What Is Leucism?

Leucism is a term used to describe a wide variety of conditions which result in the partial loss of pigmentation in an animal—which causes white, pale, or patchy coloration of the skin, hair, feathers, scales or cuticles, but not the eyes.

Leucism, or leukism, is an abnormal plumage condition caused by a genetic mutation that prevents pigment, particularly melanin, from being properly deposited on a bird’s feathers. As a result, the birds do not have the normal, classic plumage colors listed in field guides or seen in most photos. Instead, the plumage may have several color changes, including:

Bold white patches where the bird should not have any
Paler overall plumage that looks faint, diluted, or bleached
Overall white plumage with little or no color visible

The degree of leucism, including the brightness of the white and the extent of pigment loss, will vary depending on the bird’s genetic makeup. Birds that show only white patches or sections of leucistic feathers, often in symmetrical patterns, are often called pied or piebald birds, while birds with fully white plumage are referred to as leucistic birds.

Here are some pictures of a leucistic common gull in north of Norway: