Since we do not know where you are located, we cannot determine if this is actually a captive swan vs wild swan. If this is a rental area/homeowner's association, then someone probably brought a swan(s) to the area. You might ask around to see if someone actually owns the swan or introduced more than one earlier.

If initially, there was more than one swan, you might inquire as to what happened to the other swan(s). If something occurred such as an environmental catastrophe, i.e., spill, leakage, dumping, algae outbreak, then this would certainly determine if another swan could be safely introduced. Conversely, if it was a predator that killed the other swan(s), you would definitely not want to introduce any other swan(s).

Finally, captive or wild, some swans will not re-pair (accept another swan). You would have to do several things before introducing another swan.

1. Find out the above circumstances of ownership, and reason that only swan is in the area.

2. Determine if you need a license or permit to introduce/keep swans in your area.

3. Capture the swan, take it to a licensed avian/waterfowl veterinarian and determine if it is male or female.

4. Males will not accept another male, and a female may or may not accept another female. This introduction of another swan of the same gender could result in serious injury and even death to one or more of the swans.

5. If you introduce a swan of opposite gender and the swans produce cygnets, you may need a breeder's license and you will also be responsible for all veterinary care, documentation, pinioning (surgical amputation of a portion of the wings so that they cannot fly and must be performed at 1-3 weeks of age. Otherwise, you will need anesthesia which will not only be more costly, but can kill the swans. At 1-3 weeks of age, nerve, bone and tissue has not fully developed so this is considered a relatively minor procedure. After that age, it becomes a very difficult procedure and hard on the swans).
You will also be responsible for finding the cygnets a new home once the mating season begins as the parents will chase the cygnets from the pond. This creates stress on the cygnets at 6-8 months of age, leaving them open to predation and illness.

6. If you choose to introduce another swan, you will need to build a pen enclosed top to bottom so that predators cannot access the swan. The pen will need to be 1/2 in water and 1/2 on land with a feeder inside. There should be no sharp abrasive areas and a zero entrance to the pond is required so that no injury can occur to the swan's feet or legs. You will also need to check wit the homeowner's association to see if they need any permit for the pen to be erected in the pond.

Because of all of these issues, we would suggest that you first find out if the swan is being supplementally fed, if it has a good environment and if so, then we would leave everything as is and let the swan continue with a good life. Swans can do just fine without other swans. Geese, ducks and other waterfowl will keep them company. The Regal Swan