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Humans use whistled communications, the most elaborate of which are commonly called “whistled languages” or “whistled speech” because they consist of a natural type of speech. The principle of whistled speech is straightforward: people articulate words while whistling and thereby transform spoken utterances by simplifying them, syllable by syllable, into whistled melodies. One of the most striking aspects of this whistled transformation of words is that it remains intelligible to trained speakers, despite a reduced acoustic channel to convey meaning. It constitutes a natural traditional means of telecommunication that permits spoken communication at long distances in a large diversity of languages of the world. Historically, birdsong has been used as a model for vocal learning and language. But conversely, human whistled languages can serve as a model for elucidating how information may be encoded in dolphin whistle communication. In this paper, we elucidate the reasons why human whistled speech and dolphin whistles are interesting to compare. Both are characterized by similar acoustic parameters and serve a common purpose of long distance communication in natural surroundings in two large brained social species. Moreover, their differences – e.g., how they are produced, the dynamics of the whistles, and the types of information they convey – are not barriers to such a comparison. On the contrary, by exploring the structure and attributes found across human whistle languages, we highlight that they can provide an important model as to how complex information is and can be encoded in what appears at first sight to be simple whistled modulated signals. Observing details, such as processes of segmentation and coarticulation, in whistled speech can serve to advance and inform the development of new approaches for the analysis of whistle repertoires of dolphins, and eventually other species. Human whistled languages and dolphin whistles could serve as complementary test benches for the development of new methodologies and algorithms for decoding whistled communication signals by providing new perspectives on how information may be encoded structurally and organizationally.

Humans use whistled communications, the most elaborate of which are commonly called "whistled languages" or "whistled speech" because they consist of a natural type of speech. The principle of whistled speech is straightforward: people articulate words while whistling and thereby transform spoken utterances by simplifying them, syllable by syllable, into whistled melodies. One of the most striking aspects of this whistled transformation of words is that it remains intelligible to trained speakers, despite a reduced acoustic channel to convey meaning. It constitutes a natural traditional means of telecommunication that permits spoken communication at long distances in a large diversity of languages of the world. Historically, birdsong has been used as a model for vocal learning and language. But conversely, human whistled languages can serve as a model for elucidating how information may be encoded in dolphin whistle communication. In this paper, we elucidate the reasons why human whistled speech and dolphin whistles are interesting to compare. Both are characterized by similar acoustic parameters and serve a common purpose of long distance communication in natural surroundings in two large brained social species. Moreover, their differences – e.g., how they are produced, the dynamics of the whistles, and the types of information they convey – are not barriers to such a comparison. On the contrary, by exploring the structure and attributes found across human whistle languages, we highlight that they can provide an important model as to how complex information is and can be encoded in what appears at first sight to be simple whistled modulated signals. Observing details, such as processes of segmentation and coarticulation, in whistled speech can serve to advance and inform the development of new approaches for the analysis of whistle repertoires of dolphins, and eventually other species. Human whistled languages and dolphin whistles could serve as complementary test benches for the development of new methodologies and algorithms for decoding whistled communication signals by providing new perspectives on how information may be encoded structurally and organizationally. [ABSTRACT FROM AUTHOR]

Although the maximum length sequence (MLS) and iterative randomized stimulation and averaging (I-RSA) methods allow auditory brainstem response (ABR) measurements at high rates, it is not clear if high rates allow ABRs of a given quality to be measured in less time than conventional (CONV) averaging (i.e., fixed interstimulus intervals) at lower rates. In the present study, ABR signal-to-noise ratio (SNR) was examined in six bottlenose dolphins as a function of measurement time and click rate using CONV averaging at rates of 25 and 100 Hz and the MLS/I-RSA approaches at rates from 100 to 1250 Hz. Residual noise in the averaged ABR was estimated using (1) waveform amplitude following the ABR, (2) waveform amplitude after subtracting two subaverage ABRs (i.e., the "±average"), and (3) amplitude variance at a single time point. Results showed that high stimulus rates can be used to obtain dolphin ABRs with a desired SNR in less time than CONV averaging. Optimal SNRs occurred at rates of 500–750 Hz, but were only a few dB higher than that for CONV averaging at 100 Hz. Nonetheless, a 1-dB improvement in SNR could result in a 25% time savings in reaching criterion SNR. [ABSTRACT FROM AUTHOR]

Keyboards and cognitive interfaces for dolphins have a long history. Various modalities of communication (visual, acoustic) and triggering mechanisms (physical, infrared, acoustic) have been utilized. Protocols and frameworks (e.g., the model/rival approach) have improved with the adaptation of methodological techniques from primates and birds. This paper reviews the long history of human-dolphin communication studies and the pros and cons of both technology and technique.

Purse-seine vessels commonly interact with dolphins. The total number of dolphins accidentally killed in the world's purse-seine fisheries may be substantial, even if interaction rates are generally low. This paper describes an industry Code of Practice (CoP) that was established in Australian purse-seine fishery after an observer program detected high dolphin interaction rates that had not been reported in fishery logbooks. Key features of the CoP are search and delay procedures designed to prevent encirclements and release procedures that minimise mortalities. Extrapolation from observer data (3.9% of net sets observed), suggested that 449 dolphin encirclements and 423 mortalities occurred in 2004-05, the year before the CoP was established. A decade later, observer data suggest that annual encirclements and mortalities had been reduced by 87% and 97%, respectively. Searches were highly effective in detecting the presence of dolphins. Dolphins were not encircled in > 85% of net-sets made after searches determined that dolphins were absent from the fishing area. Opening the front of the net resulted in the successful release of all dolphins in > 86% of encirclement events. Discrepancies between interaction rates estimated from observer data and those recorded in logbooks have decreased over time. This study demonstrated that codes of practice that specify changes in fisher behaviour can be effective in mitigating the interactions of purse-seine fisheries with dolphins. The avoidance and release procedures documented in the CoP for the South Australian sardine fishery are simple and, if adopted in other purse-seine fisheries, could substantially reduce global mortality of dolphins. [ABSTRACT FROM AUTHOR]

This short communication reports an observation of unusual non-agonistic interactions between a juvenile harbour porpoise (Phocoena phocoena) and a group of bottlenose dolphins (Tursiops truncatus) in the Marmara Sea on 25 April 2015. [ABSTRACT FROM AUTHOR]

Previous studies have demonstrated that increasing-frequency chirp stimuli (up-chirps) can enhance human auditory brainstem response (ABR) amplitudes by compensating for temporal dispersion occurring along the cochlear partition. In this study, ABRs were measured in two bottlenose dolphins (Tursiops truncatus) in response to spectrally white clicks, up-chirps, and decreasing-frequency chirps (down-chirps). Chirp durations varied from 125 to 2000 µs. For all stimuli, frequency bandwidth was constant (10-180 kHz) and peak-equivalent sound pressure levels (peSPLs) were 115, 125, and 135 dB re 1 µPa. Up-chirps with durations less than ~1000 µs generally increased ABR peak amplitudes compared to clicks with the same peSPL or energy flux spectral density level, while down-chirps with durations from above ~250 to 500 µs decreased ABR amplitudes relative to clicks. The findings generally mirror those from human studies and suggest that the use of chirp stimuli may be an effective way to enhance broadband ABR amplitudes in larger marine mammals. [ABSTRACT FROM AUTHOR]

Focusing on the need of covert underwater acoustic communication, a camouflage underwater acoustic communication approach is proposed in this paper. The idea is to deceive the interceptor to actively exclude the communication signal as it resembles the original whistle. Based on the time and frequency modulation feature of dolphin whistles, a series of segmented chirp rate modulated signals are designed to mimic the dolphin whistles by sound characteristics. A specialized communication frame structure is designed to facilitate the information demodulation, where the original whistle is used as the synchronization signal and the mimicry signal is followed to convey information. Besides, the original synchronization whistle is also used as a transmit reference to extract the whistle contour and furthermore to get the center frequency of each chirp. Virtual time reversal mirror technique is employed to mitigate channel effect. Fractional Fourier Transform and correlation approaches are adopted to realize demodulation respectively. The feasibility and efficiency of the proposed method are verified by both simulation and sea experiment. Bit error rate less than 10 - 3 with chirp duration of 20 ms at a distance of 5.5 km is achieved in the sea trial. [ABSTRACT FROM AUTHOR]

This study focused on whistles produced by Guiana dolphin under different noise conditions in Guanabara Bay, southeastern Brazil. Recording sessions were performed with a fully calibrated recording system. Whistles and underwater noise levels registered during two behavioral states were compared separately between two areas. Noise levels differed between the two areas across all frequencies. Whistle duration differed between areas and was negatively correlated with noise levels. Whistling rate was positively correlated with noise levels, showing that whistling rate was higher in noisier conditions. Results demonstrated that underwater noise influenced Guiana dolphin acoustic behavior. [ABSTRACT FROM AUTHOR]

The present study evaluates variations in frequency and duration parameters of whistles of four dolphin species (Sotalia guianensis, Steno bredanensis, Stenella frontalis, and Tursiops truncatus), recorded in the Rio de Janeiro State Coast, Southeastern Brazil. A total of 487 whistles were analyzed. Acoustic parameters of the whistles were classified to species by discriminant function analysis. Overall classification score was 72.5%, with the highest classification score obtained for whistles of S. bredanensis and the lowest obtained for S. frontalis. Most differences were among S. bredanensis and S. guianensis, species that did not have their repertoires compared in other studies. [ABSTRACT FROM AUTHOR]

Bottlenose dolphins use whistles to communicate with their conspecifics and maintain group cohesion. We recorded 477 whistles of Indo-Pacific bottlenose dolphins ( Tursiops aduncus) in the Fremantle Inner Harbour, Western Australia, on nine occasions over a six-week period during May/June 2013. Over half (57 %) of the whistles had complex contours exhibiting at least one local extremum, while 32 % were straight upsweeps, 5 % downsweeps and 6 % constant-frequency. About 60 % of whistles occurred in trains. Fundamental frequency ranged from 1.1 to 18.4 kHz and whistle duration from 0.05 to 1.15 s. The maximum numbers of local extrema and inflection points were 7 and 9, respectively. Whistle parameters compared well to those of measurements made from other T. aduncus populations around Australia. Observed differences might be due to ambient noise rather than geographic separation. [ABSTRACT FROM AUTHOR]

Biphonic signals are nonlinear phenomena (NLPs) occurring in the repertoire of several animal groups and widespread across mammalian species. Although the mechanism of production is unclear, an adaptive meaning was suggested by their communication function, such as group or individual recognition. We document the rare recording event of a biphonic whistle emitted within a free-ranging population of bottlenose dolphins in the waters of south-western Sicily, Italy. The whistle was recorded in 2 different years, always when a photo-identified individual was present. A quantitative description of the signal is provided. The signal presents some unique characteristics in its frequency modulation pattern which is stable for a long period. Furthermore, the synchronized beginning of the two fundamental frequencies, the signal repetition within few seconds and its emission in freely interacting contexts suggest that biphonation is neither temporary nor involuntary. Also, we propose that biphonation can be produced via multiple mechanisms in bottlenose dolphins and that NLPs could represent natural recognizing marks that play a role in communication between bottlenose dolphins. [ABSTRACT FROM AUTHOR]

The process by which sound is propagated in the head of a toothed whale is still a subject of discussion. Investigating the distribution of acoustic impedance calculated by density and Young's modulus is effective for quantitative comprehension because acoustic impedance determines the reflection coefficient of a sound wave. However, the sound propagation process of the toothed whale has been mainly examined by either anatomical techniques or the measurement of density or sound velocity. In the current study, the acoustic impedance of head tissue of harbor porpoise was measured. Results of this study should be a helpful information for further discussion about the relationship between the structure of sound-producing organ and clicks property. [ABSTRACT FROM AUTHOR]

We studied the influence of trammel nets on the behaviour and spatial distribution of bottlenose dolphin in the Aeolian Archipelago, Southern Italy. Ninety-six dolphin groups were followed for 98.75 h from 2005 to 2011 during 400 boat surveys. Thirty-three dolphins were photo-identified, and their age and sex were estimated. The encounter rates, residency times, and group sizes were used to model the spatial distribution of dolphins with trammel nets and physiographic variables. Principal Component Analyses were applied to find the habitats selected for different behavioural activities. Encounter rates were significantly higher in early summer when trammel nets were more abundant. Residency times were spatially correlated to the mean number of trammel nets. Group sizes increased with distance from coast but decreased with abundance of trammel nets. Males preferred smaller groups than females, and groups with calves were larger than the other groups. Resting, socializing, and playing groups were larger than groups of dolphins engaged in travelling, foraging, and feeding. Spatial segregation between groups of dolphins with different sizes was observed. Although dolphins benefit from taking fish in trammel nets, this interaction can be dangerous because the fishermen can use harmful methods to deter dolphins from the net. Herein, we proposed that males prefer habitats where they have a higher probability of locating/capturing a desirable prey such as coastal areas with a greater amount of trammel nets; while for other activities, they may move into safer areas. On the contrary, females prefer habitats for reasons not associated with prey such as social behaviours, resting, or calf care/learning; and they may spend more time in the safest areas, at a distance from the coast, simply feeding when the opportunity presents itself. This study showed that group size/composition data are of critical importance for modeling dolphin-habitat relationships with significant consequences in terms of conservation strategies. [ABSTRACT FROM AUTHOR]

Food-related signalling is widespread in the animal kingdom with some food-associated vocalizations considered functionally referential. Food calls can, however, vary greatly in the type of information they convey. Thus, there are a multitude of purposes for which food calls are used, including social recruitment, caller spacing, the indication of type, quantity, quality, divisibility of food, the caller's hunger level and even as tools to manipulate prey behaviour. Yet little work has focused on the social aspect of food calling in animals. We investigated the association of social signals in wild bottlenose dolphins with foraging behaviour where context-specific food-associated calls are commonly produced. Our data showed that specific social signals were significantly correlated with food call production and these calls rarely occurred in the absence of food calls. We suggest that animals are sharing additional information on the food patch itself with their social affiliates. [ABSTRACT FROM AUTHOR]

The search for signals out of noise is a problem not only with radio signals from the sky but in the study of animal communication. Dolphins use multiple modalities to communicate including body postures, touch, vision, and most elaborately sound. Like SETI radio signal searches, dolphin sound analysis includes the detection, recognition, analysis, and interpretation of signals. Dolphins use both passive listening and active production to communicate. Dolphins use three main types of acoustic signals: frequency modulated whistles (narrowband with harmonics), echolocation (broadband clicks) and burst pulsed sounds (packets of closely spaced broadband clicks). Dolphin sound analysis has focused on frequency-modulated whistles, yet the most commonly used signals are burst-pulsed sounds which, due to their graded and overlapping nature and bimodal inter-click interval (ICI) rates are hard to categorize. We will look at: 1) the mechanism of sound production and categories of sound types, 2) sound analysis techniques and information content, and 3) examples of lessons learned in the study of dolphin acoustics. The goal of this paper is to provide perspective on how animal communication studies might provide insight to both passive and active SETI in the larger context of searching for life signatures. [ABSTRACT FROM AUTHOR]

The cetaceans are one of the few mammalian clades capable of vocal production learning. Evidence for this comes from synchronous changes in song patterns of baleen whales and experimental work on toothed whales in captivity. While baleen whales like many vocal learners use this skill in song displays that are involved in sexual selection, toothed whales use learned signals in individual recognition and the negotiation of social relationships. Experimental studies demonstrated that dolphins can use learned signals referentially. Studies on wild dolphins demonstrated how this skill appears to be useful in their own communication system, making them an interesting subject for comparative communication studies. [ABSTRACT FROM AUTHOR]

Whistles of bottlenose dolphins (Tursiops truncatus) and Atlantic spotted dolphins (Stenella frontalis) in the eastern Gulf of Mexico were recorded and measured with a calibrated towed hydrophone array. Surveys encountered groups of both bottlenose (N = 10) and spotted dolphins (N = 5). Analysis of those data produced 1695 bottlenose dolphin whistles and 1273 spotted dolphin whistles with a high signal-to-noise ratio. Whistle frequency metrics were lower in bottlenose than spotted dolphins, while whistle duration was longer in spotted dolphins, data that may help inform automatic classification algorithms. Source levels were estimated by determining the range and bearing of an individual dolphin from the array and then adding the predicted transmission loss to the calculated received level. The median bottlenose dolphin source level was 138 dB re 1 µPa at 1m with a range of 114-163 dB re 1 µPa at 1 m. The median spotted dolphin source level was 138 dB re 1 µPa at 1m with a range of 115-163 dB re 1 µPa at 1m. These source level measurements, in conjunction with estimates of vocalization rates and transmission loss models, can be used to improve passive acoustically determined dolphin abundance estimates in the Gulf of Mexico. [ABSTRACT FROM AUTHOR]

Two recent papers by Kuczaj et al. (Anim Cognit 18:543-550, 2015) and Eskelinen et al. (Anim Cognit 19:789-797, 2016) claim to have demonstrated that (i) bottlenose dolphins ( Tursiops truncatus) cooperated to solve a novel task and (ii) vocal signals were important for coordinating these cooperative efforts. Although it is likely that bottlenose dolphins may share communicative signals in order to achieve a common goal, we suggest that this has not been demonstrated in the aforementioned studies. Here, we discuss the two main problems that preclude any definitive conclusions being drawn on cooperative task success and vocal communication from these studies. The first lies in the experimental design. The 'cooperative task', involving an apparatus that requires two dolphins to pull in opposite directions in order to achieve a food reward, is not conducive to cooperation, but could instead reflect a competitive 'tug-of-war'. It is therefore of questionable use in distinguishing competitive from cooperative interactions. Second, the suggestion that the occurrence of burst-pulsed signals in this task was indicative of cooperation is disputable, as (i) this study could not determine which dolphins were actually producing the signals and (ii) this sound type is more commonly associated with aggressive signalling in dolphins. We commend the authors for investigating this exciting and topical area in animal communication and cognition, but the question of whether dolphins cooperate and communicate to solve a cooperative task remains as yet unanswered. [ABSTRACT FROM AUTHOR]