Socially Complex Breeding Interactions in Humpback Whales Are Mediated Using a Complex Acoustic Repertoire

Abstract

Intraspecific conflict can be costly; therefore, many species engage in ritualized contests composed of several stages. Each stage is typically characterized by different levels of aggression, arousal, and physical conflict. During these different levels of “intensity,” animals benefit from communicating potential information related to features such as resource holding potential, relative fighting ability, level of aggression, intent (i.e., fight or flight), and whether or not the competitor currently holds the resource (e.g., a receptive female). This information may be conveyed using both visual displays and a complex acoustic repertoire containing fixed (e.g., age, sex, and body size) and flexible information (e.g., motivation or arousal). Calls that contain fixed information are generally considered “discrete” or stereotyped, while calls that convey flexible information are more “graded,” existing along an acoustic continuum. The use of displays and calls, and the potential information they convey, is likely dependent on factors like intensity level. The breeding system of humpback whales (Megaptera novaeangliae) involves intense male competition for access to a relatively limited number of breeding females (the resource). Here, we investigated the behavior and acoustic repertoire of competitive groups of humpback whales to determine if an increase in intensity level of the group was correlated with an increase in the complexity of the vocal repertoire. We categorized the behavior of humpback whales in competitive groups into three mutually exclusive stages from low to high intensity. While discrete calls were infrequent compared to graded calls overall, their use was highest in “low” and “moderate” intensity groups, which may indicate that this stage of contest is important for assessing the relative resource holding potential of competitors. In contrast, visual displays, call rates, and the use of graded call types, were highest during “high intensity” competitive groups. This suggests that flexible information may be more important in “high intensity” levels as males continue to assess the motivation and intent of competitors while actively engaged in costly conflict. We have shown that the relatively complex social call repertoire and visual displays of humpback whales in competitive groups likely functions to mediate frequently changing within-group relationships.

Comparing the social signaling behavior of humpback whales in three group types on the Hawaiian breeding grounds using acoustic tags

“…Interest in the study of humpback whale calls has grown globally in recent years with research conducted in regions such as Australia (Dunlop et al, 2007;Rekdahl et al, 2013;Rekdahl et al, 2015;Dunlop, 2016;Dunlop, 2017;Cusano et al, 2020;Indeck et al, 2020;Recalde-Salas et al, 2020;Cusano et al, 2021), North America (Zoidis et al, 2008;Stimpert et al, 2011;Epp et al, 2021a;Fournet et al, 2015;Fournet M. et al, 2018), South America (Simão and Moreira, 2005;Oña et al, 2019), and Africa (Rekdahl et al, 2017). However, comparatively little work has been conducted to compare calling behavior across different group compositions using long-term datasets.…”

Three types of pulsed signal trains emitted by Indo-Pacific humpback dolphins (Sousa chinensis) in Beibu Gulf, South China Sea

“…During their long-term adaptation to marine environments with limited visibility, odontocetes can acquire information about the underwater environment through sound (Allen et al, 2018;Jiang et al, 2020;Cusano et al, 2022). They generally produce pulsed signals that form trains to allow the fine-grained discrimination of targets (Au, 1993).…”