The nature of feather construction
Numerous specialized names are applied to feathers appropriate to their location on the bird, from the face to the toes, but there are just a few basic types that should concern most fly tying needs.
Contour feathers cover the bird's body. They are close fitting, yet separated from the skin to help isolate the body from outside humidity and temperature. With the assistance of follicle muscles, the contour feathers can be erected, then lowered to adjust the depth of the protective layer. Contour feathers are typically broad, thin, curving inward toward the skin, directed toward the tail in overlapping rows, and have a combined pennaceous/plumulaceous vane. They help to smooth and streamline the body for flight. In some species they may be greatly modified for purposes of display or some other ornamental purpose. Many contour feathers have afterfeathers attached at the base. These are small plumulaceous feathers which may or may not have a shaft (hyporachis.) Usually a contour feathers' afterfeather is no more than half the length of the attached contour feather, yet exceptions always seem to occur in nature. Two birds, the Emu and the Cassowary, have afterfeathers as long as their contour feathers, while some birds such as the pigeon and ostrich have no afterfeathers.
Flight feathers include the tail feathers (rectrices) and wing feathers (remiges) as well as supplemental feathers that cover the adjacent upper and under surfaces.
The tail feathers
The tail feathers (rectrices) act as a stabilizer tilting the front of the body up and down, as well as an air brake when the bird lands, but they are not used for steering except in steep turns. Tail feathers are usually large, stiff in texture, asymmetric, have vanes that are almost entirely pennaceous, and lack afterfeathers. In most cases tail assemblies are made up of 10-12 feathers (with some pheasants having up to 24) arranged in a single horizontal row. They each overlap their lateral (outside) edge over the medial (inside) edge of the adjacent feather. The outermost feather's lateral vane is narrow, stiff, and convex compared to the softer, longer, concave barbs of the inner vane. This effect is digressive as the feathers work toward the center pair, such that the center pair's vane is fairly symmetric right to left. The turkey tail assembly when fanned clearly demonstrates this. At the bases of the tail feathers are upper tail and under tail covert feathers that smooth and streamline the tail of the bird. Exceptions do occur such as with the peacock upper tail coverts, which lack streamlining, but are useful for display.
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