No, many swans can inhabit one body of water. If you consider two primary examples, The Thames River in England as well as the Abbotsbury Swannery in Abbotsbury Swannery. There are thousands of swans in these areas. Yes, they are territorial, especially during mating and nesting season. But, they will claim a certain area of the river or fleet as their own and mingle with people who feed them along the banks. In private settings and smaller ponds, if the swans are very young (under year of age) and have lived on the water since hatching and have lived among each other and if there is an ample supply of food, nesting, etc., they will get along. They will still chase each other during nesting and mating season and you may have to pen them until the cygnets reach approximately 5 months of age so that they can escape any feather nipping, but they should do just fine. The cygnets will eventually be chased from the pond by their parents at approximately 8-10 months of age, but by that time, each should learn which territory is someone else's etc. The Regal Swan