Ask the Swan Specialist
Date: 24 June 2017
Is this the first cygnet that the "royal couple" have had? If so, then these are very young parents that have no clue how to take care of a cygnet. Geese on the other hand will actually accept other goslings and sometimes ducks and swans (hence, The Ugly Duckling story).
If the parents are not inclined to go find the cygnet, and the cygnet is not actively looking for its parents, then we would suggest to leave well enough alone. If the cygnet were to return to the parents without the parents actively looking for it, then the cygnet could be abandoned or chased by the parents so that it could become so stressed that it could be affected by illness, dehydration, starvation, injury, etc., to the point of death.
At least the goose parent will teach the cygnet how to be a wild bird, recognize and escape predators and basically, learn how to be a bird. It will also learn to how to search for food, bathe, preen and other necessities for survival. Again, this is not the worst possible scenario for the swan. He/she will do just fine.
Should the parents begin to look for the bird, (which we doubt because separation for any significant amount of time usually causes the parents to abandon the offspring), then the cygnet may be successfully reunited. The Regal Swan