Song of My People: Dialect Differences Among Sympatric Social Groups of Short-Finned Pilot Whales in Hawai’i

In many social species, acoustic dialects are used to differentiate among social groups within a local population. These acoustic dialects and their corresponding social groups are often related to distinct foraging behaviors or spatial movement patterns, and it is possible that vocal repertoire variability is one of the proximate mechanisms driving or maintaining genetic and ecological diversity at a subspecies level in social species. Short-finned pilot whales (Globicephala macrorynchus) inhabiting Hawaiian waters have a stable hierarchical social structure, with familial social units associating in larger social clusters within island associated communities. In this study, we test the hypothesis that sympatric social groups of short-finned pilot whales have acoustically differentiated dialects, which may be used to maintain the social structure. We first examined call composition of social calls collected from photographically identified social clusters of short-finned pilot whales around the Main Hawaiian Islands, using a catalog of manually classified calls, and found that call composition differed among clusters.We then conducted ANOVA and support vector machine (SVM) learning analyses of the acoustic features of social calls. Social clusters were significantly differentiated in their acoustic features, and the SVM classification accuracy was 60%. These results indicate that vocal repertoire reflects social segregation in short-finned pilot whales and may be a driving mechanism of differentiation, potentially contributing to genetic diversity within populations. This suggests divergent acoustic population structure; however, the small sample size in this study decreases the ability to detect acoustic differences among groups. Additional sampling will improve our power to detect acoustic differences among social clusters of Hawaiian pilot whales and improve classification accuracy. The pattern described here highlights the importance of increasing the spatial and temporal resolution of conservation and management plans for this species, in order to conserve subpopulation genetic and social structure.

Citation:

Van Cise, A.M., S.D. Mahaffy, R.W. Baird, T.A. Mooney, and J. Barlow. 2018. Song of My People: Dialect Differences Among Sympatric Groups of Short-Finned Pilot Whales in Hawai’i. Behavioral Ecology and Sociobiology 72: 193. doi: 10.1007/s00265-018-2596-1