Thirdly, feathers control what a bird looks like. A plucked chicken or pigeon looks very different to a fully feathered one. Feathers supply the bird with colours allowing for camouflage and secondary sexual characteristics and sexual display. Consider the tail feathers of a peacock. Feathers evolved from reptilian scales, and in fact birds still possess scales in the lower parts of their legs and feet.
Feathers grow quickly and are then sealed off at the base.
Once fully developed a feather is a dead matter like your finger nails, though there are still muscles attached the base of each feather which can move each individual feather to help keep it in place. Feathers do not last for ever, they become worn and battered and are replaced regularly by the bird once or twice a year depending on species. Feathers have a basic form of a central hollow supporting shaft called a 'rachis' and a number of fine side branches. These side branches have even finer sub-branches in contour feathers. The side branches in these are called barbs and are linked together by a set of barbules and their hooklets sometimes called 'Hamuli'.