In Russian mythology and folklore, Sirin and Alkonost are mythological creatures with the head of a woman and the body of a bird. Sirin symbolizes sorrow, suffering and despair, while Alkonost happiness and hope. There are other bird creatures in Slavic mythology, including Gamayun (bird of prophecy), Obida (bird of misfortune), Firebird or Zhar-Ptitsa (bird of paradise), and Finist (bird of war).
Both chimeras have unusually beautiful voices. Although she sang to the saints foretelling future bliss, Sirin’s song was dangerous for humans. Hearing it, they’d forget about everything, try to pursue it, and eventually die. Hearing Alkonost’s exquisite, hypnotizing songs made people want to listen to nothing else.
Although the origins of these myths are not clear, they are thought to have their origins in Greek mythology. Sirin is most likely based on the Greek myth of the sirens, whose singing enticed sailors, causing their ships to perish in the sea. Alkonost is probably based on the Greek goddess Alcyone, daughter of Aeolus, who was changed into a kingfisher. [Source]