Sarasota Bay’s dolphins produce a variety of whistles, including individually-specific signature whistles, and others for which we are trying to learn the function. This past year we added whistles from seven new dolphins to our long-term database of whistles recorded during capture-release sessions. Six of these have known mothers in the community, adding to our large database of whistles from mother-calf pairs. These recordings enable studies of the development and stability of individually distinctive signature whistles, such as those being carried out by University of St. Andrews graduate student Braulio León-López. He found that when analyzing signature whistles, no parameters of the frequency modulation pattern that carries the identity information relate in any way to the size, sex or age of the animal. This supports the idea that signature whistles are truly arbitrary signals that are invented by the caller, and serve as a label for the dolphin that uses the whistle.
Our new recordings also add to our ongoing studies of stereotyped non-signature whistles, by providing a rich data set of recordings of known individuals in which to look for these whistles. Unlike the individually distinctive signature whistles of bottlenose dolphins, little is known about non-signature whistles, although they comprise a large portion of the whistle repertoire. In our recently completed experiments in which we played back non-signature whistles to dolphins during capture-release, we found that several individuals, more often males, produced a stereotyped non-signature whistle named the “M whistle.” In collaboration with WHOI Research Assistant Claire Stuhlmann, we have since widened the search for “M” whistles in other capture-release recordings, and found 67 occurrences, of which 75% were made by a male associating with a female, and 66% were in response (within 1 sec) to another non-signature whistle. Non-signature whistles clearly play a very different role than signature whistles in the dolphin communication system. Based on these results we can conclude that non-signatures do not convey individual identity, but rather convey a form of context-specific information. While dolphins have been found to produce context-specific pulsed sounds, this is the first evidence for a shared, apparently context-specific non-signature whistle.
Our dolphin playback studies this year continued our experiments involving playbacks of unfamiliar whistles. We are testing the hypothesis that “M” whistles may actually be a response to unfamiliar, rather than strictly non-signature, whistles. Analyses of these data are currently underway, and will dictate the direction that our experiments will take next year. Ultimately we hope that these studies will provide some of the first insights into the role of non-signature whistles in the dolphin communication system.
This article appeared on page 9 in the December 2015 issue of Nicks n Notches.