Thunks: Evidence for Varied Harmonic Structure In an Atlantic Bottlenose Dolphin (Tursiops truncatus) Sound

Document Type

Article

Publication Date

1-1-2017

School

Psychology

Abstract

© 2017 International Journal of Comparative Psychology. McCowan and Reiss first reported the “thunk” sound of the Atlantic bottlenose dolphin (Tursiops truncatus) during separations and discipline behavior of mother-calf dyads. This sound has been previously described as a wide-band, low frequency contact call, however the harmonic structure of this sound is more variable than previously described. Based on preliminary observations of the graded structure of thunks within our data set, we investigated the directionality of thunks with energies at higher frequencies. We recorded a bottlenose dolphin mother with her calf during the first 30-days of life, and analyzed thunk production during separation and discipline contexts. Two classifications of the thunk sound were compared to determine calf response and whether location cues were embedded in the higher harmonics of one of the thunk types. The mother oriented towards the calf significantly more during production of both thunk types during separation and discipline contexts. This sound may have potential directional information within the harmonic structure; however, we could not draw that conclusion based on our findings. Therefore, we present data here that indicates a graded structure to the harmonics of thunk sounds.

McCowan and Reiss first reported the "thunk" sound of the Atlantic bottlenose dolphin (Tursiops truncatus) during separations and discipline behavior of mother-calf dyads. However, since this initial report, no other studies have thoroughly investigated this sound. A bottlenose dolphin mother and calf were observed during the first 30 days of life. Thunk production during separations within the mother-calf dyad and discipline behavioral events were analyzed, as thunks were predominately produced in these contexts during the original report by McCowan and Reiss. We found that variation occurs within the thunk sound, contrary to how this acoustic signal has been previously defined. We report the presence of two different types of thunks primarily present in separation events during the calf's early life: the low harmonic range (LHR) and high harmonic range (HHR) thunk. LHR and HHR thunks varied in harmonic structure, but did not have significantly different peak frequencies. Furthermore, in order to determine the salience of the thunk sound to separation and discipline events, we also report on the presence of burst pulses and signature whistles when compared to thunk production. Thunks were the most produced sound during separation events, while burst pulses were more common during the mother's discipline of the calf. The mother's signature whistle was not as common during the course of the study, suggesting that, at least within this bottlenose dolphin mother-calf dyad, other sounds were more important for dyad communication within separation and discipline events.

Publication Title

International Journal of Comparative Psychology

Volume

30

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