There are no guarantees that the remaining swan will take on a new mate. Because the pair were originally male and female, a same gender mate will probably not work as the swans may seriously injure or kill each other. Before introducing a new swan, the remaining swan must be sexed. Another real concern is if you need a breeder's license in your state to have opposite gendered swans that can produce offspring. What are you going to do with juvenile swans from each breeding, season as the parents will chase the juveniles from the habitat prior to the next nesting season? The cygnets (baby swans) must be pinioned (rendered unable to fly-as many state wildlife entities will kill a flying swan). Hence, the need for a breeder's license. Additionally, you will need to house the new swan in a pen (1/2 in water 1/2 on land with feeder inside). The pen needs to be erected so that the swan is totally encased in the pen so that predators cannot dig under the pen or climb into the pen. The swan needs to stay in the pen for approximately two weeks to allow the swan to acclimate to you, the habitat and the old swan and observe any sign of aggression from either swan. Again, with all of this preparation, the swans still may not accept each other and you may have to find the new swan a good home. Most swans do very well without a mate and will usually accept other waterfowl such as ducks. We would suggest that you get some ornamental captive ducks for companionship for the swan. You won't have to worry about cygnet's, swan breeder's license and other issues with the introduction of another swan. The Regal Swan