Dolphins are known to produce individually distinctive signature whistles. A previous study involving playback experiments with Sarasota dolphins showed that dolphins recognize one another’s signature whistles. However, it is not known what features of whistles dolphins use to recognize one another. Two possible cues are the contour, or shape of the whistle, or more subtle features commonly called “voice cues”. These are the cues that we use to recognize the voices of our friends, even if they don’t tell us who they are.
To explore these questions, recordings are played through underwater speakers to dolphins held during capture-release projects for health assessment in Sarasota Bay. An earlier set of playback experiments (2003-4) showed that dolphins are capable of recognizing synthetic signature whistle contours, suggesting that contour is the most important feature of the whistle for individual recognition. However, these experiments did not rule out the possibility that dolphins use both contour and voice cues to recognize individuals. Thus, our current experiments are looking at whether dolphins are capable of discriminating among natural non-signature, or variant, whistles. If they are capable of discriminating among these whistles, which are highly variable in contour, then they must be using voice cues for this recognition.
Aside from the intrinsic benefit of understanding how dolphins communicate with each other, this research also has potential conservation benefits. An understanding of what features of whistles are perceptually important to dolphins will improve our ability to understand how various sources of anthropogenic noise may impact their ability to communicate.
This work is currently being funded by a Protect Wild Dolphins Grant to L. Sayigh and R. Wells from the Harbor Branch Institute of Oceanography, and a Royal Society University Research Fellowship from the UK to V. M. Janik.