Little did I realise that I was stepping into a definition minefield when, after finding an oddly coloured jackdaw earlier this week, I decided to find out more about leucism. The word is a relatively new one – it isn’t, for example, included in the online Oxford Dictionary, and scientists seem to disagree about its actual meaning and about what causes the condition.
One source says the plumage of leucistic birds is pale or washed out though the normal pattern and colour is discernible, another reports that the cells of the affected plumage lack the ability to produce melanin and the lack of melanin produces white feathers, and yet another states that leucism is caused by a reduction in several types of pigment, not just melanin. The researchers at Cornell Lab of Ornithology even devoted a whole web page to citing the literature of disagreement.
So, rightly or wrongly and very simply, I’m defining my leucistic birds as those whose feathers would normally be black or some other colour but are actually white (but they’re not albino, as they have their normal eye colour). And here they are …