![]() ![]() In contrast to song displays, social calls are typically produced by both sexes, are produced as single calls or in short bouts, and function to communicate information both within and between social groups in a number of different contexts ( Lynch, 1996). These song sequences are highly stereotyped in most species and may serve a number of functions, including mate attraction and male-male competition, and song displays tend to be sex specific and related to breeding. The majority of research on call bouts has focused on the stereotyped sequences of calls produced by many species as song displays (e.g., in song birds, see review by Catchpole and Slater, 1995 in some primate species, Marler and Tenaza, 1977 Geissmann and Orgeldinger, 2000 in marine mammals such as humpback whales, Megaptera novaeangliae, Payne and McVay, 1971). These call sequences may make up a “call bout,” depending on the interval of time between adjacent calls. Rather than increasing the number of different call types in a repertoire, another way of increasing the potential for complexity in a communication system is to combine individual stereotyped call types into structured call sequences. In general, little communication complexity has been attributed to non-human animal call systems (see review by Seyfarth and Cheney, 2010). Calls presumably need to vary in structure to convey different information, leading to a number of different call types in a call repertoire. The production of individual call types within a species' communication repertoire may be tightly constrained to specific social and behavioral contexts, with different call types conveying specific information, such as alarm calls, individual or group identity calls, or group foraging calls (e.g., Bohn et al., 2008). The social calls of animals are generally studied by breaking down vocalizations into their individual components or call types. These bouts appear to be at least partially governed by rules for how individual components are combined. However, the order in which most call types were produced within bouts was non-random and dependent on the preceding call type. Although social calls tended to be produced in bouts, there were few repeated bout types. Bouts were produced significantly more when new whales joined a group compared to groups that did not change membership, and in groups containing multiple adults escorting a female and calf compared to adult only groups. Call bouts were defined through analysis of inter-call intervals, as any calls within 3.9 s of each other. Call order within bouts was investigated using call transition frequencies and information theory techniques. In this study, digital acoustic tag recordings were used to investigate social call use within bouts, the use of bouts across different social contexts, and whether particular call type combinations were favored. Humpback whales produce a repertoire of social calls, although little is known about the complexity or function of these calls. The use of stereotyped calls within structured bouts has been described for a number of species and may increase the information potential of call repertoires.
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