I was taking pictures at the John Heinz Wildlife Preserve in Philadelphia, PA. There was a pair of, what I believe are, juvenile, dark-morph Mute Swans. They were very pretty and standing very near to the boardwalk that crosses the freshwater marsh. Perhaps there was a log just submerged for them to stand on. They were focused on preening and not at all concerned with the visitors crossing the boardwalk. It was a unique opportunity to take pictures at a very close range.