Feathers are very important to birds. Apart from flight, they also help in insulation. They form a well-organized body-warmed layer of air close to skin. Feathers come in different shapes, colors and sizes. They are flight, contour, down, semi plume, filoplume and bristle. Before we learn about them, we should learn about the structure of a feather.
The structure of a feather is a more well-defined pattern which even helps identify the bird. From the central shaft which is stiff but flexible, there are fine filaments called barbs. The barbs in turn have a central shaft each. From these shaft, smaller ribs fringe outside called barbules. The barbules have tiny hooks that mesh with neighboring barbules holding the feather together.
The feathers on the wing and tail are called flight feathers. Body or contour feathers are like flight feathers but are loose and fluffy giving size and shape to the bird. The third type of feather is called filoplume. This feather is very small and has a thin and naked shaft with few barbs at the tip. Down feathers have little or no shaft, which is soft and fluffy. Bird nestlings are covered with down feathers and adults of many species have a warm undercoat of down. Down feathers provide extra insulation.
Bristle feathers are found normally under the mouth or around the eyes. These are very stiff ones with only a few barbs at the base. Semi plume feathers do not have well formed shaft or barbules which makes them rough.
Whatever be the type, birds tend to have fewer feathers in summer than in winter which when they actually need extra insulation against cold.