Temporal features and rhythmic patterns of humpback whale songs at their breeding ground in Costa Rica

Although rhythm characterizes and shapes human life, its evolutionary origins remain poorly understood. Recent comparative research has revealed the presence of rhythmic patterns in spontaneous vocalizations of non-human animals. These studies focus on the temporal features of the signals, which can convey identity, fitness, social status, and intentions. Most research focused on primates and birds, but cetaceans have recently emerged as ideal subjects for rhythm studies. Specifically, humpback whales possess complex hierarchical songs, enduring mother–calf bonds, and vocal learning ability, traits that may be connected to the presence of categorical rhythms. This project examines the temporal features of BSG population songs over two breeding seasons in Costa Rica, using both autonomous underwater recorders and boat-based systems. Following standard comparative methodology, I analyzed the distribution of inter-onset intervals (IOIs) and the IOI ratio, rk = IOI/(IOI + IOI+1), a measure used to highlight the presence of rhythmic patterns. Results suggest that humpback whales exhibit considerable temporal flexibility and evident inter-individual variability with instances of isochrony (regular timing). Isochrony may be used as a baseline that facilitates learning new songs from conspecifics. At the same time, intra-individual variability could reflect the species' ability to convey individual-specific information in the temporal domain.