One of the most distinguishing features of birds is the presence of feathers. Feathers come in a variety of shapes, colors and sizes. Here are the different types of feathers.
FEATHER TYPES
There are five major types of feathers. Contour feathers cover the body and streamline the bird. Examine a contour feather. Notice the rachis, vane, and calamus.
Semiplumes are found hidden beneath the contour feathers and along the edges of feather tracts. They are downy in appearance but have a long central rachis. They insulate and increase buoyancy in water birds.
Filoplumes are very small, highly modified feathers. They are associated with contour feathers and are positioned nestled among them. They are used to sense if the contour feathers are properly arranged.
These can be found on the ground or in a nest and can help determine the types of birds in the area, even if you can't see them.Down feathers provide insulation. The barbs are not connected and therefore do not form a vane. A short, vestigial rachis is present and it is shorter than the attached barbs. This feather provides insulation and is especially abundant on waterbirds.
Bristles are the fifth feather type. This feather has a very stiff rachis which lacks barbs except at its' base. They are most often found around the mouth and on the eyelids.
Flight feathers are highly modified contour feathers located on the wings and tail. The wing flight feathers are called remiges. The remiges are further subdivided into feathers found on the manus ("and) called primaries, which are numbered from the inside out. Those found on the forearm (ulna) are called secondaries, which are numbered from the outside in. Between the secondaries and the body are a group of contour feathers not generally considered as remiges called tertiaries or scapulars. These feathers are highly modified in some species, such as waterfowl.
The primaries are usually distinguishable from secondaries by their off-center rachis. The rachis is positioned toward the edge of the feather that intercepts the air stream. Notice that you can tell left from right wing using this character. The rachis is usually centrally positioned in the secondaries.
Note that the primaries of certain birds, such as geese, have a glossy stiffened portion of the inner vane from the base out to about 2/3 of the feather length. This is termed the tegmen and is formed by the expanded ventral ridge of each barb. The current thought about the function of the tegmen is that it acts as a valve in flight, letting air from above pass between the feathers easily on the wing's upstroke, but not from below on the down stroke.
