Black-Necked Swans are a southern hemisphere swan species and do not do well in northern climates unless they are kept indoors during the winter months. You might want to ask around to see if someone might have lost the birds or contact your wildlife officials to see if they might know of a swan owner in the area that may have lost the birds. If no such owner exists, someone may need to try and capture the birds (if they can fly this may not be possible), and see if they can offer a good safe home with accommodations for winter weather. The Regal Swan