Individual variation in the acoustic behaviour of the adult male leopard seal, Hydrurga leptonyx

Vocalisations and vocalising bouts of adult male leopard seals recorded from the Prydz Bay region, East Antarctica, were compared to determine whether they showed individual variability. There were distinct individual patterns in the sequence cif vocalisations within vocalising bouts. A sequence could be reliably ascribed to a particular individual with a high degree (83%) of certainty. Such sequences may carry information about the identity of the caller. Acoustic characteristics of the two most commonly used vocalisations, the high and low double trills, showed weak within individual variation. Although differences were observed among individuals in the high double trill few were observed in the low double trill consequently the low double trills of some individuals could not be reliably ascribed to any particular seal. For many species, individual variation occurs in acoustic characteristics of specific vocalisations rather than in the sequence in which the vocalisations are produced. The acoustic displays of solitary species such as the leopard seal, are constrained by the difficulties of detecting and recognising the signal at a distance. Vocalisation sequences may be less adversely affected by signal degradation and so could be effective for communicating information over distance. It has been suggested that individual acoustic variation is found primarily in gregarious species however findings from the current study suggest that solitary animals using long-range underwater acoustic displays may convey individual variability in their vocalising sequence patterns.