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Thanks for your answers, wildwood - some of my fish are 5LB+ ghost koi, so hopefully the kingfisher won't take them on! Didn't realise they would take fish up to their own length though and its a lot prettier than the flippin heron that actually did almost clean the pond out a few years back!
lindapinda - i'll have a look at that link, yes I do feel very lucky, its only an occasional visitor, but even so, I couldn't believe my eyes the first time I saw it sitting on a post by the pond!