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. 2017 Nov;20(6):1067-1079.
doi: 10.1007/s10071-017-1123-5. Epub 2017 Aug 8.

What's in a Voice? Dolphins Do Not Use Voice Cues for Individual Recognition

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Free PMC article

What's in a Voice? Dolphins Do Not Use Voice Cues for Individual Recognition

Laela S Sayigh et al. Anim Cogn. .
Free PMC article

Abstract

Most mammals can accomplish acoustic recognition of other individuals by means of "voice cues," whereby characteristics of the vocal tract render vocalizations of an individual uniquely identifiable. However, sound production in dolphins takes place in gas-filled nasal sacs that are affected by pressure changes, potentially resulting in a lack of reliable voice cues. It is well known that bottlenose dolphins learn to produce individually distinctive signature whistles for individual recognition, but it is not known whether they may also use voice cues. To investigate this question, we played back non-signature whistles to wild dolphins during brief capture-release events in Sarasota Bay, Florida. We hypothesized that non-signature whistles, which have varied contours that can be shared among individuals, would be recognizable to dolphins only if they contained voice cues. Following established methodology used in two previous sets of playback experiments, we found that dolphins did not respond differentially to non-signature whistles of close relatives versus known unrelated individuals. In contrast, our previous studies showed that in an identical context, dolphins reacted strongly to hearing the signature whistle or even a synthetic version of the signature whistle of a close relative. Thus, we conclude that dolphins likely do not use voice cues to identify individuals. The low reliability of voice cues and the need for individual recognition were likely strong selective forces in the evolution of vocal learning in dolphins.

Keywords: Dolphin; Individual recognition; Non-signature whistle; Playback experiment; Voice cues.

Conflict of interest statement

Conflict of interest

The authors declare that they have no conflicts of interest.

Ethical approval

All applicable international, national, and/or institutional guidelines for the care and use of animals were followed, which include carrying out research under National Marine Fisheries Service Scientific Research Permit Numbers 522-1569, 522-1785, and 15543 issued to RSW. All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted, which include Institutional Animal Care and Use Committee (IACUC) approvals from the Woods Hole Oceanographic Institution to LSS and from Mote Marine Laboratory to RSW. This article does not contain any studies with human participants performed by any of the authors.

Data availability

Datasets generated and/or analyzed during the current study are not publicly available because they are currently being used for additional studies. Once these studies are completed, they will be made available from the corresponding author on reasonable request.

Figures

Fig. 1
Fig. 1
Spectrograms of non-signature and signature whistles produced during capture-release by six different dolphins (af). For each dolphin, the first exemplar is a non-signature whistle and the remaining three are randomly selected signature whistles. Frequency (up to 30,000 Hz) is on the y axes, and time in seconds is on the x axes. Spectrogram settings included a 1024-point Hanning window with 50% overlap
Fig. 1
Fig. 1
Spectrograms of non-signature and signature whistles produced during capture-release by six different dolphins (af). For each dolphin, the first exemplar is a non-signature whistle and the remaining three are randomly selected signature whistles. Frequency (up to 30,000 Hz) is on the y axes, and time in seconds is on the x axes. Spectrogram settings included a 1024-point Hanning window with 50% overlap
Fig. 2
Fig. 2
Playback experimental setup, showing the position of the videographer (sitting on top of the ladder on the boat), the playback speaker (held by the person at the foot of the ladder wearing a blue hat), and the target dolphin with a suction cup hydrophone on its melon. Photograph courtesy of Jim Schulz, Chicago Zoological Society, taken under National Marine Fisheries Service Scientific Research Permit No. 522-1785
Fig. 3
Fig. 3
Spectrogram of copying of a noisy non-signature playback stimulus. A 22-s sequence is divided into four 5.5-s sections (top panel 0–5.5; second panel 5.5–11; third panel 11–16.5; bottom panel 16.5–22). The target animal’s signature whistle is visible at the beginning, followed by a stimulus presentation and then several stimulus-copy exchanges. Frequency (up to 15,000 Hz) is on the y axes, and time in seconds is on the x axes. Spectrogram settings included a 1024 point Hanning window with 50% overlap
Fig. 4
Fig. 4
Spectrograms of similar non-signature whistle responses (called “M” whistles) to non-signature whistle playbacks by four different males (with two examples from each of two males, FB178 and FB196). Frequency (up to 30,000 Hz) is on the y axes, and time in seconds is on the x axes. Spectrogram settings included a 1024 point Hanning window with 50% overlap

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