Leucism is the complete loss of a particular pigment, or all pigments, in feathers but not in soft-parts. It may be as slight as a single white feather or as pervasive as an all-white bird with normal eyes, bill, and legs (Buckley 1982). The condition has been documented, usually as a curiosity and under the term "albinism," in hundreds of species. Its incidence is said to differ greatly among species (e.g., Sage 1963, Gross 1965), but the data for that con-clusion are unconvincing because a high percentage of reports pertain to species that associate with, or are hunted by, man. As a result, observational bias is potentially strong. For only a few species (e.g., storm-petrels; Baptista 1966) has it been possible to consider the phenomenon more broadly and to investigate the frequency of leucism in natural populations of birds. The subject is interesting because leucism, like any variable condition, may provide indirect evidence of underlying genetic variability. Fur-thermore, if its frequency can be measured, this may allow some inferences to be drawn about the strength of selection against abnormally-colored individuals. In this paper, I present data on leucism compiled incidental to other re-search during a four-year (198 l-l 984) study of Eared Grebe (Podiceps nigricollis) biology at Mono Lake, California. Other aspects of this research have been presented else-where (Mahoney and Jehl 1985; Storer and Jehl, in press). Apparently pure white on head, body. Wings pre-sumed to be white, but that is not necessarily the case (Fig. 2). White with gray smudges on head or neck or both. Ear tufts (if present) white or very pale yellow. Wings variable; remiges or coverts or both may be pigmented (Fig. 2). Body white with occasional gray feathers on back or rump (not usually evident except at close range). Wings dark except for (normal) white patch of secondaries. Black or gray markings on crown or nape, often extending around ear tufts onto chin. Ear tufts (if present) golden or pale yellow. Body white. Gray feathers evident on back. Oth-erwise like category 3, except black area on neck is more extensive and occurs on lateral and an-terior surface. Wings as in category 3. Head, neck, and chest black, with golden ear tufts (if present). Back dark, rest of body white. Wings as in category 3. Piebald. Appears uniformly gray at a distance but plumage is a mixture of gray and white feathers. Wing pattern apparently variable. a In cate ories 2A-5A (not listed), the patterns are identical to those in categories 1 -5, but black tones are replaced by brown OT tan.