Post-Breeding Movements and Mortality in the Western Gull, Larus occidentalis

Abstract

Many species of birds move away from their breeding areas during the nonbreeding season. This movement may involve long or short distances; it may be migratory or random. In some species the pattern differs among breeding populations. Populations of the Fox Sparrow (Passerella iliaca) that breed in different localities also migrate to different localities (Swarth 1920). The Great Cormorant (Phalacrocorax carbo), although nonmigratory, shows post-breeding, colony-specific dispersal tendencies (Coulson and Brazendale 1968). These differences also have been shown in some colonial birds whose colonial habit