Homer offers one of the earliest descriptions of the Sirens in The Odyssey. It comes as Odysseus is leaving Hades, having gotten advice from just about all of the shades in his past. Circe makes it clear that there are still significant obstacles to his journey home and offers suggestions as to how to hear the "joy" of the Sirens' song without losing himself, his men, or the ship on the rocky shoals of Anthemoessa where a certain death awaits them. (You can find the text of this passage here Od. Book XII, lines 36-58, translation by Richard Latimore)
From SDR* on the "Siren problem:" There is no definitive evidence of their mythological origins which has allowed numerous and often contradictory representations of the Sirens. They do not seem to have a geneological tradition of a well-known or myth which has allowed variations of their form (birds, maidens, mermaids) and narrative meanings:
"It was precisely because neither the singer of the tales nor his audience knew much about the Sirens that Homer was able to turn them into such suggestive and ambivilent presences, endowed to the utmost degree with the power of vagueness. This is ultimately the reason why Homer chose characters like Circe and Kalypso from the vast pantheon of minor female divinities which populate Greek mythology, for it gave him the freedom he needed to suit them to his story rather than having to suit his story to a clearly defined, pre-existing character."
"One should keep in mind that the section of the Odyssey known as the Wanderings...probably drew on a vast array of folktale motifs which were adapted, combined or expanded in order to suit the Nostos ** and the character of Odysseus. One should not expect to find any direct correspondence between any given episode...and a particular type of folktale, but rather a fragmentation of various folktales and a condensation of different motifs into what became in the long process of oral composition and transmission -- a new organic tale." (Ok, this passage from SWR reads like my entire writing process! )
Connections to Circe, Goddess of Knots, Weaving, and Song.
"Circe's song and her weaving are an integral part of her character and denote her divinity: singing and weaving are her "habitual" mode of being; it is what she does when mortals are not caught in her web. There is no question that her song -- inextricably tied to her weaving--acts as a lure for her unsuspecting victims....Circe's song, like that of the Sirens, is a deceptive bait and that it represents an alluring and comforting temptation...the Sirens' song too is perceived as a feminine temptation....Throughout Greek mythology, magic song -- like weaving--apears to be a feminine prerogative, distinguishable from the more instrumental music of Orpheus or the narrative of the bard. Circe's song, like Kalypso's, is "song accompanied by the loom," and the medieval mermaid accompanying her song with a comb seems to be a descendant of this alluring combination. "
*De Sirenibus: An Inquiry into Sirens from Homer to Shakespeare by Seigfried de Rachewiltz, Garland Publishing, Inc.New York, 1987.
**And I like this reference to the word describing the theme of Odysseus' journey (and all others like him who combine heroism and a long sea journey.) "Nostos (Ancient Greek: νόστος) is a theme used in Greek literature which includes an epic hero returning home by sea. It is a high level of heroism or greatness. This journey is usually very extensive and includes being shipwrecked in an unknown location and going through certain trials that test the hero."