The social signaling behavior of humpback whales on the Hawaiian breeding grounds investigated using acoustic tags

Abstract

Humpback whales (Megaptera novaeangliae) are one of the most social of all baleen whale species. Despite extensive research into humpback whale song, gaps remain in the understanding of humpback whale communication. These gaps are particularly evident with respect to humpback whale non-song social vocalizations. This study expands upon the current understanding of non-song social call use and function by comparing call prevalence, features, and dynamics across humpback whale groups of three different compositions: dyads, escorted mother-calf pairs, and competition groups. Recordings were collected from 12 deployments of AcousondeTM acoustic and data logging tags on whales off Maui, Hawaii during the winter breeding seasons of 2019-2021. Individual social calls were selected based on visual and aural inspection of spectrograms using Raven Pro 1.6 software, with a total of 518 calls chosen throughout the 60.4 h of acoustic recordings. Of these calls, 49.2% occurred in competition groups, 33.6% in escorted mother-calf pairs, and 17.2% in dyads. Furthermore, we conducted statistical analyses to characterize and classify the social calls recorded and assess the variability of the type, quantity, and frequency of social calls used in groups of differing compositions. This study provides new insights into humpback whale vocal communication behavior in the Hawaiian Islands breeding grounds, particularly with respect to three principal social groups, whose non-song vocal communications have been understudied.