Acoustic behaviour of resident killer whales (Orcinus orca) off Vancouver Island, British Columbia

Abstract

Recordings of underwater vocalizations and behavioural observations were collected from 16 photographically identified resident pods of killer whales (Orcinus orca) off Vancouver Island, British Columbia, during 1978–1983. Vocalizations recorded during 43 days spent with three representative pods were analyzed for each of five activity states: foraging, travelling, group-resting, socializing, and beach-rubbing. The whales produced three types of sounds that were assumed to be social signals: discrete calls, variable calls, and aberrant calls. Discrete calls dominated vocalization in most contexts. An increase in production of variable and aberrant calls was observed during socializing and beach-rubbing activities. Each resident pod had a group-specific repertoire of 7–17 discrete call types (mean = 10.7) that was consistent over a number of years. The relative use of different calls varied with activity, but no call type was correlated exclusively with any behaviour or circumstance that could be identified. Discrete calls probably function as intragroup contact signals to maintain pod cohesion and coordinate activities. Structural modulations of standard call formats and variations in frequencies of call use appear to carry information on the emotional state of vocalizing individuals. Group-specific repertoires of calls may increase the effectiveness and reliability of this contact system and function as indicators of pod affiliation.