If the swans have a black bill with yellow markings they are the Bewick Swans (Cygnus bewickii bewickki), if they have orange bills they are the Mute Swan (Cygnus olor) or more yellow with some black markings Whooper Swans (Cygnus cygnus).
Food, habitat, shelter and other resources may cause the swans to move into other areas including predators. The Regal Swan « Hide