contour feather

Contour feathers are the medium-sized feathers that cover most of a bird's body, defining its external shape and streamlining it for flight. These feathers, made of keratin like reptile scales, also help waterproof the bird, with their lower parts often providing insulation.1234

Contour feathers grow in specific tracts on the bird's skin, separated by bare areas. Each feather has a central shaft (rachis) with branching barbs. These barbs have smaller branches (barbules) that interlock with hooks, forming a cohesive vane. The base of the feather may have a fluffy, unbranched section. Some contour feathers also have an aftershaft, a smaller, secondary feather growing from the base.23

Birds periodically shed and replace their contour feathers through a process called molting, typically once a year after the breeding season.23