Swans

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Swans are often a symbol of love or fidelity because of their long-lasting monogamous relationships.

See the famous swan-related operas Lohengrin and Parsifal. In the Irish legend The Wooing of Etain, the king of the Sidhe (subterranean-dwelling, supernatural beings) transforms himself and the most beautiful woman in Ireland, Etain, into swans to escape from the king of Ireland and Ireland's armies.

Swans feature strongly in mythology. In Greek mythology, the story of Leda and the Swan recounts that Helen of Troy was conceived in a union of Zeus disguised as a swan and Leda, Queen of Sparta.

Other references in classical literature include the belief that upon death the otherwise silent Mute Swan would sing beautifully - hence the phrase swan song, as well as Juvenal's sarcastic reference to a good woman being a "rare bird, as rare on earth as a black swan," from which we get the Latin phrase rara avis, rare bird.

(Source - Wikipedia)