Abstract: Colour aberrations in birds – not only albinism and leucism lead to white plumages!
The colouration of the integument of most birds is often about entirely based on both melanin colour pigments, eumelanin and phaeomelanin. If these are produced in lower or higher quantities than usual or if their quality is reduced, aberrant appearances result. The different colour aberrations were historically named according to the appearances of affected birds and not according to the genetic causes for their abnormal appearances. Even today, we lack a common nomenclature or common definitions in this respect. It is proposed to follow in the future the subdivision for genetic mutations as elaborated by van Grouw. He distinguished between albinism (no production of melanin pigments at all, neither for feathers nor for bare parts, nor for the eyes), total leucism (no delivery of melanin to feathers and possibly not to bare parts, but presence in the eyes), partial leucism (not all feathers are affected, the eyes are not affected), brown (qualitative reduc- tion of eumelanin only), ino (qualitative reduction of both eu- and phaeomelanin), dilution (quantitative reduction of melanin(s)) and different forms of melanism (in most cases, increased quantity of melanin). Besides, field ornithologists must be aware that not all aberrations are triggered by the genetic mutations described above. In many cases, an abnormal appearance is the result of progressive greying. Also, a correct assessment of the cause for an aberration is often difficult and not possible in all cases. It is therefore useful to always provide a complete description of aberrant birds. In addition, more data about life time histories of affected individuals are requested.
André Konter; Regulus Wissenschaftliche Berichte Nr 29. 2014