A substantial amount of research has been carried out on recognition behaviour in natural popu- lations of pinnipeds. This work includes detailed anecdotal and quantitative descriptions in addition to in situ experimental tests of recognition. The goals of this review are to summarize this research, and by doing so, to point out apparent patterns of social recognition among the pinnipeds, as well as important gaps in our knowledge. Following an introduction of the topic, the review is divided into three sections: (1) descriptive evidence, (2) exper- imental evidence, and (3) patterns of recognition in pinnipeds resulting from phylogenetic, ecological and life history constraints. The descriptive evi- dence mostly pertains to recognition between motherand oVspring and includes vocal stereotypy, the use of other sensory modalities, and cases of adoption and allo-suckling. Further descriptive data include recognition among territorial males and between species. The experimental evidence is also weighted heavily towards tests of mother- oVspring recognition. Recognition between pinni- ped mothers and pups, in at least one direction (i.e., mother recognizes pup or pup recognizes mother), has been experimentally demonstrated in seven pinniped species (4 otariids and 3 phocids), but is not the rule. Recent experiments have also been completed on recognition ontogeny and salient cues, as well as demonstrating long-term recog- nition. Such results provide the basis for complex social interactions among individuals. As with descriptive evidence, methodologies are an import- ant aspect of these data. Finally, all the pinniped recognition data are synthesized with respect to the variability of intra- and interspecié c pressures aVecting the evolution of recognition behaviour.

We test relationships between structure of acoustic signal used for individual recognition and nesting ecology among two gulls: the black-headed gull ( Larus ridibundus ), in which chicks remain in the nest, and the slender-billed gull ( L. genei ), in which chicks leave the nest after hatching to form crèches. A striking difference between both species is the presence of two fundamental frequencies in the slender-billed gull's call and only one in the black-headed gull's call. Our study shows that the potential for individuality coding is more important in the species where the offspring experiment the greatest constraints – due to their nesting pattern – to identify their parents.