| Summary: | The striking convergences in morphology, behaviour and physiology existing between various species of sea birds are discussed, both on the basis of personal observations, mostly carried out in the Antarctic and Sub Antarctic zones, and from data in the literature. The morphological adaptations are reviewed first. The body weight of species nesting underground is shown to be lighter than that of species nesting above ground. Plankton-feeders usually have a broad bill, while fish-feeders have a long and narrow one. There is a broad and continuons range of flight capabilities, ranging from frigate-birds and albatrosses at one extreme to flightless penguins at the other. The difficulty of a proper comparison of flight and diving abilities between different categories of sea birds is pointed out, and the results given by various measurements and indices are compared. The adaptive value of cryptic coloration of both eggs and nestlings to their background is discussed, as well as the prolective role of some immature and adult plumages. The adaptive function of sea bird ritualized displays and vocalizations is suggested. Further data supporting David Lack's (1968) conclusions on the adaptive value of variations in egg weight and incubation length are provided. Most sea birds have a low reproductive rate which is counter-balanced by a relatively high survival rate. They can be considered K-strategists. Some estimates of the resting metabolic rate of adult sea birds are given. The interdependence of the various adaptations is emphasized. To better understand the variety of adaptive strategies displayed by sea birds, the factors which are responsible for the heterogeneity of the oceanic environment are reviewed. Further, the variations in foraging distances observed in the various bird groups during the breeding season in emphasized (fig. 11). Foraging distance is significantly correlated with the average number of eggs produced per year per female, and with the aspect ratio of the wing
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