Loch of Harray Swans

This black swan has been here for some years but I was surprised to see it associating very closely with a family of mute swans. Mutes can be quite aggressive, one had dissuaded me from sitting on a lochside bench earlier, yet here was a bird close by the cygnets. I know that various ducks, like eider, will form creches of ducklings, but only after posting the shot on wildlife pages was I told that swans will sometimes 'foster' other swans young. It seems that the black swan was even seen helping incubate the eggs!