What is leucism? Can leucism be treated?
Leucism is a general term for the phenotype resulting from defects in pigment cell differentiation or migration. It is a condition in which there is a partial loss of pigmentation resulting in white, pale or patchy colouration of skin, hair, feathers, scales or cuticle, but not the eyes. Leucism can be caused by the reduction of all types of pigment, unlike albininism, which only affects the melanin production. Leucism is occasionally found in corvids, which can show a varying degree of white or pale feathers within an otherwise normal appearing plumage. These abnormal feathers are often more prone to wear and tear and make the bird potentially more conspicuous and prone for predation.
Besides primarily genetic causes, dietary deficiency caused by calcium or folic acid deficiency, or as found in Australian ravens due to a circovirus infection, can also result into this phenotype pattern. It has been also found that agricultural pesticides have a direct impact on reducing food and insect availability. Insects are an essential dietary requirement for almost all bird species, which rely on those for at least a substantial part of the nestling phase of their offspring. Pesticides lead directly and indirectly to the search for alternative and often suboptimal food substitutes and may also result into a progressive weakening of the immune system of adult and young birds, which increases mortality in general, but does more often lead to a varying degree of dietary deficiencies with subsequent plumage and skeletal aberrations.
Recognising the difference between inherited and acquired plumage aberrations is crucial, as acquired plumage problems can be corrected, whilst inherited causes cannot.