Quantifying the acoustic repertoire of a population: the vocalizations of free-ranging bottlenose dolphins in Fiordland, New Zealand

Abstract

Quantification of the vocal repertoire of a species is critical for subsequent analysis of signal functionality, geographical variation, social relevance, and transmission. While signal repertoires have been documented for numerous animal species, detailed descriptions for the cetaceans are rare. This study describes the vocalizations of free-ranging bottlenose dolphins resident to the waters of Fiordland, New Zealand. The field recordings presented in this paper were made using both audio band and broadband apparatus. Subsequent classification of vocalizations using multivariate parameters enabled a quantification of the entire vocal output of the focal animals. These results were used to propose a meaningful repertoire of signals employed by this species. A total of 12 individual signal types were described, comprising four broad structural classes: "tonal," "single bursts," "click bursts," and "repeat bursts." The proposed repertoire will allow subsequent investigation into vocal behavior. It appears that the successful description of a species' repertoire is dependent on the use of appropriate recording systems, a high number of representative recordings with good signal-to-noise ratio, and subsequent validation of the original classification system.