Orchestration: The Movement and Vocal Behavior of Free-Ranging Norwegian Killer Whales (Orcinus Orca); Doctoral thesis

摘要

Studying the social and cultural transmission of behavior among animals helps to identify patterns and content of interaction. Killer whales likely acquire traits culturally based on their stable social groups, population-specific feeding behaviors, and group-distinctive vocal repertoires. Digital tags were used to record the movements and vocalizations of Norwegian killer whales. These animals carousel feed, corralling herring into a ball before tail slapping, incapacitating and eating the fish. Periods of tail slapping were characterized by elevated movement variability, heightened vocal activity, and call types containing orientation cues. Two types of behavioral sequence preceded the tight circling of carousel feeding. First, the animals swam directionally and in 2 of 3 instances were silent, suggesting that they may have located other foraging groups by eavesdropping. Second, tagged animals made broad horizontal loops as they dove in a manner consistent with corralling. All 4 of these occasions were accompanied by vocal activity, indicating that this and tail slapping may benefit from social communication. Killer whale vocalizations traditionally have been classified into discrete call types. Using human speech processing techniques, the author considered that calls alternatively consist of shared segments that can be recombined to form the stereotyped and variable repertoire. In a classification experiment, the characterization of calls using the whole call, a set of unshared segments, or a set of shared segments yielded equivalent performance. The shared segments required less information to parse the same vocalizations, suggesting a more parsimonious system of representation. This closer examination of the movements and vocalizations of Norwegian killer whales, combined with future work on ontogeny and transmission, will inform our understanding of whether and how culture plays a role in achieving population-specific behaviors in this species.