Either of these scenarios is plausible. You need to capture both swans and have an experienced waterfowl/avian veterinarian check the swans for gender. If they are older swans, probing may suffice, but a feather sample submitted for DNA sequencing, especially for young birds will give you a reliable answer. In any case, the injured swan needs to be examined by a veterinarian to ensure he is ok and does not have internal injuries. A male swan will usually go about his life without a mate once he loses his mate. He will be just fine and does not need a mate. If the new bird is a male, this pairing will not work and one or both birds could get seriously hurt or killed. This can hold also true for a female swan introduced to an older swan's habitat. They both need a visit to the veterinarian and separated to determine the problem. If it is a predator issue, both birds need to housed indoors nightly in a structure free from being accessed by a predator. You want to make sure the predator cannot enter the shelter from climbing over, digging under or entering directly. The Regal Swan