Stereotypy and variability differ between humpback whale (Megaptera novaeangliae) phrase types offering structural support for the hypothesis that song is multi-message display

Abstract

Humpback whale studies support inter- and/or intrasexual song functions, suggesting dual functionality. Some animals produce multi-message displays with dual functionality. Stereotyped components, for mate attraction and/or male-male interactions, convey species/group membership. Variable components, for courtship, convey male quality. If humpback whale song is a multi-message display, then song should include both stereotyped and variable components. Recordings of east Australian males (2004:8, 2011:9) were used to investigate this hypothesis. Song comprises “units” arranged into sequences (“phrases”) that are repeated (“themes”). Themes are characterized by different phrase types. Variation among phrases repeated within a theme (“phrase variants”) is mostly overlooked by other studies. Whether some phrase types are more variable than stereotyped is unknown. To assess this, repertoire size (number of unit types and phrase variants) was determined per phrase type. Whether phrase variants were unique to individuals or shared were also determined. Unit types were defined by self-organizing maps. Levenshtein distances between phrases with cluster analyses determined phrase types and phrase variants illustrating a novel application of these methods. Stereotypic phrase types contained shared phrase variants and limited repertoire. Variable phrase types contained unique phrase variants and large repertoire. These results support the hypothesis that song is a multi-message display.