Thanks for being a frequent visitor to the site. As for the pen, are you absolutely 100% sure that the extra swan is a pen? Absolutely sure means DNA Sequencing or having an avian veterinarian sex the bird. You may think you have a pen, but the male bird may know more. If there is an extra male in the area, the male bird will chase it from the nesting area. He usually will not hurt a female. The female of the pair may also chase another female. She will not chase another male. Are you sure if it is the cob or the pen of the pair chasing?

The reason that this chasing may be occuring after all of this time is that the odd bird out may be getting enough courage to want to be a part of the pair and displace one of the mates. This probably will not happen if the pair has successfully mated, nested and produced offspring in the past. However, it can occur. If something bigger and better comes along, swans have been known to play the field during nesting season. So, the old adage that they pair for life is just that, a nice myth. Swans usually do pair for life. However, this pairing is totally dependent upon the species of swans (Whooper Swans have a 6% divorce rate) and the individual swan.

We would suggest that all swans come inside during the winter if your pond gets ice. Predators can access the ice and kill the swans. You may also get the swans trapped in the ice and they can drown or die from exposure. If these swans are captive (pinioned and cannot fly), then you need to bring them indoors into a safe secure pen such as a barn or other totally enclosed structure protected from the elements and predators. If this is not practical, you may need to at least bring in the odd swan or possibly find it a new home. Let us know. The Regal Swan