The issue is what you have in the way of swan gender. You may have an actual mating pair (male and female) and regardless, they will chase two swans of the same or opposite gender. You need to have all the birds sexed to find out exactly what you have. You may have all the same gender which will still cause problems during the nesting season. During the mating and nesting season, male swan hormone levels skyrocket. You may have Dr. Jekyll today and tomorrow have Mr. Hyde. There is no telling. Some swans will go about their business, a little chasing but nothing overly aggressive. If this is occurring, you must pen all the swans. If you leave two out and two penned, you are still going to have a king of the mountain situation. If you do not have a pen (1/2 in the water and 1/2 on land completely enclosed top to bottom so predators cannot access the birds, feeder inside and zero entrance), then you can use a shed, garage, barn, etc. Gather all swans and keep them indoors for a couple of days together. Monitor them closely. Things should begin to settle, especially in the next week or so when the hormones settle. We mainly call this defensive behavior vs aggressive as the swans are just being swans and marking their territories. If the defensive behavior still continues, you may need to find another home for two of the swans. If you need to find them a good home, please contact us and we will try to assist you. The Regal Swan