We have continued our studies of how dolphins use whistles to communicate with one another. This past year we finalized our analysis of whistle playbacks that were designed to test the hypothesis that dolphins can use voice cues to recognize whistles of other dolphins. Voice cues are what we use to identify the voice of a person we know well, without them having to tell us their name. For these experiments, we played back non-signature whistles of kin and familiar non-kin, following the same protocol that we have used in previous experiments with signature whistles. Since the non-signature whistle stimuli that we played back were highly variable in contour, we predicted that dolphins must use voice cues for recognition if they were capable of identifying the vocalizer. In 40 experiments, no significant difference was found in head-turning responses to non-signatures of kin vs. non- kin, indicating that dolphins were not using voice cues to identify the vocalizer. This finding, plus the fact that dolphins produce individually specific signature whistles that function like names, sets dolphins apart from other non-human mammals studied to date.
We also continued to add to our long-term database of whistles recorded during capture/release sessions. These recordings enable a variety of studies of the structure and function of individually distinctive signature whistles, as well as of non-signature whistles, and provide us with stimuli for our playback experiments. We continue to examine recordings for examples of stereotyped non-signature whistles, such as the “M” whistle that we described last year, and we carried out additional playback experiments of unfamiliar whistles this year, to test the hypothesis that “M” whistles may be a response to unfamiliar whistles.
Together with Dr. Julie Oswald, we also began a new set of experiments this year to look at whether dolphins can discriminate among whistles of different species, even if these whistles are similar in overall contour. Extensive research into the passive detection of different dolphin species has struggled to find consistent differences in their whistles to tell them apart reliably. This raises the question whether dolphins can recognize such differences themselves. Is it possible that the animals learn all the whistles of their associates and treat all other dolphin whistles they hear as strangers? Once another animal is within echolocation range, it is unlikely that a dolphin could not tell one species from another. But communication sounds, like whistles, travel over much greater distances than an echolocation click can. We are trying to work out whether species differences are relevant and detectable to dolphins at these ranges.
This article appeared on pages 10-11 of the 2017 SDRP Annual Report, Nicks n Notches.