We live on a very large pond on Long Island. We have a pair of swans and 4 cygnets, about 4 months old. Yesterday, two other swans (we call them intruder swans) came into the pond. Usually, the two parent swans are able to run off the intruders, although sometimes it takes them hours to do so. I say our swans chasing the intruders for some time before i left for dinner. Last evening, only the two intruder swans were there. No sign of our swan family. This morning, still only the intruder swans. I don't know where the family could go as the cygnets aren't flying yet. Surely the intruder swans couldn't have hurt the whole family? Any thoughts on what could have happened?