Vocal copying of individually distinctive signature whistles in bottlenose dolphins

Sex differences in the impact of social relationships on individual vocal signatures in grey mouse lemurs (Microcebus murinus)

Vocalizations coordinate social interactions between conspecifics by conveying information concerning the individual or group identity of the sender. Social accommodation is a form of vocal learning where social affinity is signalled by converging or diverging vocalizations with those of conspecifics. To investigate whether social accommodation is linked to the social lifestyle of the sender, we investigated sex-specific differences in social accommodation in a dispersed living primate, the grey mouse lemur (Microcebus murinus), where females form stable sleeping groups whereas males live solitarily. We used 482 trill calls of 36 individuals from our captive breeding colony to compare acoustic dissimilarity between individuals with genetic relatedness, social contact time and body weight. Our results showed that female trills become more similar the more time females spend with each other, independent of genetic relationship, suggesting vocal convergence. In contrast, male trills were affected more by genetic than social factors. However, focusing only on socialized males, increasing time as cage partners caused greater divergence in males' trills. Thus, grey mouse lemurs show the capacity for social accommodation, with females converging their trills to signal social closeness to sleeping group partners, whereas males do not adapt or diverge their trills to signal individual distinctiveness. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'.

African elephants address one another with individually specific name-like calls

Personal names are a universal feature of human language, yet few analogues exist in other species. While dolphins and parrots address conspecifics by imitating the calls of the addressee, human names are not imitations of the sounds typically made by the named individual. Labelling objects or individuals without relying on imitation of the sounds made by the referent radically expands the expressive power of language. Thus, if non-imitative name analogues were found in other species, this could have important implications for our understanding of language evolution. Here we present evidence that wild African elephants address one another with individually specific calls, probably without relying on imitation of the receiver. We used machine learning to demonstrate that the receiver of a call could be predicted from the call's acoustic structure, regardless of how similar the call was to the receiver's vocalizations. Moreover, elephants differentially responded to playbacks of calls originally addressed to them relative to calls addressed to a different individual. Our findings offer evidence for individual addressing of conspecifics in elephants. They further suggest that, unlike other non-human animals, elephants probably do not rely on imitation of the receiver's calls to address one another.

Vocal convergence and social proximity shape the calls of the most basal Passeriformes, New Zealand Wrens

Despite extensive research on avian vocal learning, we still lack a general understanding of how and when this ability evolved in birds. As the closest living relatives of the earliest Passeriformes, the New Zealand wrens (Acanthisitti) hold a key phylogenetic position for furthering our understanding of the evolution of vocal learning because they share a common ancestor with two vocal learners: oscines and parrots. However, the vocal learning abilities of New Zealand wrens remain unexplored. Here, we test for the presence of prerequisite behaviors for vocal learning in one of the two extant species of New Zealand wrens, the rifleman (Acanthisitta chloris). We detect the presence of unique individual vocal signatures and show how these signatures are shaped by social proximity, as demonstrated by group vocal signatures and strong acoustic similarities among distantly related individuals in close social proximity. Further, we reveal that rifleman calls share similar phenotypic variance ratios to those previously reported in the learned vocalizations of the zebra finch, Taeniopygia guttata. Together these findings provide strong evidence that riflemen vocally converge, and though the mechanism still remains to be determined, they may also suggest that this vocal convergence is the result of rudimentary vocal learning abilities.

First acoustic evidence of signature whistle production by spinner dolphins (Stenella longirostris)

A dolphin's signature whistle (SW) is a distinctive acoustic signal, issued in a bout pattern of unique frequency modulation contours; it allows individuals belonging to a given group to recognize each other and, consequently, to maintain contact and cohesion. The current study is the first scientific evidence that spinner dolphins (Stenella longirostris) produce SWs. Acoustic data were recorded at a shallow rest bay called "Biboca", in Fernando de Noronha Archipelago, Brazil. In total, 1902 whistles were analyzed; 40% (753/1,902) of them were classified as stereotyped whistles (STW). Based on the SIGID method, 63% (472/753) of all STWs were identified as SWs; subsequently, they were categorized into one of 18 SW types. SWs accounted for 25% (472/1,902) of the acoustic repertoire. External observers have shown near perfect agreement to classify whistles into the adopted SW categorization. Most acoustic and temporal variables measured for SWs showed mean values similar to those recorded in other studies with spinner dolphins, whose authors did not differentiate SWs from non-SWs. Principal component analysis has explained 78% of total SW variance, and it emphasized the relevance of shape/contour and frequency variables to SW variance. This scientific discovery helps improving bioacoustics knowledge about the investigated species. Future studies to be conducted in Fernando de Noronha Archipelago should focus on continuous investigations about SW development and use by S. longirostris, expanding individuals' identifications (Photo ID and SW Noronha Catalog), assessing long-term whistle stability and emission rates, and making mother-offspring comparisons with sex-based differences.

Bottlenose dolphin mothers modify signature whistles in the presence of their own calves

Human caregivers interacting with children typically modify their speech in ways that promote attention, bonding, and language acquisition. Although this "motherese," or child-directed communication (CDC), occurs in a variety of human cultures, evidence among nonhuman species is very rare. We looked for its occurrence in a nonhuman mammalian species with long-term mother-offspring bonds that is capable of vocal production learning, the bottlenose dolphin (Tursiops truncatus). Dolphin signature whistles provide a unique opportunity to test for CDC in nonhuman animals, because we are able to quantify changes in the same vocalizations produced in the presence or absence of calves. We analyzed recordings made during brief catch-and-release events of wild bottlenose dolphins in waters near Sarasota Bay, Florida, United States, and found that females produced signature whistles with significantly higher maximum frequencies and wider frequency ranges when they were recorded with their own dependent calves vs. not with them. These differences align with the higher fundamental frequencies and wider pitch ranges seen in human CDC. Our results provide evidence in a nonhuman mammal for changes in the same vocalizations when produced in the presence vs. absence of offspring, and thus strongly support convergent evolution of motherese, or CDC, in bottlenose dolphins. CDC may function to enhance attention, bonding, and vocal learning in dolphin calves, as it does in human children. Our data add to the growing body of evidence that dolphins provide a powerful animal model for studying the evolution of vocal learning and language.

Communication as the Origin of Consciousness

Since the middle of the 20th century, more and more data have appeared on the limited role of consciousness in determining human behavior. In this opinion paper, we hypothesize that the basis of consciousness is precisely the communicative function, and discuss relations of consciousness to other cognitive processes such sensory detection, decision-making and emotions. Within the framework of the hypothesis, consciousness is considered as a highly specialized function of the brain, which ensures encoding of personal information as communication messages. On a subjective level, mental representation just means the state of information to be shared in a human group. Accordingly, consciousness affects only those components of human behavior that are associated with the transmission of messages. Sensory detection, decision-making, emotions and other processes are only projected into consciousness during the encoding of information of them. The communication hypothesis assumes that consciousness is an adaptation that increases the efficiency of a collective way of life, and the emergence of consciousness is inextricably linked with the development of language in human culture. In the future, our view of consciousness provides an opportunity for an objective analysis of subjective phenomena by means of a directed study of the formation of messages both at the level of brain processes and at the level of interactions between individuals.

Understanding across the senses: cross-modal studies of cognition in cetaceans

Cross-modal approaches to the study of sensory perception, social recognition, cognition, and mental representation have proved fruitful in humans as well as in a variety of other species including toothed whales in revealing equivalencies that suggest that different sensory stimuli associated with objects or individuals may effectively evoke mental representations that are, respectively, object based or individual based. Building on established findings of structural equivalence in the form of spontaneous recognition of complex shapes across the modalities of echolocation and vision and behavior favoring identity echoic-visual cross-modal relationships over associative echoic-visual cross-modal relationships, examinations of transitive inference equivalencies from initially learned associations of visual and acoustic stimuli, and recent work examining spontaneous cross-modal social recognition of individual identity across acoustic and gustatory chemical modalities (i.e., the equivalence relationships among an individual's characteristics), we examine the history, utility and implications for cross-modal research in cetacean cognition. Drawing from research findings on bottlenose dolphins and beluga whales as well as other species we suggest future directions for cetacean cross-modal research to further illuminate understanding how structural and individual sensory equivalencies lead to object-centered and individual-centered mental representations, as well as to explore the potential for practical applications related to cetacean conservation.

Observing the nature of relationships in male bottlenose dolphins

As long-term studies reveal, bottlenose dolphin communities comprise a complex network of individual relationships. Individuals form strong bonds (e.g., mother-calf or male partnerships), transient relationships, and also compete against each other for resources. Evidence of bonded partnerships is typically revealed by the years-long study of associations with repeated sightings. However, quickly determining which individuals have close affiliations would benefit both field researchers working to describe individual behavior as they engage in cognitive activities such as cooperative foraging as well as caregivers in zoos who must decide which individuals should be housed together. Observations in aquariums are well-suited for collecting long-term, detailed information on how pairs interact because subjects can always be found and their behavior both above and below the water can be seen well. These are conditions that are rare for most (but not all) ocean-based studies. We used multiple measures to detect affiliated behavior across several dimensions of pairwise affiliation. Specifically, we used association indices to measure the frequency of affiliative behavior, the symmetry of the partnership, the tenor of interactions, and the stability of which partners were strongly affiliated from year to year. Synchronous behavior and reciprocity in proximity-seeking are two examples of potential markers of an affiliative relationship where individual choices–to join, to move together, and to leave–are visible to observers. We found that the combined measures were effective at identifying one pair that maintained a strong, stable relationship across years, one individual that formed a moderately strong trio relationship with both members of the most-affiliated pair, and one individual who was more variable in his relationships. These social markers provide a means of rapidly identifying bonded males in both aquarium and ocean settings, particularly when long-term knowledge of individual histories is not available.

Cross-modal perception of identity by sound and taste in bottlenose dolphins

While studies have demonstrated concept formation in animals, only humans are known to label concepts to use them in mental simulations or predictions. To investigate whether other animals use labels comparably, we studied cross-modal, individual recognition in bottlenose dolphins (Tursiops truncatus) that use signature whistles as labels for conspecifics in their own communication. First, we tested whether dolphins could use gustatory stimuli and found that they could distinguish between water and urine samples, as well as between urine from familiar and unfamiliar individuals. Then, we paired playbacks of signature whistles of known animals with urine samples from either the same dolphin or a different, familiar animal. Dolphins investigated the presentation area longer when the acoustic and gustatory sample matched than when they mismatched. This demonstrates that dolphins recognize other individuals by gustation alone and can integrate information from acoustic and taste inputs indicating a modality independent, labeled concept for known conspecifics.

Vocal production learning in mammals revisited

Vocal production learning, the ability to modify the structure of vocalizations as a result of hearing those of others, has been studied extensively in birds but less attention has been given to its occurrence in mammals. We summarize the available evidence for vocal learning in mammals from the last 25 years, updating earlier reviews on the subject. The clearest evidence comes from cetaceans, pinnipeds, elephants and bats where species have been found to copy artificial or human language sounds, or match acoustic models of different sound types. Vocal convergence, in which parameter adjustments within one sound type result in similarities between individuals, occurs in a wider range of mammalian orders with additional evidence from primates, mole-rats, goats and mice. Currently, the underlying mechanisms for convergence are unclear with vocal production learning but also usage learning or matching physiological states being possible explanations. For experimental studies, we highlight the importance of quantitative comparisons of seemingly learned sounds with vocal repertoires before learning started or with species repertoires to confirm novelty. Further studies on the mammalian orders presented here as well as others are needed to explore learning skills and limitations in greater detail. This article is part of the theme issue 'Vocal learning in animals and humans'.

The multi-dimensional nature of vocal learning

How learning affects vocalizations is a key question in the study of animal communication and human language. Parallel efforts in birds and humans have taught us much about how vocal learning works on a behavioural and neurobiological level. Subsequent efforts have revealed a variety of cases among mammals in which experience also has a major influence on vocal repertoires. Janik and Slater (Anim. Behav.60, 1-11. (doi:10.1006/anbe.2000.1410)) introduced the distinction between vocal usage and production learning, providing a general framework to categorize how different types of learning influence vocalizations. This idea was built on by Petkov and Jarvis (Front. Evol. Neurosci.4, 12. (doi:10.3389/fnevo.2012.00012)) to emphasize a more continuous distribution between limited and more complex vocal production learners. Yet, with more studies providing empirical data, the limits of the initial frameworks become apparent. We build on these frameworks to refine the categorization of vocal learning in light of advances made since their publication and widespread agreement that vocal learning is not a binary trait. We propose a novel classification system, based on the definitions by Janik and Slater, that deconstructs vocal learning into key dimensions to aid in understanding the mechanisms involved in this complex behaviour. We consider how vocalizations can change without learning, and a usage learning framework that considers context specificity and timing. We identify dimensions of vocal production learning, including the copying of auditory models (convergence/divergence on model sounds, accuracy of copying), the degree of change (type and breadth of learning) and timing (when learning takes place, the length of time it takes and how long it is retained). We consider grey areas of classification and current mechanistic understanding of these behaviours. Our framework identifies research needs and will help to inform neurobiological and evolutionary studies endeavouring to uncover the multi-dimensional nature of vocal learning. This article is part of the theme issue 'Vocal learning in animals and humans'.

Singing is not associated with social complexity across species

Based on their social bonding hypothesis, Savage et al. predict a relation between "musical" behaviors and social complexity across species. However, our qualitative comparative review suggests that, although learned contact calls are positively associated with complex social dynamics across species, songs are not. Yet, in contrast to songs, and arguably consistent with their functions, contact calls are not particularly music-like.

Vocal correlates of arousal in bottlenose dolphins (Tursiops spp.) in human care

Human-controlled regimes can entrain behavioural responses and may impact animal welfare. Therefore, understanding the influence of schedules on animal behaviour can be a valuable tool to improve welfare, however information on behaviour overnight and in the absence of husbandry staff remains rare. Bottlenose dolphins (Tursiops spp.) are highly social marine mammals and the most common cetacean found in captivity. They communicate using frequency modulated signature whistles, a whistle type that is individually distinctive and used as a contact call. We investigated the vocalisations of ten dolphins housed in three social groups at uShaka Sea World dolphinarium to determine how patterns in acoustic behaviour link to dolphinarium routines. Investigation focused on overnight behaviour, housing decisions, weekly patterns, and transitional periods between the presence and absence of husbandry staff. Recordings were made from 17h00 - 07h00 over 24 nights, spanning May to August 2018. Whistle (including signature whistle) presence and production rate decreased soon after husbandry staff left the facility, was low over night, and increased upon staff arrival. Results indicated elevated arousal states particularly associated with the morning feeding regime. Housing in the pool configuration that allowed observation of staff activities from all social groups was characterised by an increase in whistle presence and rates. Heightened arousal associated with staff presence was reflected in the structural characteristics of signature whistles, particularly maximum frequency, frequency range and number of whistle loops. We identified individual differences in both production rate and the structural modification of signature whistles under different contexts. Overall, these results revealed a link between scheduled activity and associated behavioural responses, which can be used as a baseline for future welfare monitoring where changes from normal behaviour may reflect shifts in welfare state.

Song type and song type matching are important for joint territorial defense in a duetting songbird

Birds have a diverse acoustic communication system, with species-specific repertoires facilitating more complex behaviors in terms of both within- and between-pair communications. Certain song types are produced for specific functions, such as aggressive encounters. In addition, song matching behaviors, whereby neighboring individuals match song types, can be used in aggressive interactions as a sophisticated acoustic behavior. In this study, we examined the functions of song types, in a duet context, of male yellow-breasted boubous (Laniarius atroflavus), an Afromontane bush-shrike with a vocal sexual dimorphism. We aimed at assessing whether, structurally, certain song types elicited a heightened reaction than others and also whether song matching affected response behavior. A dual speaker playback procedure was performed for 18 pairs of boubous, each pair being exposed to duets with three different male song types. We found differences in response toward the different duet types but these differences resulted from the amount at which males matched different song types. Pairs responded stronger when a focal male matched the playback type, and matching was significantly more often found in cases where the rarest type of male song was used. We found no sex differences in terms of response strength to playback type. Our results indicate a two-level way of coding aggression toward intruding pairs. The yellow-breasted boubous utilize their repertoires, linking matching with structure in order to show aggression in terms of territory defense and sexual conflict. This study also confirms joint territorial defense as a main function of duets in this species.

Evidence of stereotyped contact call use in narwhal (Monodon monoceros) mother-calf communication

Narwhals (Monodon monoceros) are gregarious toothed whales that strictly reside in the high Arctic. They produce a broad range of signal types; however, studies of narwhal vocalizations have been mostly descriptive of the sounds available in the species’ overall repertoire. Little is known regarding the functions of highly stereotyped mixed calls (i.e., biphonations with both sound elements produced simultaneously), although preliminary evidence has suggested that such vocalizations are individually distinctive and function as contact calls. Here we provide evidence that supports this notion in narwhal mother-calf communication. A female narwhal was tagged as part of larger studies on the life history and acoustic behavior of narwhals. At the time of tagging, it became apparent that the female had a calf, which remained close by during the tagging event. We found that the narwhal mother produced a distinct, highly stereotyped mixed call when separated from her calf and immediately after release from capture, which we interpret as preliminary evidence for contact call use between the mother and her calf. The mother’s mixed call production occurred continually over the 4.2 day recording period in addition to a second prominent but different stereotyped mixed call which we believe belonged to the narwhal calf. Thus, narwhal mothers produce highly stereotyped contact calls when separated from their calves, and it appears that narwhal calves similarly produce distinct, stereotyped mixed calls which we hypothesize also contribute to maintaining mother-calf contact. We compared this behavior to the acoustic behavior of two other adult females without calves, but also each with a unique, stereotyped call type. While we provide additional support for individual distinctiveness across narwhal contact calls, more research is necessary to determine whether these calls are vocal signatures which broadcast identity.

Human larynx motor cortices coordinate respiration for vocal-motor control

Vocal flexibility is a hallmark of the human species, most particularly the capacity to speak and sing. This ability is supported in part by the evolution of a direct neural pathway linking the motor cortex to the brainstem nucleus that controls the larynx the primary sound source for communication. Early brain imaging studies demonstrated that larynx motor cortex at the dorsal end of the orofacial division of motor cortex (dLMC) integrated laryngeal and respiratory control, thereby coordinating two major muscular systems that are necessary for vocalization. Neurosurgical studies have since demonstrated the existence of a second larynx motor area at the ventral extent of the orofacial motor division (vLMC) of motor cortex. The vLMC has been presumed to be less relevant to speech motor control, but its functional role remains unknown. We employed a novel ultra-high field (7T) magnetic resonance imaging paradigm that combined singing and whistling simple melodies to localise the larynx motor cortices and test their involvement in respiratory motor control. Surprisingly, whistling activated both 'larynx areas' more strongly than singing despite the reduced involvement of the larynx during whistling. We provide further evidence for the existence of two larynx motor areas in the human brain, and the first evidence that laryngeal-respiratory integration is a shared property of both larynx motor areas. We outline explicit predictions about the descending motor pathways that give these cortical areas access to both the laryngeal and respiratory systems and discuss the implications for the evolution of speech.

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

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.

No evidence for individual recognition in threespine or ninespine sticklebacks (Gasterosteus aculeatus or Pungitius pungitius)

Recognition plays an important role in the formation and organization of animal groups. Many animals are capable of class-level recognition, discriminating, for example, on the basis of species, kinship or familiarity. Individual recognition requires that animals recognize distinct cues, and learn to associate these with the specific individual from which they are derived. In this study, we asked whether sticklebacks (Gasterosteus aculeatus and Pungitius pungitius) were capable of learning to recognize individual conspecifics. We have used these fish as model organisms for studying selective social learning, and demonstrating a capacity for individual recognition in these species would provide an exciting opportunity for studying how biases for copying specific individuals shape the dynamics of information transmission. To test for individual recognition, we trained subjects to associate green illumination with the provision of a food reward close to one of two conspecifics, and, for comparison, one of two physical landmarks. Both species were capable of recognizing the rewarded landmark, but neither showed a preference for associating with the rewarded conspecific. Our study provides no evidence for individual recognition in either species. We speculate that the fission-fusion structure of their social groups may not favour a capacity for individual recognition.

Five members of a mixed-sex group of bottlenose dolphins share a stereotyped whistle contour in addition to maintaining their individually distinctive signature whistles

Most commonly, animal communication systems are driven by shared call repertoires, with some individual distinctiveness encoded as a byproduct of voice cues. We provide evidence that bottlenose dolphins produce both individually distinctive whistles, and a shared whistle type. A stereotyped whistle contour (termed the group whistle) is shared by five bottlenose dolphins that have lived, worked, and traveled together for at least 21 years. These five dolphins are members of a group of eight dolphins that work as a specialized team for the Navy Marine Mammal Program. Each dolphin is routinely recorded during periods when an individual is isolated from the others in above ground pools as part of their routine training. Each of the eight dolphins has an individually distinctive signature whistle. In addition, at least five of these dolphins share a distinct non-signature whistle type. This shared whistle contour was produced an average of 22.4% +/- 9.0% of the time during periods in which individuals were isolated. During these isolations the signature whistle was produced an average of 42.9% +/- 11.9% of the time. This is consistent with decades of signature whistle research. A group of 10 naïve observers rated the similarity of the different whistle contours. The observers rated the group whistle contour produced by all five dolphins as highly similar (P < 0.01). Their ratings further showed that the signature whistles of the five dolphins were very different (P < 0.01). These findings were further supported by discriminant function analyses. That said, the shared whistle contours still exhibited individual differences which may allow conspecifics to identify the producer even when a whistle contour is shared among multiple dolphins. This is the first in-depth analysis of a non-signature whistle type shared among multiple conspecifics.

Whistle variation in Mediterranean common bottlenose dolphin: The role of geographical, anthropogenic, social, and behavioral factors

The studies on the variation of acoustic communication in different species have provided insight that genetics, geographic isolation, and adaptation to ecological and social conditions play important roles in the variability of acoustic signals. The dolphin whistles are communication signals that can vary significantly among and within populations. Although it is known that they are influenced by different environmental and social variables, the factors influencing the variation between populations have received scant attention. In the present study, we investigated the factors associated with the acoustic variability in the whistles of common bottlenose dolphin (Tursiops truncatus), inhabiting two Mediterranean areas (Sardinia and Croatia). We explored which factors, among (a) geographical isolation of populations, (b) different environments in terms of noise and boat presence, and (c) social factors (including group size, behavior, and presence of calves), were associated with whistle characteristics. We first applied a principal component analysis to reduce the number of collinear whistle frequency and temporal characteristics and then generalized linear mixed models on the first two principal components. The study revealed that both geographic distance/isolation and local environment are associated with whistle variations between localities. The prominent differences in the acoustic environments between the two areas, which contributed to the acoustic variability in the first principal component (PC1), were found. The calf's presence and foraging and social behavior were also found to be associated with dolphin whistle variation. The second principal component (PC2) was associated only with locality and group size, showing that longer and more complex tonal sound may facilitate individual recognition and cohesion in social groups. Thus, both social and behavioral context influenced significantly the structure of whistles, and they should be considered when investigating acoustic variability among distant dolphin populations to avoid confounding factors.

Pulsed call sequences as contact calls in Pacific white-sided dolphins (Lagenorhynchus obliquidens)

Pacific white-sided dolphins are a group-living species and appear to exchange "contact calls" to maintain group cohesion. The aim of this study was to find and characterize their contact calls. Calls were recorded from two females at Osaka Aquarium KAIYUKAN (OAK) and three females at Izu-Mito Sea Paradise (IMSP). Because they often produced pulsed calls consecutively, a "pulsed call sequence" was defined as three or more successive pulsed calls occurring within 325 ms, which was calculated using a bout analysis. The pulsed call sequences increased during separation periods and decreased during reunions and were used for vocal exchange, suggesting that the sequences are contact calls in Pacific white-sided dolphins. Most of the pulsed call sequences were classified into unique types; several stereotyped, repeated patterns were found. One sequence type was found at OAK and the two dolphins shared the type; they exchanged sequences with type matching. On the other hand, three sequence types were found in IMSP and the three dolphins shared all of the types; however, each dolphin preferentially used different types and frequently exchanged with their own favorite types but not with type matching. These results suggest that the sequence type may function as an individual and/or group identity.

Interspecific voice discrimination in dogs

BACKGROUND AND AIMS

Conspecific individual recognition using vocal cues has been shown in a wide range of species but there is no published evidence that dogs are able to recognize their owner based on his/her voice alone (interspecific individual recognition).

METHODS

In our test, dogs had to rely on vocal cues to find their hidden owner in a two-way choice task. From behind an opaque screen, both the owner and a control person uttered neutral speech (reading sentences from a receipt) before the dogs were allowed to make their choice. Correct choices were reinforced by food and by verbal praise.

RESULTS

During the six-choice trials, dogs chose their owner's voice significantly more often than the control person's voice. There was no effect of learning throughout the trials, and dogs did not show side preference.

DISCUSSION

Thus, dogs are able to discriminate interspecific voices, suggesting that they are able to identify their owner based on vocal cues alone. This experimental design allows exploration of the role of individual acoustic parameters (such as fundamental frequency) in voice discrimination.

Poor neuro-motor tuning of the human larynx: a comparison of sung and whistled pitch imitation

Vocal imitation is a hallmark of human communication that underlies the capacity to learn to speak and sing. Even so, poor vocal imitation abilities are surprisingly common in the general population and even expert vocalists cannot match the precision of a musical instrument. Although humans have evolved a greater degree of control over the laryngeal muscles that govern voice production, this ability may be underdeveloped compared with control over the articulatory muscles, such as the tongue and lips, volitional control of which emerged earlier in primate evolution. Human participants imitated simple melodies by either singing (i.e. producing pitch with the larynx) or whistling (i.e. producing pitch with the lips and tongue). Sung notes were systematically biased towards each individual's habitual pitch, which we hypothesize may act to conserve muscular effort. Furthermore, while participants who sung more precisely also whistled more precisely, sung imitations were less precise than whistled imitations. The laryngeal muscles that control voice production are under less precise control than the oral muscles that are involved in whistling. This imprecision may be due to the relatively recent evolution of volitional laryngeal-motor control in humans, which may be tuned just well enough for the coarse modulation of vocal-pitch in speech.

Captive Bottlenose Dolphins Do Discriminate Human-Made Sounds Both Underwater and in the Air

Bottlenose dolphins (Tursiops truncatus) spontaneously emit individual acoustic signals that identify them to group members. We tested whether these cetaceans could learn artificial individual sound cues played underwater and whether they would generalize this learning to airborne sounds. Dolphins are thought to perceive only underwater sounds and their training depends largely on visual signals. We investigated the behavioral responses of seven dolphins in a group to learned human-made individual sound cues, played underwater and in the air. Dolphins recognized their own sound cue after hearing it underwater as they immediately moved toward the source, whereas when it was airborne they gazed more at the source of their own sound cue but did not approach it. We hypothesize that they perhaps detected modifications of the sound induced by air or were confused by the novelty of the situation, but nevertheless recognized they were being “targeted.” They did not respond when hearing another group member’s cue in either situation. This study provides further evidence that dolphins respond to individual-specific sounds and that these marine mammals possess some capacity for processing airborne acoustic signals.

A beluga whale socialized with bottlenose dolphins imitates their whistles

The research on imitation in the animal kingdom has more than a century-long history. A specific kind of imitation, auditory-vocal imitation, is well known in birds, especially among songbirds and parrots, but data for mammals are limited to elephants, marine mammals, and humans. Cetaceans are reported to imitate various signals, including species-specific calls, artificial sounds, and even vocalizations from other species if they share the same habitat. Here we describe the changes in the vocal repertoire of a beluga whale that was housed with a group of bottlenose dolphins. Two months after the beluga's introduction into a new facility, we found that it began to imitate whistles of the dolphins, whereas one type of its own calls seemed to disappear. The case reported here may be considered as an interesting phenomenon of vocal accommodation to new social companions and cross-species socialization in cetaceans.

What's in a voice? Dolphins do not use voice cues for individual recognition

Most mammals can accomplish acoustic recognition of other individuals by means of “voice cues,” whereby characteristics of the vocal tract render vocalizations of an individual uniquely identifiable. However, sound production in dolphins takes place in gas-filled nasal sacs that are affected by pressure changes, potentially resulting in a lack of reliable voice cues. It is well known that bottlenose dolphins learn to produce individually distinctive signature whistles for individual recognition, but it is not known whether they may also use voice cues. To investigate this question, we played back non-signature whistles to wild dolphins during brief capture-release events in Sarasota Bay, Florida. We hypothesized that non-signature whistles, which have varied contours that can be shared among individuals, would be recognizable to dolphins only if they contained voice cues. Following established methodology used in two previous sets of playback experiments, we found that dolphins did not respond differentially to non-signature whistles of close relatives versus known unrelated individuals. In contrast, our previous studies showed that in an identical context, dolphins reacted strongly to hearing the signature whistle or even a synthetic version of the signature whistle of a close relative. Thus, we conclude that dolphins likely do not use voice cues to identify individuals. The low reliability of voice cues and the need for individual recognition were likely strong selective forces in the evolution of vocal learning in dolphins.

Social sounds produced by franciscana dolphins, Pontoporia blainvillei (Cetartiodactyla, Pontoporiidae)

Franciscana dolphin (Pontoporia blainvillei) whistles were documented for the first time during 2003-2013 in Babitonga Bay estuary, South Brazil, together with burst pulses. Recordings were made from small boats under good sea conditions, and recording equipment that allowed analysis of sounds up to 96 kHz. The recordings were made in the presence of 2-31 franciscana dolphins. During 23 h and 53 min, 90 whistles and 51 burst pulse series were recorded. Although Guiana dolphins (Sotalia guianensis) inhabit nearby waters, none were observed in the area during the recordings. The authors recorded ten types of whistles. The initial frequency varied between 1.6 and 94.6 kHz, and the final frequency varied between 0.7 and 94.5 kHz; the authors were not able to determine if dolphin whistles exceeded the 96 kHz recording limit of the authors' equipment, although that is likely, especially because some whistles showed harmonics. Whistle duration varied between 0.008 and 0.361 s. Burst pulses had initial frequencies between 69 and 82.1 kHz (77 ± 3.81). These results showed that P. blainvillei produces whistles and burst pulses, although they seem to be produced infrequently.

Underwater observations of dolphin reactions to a distressed conspecific

This report describes the epimeletic (or "caregiving") behavior produced by members of a group of Atlantic bottlenose dolphins (Tursiops truncatus) and the possible role of the ailing animal's distress call in eliciting such behavior. Epimeletic behavior in cetaceans most typically involves forms of support provided to a distressed, injured, or dying animal (Caldwell & Caldwell, 1966). Analyses of underwater video and corresponding acoustic recordings revealed a distressed dolphin (the DD) that frequently produced what are most likely distress calls, often paired with the emission of long bubble streams. The frequency of her whistle production was positively correlated with the frequency of the supporting behaviors the DD received from other dolphins. These helping behaviors included raft formations, lifts, and stimulating pushes that were predominantly directed toward the upper third of the DD's body, all of which appeared to be directed towards bringing the DD toward the surface so that she could breathe. This is the first documented underwater account of multiple wild bottlenose dolphins providing epimeletic care to a distressed conspecific, and highlights the possible role of distress calls in such scenarios.

Vocal matching: the what, the why and the how

Over the years, vocal matching has progressed beyond being an interesting behavioural phenomenon to one that now has relevance to a wide range of fields. In this review, we use birds and cetaceans to explain what vocal matching is, why animals vocally match and how vocal matching can be identified. We show that while the functional aspects of vocal matching are similar, the contexts in which matching is used can differ between taxa. Whereas vocal matching in songbirds facilitates mate attraction and the immediate defence of resources, in parrots and cetaceans it plays a role in the maintenance of social bonds and the promotion of behavioural synchrony. We propose criteria for defining vocal matching with the aim of stimulating more matching studies across a wider range of taxa, including those using other, non-vocal, communication modalities. Finally, we encourage future studies to explore the importance of vocal learning in the development of vocal matching, and the information it may provide to third parties in the communication network.

Individual, unit and vocal clan level identity cues in sperm whale codas

The 'social complexity hypothesis' suggests that complex social structure is a driver of diversity in animal communication systems. Sperm whales have a hierarchically structured society in which the largest affiliative structures, the vocal clans, are marked on ocean-basin scales by culturally transmitted dialects of acoustic signals known as 'codas'. We examined variation in coda repertoires among both individual whales and social units-the basic element of sperm whale society-using data from nine Caribbean social units across six years. Codas were assigned to individuals using photo-identification and acoustic size measurement, and we calculated similarity between repertoires using both continuous and categorical methods. We identified 21 coda types. Two of those ('1+1+3' and '5R1') made up 65% of the codas recorded, were shared across all units and have dominated repertoires in this population for at least 30 years. Individuals appear to differ in the way they produce '5R1' but not '1+1+3' coda. Units use distinct 4-click coda types which contribute to making unit repertoires distinctive. Our results support the social complexity hypothesis in a marine species as different patterns of variation between coda types suggest divergent functions, perhaps representing selection for identity signals at several levels of social structure.

Individuality embedded in the isolation calls of captive beluga whales (Delphinapterus leucas)

INTRODUCTION

Species with fission-fusion social systems tend to exchange individualized contact calls to maintain group cohesion. Signature whistles by bottlenose dolphins are unique compared to the contact calls of other non-human animals in that they include identity information independent of voice cues. Further, dolphins copy the signatures of conspecifics and use them to label specific individuals. Increasing our knowledge of the contact calls of other cetaceans that have a fluid social structure may thus help us better understand the evolutionary and adaptive significance of all forms of individually distinctive calls. It was recently reported that one type of broadband pulsed sounds (PS1), rather than whistles, may function as individualized contact calls in captive belugas. The objective of this study was to assess the function and individual distinctiveness of PS1 calls in an isolation context. Recordings were made from five captive belugas, including both sexes and various ages.

RESULTS

PS1 was the predominant call type (38 % in total) out of five broader sound categories. One sub-adult and three adults had individually distinctive and stereotyped pulse repetition pattern in PS1; one calf showed no clear stereotyped pulse repetition pattern. While visual inspection of the PS1 power spectra uncovered no apparent individual specificity, statistical analyses revealed that both temporal and spectral parameters had inter-individual differences and that there was greater inter-individual than intra-individual variability. Discriminant function analysis based on five temporal and spectral parameters classified PS1 calls into individuals with an overall correct classification rate of 80.5 %, and the most informative parameter was the average Inter-pulse interval, followed by peak frequency.

CONCLUSION

These results suggest that belugas use individually distinctive contact calls in an isolation context. If belugas encode signature information in PS1 calls, as seen in bottlenose dolphins, the pulse repetition pattern may be the carrier, as it is individually stereotyped and appears to require vocal development. This idea is supported by the finding that the average inter-pulse interval is the most powerful discriminator in discriminant analysis. Playback experiments will elucidate which parameters are perceived as individual characteristics, and whether one of the parameters functions as a signature.

Forebrain circuits underlying the social modulation of vocal communication signals

Across vertebrate species, signalers alter the structure of their communication signals based on the social context. For example, male Bengalese finches produce faster and more stereotyped songs when directing song to females (female-directed [FD] song) than when singing in isolation (undirected [UD] song), and such changes have been found to increase the attractiveness of a male's song. Despite the importance of such social influences, little is known about the mechanisms underlying the social modulation of communication signals. To this end, we analyzed differences in immediate early gene (EGR-1) expression when Bengalese finches produced FD or UD song. Relative to silent birds, EGR-1 expression was elevated in birds producing either FD or UD song throughout vocal control circuitry, including the interface nucleus of the nidopallium (NIf), HVC, the robust nucleus of the arcopallium (RA), Area X, and the lateral magnocellular nucleus of the anterior nidopallium (LMAN). Moreover, EGR-1 expression was higher in HVC, RA, Area X, and LMAN in males producing UD song than in males producing FD song, indicating that social context modulated EGR-1 expression in these areas. However, EGR-1 expression was not significantly different between males producing FD or UD song in NIf, the primary vocal motor input into HVC, suggesting that context-dependent changes could arise de novo in HVC. The pattern of context-dependent differences in EGR-1 expression in the Bengalese finch was highly similar to that in the zebra finch and suggests that social context affects song structure by modulating activity throughout vocal control nuclei.

Come dine with me: food-associated social signalling in wild bottlenose dolphins (Tursiops truncatus)

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.

Cultural evolution of killer whale calls: background, mechanisms and consequences

Cultural evolution is a powerful process shaping behavioural phenotypes of many species including our own. Killer whales are one of the species with relatively well-studied vocal culture. Pods have distinct dialects comprising a mix of unique and shared call types; calves adopt the call repertoire of their matriline through social learning. We review different aspects of killer whale acoustic communication to provide insights into the cultural transmission and gene-culture co-evolution processes that produce the extreme diversity of group and population repertoires. We argue that the cultural evolution of killer whale calls is not a random process driven by steady error accumulation alone: temporal change occurs at different speeds in different components of killer whale repertoires, and constraints in call structure and horizontal transmission often degrade the phylogenetic signal. We discuss the implications from bird song and human linguistic studies, and propose several hypotheses of killer whale dialect evolution.

Further evidence of a context-specific agonistic signal in bottlenose dolphins: the influence of consortships and group size on the pop vocalization

Pops are a low-frequency, pulsed vocalization produced by Indo-Pacific bottlenose dolphins (Tursiopscf.aduncus) in Shark Bay, Western Australia and are often heard when male alliances are consorting or ‘herding’ a female. Previous research indicated that pops produced in this context are an agonistic ‘come-hither’ demand produced by males and directed at female consorts. Here we examine pop occurrence during focal follows on bottlenose dolphin alliances with and without female consorts present. Regression analysis was conducted to determine if pop numbers were higher in the presence of female consorts, and if variables including group size alone and the interaction between presence/absence of a consortship and group size, influenced pop production. While the presence or absence of a consortship significantly affected the number of pops, average group size had no significant effect on pop production. Our research provides further evidence that the pop vocalization plays an important role in consortships.

Evidence for signature whistles in Guiana dolphins (Sotalia guianensis) in Ilhéus, northeastern Brazil

Signature whistles have been widely studied in bottlenose dolphins (Tursiops truncatus). A recent study suggested the occurrence of signature whistles in Guiana dolphins (Sotalia guianensis) but could not identify the whistlers. The objective of this study is to describe the whistle characteristics in the population of S. guianensis from Ilhéus and investigate the occurrence of signature whistles. Dolphins from 55 groups were photographed and sound emissions from 21 groups were recorded. The frequency parameters and duration of the 847 recorded whistles were similar to those recorded in 12 other populations, on an intermediate position of a latitudinal gradient. The visual classification method was applied to the spectrograms of 68 stereotyped potential signature whistles. Five out of 6 human judges agreed on the formation of 13 groups. The presence of the same individuals in different recording occasions of stereotyped whistles suggests that some whistle types are produced by specific individuals. The study is the first to use the photo-identification technique to identify Guiana dolphins emitting whistles and the results reinforce the hypothesis of signature whistles in this species.

Differences in acoustic features of vocalizations produced by killer whales cross-socialized with bottlenose dolphins

Limited previous evidence suggests that killer whales (Orcinus orca) are capable of vocal production learning. However, vocal contextual learning has not been studied, nor the factors promoting learning. Vocalizations were collected from three killer whales with a history of exposure to bottlenose dolphins (Tursiops truncatus) and compared with data from seven killer whales held with conspecifics and nine bottlenose dolphins. The three whales' repertoires were distinguishable by a higher proportion of click trains and whistles. Time-domain features of click trains were intermediate between those of whales held with conspecifics and dolphins. These differences provided evidence for contextual learning. One killer whale spontaneously learned to produce artificial chirps taught to dolphins; acoustic features fell within the range of inter-individual differences among the dolphins. This whale also produced whistles similar to a stereotyped whistle produced by one dolphin. Thus, results provide further support for vocal production learning and show that killer whales are capable of contextual learning. That killer whales produce similar repertoires when associated with another species suggests substantial vocal plasticity and motivation for vocal conformity with social associates.