Feathers are of course essential for flight, but they also perform a host of other important functions such as maintaining the internal temperature of birds which, like mammals, are warm-blooded animals. In fact, the plumage plays the same role as the coat, protecting the body against cold, wind, rain, etc. Thus, the down insulates against the cold, while the covert feathers, present all over the body, protect the bird from bad weather. Some types of feathers are only intended for flight, such as rectrices, tail feathers that serve as a rudder.
The colors of the plumage also play an important social role since they allow the bird to camouflage itself in its environment and thus escape from predators. The colored hues also provide information on the age and sex of the individual, especially during courtship, and are used to defend the territory. Perhaps you have already observed a male robin puffing out its orange chest to intimidate its potential competitors…