You would need to capture the bird and find out the gender by taking her to a veterinarian.

In most states, captive swans are considered non-native (which is an argument that many dispute and we will not get into at this time), but they are not supposed to be allowed to fly and start a feral population. Because the owner did not pinion (render the swan permanently unable to fly), he could possibly face a fine if the state wildlife officials find out about the escape. Note, some wildlife officials will shoot the bird out of the sky, fine the owner for each day it flies if they find out that the swan can fly.

The best thing to do would be to enhance her to come to you and get friendly by feeding her. Hopefully, she would get close enough for you or the previous owner to capture and return her to the rest of the group from which she escaped and keep her confined.

There are no guarantees that she or he will take a mate and you may need to have a permit to take on another swan. You may even need a permit to have a pair of swans that can mate and produce offspring, hence a breeder's license. If you get a swan of the same gender and the swan that you now have is an older swan, a same gender swan can result in both swans being seriously injured or even killed as they will usually not take a same gendered swan as a mate once they get older.

So, you will need to find out about permits by contacting your local wildlife officials. The Regal Swan