Although feathers cover most of the bird's body, they arise only from certain well-defined tracts on the skin. They aid in flight, thermal insulation, and waterproofing. In addition, coloration helps in communication and protection. Plumology (or plumage science) is the name for the science that is associated with the study of feathers.
Feathers have a number of utilitarian, cultural, and religious uses. Feathers are both soft and excellent at trapping
Feather derives from the Old English "feþer", which is of Germanic origin; related to Dutch "veer" and German "Feder", from an Indo-European root shared by Sanskrit's "patra" meaning ‘wing’, Latin's "penna" meaning ‘feather’, and Greek's "pteron", "pterux" meaning ‘wing’.
Because of feathers being an integral part of quills, which were early pens used for writing, the word pen itself is derived from the Latin penna, meaning feather. The French word plume can mean feather, quill, or pen.
Structures and characteristics
- Shaft, rachis
- Aftershaft, afterfeather
- Quill, calamus
Feathers are among the most complex
There are two basic types of feather: vaned feathers which cover the exterior of the body, and down feathers which are underneath the vaned feathers. The pennaceous feathers are vaned feathers. Also called contour feathers, pennaceous feathers arise from tracts and cover the entire body. A third rarer type of feather, the filoplume, is hairlike and are closely associated with pennaceous feathers and are often entirely hidden by them, with one or two filoplumes attached and sprouting from near the same point of the skin as each pennaceous feather, at least on a bird's head, neck and trunk. Filoplumes are entirely absent in ratites. In some passerines, filoplumes arise exposed beyond the pennaceous feathers on the neck. The remiges, or flight feathers of the wing, and rectrices, or flight feathers of the tail, are the most important feathers for flight. A typical vaned feather features a main shaft, called the rachis. Fused to the rachis are a series of branches, or barbs; the barbs themselves are also branched and form the barbules. These barbules have minute hooks called barbicels for cross-attachment. Down feathers are fluffy because they lack barbicels, so the barbules float free of each other, allowing the down to trap air and provide excellent thermal insulation. At the base of the feather, the rachis expands to form the hollow tubular calamus (or quill) which inserts into a follicle in the skin. The basal part of the calamus is without vanes. This part is embedded within the skin follicle and has an opening at the base (proximal umbilicus) and a small opening on the side (distal umbilicus).
Hatchling birds of some species have a special kind of natal down feathers (neossoptiles) which are pushed out when the normal feathers (teleoptiles) emerge.
Flight feathers are stiffened so as to work against the air in the downstroke but yield in other directions. It has been observed that the orientation pattern of β-keratin fibers in the feathers of flying birds differs from that in flightless birds: the fibers are better aligned along the shaft axis direction towards the tip, and the lateral walls of rachis region show structure of crossed fibers.
Feathers insulate birds from water and cold temperatures. They may also be plucked to line the nest and provide insulation to the eggs and young. The individual feathers in the wings and tail play important roles in controlling flight.
Some birds have a supply of
Grebes are peculiar in their habit of ingesting their own feathers and feeding them to their young. Observations on their diet of fish and the frequency of feather eating suggest that ingesting feathers, particularly down from their flanks, aids in forming easily ejectable pellets.
Contour feathers are not uniformly distributed on the skin of the bird except in some groups such as the
The colors of feathers are produced by pigments, by microscopic structures that can refract, reflect, or scatter selected wavelengths of light, or by a combination of both.
Most feather pigments are
The blues and bright greens of many parrots are produced by constructive interference of light reflecting from different layers of structures in feathers. In the case of green plumage, in addition to yellow, the specific feather structure involved is called by some the Dyck texture. Melanin is often involved in the absorption of light; in combination with a yellow pigment, it produces a dull olive-green.
In some birds, feather colors may be created, or altered, by secretions from the uropygial gland, also called the preen gland. The yellow bill colors of many hornbills are produced by such secretions. It has been suggested that there are other color differences that may be visible only in the ultraviolet region, but studies have failed to find evidence. The oil secretion from the uropygial gland may also have an inhibitory effect on feather bacteria.
The reds, orange and yellow colors of many feathers are caused by various carotenoids. Carotenoid-based pigments might be honest signals of fitness because they are derived from special diets and hence might be difficult to obtain, and/or because carotenoids are required for immune function and hence sexual displays come at the expense of health.
A bird's feathers undergo wear and tear and are replaced periodically during the bird's life through
Although sexual selection plays a major role in the development of feathers, in particular, the color of the feathers it is not the only conclusion available. New studies are suggesting that the unique feathers of birds are also a large influence on many important aspects of avian behavior, such as the height at which different species build their nests. Since females are the prime caregivers, evolution has helped select females to display duller colors down so that they may blend into the nesting environment. The position of the nest and whether it has a greater chance of being under predation has exerted constraints on female birds' plumage. A species of bird that nests on the ground, rather than the canopy of the trees, will need to have much duller colors in order not to attract attention to the nest. The height study found that birds that nest in the canopies of trees often have many more predator attacks due to the brighter color of feathers that the female displays. Another influence of evolution that could play a part in why feathers of birds are so colorful and display so many patterns could be due to that birds developed their bright colors from the vegetation and flowers that thrive around them. Birds develop their bright colors from living around certain colors. Most bird species often blend into their environment, due to some degree of camouflage, so if the species habitat is full of colors and patterns, the species would eventually evolve to blend in to avoid being eaten. Birds' feathers show a large range of colors, even exceeding the variety of many plants, leaf, and flower colors.
The feather surface is the home for some ectoparasites, notably feather lice (
Parasitic cuckoos which grow up in the nests of other species also have host-specific feather lice and these seem to be transmitted only after the young cuckoos leave the host nest.
Birds maintain their feather condition by
Bird feathers have long been used for
Feathers are also valuable in aiding the identification of species in forensic studies, particularly in bird strikes to aircraft. The ratios of hydrogen isotopes in feathers help in determining the geographic origins of birds. Feathers may also be useful in the non-destructive sampling of pollutants.
The poultry industry produces a large amount of feathers as waste, which, like other forms of keratin, are slow to decompose. Feather waste has been used in a number of industrial applications as a medium for culturing microbes, biodegradable polymers, and production of enzymes. Feather proteins have been tried as an adhesive for wood board.
Some groups of Native people in Alaska have used ptarmigan feathers as temper (non-plastic additives) in pottery manufacture since the first millennium BC in order to promote thermal shock resistance and strength.
In religion and culture
Eagle feathers have great cultural and spiritual value to American Indians in the US and First Nations peoples in Canada as religious objects. In the United States, the religious use of eagle and hawk feathers is governed by the eagle feather law, a federal law limiting the possession of eagle feathers to certified and enrolled members of federally recognized Native American tribes.
In South America, brews made from the feathers of
Members of Scotland's Clan Campbell are known to wear feathers on their bonnets to signify authority within the clan. Clan chiefs wear three, chieftains wear two and an armiger wears one. Any member of the clan who does not meet the criteria is not authorized to wear feathers as part of traditional garb and doing so is considered presumptuous.
During the 18th, 19th, and early 20th centuries, there was a booming international trade in plumes for extravagant women's hats and other headgear (including in
Feather products manufacturing in Europe has declined in the last 60 years, mainly due to competition from Asia. Feathers have adorned hats at many prestigious events such as weddings and Ladies Day at racecourses (Royal Ascot).
The functional view on the evolution of feathers has traditionally focused on insulation, flight and display. Discoveries of non-flying Late Cretaceous feathered dinosaurs in China,
Several genes have been found to determine feather development. They will be key to understand the evolution of feathers. For instance, some genes convert scales into feathers or feather-like structures when expressed or induced in bird feet, such as the scale-feather converters Sox2, Zic1, Grem1, Spry2, and Sox18.
Feathers and scales are made up of two distinct forms of
This may suggest that crocodilian scales, bird and dinosaur feathers, and pterosaur