“ They'll strip everyone to bones if we don't drive them away! ”
–- Annabeth, talking about Stymphalian Birds.
In Greek mythology, Hercules' sixth labor was to beat the Stymphalian birds. He did it by using brass bells given to him by Athena to scare them into the air, and when the birds took off from the swamp that they rested in, Hercules shot many of them down with his bow and arrows. Although some escaped, they never returned to the area that they were terrorizing.
Stymphalian birds attack Camp Half-Blood during a chariot race, and are able to enter the camp's borders due to the fact that Thalia's tree is dying. Percy Jackson and Annabeth Chase used Chiron's music from a portable stereo to confuse the birds, so Apollo's cabin could shoot them down. Tantalus apparently then cooked and served them for the winning camper's prize-dinner.
Stymphalian birds attack the Argo II, but Festus torches them.
Stymphalian birds have sharp Celestial Bronze beaks that can tear through flesh. They also have the ability to use their feathers like arrows, being able to shoot them down at their prey from above.