Leucism and Albinism in Birds
The ornithological literature is quite confusing regarding definitions of leucism and various states of albinism. Whereas recent ornithological texts define albinism (e.g., Welty and Baptista 1988, Gill 1990, Clark 2001), none refers specifically to leucism. Thomson (1964) states that leucism “results from varying degrees of dilution of normal pigmentation.”
In a review of albinism in British birds, Sage (1962) referred to leucistic individuals “in which the normal pattern and colour of the plumage is discernable but very pale or washed out in appearance” and (citing Hutt 1949) distinguished this dilution of all pigments from albinism, which affects melanin but not necessarily the carotenoid pigments. Lucas and Stettenheim (1972) point out that a genetically complete albino could still have highly colored feathers if a pigment other than melanin were present.
According to these authors, leucism is caused not by a lack of pigment, but by a reduced deposition of pigment in the feathers. Several of these references refer further to partial albinism as the lack of melanin from part of the plumage, either symmetrically or asymmetrically (Gross 1965, Lucas and Stettenheim 1972, Clark 2001).
Harrison (1963) made a different distinction, stating that leucistic individuals have melanin in the body, giving dark eyes and colored soft parts, but the melanin does not enter the feather structure and the plumage is white, whereas albinistic individuals lack melanin in the body as well as the plumage. Other recent authors follow this “all-or-none” definition of albinism and believe that a bird with any amount of abnormal white in the plumage, but with dark eyes, would be leucistic (e.g. Jehl 1985, Cooke and Buckley 1987, Lawrence 1989).
Whether the result of partial albinism or leucism, the presence of atypical white patches in normally darker plumaged birds gives rise to the terms “pied” or “piebald.” The latter terms originated in the literature on domestic poultry and do not appear to have unique scientific meaning. The white Pileated Woodpecker described from the White River region would be termed a partial or even "nearly complete" albino by some authors (because melanin appears to be completely lacking through most of the plumage), but based on most recent technical definitions we might best consider it leucistic.
—Kenneth V. Rosenberg, Martjan Lammertink, Keith Brady, Sonny Bass, and Utami Setiorini
Clark, G. A., Jr. 2001. Form and function: the external bird. In Handbook of Bird Biology (S. Podulka, R. Rohrbaugh, Jr., and R. Bonney, eds.) The Cornell Lab of Ornithology, Ithaca, NY.
Cooke, F., and P. A. Buckley. 1987. Avian Genetics: A population and ecological approach. Academic Press Inc., Orlando, FL.
Gill, F. B. 1990. Ornithology. W. H. Freeman and Company, New York.
Gross, A. O. 1965. The incidence of albinism in North American Birds. Bird Banding 36:67-71.
Harrison, C. J. O. 1962. Non-melanic, carotenistic and allied variant plumages in birds. Bull. British Ornithol. Club 83: 90-96.
Jehl, J. R., Jr. 1985. Leucism in Eared Grebes in Western North America. Condor 87:439-441.
Lawrence, E. (ed). 1989. Henderson’s dictionary of biological terms. Wiley/ Intersciences, Harlow, UK.
Lucas, A. M., and P. R. Stettenheim. 1972. Avian Anatomy Integument Part II. U.S. Department of Agriculture Handbook 362. Washington, D. C.
Sage, B. L. 1962. Albinism and melanism in birds. British Birds 55: 201-225.Thomson, A. L. (Ed.) 1963. A new dictionary of birds. McGraw-Hill, New York.
Welty, J. C. and L. Baptista. 1988. The Life of Birds, fourth edition. Saunders College Publishing. New York.
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