Social calling behavior of Southeast Alaskan humpback whales (Megaptera novaeangliae) : classification and context Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/th83m254x

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  • Humpback whales (Megaptera novaeangliae) are vocal baleen whales that exhibit complex social interactions that vary spatially and seasonally. Across their range, humpback whales produce a wide array of vocalizations including ‘song’, foraging vocalizations, and a range of vocalizations known as social calls -- unclassified non-song vocalizations. This study investigates the vocal repertoire and social calling behavior of Southeast Alaskan humpback whales from a sample of 299 vocalizations paired with 365 visual surveys collected over a three-month period on a foraging ground in Frederick Sound in Southeast Alaska. The results of this study describe a more varied and diverse repertoire of social vocalizations than has been previously documented, and identifies variability in vocal behavior as a function of social-spatial context. We used a three-part classification system that included aural-visual analysis, statistical cluster analyses, and discriminant function analysis to describe and classify social vocalizations. Vocalizations were classified into sixteen individual call types nested in seven vocal subclasses, within four vocal classes. The vocal repertoire of Southeast Alaskan humpbacks shows that call stereotypy ranges from discrete to continuous. This discrimination occurs at the vocal class and vocal subclass levels, and may be associated with call function. Social calls from Southeast Alaska showed anecdotal overlap with song from the 2012 North Pacific breeding season, and moderate overlap with vocalizations recorded in North Atlantic foraging grounds and along the East Australian migratory corridor. At the vocal class level aural-visual analysis had 83% agreement with cluster analysis and 90% agreement with discriminant function analysis. Results indicate that call use is not indiscriminant, and that some call types were commonly produced while others were rare. Moreover, calling rates in one vocal class, the pulsed (P) vocal class, were negatively correlated with mean nearest neighbor distance, indicating that P calling rates increased as animals clustered. This suggests the use of P calls may be spatially mediated. Results of a Poisson log linear (PLL) regression indicated that whale abundance in the survey area had no effect on vocal behavior; however, vocal behavior did vary significantly based on the spatial proximity of animals. The highest calling diversity occurred when whales were in clustered dispersion states, while the lowest calling diversity occurred when only a single whale was present. The type of calls produced during each dispersion state (clustered, random, evenly dispersed, single) varied significantly. While calls from all four vocal classes were detected during surveys containing clustered or randomly dispersed whales, calls from only two of the four classes were detected when whales were evenly distributed, and only one vocal class was detected from solitary whales. Our results indicated that vocal behavior is not correlated with abundance, that vocal behavior does vary based on social context, and that vocal behavior trends toward complexity as the potential for social interactions increases. Our evidence supports the hypothesis that social vocalizations serve a communicative purpose and may be used to maintain animal spatial proximity.
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