| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2000 This thesis presents data on the structure and use of acoustic signals produced by free-ranging resident killer whales. The analysis focuses on signal features that might be useful for animals to maintain contact and coordinate activities with preferred associates, including: distinctiveness by group or individual, call amplitude, and directionality cues that might cue the direction-of-movement of the signaler. Research was conducted in Haro and Johnstone Straits off Vancouver Island, British Columbia, where killer whales have been the focus of a long-term photo-identification effort. Extensive previous research on this population has demonstrated stable kin-based matrilineal social groups and pod-specific calling behavior. Individually-distinctive markings and pigmentation patterns were used to identify groups or individuals from which sounds were recorded. Recordings from each of the three matrilineal groups composing pod Al were made when each subgroup was isolated from the two other subgroups. Analysis of call use and structure revealed subgroup-specificity that was qualitatively similar to previously observed differences between pods, although more subtle. This finding suggests that pod-specific calling arises primarily as a consequence of accumulated drift or divergence of calls between highly cohesive matrilineal subgroups as they gradually separate into different pods. A new towed array beamforming system was developed to identify vocalizing killer whales concurrent with focal behavioral observations. Carefully positioning the array relative to the animals and linking visual observations of whale position with the angle-of-arrival of sounds on the towed array allows reliable identification of signalers in many circumstances. Using this new system, a sample of 140 calls was recorded from identified individuals ...
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