Feather

Feathers are epidermal growths that form the distinctive outer covering, or plumage, on birds, other extinct species of dinosaurs, and possibly pterosaurs. They are considered the most complex integumentary structures found in vertebrates[1][2] and a premier example of a complex evolutionary novelty.[3] They are among the characteristics that distinguish the extant birds from other living groups.[4]

Although feathers cover most of the bird's bodies, 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.[5] Plumology (or plumage science) is the name for the science that is associated with the study of feathers.[6][7]

Types de plumes. - Larousse pour tous, -1907-1910-
Feather variations

Structures and characteristics

Parts of feather modified
Parts of a feather:
  1. Vane
  2. Rachis
  3. Barb
  4. Afterfeather
  5. Hollow shaft, calamus
Parrot-feather
Feather structure of a blue-and-yellow macaw
Pigeon down SEM
Anterior region of a contour feather from a rock pigeon, visualized using scanning electron microscopy. Interlocking barbules are clearly seen in the middle image.

Feathers are among the most complex integumentary appendages found in vertebrates and are formed in tiny follicles in the epidermis, or outer skin layer, that produce keratin proteins. The β-keratins in feathers, beaks and claws — and the claws, scales and shells of reptiles — are composed of protein strands hydrogen-bonded into β-pleated sheets, which are then further twisted and crosslinked by disulfide bridges into structures even tougher than the α-keratins of mammalian hair, horns and hoof.[8][9] 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.[10]

FeatherLocking
Feather microstructure showing interlocking barbules

Classification

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 (if present in a bird; they are entirely absent in ratites[11]) are closely associated with contour 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 contour feather, at least on a bird's head, neck and trunk.[12][13] In some passerines, filoplumes arise exposed beyond the contour feathers on the neck.[1] The remiges, or flight feathers 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. 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).[14]

Hatchling birds of some species have a special kind of natal down feathers (neossoptiles) which are pushed out when the normal feathers (teleoptiles) emerge.[1]

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,[15][16] and the lateral walls of rachis region show structure of crossed fibers.[17][18]

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.[17] 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 against predators for birds in their habitats, and serve as camouflage for predators looking for a meal. As with fish, the top and bottom colors may be different, in order to provide camouflage during flight. Striking differences in feather patterns and colors are part of the sexual dimorphism 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.[19] The wing feathers of male club-winged manakins Machaeropterus deliciosus have special structures that are used to produce sounds by stridulation.[20]

GuineaFeather
A contour feather from a Guinea fowl

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 that sifts through the feathers on the bird's body and acts as a waterproofing agent and a feather conditioner. Powder down has evolved independently in several taxa and can be found in down as well as in pennaceous feathers. They may be scattered in plumage as 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 powder down feathers and to spread them, while cockatoos may use their head as a powder puff to apply the powder.[21] Waterproofing can be lost by exposure to emulsifying agents due to human pollution. Feathers can then become waterlogged, causing the bird to sink. It is also very difficult to clean and rescue birds whose feathers have been fouled by oil spills. The feathers of cormorants soak up water and help to reduce buoyancy, thereby allowing the birds to swim submerged.[22]

BarbetRictalBristle
Rictal bristles of a white-cheeked barbet

Bristles are stiff, tapering feathers with a large rachis but few barbs. Rictal bristles are found around the eyes and bill. They may serve a similar purpose to eyelashes and vibrissae in mammals. Although there is as yet no clear evidence, it has been suggested that rictal bristles have sensory functions and may help insectivorous birds to capture prey.[23] In one study, willow flycatchers (Empidonax traillii) were found to catch insects equally well before and after removal of the rictal bristles.[24]

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.[25]

Distribution

Pterylae
Feather tracts or pterylae and their naming

Contour feathers are not uniformly distributed on the skin of the bird except in some groups such as the penguins, ratites and screamers.[26] In most birds the feathers grow from specific tracts of skin called pterylae; between the pterylae there are regions which are free of feathers called apterylae (or apteria). Filoplumes and down may arise from the apterylae. 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.[27][28]

Coloration

Red feather pigments
Colors resulting from different feather pigments
Left: turacin (red) and turacoverdin (green, with some structural blue iridescence at lower end) on the wing of Tauraco bannermani
Right: carotenoids (red) and melanins (dark) on belly/wings of Ramphocelus bresilius

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 melanins (brown and beige pheomelanins, black and grey eumelanins) and carotenoids (red, yellow, orange); other pigments occur only in certain taxa – the yellow to red psittacofulvins[29] (found in some parrots) and the red turacin and green turacoverdin (porphyrin pigments found only in turacos).

Structural coloration[5][30][31] is involved in the production of blue colors, iridescence, most ultraviolet reflectance and in the enhancement of pigmentary colors. Structural iridescence has been reported[32] in fossil feathers dating back 40 million years. White feathers lack pigment and scatter light diffusely; albinism in birds is caused by defective pigment production, though structural coloration will not be affected (as can be seen, for example, in blue-and-white budgerigars).

BWfeather
A feather with no pigment

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.[33][34] 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,[21] but studies have failed to find evidence.[35] The oil secretion from the uropygial gland may also have an inhibitory effect on feather bacteria.[36]

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,[37][38] and/or because carotenoids are required for immune function and hence sexual displays come at the expense of health.[39]

A bird's feathers undergo wear and tear and are replaced periodically during the bird's life through molting. New feathers, known when developing as blood, or pin feathers, depending on the stage of growth, are formed through the same follicles from which the old ones were fledged. The presence of melanin in feathers increases their resistance to abrasion.[40] 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.[41] 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; the authors 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.[42]

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 is also a large influence on many important aspects of avian behavior, such as the height at which a different species build their nests. Since females are the prime care givers, evolution has helped select females to display duller colored 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.[43] 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. Since the female is the main care giver in some species of birds, evolution has helped select traits that make her feathers dull and often allow her to blend into the surroundings. 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.[43] 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.[44]

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, between mating birds, and, occasionally, by phoresy. This life history has resulted in most of the parasite species being specific to the host and coevolving with the host, making them of interest in phylogenetic studies.[45]

Feather holes are chewing traces of lice (most probably Brueelia spp. lice) on the wing and tail feathers. They were described on barn swallows, and because of easy countability, many evolutionary, ecological, and behavioral publications use them to quantify the intensity of infestation.

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.[46]

Birds maintain their feather condition by preening and bathing in water or dust. It has been suggested that a peculiar behavior of birds, anting, in which ants are introduced into the plumage, helps to reduce parasites, but no supporting evidence has been found.[47]

Human usage

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

Utilitarian functions

Fully feathered basket Santa Roas College
Pomo fully feathered basket curated at the Jesse Peter Multicultural Museum, Santa Rosa College
Female model with feathers
Female model with feathers

Feathers are both soft and excellent at trapping heat; thus, they are sometimes used in high-class bedding, especially pillows, blankets, and mattresses. They are also used as filling for winter clothing and outdoor bedding, such as quilted coats and sleeping bags. Goose and eider down have great loft, the ability to expand from a compressed, stored state to trap large amounts of compartmentalized, insulating air.[48]

Bird feathers have long been used for fletching arrows. Colorful feathers such as those belonging to pheasants have been used to decorate fishing lures.

Feathers of large birds (most often geese) have been and are used to make quill pens. The word pen itself is derived from the Latin penna, meaning feather.[49] The French word 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.[50] Feathers may also be useful in the non-destructive sampling of pollutants.[51]

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,[52] biodegradeable polymers,[53] and production of enzymes.[54] Feather proteins have been tried as an adhesive for wood board.[55]

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.[56]

The hunting of birds for decorative and ornamental feathers (including in Victorian fashion) has endangered some species. For instance, South American hummingbird feathers were used in the past to dress some of the miniature birds featured in singing bird boxes.

In religion and culture

San Isidro labrador
Mexican featherwork painting of Isidore the Laborer made from duck, hummingbird and canary feathers. This style of painting, popular during the Novohispanic era, integrates featherwork of pre-Hispanic origin with Christian iconography. 18th century, Museo Soumaya

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 condors are used in traditional medications.[57] In India, feathers of the Indian peacock have been used in traditional medicine for snakebite, infertility, and coughs.[58][59]

During the 18th, 19th, and early 20th centuries, there was a booming international trade in plumes for extravagant women's hats and other headgear. Frank Chapman noted in 1886 that feathers of 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.[60] This trade caused severe losses to bird populations (for example, egrets and whooping cranes). Conservationists led a major campaign against the use of feathers in hats. This contributed to passage of the Lacey Act in 1900, and to changes in fashion. The ornamental feather market then largely collapsed.[61][62]

More recently, rooster plumage has become a popular trend as a hairstyle accessory, with feathers formerly used as fishing lures now being used to provide color and style to hair.[63] Today, feathers used in fashion and in military headresses and clothes are obtained as a waste product of poultry farming, including chickens, geese, turkeys, pheasants, and ostriches. These feathers are dyed and manipulated to enhance their appearance, as poultry feathers are naturally often dull in appearance compared to the feathers of wild birds.

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 race courses (Royal Ascot).

Evolution

Archaeopteryx (Feather)
Fossil feather of an unidentified dinosaur

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,[64] however, suggest that flight could not have been the original primary function as the feathers simply would not have been capable of providing any form of lift.[65][66] 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.[67] Recent discoveries are argued to support a thermoregulatory function, at least in smaller dinosaurs.[68][69] While feathers have been suggested as having evolved from reptilian scales, there are numerous objections to that idea, and more recent explanations have arisen from the paradigm of evolutionary developmental biology.[2] Theories of the scale-based origins of feathers suggest that the planar scale structure was modified for development into feathers by splitting to form the webbing; however, that developmental process involves a tubular structure arising from a follicle and the tube splitting longitudinally to form the webbing.[1][2] The number of feathers per unit area of skin is higher in smaller birds than in larger birds, and this trend points to 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.[5] The miniaturization of birds also played a role in the evolution of powered flight.[70] The coloration of feathers is believed to have evolved primarily in response to sexual selection. In one fossil specimen of the Parave Anchiornis huxleyi, the features are so well preserved that the melanosome (pigment cells) structure can be observed. By comparing the shape of the fossil melanosomes to melanosomes from extant birds, the color and pattern of the feathers on Anchiornis could be determined.[71] Anchiornis was found to have black-and-white-patterned feathers on the forelimbs and hindlimbs, with a reddish-brown crest. This pattern is similar to the coloration of many extant bird species, which use plumage coloration for display and communication, including sexual selection and camouflage. It is likely that non-avian dinosaur species utilized plumage patterns for similar functions as modern birds before the origin of flight. 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.[72][73]

Feathers and scales are made up of two distinct forms of keratin, and it was long thought that each type of keratin was exclusive to each skin structure (feathers and scales). However, a study published in 2006 confirmed the presence of feather keratin in the early stages of development of American alligator scales. This type of keratin, previously thought to be specific to feathers, is suppressed during embryological development of the alligator and so is not present in the scales of mature alligators. The presence of this homologous keratin in both birds and crocodilians indicates that it was inherited from a common ancestor. This may suggest that crocodilian scales, bird and dinosaur feathers, and pterosaur pycnofibres are all developmental expressions of the same primitive archosaur skin structures; suggesting that feathers and pycnofibers could be homologous.[74]

Feathered dinosaurs

Archaeopteryx lithographica (Berlin specimen)
Archaeopteryx lithographica (Berlin specimen)

Several non-avian dinosaurs had feathers on their limbs that would not have functioned for flight.[64][2] One theory suggests that feathers originally evolved on dinosaurs as a result of their insulation properties; small dinosaur species that grew longer; feathers may have found them helpful in gliding, leading to the evolution of proto-birds like Archaeopteryx and Microraptor zhaoianus. Another theory posits that the original adaptive advantage of early feathers was their pigmentation or iridescence, contributing to sexual preference in mate selection.[75] Dinosaurs that had feathers or protofeathers include Pedopenna daohugouensis[76] and Dilong paradoxus, a tyrannosauroid which is 60 to 70 million years older than Tyrannosaurus rex.[77]

The majority of dinosaurs known to have had feathers or protofeathers are theropods, however featherlike "filamentous integumentary structures" are also known from the ornithischian dinosaurs Tianyulong and Psittacosaurus.[78] The exact nature of these structures is still under study. However, it is believed that the stage-1 feathers (see Evolutionary stages section below) such as those seen in these two ornithischians likely functioned in display.[79] In 2014, the ornithischian Kulindadromeus was reported as having structures resembling stage-3 feathers.[80]

Since the 1990s, dozens of feathered dinosaurs have been discovered in the clade Maniraptora, which includes the clade Avialae and the recent common ancestors of birds, Oviraptorosauria and Deinonychosauria. In 1998, the discovery of a feathered oviraptorosaurian, Caudipteryx zoui, challenged the notion of feathers as a structure exclusive to Avialae.[81] 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 and Dromaeosauridae. Branched feathers with rachis, barbs, and barbules were discovered in many members including Sinornithosaurus millenii, a dromaeosaurid found in the Yixian formation (124.6 MYA).[82]

Previously, a temporal paradox existed in the evolution of feathers—theropods with highly derived bird-like characteristics occurred at a later time than Archaeopteryx—suggesting that the descendants of birds arose before the ancestor. However, the discovery of Anchiornis huxleyi in the Late Jurassic Tiaojishan Formation (160 MYA) in western Liaoning in 2009[83][84] resolved this paradox. By predating Archaeopteryx, Anchiornis 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.[85] 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.[86]

Two small wings trapped in amber dating to 100 mya show plumage existed in some bird predecessors. The wings most probably belonged to enantiornithes, a diverse group of avian dinosaurs.[87][88]

A large phylogenetic analysis of early dinosaurs by Matthew Baron, David B. Norman and Paul Barrett (2017) found that Theropoda is actually more closely related to Ornithischia, to which it formed the sister group within the clade Ornithoscelida. The study also suggested that if the feather-like structures of theropods and ornithischians are of common evolutionary origin then it would be possible that feathers were restricted to Ornithoscelida. If so, then the origin of feathers would have likely occurred as early as the Middle Triassic.[89]

Evolutionary stages

Feather stages diagram
Diagram illustrating stages of evolution

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 broken down into the following stages by Xu and Guo in 2009:[79]

  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.[90]

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)[79] modified with the findings of Foth (2011).[90] 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.

See also

References

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Further reading

  • Hanson, Thor (2011). Feathers: The Evolution of a Natural Miracle. New York: Basic Books. ISBN 9780465020133. OCLC 727106416.

External links

Abnormal behaviour of birds in captivity

Abnormal behavior of birds in captivity can be defined in several ways. Statistically, 'abnormal' is when the occurrence, frequency or intensity of a behaviour varies statistically significantly, either more or less, from the normal value. This means that theoretically, almost any behaviour could become 'abnormal' in an individual. Less formally, 'abnormal' includes any activity judged to be outside the normal behaviour pattern for captive birds of that particular class or age. For example, running rather than flying may be a normal behaviour and regularly observed in one species, however, in another species it might be normal but becomes 'abnormal' if it reaches a high frequency, or in another species it is rarely observed and any incidence is considered 'abnormal'. This article does not include 'one-off' behaviours performed by individual birds that might be considered abnormal for that individual, unless these are performed repeatedly by other individuals in the species and are recognised as part of the ethogram of that species.

Most abnormal behaviours can be categorised collectively (e.g., eliminative, ingestive, stereotypies), however, many abnormal behaviours fall debatebly into several of these categories and categorisation is therefore not attempted in this article. Abnormal behaviours here are considered to be related to captive housing but may also be due to medical conditions. The article does not include behaviours in birds that are genetically modified to express abnormal behaviour.

When housed under captive or commercial conditions, birds often show a range of abnormal behaviours. These are often self-injurious or harmful to other individuals, and include:

Feather pecking

Cannibalism

Vent pecking

Toe pecking

Feather plucking

Stereotypies

Polydipsia

Sham or "vacuum" dustbathing

Jealous, over-possessive parrot

Chronic egg layingWhen analyzing the behaviour of birds in captivity, what is considered normal or abnormal behaviour is dependent on the form and frequency that the particular behaviour is expressed in the natural environment. Birds raised in pet stores tend to be raised with other birds, however, after being sold and taken to the owner's home, birds in captivity are often housed in isolation and in environments lacking abundant resources or complex stimuli. In the United States, it is estimated that forty million birds are kept caged and improperly cared for. Because of these inappropriate housing conditions, abnormal behaviour patterns may appear in caged birds kept as pets. Once established, these abnormal behaviours in birds are often not alterable.When social interactions amongst birds are absent or inadequate, abnormal social behaviour may develop. For example, a study regarding parrots that had been isolated in cages demonstrated that most birds showing this social deprivation had significant behavioural disturbances, such as aggressive behaviour, feather picking, self-mutilation, restlessness, screaming, apathetic behavior, and stereotypies. Cannibalism often occurs in large animal husbandry systems, which are usually impoverished environments with a lack of opportunities. In addition, studies of caged canaries have revealed two common stereotypies. These include spot picking, where birds repeatedly touch a particular spot in the environment with the tip of their beak, and route tracing, a pacing behaviour associated with physical restrictions in movement imposed by the cage. The absence of song learning in zebra finches has also been implicated as a behavioural abnormality. In these birds, the social interaction of a young male with his song tutor is important for normal song development. Without the stimulus, the song, which is necessary for mating behavior, will not be learned.

Researchers have analyzed ways to alleviate some abnormal behaviours in caged birds. Presenting these birds with novel stimuli e.g. a mirror or plastic birds, and social stimuli, such as a brief view of a bird in another cage, significantly reduced stereotypies. In addition, it has been suggested that keeping caged birds in pairs or small groups may reduce the development of abnormal behaviours, however, little quantitative evidence has thus far been collected to support this claim.

Archaeopteryx

Archaeopteryx (), meaning "old wing" (sometimes referred to by its German name Urvogel ("original bird" or "first bird")), is a genus of bird-like dinosaurs that is transitional between non-avian feathered dinosaurs and modern birds. The name derives from the ancient Greek ἀρχαῖος (archaīos) meaning "ancient", and πτέρυξ (ptéryx), meaning "feather" or "wing". Between the late nineteenth century and the early twenty-first century, Archaeopteryx had been generally accepted by palaeontologists and popular reference books as the oldest known bird (member of the group Avialae). Older potential avialans have since been identified, including Anchiornis, Xiaotingia, and Aurornis.Archaeopteryx lived in the Late Jurassic around 150 million years ago, in what is now southern Germany during a time when Europe was an archipelago of islands in a shallow warm tropical sea, much closer to the equator than it is now. Similar in size to a Eurasian magpie, with the largest individuals possibly attaining the size of a raven, the largest species of Archaeopteryx could grow to about 0.5 m (1 ft 8 in) in length. Despite their small size, broad wings, and inferred ability to fly or glide, Archaeopteryx had more in common with other small Mesozoic dinosaurs than with modern birds. In particular, they shared the following features with the dromaeosaurids and troodontids: jaws with sharp teeth, three fingers with claws, a long bony tail, hyperextensible second toes ("killing claw"), feathers (which also suggest warm-bloodedness), and various features of the skeleton.These features make Archaeopteryx a clear candidate for a transitional fossil between non-avian dinosaurs and birds. Thus, Archaeopteryx plays an important role, not only in the study of the origin of birds, but in the study of dinosaurs. It was named from a single feather in 1861, though that feather would eventually prove to be non-avian. That same year, the first complete specimen of Archaeopteryx was announced. Over the years, ten more fossils of Archaeopteryx have surfaced. Despite variation among these fossils, most experts regard all the remains that have been discovered as belonging to a single species, although this is still debated.

Most of these eleven fossils include impressions of feathers. Because these feathers are of an advanced form (flight feathers), these fossils are evidence that the evolution of feathers began before the Late Jurassic. The type specimen of Archaeopteryx was discovered just two years after Charles Darwin published On the Origin of Species. Archaeopteryx seemed to confirm Darwin's theories and has since become a key piece of evidence for the origin of birds, the transitional fossils debate, and confirmation of evolution.

In March 2018, scientists reported that Archaeopteryx was likely capable of flight, but in a manner substantially different from that of modern birds.

Birds of a Feather

Birds of a Feather (commonly abbreviated to BOAF) is a British sitcom originally broadcast on BBC One from 16 October 1989 to 24 December 1998, then revived on ITV from 2 January 2014. Starring Pauline Quirke, Linda Robson and Lesley Joseph, it was created by Laurence Marks and Maurice Gran, who also wrote some of the episodes along with many other writers.

The first episode sees sisters Tracey Stubbs (Linda Robson) and Sharon Theodopolopodous (Pauline Quirke) brought together when their husbands are sent to prison for armed robbery. Sharon, who lived in an Edmonton council flat, moves into Tracey's expensive house in Chigwell, Essex. Their next-door neighbour and later friend, Dorien Green (Lesley Joseph), is a middle-aged married Jewish woman who is constantly having affairs with younger men. In the last two BBC series, the location is changed to nearby Hainault, Essex before returning to Chigwell in series 10 (the first aired on ITV).

The series ended its original BBC One run on Christmas Eve 1998 after nine years, but returned just over 15 years later, on 2 January 2014, on ITV, for its tenth series overall, running for eight episodes. The opening episode of the new series attracted almost eight million viewers, giving ITV its highest-rated comedy since Barbara in 2000. In 2015, there was an eleventh series (the second series on ITV) aired from December 2014 – January 2015. A twelfth series (the third on ITV) aired in 2016. A Christmas special was filmed in Malta, and aired on Christmas Eve 2016. Another Christmas special aired on 18 December 2017. A thirteenth series (the fourth on ITV) has been commissioned but it is uncertain when or if this will happen.

Confusion occurred in February 2019 when Nigel Lythgoe seemed to suggest the series had ended. However an ITV representative later confirmed this story was false and both Birds of A Feather and Bad Move had not been 'axed'.

Covert feather

A covert feather or tectrix on a bird is one of a set of feathers, called coverts (or tectrices), which, as the name implies, cover other feathers. The coverts help to smooth airflow over the wings and tail.

Crinoid

Crinoids are marine animals that make up the class Crinoidea, one of the classes of the phylum Echinodermata, which also includes the starfish, brittle stars, sea urchins and sea cucumbers. Those crinoids which in their adult form are attached to the sea bottom by a stalk are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, being members of the largest crinoid order Comatulida.

Adult crinoids are characterised by having the mouth located on the upper surface. This is surrounded by feeding arms, and is linked to a U-shaped gut, with the anus being located on the oral disc near the mouth. Although the basic echinoderm pattern of fivefold symmetry can be recognised, in most crinoids the five arms are subdivided into ten or more. These have feathery pinnules and are spread wide to gather planktonic particles from the water. At some stage in their life, most crinoids have a stem used to attach themselves to the substrate, but many live attached only as juveniles and become free-swimming as adults.

There are only about 600 living species of crinoid, but the class was much more abundant and diverse in the past. Some thick limestone beds dating to the mid- to late-Paleozoic era are almost entirely made up of disarticulated crinoid fragments.

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 (duvets), pillows and sleeping bags. The discovery of feathers trapped in ancient amber suggests that some species of dinosaur may have possessed down-like feathers.

Feather Falls, California

Feather Falls (formerly Mooretown, Moresville, and Feather River) is a rural unincorporated community in Butte County, California north and east of Lake Oroville. It lies at an elevation of 2982 feet (909 m). It is home to Feather Falls Elementary School, a K-8 facility. It takes its name from nearby Feather Falls, which was recently measured to be 410 feet tall. This concurs with the USGS Brush Creek 7½" quadrangle information.There are large forested areas with not many towns on maps of the area. This part of the county is partly inside of Plumas National Forest. Three other small communities are about five miles (8 km) distant in different directions. Camp Eighteen lies 4.9 miles (7.9 km) distant at 61 degrees off true North, straight-line distance. Clipper Mills is about 6.5 miles (10.5 km) at 128 degrees off true North. Forbestown is roughly 5.3 miles (8.5 km) at 188 degrees off true North.

The US Geological Survey defines it as a populated place with a feature ID of 1656010. The community is 2,980 feet (910 m) above mean sea level. The area is inside area code 530. The community's ZIP code is 95940, which is shared with part of Oroville.

Feather River

The Feather River is the principal tributary of the Sacramento River, in the Sacramento Valley of Northern California. The river's main stem is about 73 miles (117 km) long. Its length to its most distant headwater tributary is just over 210 miles (340 km). The main stem Feather River begins in Lake Oroville, where its four long tributary forks join together—the South Fork, Middle Fork, North Fork, and West Branch Feather Rivers. These and other tributaries drain part of the northern Sierra Nevada, and the extreme southern Cascades, as well as a small portion of the Sacramento Valley. The total drainage basin is about 6,200 square miles (16,000 km2), with approximately 3,604 square miles (9,330 km2) above Lake Oroville.The Feather River and its forks were a center of gold mining during the 19th century. Since the 1960s, the river has provided water to central and southern California, as the main source of water for the California State Water Project. Its water is also used for hydroelectricity generation. The average annual flow of the Feather River is more than 7 million acre feet (3.3 km3).The Feather is unique in that two of its tributaries, the East Branch and Middle Fork, originate east of the Sierra Nevada in the Diamond Mountains and breach the crest of the Sierra as they flow west.

Feather bonnet

The feather bonnet is a type of military headdress used mainly by the Scottish Highland infantry regiments of the British Army from about 1763 until the outbreak of World War I. It is now mostly worn by pipers and drummers in various bands throughout the world. It is also worn in a similar fashion by regiments in various Commonwealth armies.

Feather cloak

Feather cloaks have been used by several cultures.

Featherweight

Featherweight is a weight class in the combat sports of boxing, kickboxing, mixed martial arts, and Greco-Roman wrestling.

Flight feather

Flight feathers (Pennae volatus) are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those on the tail are called rectrices (), singular rectrix (). The primary function of the flight feathers is to aid in the generation of both thrust and lift, thereby enabling flight. The flight feathers of some birds have evolved to perform additional functions, generally associated with territorial displays, courtship rituals or feeding methods. In some species, these feathers have developed into long showy plumes used in visual courtship displays, while in others they create a sound during display flights. Tiny serrations on the leading edge of their remiges help owls to fly silently (and therefore hunt more successfully), while the extra-stiff rectrices of woodpeckers help them to brace against tree trunks as they hammer on them. Even flightless birds still retain flight feathers, though sometimes in radically modified forms.

The moult of their flight feathers can cause serious problems for birds, as it can impair their ability to fly. Different species have evolved different strategies for coping with this, ranging from dropping all their flight feathers at once (and thus becoming flightless for some relatively short period of time) to extending the moult over a period of several years.

Leonard Feather

Leonard Geoffrey Feather (13 September 1914 – 22 September 1994) was a British-born jazz pianist, composer, and producer who was best known for his music journalism and other writing.

Maat

Maat or Maʽat (Egyptian mꜣꜥt /ˈmuʀʕat/) refers to the ancient Egyptian concepts of truth, balance, order, harmony, law, morality, and justice. Maat was also the goddess who personified these concepts, and regulated the stars, seasons, and the actions of mortals and the deities who had brought order from chaos at the moment of creation. Her ideological opposite was Isfet (Egyptian jzft), meaning injustice, chaos, violence or to do evil.

Peafowl

Peafowl is a common name for three species of birds in the genera Pavo and Afropavo of the Phasianidae family, the pheasants and their allies. Male peafowl are referred to as peacocks, and female peafowl as peahens. The two Asiatic species are the blue or Indian peafowl originally of the Indian subcontinent, and the green peafowl of Southeast Asia; the one African species is the Congo peafowl, native only to the Congo Basin. Male peafowl are known for their piercing calls and their extravagant plumage. The latter is especially prominent in the Asiatic species, which have an eye-spotted "tail" or "train" of covert feathers, which they display as part of a courtship ritual.

The functions of the elaborate iridescent colouration and large "train" of peacocks have been the subject of extensive scientific debate. Charles Darwin suggested they served to attract females, and the showy features of the males had evolved by sexual selection. More recently, Amotz Zahavi proposed in his handicap theory that these features acted as honest signals of the males' fitness, since less-fit males would be disadvantaged by the difficulty of surviving with such large and conspicuous structures.

Plumage

Plumage (Latin: plūma "feather") 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 differ between species and subspecies and may vary with age classes. Within species, there can be different colour morphs. The placement of feathers on a bird is not haphazard, but rather emerge in organized, overlapping rows and groups, and these feather tracts are known by standardized names.Most birds moult twice a year, resulting in a breeding or nuptial plumage and a basic plumage. Many ducks and some other species such as the red junglefowl have males wearing a bright nuptial plumage while breeding and a drab eclipse plumage for some months afterward. The painted bunting's juveniles have two inserted moults in their first autumn, each yielding plumage like an adult female. The first starts a few days after fledging replacing the juvenile plumage with an auxiliary formative plumage; the second a month or so later giving the formative plumage.Abnormal plumages include a variety of conditions. Albinism, total loss of colour, is rare, but partial loss of colours is more common. Some species are colour polymorphic, having two or more colour variants. A few species have special types of polymorphism, as in the male ruff which has an assortment of different colours around the head and neck in the breeding season only.

Hen feathering is an inherited plumage character in domestic fowl controlled by a single gene. Plumology (or plumage science) is the name for the science that is associated with the study of feathers.

Plume (feather)

A plume is a special type of bird feather, possessed by egrets, ostriches, birds of paradise, quetzals, pheasants and peacocks. They often have a decorative or ornamental purpose, commonly used among marching bands and the military, worn on the hat or helmet of the wearer. When used on military headdresses, the clipped feather plume is referred to as the hackle.

Brightly colored plumes are used by American coot chicks to entice their parents to feed them more food. It is a form of chick ornament.

Ptiliidae

Ptiliidae is a family of very tiny beetles with a cosmopolitan distribution. This family contains the smallest of all beetles, with a length when fully grown of 0.3–4.0 millimetres (0.01–0.16 in). The weight is approximately 0.4 milligrams. They are colloquially called featherwing beetles, because the hindwings are narrow and feathery. The eggs are very large in comparison to the adult female (maybe half the length) so only one egg at a time can be developed and laid. Parthenogenesis is exhibited by several species.The small size has forced many species to sacrifice some of their anatomy, like the heart, crop and gizzard. While the exoskeleton and respiration system of the insects seems to be the major limiting factors regarding how large they can get, the limit for how small they can become appears to be related to the space required for their nervous and reproductive systems.

There are around 600 described species in 80 genera, but large numbers of specimens in collections await description and the true number of species is likely to be much higher than this. Fossil ptiliids have been recorded from the Oligocene, roughly 30 million years ago from the Eocene, 46.2–43.5 million years ago, and from the Cretaceous Lebanese and Myanmar amber, dated to 125 and 95 million years ago, respectively. The family is divided into 3 subfamilies:

Acrotrichinae

Cephaloplectinae

Ptiliinae

Quill

A quill pen is a writing implement made from a moulted flight feather (preferably a primary wing-feather) of a large bird. Quills were used for writing with ink before the invention of the dip pen, the metal-nibbed pen, the fountain pen, and, eventually, the ballpoint pen. The hand-cut goose quill is rarely used as a calligraphy tool, because many papers are now derived from wood pulp and wear down the quill very quickly. However, it is still the tool of choice for a few scribes who noted that quills provide an unmatched sharp stroke as well as greater flexibility than a steel pen.

Birds (class: Aves)
Anatomy
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Evolution
Fossil birds
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Feather tracts

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