White feathers in black birds

Abstract

The most common plumage abnormalities in birds involve some form of white feathering, ranging from birds with just a few white feathers to individuals that are completely white. The causes of aberrant white feathers are diverse and, in many cases, unknown. Some are heritable, based on simple, genetically determined changes in the pigmentation process. More commonly, the causes are less clear-cut and can include environmental conditions (particularly in relation to food availability), and the physical condition and/or age of the bird. In this paper, white feathering is explored in three common species: Carrion Crow Corvus corone, Hooded Crow C. cornix and Blackbird Turdus merula. Results from the BTO Abnormal Plumage Survey are summarised, and data from a museum-based study of Blackbirds with plumage abnormalities are reported. In all three species, partly white plumage is recorded regularly and is often referred to incorrectly as albinism or leucism.