Cultural revolutions reduce complexity in the songs of humpback whales

Abstract

Much evidence for non-human culture comes from vocally learned displays, such as the vocal dialects and song displays of birds and cetaceans. While many oscine birds use song complexity to assess male fitness, the role of complexity in humpback whale ( Megaptera novaeangliae ) song is uncertain owing to population-wide conformity to one song pattern. Although songs change gradually each year, the eastern Australian population also completely replaces their song every few years in cultural ‘revolutions’. Revolutions involve learning large amounts of novel material introduced from the Western Australian population. We examined two measures of song structure, complexity and entropy, in the eastern Australian population over 13 consecutive years. These measures aimed to identify the role of complexity and information content in the vocal learning processes of humpback whales. Complexity was quantified at two hierarchical levels: the entire sequence of individual sound ‘units’ and the stereotyped arrangements of units which comprise a ‘theme’. Complexity increased as songs evolved over time but decreased when revolutions occurred. No correlation between complexity and entropy estimates suggests that changes to complexity may represent embellishment to the song which could allow males to stand out amidst population-wide conformity. The consistent reduction in complexity during song revolutions suggests a potential limit to the social learning capacity of novel material in humpback whales.

Cultural Transmission, Evolution, and Revolution in Vocal Displays: Insights From Bird and Whale Song

“…The appearance of a new song type presents the whales with a substantial amount of novel material that requires rapid learning to mirror the pattern we observe. Allen et al (2018) investigated the complexity of song in the east Australian population over 13 consecutive years. As songs evolved, complexity increased; however, song revolutions were significantly less complex than their predecessor.…”

“…As songs evolved, complexity increased; however, song revolutions were significantly less complex than their predecessor. The relative complexity of songs in song revolutions may represent an upper limit to song learning ( Allen et al, 2018 ). It may also support the “cognitive capacity hypothesis,” where song complexity may convey an individual’s overall cognitive ability and could be used by prospective mates.…”

Cultural evolution of music

“…Note also that there is nothing about progress or direction contained in the above definition: evolution simply refers to changes in the frequencies of heritable variants. These changes can be in the direction of simple to complex-and it is possible that there may be a general trend towards complexity (McShea and Brandon, 2010;Currie and Mace, 2011)-but the reverse is also possible (Allen et al, 2018), as are non-directional changes with little or no functional consequences (Nei et al, 2010).…”

Songbird presumed to be age‐limited learner may change repertoire size and composition throughout their life

“…Regional dialects, long‐term signal stability or even the sudden appearance of new memes are phenomena observed in bird song. These seem equivalent to other behaviours including tools use in chimpanzees or New Caledonian crows, the opening of milk bottles in parids or cultural revolutions in humpback whales Megaptera novaeangliae (Whiten et al ., ; Allen et al ., ; Aplin, ). Studies on culturally transmitted traits in most cases show the qualitative and/or quantitative status of these traits (e.g.…”