Vocal communication and individual variation in breeding South American sea lions

The purpose of this study was to analyse the structure, social contexts, an d individual variation of South American sea lion (Otaria flavescens) airbo rne vocal communication during the breeding season. This is the first compr ehensive analysis of the vocal repertoire of this species. Since breeding c olonies 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 m ales: high pitched call or HPC (aggressive interactions, such as attack and retreat displays, and fights), bark (aggressive interactions, territory es tablishment, and usually combined with growls), growl (male-female interact ions), and exhalation (after agonistic encounters); and two for adult femal es: mother primary call or MPC (female-pup interactions, such as after birt h, during pup separation, and pup development), and grunt (agonistic intera ctions between females). Juveniles vocalized yearling primary calls or YPC (searching for their mothers or after being threatened by females), pups ga ve pup primary calls or PPC (in response to MPCs, when hungry, searching fo r their mothers, if nursing was interrupted, or when frying 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 wi th 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 colon ial life to overcome the high noise levels within pinniped breeding colonie s.