Cob = male swan, Pen = female swan. The Bill Saunders COB Swan Call = The most realistic and easy blowing tundra swan ever created. The COB easily creates the woo and trill of the tundra swan. With a wide range of volume for getting attention of distant flocks and still being able to finish birds feet down in your decoys. Constructed of ivory acrylic and hand tuned to ensure each call is ready for the field. A must have tool for anyone targeting these big birds.