AIRBORNE VOCAL COMMUNICATION IN CALIFORNIA SEA LION ZALOPHUS CALIFORNIANUS

Airborne vocalizations play an important role in the communication system involved in the establishment and maintenance of social organization of breeding California sea lions. The vocalizations of adult males relate primarily to territorial behaviour and social status. They have only a single major type of vocalization, the bark, but vary its rhythm, repetition, loudness, and direction according to social context. Immature males employ an adult-type bark during play. The vocalizations of adult females relate to aggressive behaviour and mother-infant interactions. They use a bark, but somewhat higher in pitch than that of the males, as a mild threat, and employ harsh and noisy squeals, belches, and growls during more vigorous short-range altercations. The females have a loud, highly directional, bawling vocalization, the pup-attraction call which helps mother and pup to locate each other. Pups have mother-response calls which serve the same function. Both the pup-attraction and mother-response calls vary markedly from individual to individual, which presumably facilitates individual identification. The first vocalization of the pup is a bleat, which is used as both an alarm call and a threat. By the age of six weeks the pups begin to modify the bleat into a bark. The amphibious mode of life appears to have imposed conditions that have made pinnipeds especially dependent upon acoustic communication for maintenance of social organization while on land. A tabulation of the inferred information content of the calls and their acoustic properties suggests several correlations between functions of a vocalization and its physical structure. The ontogeny of the vocalizations shows little evidence that learning is important in acquisition of the basic repertoire. © 1969.