What is the Central Cylinder of a Bird Feather?

Birds have various feather types to keep them warm and dry and to help them fly. They replace these feathers sometime in the year in a process called molting. As new feathers grow, they start out as simply central cylinders. These grow longer and develops feathers. Central cylinders' purpose change as feathers matures, but all feathers have these cylinders.

  1. Shaft and Quill

    • Often referred to as the shaft, the center feather cylinder is technically called the rachis. The end that attaches to the bird's skin, which is typically the thickest area of the shaft, is known as the quill. This widest end functions as the firm base that holds the feather stiffly; the feather becomes more flexible as the shaft narrows.

    Feather Types

    • All feathers have central shafts, but not all feathers are created alike. Flight feathers, which usually are the largest of a bird's feathers, have thick shafts with smooth feathers branching out from each side. Down and semiplume feathers have narrower shafts, and the feathers are softer and not as tightly formed as flight feathers. These are more fluffy, and they provide insulation to keep the bird dry. Contour feathers tend to be fluffy at the bottom, with more structured shape at the top and central shafts that are more flexible than those of flight feathers. These feathers help protect the bird from the elements.

    The Central Cylinder

    • The wider base and thinner tops of feathers, especially flight feathers, serve a couple of purposes. The base helps keep the feathers firmly connected to the follicles in the bird's skin, at least until it's time to molt. The shafts are made of keratin, a lightweight material similar to that of your fingernails. As it narrows, it flexes more, which is essential during flight. A feather that doesn't flex slightly with wind currents can break. Flexing feathers help provide lift and allow birds to change directions easier without breaking.

    Pin Feathers

    • When a bird molts, or loses old feathers, new feathers replace the old ones right away. These start out as pin feathers, which are basically the hard shafts growing out of skin follicles. They are often dark because they are filled with blood; the feathers are growing inside the shaft, so they need nutrients from the blood to complete the transformation. As the stiff shafts get closer to their final lengths, the blood vessels shrink back into the skin, and the outer layer of the shafts start to flake off so the fluffy feather branches can bloom free. A line of keratin -- the quill and rachis -- remains in the center to give the feather its structure.