C.D.C. is an abbreviation of the French term Cul De Canard which roughly translated means from the rump or butt of the duck. As the description implies, these are the feathers that surround the preen gland on the back of the bird slightly ahead of the tail. Ducks use secretions from this gland to condition and waterproof their feathers. As a result the feathers surrounding the preen gland are of great value to fly tyers wanting to add buoyancy to their flies.
Generally speaking, there are two different types of C.D.C. feathers. The first is the plume or what is sometimes referred to as an oiler puff. These small feathers are ideal for use in midge patterns, small dry flies, spinners, and emergers.