Hi John. Yes this is normal behavior. All species, especially their young are part of the food chain. If a swan parent is not observant, any predator such as turtle, egret, heron, owl, hawk, alligator, mink, fox etc., can kill the cygnets. If the swans are new parents, this predation is more likely to occur because the new parents do not know how to take care of the cygnets. As each year passes and with more practice, the swan parents will usually get better at protecting their young. The Regal Swan