While some versions have depicted Sirens as woman-headed birds, other versions depict them as mermaids.

The sirens of Greek mythology first appeared in Homer’s Odyssey, where Homer did not provide any physical descriptions, and their visual appearance was left to the readers’ imagination. By the 7th century BC, sirens were regularly depicted in art as human-headed birds. Apollonius of Rhodes in Argonautica (3rd century BC) described the sirens in writing as part woman and part bird. They may have been influenced by the ba-bird of Egyptian religion. In early Greek art, the sirens were generally represented as large birds with women’s heads, bird feathers and scaly feet. Later depictions shifted to show sirens with human upper bodies and bird legs, with or without wings. They were often shown playing a variety of musical instruments, especially the lyre, kithara, and aulos.

The tenth-century Byzantine dictionary Suda stated that sirens had the form of sparrows from their chests up, and below they were women or that they were little birds with women’s faces.

Originally, sirens were shown as male or female, but the male siren disappeared from art around the fifth century BC.

Some surviving Classical period examples had already depicted the siren as mermaid-like. The sirens are described as mermaids or “tritonesses” in examples dating to the 3rd century BC, including an earthenware bowl found in Athens and a terracotta oil lamp possibly from the Roman period.

The first known literary attestation of siren as a “mermaid” appeared in the Anglo-Latin catalogue Liber Monstrorum (early 8th century AD), where it says that sirens were “sea-girls… with the body of a maiden, but have scaly fishes’ tails”.

☞ https://en.wikipedia.org/wiki/Siren_(mythology)