it is getting close to another mating season and the adults are beginning to let the cygnets know that the time to leave the area, find a mate and start their own family is drawing near. Penning may help, but once mating, nesting and new cygnets arrive the territorial behavior will only increase. You may have to find the cygnets a new home away from the breeding pair. Unfortunately this will be an ongoing problem each year. The Regal Swan