Depends on sources.
Here is Sibley's take: http://www.sibleyguides.com/2011/08/...nin-reduction/
I have the 1985 edition of "A Dictionary of Birds" edited by Campbell and Lack. An entry by C.J.O. Harrison lists the following types of abnormal plumage:
Abnormal Pigmentation, Atypical pigmentation, Schizochroism, Pigment replacement, Gynandromorphs, Pigment deficiency, Pattern variations, and Feather structure abnormalities.
The following appears in the discussion under "Atypical pigmentation:"
"Partial loss of pigment, affecting all the colours present and reducing them in intensity, is rare. It is called 'dilution' by bird breeders and 'leucism' in scientific writings, although the latter term is also used at times for various forms of schizochroic loss (see below) of single pigments which make the plumage appear paler...."
So defined, the phenomenon of true leucism (dilution of all pigments) is much rarer than schizochroism (involving a loss or dilution of only some pigments), so "leucistic" should probably be used rarely, and not merely as a jargon replacement for the more popular vernacular "partial albino."
Originally Posted by andyadcock
Seems not to be true according to people who know more than me.
'Leucism (/ˈluːsɪzəm, -kɪz-/) is a condition in which there is partial loss of pigmentation in an animal resulting in white, pale, or patchy coloration of the skin, hair, feathers, scales or cuticle, but not the eyes. It is occasionally spelled leukism. Unlike albinism, it is caused by a reduction in multiple types of pigment, not just melanin.'
Leucism is a general term for the phenotype resulting from defects in pigment cell differentiation and/or migration from the neural crest to skin, hair, or feathers during development. This results in either the entire surface (if all pigment cells fail to develop) or patches of body surface (if only a subset are defective) having a lack of cells capable of making pigment.