Minor individual plumage variation in gulls is one of many factors confounding field identification of this notoriously difficult group. Plumage variation can sometimes take the form of more extreme anomalies such as leucism and albinism (Grant 1986). A well-known variant of the Heermann’s Gull (Larus heermanni) shows patches of white on the greater primary-coverts (Hubbs and Bartholomew 1951), as depicted, for example, by Sibley (2000); some individuals have additional white on other wing coverts, scapulars, or remiges (pers. obs.).