A fake beak is an item used in the Eagles' Peak quest. Along with the eagle cape, it is needed to make a convincing disguise to prevent players from taking damage from the mother eagle. It is made by taking Yellow dye and Swamp tar to the Fancy Dress Shop in Varrock. If players lose it and need another one, they can get it from the Fancy Dress Shop.
Although the beak should be in the place of the mouth, in game it sits above the nose.