As long as the runt is eating, there is nothing anatomically wrong or he is not ill, is keeping up with the parents and the parents are still looking after it, then he has a great chance of growing up although he still may remain a little smaller than the other swans. We have actually seen runts grow up to be larger than the rest of the siblings. It totally depends on his health and the parent's continual care. Should he stop keeping up with the family, he will be abandoned and be very susceptible to predation. The Regal Swan