences in waterbird communities of two natural (Bundala Ramsar site) and seven artificial wetlands (irrigation tanks, salt ponds, rice paddies) in south-east Sri Lanka. Eight species exclusively used natural and one species artificial wetlands. Migratory species (shorebirds 64%, terns 47%) dominated species’ richness of natural lagoons, with densities of shorebirds 3–6 times greater than on artificial wetlands. Contrastingly, resident species (dabbling ducks, gallinules) contributed most to the diversity (59%) and density of waterbirds on artificial irrigation tanks. Cattle egrets dominated waterbird density (>70%) of rice paddies. Waterbird communities reflected physical and chemical character of wetlands: natural wetlands were shallow ( 1000 msm −1 ) compared to deep (>2 m) and freshwater (EC −1 ) artificial wetlands. Artificial inputs of water drained into the natural Embilikala lagoon changing its physico-chemical profile and disrupting the natural seasonal drying. Consequently its waterbird community was similar to artificial irrigation tanks, with shorebird species particularly impacted: densities half that of the other natural lagoon. Artificial salt ponds had similar physico-chemical properties to the natural Bundala lagoon and a similar waterbird community. Even though artificial wetlands supported waterbirds, they were not adequate replacements for loss of natural wetlands, favouring some species. Imposed hydrological stability degraded habitat quality for migratory shorebirds on one of our Ramsar site lagoons.