Whistles Of Dolphins Research Articles

Probable signature whistle production in Atlantic white‐sided (Lagenorhynchus acutus) and short‐beaked common (Delphinus delphis) dolphins near Cape Cod, Massachusetts

Probable signature whistle production in Atlantic white‐sided (<i>Lagenorhynchus acutus</i>) and short‐beaked common (<i>Delphinus delphis</i>) dolphins near Cape Cod, Massachusetts

The Sarasota Dolphin Whistle Database: A unique long-term resource for understanding dolphin communication

Common bottlenose dolphins (Tursiops truncatus) produce individually distinctive signature whistles that are learned early in life and that help animals recognize and maintain contact with conspecifics. Signature whistles are the predominant whistle type produced when animals are isolated from conspecifics. Health assessments of dolphins in Sarasota, Florida (USA) provide a unique opportunity to record signature whistles, as dolphins are briefly separated from conspecifics. Recordings were first made in the mid 1970’s, and then nearly annually since 1984. The Sarasota Dolphin Whistle Database (SDWD) now contains 926 recording sessions of 293 individual dolphins, most of known age, sex, and matrilineal relatedness. The longest time span over which an individual has been recorded is 43 years, and 85 individuals have been recorded over a decade or more. Here we describe insights about signature whistle structure revealed by this unique and expansive dataset. Signature whistles of different dolphins show great variety in their fundamental frequency contours. Signature whistle types (with ‘whistle type’ defined as all whistles visually categorized as sharing a particular frequency modulation pattern) can consist of a single stereotyped element, or loop (single-loop whistles), or of multiple stereotyped loops with or without gaps (multi-loop whistles). Multi-loop signature whistle types can also show extensive variation in both number and contour of loops. In addition, fundamental frequency contours of all signature whistle types can be truncated (deletions) or embellished (additions), and other features are also occasionally incorporated. However, even with these variable features, signature whistle types tend to be highly stereotyped and easily distinguishable due to the extensive variability in contours among individuals. In an effort to quantify this individual distinctiveness, and to compare it to other species, we calculated Beecher’s Information Statistic and found it to be higher than for any other animal signal studied so far. Thus, signature whistles have an unusually high capacity to convey information on individual identity. We briefly review the large range of research projects that the SDWD has enabled thus far, and look ahead to its potential to answer a broad suite of questions about dolphin communication.

Dolphin-Watching Boats Affect Whistle Frequency Modulation in Bottlenose Dolphins

Bottlenose dolphins’ whistles are key in social communication, conveying information about conspecifics and the environment. Therefore, their study can help to infer habitat use and identify areas of concern due to human activities. Here we studied the whistles of bottlenose dolphins (Tursiops truncatus) in two sites of the archipelago of Bocas del Toro, Panama, that contrast in boat traffic. Almirante Bay is a site dominated by taxi-boats and Dolphin Bay is a major location for boat-based dolphin watching. Recordings were made using bottom-mounted hydrophones and from the research boat using an over-the-side hydrophone and a broadband recording system. A total recording effort time of 1,726 h was analyzed. Our results show significant differences in boat detection between sites, and a higher number of whistles detected per minute in the site with tour-boat traffic. Furthermore, whistle modulation accounted for most of the differences between sites, boat presence, and whistle types. Dolphin whistle modulation is thought to be a potential indicator of emotional states including danger, alertness, and stress. In this study, dolphin signature whistle modulation increased significantly with boat presence in both sites but changes in modulation were greater in Dolphin Bay where tour-boats directly and sometimes aggressively interact with the animals. These results support a potential association between whistle modulation and stress (or alertness). These findings indicate that if tour-boat captains behave more like taxi-boat captains by e.g., reducing the distance of approach and contact time during dolphin interactions, dolphin communication, and emotional state would be less disrupted. These measures are implemented in the national guidelines for whale-watching and are known to tour-boat operators. The key to protecting these dolphins is in finding ways to effectively enforce these operator guidelines.

First description of whistles of Black Sea short-beaked common dolphins, Delphinus delphis ponticus

ABSTRACT The study presents the first quantitative description of whistles (N = 1,017) recorded from free-range short-beaked common dolphins D. delphis ponticus, an endemic subspecies from the Black Sea. The dolphins produced high-pitched frequency-modulated whistles with the fundamental frequency of 1.6–33.2 kHz, the median values of minimum and maximum frequencies being 8.6 kHz and 16.0 kHz, respectively. Whistle duration varied from 0.16 to 2.94 s, with a median value of 1.04 s. Whistle contours with inflection points were the most common (74% of the whistles), followed by simpler whistles: downsweep (13%), upsweep (12%), and flat (1%). Stereotyped repeated frequency-modulated whistles registered in this and previous studies may serve as individual distinctive ‘signature whistles’ in common dolphins. Whistle parameters of the Black Sea subspecies correspond to those reported for D. delphis recorded in neighbouring regions: the Mediterranean Sea and Central–Eastern North Atlantic Ocean. Maximum whistle frequency in common dolphins exhibits a relationship with the body size, similarly to some other dolphin species. Together with minimum frequency, these are parameters with the least coefficients of variation; thus, they may be species-specific acoustic characteristics. This information can be used to distinguish between sympatric dolphin species during their passive acoustic monitoring.

Mark–recapture of individually distinctive calls—a case study with signature whistles of bottlenose dolphins (Tursiops truncatus)

Abstract Robust abundance estimates of wild animal populations are needed to inform management policies and are often obtained through mark–recapture (MR) studies. Visual methods are commonly used, which limits data collection to daylight hours and good weather conditions. Passive acoustic monitoring offers an alternative, particularly if acoustic cues are naturally produced and individually distinctive. Here we investigate the potential of using individually distinctive signature whistles in a MR framework and evaluate different components of study design. We analyzed signature whistles of common bottlenose dolphins, Tursiops truncatus, using data collected from static acoustic monitoring devices deployed in Walvis Bay, Namibia. Signature whistle types (SWTs) were identified using a bout analysis approach (SIGnature IDentification [SIGID]—Janik et al. 2013). We investigated spatial variation in capture by comparing 21 synchronized recording days across four sites, and temporal variation from 125 recording days at one high-use site (Aphrodite Beach). Despite dolphin vocalizations (i.e., echolocation clicks) being detected at each site, SWTs were not detected at all sites and there was high variability in capture rates among sites where SWTs were detected (range 0–21 SWTs detected). At Aphrodite Beach, 53 SWTs were captured over 6 months and discovery curves showed an initial increase in newly detected SWTs, approaching asymptote during the fourth month. A Huggins closed capture model constructed from SWT capture histories at Aphrodite Beach estimated a population of 54–68 individuals from acoustic detection, which overlaps with the known population size (54–76 individuals—Elwen et al. 2019). This study demonstrates the potential power of using signature whistles as proxies for individual occurrence and in MR abundance estimation, but also highlights challenges in using this approach.

Geographic variation in the whistles of bottlenose dolphins (Tursiops spp.) in the southwestern Atlantic Ocean

Geographic variation in the whistles of bottlenose dolphins (<i>Tursiops</i> spp.) in the southwestern Atlantic Ocean

Spatial-temporal dynamics of a local population of Black Sea Bottlenose dolphins (tursiops truncatus ponticus barabash, 1940): visual and acoustic methods of description

This work is devoted to research of the Sudak – Novy Svet (Crimea) local population of Black Sea Bottlenose dolphins. Observations and acoustic records were carried out all the year round in 2014 and 2015. Along with visual identification of individuals, for the first time in our country the method of «acoustic identification» was applied (according to the made catalog of «signature whistles»). «Signature whistles» are defined as tonal signals having a frequency contour, unique for each animal, and dominating in its repertoire. In such aspect «signature whistle» can be considered as a peculiar «acoustic marker» of this individual. In the analysis of all volume of the registered whistles of dolphins (about 30 thousands of signals) 206 dominating types (i.e. «signature whistles») have been defined. On the basis of comparison of visual and acoustic data the structure of groups, making the studied population, has been described; the seasonal picture of visit of the water area by various groups has been presented as well as «transit» and «resident» groups have been allocated.

Underwater recordings of the whistles of bottlenose dolphins in Fremantle Inner Harbour, Western Australia

Dolphins use frequency-modulated whistles for a variety of social functions. Whistles vary in their characteristics according to context, such as activity state, group size, group composition, geographic location, and ambient noise levels. Therefore, comparison of whistle characteristics can be used to address numerous research questions regarding dolphin populations and behaviour. However, logistical and economic constraints on dolphin research have resulted in data collection biases, inconsistent analytical approaches, and knowledge gaps. This Data Descriptor presents an acoustic dataset of bottlenose dolphin (Tursiops aduncus) whistles recorded in the Fremantle Inner Harbour, Western Australia. Data were collected using an autonomous recorder and analysed using a range of acoustic measurements. Acoustic data review identified 336 whistles, which were subsequently measured for six key characteristics using Raven Pro software. Of these, 164 ‘high-quality’ whistles were manually measured to provide an additional five acoustic characteristics. Digital files of individual whistles and corresponding measurements make this dataset available to researchers to address future questions regarding variations within and between dolphin communities.

Regional differences in the whistles of Australasian humpback dolphins (genus Sousa)

Characteristics of whistles may be used to study differentiation in dolphins to complement morphological and genetic studies. The whistles of four populations of Chinese humpback dolphins (Sousa chinensis chinensis (Osbeck, 1765)), one population of Taiwanese humpback dolphins (Sousa chinensis taiwanensis Wang, Yang, and Hung, 2015), and one population of Australian humpback dolphins (Sousa sahulensis Jefferson and Rosenbaum, 2014) were compared to determine if differences in whistles support current views of population structure and regional and species differentiation in the genus Sousa Gray, 1866. Acoustic features were extracted from whistles captured by broadband recording systems. Permutational MANOVAs were conducted to test for differences between populations, regions, and species. Random forest trees were also used to classify similar whistles. A significant amount of variation in acoustic features was explained by population (pseudo F[5,2742] = 191.66, p &lt; 0.001), regional (pseudo F[3,2741] = 280.62, p &lt; 0.001), and species (pseudo F[1,999] = 3.7, p &lt; 0.05) differences in humpback dolphin whistles. Random forest trees correctly classified whistles into populations from 40% to 67%, regions from 51% to 80%, and species from 74% to 80%. Differences in whistles were consistent with the current ideas of population-, regional-, and species-level differences within the genus Sousa, based on morphological and genetic data, as well as geographic distance and barriers to movement.

Acoustic response of Indo-Pacific humpback dolphins to the variability of marine soundscape

Marine mammals can adjust their vocal behaviors when they encounter anthropogenic noise. The acoustic divergence among different populations has also been considered as the effect of ambient noise. The recent studies discover that the marine soundscape is highly dynamic; however, it remains unclear how marine mammals alter their vocal behaviors under various acoustic environments. In this study, autonomous sound recorders were deployed in western Taiwan waters between 2012 and 2015. Soundscape scenes were unsupervised classified according to acoustic features measured in each 5 min interval. Non-negative matrix factorization was used to separate different scenes and to inverse the temporal occurrence of each soundscape scene. Echolocation clicks and whistles of Indo-Pacific humpback dolphins, which represent the only marine mammal species occurred in the study area, were automatically detected and analyzed. The preliminary result indicates the soundscape scenes dominated by biological sounds are correlated with the acoustic detection rate of humpback dolphins. Besides, the dolphin whistles are much complex when the prey associated scene is prominent in the local soundscape. In the future, the soundscape information may be used to predict the occurrence and habitat use of marine mammals.

Apparent source levels and active communication space of whistles of free-ranging Indo-Pacific humpback dolphins (Sousa chinensis) in the Pearl River Estuary and Beibu Gulf, China.

Background. Knowledge of species-specific vocalization characteristics and their associated active communication space, the effective range over which a communication signal can be detected by a conspecific, is critical for understanding the impacts of underwater acoustic pollution, as well as other threats.Methods. We used a two-dimensional cross-shaped hydrophone array system to record the whistles of free-ranging Indo-Pacific humpback dolphins (Sousa chinensis) in shallow-water environments of the Pearl River Estuary (PRE) and Beibu Gulf (BG), China. Using hyperbolic position fixing, which exploits time differences of arrival of a signal between pairs of hydrophone receivers, we obtained source location estimates for whistles with good signal-to-noise ratio (SNR ≥10 dB) and not polluted by other sounds and back-calculated their apparent source levels (ASL). Combining with the masking levels (including simultaneous noise levels, masking tonal threshold, and the Sousa auditory threshold) and the custom made site-specific sound propagation models, we further estimated their active communication space (ACS).Results. Humpback dolphins produced whistles with average root-mean-square ASL of 138.5 ± 6.8 (mean ± standard deviation) and 137.2 ± 7.0 dB re 1 µPa in PRE (N = 33) and BG (N = 209), respectively. We found statistically significant differences in ASLs among different whistle contour types. The mean and maximum ACS of whistles were estimated to be 14.7 ± 2.6 (median ± quartile deviation) and 17.1± 3.5 m in PRE, and 34.2 ± 9.5 and 43.5 ± 12.2 m in BG. Using just the auditory threshold as the masking level produced the mean and maximum ACSat of 24.3 ± 4.8 and 35.7 ± 4.6 m for PRE, and 60.7 ± 18.1 and 74.3 ± 25.3 m for BG. The small ACSs were due to the high ambient noise level. Significant differences in ACSs were also observed among different whistle contour types.Discussion. Besides shedding some light for evaluating appropriate noise exposure levels and information for the regulation of underwater acoustic pollution, these baseline data can also be used for aiding the passive acoustic monitoring of dolphin populations, defining the boundaries of separate groups in a more biologically meaningful way during field surveys, and guiding the appropriate approach distance for local dolphin-watching boats and research boat during focal group following.

Whistle Characteristics of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) in the Fremantle Inner Harbour, Western Australia

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.

Whistle source levels of free-ranging bottlenose dolphins and Atlantic spotted dolphins in the Gulf of Mexico

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 1μPa at 1 m with a range of 114-163 dB re 1μPa at 1 m. The median spotted dolphin source level was 138 dB re 1μPa at 1 m with a range of 115-163 dB re 1μPa at 1 m. 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.

Characteristics of whistles from rough-toothed dolphins (Steno bredanensis) in Rio de Janeiro coast, southeastern Brazil

There is no information about the whistles of rough-toothed dolphins in the South Atlantic Ocean. This study characterizes the whistle structure of free-ranging rough-toothed dolphins recorded on the Rio de Janeiro coast, southeastern Brazil, and compares it to that of the same species in other regions. A total of 340 whistles were analyzed. Constant (N = 115; 33.8%) and ascending (N = 99; 29.1%) whistles were the most common contours. The whistles recorded had their fundamental frequencies between 2.24 and 13.94 kHz. Whistles without inflection points were frequently emitted (N = 255; 75%). Some signals presented breaks or steps in their contour (N = 97; 28.5%). Whistle duration was short (347 ± 236 ms and 89.7% of the whistles lasted <600 ms). Seventy-eight whistle contour types were found in the total of whistles analyzed, and 27 (7.9%) of these occurred only once. Most of the whistle types were unique to a particular recording session (N = 43). The signals emitted by the rough-toothed dolphins in southeastern Brazil were characterized by low frequency modulation, short duration, low number of inflection points, and breaks. Differences in the mean values of the whistle parameters were found between this and other studies that recorded Steno bredanensis, but as in other localities, whistles above 14 kHz are rare.

Estimated communication range and energetic cost of bottlenose dolphin whistles in a tropical habitat

Bottlenose dolphins (Tursiops sp.) depend on frequency-modulated whistles for many aspects of their social behavior, including group cohesion and recognition of familiar individuals. Vocalization amplitude and frequency influences communication range and may be shaped by many ecological and physiological factors including energetic costs. Here, a calibrated GPS-synchronized hydrophone array was used to record the whistles of bottlenose dolphins in a tropical shallow-water environment with high ambient noise levels. Acoustic localization techniques were used to estimate the source levels and energy content of individual whistles. Bottlenose dolphins produced whistles with mean source levels of 146.7 ± 6.2 dB re. 1 μPa(RMS). These were lower than source levels estimated for a population inhabiting the quieter Moray Firth, indicating that dolphins do not necessarily compensate for the high noise levels found in noisy tropical habitats by increasing their source level. Combined with measured transmission loss and noise levels, these source levels provided estimated median communication ranges of 750 m and maximum communication ranges up to 5740 m. Whistles contained less than 17 mJ of acoustic energy, showing that the energetic cost of whistling is small compared to the high metabolic rate of these aquatic mammals, and unlikely to limit the vocal activity of toothed whales.

Geographic variations in the whistles of bottlenose dolphins (Tursiops aduncus) along the east and west coasts of Australia

Macrogeographic variations in the structure and repertoire of whistles from four geographically separated bottlenose dolphin (Tursiops aduncus) populations from the east and west coasts of Australia were investigated. Microgeographic variations were examined from two adjacent social groups from the same east coast population. Whistles were divided into five different tonal classes; sine, rise, down-sweep, flat and concave. The acoustic parameters of whistles; start, end, low, high and carrier frequencies and the number of inflection points and harmonics were measured and compared. These features were used to identify and define distinct whistle types. Differences in acoustic parameters of whistles between populations varied with the tonal class and the acoustic parameter being tested and were likely to be driven by localized environmental conditions. There were few differences in the acoustic parameters of whistles between social groups which was likely a result of vocal learning and mimicry from intermixing of individuals. There were small percentages of distinct whistle types that were shared between the both intermixing social groups and geographically separated populations, however, the majority of the whistle repertoires were unique. The development of the unique whistle repertoires may be primarily driven by the complex social organization of the bottlenose dolphin.

Detecting and identifying cetaceans species from their acoustic emissions.

In the past decade, the use of autonomous remote passive acoustic recorders to detect the presence of cetaceans has grown enormously throughout the world. Since these devices digitize acoustic signals at sampling rates in the tens of kHz, a single device can quickly accumulate many Gbytes of data in a short time. Therefore, automatic detection and recognition algorithms must be developed to handle the large amount of data. There is no general signal method processing method that can be applied to all species of cetacean. The algorithm by the name of ROCCA (real-time odontocete call classification algorithm) developed by Dr. Julie Oswald is probably the most general one that has been applied to the whistles of dolphins. The program, extensible bio acoustics tool (XBAT) developed by Harold Figueroa, is probably the most general tool for use with baleen whales. However, investigators also tend to develop their own algorithms to suit their requirements. The problems and difficulties in developing automatic detection and recognition algorithms will be the focus of this presentation. General principles associated with the geography, biology, and the characteristics of sound emissions in relation to the development of algorithms will be discussed along with examples of different approaches.

A Comparison of Bottlenose Dolphin Whistles in the Atlantic Ocean: Factors Promoting Whistle Variation

Whistles are narrowband, frequency-modulated sounds produced by many cetaceans. Whistles are extensively studied in delphinids, where several factors have been proposed to explain between- and within-species variation. We examined factors associated with geographic variation in whistles of common bottlenose dolphins (Tursiops truncatus) by assessing the role of ambient noise, noise from boats, and sympatry with other dolphin species, and reviewing and comparing whistle structure across populations in the western and eastern Atlantic Ocean. Whistles of adjacent populations differed, particularly in frequency parameters. A combination of factors may contribute to microgeographic whistle variation, including differences in ambient noise levels (dolphins produced relatively higher frequency whistles in the noisiest habitat), and differences in number of boats present (when multiple boats were present, dolphins whistled with greater frequency modulation and whistles were higher in maximum frequency and longer than when a single boat was present). Whistles produced by adjacent populations were relatively similar in structure. However, for clearly separated populations, the distance between them did not relate directly to whistle structure. We propose that plasticity in bottlenose dolphin whistles facilitates adaptation to local and changing conditions of their habitat, thus promoting variation between populations at different geographic scales.

Unsupervised clustering of whistle‐sounds of bottlenose dolphins (Tursiops truncatus)

An unsupervised symbolic clustering algorithm for whistles of bottlenose dolphins (Tursiops truncatus) was tuned on an artificial data set containing 12 ideal synthetic signature whistles. Afterwards approximately 25,000 representations of natural whistles were clustered with the tuned algorithm. Recordings were made from a group of twelve adult semi‐free living animals in Eilat (Israel). Obtained clusters were evaluated with the help of their individual compression rates. The clustering algorithm perfectly converged on all twelve artificial whistle types. Also, automatic whistle extraction produced good representations of both artificial and natural whistles, but clustering of natural whistles provided low support for the signature whistle hypothesis: The six most frequent induced whistle types could be interpreted as slight variations of only two signature whistles. Also, a great variety of different but rare types in automatically generated clusters could be observed. Results suggest that certain aspects of the group behavior are manifest in the frequency whistle types occur.

Differences in whistles of bottlenose dolphins between two populations in southeastern Australia

The acoustic repertoires of two populations of Indo-Pacific bottlenose dolphins, Tursiops aduncus, have been studied in comparison with surface behaviors in southeast Australia. These populations are largely genetically differentiated and geographically isolated, one being in Port Stephens and the other in Jervis Bay about 300 km to the south. Ten variables were measured from the fundamental frequency of 200 whistle contours from each population, recorded in various behavioral contexts. Principal component analysis revealed significant differences between the populations. The Port Stephens dolphin population have less complex whistles of a higher frequency than those in Jervis Bay. Although significant differences were observed in phonation rates between behaviors at either site, there was no interaction between site and behavior. The genetic difference and degree of isolation of the populations suggest that cultural drift may play a part in the differences in whistles between sites. Ambient noise measured during observations showed significant differences between sites, but the measurements did not fully sample the range of ambient noise and differences are small compared to the expected temporal variation.