Maintaining Contact: Design and Use of Acoustic Signals in Killer Whales, Orcinus Orca

摘要

This thesis describes the structure and use of acoustic signals produced by resident killer whales off Vancouver Island. Calling of isolated subpods differed similarly but more subtly than across pods, suggesting that pod-specific calling arises as a consequence of drift between subgroups as they gradually separate into different pods. A towed array beamforming system was developed to identify vocalizing killer whales concurrent with focal behavioral observations. A sample of 140 calls was recorded from three members of one matrilineal subgroup showing they shared at least four call types, suggesting matrilineal group members use calls in a similar fashion. Source levels measured using two beamforming arrays towed in series were combined with a model of sound propagation and perception to estimate the maximum range of detectability of each sound in quiet conditions. The estimated range of 4.5 to 26.2 km suggests killer whales can maintain acoustic contact over long distances. The frequency structure of 263 calls recorded directly in front and behind animals depended on signaler orientation, with high-frequencies attenuated when the signaler was oriented away. This directionality pattern appears to provide a simple and reliable cue of signaler direction-of-movement, helping killer whales regulate their spacing relative to each other.