Leucism. -Albinism.- Xanthochroids
Leucism is a very unusual condition whereby the pigmentation cells in an animal or bird fail to develop properly. This can result in unusual white patches appearing on the animal, or, more rarely, completely white creatures.
Albinism is a different condition. The easiest way to tell the difference between the two is that in albinism the eyes are usually pink or red, and albinism affects the entire animal, not just patches.
This occasionaly causes very excited biologists to think they have discovered a new species, when in fact leucism is the cause of the unusual markings they have seen.
Xanthochroids Birds can show this condition in one of two ways: either there is an excess of yellow in the plumage or the yellow replaces another colour (in this instance the red). The condition has been reported in a number of species, including other species of woodpecker (in North America), and in many instances the colour replaced is red.
Wild life extra which has now closed down their website
Leucistic Dunnock - Prunella modularisDevon 2013