Well the swans were purchased a year ago from a man who sells them specifically to keep the geese away. A builder in a subdivision purchased them and asked that I take care of them. They've recently started to become very aggressive towards them and have been doing a great job of not letting them get into the pond at all. I can only assume one is male and one is female. The knob is larger on one. The same one appears to have a thicker neck. Other than that, I have no idea. I've added a picture which obviously doesn't show them too well, but I can try to get a better one. Thanks for your help.

Carol