Once the cygnets are old enough to explore, the parents will take them further up or down the river to introduce them to their surrounding habitat. This is probably what occurred. A couple of the swans may have decided to come back to their original nesting area since it is beginning of the migration period. If they get bored, or the food resources are lessened, they will go to find other areas to forage. There is even the possibility that these two swans are not even related to the original family, just young swans out exploring their habitat.

If you are concerned about the family, you might contact Wendy Hermon at Swan Lifeline in Eton, to see if she has had any rescues or other problems in the area. She would be the one that would be contacted if something goes wrong in the area with swans. The Regal Swan