There looks to be a great disparity in growth between all the cygnets. Age, i.e., first or last (runt) hatched, individual attributes and gender will determine size and growth rates. If the cygnets are normal, no illness or abnormality, they all should catch up in size and be within the same general range within 6 months. Again, being a runt or female could still keep do them slightly smaller, but within the general range at 6 months of age. The Regal Swan