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The closest relatives of the southern black-back are to be found in the northern hemisphere, amongst the interbreeding assemblage of subspecies of the herring and lesser black-backed gulls. The limited available literature taken together with the results of this study shows that as far as general behaviour is concerned, no significant differences can be detected between the three species, but features of the alarm calls indicate that the southern black-back is related rather more closely to the lesser black-back than to the herring gull. General, pair-forming and hostile calls and postures have been outlined, and roosting and some aspects of general flock behaviour described. Most birds with which the gulls are in contact will concede food or space, notable exceptions being the Arctic skua and giant petrel.