swans

[jane4464]

do swans often kill ducks or ducklings,

[wildwood]

Swans get pretty stroppy in the breeding season and have even been known to attack humans. Ducks are competition for food and - in their mind - must be eliminated from their territory.

[heathfield]

I've seen a swan deliberately drowning a lone duckling. It's reported that they'll kill ducks and attack all water birds, even geese, and cause other birds to abandon their nest sites.

[WendyS]

Yes I too have seen a swan kill a lone duckling which was straggling a little further behind in the convoy behind its mother. It was a quick and viscious attack and nothing the mother duck could do to defend it.