The description "Cul de Canard" is attributed to 1950's era French tier tier Henry Bresson. In English Cul de Canard translates to "butt of the duck". However CDC Feathers surround the preen (uropygial) gland of many birds. This gland protrudes like a knob, from the back of the bird, slightly ahead of the tail. Waterfowl preen, recondition, and waterproof their feathers with oil secreted from their preen glands. As the size of the bird increases, so does the size of the feathers. While the natural oils in the feather assist in repelling water, it is the structure of the feather itself which gives it buoyancy.