After cleaning the Augean Stables, Eurystheus sent Hercules to defeat the Stymphalian Birds, man-eating birds with beaks of bronze and sharp metallic feathers they could launch at their victims; they were sacred to Ares, the god of war.
Furthermore, their dung was highly toxic. They had migrated to Lake Stymphalia in Arcadia, where they bred quickly and took over the countryside, destroying local crops, fruit trees and townspeople. Hercules 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. Hercules shook the rattle and frightened the birds into the air. Hercules then shot many of them with his arrows. The rest flew far away, never to return. The Argonauts would later encounter them.