Here's some bit of mythology Naoko-sensei used that concerns Siren. It's quite intresting to know and it's long....you've been warned.
The Sirens
In Greek mythology, Sirens are creatures
with the head of a female and the body of a bird 0_o They lived on an island called
Sirenum Scopuli (three small rocky islands). They could sing very well and with the
irresistible charm of their song they lured sailors to their deaths on the rocks
surrounding the island.
The Argonauts escaped the Sirenas because when he heard their song, Orpheus immediately
realized the danger they were facing. He took out his lyre and sang a song so clear and
ringing that it drowned the sound of the Sirens' lovely voices. On another journey the
Argonauts passed the island once again, Odysseus had the sailors stuff their ears with
wax. He had himself tied to the mast for he wanted to hear their beautiful voices. The
Sirens sang when they approached, their words even more enticing than the melody. They
would give knowledge to every man who came to them, they said, ripe wisdom and a
quickening of the spirit. Odysseys' heart ran with longing but the ropes held him and the
ship quickly sailed to safer waters. He was thus saved.
Homer mentioned only two sirens, but later authors mention three or four of them. They were regarded as the daughters of Phorcys, or the storm god Achelous. According to Ovid, they were nymphs and the play-mates of Persephone. They were present when she was abducted and because they did not interfere, Demeter changed them into birds with female faces.
Well, we can all see the Siren connection but we can't link this to the bird-women connection. Does that thing on Siren's earrings remind you of a wing? Fish fins don't usuallt look like that.
Mermaids
A Mermaid is a marine/sea creature with
the head and upper body of a beautiful young maiden and with the lower body of a fish. She
can be found in seas and lakes, or lying on a rock and combing her hair with one hand
while holding a mirror in the other. Mermaids sometimes foretell the future and are often
accompanied by seals (then how come Siren doesn't have a guardian seal? lame
question.....).
According to a myth, they lure sailors by singing and with lovely music (again, the music
theory). They live in a kingdom on the bottom of the sea, and it is there where they take
their prisoners to. From this story, the fear amongst the sailors grew and they thought
that by seeing a mermaid that would cause bad luck: it could predict death by drowning
(lovely, it's her job!)
The belief in mermaids is not limited to a few countries, but there are tales from all
over the world (in India, for instance, there are the Apsara, beautiful water nymphs, and
Japanese mermaids are all evil). However, most of those tales were told by sailors who
"saw" them on their long journeys. The idea of mermaids and mermen (the male
equivalent of a mermaid) could be based on creatures from Greek and Babylonian mythology:
Sirens and Tritons of the Greeks, and the fish gods, who were half human and half fish,
from the Babylonians.
Japanese Mermaids
Japanese mermaids, who are known as "ningyo" are in no way similar to those you find in Never-Never land (heh...Perter Pan). Instead they are bad omens, and seeing one means that a war is coming. They don't really have a very nice appearence and are typically depicted as a fish (with a long long tail) with only a human head which cries pearls instead of tears (can those tears signify the pearl necklace Siren wears?). A woman who can catch and eat a Ningyo gains eternal youth and beauty, if a man eats it he will die. They are described to have sharp teeth, claws and all that (those are for self defence). All really ugly, since most...if not all Japanese ghosts/monsters look horrible. Think of those kappas and one footed, one eyed, long tongue thingies ew....Thank goodness Naoko-sensei did the total opposite and did not make Siren look so hideous!
Someone (sorry...I deleted your email by accident and forgot who you were!) told me that there's a story called Mermaid's Forest but the one I managed to get info on was Mermaid's Scar (Ningyo no Kizu) are they the same series? The story makes use of this ningyo lengend and their mermaids aren't so revolting.
most of the mythology information from Pantheon.org