Unfortunately, this is something that is seen frequently in not only swans, but all forms of wildlife. Swans will attack babies that are not their own. Nature ensures that a particular species survives even if it means destroying other species in the area to prevent competition for food and other habitat resources.

A prime example are certain bird species that lay their eggs in other birds' nests. The invading species' eggs and young are much bigger than the young of the birds that build the nests and therefore, mom bird feeds the bigger young (invader) and their own young starve. Again, nature works in a different manner than humans are accustomed to ensure survival. The Regal Swan