How old were the baby swans? If they were less than 8 months of age, they usually will not survive in any habitat as they will be prey for predators. Even if they are adults, if predators are present, the swans will usually not survive. If there are bite marks, it means that a predator took a nip and released the dead swan. The predator just did not finish the job by eating the carcass. The second swan probably saw the attack and is now petrified to go back into the water. The young bird probably needs to be taken back to the farm and raised with its parents or more juvenile swans until it can learn how to protect itself from predators. The Regal Swan