Newly hatched ducklings are a target for most predators. I have seen pike take them, Carrion crows will eat one or two and kill any others they can get, Herring Gulls will just swallow them one after another. This is the reason ducks lay so many eggs and hatch so many young. As for Cygnets, Swans are far more protective than ducks of there young and due to there larger size tend not to suffer the mortality rate of ducklings, Hence fewer eggs and young hatched,