Leucistic Red-backed Shrike. Photo: Rudy Erasmus
Leucism is a reduction in intensity of pigments in the feathers and is fairly common. There have been various letters from Africa Birds & Birding regarding leucistic birds over the years from Blue Crane Anthropoides paradiseus to Cape Sugarbird Promerops cafer and Natal Francolin Pternistes natalensis. (See Vol. 5(5):21, Vol. 10(1):14, Vol. 10(4):9). Whilst a large proportion of the bird’s feathers are white, the eyes remain dark and there is a vestige of some other feather coloration as well. In short, leucism is a genetic mutation in which the bird may have anywhere from one white feather to all white feathers, but coloured eyes or legs or beak. The dangers of leucism are numerous although it is often recorded that the bird appears to lead a ‘normal’ life, albeit in a different coloured dress to his mates.
The bird is obviously more conspicuous, thus a greater risk to predation. It is also generally accepted that leucistic birds have a shorter lifespan. The loss in pigments leads to a weakened feather structure over time with resultant increased wear. The retina of the eye is also often affected resulting in increased light sensitivity and even blindness from the sun. The success at mate attraction, based on visual feather cues could also be compromised, although leucistic birds often breed and rear young. Flock living species will often not accept a leucistic bird. Albinism, on the other hand, is the complete absence of pigmentation due to inability to produce melanin. All the feathers are snow white and the soft parts are pinkish. The eye colour is also pink as a result of blood vessels showing through in the absence of darker colours. Albinism is normally caused by a genetic mutation that can be inherited if both parents have the albino gene. These birds generally do not survive more than a few days and are rarely seen.
Article 25 bullet 08 March 2007
Avian Colour Oddities, from bird info.co.za
by Martin Benadie