Managed marshes can be good alternatives to natural marshes as breeding habitats for birds

Loss of natural tidal marshes has caused rapid population declines for many bird species, raising the question about whether managed marshes can be used for bird conservation. Although many studies have indicated that managed marshes can provide a complementary habitat for birds, it is unclear how the breeding habitats provided by managed marshes compare with those provided by natural marshes. We compared habitat conditions (vegetation and food) and breeding performance of a common reed specialist, the Oriental reed warbler (Acrocephalus orientalis), in natural and managed artificial reed marshes (about 2 km × 5 km) at Chongming Dongtan, an estuarine wetland in China. We found that vegetation was denser and warbler food resources were greater in managed than in natural marshes. The density of breeding territories, nest density, clutch size, egg size, and fledgling number per nest were greater in managed than in natural marshes. Breeding failure was reduced in managed marshes because of a reduced risk of nest predation. However, the high nest position on the reeds in the managed marshes increased the risk of nest destruction by strong wind. The better breeding performance in managed than in natural marshes could be attributed to the following factors: the high and stable water level in the managed marshes increased reed growth and arthropod reproduction and decreased access by terrestrial predators; dense vegetation helped conceal nests from predators; and human activities in the managed marshes deterred nest predators. The results suggest that managed marshes can provide quality breeding habitat for the Oriental reed warbler and probably for other marsh birds and can therefore help compensate for the loss of natural marshes. The preference of the Oriental reed warbler for managed marshes largely depends on the suitable habitat conditions. The current study highlights the importance of maintaining a relatively high and stable water level.