In reply to elsewhere:
I remember a picnic by a lake a few years back... 4 of us sat down eating, and Mr & Mrs Swann swam over with their fairly grown up brood, got out of the river and came and sat all round us. was a bit nervy, but they were fine, and we stayed calm and avoided sudden movements and all was well so we stayed put and occasionally fed one of the Signets a morsel or too from our plates (I say that - it wasn't voluntary)
About half an hour later some dozy woman wanders towards us with a dog off the lead, and everything goes batshit crazy... Daddy swan is suddenly 6ft high, flapping wings and hissing, Mummy swan just went for the Dog and got a good chunk of it, and the signets basically tried to get in the middle where we were sat.
After everything had calmed down, half our pic nic was in the lake, there was signet shit everywhere, a wounded dog, and a demented woman complaining that Swans should be banned because they hurt her dog. Needless to say she got a lecture about keeping her mutt under-control near wildlife