Swans are birds of the family Anatidae, which also includes 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. Swans usually mate for life, though 'divorce' does sometimes occur, particularly following nesting failure. The number of eggs in each clutch ranges from three to eight.
The word "swan" is derived from Old English swan, akin to the German Schwan and Dutch zwaan, in turn derived from Indo-European root *swen (to sound, to sing), whence Latin derives sonus (sound). (Webster's New World Dictionary) Young swans are known as cygnets, from the Latin word for swan, cygnus. An adult male is a cob, from Middle English cobbe (leader of a group); an adult female is a pen from the Welsh word for loud, pynne.
The legs of swans are dark blackish grey, except for the two South American species, which have pink legs. Bill colour varies: the four subarctic species have black bills with varying amounts of yellow, and all the others are patterned red and black. The Mute Swan and Black-necked Swan have a lump at the base of the bill on the upper mandible.
The Australian Black Swan (Cygnus atratus) has been noted for swimming with only one leg, the other leg being rotated over the body and tucked under its furled wings. Cygnets do this from a young age.
The fossil record of the genus Cygnus is quite impressive, although allocation to the subgenera is often tentative; as indicated above, at least the early forms probably belong to the C. olor - Southern Hemisphere lineage, whereas the Pleistocene taxa from North America would be placed in Olor. A number of prehistoric species have been described, mostly from the Northern Hemisphere. Among them was the giant Siculo-Maltese C. falconeri which was taller (though not heavier) than the contemporary local dwarf elephants (Elephas falconeri).
The supposed fossil swans "Cygnus" bilinicus and "Cygnus" herrenthalsi were, respectively, a stork and some large bird of unknown affinity (due to the bad state of preservation of the referred material). Anser atavus is sometimes placed in Cygnus.
The Coscoroba Swan (Coscoroba coscoroba) from South America, the only species of its genus, is apparently not a true swan. Its phylogenetic position is not fully resolved; it is in some aspects more similar to geese and shelducks.
Many of the cultural aspects refer to the Mute Swan of Europe. Perhaps the best known story about a swan is The Ugly Duckling fable. The story centres around a duckling who is mistreated until it becomes evident he is a swan and is accepted into the habitat. He was mistreated because real ducklings are, according to many, more attractive than a cygnet, yet cygnets become swans, which are very attractive creatures. 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.
In Norse mythology, there are two swans that drink from the sacred Well of Urd in the realm of Asgard, home of the gods. According to the Prose Edda, the water of this well is so pure and holy that all things that touch it turn white, including this original pair of swans and all others descended from them. The poem Volundarkvida, or the Lay of Volund, part of the Poetic Edda, also features swan maidens.
In the Finnish epic Kalevala, a swan lives in the Tuoni river located in Tuonela, the underworld realm of the dead. According to the story, whoever killed a swan would perish as well. Jean Sibelius composed the Lemminkäinen Suite based on Kalevala, with the second piece entitled Swan of Tuonela (Tuonelan joutsen). Today, five flying swans are the symbol of the Nordic Countries and the whooper swan (Cygnus cygnus) is the national bird of Finland.
In Latin American literature, the Nicaraguan poet Ruben Darío (1867-1916) consecrated the swan as a symbol of artistic inspiration by drawing attention to the constancy of swan imagery in Western culture, beginning with the rape of Leda and ending with Wagner's Lohengrin. Darío's most famous poem in this regard is Blasón - "Coat of Arms" (1896), and his use of the swan made it a symbol for the Modernismo poetic movement that dominated Spanish language poetry from the 1880s until the First World War. Such was the dominance of Modernismo in Spanish language poetry that the Mexican poet Enrique González Martínez attempted to announce the end of Modernismo with a sonnet provocatively entitled, Tuércele el cuello al cisne - "Wring the Swan's Neck" (1910).
Swans are revered in many religions and cultures, especially Hinduism. The Sanskrit word for swan is hamsa or hansa, and it is the vehicle of many deities like the goddess Saraswati. It is mentioned several times in the Vedic literature, and persons who have attained great spiritual capabilities are sometimes called Paramahamsa ("Great Swan") on account of their spiritual grace and ability to travel between various spiritual worlds. In the Vedas, swans are said to reside in the summer on Lake Manasarovar and migrate to Indian lakes for the winter, eat pearls, and separate milk from water in a mixture of both. Hindu iconography typically shows the Mute Swan. It is wrongly supposed by many historians that the word hamsa only refers to a goose, since today swans are no longer found in India, not even in most zoos. However, ornithological checklists clearly classify several species of swans as vagrant birds in India.
The ballet "Swan Lake" by Pyotr Tchaikovsky is considered among both the most important works of this composer and among the often-performed classics of ballet. It is partially based on an ancient German legend, which tells the story of Odette, a princess turned into a swan by an evil sorcerer's curse - to which were added similar elements from Russian Russian folk tales. Some major elements (girls turned to swans and living in a lake, and a hero falling in love with one of them) are also shared by the Irish Mythology story of Caer Ibormeith.
The 1994 American animated film, The Swan Princess, is also derived from the same ancient sources, featuring an evil sorcerer who kidnaps a princess named Odette and curses her so that she is a swan by day and a woman by night, until the prince comes to rescue her.
Today swans are used symbolically or as brands. The Sydney Swans AFL Team uses a swan as its club emblem/mascot, and Swansea City A.F.C.'s mascot is a swan called Cyril the Swan. Swan is also the name of a character in the film "The Warriors."
Carl Orff's cantata, Carmina Burana (and presumably also the collection of poetry upon which it is based) includes a text describing the roasting (and serving) of a swan as described from the swan's point of view.