Sorry to hear about your loss. The most important consideration is to protect the male so that he does not face the same fate. Did the male swan see the female killed? If so, he obviously knows she is not coming back.

Most male swans who have lost their mate are usually not interested in another mate. See how he progresses, wait a couple of weeks/months to see how he is reacting. If he is acting normal and does not seem to miss the mate, you can opt to either leave him alone or get him a mate.

If you choose to get a mate, wait until after nesting season so that they have about a year to get used to each other before trying to nest and raising cygnets. When introducing the female, place her in a pen (half in the water and half on the bank with a feeder. This will allow her time to acclimate to this new pond and he and she can get used to each other without direct contact. If the male shows aggression, then, you do not want to introduce her directly on the pond as the male my hurt her. If there is no sign of aggression, you can introduce her onto the pond after about 2 weeks. The Regal Swan