Description: Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Marine Mammal Science 25 (2009): 976-986, doi:10.1111/j.1748-7692.2009.00289.x.

Description: Bottlenose dolphins (Tursiops truncatus) produce individually distinctive vocalizations called signature whistles, first described by Melba and David Caldwell (1965). The Caldwells observed that isolated, captive dolphins produced whistles with individually distinctive frequency contours, or patterns of frequency changes over time, and hypothesized that these whistles were used to transmit identity information (Caldwell and Caldwell 1965; Caldwell et al. 1990). Since the Caldwell’s work with isolated, captive dolphins, several studies have documented signature whistles in a variety of contexts, including free-swimming captive dolphins (e.g., Janik and Slater 1998; Tyack 1986), briefly restrained wild dolphins (e.g., Sayigh et al. 1990, 2007, Watwood et al. 2005), and free-ranging wild dolphins (e.g., Watwood 2003; Watwood et al. 2004, 2005; Buckstaff 2004; Cook et al. 2004). Janik and Slater (1998) demonstrated that signature whistles are used to maintain group cohesion, thus supporting the Caldwells’ hypothesis. Janik et al. (2006) verified experimentally that bottlenose dolphins respond to signature whistles produced by familiar conspecifics even after voice featured have been removed, reinforcing the notion that the contour of a signature whistle carries identity information.

Description: This work was funded by a Protect Wild Dolphins grant from the Harbor Branch Oceanographic Institution, issued to LSS and RSW.

Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Proceedings of the Royal Society B Biological Sciences 280 (2013): 20130053, doi:10.1098/rspb.2013.0053.

Description: Vocal learning is relatively common in birds but less so in mammals. Sexual selection and individual or group recognition have been identified as major forces in its evolution. While important in the development of vocal displays, vocal learning also allows signal copying in social interactions. Such copying can function in addressing or labelling selected conspecifics. Most examples of addressing in non-humans come from bird song, where matching occurs in an aggressive context. However, in other animals, addressing with learned signals is very much an affiliative signal. We studied the function of vocal copying in a mammal that shows vocal learning as well as complex cognitive and social behaviour, the bottlenose dolphin (Tursiops truncatus). Copying occurred almost exclusively between close associates such as mother–calf pairs and male alliances during separation and was not followed by aggression. All copies were clearly recognizable as such because copiers consistently modified some acoustic parameters of a signal when copying it. We found no evidence for the use of copying in aggression or deception. This use of vocal copying is similar to its use in human language, where the maintenance of social bonds appears to be more important than the immediate defence of resources.

Description: This work was supported by a BBSRC Doctoral Training Grant, Dolphin Quest, the Chicago Zoological Society, the National Oceanic and Atmospheric Administration (NOAA) Fisheries Service, Disney’s Animals, Science and Environment, Dolphin Biology Research Institute, Mote Marine Laboratory, Harbor Branch Oceanographic Institute and a Royal Society University Research Fellowship and a Fellowship of the Wissenschaftskolleg zu Berlin to V.M.J.

Description: Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Marine Mammal Science 29 (2013): 109–122, doi:10.1111/j.1748-7692.2011.00549.x.

Description: Bottlenose dolphins (Tursiops truncatus) have individually-distinctive signature whistles. Each individual dolphin develops its own unique frequency modulation pattern and uses it to broadcast its identity. However, underwater sound localization is challenging, and researchers have had difficulties identifying signature whistles. The traditional method to identify them involved isolating individuals. In this context, the signature whistle is the most commonly produced whistle type of an animal. However, most studies on wild dolphins cannot isolate animals. We present a novel method, SIGID, that can identify signature whistles in recordings of groups of dolphins recorded via a single hydrophone. We found that signature whistles tend to be delivered in bouts with whistles of the same type occurring within 1-10 s of each other. Non-signature whistles occur over longer or shorter periods, and this distinction can be used to identify signature whistles in a recording. We tested this method on recordings from wild and captive bottlenose dolphins and show thresholds needed to identify signature whistles reliably. SIGID will facilitate the study of signature whistle use in the wild, signature whistle diversity between different populations, and potentially allow signature whistles to be used in mark-recapture studies.

Description: This work was supported by Dolphin Quest, National Oceanic and Atmospheric Administration (NOAA) Fisheries Service, Disney’s Animal Programs and Mote Marine Laboratory (R.S.W.), Harbor Branch Oceanographic Institute (L.S.S. and R.S.W.), and a Royal Society University Research Fellowship (V.M.J.).

Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS ONE 8 (2013): e77671, doi:10.1371/journal.pone.0077671.

Description: Bottlenose dolphins (Tursiops truncatus) produce many vocalisations, including whistles that are unique to the individual producing them. Such “signature whistles” play a role in individual recognition and maintaining group integrity. Previous work has shown that humans can successfully group the spectrographic representations of signature whistles according to the individual dolphins that produced them. However, attempts at using mathematical algorithms to perform a similar task have been less successful. A greater understanding of the encoding of identity information in signature whistles is important for assessing similarity of whistles and thus social influences on the development of these learned calls. We re-examined 400 signature whistles from 20 individual dolphins used in a previous study, and tested the performance of new mathematical algorithms. We compared the measure used in the original study (correlation matrix of evenly sampled frequency measurements) to one used in several previous studies (similarity matrix of time-warped whistles), and to a new algorithm based on the Parsons code, used in music retrieval databases. The Parsons code records the direction of frequency change at each time step, and is effective at capturing human perception of music. We analysed similarity matrices from each of these three techniques, as well as a random control, by unsupervised clustering using three separate techniques: k-means clustering, hierarchical clustering, and an adaptive resonance theory neural network. For each of the three clustering techniques, a seven-level Parsons algorithm provided better clustering than the correlation and dynamic time warping algorithms, and was closer to the near-perfect visual categorisations of human judges. Thus, the Parsons code captures much of the individual identity information present in signature whistles, and may prove useful in studies requiring quantification of whistle similarity.

Description: Arik Kershenbaum is a Postdoctoral Fellow at the National Institute for Mathematical and Biological Synthesis, an Institute sponsored by the National Science Foundation, the U.S. Department of Homeland Security, and the U.S. Department of Agriculture through NSF Award #EF-0832858, with additional support from The University of Tennessee, Knoxville. Part of this work was conducted while Arik Kershenbaum was provided with a doctoral scholarship by the University of Haifa. Funding for access to the dolphins for recordings was provided by Dolphin Quest and the Chicago Zoological Society.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1992

Description: This thesis presents data on the development and functions of individually distinctive signature whistles of free-ranging bottlenose dolphins, Tursiops tnmcatus. Research was conducted at a study site near Sarasota, Florida, where a resident community of bottlenose dolphins have been the focus of a long-term, ongoing study. Through observations and censuses, researchers have gained information on home ranges and association patterns among individuals. A temporary capture and release program has provided opportunities to collect basic information regarding age, sex, genetic relationships, and life history of individuals, as well as to record vocalizations of known individuals. During the periods 1975-1976 and 1984-1992, 134 different individuals were recorded during temporary capture. More than half of these were recorded on two or more (up to 10) different occasions. These recordings demonstrate that free-ranging dolphins produce individually distinctive signature whistles, as was previously documented for captive dolphins. Each dolphin produced a distinctive frequency contour, or pattern of frequency changes over time, and this whistle comprised a large portion of all whistles produced. Comparisons of whistles recorded from the same individuals over periods of more than a decade indicate that these signature whistle contours are markedly stable. This extensive database of recordings of signature whistles produced by known individuals formed the basis for much of the work described in this thesis. Playback experiments conducted during temporary capture-release projects indicated that free-ranging dolphins were able to discriminate among signature whistles of familiar individuals. When these results are taken in the context of what is known about dolphin societies, which are characterized by stable individual associations intermixed with fluid patterns of association among many individuals, it appears highly likely that dolphins use signature whistles to recognize one another as individuals. Sex differences in whistle production were documented through analysis of whistles recorded during temporary capture. Naive judges rated the similarity of signature whistle contours of 42 Sarasota calves and their mothers, and found that males were more likely than females to produce signature whistle contours highly similar to those of their mothers. Conversely, females were more likely than males to produce contours highly distinct from those of their mothers. In addition, preliminary results indicated that male calves were more likely than female calves to produce whistles other than the signature whistle (called "variant" whistles). It was hypothesized that these sex differences may relate to the different roles males and females play in the social structure of the community. Comparisons of whistle contours of parents and offspring, both in the wild (Sarasota) and in captivity (Miami Seaquarium), do not indicate that signature whistle structure is strictly inherited. Instead, it appears that learning plays a role in determining whistle structure. This contrasts with other non-human mammalian species, where learning does not appear to be involved in vocal development. Focal observations and acoustic recordings of four free-ranging Sarasota mother-calf pairs were conducted in order to examine the effects of the early social and auditory environment on signature whistle development. Although there was considerable individual variability among these four calves, this study provided some preliminary insights into factors affecting the time course and outcome of signature whistle development in the wild. Two calves which exhibited relatively rapid whistle development and produced contours that resembled those of their mothers also heard proportionately more of their mothers' signature contours than did the other two calves. The other two calves exhibited more prolonged whistle development and produced contours that did not resemble those of their mothers. Preliminary data indicated that these two mothers may have actively taught their calves to produce a distinctive whistle contour by producing "model" contours while their calves were very young. Strength of the mother-calf association, number of associates other than the mother, overall number of whistles heard, and number of whistles produced by the mother all may affect the time course of whistle development and whether or not a calf develops a contour similar to that of its mother.

Description: This work was supported by the Education office of the Woods Hole Oceanographic Institution, two Ocean Ventures Fund awards, the American Cetacean Society, and National Science Foundation Doctoral Dissertation Research Grant No. BNS-9014545. Additional support was provided from NIH Grant No. 1R29NS25290 and ONR Grant No. N00014-87-K-0236, both to Peter Tyack.

Description: Author Posting. © Acoustical Society of America, 2014. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 136 (2014): 1394, doi:10.1121/1.4892759.

Description: Melon-headed whales are pantropical odontocetes that are often found near oceanic islands. While considered sound-sensitive, their bioacoustic characteristics are relatively poorly studied. The goal of this study was to characterize the vocal repertoire of melon-headed whales to determine whether they produce repeated calls that could assist in recognition of conspecifics. The first tag-based acoustic recordings of three melon-headed whales were analyzed. Tag records were visually and aurally inspected and all calls were individually extracted. Non-overlapping calls with sufficient signal-to-noise were then parameterized and visually grouped into categories of repeated call types. Thirty-six call categories emerged. Categories differed significantly in duration, peak and centroid frequency, and −3 dB bandwidth. Calls of a given type were more likely to follow each other than expected. These data suggest that repeated calls may function in individual, subgroup, or group recognition. Repeated call production could also serve to enhance signal detection in large groups with many individuals producing simultaneous calls. Results suggest that caution should be used in developing automatic classification algorithms for this species based on small sample sizes, as they may be dominated by repeated calls from a few individuals, and thus not representative of species- or population-specific acoustic parameters.

Description: This project was funded by the Office of Naval Research (award number: N000141110612; Program Manager Michael J. Weise), WHOI Marine Mammal Center, and the Sawyer and Penzance Endowed Funds, with additional field time funded by grants through Cascadia Research Collective by the National Oceanographic Partnership Program (through the Alaska SeaLife Center) and the Pacific Islands Fisheries Science Center.