Humpback whale (Megaptera novaeangliae) sonar: Ten predictions.

Abstract

Bats and dolphins echolocate ultrasonically while foraging, an active mode of perception that is effective for intercepting small, fast-moving targets, but less so for tracking large targets from long distances. Unlike toothed whales, humpback whales and other baleen whales are widely assumed not to echolocate. Echoes generated by humpback whale vocalizations often have been viewed either as low-level background noise that minimally affects acoustic communication between whales or as indirect cues to large environmental features. An additional possibility is that vocalizing humpback whales (and perhaps other whales) produce sonic sounds to actively generate echoes that they localize and interpret. Animals attempting to echolocate using lower frequency sounds underwater face some of the same signal processing challenges faced by ultrasonic echolocators, as well as some unique challenges. The extent to which listening whales can meet these challenges largely determines what they can actively perceive by monitoring self-generated echoes. In the absence of psychophysical experiments with baleen whales, comparisons with auditory processing by echolocating species provide the best indications of what humpback whales may echoically perceive. Empirical tests of key predictions derived from the hypothesis that humpback whales echolocate are also critical to understanding how they use sound. Recognizing that sonic echolocation by whales may differ substantially from ultrasonic echolocation in smaller species is an important step toward clarifying the role that active auditory perception plays in whale behavior.

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

“…Recent acoustic analyses of humpback whale songs produced in multiple regions around the world have revealed that although singers are capable of producing units with frequency content ranging from 20 to 8,000 Hz, they concentrate most of their energy into three relatively narrow frequency bands (Perazio & Mercado, 2018; Ryan et al, 2019). The specific focal frequencies vary slightly over time within populations (Perazio & Mercado, 2018), and even across consecutive songs produced by individual whales (Mercado, 2018a), but all populations measured to date appear to conform to similar distributions of frequencies. Published spectrograms depicting changes in frequency usage within song cycles further suggest that singers may use these three bands in stereotypical orders while singing (Español-Jiménez & van der Schaar, 2018; Helble et al, 2015; Kowarski et al, 2018; Mercado, 2016; Mercado & Handel, 2012; Mercado et al, 2010; Mercado & Sturdy, 2017).…”

“…Consequently, analyses showing high complexity in vocal sequences are sometimes used to argue that a species is more cognitively capable. For instance, vocal variations produced by cetaceans have been pointed to as evidence of prodigious memory (Guinee & Payne, 1988), innovativeness (Payne, 2000), complex cognition (Marino et al, 2007), sophisticated auditory scene analysis (Mercado, 2018b; Mercado, 2020), vocal imitation (Payne et al, 1983), and even culture (Rendell & Whitehead, 2001b).…”

“…A second aim of this study was to evaluate the relationship between subjectively salient features of the vocal sequences produced by singing humpback whales and more objective measures of their acoustic properties, particularly with respect to variations in the frequency content of songs. Recent analyses suggest that singers in different populations focus most of their vocal effort within predictable frequency bands, regardless of the environmental conditions within which they are singing (Mercado, 2018a; Perazio & Mercado, 2018; Ryan et al, 2019; Seger et al, 2016). Qualitative comparisons of published spectrograms illustrating segments of song sessions further suggest that not only are singers emphasizing core frequency bands, they also may be consistently cycling through these bands in a predictable sequence (Español-Jiménez & van der Schaar, 2018; Helble et al, 2015; Mercado, 2016; Mercado & Handel, 2012).…”