More on Leucism & Albinism
- It appears that what most bird books say about the difference between the
two is, well, for the birds. Nor does the semi-professional literature
seem much more reliable. For example, the often repeated environmental vs.
genetic distinction (leucism vs. albinism) looks to be pure bird lime.
Both conditions are well known among vertebrates of all classes, and have
been most systematically studied among mammals. As I'd guessed based on
human coloration, patterns of melanin deposition among vertebrates are
quasi-independent with regard to iris, skin and keratin-bearing
I'm pretty sure that the iris and the epidermis arise from different
embryological layers, so it makes sense they could melanize differently,
but I thought the keratin-bearing tissues were epidermal, so I'm not sure
why they would color differently from the skin, except in the case of
bleaching. However, many organisms, notably among winter snowy-landscape
dwelling mammals, seasonally or perennially grow out relatively or mostly
colorless fur: arctic foxes, weasels, polar bears. And that's apparently
the crux of leucism.
Both leucism and albinism are genetic in origin. The general agreement is
that leucism involves limited or absent melanin deposition in the
keratin-bearing tissues: leucistic organisms apparently produce melanin
normally. (Polar bears are just leucistic grizzlies with black
noses.) Albinos, on the other hand, are faulty producers of melanin in
general. At least one source asserted that all albinos produce at least
some melanin, just not enough to be observed grossly.
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- True albinos completely lack all pigments; leucistic
individuals lack some but not all pigments. Albinism
is always hereditary. Leucism may be hereditary or
environmentally induced (usually related to diet).
Many years ago I collected the classic texts on
plumage abnormalities in birds (see citations below).
If there are any recent comprehensive reviews, please
let me know.
Buckley, P. A. 1982. Avian genetics. Pp. 21-110 in M.
Petrak (ed.), Diseases of cage and aviary birds, 2nd
ed. Lea and Febiger, Philadelphia. [pp. 65-74 discuss
Deane, R. 1876. Albinism and melanism among North
American birds. Bulletin of the Nuttall Ornithological
Gross, A. O. 1965. Melanism in North American birds.
Gross, A. O. 1965. The incidence of albinism in North
American birds. Bird-Banding 36:67-71.
Hailman, J. P. 1984. On describing color abnormalities
in birds. Florida Field Naturalist 12:36-38.
Harrison, C. J. O. 1963. Non-melanic, carotenistic and
allied variant plumages in birds. Bulletin of the
British Ornithologists' Club 83:90-96.
Harrison, C. J. O. 1963. Grey and fawn variant
plumages. Bird Study 10:219-233.
Rollin, N. 1962. Abnormal white, yellow and fawn
plumages. Bulletin of the British Ornithologists' Club
Rollin, N. 1964. Non-hereditary and hereditary
abnormal plumage. Bird Research 2:1-44.
Ross, C. C. 1963. Albinism among North American birds.
Ross, C. C. 1973. Some additional records of albinism
in North American birds. Cassinia 54:18-19.
Sage, B. L. 1962. Albinism and melanism in birds.
British Birds 55:201-225.
Sage, B. L. 1962. The incidence of albinism and
melanism in British birds. British Birds 56:409-416.
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