Whistle playback studies
By Vincent Janik, PhD, Sea Mammal Research Unit and Laela Sayigh, PhD, Woods Hole Oceanographic Institution and University of North Carolina, Wilmington

Our playback studies are designed to test specific questions that arise from the observational studies on dolphin communication that we conduct. All of our playback studies are carried out during brief capture-release events, allowing us to carefully observe the dolphins' reactions, such as whether they turn their head towards the speaker when they hear a sound. We are particularly interested in the design and function of the signature whistle system that dolphins use to maintain contact with each other. Dolphins make up their own distinctive frequency modulation pattern (like a melody of a whistled tune) that they use to identify themselves. In May 2006 we published results from our Sarasota study that tested whether other dolphins learn to recognize this particular feature of the dolphin whistle (Janik, Sayigh and Wells 2006, PNAS 103: 8293-8297). We showed that dolphins recognized individual whistles even if we removed all voice features and only played a computer tone that mimicked the distinctive frequency modulation belonging to a close relative. This makes signature whistles similar to human names. Our study received a lot of media interest and was reported about by, amongst others, ABC, NBC, BBC, the New York Times and National Geographic.

Using the same techniques we are continuing our experiments to find out whether dolphins can recognize each other by voice as well. As described above, we now know that they can recognize the frequency modulation patterns of other individuals. But can they recognize animals just by the tone of their voice? Humans are good at this and do not need to hear a person’s name to recognize them on the phone. To find out, we are now playing non-signature whistles to dolphins to see whether they recognize who produced them.

Spectrograms of the original and the synthetic version of a signature whistle used in playback experiments.

A third study that is underway looks at how dolphins react when their own signature whistle is copied by someone else. Wild dolphins sometimes mimic the signatures of others, presumably to address or find a specific animal they are looking for. In this study we want to test whether dolphins react more to a copy of their own whistle than they do to other whistles. This would clarify whether dolphin signature whistles really are used like human names to address individuals.

We continue to build the unique Sarasota Dolphin Whistle Database, by making baseline recordings during capture-release projects. This database is almost fully digitized now, making it more accessible to other researchers. The Sarasota community is the only dolphin population that we can use to ask these questions, since we have long-term data from each individual on signature whistles and social partners. Through our work we can raise public awareness of the uniqueness of these animals and help to inform conservation efforts by providing data on how dolphins use sounds. This information can then be used to assess the effects of anthropogenic noise on dolphins.

This work is currently being funded by a Harbor Branch Oceanographic Institution Protect Wild Dolphins grant to L. Sayigh and R. Wells, and a Royal Society University Research Fellowship from the UK to V. M. Janik.