Male Dolphins Research Articles

Cytochrome P4501A1 expression, polychlorinated biphenyls and hydroxylated metabolites, and adipocyte size of bottlenose dolphins from the Southeast United States

Persistent organic pollutants (POPs) bioaccumulate in blubber of marine mammals. Therefore, it is important to understand the structure and dynamics of blubber layers and how they affect the accumulation of POPs and subsequent biochemical responses. We used established histological and immunohistochemical methods to document the structure of bottlenose dolphin ( Tursiops truncatus) blubber and to assess the expression of cytochrome P4501A1 (CYP1A1) in skin-blubber biopsies of dolphins sampled in the waters off Charleston, SC (CHS) ( N = 38), and Indian River Lagoon, FL (IRL) ( N = 36). CYP1A1 expression was strongest and most frequent in capillary endothelial cells and was stratified in blubber; the greatest CYP1A1 staining was in the deepest layer. CYP1A1 expression in deep blubber and 2,3,7,8-TCDD Toxic Equivalents measured in the entire blubber were significantly higher in dolphins from CHS as compared to those from IRL. Adipocyte size was associated with the extent of CYP1A1 expression. Male dolphins with smaller adipocytes from CHS and IRL had higher levels of CYP1A1 expression in deep blubber. In CHS females, CYP1A1 expression in vascular endothelial cells varied with reproductive status. CYP1A1 expression in the deep layer was highest in simultaneously pregnant-lactating dolphins, and these dolphins had the smallest adipocytes in deep blubber. In all dolphins, CYP1A1 expression in the deep blubber layer was positively related to concentrations of hydroxylated PCBs (OH-PCBs) in plasma. In summary, redistribution of AHR agonists from blubber into the circulatory system may enhance PCB metabolism and production of OH-PCBs by induction of CYP1A1 in hepatocytes and, possibly, by induction of CYP1A1 in endothelial cells of the deep blubber. The OH-PCBs thus formed have the potential to interfere with thyroid hormone homeostasis.

Use of a serum‐based glomerular filtration rate prediction equation to assess renal function by age, sex, fasting, and health status in bottlenose dolphins (Tursiops truncatus)

AbstractGlomerular filtration rate (GFR) is a direct measurement of renal function. Although clearance tests using 24‐h urine collection or blood sample series are gold standards for measuring GFR, serum‐based prediction of GFR based upon the Modification of Diet in Renal Disease (MDRD) Study equation is acceptable for routine use in human adults. The purpose of our study was to assess the ability for a modified MDRD Study equation to predict expected changes in GFR in bottlenose dolphins (Tursiops truncatus) using a healthy dolphin population represented by 1,103 routine serum samples collected from 50 dolphins of all age groups, years 1998–2005. Predicted GFR was also calculated from serum collected from a 32‐yr‐old male dolphin with end‐stage renal disease. The dolphin‐adjusted MDRD equation predicted GFR changes in our population that paralleled what has previously been reported in other mammals, including decreasing predicted GFR with age (P < 0.01), higher predicted GFR in dolphins that had recently eaten (P < 0.01), and rapidly decreasing predicted GFR in the animal with end‐stage renal disease. We conclude that a serum‐based GFR prediction equation may be a feasible means of detecting and tracking renal function in bottlenose dolphins.

Synergy Goes to War: A Bioeconomic Theory of Collective Violence

Synergy – here defined as otherwise unattainable combined effects that are produced by two or more elements, parts or individuals – has played a key causal role in the evolution of complexity, from the very origins of life to the evolution of humankind and complex societies. This theory – known as the ‘Synergism Hypothesis’ – also applies to social behavior, including the use of collective violence for various purposes: predation, defense against predators, the acquisition of needed resources and the defense of these resources against other groups and species. Among other things, there have been (1) synergies of scale, (2) cost and risk sharing, (3) a division of labor (or, better said, a ‘combination of labor’), (4) functional complementarities, (5) information sharing and collective ‘intelligence’, and (6) tool and technology ‘symbioses’. Many examples can be seen in the natural world – from predatory bacteria like Myxococcus xanthus to social insects like the predatory army ants and the colonial raiders Messor pergandei, mobbing birds like the common raven, cooperative pack-hunting mammals like wolves, wild dogs, hyenas and lions, coalitions of mate-seeking and mate-guarding male dolphins, the well-armed troops of savanna baboons, and, closest to humans, the group-hunting, group-raiding and even ‘warring’ communities of chimpanzees. Equally significant, there is reason to believe that various forms of collective violence were of vital importance to our own ancestors’ transition, over several million years, from an arboreal, frugivorous, mostly quadrupedal ape to a world-traveling, omnivorous, large-brained, tool-dependent, loquacious biped. The thesis that warfare is not a recent ‘historical’ invention will be briefly reviewed in this paper. This does not mean that humans are, after all, ‘killer apes’ with a reflexive blood-lust or an aggressive ‘drive’. The biological, psychological and cultural underpinnings of collective violence are far more subtle and complex. Most important, the incidence of collective violence – in nature and human societies alike – is greatly influenced by synergies of various kinds, which shape the ‘bioeconomic’ benefits, costs and risks. Synergy is a necessary (but not sufficient) causal agency. Though there are notable exceptions (and some significant qualifiers), collective violence is, by and large, an evolved, synergy-driven instrumentality in humankind, not a mindless instinct or a reproductive strategy run amok.

Polybrominated Diphenyl Ethers (PBDEs) in Blubber of Free-Ranging Bottlenose Dolphins (Tursiops Truncatus) from Two Southeast Atlantic Estuarine Areas

Blubber tissue samples from bottlenose dolphins collected during the summers of 2003 and 2004 were screened for 13 (17, 28, 47, 66, 71, 85, 99, 100, 138, 154, 153, 183, 190) polybrominated diphenyl ethers (PBDEs) from dolphin populations in the Indian River Lagoon, FL (n = 58) and the Charleston Harbor estuary, SC (n = 53). Within each population, we investigated contaminant levels of PBDEs and the effects of factors including age, sex, the interaction of age and sex, and location. Six PBDE congeners (28, 47, 99, 100, 153, and 154) were routinely detected in all samples using gas chromatography/mass spectometry methods. Significantly higher (p <or= 0.0001) mean SigmaPBDE blubber concentrations were observed for Charleston dolphins (X = 5,860 ng/g lipid; range = 429-22,780 ng/g lipid) when compared to Indian River Lagoon dolphins (X= 1,260 ng/g lipid; range = 195-3,790 ng/g lipid). PBDE 47 was the major congener representing approximately 61% of the SigmaPBDE in both dolphin populations, followed by BDE100, BDE154, BDE99, BDE153, and BDE28, respectively. Significantly higher (p < 0.0001) mean SigmaPBDE were observed in adult male dolphins compared to pregnant and adult female dolphins at both sites, with gender differences two-fold in the Indian River Lagoon and twelve-fold for Charleston. For Charleston dolphins, the juveniles in addition to the adult males also had significantly higher levels compared to pregnant and adult females. This study establishes baseline levels of PBDEs in bottlenose dolphins for these two areas and is the first assessment of PBDEs in free-ranging dolphins. The levels of PBDEs in Charleston dolphins represent some of the highest measured in marine mammals and warrants further investigation of these emerging, bioaccumulative chemicals and their potential deleterious effects.

The Orbital Harderian Gland of the Male Atlantic Bottlenose Dolphin (Tursiops truncatus): A Morphological Study

The ultrastructure of the Atlantic Bottlenose dolphin Harderian gland (HG) has been described but some questions remain unanswered. The purpose of this work was to define the gland's structure, ultrastructure and the differences between cells (types I and II) of the male dolphin using optic, fluorescence and electron transmission microscopy. Three different cells were observed under optic and fluorescence microscopic examination, while only two cell types (types I and II) were distinguished by electron transmission microscopy. Type I (oval nuclear envelope) exhibited three different cell populations and type II (indented nuclear envelope) exhibited two different cell populations. Although, we observed both types of vesicles in both types of cells they differed, principally, in quantity. The glands also possessed prominent duct systems, with three orders of complexity. The dolphin orbital HG appears to function as a mixed heterologous gland with two types of cells that exhibit both types of vesicles and other distinguishable differences.

Auditory evoked potential hearing measures of a group of bottlenosed dolphins (Tursiops truncatus)

The hearing of the bottlenosed dolphins at Kolmrdens Djurpark, Sweden, was examined using a portable auditory evoked potential (AEP) system in order to examine the hearing capabilities of dolphins housed in quiet environments with an emphasis on age-related hearing variation. Audiograms were measured on two dolphins and modulation rate transfer functions (MRTF) were also measured on two animals. A complete audiogram (4–200 kHz) was obtained for the oldest dolphin, a 34 year old female named Vicky. Her audiogram showed no evidence of high-frequency hearing loss. Notwithstanding this finding, her click evoked auditory brainstem response (ABR) revealed a marked increase in interpeak latency that could be indicative of an underlying hearing defect. The audiogram obtained from for the male dolphin, a 24 year old named Pichi (measured from 4–107 kHz), demonstrated profound hearing loss at all frequencies. The measured MRTF results indicated typical odontocete following responses to rates exceeding 1000 Hz.

Introduction. Social intelligence: from brain to culture

Humans are perhaps the most social animals. Although some eusocial insects, herd mammals and seabirds live in colonies comprising millions of individuals, no other species lives in such a variety of social groups as Homo sapiens . We live in many different sized societies, from small, nomadic hunter

Evaluation of Human Interactions with a Provisioned Wild Bottlenose Dolphin (&lt;I&gt;Tursiops truncatus&lt;/I&gt;) near Sarasota Bay, Florida, and Efforts to Curtail the Interactions

Boaters have provisioned a free-ranging bottlenose male dolphin (Tursiops truncatus) for more than 15 years near Nokomis, Florida. The dolphin is a well-known attraction to tourists and local boaters because of his predictable presence in a narrow section of the Intracoastal Waterway near the Albee Road Bridge. Observations and records collected since 1990 documented this animal being fed by and interacting with humans, sometimes resulting in injury to the humans attempting to touch, feed, or swim with it. We initiated a study in 1997 to document the dolphin’s interactions with boaters, to characterize the frequency and types of boater interactions with the animal, and to evaluate the effectiveness of public education and enforcement efforts to curtail these illegal activities. The project consisted of three phases: (1) a baseline study, (2) a docent program, and (3) a follow-up study. Approximately 26% of the 1,797 interactions observed during the baseline study involved touching, teasing, or splashing, and 11% of interactions involved feeding. The docent program involved increased signage and the operation of a marked vessel to shadow the dolphin, monitor the types and frequencies of interactions, and offer educational materials about responsible wildlife viewing. Only 1.3% of boaters interacted with the dolphin in the presence of the docents; more than half of those questioned indicated that they were aware of the illegality of their actions. During follow-up observations to assess the effectiveness of the docent program and minimally increased law enforcement efforts, boater interactions with the dolphin increased by 5% after docent discussions. The docent and follow-up studies demonstrated that a small segment of the boating public continue to interact with the dolphin in spite of highly visible public education efforts. Increased law enforcement efforts, including the application of well-publicized punitive sanctions, may be required to bring about a further reduction in dolphin-human interactions in this area.

Reproduction in short-beaked common dolphins (Delphinus delphis) from the western North Atlantic

A single population of short-beaked common dolphins (Delphinus delphis Linnaeus) occurs in the western North Atlantic from Florida to Newfoundland. Dolphins killed in a swordfish driftnet fishery between 1989 and 1998 provided samples for the present study. These were combined with additional observations from carcasses collected from stranding programs. Samples were examined from 74 female and 161 male short-beaked common dolphins. A highly significant male bias in the sex ratio of both the bycatch and stranding samples suggests that sex-based habitat partitioning or school segregation occurs in this population. Age was estimated from decalcified thin sections of teeth and testis and ovarian samples were examined both macro- and microscopically. Analyses showed that reproduction was both seasonal and synchronized. Females reached sexual maturation at approximately age eight; males matured at 9.5 years. Conception occurred during July and August (mean day 24 July). Gestation was estimated to last just under a year, so most females gave birth during July and August (mean day 15 July). Annual pregnancy rate was estimated to be between 25 and 33%. Males undergo a fivefold seasonal increase in testes mass and a twofold increase in seminiferous tubule diameter. Peak sperm production potential was observed in July. At the end of the breeding season testis size and activity decreased after August. Male dolphins in this population are hypothesized to engage in some form of sperm competition.

Stratification and intra- and inter-specific differences in fatty acid composition of common dolphin ( Delphinus sp.) blubber: Implications for dietary analysis

Sixty-five fatty acids were quantified in the blubber of common dolphins ( Delphinus delphis, D. capensis) incidentally caught off the coast of southern California. Dolphins were grouped by sex, reproductive status and species, and a blubber sample was collected at a mid-lateral site located caudal to the trailing edge of the dorsal fin. Samples were divided horizontally into inner, middle and outer layers and gradients in fatty acid content (mass percent) were observed across the depth of the blubber. Levels of monounsaturated fatty acids were greatest in the outer layer, whereas levels of saturated and polyunsaturated fatty acids were greatest in the inner layer. Degree of stratification was greatest in sexually mature dolphins. Blubber of sexually immature, but physically mature, male dolphins was also highly stratified, suggesting that this difference may be attributed to differences in diet. Classification and regression tree analysis resulted in the fewest misclassifications when dolphins were grouped by species, possibly indicating that these closely related animals forage on different prey species. Dietary-derived fatty acids were typically selected as splitting criteria in classification and regression tree analyses, suggesting that the observed differences in fatty acid composition between the various groups of dolphins may be attributed to differences in diet.

MATING STRATEGY IN THE MALE COMMON DOLPHIN (DELPHINUS DELPHIS): WHAT GONADAL ANALYSIS TELLS US

Gonadal development in immature, pubertal, young mature, and sexually mature male common dolphins (Delphinus delphis) was assessed for 212 dolphins collected between 1991 and 2003. The sample consisted of animals stranded along the Irish and French coasts, and also bycatch samples from Irish and French observer programs. Through histological analysis of the testes, individuals were categorized into reproductive stages by using characteristics of their gonadal morphology. These stages were immature, pubescent, young mature, and sexually mature. Male common dolphins were 102–233 cm in length and 0–28 years of age. Sexually mature individuals were 195–233 cm in length and 8–28 years of age, and the average age at attainment of sexual maturity was 11.86 years. Combined testes weight for mature male dolphins ranged from 0.45 to 5 kg, which is relatively large considering the overall size of the dolphin. Reproductive seasonality was found to occur, as evidenced by marked seasonal changes in both testes weights and cellular activity in testes outside the mating period; the mating period was estimated to take place during May-September. Moderate sexual dimorphism and large testes suggest sperm competition and a promiscuous mating system, with female common dolphins mating with multiple mates.

Effect of organochlorine contaminants and individual biological traits on blubber retinoid concentrations in bottlenose dolphins (Tursiops truncatus)

Here we assessed retinoids as biomarkers of contaminant exposure by studying whether the sex, age, lipid content and organochlorine concentrations of bottlenose dolphins induced variation in retinoid status and its deposition in blubber. Blubber samples were collected from 47 individuals of known age and gender from Sarasota Bay in June 2000 and 2001. The sample included a representative cross-section of the resident dolphin community, with ages ranging from 2 to 50 years. Organochlorine levels showed the age- and sex-related variation commonly observed in other species, with concentrations increasing in youngsters of both sexes and in adult males, and decreasing in adult females after the onset of maturity. Blubber lipid content was low in the overall population and significantly decreased with age in adult males. Retinoid blubber concentrations were comparable to other odontocete species previously studied, and were strongly determined by lipid content. As a consequence of the latter, retinoid concentration was observed to decrease with age in adult males. This effect could not be statistically dissociated from the negative correlation observed between levels of organochlorines and retinoid blubber concentration. Consequently, we could not clarify whether high organochlorine loads in this population lowered retinoid concentrations or, conversely, whether depleted lipid reserves were indeed responsible for the high organochlorine concentrations and the low retinoid levels detected in blubber. With the current knowledge, both options should be considered and investigated, with initial focus on male dolphins.

Morphometry and sexual dimorphism of the coastal spotted dolphin, Stenella attenuata graffmani, from Bahía de Banderas, Mexico

AbstractExternal measurements and size differences between the sexes were examined in the coastal spotted dolphin, Stenella attenuata graffmani, in Bahía de Banderas, on the Mexican Pacific coast. The dolphins were collected by local fishermen and 29 external characteristics were measured by members of the Marine Mammals Laboratory, University of Mexico. The length of each characteristic with respect to total length was analysed through adjustment of the data to a power equation. A stepwise discriminant analysis was applied to the absolute values and to those expressed as proportions to analyse the differences between the sexes. Results indicate that growth in these dolphins is generally negatively allometric, and most of the characteristics measured were, in both absolute and proportional terms, greater in male dolphins than in female dolphins. As found in many species of odontocetes, the discriminant analysis showed that the main differences between the sexes for this coastal subspecies include the relative positions of the umbilicus, the genital aperture and the anus. The morphometric data provided by this study, corresponding to 29 specimens of S. a. graffmani collected in a restricted locality of the Mexican Pacific coast, are particularly interesting to studies documenting latitudinal morphological differences in the coastal spotted dolphin.

Whistle sharing in paired male bottlenose dolphins, Tursiops truncatus

The signature whistle hypothesis states that dolphins produce highly stereotyped, individually distinctive whistles when in isolation. The presence of signature whistles has been called into question by recent studies proposing that dolphins produce a shared, simple upsweep whistle when in isolation, and that whistles produced by socializing dolphins are shared across individuals and social groups. This shared repertoire hypothesis suggests that when two animals produce the same whistle type, it is due to sharing the same common repertoire rather than one animal learning to produce the whistle of another. One difference between studies supporting or denying the existence of signature whistles is the method used to classify whistle types. We examined whistle production by 17 free-ranging bottlenose dolphins while temporarily restrained. We used both a quantitative comparison technique similar to that used to support the shared repertoire hypothesis and human judges to classify whistle types and quantify similarity between types. Contrary to recent studies that emphasize shared whistles, overall whistle sharing between isolated individuals was low (25%) and a simple upsweep did not account for the most common whistle type in half of the animals. Some species of birds, bats, and primates with stable social groups use vocal learning to converge over time to one common group distinctive call type. We examined whistle similarity between adult male dolphins that are partners in a close social alliance in order to test whether vocal learning may enable a similar vocal convergence. Whistle similarity was rated very high between partners and low between non-partners by both the quantitative technique and human observers. This suggests that as in songbirds and some other mammals, adult male bottlenose dolphins may use vocal learning to converge on similar whistles as they develop affiliative social relationships.

Geographic variation in polychorinated biphenyl and organochlorine pesticide concentrations in the blubber of bottlenose dolphins from the US Atlantic coast

Concentrations of polychorinated biphenyls (PCBs) and other organochlorine contaminants (OCs) were measured in blubber collected from live bottlenose dolphins ( Tursiops truncatus) at three sites along the United States Atlantic coast. Dolphins were sampled via surgical biopsy during capture–release studies near Charleston, South Carolina and Beaufort, North Carolina. Additional animals were sampled using remote biopsy techniques in estuarine waters near Charleston and from the Indian River Lagoon, Florida. Overall concentrations of major contaminant groups were found to vary between sites and mean concentrations of most OCs from male dolphins in the Indian River Lagoon were less than half of those measured from Charleston and Beaufort males. Geometric mean total PCB concentrations were 30, 27 and 14 μg/g lipid for male dolphins sampled in Beaufort, Charleston and the Indian River Lagoon, respectively. Significant variation related to sex- and age-class, as well as geographic sampling location, was seen in the PCB congener profiles. The measured PCB concentrations, although lower than those reported for stranded animals from the 1987/1988 epizootic along the United States mid-Atlantic coast, are sufficiently high to warrant concern for the health of dolphins from the sampled populations, particularly the animals near Charleston and Beaufort.

Chlorinated pesticides and polychlorinated biphenyls in marine tucuxi dolphins ( Sotalia fluviatilis) from the Cananéia estuary, southeastern Brazil

The Cananéia estuary is an important biological area on the southeast coast of Brazil. In the past, it was impacted by both chlorinated pesticides and polychlorinated biphenyls (PCBs) due to its natural location. The marine tucuxi dolphin ( Sotalia fluviatilis) is a top predator in this ecosystem and can be found year round in Cananéia estuarine waters that represent an important nursing area for the species. This work investigated chlorinated compounds in the blubber of nine individuals from the Cananéia estuary. Residue levels of DDTs (0.541–125 μg g −1 lipid wt.) were the highest, followed by PCBs (0.2–9.22 μg g −1 lipid wt.), mirex (0.014–0.312 μg g −1 lipid wt.), chlordanes (0.001–0.047 μg g −1 lipid wt.), HCHs (<0.003–0.044 μg g −1 lipid wt.), and HCB (n.d.−0.024 μg g −1 lipid wt.). The mean p, p′-DDE/Σ DDT ratio was approximately 0.8 and is indicative of the former DDT application in the study area. PCB contamination is suggested to be associated with atmospheric transport and relative proximity to the Cubatão industrial complex—the most important along the Brazilian coast. Low levels of HCHs and HCB can be attributed to their high volatility in tropical environments. Concentrations of organochlorines in the blubber of marine tucuxis from the Cananéia estuary were lower than levels found in small cetacean species from developed countries, where the input of these compounds was considerably greater than in Brazil. At extremes, male dolphins can present DDT burden several orders of magnitude higher than females. Despite the high levels of total DDT found in males, the major detected compound was p, p′-DDE which is considered to be of low toxicity.

Assessment of dolphin (Tursiops truncatus) auditory sensitivity and hearing loss using jawphones.

Devices known as jawphones have previously been used to measure interaural time and intensity discrimination in dolphins. This study introduces their use for measuring hearing sensitivity in dolphins. Auditory thresholds were measured behaviorally against natural background noise for two bottlenose dolphins (Tursiops truncatus); a 14-year-old female and a 33-year-old male. Stimuli were delivered to each ear independently by placing jawphones directly over the pan bone of the dolphin's lower jaw, the assumed site of best reception. The shape of the female dolphin's auditory functions, including comparison measurements made in the free field, favorably matches that of the accepted standard audiogram for the species. Thresholds previously measured for the male dolphin at 26 years of age indicated a sensitivity difference between the ears of 2-3 dB between 4-10 kHz, which was considered unremarkable at the time. Thresholds for the male dolphin reported in this study suggest a high-frequency loss compared to the standard audiogram. Both of the male's ears have lost sensitivity to frequencies above 55 kHz and the right ear is 16-33 dB less sensitive than the left ear over the 10-40 kHz range, suggesting that males of the species may lose sensitivity as a function of age. The results of this study support the use of jawphones for the measurement of dolphin auditory sensitivity.

Species, tissue and gender-related organochlorine bioaccumulation in white-sided dolphins, pilot whales and their common prey in the northwest Atlantic

Organochlorine concentrations were measured in white-sided dolphins, pilot whales, and their prey from the Gulf of Maine and used to identify species, tissue, and gender differences, and trophic transfer trends, in bioaccumulation. Polychlorinated biphenyl concentrations ([PCB]) in dolphin blubber (13±7.1 μg/g fresh wt.) were twice those in pilot whales, but pesticide concentrations (20±13 μg/g fresh) were similar between species. 4,4′-DDE, trans-nonachlor, Cl 6(153) and Cl 6(138) concentrations were highest. Skin tissues had more recalcitrant organochlorines than the internal organs. Male dolphins bioaccumulated higher concentrations of nonmetabolizable PCBs and hexachlorocyclohexane (HCH) isomers, whereas pilot whales had no gender-related differences in bioaccumulation. Pilot whales, mackerel, and herring had proportionately higher concentrations of DDTs, whereas [PCB] were higher in dolphins and squid. Although these odontocetes feed at the same trophic level and store a similar suite of contaminants, dolphins bioaccumulated higher and potentially hazardous 4,4′-DDE and PCB concentrations from food in their more geographically restricted range.

Ultrasonographic imaging of the testis and epididymis of the bottlenose dolphin, Tursiops truncatus aduncas.

Eight male bottlenose dolphins, Tursiops truncatus aduncas, underwent examination of the reproductive organs to investigate the use of real-time B-mode ultrasonography in assessment of reproductive status and to establish normal ultrasonographic appearances. Ultrasonography allowed repeatable examinations which were well tolerated by all animals. Ultrasonography was used to examine the testes, epididymides, vasa deferentia, penis, bulbourethral and bulbocavernosal muscles; the prostate was not convincingly distinguished from surrounding muscles. Testicular echopatterns and size differed among individuals. Three distinct testicular echopatterns were discerned and could be used to differentiate males of different reproductive status. Ultrasonographic appearance of the testes provides useful data in assessing the reproductive status of male dolphins.

Flipper Makes a Pass

Learning to whistle the same tune may help gangs of male bottlenose dolphins stake a claim on females. Researchers have long known that small groups of male dolphins form alliances to scare off rivals for the attentions of females. And they have recognized that individual dolphins appear to adopt a distinctive “signature” whistle by the time they are 6 months old. But studying how they communicate in the wild is tricky, as it can be impossible to pinpoint which animal in a swirling school is producing a particular whistle.