In Greek mythology, the Stymphalian Birds lived by Lake Stymphalus in Arcadia. They had migrated there to escape a herd of wolves. They bred quickly and took over the countryside. They had sharp metallic feathers that they shot at people, claws of brass they used to eviscerate flesh, and they destroyed local crops and fruit trees. Some sources claim these were the same birds that attacked the Argonauts.
The forest around Lake Stymphalus was very dense and too dark to see much. Athena and Hephaestus helped Heracles kill the birds as the sixth of his Twelve Labours. Hephaestus made huge bronze clappers to drive the birds into flight, and Heracles shot them with his arrows or a catapault. The birds that survived never returned to Greece.
Origin
When the sun is in the sign of Sagittarius, the constellations Lyra, Aquila, and Cygnus, rise. Aquila is an eagle, and Cygnus is a swan, wheras Lyra is a lyre, but originally Lyra was a vulture, gaining the lyre over time, and eventually becoming it. At this time of year (i.e. during Sagittarius), the evenings darken, and thus the bird constellation were considered evil. Also around this time, the rain season in Greece starts, creating swampland from previously drier areas.
To the Greeks, Sagittarius (the constellation) had various different interpretations, including as a rattle. Also, the next constellation on the sun's transit after the birds is Delphinus, whose myth concerns the saving of Arion, a court musician, by a dolphin. Herakles scared off the Stymphalian Birds (who lived in a swamp) with noise, and firing an arrow at them (the constellation Sagitta, an arrow, is aiming towards Aquila).
