Editing Plumage (section)

==Abnormal plumages==
[[File:Blue male budgie.jpg|thumb|right|Axanthic [[budgerigar]]]]
[[File:Snowdrop.penguin.600pix.jpg|thumb|upright|An albino [[African penguin]]]]
There are hereditary as well as non-hereditary variations in plumage that are rare and termed abnormal or aberrant plumages. Melanism refers to an excess of black or dark colours. Erythromelanism or [[erythrism]] is the result of excessive reddish-brown erythromelanin deposition in feathers that normally lack melanin. Melanin of different forms combine with xanthophylls to produce colour mixtures and when this combination is imbalanced it produces colour shifts that are termed schizochroisms (including [[xanthochromism]] – an overabundance of yellow – and axanthism – lack of yellow – which are commonly bred in [[cagebird]]s such as [[budgerigars]]). A reduction in eumelanin leads to non-eumelanin schizochroism with an overall fawn plumage while a lack of phaeomelanin results in grey-coloured non-phaeomelanin schizochroism. Carotenism refers to the abnormal distribution of [[carotenoid]] pigments.<!-- source may also be Buckley, as below -->

The term "dilution" is used for situations where the colour is of a lower intensity overall; it is caused by decreased deposition of pigment in the developing feather, and can thus not occur in [[structural coloration]] (i.e., "dilute blue" does not exist); pale structural colors are instead achieved by shifting the peak wavelength at which light is refracted.<ref>{{Cite web|url=http://mafija.fmf.uni-lj.si/seminar/files/2013_2014/hana_majaron_structural_colors_fin2.pdf|title=Structural coloration|last=Majaron|first=Hana|date=December 2013|website=mafija.fmf.uni-lj.si}}</ref><!-- anything about the process by which structural colors are produced should provide sufficient info --> Dilution regularly occurs in normal plumage (grey, buff, pink and cream colours are usually produced by this process), but may in addition occur as an aberration (e.g., all normally black plumage becoming grey).<ref>Buckley, P.A. 1982. Avian Genetics. In: Petrak, M. (ed.). Diseases of cage and aviary birds, 2nd ed. pp. 21–110. Lea and Febiger, Philadelphia.</ref>

In some birds – many [[true owl]]s (Strigidae), some [[nightjar]]s (Caprimulgidae) and a few [[cuckoo]]s (''[[Cuculus]]'' and relatives) being widely known examples – there is colour [[Polymorphism (biology)|polymorphism]]. This means that two or more colour variants are numerous within their [[population]]s during all or at least most seasons and plumages; in the above-mentioned examples a brown (phaeomelanin) and grey (eumelanin) morph exist, termed "hepatic form" particularly in the cuckoos. Other cases of natural polymorphism are of various kinds; many are melanic/nonmelanic (some [[paradise-flycatcher]]s, ''Terpsiphone'', for example), but more unusual types of polymorphism exist – the face colour of the [[Gouldian finch]] (''Erythrura''<ref>{{cite iucn |author=BirdLife International |date=2016 |title=''Chloebia gouldiae'' |volume=2016 |page=e.T22719744A94642482 |doi=10.2305/IUCN.UK.2016-3.RLTS.T22719744A94642482.en |access-date=11 November 2021}}</ref><ref>{{Cite web|url=https://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=413|title=Erythrura gouldiae – Gouldian Finch|website=Australian Government – Department of the Environment and Energy}}</ref>''<!-- Chloebia? --> gouldiae'') or the courtship types of male [[Ruff (bird)|ruff]]s (''Philomachus pugnax'').<ref>{{Cite web|url=https://eprints.whiterose.ac.uk/83236/1/2014%20Farrell%20J%20Hered%20online.pdf|title=Major Breeding Plumage Color Differences of Male Ruffs (Philomachuspugnax) Are Not Associated With Coding Sequence Variation in the MC1R Gene|last=Lindsay L. Farrell, Clemens Küpper, Terry Burke, and David B. Lank|date=December 2014|website=White Rose Research Online}}</ref>

=== Albinism ===
[[Albinism]] in birds is rare, occurring to any extent in perhaps one in 1800 individuals. It involves loss of colour in all parts including the iris of the eyes, bills, skin, legs, and feet. It is usually the result of a genetic mutation causing the absence of [[tyrosinase]], an enzyme essential for melanin synthesis. [[Leucism]] (which includes what used to be termed as "partial albinism") refers to loss of pigments in some or all parts of feathers. A bird that is [[Albinism|albino]] (from the [[Latin]] ''albus'', "white") has white [[feather]]s in place of coloured ones on some portion of its body. A bird that is naturally white, such as a [[swan]], [[goose]], or [[egret]], is not an albino, nor is a bird that has seasonally alternating white plumage.<ref name="Terres 1980">"Albinism". Terres, John. K. ''The Audubon Society Encyclopedia of North American Birds'', New York: Alfred A. Knopf, 1980. {{ISBN|0-394-46651-9}}.</ref>

Four degrees of albinism have been described. The most common form is termed ''partial albinism'', in which local areas of the bird's body, such as certain feathers, are lacking the pigment [[melanin]]. The white areas may be symmetrical, with both sides of the bird showing a similar pattern.  In ''imperfect albinism'', the pigment is partially inhibited in the [[skin]], [[eye]]s, or feathers, but is not absent from any of them. ''Incomplete albinism'' is the complete absence of pigment from the skin, eyes, or feathers, but not all three.<ref name="Terres 1980" />

[[File:Albino crow and its mother.JPG|thumb|right|An albino juvenile [[house crow]] in [[Malacca]], [[Malaysia]], next to its normal-coloured parent]]
A completely albino bird is the most rare. The eyes in this case are pink or red, because [[blood]] shows through in the absence of pigment in the [[iris (anatomy)|iris]]es. The [[beak]], legs, and feet are very pale or white. Albino adults are rare in the wild because their eyesight is poor resulting in greater risk of predation.<ref>{{Cite journal|title=Not every white bird is an albino: sense and nonsense about colour aberrations in birds|author=Grouw, Hein van|url=http://www.vogelringschier.nl/DB28%282%2979-89_2006.pdf|journal=Dutch Birding|volume=28|year=2006|pages=79–89|url-status=live|archive-url=https://web.archive.org/web/20170808092233/http://www.vogelringschier.nl/DB28(2)79-89_2006.pdf|archive-date=8 August 2017}}</ref> They are likely easier targets for [[predator]]s because their colour distinguishes them from their environment. [[Falconry|Falconers]] have observed that their trained birds are likely to attack a white [[pigeon]] in a [[Flock (birds)|flock]] because it is conspicuous. A complete albino often has weak eyesight and brittle wing and tail feathers, which may reduce its ability to fly. In flocks, albinos are often harassed by their own species. Such observations have been made among [[red-winged blackbird]]s, [[barn swallow]]s, and [[African penguin]]s. In a nesting colony of the latter, three unusual juveniles—one black-headed, one white-headed, and one full albino—were shunned and abused by companions.<ref name="Terres 1980" />

Albinism has been reported in all [[order (biology)|order]]s and in 54 [[family (biology)|families]] of North American birds. The [[American robin]] and [[house sparrow]] led bird species in the [[Incidence (epidemiology)|incidence]] of albinism. Albinistic white appears to replace brown pigments more often than red or yellow ones; records suggest a greater incidence in [[crow]]s, [[raven]]s, and [[hawk]]s than in [[American goldfinch|goldfinch]]es or [[New World oriole|oriole]]s.<ref name="Terres 1980" />

Several kinds of [[Solid white (chicken plumage)#Albinism and partial albinism|albinism in chickens]] has been described: A complete albinism controlled by an autosomal recessive gene<ref>{{cite journal | author = Warren D.C. | year = 1933 | title = Inheritance of albinism in the domestic fowl | journal = Journal of Heredity | volume = 24 | pages = 379–383 }}</ref> and two different kinds of partial albinism. One of the partial albinisms is sex-linked<ref>^ Mueller, C.D. and Hutt, F.B. 1941 Genetics of the fowl. 12. Sex-linked imperfect albinism, Journal of Heredity. 32, 71–80.</ref> and the other is autosomal recessive.<ref>{{cite journal |author1=Brumbaugh J.A. |author2=Bargar T.W. |author3=Oetting W.S. | year = 1983 | title = A "new" allele at the C pigment locus in the fowl | journal = Journal of Heredity | volume = 74 | issue = 5| pages = 331–336 |doi=10.1093/oxfordjournals.jhered.a109804 }}</ref> A fourth kind of albinism severely reduce pigmentation in the eyes, but only dilutes the pigment in the plumage.<ref>{{cite journal | author = Warren D.C. | year = 1940 | title = Inheritance of pinkeye in the fowl | journal = Journal of Heredity | volume = 31 | issue = 6| pages = 291–292 | doi = 10.1093/oxfordjournals.jhered.a104904 }}</ref>

Abnormally white feathers are not always due to albinism. Injury or disease may change their color, including dietary deficiencies or circulatory problems during feather development. Aging may also turn a bird's feathers white.<ref name="Terres 1980" />

===Hen feathering in cocks===
{{Main|Hen feathering}}

Hen feathering in cocks is a genetically conditioned character in domestic fowl ([[Gallus gallus domesticus]]). Males with this condition develop a female-type plumage, although otherwise look and respond like virile males. In some breeds, one can see males that have a plumage completely similar in all aspects to that of females. The trait is controlled by a simple [[autosome|autosomic]] [[dominant gene]], whose expression is limited to the male sex.<ref name=j3/><ref name=j4/><ref name="somes"/> The condition is due to an enhanced activity of the aromatase complex of [[enzyme]]s responsible for [[estrogen]] synthesis. So estrogen formation in the skin is as much as several hundred-fold higher than that of normal chickens.<ref name=j5/>