Development of aggressive vocalizations in male southern elephant seals (Mirounga leonina):: maturation or learning?

Vocalizations are an important component of male elephant seat agonistic behaviour. Acoustic and behavioural components of vocalizations emitted during agonistic contests show gross differences between young and old males, but the variation with age depends on the specific feature. Vocalizations become more frequent and effective at later ages. Acoustic features that are constrained by structural phenotype, which changes with age, also should change with age, while acoustic features that are independent from structural phenotype should show no relationship with age. We demonstrate that, in southern elephant seals, formant frequencies, which are constrained by the vocal tract length and, therefore, by body size, show a clear decrease with age, whereas temporal and structural features of sounds, which potentially are unconstrained, show no correlation with age. Formants ontogeny seems, therefore, to be mostly the result of body maturation, and hence formants may be reliable signals of age. In contrast, acoustic features such as temporal features and syllable structure, are free to change, and hence may serve as the raw material for vocal learning and individual recognition.