In Greek mythology, the Stymphalian birds (Greek: Στυμφαλίδες ὄρνιθες, Stymphalídes órnithes) were man-eating birds with beaks of bronze and sharp metallic feathers they could launch at their victims, and were pets of Ares, the god of war. Furthermore, their dung was highly toxic. They had migrated to a lake in Arcadia to escape a pack of wolves, and bred quickly and took over the countryside, destroying local crops, fruit trees and townspeople.
After cleaning the Augean Stables, Eurystheus sent Heracles to defeat the Stymphalian birds. Heracles could not go too far into the swamp, for it would not support his weight. Athena, noticing the hero's plight, gave Heracles a rattle which Hephaestus had made especially for the occasion. Heracles shook the rattle and frightened the birds into the air. Heracles then shot many of them down with his poisoned arrows. The rest flew far away, never to plague the marshes again. Heracles then brought some of the birds he had killed to Eurystheus, who then sent Heracles to capture the Cretan Bull. The surviving birds made a new home on an island in the Euxine Sea. The Argonauts would later encounter them there.