Feathers are actually complex branched skin appendages. A feather develops from a follicle, which is found in the dermal and epidermal layers of the skin. To me, the way the bird’s skin cells are able to develop a large, primary feather, complete with shaft, barbs and barbules is one of those miracles of nature. While a feather is actively growing from the follicle, there is one artery and one vein that runs through the feather to support the growth. Once the feather has reached the full size, the blood supply is no longer needed and the vessels shrivel up. However, the follicle maintains a blood supply in the skin.
A newly emerging feather is called a pin feather. As the new feather emerges from the follicle, there is a sheath covering and surrounding the new feather. You will notice a silvery, shiny sheath on the new pin feathers. These are most obvious on the top of the head and can appear as little silver spikes. Some birds are experts are removing their own sheaths with either the beak or by scratching at the feathers with foot. Birds housed together often preen and groom each other to remove each other’s sheaths. Many owners enjoy preening their pet birds by gently rolling the pin feathers through their finger tips, assisting in the removal process. Some of the bird’s follicles and pin feathers are very sensitive and the bird may resist any help in removing the sheaths.
In some cases, the entire sheath or a portion of a sheath might not flake off in a timely fashion, and can become retained. If this occurs, when the sheath is removed, it might result in an abnormal appearance to the feather, which can be mistaken for a stress bar. Some birds seem to ignore sheaths on the long tail feathers and might require help in removing them by gently rolling the feather between finger tips or by gently pinching the shaft.
If a feather is plucked, instead of falling out normally, some of the dead cells of the follicle remain attached to the plucked feather. Cells in the follicle are also damaged or destroyed by the plucking process, as well. When the feather is plucked out, bleeding occurs into the empty follicle and stops when a clot forms in the follicle. Unless the bird has liver damage, psittacosis or another disease that results in clotting problems, the amount of bleeding that occurs when plucking a feather out is inconsequential.
However, if a blood feather is plucked out, there is a chance that the bleeding can become more significant. Also, damage to the follicle can also be more serious. Repeated plucking of a feather from the same follicle can eventually result in the follicle becoming damaged to the point that it can no longer replace a feather. We have all seen chronic feather-picking birds with a naked chest and no visible feathers, and no signs of active follicle activity. This is from continual plucking resulting in follicles no longer being able to replace feathers normally. For this reason, I always think twice before plucking any feather from a bird’s body, especially the large primary and secondary wing and tail feathers.