VOCAL COMMUNICATION AND INDIVIDUAL VARIATION IN BREEDING SOUTH AMERICAN SEA LIONS

The purpose of this study was to analyse the structure, social contexts, and individual variation of South American sea lion (Otaria flavescens) airborne vocal communication during the breeding season. This is the first comprehensive analysis of the vocal repertoire of this species. Since breeding colonies are complex acoustic environments, we expect that male, female, and pup vocalizations would show individuality, and that individual variation would rely on several acoustic traits. We identified four calls for adult males: high pitched call or HPC (aggressive interactions, such as attack and retreat displays, and fights), bark (aggressive interactions, territory establishment, and usually combined with growls), growl (male-female interactions), and exhalation (after agonistic encounters); and two for adult females: mother primary call or MPC (female-pup interactions, such as after birth, during pup separation, and pup development), and grunt (agonistic interactions between females). Juveniles vocalized yearling primary calls or YPC (searching for their mothers or after being threatened by females), pups gave pup primary calls or PPC (in response to MPCs, when hungry, searching for their mothers, if nursing was interrupted, or when trying to nurse). Our results suggest that male's HPC and bark, female's MPC, and pup's PPC have acoustic features that support individuality. These calls are associated with contexts in which recognition of neighbours (HPC and bark) or relatives (MPC and PPC) may confer a relative advantage in reproductive performance. Individual variation depended on frequency, temporal, and intensity traits; such multi-trait individuality could be regarded as an adaptation to colonial life to overcome the high noise levels within pinniped breeding colonies.