Notes on colour aberrations in Common Guillemot Uria aalge and Northern Gannet Morus bassanus

Abstract

Colour aberrations in birds are not uncommon and many observations have been published over the years in the ornithological literature. Unfortunately, ornithol- ogists tend to use descriptive names that refer to the colour of a particular bird with unusual plumage. However this is confusing, as for each species the normal plumage colour varies, and therefore the appearance of any given mutation will be different for each species.