Leucism (leukism) is a condition where there is complete lack of melanin from all or part of the plumage in a bird with resultant white or pale discolouration of the feathers. This is not the same as albinism where there is a complete lack of melanin in both the plumage, bare parts and, most importantly, the eyes (with associated poor vision and poor outcomes in the wild).
Leucism in birds is not uncommon and many of us would have spotted the odd bird from time to time. Leucism may be due to genetics, diet or injury.
This week I observed a leucistic Large-billed Crow (Corvus macrorhynchos). It had some white feathers on the breast, back of the neck and pale shafts on the thigh. The pigmentation of the iris was normal (see first two images). The bird was observed alone, which is uncommon for this species in the Ipoh area; suggesting perhaps social isolation.
In the past I have seen a leucistic House Crow (Corvus splendens) in the Klang Valley that had more extensive leucism and was mobbed by other crows (see additional two images). This social behaviour has also been reported locally by Daisy O’Neill (2009)
Guay, Potvin, and Robinson (2012) describe the many pigmentary changes possible and also include:
- Schizochroism– characterised by the lack of a single pigment from part or all of the plumage.
- Melanism– an abnormally high level of melanin is deposited in feathers or melanin replaces carotenoids in part or all of the plumage (melanistic birds are darker overall).
- Carotenism– an abnormality of the amount, distribution or composition of carotenoid pigments (plumage colour shifts toward either red or yellow).
- Dilution– overall decrease in deposition of all pigment in feathers over the whole body, resulting in a faded appearance.
References:
- Guay, P.J., Potvin, D.A., and Robinson, R.W. (2012). Abberations in plumage coloration in birds. Australian Field Ornithology 29 23-30. Available here: <https://www.researchgate.net/publication/235998351_Aberrations_in_plumage_coloration_in_birds>
- Daisy O’Neill (2009). Leucism in crows. Bird Ecology Study Group. <https://besgroup.org/2009/05/27/leucism-in-crows/>
- Melissa Mayntz (2020). Bird Leucism: About Leucistic Birds and Abnormal Plumages. The Spruce. Dotdash Meredith Publishing. <https://www.thespruce.com/bird-leucism-387342>
Dato’ Dr Amar-Singh HSS
Ipoh, Perak, Malaysia
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