UBC Theses and Dissertations
Call traditions and dialects of killer whales (Orcinus orca) in British Columbia Ford, John Kenneth Baker
Underwater vocalizations were recorded from pods of wild killer whales (Oreinus orca) off Vancouver Island, British Columbia, during 1978-83. Acoustic exchanges within pods are dominated by repetitious, pulsed calls which can be organized into discrete categories. Repeated encounters with 16 photographically-identified 'resident' pods demonstrate that each pod produces a repertoire of 7 to 17 (mean = 10.7) discrete call types. Recordings of captive whales of known pod origin and historical field recordings indicate that pod repertoires remain stable for periods of at least 18 years (1965-83) and possibly 25 years (1958-83). Each individual whale appears capable of producing most or all of the calls in it's pod's repertoire. Repertoires are apparently learned. All discrete call types tend to be used in all 'active' contexts, which consist mainly of foraging and travelling. Few call types are clearly correlated with specific behaviours. Activities involving tight group formation and physical interaction among pod members were accompanied by an increase in the use of whistles and variable pulsed sounds. Significant differences exist among the call repertoires of different pods. The 16 resident pods on the B.C. coast can be arranged into 4 acoustic associations, each of which has a unique set of discrete call types. These associations are referred to as 'call traditions', and the pods belonging to a tradition form a 'clan'. Pods within each clan share some call types, but may also produce unique calls. Shared calls often have different pod-specific renditions. These differences form a system of related dialects within each call tradition. Three of the four resident clans belong to a single community, and pods from these clans frequently associate with one another. Observed patterns of association were often unrelated to acoustic relationships. The fourth resident clan forms a community with a separate range. A community of 17 'transient' pods is sympatric with but socially isolated from the resident communities. This community has a wide range, and appears to consist of a single call tradition. The call traditions and dialects described here are apparently unique among mammals. Various hypotheses to account for their origin and adaptive significance are discussed. Clans could represent independent lineages which arrived on the B.C. coast through a series of unrelated founding events. As the founding pod of each clan grew and divided, its group-specific call repertoire diverged, either through functionless cultural drift or by an active process promoting acoustic differentiation of related groups. Dialects may have no selective value, or they may serve as kin-recognition signals for maintaining pod cohesion and identity or avoiding excessive inbreeding.