Description:
<jats:p>Analyses of consecutive songs produced by singing humpback whales recorded off the coast of Hawaii revealed that singers constantly vary the acoustic qualities of their songs across “repetitions." Unlike the progressive changes in song structure that singing humpback whales make across years, intra-individual acoustic variations within song sessions appear to be largely stochastic. Four sequentially produced song components (themes) were each found to vary in unique ways. The most extensively used theme was highly variable in overall duration within and across song sessions, but varied relatively little in frequency content. In contrast, the remaining themes varied greatly in frequency content, but showed less variation in duration. Analyses of variations in the amount of time singers spent producing different themes suggest that the mechanisms that determine when singers transition between themes may be comparable to those that control how long terrestrial animals fixate while scanning visual scenes. The dynamic changes that individual singers make to songs within song sessions are counterproductive if songs serve mainly to provide conspecifics with indications of a singer’s fitness. Instead, within-session changes to acoustic features of songs may serve to enhance a singer’s capacity to echoically detect, localize, and track conspecifics from long distances.</jats:p>