Vocal interactions between singing humpback whales, Megaptera novaeangliae

Humpback whales construct predictably patterned sequences within multihour sessions of sound production. These sequences (called ‘songs’) are some of the most structurally and acoustically complex vocal patterns produced by any mammal. Humpback whale song production is highly dynamic in that individuals constantly modify the properties of songs across multiple timescales throughout their adult lives. Past analyses of co-vocalizing humpback whales suggest that singers within earshot of one another may dynamically and interactively adjust their vocalizations in reaction to what they hear. The current study investigated whether singing humpback whales coordinate their production of concurrent songs either by overlapping similar sound patterns more than expected by chance or by modulating the spectral properties of sound sequences, thereby decreasing acoustic interference. Our results show that the vocal adjustments co-singing humpback whales make are diverse and appear to depend on the acoustic context. No evidence was found of singers adjusting the number or timing of sound pattern repetitions to alter pattern overlap. In contrast, most singers modified the spectral features of sound patterns after a second singer began singing. Co-singers appeared to intermittently alter produced pitches in reaction to each other’s vocal actions, suggesting that singing humpbacks attend to other audible singers and may sometimes alter song content to initiate social interactions from long distances. Understanding how and when singing whales vocally interact can provide new insights into the various roles singing plays in coordinating vertebrate behaviour. • Singing whales may vocally interact to actively explore their social worlds. • Hawaiian singers subtly shifted pitches of units when singing in dyads. • Co-singers appear to rapidly adjust unit trajectories based on what they hear.