Individuality in South American sea lion (Otaria flavescens) mother–pup vocalizations: Implications of ecological constraints and geographical variations?

Frequent mother–pup separations and reunions occurring in the South American sea lion Otaria flavescens require a well-developed individual recognition system. Individuality in mothers’ and pups’ calls of this species has been found in Península Valdés (PV), Argentina (with individuality rates of 95% and 89%, respectively). In order to test the hypotheses of ecological constraints (i.e., population density, habitat) and geographic variation affecting the characteristics and/or the individuality of vocalizations, we studied another population at Isla de Lobos (IL), Uruguay, separated by approx. 1200 km from PV. DFAs showed classification rates of 63.2% in mothers and 53.3% in pups. This lower degree of individuality can be explained by differences in population density. Differences in acoustic characteristics were also found: at IL mother and pup calls tended to be shorter in duration and mother calls lower-pitched. This can be explained by an adaptation to the local environment: at IL sea lions breed in sympatry with South American fur seals in an obstructed habitat whereas PV sea lions are the unique species in the colony constituted by an open habitat. Finally, the acoustic differences can also be a consequence of the genetic isolation that has been found between these two colonies of O. flavescens.