This youngster is more than ten months old and is raising his wings to another swan that had just landed on his patch of water. Most juveniles will have left their parents well before this time, but two years after this picture was taken, he was still residing within his parent's territory. The reason being that he cannot fly. If you look towards the bottom part of his wing, you can see that there's a small group of feathers missing.
Please click on the links below for some general information on mute swans.