| Summary: | Includes bibliographical references. I surveyed the literature on the breeding biology of 19 species of North American gulls and presented the data to compare gull breeding strategies. The species studied were cited in the American Ornithologists' Union Check-list of North American Birds (1957) as species breeding within North America north of Mexico, including Greenland, Bermuda and Baja California; I also included all locations north of the Arctic Circle. The information on breeding strategies was divided into 5 categories: Chronology of Breeding Activities, Characteristics of the Breeding Site, Spatial Distribution of Individual Pairs, Nest Construction, and Clutch and Egg Characteristics. I found that gulls were relatively uniform in their breeding chronologies. Differences that did exist between species appeared to result from latitudinal differences in breeding location. Gulls used islands and mainland locations as colony sites, in about equal frequency. The habitat and substrate types used at these locations may be a function of species range and geographical location of the breeding site. All but one of the 19 gull species studied were documented to have bred in a "colonial" distribution of pairs at some breeding sites, and as solitary pairs in other situations. This was influenced by the topography at their colony sites and intra-specific distribution was limited by the size of the site and proximity of vegetation. Gulls usually built their nests out of locally available plant material and the size and shape of the nest was dependent on the size of the bird and physical placement of the nest. Clutch size varied from 1 to 5 eggs (X=3); egg size was correlated with body size. The 19 gull species in North America exhibited a wide range of inter-specific variation in their reproductive strategies. Reproductive parameters may be a critical factor in determining the ecological segregation of the species over the North American continent. M.S. (Master of Science)
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