Swans are birds of the family Anatidae within the genus Cygnus. The swans` close relatives include the geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini. Sometimes, they are considered a distinct subfamily, Cygninae. There are six or seven species of swan in the genus Cygnus; in addition there is another species known as the coscoroba swan, although this species is no longer considered one of the true swans. Swans usually mate for life, though `divorce` does sometimes occur, particularly following nesting failure, and if a mate dies, the remaining swan will take up with another. The number of eggs in each clutch ranges from three to eight.

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