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All units are equal in humpback whale songs, but some are more equal than others

Abstract

Flexible production and perception of vocalizations is linked to an impressive array of cognitive capacities including language acquisition by humans, song learning by birds, biosonar in bats, and vocal imitation by cetaceans. Here, we characterize a portion of the repertoire of one of the most impressive vocalizers in nature: the humpback whale. Qualitative and quantitative analyses of sounds (units) produced by humpback whales revealed that singers gradually morphed streams of units along multiple acoustic dimensions within songs, maintaining the continuity of spectral content across subjectively dissimilar unit “types.” Singers consistently produced some unit forms more frequently and intensely than others, suggesting that units are functionally heterogeneous. The precision with which singing humpback whales continuously adjusted the acoustic characteristics of units shows that they possess exquisite vocal control mechanisms and vocal flexibility beyond what is seen in most animals other than humans. The gradual morphing of units within songs that we observed is inconsistent with past claims that humpback whales construct songs from a fixed repertoire of discrete unit types. These findings challenge the results of past studies based on fixed-unit classification methods and argue for the development of new metrics for characterizing the graded structure of units. The specific vocal variations that singers produced suggest that humpback whale songs are unlikely to provide detailed information about a singer’s reproductive fitness, but can reveal the precise locations and movements of singers from long distances and may enhance the effectiveness of units as sonar signals.

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Data availability

All recordings analyzed in this paper are available either through the Macaulay Library at Cornell University or by request via C. Perazio.

Code availability

Customized Matlab scripts used to analyze sounds are available from E. Mercado on request.

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Acknowledgements

Natalia Botero Acosta, Andrés Cañas, Esteban Duque, Nohelia Farías, Andrea Caicedo González, Juliana López Marulanda, María Camila Medina, Kerri Seger, Kyle Williams, and Madre Agua Ecoturismo assisted with the collection and preparation of recordings from Colombia.

Funding

Funding for data collection and equipment procurement in Colombia was provided by Cetacean Society International, a Grant-In-Aid of Research from Sigma Xi The Scientific Research Society, Idea Wild, The Rufford Small Grants Foundation, https://www.indiegogo.com/ and The Society for Marine Mammalogy.

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Correspondence to Eduardo Mercado III.

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The authors declare that they have no conflicts of interest.

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Mercado, E., Perazio, C.E. All units are equal in humpback whale songs, but some are more equal than others. Anim Cogn 25, 149–177 (2022). https://doi.org/10.1007/s10071-021-01539-8

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  • DOI: https://doi.org/10.1007/s10071-021-01539-8

Keywords

  • Acoustic communication
  • Cetacean
  • Mysticete
  • Vocal learning
  • Bioacoustics