Coda repertoire and vocal clans of sperm whales in the western Atlantic Ocean

Abstract

Sperm whales live in culture-based multilevel societies in which the fundamental social level is the nearly permanent social unit of females and immature individuals, and the largest level is the clan constituted by social units that share a common coda repertoire. This study describes the coda repertoire and vocal clans of sperm whales in Brazilian waters recorded between 2011 and 2016. Inter-click intervals of codas were used to quantify similarity between repertoires. The analysis showed two evident clans, in the north and the south, distinct in their repertoires. The clan of the north, termed the “5R” clan, presented a predominant production of codas containing five regularly spaced clicks, not found in the clan of the south, termed “D” clan, which repertoire was dominated by long codas with 10–13 clicks with descending inter-click intervals. Codas with five regularly spaced clicks with the same rhythm and tempo as those found in the “5R” clan of Brazil are also predominant in sperm whales recorded in the Island of Dominica, at a distance of approximately 2700 km from the north of Brazil, which corresponds to the extension of the areas of sympatric clans. The sharing of 5R type by the both distinct clans is likely the result of cultural transmission in which conformism through social learning homogenizes coda repertoire. The results of this study corroborated the hypothesis that social boundaries, here the clan level, are maintained by cultural identities.