The evil chicken head is an item that can be obtained from offering bird's eggs to the shrine in the Woodcutting Guild. It is part of the evil chicken outfit. There is a 1/300 chance of obtaining a piece of the outfit.
If the "Flap" emote has been unlocked from the Stronghold of Security, when wearing all the pieces of the set, players can do an enhanced "Flap" emote where their character lifts off the ground slightly as if flying.