A technique for characterizing rhythms produced by singing whales

Abstract

Structured sound sequences produced by baleen whales show strong rhythmicity. Such temporal regularity is widely acknowledged, but rarely analyzed. Researchers instead have focused heavily on describing progressive changes in sequential patterns of sounds revealed through spectrographic and aural impressions. Recent production-based analyses of humpback whale sounds suggest that the acoustic qualities of individual sounds can provide useful information about how whales are generating sounds and also may reveal constraints on cyclical production of sounds that help determine rhythmic patterns. Because past analyses have largely ignored the temporal dynamics of sound production, the extent to which whales vary the rhythmicity of sound production over time is essentially unknown. Production-based analyses can be combined with automated measures of temporal patterns of sound production to generate spectrogram-like images that directly reveal rhythmic variability within sound sequences. Rhythm spectrograms can reveal long-term regularities in the temporal dynamics of sound sequences that may provide new insights into how whales produce sequences as well as how they use them.