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These animals range in size from 1. Table 1 shows three size-specific comparisons revealing 2. Members of the porpoise family Phocoenidae, appear to have brains of intermediate size Marino ; Connor et al. Recent phylogenies confirm that the sperm whale is an ancient sister group to other odontocetes Cassens et al.

Thus, the large sperm whale brain was most likely derived independently and will be considered separately. This distinction is also interesting given the remarkable convergence between sperm whales and elephants Weilgart et al. Three brain size comparisons for small odontocetes of approximately the same body size. Sotalia , Dephinus and Tursiops belong to the family Delphinidae. Each of the others belongs to a different family with only 1—2 species in each Adapted from Connor et al.

Brain—body slopes differ between orders and, in some orders, with taxonomic level. Thus, evaluating the encephalization of cetaceans with the overall mammalian slope usually close to 0. A grade difference is implied when regression lines for two groups at a given taxonomic level are found to have similar slopes but differ in their vertical displacement.

Associated Data

The vertical displacement is taken to represent an adaptive shift in relative brain size Martin For example, Manger argues that large brain evolution in odontocetes was driven by selection for increased thermogenesis in cold water, a feat he contends is accomplished by increasing the number of glial cells. Manger considers the encephalization of the bottlenose dolphin Tursiops truncatus to be similar to the much smaller harbour porpoise Phocoena phocoena based on similar EQs calculated from the general slope for mammals note that Marino , calculated lower EQs for Phocoena phocoena.

However, comparison of similar sized delphinids and phocoenids removes the scaling problem and suggests that the delphinids may be more encephalized tables in Connor et al. Selection should, for example, strongly favour a smaller brain in delphinids that live in warm water habitats. The warm water riverine but highly encephalized delphinid, Sotalia shows this not to be a necessary outcome.

Some hypotheses to explain primate brain size differences focused exclusively on costs e. However, relative brain size differences among mammals must be determined partly by differences in available energy. It is worth noting that the metabolic costs of a large brain for dolphins may be even less than indicated by their basal metabolic rate BMR. What really matters, of course, is the proportion of the total energy budget used by the brain. The BMR was established as a standard by which different species could be compared. BMR comparisons will reflect relative brain costs only if BMR correlates closely with the total energy budget.

Evidence suggests, however, that many dolphins do not remain at rest for such extended periods and may continue to travel for nearly the entire day see Connor The Ganges River platanistid, the susu, swims continuously in captivity, a habit Pilleri et al. In primates, brain size differences are sometimes associated with categorical differences in the energy yield of the diet, e.

Pontoporia is an especially interesting case because, unlike the slower swimming river dolphins, they live in the marine habitat and have a scapular morphology indicating that they are stronger, more manoeuvrable swimmers than the small-brained riverine species Strickler An extensive recent study of diet in this species could have been taken from the delphinid playbook, revealing Pontoporia to be an opportunistic feeder eating a variety of schooling and solitary fish and squid Bassoi At this juncture, the data do not suggest a strong correlation between brain size and available energy in odontocetes.

The data on metabolic rate in Phocoenoides clearly contradict the energy availability hypothesis, but they cannot be refuted for the smallest brained dolphins, Inia, Platanista, Lipotes and Pontoporia. To encourage further work in this area, I construct a diet-related hypothesis that takes into account the lack of obvious categorical differences in food type among small- and large-brained dolphins. Schooling fish offer a possibility. Fish schools represent a large patch of high quality but also highly mobile food. Dolphins digest quickly and with a high efficiency of assimilation Shapunov using a longer than expected small intestine Williams et al.

It allows dolphins to eat a lot quickly and move rapidly over long distances between schools. Operating on a higher energy budget would render a larger brain more affordable. An obvious weakness of this hypothesis is that even the small-brained Pontoporia feeds on schooling fish Bassoi However, if the early delphinids specialized more on schooling fish than other groups, and this specialization was associated with coordinated group feeding to corral or trap fish schools as occurs in a wide variety of delphinids, e.

I also note that a prominent function of the delphinid whistle is to maintain contact over distances Smolker et al. Delphinid whistles are so different from those of other species that Podos et al. The delphinid whistle may be adapted to provide information to others about orientation as well as distance. While delphinids are racing around digesting all those schooling fish, they are generating a lot of metabolic heat.

Thus, the same adaptations that might have allowed dolphins to take full advantage of this rich resource generated additional body heat that allowed them to inhabit colder water. Can we distinguish these ideas conceptually? Consider an ancestral, sluggish, warm water dolphin. Selection acted to increase the energy budget, allowing investment in the musculature and digestive tissue needed to travel further and faster to capture and digest, quickly and efficiently, schooling fish. The benefit of this investment had to be greater reproductive success. Assume that the reproductive returns were associated with additional energy intake as opposed to, for example, reduced predation risk so the dolphins were essentially paying 5 to get If the benefit of consuming additional energy was entirely heat production then the reproductive advantages might be associated with being able to live in new habitats and exploit new prey or, yes, avoid predators.

The schooling fish hypothesis is independent of the thermoregulation hypothesis only to the extent that the additional energy from feeding on schooling fish was associated with increasing fat stores and the ability to invest in offspring. Most likely, given that heat production from increased digestion was inevitable, the two selective factors often operated in tandem.

Differences in encephalization between delphinids and phocoenids suggest that the distinction may be useful. The large sperm whale brain may have evolved independently, eased as well by a squid and fish diet, and additionally, a large body size. As noted by Whitehead , the fraction of metabolism devoted to the brain depends on relative brain size which declines with increasing body size. Simply, other things being equal, big brains are cheaper for larger animals such as elephants and sperm whales. Elephants do not consume the high quality food of sperm whales, but may compensate by processing a lot of food at a high rate Clauss et al.

Although the focus here is on social cognition, I would be remiss not to discuss, at least briefly, how resource acquisition may have favoured enhanced cognitive abilities in dolphins and sperm whales.

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Cetaceans have enormous day and home ranges relative to terrestrial mammals and often feed on food that is distributed in patches Connor A bottlenose dolphin in Shark Bay may seek mobile patches of schooling prey or feed on benthic prey that occur only on patchily distributed shallow water banks. A sperm whale may move between patches separated by hundreds of kilometres and given areas may change productivity over periods of months or longer Whitehead , Greater memory and spatial knowledge may be favoured to the extent to which patch availability fluctuates predictably in space and time.

Ridgway , , has argued that the large delphinid brain was driven by the demand for more neural tissue to map acoustically the dolphins' environment in real time. However, it is not clear why delphinids would need to map a larger area in real time than, for example, the wide ranging, pelagic and deep diving but smaller brained beaked whales of the family Ziphiidae. As Nicholas Humphrey was writing his essay, he would have been pleasantly surprised to learn what we know today: Bottlenose dolphins exhibit a remarkable range of feeding behaviours that they employ throughout the water column and even into the air, onto the beach and into the substrate reviewed in Connor et al.

Moreover, compared with terrestrial environments, the marine habitat also seems to be the one that favours learned individual foraging specializations. Connor suggested that any or all of the following four factors might explain why individual foraging specializations are more prominent in the marine environment: Whitehead , suggests that significant differences in reproductive success between groups of matrilineal whales may result from innovations developed in one group and transmitted vertically. In many primates, individuals compete for high-ranking alliance partners and solicit help in contests from those that outrank themselves and their opponent see Harcourt This behaviour implies that individuals know the rank relations of others in the group, a challenging task when group size is large.

The claims of Harcourt and others for the uniqueness of primate strategic alliances were challenged with the finding that hyenas can also recognize third party relations in the context of coalition formation Engh et al. In hindsight, as usual, the findings of Engh et al. Greater social cognition would be required if individual rank or kinship were less of a deciding factor so that other strategies, such as cultivating friends based on more than simple rank, were employed to maximize reproductive success see Cords ; Silk What of the very largest mammalian brains?

Among mammals that usually includes humans, with brains three times larger than similar sized apes, many delphinids, who place second behind humans in relative brain size and which boast brains 2—3 times larger than similar sized non-delphinid odontocetes table 1 , Jerison ; Connor et al. Alexander , , reviewed in Flynn et al. This is the social equivalent of Jerison's original argument that brains provided a model of the external world. Mental simulations might permit an individual to preview alternative future social outcomes based on choosing different options e.

A or B as an ally. A socially skilled brain must not only model the complexities of the current world but mentally play out the longer-term consequences of alternative scenarios smack this individual, embrace that one. Recognizing third party relationships might be the basic foundation upon which increasingly sophisticated abilities to model social scenarios are based.

And as I suggested earlier, it may not be the ability to learn third party relations that matters for big-brained mammals, but trying to keep track of many third party relations when the size of the social network and pattern of grouping constantly introduce varying degrees of uncertainty in that knowledge.

Why did humans get shunted down this path? Alexander argues that it was not predators but other human groups that drove the extraordinary evolution of the human brain. Ecologically removed from the risk of predation, inter-group conflict became the greatest threat to humans. As mutual dependence increased exponentially, so did the importance of coalition cognition. In primates, there is a weak relationship between arboreality and life history but not arboreality and brain size. Humans, dolphins, sperm whales and elephants all depend on group living, and in some cases large size, to reduce mortality risk necessary for the evolution of long lives and large brains.

Alexander , made a persuasive case for extreme mutual dependence based on inter-group conflict during human evolution. A positive feedback loop may develop between sociality, group defence, reduced adult mortality and slow life-history processes for those species with a high investment in vulnerable offspring see Whitehead The extraordinary mutual dependence among individuals in these groups creates exactly the situation that leads to high risk social strategies.

Individuals are in social competition with the same individuals their lives depend on: The key is that as group living, and in some cases large size, reduced adult mortality, smaller infants remained extremely vulnerable. As longer-lived adults invest proportionally more in fewer offspring, mutual dependence increases in two ways. First, each offspring represents a higher proportion of lifetime reproduction. Second, as the period of parental dependency increases, so does the total number of predation attempts that have to be prevented or, more exactly, the larger dependent offspring of larger, longer-lived mothers will be less vulnerable to the smaller, more abundant, predators and so will be attacked less often.

However, this decrease in attack rate should not be in proportion to the increased duration of parental dependency, i. We can consider also whether the source of the mutual dependence experienced by humans, toothed whales and elephants have elements in common. We have assigned the extreme mutual dependence in humans to other human groups and the elephants and toothed whales to predators.

A male-biased operational sex ratio may impact directly the formation of alliances.

Another impact of slow life histories is less direct but no less important. By investing more in fewer offspring, long-lived animals reduce the options for forming same-sex alliances with close kin. If kin are favoured, and females produce litters with several males, then ready-made alliances of kin may be the preferred option. This eliminates the need for choosing partnerships strategically with the development of friendships and constant testing of bonds Zahavi Longer inter-birth intervals also reduce the chance that a single born male will have close male relatives available as potential allies.

Dolphins are at one extreme, where a female gives birth to one calf at a time several years apart. Consistent adherence to a simple rule such as ally with close kin will be less viable compared with offspring that are part of litters, or even better, synchronized litters of related females, e.

As it is clear that some male dolphins form alliances with close kin, but many and probably most do not, it is likely that kinship is the only one factor influencing their partner choice although it may be a highly preferred characteristic when similar age relatives are available. It is appropriate to end this discussion of peaks in mammalian brain evolution with communication, because humans have the largest brain relative to body size and only humans have the facility of language.

Language opened possibilities for social manoeuvring and manipulation that were not possible before. It is easy to imagine how just one of the abilities bestowed by language, communication about others in their absence, might have been put to advantage by those skilled in using and dispensing such information and misinformation to enhance their social position e.

It follows that language may have become more than a tool necessary to maintain a large number of relationships Dunbar ; by opening new frontiers in social manoeuvring, language itself may have generated selection for greater social intelligence. It is easy to argue that our language facility is what really separates humans from other large-brained mammals such as elephants and dolphins, but if history teaches us anything, it would be to proceed cautiously with this conjecture.

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

A lack of language does not preclude a priori complex communication about relationships, even relationships of those not present. It will be useful to illustrate how such a system might work, given what we know of dolphin vocalizations. Consider our current understanding of social communication in dolphins which means the bottlenose dolphin, Tursiops. Dolphins produce a bewildering range of vocalizations that are easily divided into two types: The communication functions of pulsed sounds have been studied hardly at all, primarily because they are difficult; they often appear to be graded and they are certainly difficult to quantify.

Whistles come in discrete research-friendly packages which can be recorded and played back to dolphins with relative ease. The possibilities get very interesting when the dolphins' imitative abilities are juxtaposed with the recent finding that it is the contour of the signature whistle that conveys identity Janik et al. Dolphins certainly can imitate whistles, and a variety of other artificial sounds, with astonishing speed Richards et al.

Obviously, similar data from a larger number of individuals would be more convincing. Similar whistle sharing was reported for allied males in Sarasota Bay, Florida Watwood et al. Using a hydrophone array to localize underwater sounds, Janik reported whistle matching by unidentified individuals in the Moray Firth, Scotland.

In one case three individuals produced the same whistle. The distance between individuals producing matching whistles was significantly less than for non-matching whistle interactions. Given the long duration of parental care and the continued use of their natal range by males and females, the matching exchanges in the Moray Firth might be between mothers and offspring that have very similar signature whistles or allied males that have converged on a whistle type. In sum, the evidence for context-dependent signature whistle imitation in bottlenose dolphins, i. Evidence confirming spontaneous and context-specific whistle matching should not surprise us; rather, it would be surprising if the complexity of social relationships we find in Shark Bay is not matched by complexity in social communication.

I thank Richard Wrangham for, as always, encouraging me to think more about cost-saving adaptations. Lori Marino and Louis M. Herman provided numerous helpful suggestions to improve the manuscript. The Monkey Mia Dolphin Resort has provided 15 years of financial and logistic support. CALM has also provided assistance. National Center for Biotechnology Information , U. Published online Feb Author information Copyright and License information Disclaimer.

This article has been cited by other articles in PMC. Abstract Bottlenose dolphins in Shark Bay, Australia, live in a large, unbounded society with a fission—fusion grouping pattern. The Shark Bay dolphins: Open in a separate window. The duration of relationships: The structure of male dolphin alliances in Shark Bay Males in Shark Bay form two, and possibly three, distinct levels of alliance within their social network Connor et al.

Alliance relationships and social complexity Alliances and coalitions are, at a minimum, an important category of relationship, usefully illustrative of how social interactions can become complex, and at most, may be the kind of relationship that drove large brain evolution generally Alexander ; Cords ; Harcourt ; Connor b.

Levels of alliance As pointed out by Kummer , within-group alliances are complex because they involve triadic interactions. The ecology of alliance formation a First-order alliance size Given that most consortships involve three males, but a minority two, it was commonly speculated among our research group that the optimal size of first-order alliances was a bit less than three males. Ecological influences on social cognition The differences we find between the Sarasota and Shark Bay bottlenose dolphin populations are likely ecological but possibly owe to morphology or even phylogeny; see Connor et al.

Table 1 Three brain size comparisons for small odontocetes of approximately the same body size. Paying the costs a Brains, food and metabolic rates in dolphins Some hypotheses to explain primate brain size differences focused exclusively on costs e. Reaping the benefits a The non-social cognitive challenges: The social competition hypothesis In many primates, individuals compete for high-ranking alliance partners and solicit help in contests from those that outrank themselves and their opponent see Harcourt Life history and social cognition: Communication It is appropriate to end this discussion of peaks in mammalian brain evolution with communication, because humans have the largest brain relative to body size and only humans have the facility of language.

Acknowledgments I thank Richard Wrangham for, as always, encouraging me to think more about cost-saving adaptations. Evolution of the human psyche. Mellars P, Stringer C, editors. A look at relative brain size in mammals. Relative brain size and metabolism in mammals. Mitogenomic analysis provides new insights into cetacean origin and evolution.

Female choice in the synchronously waving fiddler crab Uca annulipes. Neocortex size and behavioural ecology in primates. Feeding ecology of franciscana dolphin, Pontoporia blainvillei Cetacea: Pontoporiidae , and oceanographic processes on the southern Brazilian coast. Prey dynamics affect foraging by a pelagic predator Stenella longirostris over a range of spatial and temporal scales. C, da Silva V.

Amazon river dolphin, boto, Inia geoffrensis de Blainville, In: H, Harrison R, editors. Handbook of marine mammals. River dolphins and the larger toothed whales. Communication signals of the Black Sea bottlenose dolphin. Individual whistle contours in bottlenose dolphins Tursiops truncatus Nature. Review of the signature—whistle hypothesis for the Atlantic bottlenose dolphin.

Leatherwood S, Reeves R. Call J, Carpenter M. Three sources of information in social learning. Dautenhahn K, Nehaniv C. Imitation in animals and artifacts. Cassens I, et al. Independent adaptation to riverine habitats allowed survival of ancient cetacean lineages. Studies on feed digestibilities in captive Asian elephants Elephas maximus J. Primates, brains and ecology. Group living in whales and dolphins. Individual foraging specializations in marine mammals: Levels and patterns in dolphin alliance formation.

Social cognition in the wild: Hurley S, Nudds M, editors. Are dolphins reciprocal altruists? Dolphin alliances and coalitions. H, de Waal F. Coalitions and alliances in animals and humans. Two levels of alliance formation among male bottlenose dolphins Tursiops sp. Patterns of female attractiveness in Indian Ocean bottlenose dolphins. C, Mann J, Tyack P. Social evolution in toothed whales.

Super-alliance of bottlenose dolphins. The number of social relationships in an open fission—fusion society. Friendships, alliances, reciprocity and repair. Whiten A, Byrne R. Wiley; New York, NY: A, van Schaik C. Primate brains and life histories: Primate life histories and socioecology. The social complexity of spotted hyenas. Neocortex size as a constraint on group size in primates. Maternal rank inheritance in the spotted hyena. Patterns of alliance formation and post-conflict aggression indicate spotted hyenas recognize third party relationships. Ecological dominance, social competition, and coalitionary arms races: C, Edgar R, Cox F.

A division of labor with role specialization in group-hunting bottlenose dolphins Tursiops truncatus off Cedar Key, Florida. Music and dance as a coalition signaling system. Alliances in contests and social intelligence. W, Whiten A, editors. Clarendon Press; Oxford, UK: Coalitions and alliances in humans and other animals. Vocal, social, and self-imitation by bottlenosed dolphins. Intelligence and rational behaviour in the bottlenosed dolphin. The communication systems of cetaceans.

Sperm whale phologeny revisited: The social function of intellect. Growing points in ethology. Whistle matching in wild bottlenose dolphins Tursiops truncatus Science. Context-specific use suggests that bottlenose dolphin signature whistles are cohesion calls. Signature whistle shape conveys identity information to bottlenose dolphins. Predicting group size in primates: Evolution of the brain and intelligence. Brain and intelligence in whales. Contrasting relatedness patterns in bottlenose dolphins Tursiops sp.

B, Berggren P, Gales N. Population structure in an inshore cetacean revealed by microsatellite and mtDNA analysis: Tripartite relations in hamadryas baboons. Social communication among primates. Directionality in the whistles of Hawaiian spinner dolphins Stenella longirostris: Social and ecological correlates of vision and visual appearance. An examination of cetacean brain structure with a novel hypothesis correlating thermogenesis to the evolution of a big brain. Like mother, like calf: Fragaszy D, Perry S, editors. The biology of traditions: Mann J, Connor R.

Female reproductive success in bottlenose dolphins Tursiops sp. Intergroup aggression in chimpanzees and humans. A comparison of encephalization between odontocete cetaceans and anthropoid primates. Origin and evolution of large brains in toothed whales. Dolphins were positioned with their backs to the main trainer avoiding the possible use of echolocation , in the same position for all trials, and the sound source was hidden behind a plastic screen to ensure that sound was the only cue for dolphins but also that trainers could not guess which dolphin would be called.

Other trainers were instructed not to gesticulate or look at the subjects when the test started. The other trainers were not aware of the sound tested during a given trial and those familiar with the instrument allocated to each subject wore earplugs. When all the dolphins were in place with the right orientation, one of the seven instruments was played by the main trainer on the opposite side of the pool.

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The instrument was positioned approximately 30 cm under the surface of water Experiment 1 or approximately 50 cm above the surface Experiment 2. All successful responses a dolphin moves toward its designated sound, or it does not move when the sound is not its own specific sound cue were rewarded when the dolphin arrived at the sound source or after 10 s when the dolphin did not move after hearing another sound cue. The behavior of the dolphins during the 10 s following playback was further analyzed: Apart from locomotion, we also scored visual attention, estimated from head orientation as in Xitco et al.

Dolphin behavior was recorded during the trials with three cameras: The experiments described in this paper were carried out in accordance with the current laws of the country in which they were performed. No further permit was needed as only behavioral observations were performed. The behavioral data for the seven dolphins were analyzed using the focal sampling method Altmann, during the 10 s of each test following the playing of an instrument. We analyzed the first reaction i. A binomial test compared movement toward source between own and other sounds.

Chi-square tests compared the numbers of dolphins performing each behavior in each situation. In order to compare changes of gaze direction, duration and latency in relation to the type of sound i. We performed all statistical analyses with the software R 3. R Core Team, In the first experiment, dolphins were exposed to sounds emanating from one of seven instruments played underwater. Each dolphin was trained to respond to the sound of only one instrument. Responses to each instrument were recorded, as were latencies to approach. They did not move in Overall, the dolphins were successful, The target animal did not gaze before departing.

Throughout the session the other dolphins looked either at their trainer mean: Dolphin reactions to their own individual sound cue and to other sound cues broadcast underwater left and in the air right. B Latencies of first reactions to the sound: One behavior predominated in each situation: In the second experiment, dolphins were exposed to sounds emanating from the same seven instruments, but this time played in the air. Dolphins had only been trained to respond to these sounds when played underwater. Responses to each instrument were recorded, as were duration and latencies of gazing at the sound source, at a trainer or at other objects of the environment.

Behavioral responses indicated that the dolphins not only heard the sounds but even discriminated between them: Number and duration of gazes toward the sound source were significantly higher when the broadcast was aerial Wilcoxon Tests: As a consequence, duration of gazes toward conspecifics was significantly shorter in the aerial condition than in the underwater condition 0. This study provides the first evidence that bottlenose dolphins can recognize a human-made sound cue played underwater, even when transposed to the aerial environment.

Prior to these experiments, dolphins had been trained individually with the possible help of visual cues. In the first experiment, the dolphins performed the trained response moved toward the source. Operant conditioning is widely used for the management and training of captive dolphins. Daily training and public performances are based on teaching the animals gestures associated with specific behaviors. Dolphins are able to associate a human movement with a specific action, or a specific part of their body, and can respond to orders combining these different elements thanks to their understanding of simple syntax rules Herman, ; Herman et al.

Furthermore, they can incorporate features of artificial sounds made by humans into their whistles Miksis et al. They are also said to be self-aware, notably because they recognize their bodies in a mirror Reiss and Marino, Their high-level cognitive abilities are further shown by imitation of computer-generated sounds, and of postural or motor behaviors of non-cetacean species and dolphin tank mates Richards et al. They signal individual identity through signature whistles that they can share with other dolphins through affiliative copying Harley, ; King et al.

Our findings suggest that dolphins can associate sound cues with individual identities and we believe that this contributes to the debate regarding the potential existence of a concept of self-identity in dolphins. Further experiments could test their ability to associate a given sound cue to the image of the appropriate group member, for example.

In the second experiment, dolphins responded differently when the sounds were played in the air: Thus, they gazed more often and for longer toward the sound source and reacted faster when their own sound cue was being broadcast. The aerial hearing sensitivity of dolphins has been debated, and some authors doubt that cetaceans are really able to hear sounds emitted in the air Ketten, Marine mammal ears are adapted to aquatic life Breathnach et al.

Nonetheless, most auditory studies have focused on reception of waterborne sounds review in Erbe et al. Babushina, ; harbor porpoises: These authors suggested that dolphins are able to perceive acoustic stimuli broadcast in air. The fact that our dolphins reacted faster when the sound signal broadcast was their own sound cue than when it was that of a conspecific shows that the dolphins were able to perceive and recognize sound signals diffused in the air.

The difference in reactions to underwater and airborne acoustic stimuli may be due to either poor hearing Liebschner et al. They gazed more at the sound source when the instrument was played in the aerial condition, which could be an indication that they were trying to understand the demand, as shown in other studies when humans behaved unexpectedly or differently Xitco et al. Thus, horses increased their monitoring behavior after hearing a familiar order given by an unknown person Sankey et al. Dolphins look more at their trainer when their performance is inconsistent during a familiar task Xitco et al.

Dolphins could use cues based on human movements, as they are trained to be very attentive to gestures during training sessions Tomonaga et al. The fact that dolphins possibly search for clues given by human postures could explain the multiple gazes toward the source. This study shows evidence that bottlenose dolphins are able to respond to individual sound cues produced by humans, even when sounds are emitted in the air.

This evidence contributes to our knowledge of the cognitive capacities of this species and the extension of its hearing capabilities. Further studies could test if dolphins can associate these sound cues with individual identities.

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

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Louazon EthoS for his technical assistance. They are grateful to A. Cloarec and to A. Craig for correcting the English. National Center for Biotechnology Information , U. Journal List Front Psychol v. Published online Jan Author information Article notes Copyright and License information Disclaimer. This article was submitted to Comparative Psychology, a section of the journal Frontiers in Psychology.

Received Aug 23; Accepted Jan The use, distribution or reproduction in other forums is permitted, provided the original author s and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Abstract Bottlenose dolphins Tursiops truncatus spontaneously emit individual acoustic signals that identify them to group members.

Table 1 Instruments assigned to each individual and characteristics of the animals M: Open in a separate window. Experimental Approach Our first goal was to test under standardized conditions, whether dolphins successfully learned to respond to their individual sound source without the help of any visual cues trainer gaze and gesture, instrument shape , without being influenced by the possible responses of the other group members, and without the need to play the instrument repeatedly to motivate the animal. Ethics Statement The experiments described in this paper were carried out in accordance with the current laws of the country in which they were performed.

Data and Statistical Analyses The behavioral data for the seven dolphins were analyzed using the focal sampling method Altmann, during the 10 s of each test following the playing of an instrument. Table 2 Terminology of behaviors observed during the experiment. Behavior Description Movement Source Dolphin moves to the sound source. Trainer Dolphin moves to another trainer. Other Dolphin moves in a direction other than that of the sound source or a trainer. Gaze Starting position - Dolphin on the edge of the pool Source Dolphin looks in the direction of the sound source.

Trainer Dolphin looks in the direction of one of the trainers. Conspecific Dolphin looks in the direction of a conspecific. Other Dolphin looks in a direction that does not correspond to trainers, sound source or conspecific. Underwater Broadcast Conditions In the first experiment, dolphins were exposed to sounds emanating from one of seven instruments played underwater. Comparison between Underwater and Aerial Conditions Number and duration of gazes toward the sound source were significantly higher when the broadcast was aerial Wilcoxon Tests: Discussion This study provides the first evidence that bottlenose dolphins can recognize a human-made sound cue played underwater, even when transposed to the aerial environment.

Conclusion This study shows evidence that bottlenose dolphins are able to respond to individual sound cues produced by humans, even when sounds are emitted in the air. Conflict of Interest Statement The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Observational study of behavior - sampling methods. Localization by dolphin of sources of tone and pulse signals in the water and air. Communication masking in marine mammals: