Find the new swan a good home and let the original bird live alone on its lake. Same gender pairing usually works when cygnets are young and have never had a mate. There are no guarantees that any swan will re-pair after losing its mate. Do you know how or why the swan died, i.e., age, illness, disease, poisoning or predation. If he did not died from age but rather something else, the same thing could happen to its mate and and other introduced swan. The Regal Swan