More than likely this was a cygnet from another family. He was being taught to go home and not get into other swan families' habitat. The only other possibility would be if there was something wrong with the young bird and it was being chased from the area. Swan parents don't want a predator to follow sick or injured young to the rest of the family. If the bird was sick, the parents do not want it to spread the disease to the rest of the family or flock. The last possibility is that it was misbehaving and the parent was disciplining the youngster. Just because you did not see the cygnet when you returned, does not necessarily mean it was actually abandoned or lost. It may have been in the area just not visible. The Regal Swan