Mother–offspring reunion in the South American sea lion Otaria flavescens at Isla de Lobos (Uruguay): use of spatial, acoustic and olfactory cues

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In the South American sea lion (Otaria flavescens), mothers and pups are regularly separated throughout lactation, demanding a well-developed individual recognition system. The aim of this study was to investigate and quantify the searching and reunion behaviour between mothers and pups at Isla de Lobos, Uruguay. We recorded details of searches and reunions using focal animal sampling during two breeding seasons. Our results support the hypotheses that mother–pup dyads combine spatial, acoustic and olfactory cues for successful recognition and reunion behaviour and that pups play an active role in the process. A total of 74% of the females returning from sea visited the last zone (4 × 4 m grid cell) where they had been with their pup prior to separating. Pups spent close to 23% of their time at that location while their mothers were away foraging at sea. Female call rate was significantly higher in successful searches (i.e. those resulting in a reunion) compared to unsuccessful ones (Mann–Whitney test U = 72.5, P < 0.001). During reunions, 90% of the pups called prior to physical contact and search success varied significantly with their movement towards the mother (Fisher exact test P = 0.039). Lastly, mothers conducted olfactory investigations of their offspring during 97.6% of the reunions; they also conducted olfactory investigations of 53.6% of the non-offspring that approached them. In sum, multiple sensory modalities appear to play important roles during O. flavescens mother–offspring reunion behaviour, as has often been described but rarely quantified for other otariid species.