With recognition of the Yellow-footed Gull (Larus livens) as a distinct species, separate from the Western Gull (Larus occidentalis) (American Ornithologists Union 1982), there is renewed interest in the dark-mantled gulls of western North America. In order to correctly identify these birds it is important to understand how they progress from juvenal to adult plumage, and when molts occur.
Jonathan Dwight’s definitive work, The Gulls of the World (1925), includes much valuable information on plumages and molts, but was designed for museum workers with specimens in hand, and is now difficult to obtain, being long out of print. Recently, Peter Grant (1982) provided a masterpiece on all the gulls known to occur in the western Palearctic, Gulls: A Guide to Identification, with emphasis on field identification. It is from this book that the chart showing the sequence of plumages and molts, as well as the topographical terminology, is taken.