Extract from the book Heracles:
[…] in the lake of Stymphalia there lived some hideous birds of prey which had laid waste the surrounding countryside. Their wings were of bronze, their beaks and claws of iron, and they were both immense and bloodthirsty. Neither man nor beast could approach the lake, for as soon as the birds saw either they would shower them with bronze feathers as heavy and sharp as arrows, then dive on their wounded victims and devour them. Such were the terrible Stymphalian birds, and, guided once again by Hera, Eurystheus commanded Heracles to destroy them.
The hero set off for the lake accompanied once more by Iolaus. As before, he was protected by the lion’s pelt, while the young man carried a huge shield. When they reached Stymphalia, everything was silent. The birds were nowhere to be seen. But on the ground there lay some large feathers, some sunk deep into the earth.
Heracles picked one up, looked at it with interest, weighed it in the palm of his hand and said:
“It’s made of solid bronze. What an arrow! Imagine what these can do when they fall like rain. But don’t worry; your shield is strong and all you need is a little care. And I have the lion skin, so nothing can harm me.”
The trouble was, all the birds were roosting in their nests and there was not one to be seen. Eventually, two did appear. They launched a few bronze feathers at random, but had no time to perfect their aim. Two of Heracles’ arrows sent them tumbling from the sky and they were swallowed by the waters of the lake.
But the problem was not to be solved by shooting down the odd bird or two as they appeared. The region had to be cleared of them forever, and report had it there were so many that they were beyond all count.
Also available in greek language under the title “Ηρακλής”.