There is a legend, stemming from ancient myth, that swans sing an exquisitely beautiful song just before dying. There’s no truth to it, but that’s the legend and the origin of the phrase. From Ovid’s Metamorphoses (14:426-430):
ultimus adspexit Thybris luctuque viaque fessam et iam longa ponentem corpora ripa. illic cum lacrimis ipso modulata dolore verba sono tenui maerens fundebat, ut olim carmina iam moriens canit exequialia cycnus.
(Tiber was last to see her, as she lay down, weary with grief and journeying, on his wide banks. There, she poured out her words of grief, tearfully, in faint tones, in harmony with sadness, just as the swan sings once, in dying, its own funeral song.)
In English, literary allusions to the legend date back to Chaucer’s Anelida and Arcite, c. 1374:
Þe swane...Ageynist his dethe shall synge his penavnse.
(The swan...against his death shall sing his penance.)
The phrase swan song itself appears in the early 19th century. The English phrase is a calque of the German Schwanengesang, which was the name of a posthumous collection of Franz Schubert’s music, published in 1828. The English phrase first appears a few years later in Thomas Carlyle’s 1831 Sartor Resartus:
The Phoenix soars aloft,...or, as now, she sinks, and with spheral swan-song immolates herself in flame.
(Sources: Oxford English Dictionary, 2nd Edition; Ovid, Metamorphoses (Kline) 14: 397-434: The Fate of Canens, the Ovid Collection, Univ. of Virginia E-Text Center, University of Virginia.)
Copyright 1997-2015, by David Wilton