Data from: Cultural revolutions reduce complexity in the songs of humpback whales

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
due 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.