Looking in a mirror and seeing another bird may cause the bird to think there is a competing male or a companion female. In any case, this does not necessarily mean that the swan is lonely.

Now, having said this and since you have a female, the problem is the introduction. You cannot just drop another swan into the habitat of a swan and expect them to accept each other. You will need to build a pen (totally enclosed top to bottom so that predators cannot dig under or climb over into the pen) in the male swan's pond. The pen should be 1/2 in water and 1/2 on land with a zero entrance so that the swan cannot hurt her legs or feet. A feeder should be placed in the pen. The female swan should be kept in the pen for approximately 1.5-2 weeks.

Monitor the swans to ensure there is no defensive/aggressive behavior on the male's part. This formal introduction will allow each swan to get to know each other on the male's pond, will expedite the acceptance process if it is going to occur, will allow the female swan to get used to her new habitat, accept you as her swan keeper and your feeding system. After two weeks, release the female onto the pond and see if the male accepts her and does not exhibit any aggressiveness or chase her.

Always keep some type of rescue device (boat, kayak, etc.) nearby to rescue her if the male suddenly turns on her. This rescue equipment will also help you should one of the swans get injured or ill and you need to capture them. The pen can be used for this same purpose or veterinary care. So, once the pen is built, you can keep it for emergency needs. It should be approximately 8 feet in width and 12 feet in length. If there is aggressive behavior after the penning process, then you need to find the female a new home. The Regal Swan