Not every white bird is an albino: sense and nonsense about colour aberrations in birds

n the birding world, general confusion seems to exist about colour mutations in wild birds and the correct naming of these aberrations. Almost all whitish aberrations are called ‘(partial) albino’. However, most of these are not albino and ‘partial albinism’ is – by definition – not even possible. Some mutations are hard to distinguish in the field (and in museum collections) because the colour of feathers with a pigment reduction is easily bleached by sunlight and can even become almost white. For the correct identification and naming of colour mutations, it is necessary to know which changes have occurred in the original pigmentation. But first of all, it is necessary to understand which pigments determine the normal colours of feathers and how these pigments are formed. All colour aberrations described here have a genetic basis, ie, they are caused by a mutation. There are more possible colour mutations in birds than those described below. However, the ones dealt with here are those occurring most frequently and are more or less clearly recognizable, either in the field or in museum specimens. The aim of this paper is to present clear definitions of the most common types of colour mutations in birds and to give a basic insight into the genetic or food-related mechanisms that cause or influence these mutations. The paper is based on the study of colour mutation genetics and the study of many 1000s of bird skins and live birds during the course of 15 years of working with cage birds and as bird collection manager and taxidermist of the Nationaal Natuurhistorisch Museum Naturalis at Leiden, Zuid-Holland, the Netherlands, as well as in other European natural history museums (van Grouw 1997, 2000ab).