Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini.

[5] The genus Cygnus was introduced in 1764 by the French naturalist François Alexandre Pierre de Garsault.

[6][7] The English word swan, akin to the German Schwan, Dutch zwaan and Swedish svan, is derived from the Indo-European root *swen(H) ('to sound, to sing').

Its disappearance is thought to have resulted from extreme climate fluctuations or the arrival of superior predators and competitors.

[16] There is some evidence that the black-necked swan is migratory over part of its range, but detailed studies have not established whether these movements are long or short-range migration.

In the water, food is obtained by up-ending or dabbling, and their diet is composed of the roots, tubers, stems and leaves of aquatic and submerged plants.

[16] A familiar behaviour of swans is that they mate for life, and typically bond even before they reach sexual maturity.

Trumpeter swans, for example, can live as long as 24 years and only start breeding at the age of 4–7, forming monogamous pair bonds as early as 20 months.

[24] The pair bonds are maintained year-round, even in gregarious and migratory species like the tundra swan, which congregate in large flocks in the wintering grounds.

Unlike many other ducks and geese, the male helps with the nest construction, and will also take turns incubating the eggs.

[30] Evidence suggests that the genus Cygnus evolved in Europe or western Eurasia during the Miocene, spreading all over the Northern Hemisphere until the Pliocene.

Given the biogeography and appearance of the subgenus Olor, it seems likely that these are of a more recent origin, as evidenced shows by their modern ranges (which were mostly uninhabitable during the last ice age) and great similarity between the taxa.

The Illustrious Brotherhood of Our Blessed Lady, a religious confraternity which existed in 's-Hertogenbosch in the late Middle Ages, had "sworn members", also called "swan-brethren" because they used to donate a swan for the yearly banquet.

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.

Jean Sibelius composed the Lemminkäinen Suite based on the Kalevala, with the second piece entitled Swan of Tuonela (Tuonelan joutsen).

Based on the 1875–76 score by Pyotr Ilyich Tchaikovsky, the most promulgated choreographic version was created by Marius Petipa and Lev Ivanov (1895), the premiere of which was danced by the Imperial Ballet at the Mariinsky Theater in St. Petersburg.

[51] In Latin American literature, the Nicaraguan poet Rubén 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).