Was the swan killed by the dog or was it taken to a rehab center to be returned later? Usually, the male does help protect the overall family, but the female can get along just fine without the male. As long as nothing happens to the female, the cygnets will do just fine with the female. Cygnets can feed on their own 24 hours after hatching. The only reason that they need their parents is for protection against predators and to learn how to be a swan. The Regal Swan