In 2008, we completed experiments (described in previous issues of Nicks’n’Notches) aimed at determining whether dolphins can recognize each others’ whistles by means of voice cues, in the same manner that most people recognize the voices of people that they know. Data are being prepared for publication, and analyses so far indicate that dolphins do not use voice cues to recognize whistles of other individuals. This is an interesting finding, indicating that dolphins are apparently unique in the animal kingdom in their use of the frequency modulation patterns of whistles alone to recognize conspecifics (members of the same species).
        We also continued two other studies started in previous years. We continued our playback experiments that are looking at how dolphins react when their own signature whistle is copied by someone else. This copying is common in the wild and we would like to know how animals react to it. Our preliminary data suggest that they show a much stronger response to a playback of their own whistle than to hearing signature whistles of others. This supports the idea that signature whistle copying can be used by dolphins to address or find another dolphin at sea. We also continued our ongoing study of signature whistle development. Bottlenose dolphins are unusual among mammals in that they learn their individually distinctive signature whistles. With a dataset of 111 calves born from 56 mothers since 1975, we are looking at factors that influence the whistle development process. We used both visual assessments and a neural network whistle classification program called ARTWARP to assess the similarity of whistles of mothers and calves. So far, results from this program are in good agreement with the visual classifications. For 103 calves of known sex, 38 (36.9%) produced whistles similar to those of their mothers. We are currently examining possible factors that may be influencing the tendency of calves to produce whistles similar to or different from those of their mothers, including group size and birth order.
       

Whistle playback experiment near Longboat Pass

        Another important part of our studies is to collect acoustic recordings to add to the Sarasota Whistle Database, and we continue to work on digitizing this resource so that it can be freely accessible to researchers. This data set represents a unique resource to study dolphin communication. In 2008, we used it to develop a signature whistle identification method that can be used on any recordings from the wild. This was needed since not all field sites are suitable for capture-release projects, where signature whistles can be easily identified. We found that signature whistles are delivered in specific sequential patterns. Using ARTWARP and whistle bout analysis we can find these patterns that indicate signature whistles. This is an important breakthrough which now allows us to use signature whistles in mark-recapture studies, in which we can monitor habitat usage in dolphins by deploying automatic recording devices at sea, even when capture-release studies are not possible. Thus, we were able to provide a new tool for monitoring dolphin abundance and ecology, which will help conservation efforts worldwide.
        This work was funded by a Protect Wild Dolphins Grant to L. Sayigh and R. Wells from the Harbor Branch Oceanographic Institute Protect Wild Dolphins Program, and a Royal Society University Research Fellowship from the UK to V. M. Janik.