Feather Growth: How do feathers develop?

Feathers are dead structures that cannot repair themselves when damaged. Because a healthy and functional coat is critical to survival, each year birds shed their old feathers and then grow a whole new set. This moltingmolt:in birds, the process of losing and regrowing feathers on a regular cycle process is a carefully timed affair in which feathers are shed and regenerate in turn over a period of weeks so the bird can maintain its protective outer layer and ability to fly. Once the new set of feathers has matured, molt is complete and new growth only occurs before the next molt cycle when feathers are accidentally lost.

The growth process

Feather growth stages illustration by Andrew Leach
A close look at feather growth reveals how these intricate structures form.

  1. Each new feather grows from a small outgrowth of skin called the papilla.
  2. As feathers mature, their tips get pushed away from the papilla, where the newest parts of the feather form. Like human hair, feathers are youngest at their base.
  3. The feather’s structure develops as proteins are laid down around the surface of this bump of skin. It’s here that the branching patterns form by smaller branches fusing at the base to make thicker ones—barbulesbarbule:barb-YOOLone of the secondary branches off a feather barb fuse into barbsbarb:one of the main branches off the central shaft of a feather and barbs fuse into a rachisrachis:RAY-kissthe stiff central shaft of a feather from which barbs branch.
  4. As the feather grows, it stays curled in a tubular shape around the papilla until it is pushed away from the growth area.
  5. A protective sheath maintains the feather’s cylindrical shape until it starts to disintegrate near the tip, allowing the mature part of the feather to unfurl.
  6. The sheath falls off and the growth process is complete.

Once the feather unfurls, its interlocking structure is fully formed. Throughout the year, the bird maintains its mature feathers through regular care, or preeningpreen:using the beak to maintain the health and structure of feathers. Whenever the barbulesbarbule:barb-YOOLone of the secondary branches off a feather barb become disturbed, the bird uses its beak to carefully guide them back into place. By the following molt season, many of the bird’s feathers have experienced enough wear and tear that preening can no longer maintain their structure. Fortunately, during molt the bird grows a completely new set.

Osprey Loses Primary
Osprey losing primary feather photo by: Laurie-B


Further Learning

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