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Redefinition and Sexual Difference of Contact Calls in Belugas (Delphinapterus leucas)
Abstract: Previous studies have suggested that belugas (Delphinapterus leucas) use pulsed calls both with and without tone-like components for contact calls. However, call classification differs among researchers, and the definition of contact calls remains ambiguous. The objective of this study is to organize and integrate this information to redefine the contact calls of belugas. Our previous studies termed their contact call as PS1, which was exchanged among the belugas and was the predominant call type in isolation. PS1 is a broadband pulsed call that sounds like a door creaking and has a duration of 0.15 to 1.5 s. Individual distinctiveness was found within a typical pulse repetition pattern of PS1. The PS1 characteristics initially described were based on one captive population. In this study, calls from another population of seven belugas of both sexes and various ages at Shimane Aquarium, Japan, were recorded from October 2014 to March 2015. The PS1 definition was expanded to broadband pulsed calls continuing for > 0.15 s, and the PS1 calls were explored from their calls. The belugas exchanged PS1 calls, but the pulse repetition pattern had various forms instead of the typical pattern suggested in previous PS1 studies. Additionally, all the PS1 calls contained a tone-like component. By reflecting on these results and referring to other previous studies, we renamed these contact calls creaking calls. Moreover, this study shows sex differences in the creaking calls. The females and juvenile male had creaking calls with an individually distinct pulse repetition pattern, while adult males had variations in pattern during free swimming. Each adult male, however, used only an individually distinct stereotype of pulse repetition pattern in a visual reunion and first-sighting context. This suggests that adult males have individualized and non-individualized creaking calls, and they use the former to advertise identity in separation, reunion, or greeting contexts.
Key Words: acoustic communication, vocal exchange, individuality, repertoire, classification, Delphinidae, cetacean
Page Numbers: 538-554