Feather

Feather

Overview
Feathers are one of the epidermal
Epidermis (zoology)
The Epidermis is an epithelium that covers the body of an eumetazoan . Eumetazoa have a cavity lined with a similar epithelium, the gastrodermis, which forms a boundary with the epidermis at the mouth.Sponges have no epithelium, and therefore no epidermis or gastrodermis...

 growths that form the distinctive outer covering, or plumage
Plumage
Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...

, on bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They are among the characteristics that distinguish the extant Aves from other living groups. Feathers have also been noticed in those Theropoda
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...

 which have been termed feathered dinosaurs
Feathered dinosaurs
The realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers...

.
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Encyclopedia
Feathers are one of the epidermal
Epidermis (zoology)
The Epidermis is an epithelium that covers the body of an eumetazoan . Eumetazoa have a cavity lined with a similar epithelium, the gastrodermis, which forms a boundary with the epidermis at the mouth.Sponges have no epithelium, and therefore no epidermis or gastrodermis...

 growths that form the distinctive outer covering, or plumage
Plumage
Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...

, on bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They are among the characteristics that distinguish the extant Aves from other living groups. Feathers have also been noticed in those Theropoda
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...

 which have been termed feathered dinosaurs
Feathered dinosaurs
The realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers...

. Although feathers cover most parts of the body of birds, they arise only from certain well-defined tracts on the skin. They aid in flight, thermal insulation, waterproofing and coloration that helps in communication and protection
Crypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...

.

Structure and characteristics


Feathers are among the most complex integument
Integumentary system
The integumentary system is the organ system that protects the body from damage, comprising the skin and its appendages...

ary appendages found in vertebrates and are formed in tiny follicles in the epidermis
Epidermis (zoology)
The Epidermis is an epithelium that covers the body of an eumetazoan . Eumetazoa have a cavity lined with a similar epithelium, the gastrodermis, which forms a boundary with the epidermis at the mouth.Sponges have no epithelium, and therefore no epidermis or gastrodermis...

, or outer skin layer, that produce keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...

 protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s. The β-keratins in feathers, beak
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...

s and claws — and the claw
Claw
A claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end...

s, scale
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...

s and shells of reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s — are composed of protein strands hydrogen-bonded
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...

 into β-pleated sheets
Beta sheet
The β sheet is the second form of regular secondary structure in proteins, only somewhat less common than the alpha helix. Beta sheets consist of beta strands connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet...

, which are then further twisted and crosslinked
Cross-link
Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...

 by disulfide
Disulfide
In chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms. Disulfide usually refer to a chemical compound that contains a disulfide bond, such as diphenyl disulfide, C6H5S-SC6H5....

 bridges into structures even tougher than the α-keratins of mammalian hair
Hair
Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....

, horns
Horn (anatomy)
A horn is a pointed projection of the skin on the head of various animals, consisting of a covering of horn surrounding a core of living bone. True horns are found mainly among the ruminant artiodactyls, in the families Antilocapridae and Bovidae...

 and hoof
Hoof
A hoof , plural hooves or hoofs , is the tip of a toe of an ungulate mammal, strengthened by a thick horny covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick nail rolled around the tip of the toe. The weight of the animal is normally borne by both the sole...

. The exact signals that induce the growth of feathers on the skin are not known but it has been found that the transcription factor cDermo-1 induces the growth of feathers on skin and scales on the leg.

Classification



There are two basic types of feather: vaned feathers which cover the exterior of the body, and down feather
Down feather
The down of birds is a layer of fine feathers found under the tougher exterior feathers. Very young birds are clad only in down. Powder down is a specialized type of down found only in a few groups of birds. Down is a fine thermal insulator and padding, used in goods such as jackets, bedding,...

s
which are underneath the vaned feathers. The pennaceous feather
Pennaceous feather
Pennaceous feathers are also known as contour feathers. This type of feather is present in most modern birds, and has been shown in some species of maniraptoran dinosaurs....

s are vaned feathers. Also called contour feathers, pennaceous feathers arise from tracts and cover the whole body. A third rarer type of feathers, filoplumes, is hairlike and (if present in a bird) grows along the fluffy down feathers. In some passerines, filoplumes arise exposed beyond the contour feathers on the neck. The remiges, or flight feather
Flight feather
Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings or tail of a bird; those on the wings are called remiges while those on the tail are called rectrices . Their primary function is to aid in the generation of both thrust and lift, thereby...

s of the wing, and rectrices, the flight feathers of the tail are the most important feathers for flight. A typical vaned feather features a main shaft, called the rachis
Rachis
Rachis is a biological term for a main axis or "shaft".-In zoology:In vertebrates a rachis can refer to the series of articulated vertebrae, which encase the spinal cord. In this case the rachis usually form the supporting axis of the body and is then called the spine or vertebral column...

. 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 much air and provide excellent thermal insulation. At the base of the feather, the rachis expands to form the hollow tubular calamus (or quill
Quill
A quill pen is a writing implement made from a flight feather of a large bird. Quills were used for writing with ink before the invention of the dip pen, metal-nibbed pens, the fountain pen, and, eventually, the ballpoint pen...

) which inserts into a follicle
Hair follicle
A hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....

 in the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

. 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 (neossoptiles) and these 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 is noted that the pattern of orientation of β-keratin fibers in the feathers of flying birds differs from that in flightless birds. The fibers are better aligned in the middle of the feather and less aligned towards the tips.

Functions


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 species have a crest of feathers on their heads. Although feathers are light, a bird's plumage weighs two or three times more than its skeleton, since many bones are hollow and contain air sacs. Color patterns serve as camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...

 against predators for birds in their habitats, and by predators looking for a meal. As with fish, the top and bottom colors may be different to provide camouflage during flight. Striking differences in feather patterns and colors are part of the sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...

 of many bird species and are particularly important in selection of mating pairs. In some cases there are differences in the UV reflectivity of feathers across sexes even though no differences in color are noted in the visible range. The wing feathers of male Club-winged Manakin
Club-winged Manakin
The Club-winged Manakin is a small passerine bird which is a resident breeding species in the cloud forest on the western slopes of the Andes Mountains of Colombia and northwestern Ecuador...

s Machaeropterus deliciosus have special structures that are used to produce sounds by stridulation
Stridulation
Stridulation is the act of producing sound by rubbing together certain body parts. This behavior is mostly associated with insects, but other animals are known to do this as well, such as a number of species of fishes, snakes and spiders...

.

Some birds have a supply of powder down feathers which grow continuously, with small particles regularly breaking off from the ends of the barbules. These particles produce a powder
Powder (substance)
A powder is a dry,thick bulk solid composed of a large number of very fine particles that may flow freely when shaken or tilted. Powders are a special sub-class of granular materials, although the terms powder and granular are sometimes used to distinguish separate classes of material...

 that sifts through the feathers on the bird's body and acts as a waterproofing agent and a feather conditioner
Conditioner (chemistry)
A conditioner is something that improves the quality of another material.Conditioning agents are also called moisturizers in some cases and usually are composed of various oils and lubricants...

. Powder down has evolved independently in several taxa and can be found in down as well as pennaceous feathers. They may be scattered in plumage in the pigeons and parrots or in localized patches on the breast, belly or flanks as in herons and frogmouths. Herons use their bill to break the feathers and to spread them while cockatoos may use their head as a powder puff to apply the powder. Waterproofing can be lost by exposure to emulsifying agents
Emulsion
An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...

 due to human pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

. Feathers can become waterlogged and birds may sink. It is also very difficult to clean and rescue birds whose feathers have been fouled by oil spill
Oil spill
An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially marine areas, due to human activity, and is a form of pollution. The term is mostly used to describe marine oil spills, where oil is released into the ocean or coastal waters...

s. The feathers of cormorants soak up water and help in reducing buoyancy and thereby allowing the birds to swim submerged.

Bristle
Bristle
A bristle is a stiff hair or feather. Also used are synthetic materials such as nylon in items such as brooms and sweepers. Bristles are often used to make brushes for cleaning uses, as they are strongly abrasive; common examples include the toothbrush and toilet brush...

s are stiff, tapering feathers with a large rachis but few barbs. Rictal bristles are bristles found around the eyes and bill. They may serve a similar purpose to eyelash
Eyelash
An eyelash or simply lash is one of the hairs that grow at the edge of the eyelid. Eyelashes protect the eye from debris and perform some of the same function as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object is near...

es and vibrissae
Vibrissae
Vibrissae , or whiskers, are specialized hairs usually employed for tactile sensation. The term may also refer to the thick hairs found inside human nostrils, but these have no sensorial function and only operate as an airborne particulate barrier...

 in mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s. It has been suggested that they may aid insectivorous birds in prey capture or that it may have sensory functions, however there is no clear evidence. In one study, Willow Flycatchers (Empidonax traillii) were found to catch insects equally well before and after removal of the rictal bristles.

Grebe
Grebe
A grebe is a member of the Podicipediformes order, a widely distributed order of freshwater diving birds, some of which visit the sea when migrating and in winter...

s are peculiar in their habit of ingesting their own feathers and also feeding them to their young. Observations on the diet and feather eating frequency suggest that ingesting feathers particularly down from their flanks aids in forming easily ejectable pellets along with their diet of fish.

Distribution



Contour feathers are not uniformly distributed on the skin of the bird except in some groups such as the Penguin
Penguin
Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...

s, ratites and screamers. In most birds the feathers grow from specific tracts of skin called pterylae while there are regions which are free of feathers called apterylae. Filoplumes and down may arise from the apteriae, regions between the pterylae. The arrangement of these feather tracts, pterylosis or pterylography, varies across bird families and has been used in the past as a means for determining the evolutionary relationships of bird families.

Coloration



The colors of feathers are produced by the presence of pigments, or by microscopic refractive
Refraction
Refraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...

 structures, or by a combination of both.

Most feather pigments are melanin
Melanin
Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

s (brown and beige pheomelanins, black and grey eumelanins) and carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...

s (red, yellow, orange); other pigments occur only in certain taxa – the yellow to red psittacofulvin
Psittacofulvin
Psittacofulvin pigments cause the bright-red, orange, and yellow colours of parrots. Colourful feathers with high levels of psittacofulvin resist feather-degrading Bacillus licheniformis better than white ones....

s (found in some parrots) and the red turacin
Turacin
Turacin is a naturally occurring red pigment that is 6% copper complexed to uroporphyrin 111. Arthur Herbert Church discovered turacin in 1869.It is found only in the bird family Musophagidae, the turacos...

 and green turacoverdin
Turacoverdin
Turacoverdin is a unique copper uroporphyrin pigment responsible for the bright green coloration of several birds of the family Musophagidae, most notably the turaco. It is chemically related to turacin, a red pigment also found almost exclusively in turacos...

 (porphyrin
Porphyrin
Porphyrins are a group of organic compounds, many naturally occurring. One of the best-known porphyrins is heme, the pigment in red blood cells; heme is a cofactor of the protein hemoglobin. Porphyrins are heterocyclic macrocycles composed of four modified pyrrole subunits interconnected at...

 pigments found only in turaco
Turaco
The turacos make up the bird family Musophagidae , which includes plantain-eaters and go-away-birds. In southern Africa both turacos and go-away-birds are commonly known as louries. They are semi-zygodactylous - the fourth toe can be switched back and forth...

s). Structural coloration is involved in the production of blue colors, iridescence
Iridescence
Iridescence is generally known as the property of certain surfaces which appear to change color as the angle of view or the angle of illumination changes...

, most ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 reflectance and in the enhancement of pigmentary colors; structural iridescence has been reported in fossil feathers dating back 40 million years. White feathers lack pigment and scatter light diffusely; albinism in birds
Albinism in birds
Albinism in birds is rare, occurring to any extent in perhaps one in 1800 individuals . A bird that is albino has white feathers in place of coloured ones on some portion of its body...

 is caused by defective pigment production, though structural coloration will not be affected (as can be seen e.g. in blue-and-white budgerigar
Budgerigar
The Budgerigar , also known as Common Pet Parakeet or Shell Parakeet informally nicknamed the budgie, is a small, long-tailed, seed-eating parrot, and the only species in the Australian genus Melopsittacus...

s).
For example, the blues and bright greens of many parrot
Parrot
Parrots, also known as psittacines , are birds of the roughly 372 species in 86 genera that make up the order Psittaciformes, found in most tropical and subtropical regions. The order is subdivided into three families: the Psittacidae , the Cacatuidae and the Strigopidae...

s are produced by constructive interference of light reflecting from different layers of the structures in feathers, in the case of green plumage in addition to the yellow pigments; the specific feather structure involved is sometimes called the Dyck texture. Melanin is often involved in the absorption of some of the light; in combination with yellow pigment it produces dull olive-greens.

In some birds, the feather colors may be created or altered by uropygial gland secretions. The yellow bill colors of many hornbills are produced by preen gland secretions. Other differences that may only be visible in the ultraviolet region have been suggested but studies have failed to find evidence. Uropygial oil secretion may also have an inhibitory effect on feather bacteria.

A bird's feathers undergo wear and tear and are replaced periodically during its life through molting. New feathers, known as blood, or pin feathers (depending on the stage of growth) when developing, are formed through the same follicle from which the old ones were fledged. The presence of melanin in feathers increases their resistance to abrasion. One study notes that melanin based feathers were observed to degrade more quickly under bacterial action, even compared to unpigmented feathers from the same species, than those unpigmented or with carotenoid pigments. However, another study the same year compared the action of bacteria on pigmentations of two song sparrow species and observed that the darker pigmented feathers were more resistant and they cited other research also published in 2004 that stated increased melanin provided greater resistance. They observed that the greater resistance of the darker birds confirmed Gloger's rule
Gloger's rule
Gloger's Rule is a zoological rule which states that within a species of endotherms, more heavily pigmented forms tend to be found in more humid environments, e.g. near the equator. It was named after the zoologist Constantin Wilhelm Lambert Gloger, who first remarked upon this phenomenon in 1833...

. The evolution of coloration is based on sexual selection and it has been suggested that carotenoid-based pigments may have evolved since they are likely to be more honest signals of fitness because they are derived from special diets, or because carotenoids are also required for immune function.

Parasites


The feather surface is the home for some ectoparasites, notably feather lice (Phthiraptera) and feather mites. Feather lice typically live on a single host and can move only from parents to chicks or mating birds and occasionally by phoresy. This life history has resulted in most of the species being specific to the host and coevolving with the host, making them of interest in phylogenetic studies.

Feather holes
Feather holes
Feather holes often characteristically occur on wing and tail feathers of some small-bodied species of passerines. In the case of Barn Swallows, it was suggested that the holes were feeding traces of avian lice, either Machaerilaemus malleus and/or Myrsidea rustica .Hole counts were shown to be...

 are chewing traces of lice (most probably Brueelia
Brueelia
Brueelia is a genus of lice in the family Philopteridae, containing the following species:* Brueelia amandavae Rekasi & Saxena, 2005* Brueelia astrildae Tendeiro & Mendes, 1994* Bureelia cantans Sychra, 2010...

spp. lice) on the wing and tail feathers. They were described on barn swallow
Barn Swallow
The Barn Swallow is the most widespread species of swallow in the world. It is a distinctive passerine bird with blue upperparts, a long, deeply forked tail and curved, pointed wings. It is found in Europe, Asia, Africa and the Americas...

s, and because of easy countability, many evolutionary, ecological, and behavioral publications use them to quantify the intensity of infestation.

Interestingly, 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 they leave the host nest.

Birds maintain their feather condition by bathing in water, dust bathing and preening. A peculiar behavior of birds, anting
Anting (bird activity)
In the behavior called anting, birds rub insects on their feathers, usually ants, which secrete liquids containing chemicals such as formic acid, that can act as an insecticide, miticide, fungicide, bactericide, or to make them edible by removing the distasteful acid. It possibly also supplements...

, where ants are introduced into the plumage was suggested to help in reducing parasites but no supporting evidence has been found.

Human usage



Feathers have a number of utilitarian, cultural and religious uses.

Utilitarian functions


Feathers are both soft and excellent at trapping heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

; thus, they are sometimes used in high-class bedding
Bedding
Bedding refers to the materials laid above the mattress of a bed for hygiene, warmth, to protect the mattress, and for decorative effect. Bedding is the removable and washable portion of a human sleeping environment. It is more easily and economically replaced than the bed itself...

, especially pillow
Pillow
A pillow is a large cushion support for the head, usually used while sleeping in a bed, or for the body as used on a couch or chair. There are also throw pillows , which are pillows that are purely decorative and not designed for support or comfort...

s, blanket
Blanket
A blanket is a type of bedding, generally speaking, a large piece of cloth, intended to keep the user warm, especially while sleeping. Blankets are distinguished from sheets by their thickness and purpose; the thickest sheet is still thinner than the lightest blanket. Blankets are generally used...

s, and mattress
Mattress
A mattress is a manufactured product to sleep or lie on, consisting of resilient materials and covered with an outer fabric or ticking. In the developed world it is typically part of a bed set and is placed upon a foundation....

es. They are also used as filling for winter clothing
Clothing
Clothing refers to any covering for the human body that is worn. The wearing of clothing is exclusively a human characteristic and is a feature of nearly all human societies...

, such as quilted coat
Coat (clothing)
A coat is a long garment worn by both men and women, for warmth or fashion. Coats typically have long sleeves and are open down the front, closing by means of buttons, zippers, hook-and-loop fasteners, toggles, a belt, or a combination of some of these...

s and sleeping bag
Sleeping bag
A sleeping bag is a protective "bag" for a person to sleep in, essentially a blanket that can be closed with a zipper or similar means, and functions as a bed in situations where a bed is unavailable . Its primary purpose is to provide warmth and thermal insulation...

s; goose
Goose
The word goose is the English name for a group of waterfowl, belonging to the family Anatidae. This family also includes swans, most of which are larger than true geese, and ducks, which are smaller....

 and eider
Eider
Eiders are large seaducks in the genus Somateria. Steller's Eider, despite its name, is in a different genus.The three extant species all breed in the cooler latitudes of the Northern hemisphere....

 down have great loft, the ability to expand from a compressed, stored state to trap large amounts of compartmentalized, insulating air.

Bird feathers have long been used for fletching
Fletching
Fletching is the aerodynamic stabilization of arrows or darts with materials such as feathers, each piece of which is referred to as a fletch. The word is related to the French word flèche, meaning "arrow," via Old French; the ultimate root is Frankish fliukka...

 arrows. Colorful feathers such as those belonging to pheasant
Pheasant
Pheasants refer to some members of the Phasianinae subfamily of Phasianidae in the order Galliformes.Pheasants are characterised by strong sexual dimorphism, males being highly ornate with bright colours and adornments such as wattles and long tails. Males are usually larger than females and have...

s have been used to decorate fishing lure
Fishing lure
A fishing lure is an object attached to the end of a fishing line which is designed to resemble and move like the prey of a fish. The purpose of the lure is to use movement, vibration, and colour to catch the fish's attention so it bites the hook...

s.

Feathers of large birds (most often geese
Goose
The word goose is the English name for a group of waterfowl, belonging to the family Anatidae. This family also includes swans, most of which are larger than true geese, and ducks, which are smaller....

) have been and are used to make quill
Quill
A quill pen is a writing implement made from a flight feather of a large bird. Quills were used for writing with ink before the invention of the dip pen, metal-nibbed pens, the fountain pen, and, eventually, the ballpoint pen...

 pens. The word pen itself is derived from the Latin penna for feather. In French, plume can mean either feather or pen.

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, and like other forms of keratin, these are slow in their decomposition. Feather waste has been used in a number of industrial applications as a medium for culturing microbes, biodegradeable polymers, and production of enzymes. Feather proteins have been tried as an adhesive for wood board.

In religion and culture


Eagle
Eagle
Eagles are members of the bird family Accipitridae, and belong to several genera which are not necessarily closely related to each other. Most of the more than 60 species occur in Eurasia and Africa. Outside this area, just two species can be found in the United States and Canada, nine more in...

 feathers have great cultural and spiritual
Spirituality
Spirituality can refer to an ultimate or an alleged immaterial reality; an inner path enabling a person to discover the essence of his/her being; or the “deepest values and meanings by which people live.” Spiritual practices, including meditation, prayer and contemplation, are intended to develop...

 value to American Indians
Native Americans in the United States
Native Americans in the United States are the indigenous peoples in North America within the boundaries of the present-day continental United States, parts of Alaska, and the island state of Hawaii. They are composed of numerous, distinct tribes, states, and ethnic groups, many of which survive as...

 in the USA and First Nations
First Nations
First Nations is a term that collectively refers to various Aboriginal peoples in Canada who are neither Inuit nor Métis. There are currently over 630 recognised First Nations governments or bands spread across Canada, roughly half of which are in the provinces of Ontario and British Columbia. The...

 peoples in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

 as religious objects. In the United States the religious use of eagle
Eagle
Eagles are members of the bird family Accipitridae, and belong to several genera which are not necessarily closely related to each other. Most of the more than 60 species occur in Eurasia and Africa. Outside this area, just two species can be found in the United States and Canada, nine more in...

 and hawk
Hawk
The term hawk can be used in several ways:* In strict usage in Australia and Africa, to mean any of the species in the subfamily Accipitrinae, which comprises the genera Accipiter, Micronisus, Melierax, Urotriorchis and Megatriorchis. The large and widespread Accipiter genus includes goshawks,...

 feathers are governed by the eagle feather law
Eagle feather law
The eagle feather law provides many exceptions to federal wildlife laws regarding eagles and other migratory birds to enable Native Americans to continue their traditional practices....

, a federal law limiting the possession of eagle feathers to certified and enrolled members of federally recognized Native American tribes.

Various birds and their plumages serve as cultural icons throughout the world, from the hawk in ancient Egypt to the bald eagle and the turkey (bird)
Turkey (bird)
A turkey is a large bird in the genus Meleagris. One species, Meleagris gallopavo, commonly known as the Wild Turkey, is native to the forests of North America. The domestic turkey is a descendant of this species...

 in the United States. In Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

, Daedelus the inventor and Icarus
Icarus (mythology)
In Greek mythology, Icarus is the son of the master craftsman Daedalus. The main story told about Icarus is his attempt to escape from Crete by means of wings that his father constructed from feathers and wax...

 tried to escape his prison by attaching feathered wings to his shoulders with wax, which was melted by the Sun.

In South America, brews made from the feathers of Condors are used in traditional medications. In India, feathers of the Indian Peacock have been used in traditional medicine for snakebite, infertility and coughs.

During the 18th, 19th, and even 20th Centuries a booming international trade in plumes, to satisfy market demand in North America and Europe for extravagant head-dresses
Headgear
Headgear, headwear or headdress is the name given to any element of clothing which is worn on one's head.Headgear serve a variety of purposes:...

 as adornment for fashionable women, caused so much destruction (for example, to egret
Egret
An egret is any of several herons, most of which are white or buff, and several of which develop fine plumes during the breeding season. Many egrets are members of the genera Egretta or Ardea which contain other species named as herons rather than egrets...

 breeding colonies) that a major campaign against it by conservationists led to the Lacey Act
Lacey Act
The Lacey Act of 1900, or more commonly The Lacey Act is a conservation law introduced by Iowa Rep. John F. Lacey. Protecting both plants and wildlife by creating civil and criminal penalties for a wide array of violations, the Act most notably prohibits trade in wildlife, fish, and plants that...

 and caused the fashion to change and the market to finally collapse. Frank Chapman
Frank Chapman
Frank Michler Chapman was a U.S. ornithologist and pioneering writer of field guides.Chapman was born in West Englewood, New Jersey and attended Englewood Academy. He joined the staff of the American Museum of Natural History in 1888 as assistant to Joel Asaph Allen...

 noted in 1886 that as many as 40 species of birds were used in about three-fourths of the 700 ladies' hats that he observed in New York City.

More recently, rooster plumage has become a popular trend as a hairstyle accessory, with feathers formerly used solely as fishing lures being now used to provide color and style to hair.

Evolution


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 however suggest that flight could not have been the original primary function. There have been suggestions that feathers may have had their original function in thermoregulation, waterproofing or even as sinks for metabolic wastes such as sulphur. While feathers have been suggested as having evolved from reptilian scales
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...

, there are numerous objections, and more recent explanations have arisen from the paradigm of evolutionary developmental biology
Evolutionary developmental biology
Evolutionary developmental biology is a field of biology that compares the developmental processes of different organisms to determine the ancestral relationship between them, and to discover how developmental processes evolved...

. Theories of the scale-based origins of feathers suggest that the planar scale structure was modified for their development into feathers by splitting to form the webbing; however, the developmental process involves a tubular structure arising from a follicle and the tube splitting longitudinally to form the webbing. The number of feathers per unit area of skin is higher in smaller birds than in larger birds, and this trend indicates their important role in thermal insulation, since smaller birds lose more heat due to the relatively larger surface area in proportion to their body weight. The miniaturization of birds also played a role in the evolution of powered flight. The coloration of feathers is believed to be primarily evolved in response to sexual selection
Sexual selection
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...

. In many cases the physiological condition of the birds (especially males) is indicated by the quality of their feathers and this is used (by the females) in mate choice
Mate choice
Mate choice, or intersexual selection, is an evolutionary process in which selection of a mate depends on attractiveness of its traits. It is one of two components of sexual selection...

.

Feathered dinosaurs


Several non-avian dinosaurs
Feathered dinosaurs
The realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers...

 had feathers on their limbs that would not have functioned for flight. One theory is that feathers originally evolved on dinosaurs as a result of insulation
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...

 properties; those small dinosaurs that then grew longer feathers may have found them helpful in gliding, leading to the evolution of proto-birds like Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...

and Microraptor
Microraptor
Microraptor is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China...

 zhaoianus
. Dinosaurs that had feathers or protofeathers include Pedopenna
Pedopenna
Pedopenna is a genus of small, feathered, maniraptoran dinosaur from the Daohugou Beds in China. It is possibly older than Archaeopteryx, though the age of the Daohugou Beds where it was found is debated...

 daohugouensis
,
and Dilong paradoxus, a tyrannosauroid which is 60 to 70 million years older than Tyrannosaurus rex
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...

.

The majority of dinosaurs known to have had feathers or protofeathers are saurischians, however featherlike "filamentous integumentary structures" are also known from the ornithischians Tianyulong
Tianyulong
Tianyulong is a genus of heterodontosaurid ornithischian dinosaur. The only species is T. confuciusi, whose remains were discovered in Jianchang County, Western Liaoning Province, China...

and Psittacosaurus
Psittacosaurus
Psittacosaurus is a genus of psittacosaurid ceratopsian dinosaur from the Early Cretaceous Period of what is now Asia, about 130 to 100 million years ago. It is notable for being the most species-rich dinosaur genus...

. The exact nature of these structures is still under study. However, it is believed that the stage 1 feathers such as those seen in these two ornithischians likely functioned in display.

Since the 1990s, dozens of feathered dinosaurs have been discovered in the clade Maniraptora
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...

, which includes the clade Avialae and the recent common ancestors of birds, Oviraptorosauria
Oviraptorosauria
Oviraptorosaurs are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot - like skulls, with or without bony crests atop the head...

 and Deinonychosauria
Deinonychosauria
The Deinonychosauria were a clade of coelurosaurian theropod dinosaurs from the Late Jurassic and Cretaceous periods. These omnivores and carnivores are known for their switchblade-like second toe claws and for displaying numerous bird-like characteristics. The clade has been divided into two...

. In 1998, the discovery of a feathered oviraptorosaurian, Caudipteryx zoui, challenged the notion that feathers were an exclusive structure of Avialae. Buried in the Yixian Formation in Liaoning, China, C. zoui lived during the Early Cretaceous Period. Present on the forelimbs and tails, their integumentary structure has been accepted as pennaceous vaned feathers based on the rachis and herringbone pattern of the barbs. In the clade Deinonychosauria, the continued divergence of feathers is also apparent in the families Troodontidae
Troodontidae
Troodontidae is a family of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and scrappy and they have therefore been allied, at various times, with many dinosaurian lineages...

 and Dromaeosauridae
Dromaeosauridae
Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...

. Branched feathers with ranchis, barbs, and barbules were discovered in many members including Sinornithosaurus millenii, a dromaeosaurid found in the Yixian formation (124.6 MYA).

Previously, a temporal paradox existed in the evolution of feathers - theropods with highly derived bird-like characteristics occurred at a later time than Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...

, suggesting that the descendants of birds arose before the ancestor. However, this paradox was resolved in 2009 with the discovery of Anchiornis huxleyi, found in the Late Jurassic Tiaojishan Formation (160 MYA) in western Liaoning. By predating Archaeopteryx, Anchornis proves the existence of a modernly feathered theropod ancestor, providing insight into the dinosaur-bird transition. The specimen shows distribution of large pennaceous feathers on the forelimbs and tail, implying that pennaceous feathers spread to the rest of the body at an earlier stage in theropod evolution. The discovery, in 2011, of feathers preserved in amber, within samples dating to 80 mya, suggests the coexistence of theropods and birds, with both theropod and avian feather types commingled in the samples.
x

Evolutionary stages



Several studies of feather development in the embryos of modern birds, coupled with the distribution of feather types among various prehistoric bird precursors, have allowed scientists to attempt a reconstruction of the sequence in which feathers first evolved and developed into the types found on modern birds.

Feather evolution was been broken down into the following stages by Xu and Guo in 2009:
  1. Single filament
  2. Multiple filaments joined at their base
  3. Multiple filaments joined at their base to a central filament
  4. Multiple filaments along the length of a central filament
  5. Multiple filaments arising from the edge of a membranous structure
  6. Pennaceous feather with vane of barbs and barbules and central rachis
  7. Pennaceous feather with an asymmetrical rachis
  8. Undifferentiated vane with central rachis


However, Foth (2011) showed that some of these purported stages (stages 2 and 5 in particular) are likely simply artifacts of preservation caused by the way fossil feathers are crushed and the feather remains or imprints are preserved. Foth re-interpreted stage 2 feathers as crushed or misidentified feathers of at least stage 3, and stage 5 feathers as crushed stage 6 feathers.

The following simplified diagram of dinosaur relationships follows these results, and shows the likely distribution of plumaceous (downy) and pennaceous (vaned) feathers among dinosaurs and prehistoric birds. The diagram follows one presented by Xu and Guo (2009) modified with the findings of Foth (2011). The numbers accompanying each name refer to the presence of specific feather stages. Note that 's' indicates the known presence of scales on the body.

External links