More than likely, the three swans were two parents and a juvenile female which the parents dropped off to find a mate and a new habitat. Your male swan may or may not accept her as a mate as male swans usually do not re-pair if something happens to their mate. However, even though he chased the young female he still allows her to stay in the habitat. This is a good sign. Even if he does not take her as a mate, he may still allow her to stay in the habitat and eventually she will learn from him. She will eat as nature will not allow species to starve just because they do not have a mate. You may not see her eating, but she will eat throughout the day and night. Both swans should be just fine as a male will not normally attack a female swan. The Regal Swan