A substantial amount of research has been carried out on recognition behaviour in natural populations 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) experimental evidence, and (3) patterns of recognition in pinnipeds resulting from phylogenetic, ecological and life history constraints. The descriptive evidence mostly pertains to recognition between mother and 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 pinniped 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 recognition. Such results provide the basis for complex social interactions among individuals. As with descriptive evidence, methodologies are an important aspect of these data. Finally, all the pinniped recognition data are synthesized with respect to the variability of intra-and interspeci c pressures aVecting the evolution of recognition behaviour.
The ability to recognize and remember individual identities for long periods of time has important implications for the evolution of animal social behaviour, particularly complex interactions such as cooperation or mate choice. Despite this importance, there is only a single example of long-term individual recognition in nature, the 8-month retention of neighbour's song among male hooded warblers, Wilsonia citrina, and there is none for a non-human mammal. Associations between individuals spanning years, which are especially prevalent in carnivores, primates and seabirds, and evidence of mate fidelity provide indirect support for the ability of long-term recognition. In many of these instances, however, individuals do not separate for extended periods, and thus long-term recognition, although often assumed, may be both unnecessary and nonexistent. Furthermore, site fidelity rather than individual recognition may explain many instances of mate fidelity. Here I show that mother-offspring pairs of a migratory otariid pinniped--the northern fur seal (Callorhinus ursinus)--not only have the ability to recognize each other's vocalizations during the course of a breeding season, but are also able to retain these memories for at least 4 years.
I have compared structural variation of the primary vocalizations used between mother-offspring pairs in two species of pinnipeds that differ fundamentally in their breeding behaviour: northern elephant seal (Mirounga angustirostris) mothers and offspring normally are together throughout the nursing period; northern fur seal (Callorhinus ursinus) females regularly separate from their offspring while nursing. Two predictions were tested: (1) these vocalizations should be individually-distinct (stereotyped) in females and pups of both species if they serve to function for recognition, and (2) because individuality should be more pronounced in a species where separations and reunions are common, the vocalizations used between northern fur seal mother-offspring pairs should be more individually-stereotyped than those of the northern elephant seal. Principal components analyses revealed structural differences between the calls of females and pups in both species. Analysis of variance showed the calls of individual seals to be acoustically distinct in all cases. The calls used between mother-offspring pairs of northern fur seals were more stereotyped than those of northern elephant seals. These calls had less within-individual variation, greater among-individual variation and were more often correctly predicted in discriminant analyses. The results indicate that selective pressure to develop vocal recognition exists in both species but is greater in the northern fur seal.
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