Editing Plumage (section)

=== 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" />