The Stymphalian birds were a group of monstrous birds in Greek mythology. They devoured humans, and had beaks made of bronze. Their feathers were sharp and metallic and could be thrown against their prey, while their dung was poisonous. They were created by the god of war, Ares, and were hunted down by wolves; to escape, the birds reached the lake Stymphalia in the Greek region of Arcadia, where they reproduced quickly and destroyed farmlands and the countryside.
Killing the Stymphalian birds was the sixth task that was appointed to the demigod hero Heracles during the myth of the Labours of Heracles. King Eurystheus asked him to kill the birds, hoping that the hero would fail. The land around the lake was a marsh and Heracles could not step safely there in order to reach the nests. So, the goddess Athena, wanting to help him, gave him a rattle that the blacksmith god Hephaestus had specifically made for this occasion. Heracles used the rattle and scared the birds which abandoned their nests and started flying. He then shot most of them down using arrows which he had previously dipped into the poisonous blood of the monster Hydra. The remaining birds flew away, abandoning Arcadia and reaching an island in the Euxine Sea. They were encountered later by the Argonauts.