My neighbour had most of his ducks killed by an otter sadly. His pond was part of a big ditch that ran through the farm which he had widened and dammed at one end. He put out a trap and caught it but another neighbour found it and released it as it's illegal to trap them (I think). it was definitley an otter that killed the ducks and not a mink, there's no mink up here to my knowledge but it's swarming with otters. Not a lot you can do about it if it does take one of your birds (not sure if you have ducks). They're usually not a problem having said that, and it's the only otter-related predation incident I know of in poultry circles.