Gizmo

Feathers experience wear and tear and get replaced annually in a process called molting.  Since feathers are critical for flight, thermoregulation, weather protection, and camouflage, birds usually don’t shed all of their feathers all at once.  It can take several weeks to finish.  You may see scraggly birds but hardly ever bare birds in the wild!   Old feathers fall out in a fairly predictable sequence and new ones start growing out.  The new ones are encased in a thin sheath of keratin to protect the feather as it is growing.  They sort of look like pins growing out of the skin and are called pin feathers.  They are also called blood feathers because there is an active supply of blood to deliver nutrients to the growing feather.  The blood supply is cut off when the feather is fully developed.