Construction of artificial wetlands is one of the measurements to provide alternative habitats for compensating loss of natural wetlands. Although many studies compared difference of natural and artificial wetlands in supporting waterbirds, it’s still unclear the function of artificial wetlands in supporting saltmarsh breeding passerines. In this study we compared breeding ecology of Oriental reed warblers Acrocephalus orientalis in natural reed beds on tidal marsh and artificial reed beds, which is constructed by enclosing original tidal marsh invaded by exotic Spartina alterniflora, in the Yangtze estuary, China. Spartina alterniflora was removed and planted reed instead in the artificial wetlands. Affected by tidal rhythm, natural tidal marsh was periodically submerged by tidewater while artificial wetlands kept stable water level during the study period. We compared the territory time, nest density, food abundance (individual density of arthropod collected by sweeping method), and growth rate of the nestlings. Breeding success and reasons of breeding failure were monitored using automatic cameras. We tested whether artificial wetlands are good alternatives to natural tidal marsh for the breeding of saltmarsh birds.
Results/Conclusions
Reed density and food abundance were higher in artificial than natural wetlands. Oriental reed warblers firstly took artificial wetlands as nesting sites, and nest density was higher in artificial than natural wetlands. Egg mass of birds did not significantly differ between natural and artificial wetlands, and growth rate of nestlings was similar between the two wetland types. Nest predators included mammals, snakes, crabs, and cuckoos, the nest parasites. In natural tidal marshes crabs (Chiromantes dehaani) were the major nest predators. They can climb on reeds and ate eggs or killed nestlings in the nests. In contrast, crabs were only occasionally recorded in artificial wetlands, which might be related to that crabs avoided stable water level in artificial wetlands. As a consequence, Oriental reed warblers had higher breeding success in artificial than natural wetlands. This study indicated that artificial wetlands with stable water level provide suitable breeding habitats for Oriental reed warblers by enemy release effects. Effective management on water condition is important to maintain high breeding success of saltmarsh birds in artificial wetlands.