I didn't know about this until a friend informed me. I Googled and found this:

December 5: Faunus
A Roman festival in honor of Faunus, the consort of Fauna (see December 1). Faunus is the rustic god of woods and flocks, a Roman Pan, the original Green Man. Faunus was the son of Picus, whom Circe turned into a woodpecker for spurning her love. According to Robert Graves, the tomb of Faunus on Crete bore the inscription "Here lies the woodpecker who was also Zeus." Pan, the Greek god of the wild woods, and Hermes were also both associated with woodpeckers. Graves says all three are rain-making shepherd gods.

Graves, Robert, The Greek Myths, Penguin 1955