Structural variation and communicative functions of long-finned pilot whale (Globicephala melas) pulsed calls and complex whistles

Long-finned pilot whales (Globicephala melas) are an extremely vocal species, producing clicks, whistles and pulsed calls during a variety of contexts. For mobile marine mammals, the acoustic channel is often the primary method of communication between individuals, and pilot whale vocalizations likely play an important role in both social and behavioural interactions. I examined the pulsed calls and complex whistles of a population of pilot whales off the northwest coast of Cape Breton, Nova Scotia using recordings made during 4 field seasons spanning 8 years. Pilot whale pulsed calls were found to be physically complex, with multiple components that are likely rich in information and difficult for eavesdroppers to imitate. The structure of pilot whale pulsed calls was highly similar to those of killer whales (Orcinus orca), which raises the question of whether the distantly related species, sharing a common rare social structure, evolved similar call structures to solve similar communication problems.;Both the pilot whale pulsed calls and whistles appear to be non-discrete. Statistical measures of similarity from measurements of call spectrograms and perceptual measures of similarity from human observers were used to produce similarity matrices for pulsed calls and complex whistles. Naive and experienced human participants were highly consistent with each other when rating both sound classes, although the statistical and perceptual methods were only moderately correlated. Each method of rating call similarity had important advantages, and thus both were used to examine the similarity of complex whistles and pulsed calls across social, behavioural and group composition contexts.;Pulsed calls vary strongly between social units or groups producing the calls, as well as among the behavioural or arousal states of the whales. The similarity of aspects of pulsed call structure within clusters of social units suggests the possibility of broader vocal clans. The structure of complex whistles, which are produced mainly during active behaviours, is instead most strongly influenced by the average number of whales present. Pulsed calls may function in unit membership identification, group cohesion and the transmission of information during social interactions. Complex whistles may serve a more population-wide function, facilitating group coordination during active behaviour and over large distances.