Comment on: "Variability in humpback whale songs reveals how individuals can be distinctive when sharing a complex vocal display" [J. Acoust. Soc. Am. 153, 2238-2250 (2023)].

Lamoni, Garland, Allen, Coxon, Noad, and Rendell [(2023). J. Acoust. Soc. Am. 153, 2238-2250] analyzed variations in humpback whale song structure to assess how individual singers can produce distinctive patterns that communicate desirable individual qualities to potential mates. Their analyses revealed that singers rarely produced individually specific sound patterns and that singers varied subjectively distinctive structural features of songs differently across years. These findings provide the strongest evidence to date that singing humpback whales are not varying song structure in ways that reliably reveal individual singers' physical or cognitive characteristics. Surprisingly, the authors appear to reach the opposite conclusion. Objective strategies for quantitatively comparing song properties are crucial for evaluating competing hypotheses regarding the nature and function of humpback whale songs, but the value of such strategies is reduced when the objectivity of the analyses is suspect and when negative evidence is framed as supporting prior beliefs.

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

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.

Similarities in composition and transformations of songs by humpback whales (Megaptera novaeangliae) over time and space.

The complex songs produced by humpback whales have been cited as evidence of prodigious memory, innovativeness, sophisticated auditory scene analysis, vocal imitation, and even culture. Researchers believe humpbacks learn their songs culturally because songs appear to change rapidly, consistently, and irreversibly across whales within a population. Here, we present evidence of similarities in song structure both across populations and decades that strongly challenge claims that social learning is the main driver of variations in humpback whale songs over time. Groups of humpback whales that were not in acoustic contact (recorded in Puerto Rico in 1970, Hawaii in 2012, and Colombia in 2013-2019) produced songs in acoustically comparable cycles, suggesting that progression through sound patterns within and across songs is not simply determined by vocal imitation of innovative patterns, but may instead be controlled by production templates that prescribe how singers construct and transform songs over time. Identifying universal constraints on song production is critical to evaluating the role of vocal imitation and cultural transmission in the progressive changes that humpback whales make to their songs and for evaluating the functional relevance of such changes. The current findings illustrate how information theoretic analyses of vocal sequences can potentially obscure key acoustic qualities of signals that may be critical to understanding how vocalizers produce, perceive, and use those sequences. (PsycInfo Database Record (c) 2021 APA, all rights reserved).