Are you absolutely sure that this is the male bird? We have seen male birds completely leave the parenting to the female and go off for some time before returning later. Usually, the males do not primarily raise the cygnets. They support the female by protecting the family and will patrol the habitat and surrounding areas which is why they go away for some time. However, having said this, there is the possibility that this bird took over the parenting if something did in fact happen to the female.

Usually, the cygnets will stay with the parents for approximately 8-10 months of age. Once they begin to turn white, the adults will chase them from the habitat prior to the new breeding season. The Regal Swan