The term is found in reference to plumage colouring in the bird species names isabelline bush-hen, isabelline wheatear, and isabelline shrike, as well as in other descriptions of birds. The genetic pigmentation disorder isabellinism seen in birds is derived from the colour word and is a form of leucism caused by a uniform reduction in the production and expression of melanin resulting in areas of plumage on the back of the bird, normally black, being strongly faded, or isabelline, in appearance.[9] Isabellinism has been reported in several species of penguin.[10][11]