For those readers who may not be familiar with the term, "creche", it is the zoological term for raising young by adults which are not their parents or providing a nursery (day care) type setting.

This would be a highly unusual behavior for swans as most adult swans will chase, severely injure or even kill cygnets that are not part of their own family.

Swans are extremely territorial and know exactly how many cygnets they have as well as recognize them from another family of cygnets. The situation you describe was probably a parent of the five cygnets just hanging out with them for protection.

If the adult swan was trying to catch up to the cygnets to give chase or was actually chasing, then it was an adult swan from another family chasing the cygnets from his/her area. The Regal Swan