Wild Bottlenose Dolphins Research Articles

Sex bias in mortality risk changes over the lifespan of bottlenose dolphins.

Research on sex biases in longevity in mammals often assumes that male investment in competition results in a female survival advantage that is constant throughout life. We use 35 years of longitudinal data on 1003 wild bottlenose dolphins (Tursiops aduncus) to examine age-specific mortality, demonstrating a time-varying effect of sex on mortality hazard over the five-decade lifespan of a social mammal. Males are at higher risk of mortality than females during the juvenile period, but the gap between male and female mortality hazard closes in the mid-teens, coincident with the onset of female reproduction. Female mortality hazard is non-significantly higher than male mortality hazard in adulthood, resulting in a moderate male bias in the oldest age class. Bottlenose dolphins have an intensely male-competitive mating system, and juvenile male mortality has been linked to social competition. Contrary to predictions from sexual selection theory, however, male-male competition does not result in sustained male-biased mortality. As female dolphins experience high costs of sexual coercion in addition to long and energetically expensive periods of gestation and lactation, this suggests that substantial female investment in reproduction can elevate female mortality risk and impact sex biases in lifespan.

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.

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

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

Untargeted plasma metabolomic analysis of wild bottlenose dolphins (Tursiops truncatus) indicate protein degradation when in poorer health

Cumulative exposure to sub-lethal anthropogenic stressors can affect the health and reproduction of coastal cetaceans and hence their population viability. To date, we do not have a clear understanding of the notion of health for cetaceans in an ecological context; that is, how health status affects the ability of individuals to survive and reproduce. Here, we make use of a unique health-monitoring programme of estuarine bottlenose dolphins in South Carolina and Florida to determine de novo changes in biological pathways, using untargeted plasma metabolomics, depending on the health status of individuals obtained from veterinary screening. We found that individuals that were in a poor health state had lower circulating amino acids pointing towards increased involvement of gluconeogenesis (i.e., new formation of glucose). More mechanistic work is needed to disentangle the interconnection between health and energy metabolism in cetaceans to mediate potential metabolic constraints they may face during periods of stress.

Parameterizing animal sounds and motion with animal-attached tags to study acoustic communication

Stemming from the traditional use of field observers to score states and events, the study of animal behaviour often relies on analyses of discrete behavioural categories. Many studies of acoustic communication record sequences of animal sounds, classify vocalizations, and then examine how call categories are used relative to behavioural states and events. However, acoustic parameters can also convey information independent of call type, offering complementary study approaches to call classifications. Animal-attached tags can continuously sample high-resolution behavioural data on sounds and movements, which enables testing how acoustic parameters of signals relate to parameters of animal motion. Here, we present this approach through case studies on wild common bottlenose dolphins (Tursiops truncatus). Using data from sound-and-movement recording tags deployed in Sarasota (FL), we parameterized dolphin vocalizations and motion to investigate how senders and receivers modified movement parameters (including vectorial dynamic body acceleration, “VeDBA”, a proxy for activity intensity) as a function of signal parameters. We show that (1) VeDBA of one female during consortships had a negative relationship with centroid frequency of male calls, matching predictions about agonistic interactions based on motivation-structural rules; (2) VeDBA of four males had a positive relationship with modulation rate of their pulsed vocalizations, confirming predictions that click-repetition rate of these calls increases with agonism intensity. Tags offer opportunities to study animal behaviour through analyses of continuously sampled quantitative parameters, which can complement traditional methods and facilitate research replication. Our case studies illustrate the value of this approach to investigate communicative roles of acoustic parameter changes.Significance statementStudies of animal behaviour have traditionally relied on classification of behavioural patterns and analyses of discrete behavioural categories. Today, technologies such as animal-attached tags enable novel approaches, facilitating the use of quantitative metrics to characterize behaviour. In the field of acoustic communication, researchers typically classify vocalizations and examine usage of call categories. Through case studies of bottlenose dolphin social interactions, we present here a novel tag-based complementary approach. We used high-resolution tag data to parameterize dolphin sounds and motion, and we applied continuously sampled parameters to examine how individual dolphins responded to conspecifics’ signals and moved while producing sounds. Activity intensity of senders and receivers changed with specific call parameters, matching our predictions and illustrating the value of our approach to test communicative roles of acoustic parameter changes. Parametric approaches can complement traditional methods for animal behaviour and facilitate research replication.

Multi-Tissue Methylation Clocks for Age and Sex Estimation in the Common Bottlenose Dolphin

Accurate identification of individual ages within wild bottlenose dolphins (Tursiops truncatus) is critical for determining population health and the development of population management strategies. As such, we analyzed DNA methylation (DNAm) patterns by applying a custom methylation array (HorvathMammalMethyl40) to both blood (n= 140) and skin samples (n= 87) from known age or approximate age (0–57 years) bottlenose dolphins. We present three bottlenose dolphin specific age estimation clocks using combined blood and skin [48 CpGs,R= 0.93, median absolute error (MAE) = 2.13 years], blood only (64 CpGs, R = 0.97, error = 1.46 years) and skin only (39 CpGs,R= 0.95, error = 2.53). We characterized individual cytosines that correlate with sex and age in dolphins and developed a sex estimator based on 71 CpGs that predicts the sex of any odontocete species with 99.5% accuracy. The presented epigenetic clocks are expected to be useful for conservation efforts and for determining if anthropogenic events affect aging rates in wild populations.

A field study of chemical senses in bottlenose dolphins and pilot whales.

For most marine vertebrates, chemical cues provide crucial information during navigation and foraging, but their use by cetaceans is still poorly understood. In contrast to baleen whales, toothed whales (odontocetes) are scarcely equipped for chemoreception: they lack the conventional anatomical structures (i.e., olfactory epithelium, nerves and bulbs) involved in olfaction and have reduced taste buds on the tongue. Several behavioral studies have however shown that captive dolphins can perceive chemical solutions, including odorants, in their oral cavity. To investigate whether odontocetes could use infochemicals in their foraging ecology, we implemented a behavioral response experiment in wild bottlenose dolphins and long-finned pilot whales. We tested dimethyl sulfide (DMS) as a potentially attractive stimulus since it is a chemical signature of highly productive marine areas, known to attract several marine predators including fishes and seabirds. We assessed cetacean responses to DMS exposure by analyzing their movements and surface behaviors recorded by onboard observers. In both species, results did not reveal any significant attraction or behavioral reaction toward DMS when compared to a control chemical stimulus, apart from a short-distance response in bottlenose dolphins. These results suggest that while odontocetes may perceive DMS in water, it apparently does not play a significant role in their foraging ecology. Testing potentially more attractive compounds such as prey extracts with the present method and analyzing surface, underwater and acoustic responses would provide further insights on odontocete feeding behavior. It would also provide valuable clues to studies on the anatomical structures involved in their chemosenses.

Lifetime stability of social traits in bottlenose dolphins

Behavioral phenotypic traits or “animal personalities” drive critical evolutionary processes such as fitness, disease and information spread. Yet the stability of behavioral traits, essential by definition, has rarely been measured over developmentally significant periods of time, limiting our understanding of how behavioral stability interacts with ontogeny. Based on 32 years of social behavioral data for 179 wild bottlenose dolphins, we show that social traits (associate number, time alone and in large groups) are stable from infancy to late adulthood. Multivariate analysis revealed strong relationships between these stable metrics within individuals, suggesting a complex behavioral syndrome comparable to human extraversion. Maternal effects (particularly vertical social learning) and sex-specific reproductive strategies are likely proximate and ultimate drivers for these patterns. We provide rare empirical evidence to demonstrate the persistence of social behavioral traits over decades in a non-human animal.

Elevated Calf Mortality and Long-Term Responses of Wild Bottlenose Dolphins to Extreme Climate Events: Impacts of Foraging Specialization and Provisioning

As demands for wildlife tourism increase, provisioning has become a popular means of providing up-close viewing to the public. At Monkey Mia, Shark Bay, Australia, up to five adult female Indo-Pacific bottlenose dolphins (Tursiops aduncus) visit a 100 m stretch of beach daily to receive fish handouts. In 2011, a severe marine heatwave (MHW) devastated seagrass and fish populations in Shark Bay. Offspring survival declined precipitously among seagrass specialists (dolphins that forage disproportionately in seagrass habitat). As all provisioned dolphins at the site are seagrass specialists, we examined how provisioned and non-provisioned seagrass specialists responded to the MHW. Using 27 years of data we compare habitat use, home range size, calf mortality, and predation risk between provisioned and non-provisioned females and their offspring before and after the MHW. Our results show that provisioned females have extremely small home ranges compared to non-provisioned females, a pattern attributable to their efforts to remain near the site of fish handouts. However, weaned offspring (juveniles) born to provisioned females who are not provisioned themselves also had much smaller home ranges, suggesting a persistent maternal effect on their behavior. After the MHW, adult females increased their use of seagrass habitats, but not their home range size. Provisioned females had significantlylowercalf mortality than non-provisioned females, a pattern most evident pre-MHW, and, in the first 5 years after the MHW (peri-MHW, 2011–2015), calf mortality did not significantly increase for either group. However, the ecosystem did not recover, and post-MHW (2016–2020), calf mortality was substantially higher, regardless of provisioning status. With few survivors, the impact of the MHW on juvenile mortality post-weaning is not known. However, over three decades, juvenile mortality among offspring of provisioned vs. non-provisioned females did not statistically differ. Thus, the survival benefits accrued to calves in the provisioned group likely cease after weaning. Finally, although shark attack rates on seagrass specialists did not change over time, elevated predation on calves cannot be ruled out as a cause of death post-MHW. We discuss our results as they relate to anthropogenic influences on dolphin behavioral plasticity and responses to extreme climate events.

To question of dystocia distribution and etiology in black sea bottlenose dolphins female

Pregnancy is the most important period in the life of cetaceans, including those kept in captivity, associated with the growth and development of the fetus. The timely diagnosis of pregnancy, establishment of its exact term, features of the course and the prevention of the onset of dystocia - difficult childbirth caused by the presence of abnormalities in the fetus or mother - are becoming more and more urgent. The most common cause of difficult labor is obstruction of the labor act due to fetal abnormalities with large fetuses or incorrect presentation. Difficulty in labor due to maternal pathology may result from the presence of a too narrow pelvis in the female, weak contraction of the uterine muscles, or insufficient dilatation of the cervix during childbirth. The authors studied the distribution and etiological factors of the onset of dystocia in female Black Sea bottlenose dolphins. One of the main indicators of good conditions for keeping wild animals, including dolphins, is the production of offspring, since stress and unsatisfactory conditions of keeping, feeding, etc. negatively affect the reproductive ability. Studies to clarify the causes of difficult childbirth in female Black Sea bottlenose dolphins showed that in the anamnesis 51-60% of females previously recorded and treated intestinal dysbiosis caused by increased gastric acidity or abnormal liver function due to damage to its cells during toxicosis. Research data have shown that microorganisms in the distal intestine of wild bottlenose dolphins are represented mainly by the same species that are found in other animals and humans. The largest numbers in feces were non-hemolytic bacteria from the E. coli group, lactic acid bacteria and clostridia. In captivity, including pregnant bottlenose dolphins, coliform bacteria, as well as staphylococci, clostridia, bifidobacteria, lactic acid bacteria, streptococci were detected in the rectum. The authors found that the possible reasons for the development of dysbiosis in pregnant Black Sea bottlenose dolphins females include increased stomach acidity, the development of toxicosis or the appearance of diseases leading to liver dysfunction.

Interactions between the imperiled West Indian manatee, Trichechus manatus, and mosquitoes (Diptera: Culicidae) in Everglades National Park, Florida, USA

Arthropod-borne viruses (arboviruses), including those vectored by mosquitoes, have recently been cited as potential emerging health threats to marine mammals. Despite the fully aquatic habits of cetaceans, immunologic exposure to arboviruses including West Nile virus and Eastern equine encephalitis virus has been detected in wild Atlantic bottlenose dolphins, and captive orcas have been killed by West Nile virus and St. Louis encephalitis virus. Currently, there is no evidence of direct interactions between mosquitoes and marine mammals in nature, and it remains unknown how wild cetaceans are exposed to mosquito-vectored pathogens. Here, we report the first evidence of direct interactions between an aquatic mammal, the West Indian manatee, a federally threatened species, and mosquitoes in nature. Observations of manatees in Everglades National Park, Florida, USA, indicate that mosquitoes of three genera, Aedes, Anopheles, and Culex are able to locate and land on surface-active manatees, and at minimum, penetrate and probe manatee epidermis with their mouthparts. Whether mosquitoes can successfully take a blood meal is not known; however, an arbovirus-infected mosquito can inoculate extravascular host tissues with virus-infected saliva during probing. These observations suggest that it is possible for marine mammals to be exposed to mosquito-vectored pathogens through direct interactions with mosquitoes.

The use of Unmanned Aerial Vehicles (UAVs) to sample the blow microbiome of small cetaceans.

Recent studies describe the use of UAVs in collecting blow samples from large whales to analyze the microbial and viral community in exhaled air. Unfortunately, attempts to collect blow from small cetaceans have not been successful due to their swimming and diving behavior. In order to overcome these limitations, in this study we investigated the application of a specific sampling tool attached to a UAV to analyze the blow from small cetaceans and their respiratory microbiome. Preliminary trials to set up the sampling tool were conducted on a group of 6 bottlenose dolphins (Tursiops truncatus) under human care, housed at Acquario di Genova, with approximately 1 meter distance between the blowing animal and the tool to obtain suitable samples. The same sampling kit, suspended via a 2 meter rope assembled on a waterproof UAV, flying 3 meters above the animals, was used to sample the blows of 5 wild bottlenose dolphins in the Gulf of Ambracia (Greece) and a sperm whale (Physeter macrocephalus) in the southern Tyrrhenian Sea (Italy), to investigate whether this experimental assembly also works for large whale sampling. In order to distinguish between blow-associated microbes and seawater microbes, we pooled 5 seawater samples from the same area where blow samples’ collection were carried out. The the respiratory microbiota was assessed by using the V3-V4 region of the 16S rRNA gene via Illumina Amplicon Sequencing. The pooled water samples contained more bacterial taxa than the blow samples of both wild animals and the sequenced dolphin maintained under human care. The composition of the bacterial community differed between the water samples and between the blow samples of wild cetaceans and that under human care, but these differences may have been mediated by different microbial communities between seawater and aquarium water. The sperm whale’s respiratory microbiome was more similar to the results obtained from wild bottlenose dolphins. Although the number of samples used in this study was limited and sampling and analyses were impaired by several limitations, the results are rather encouraging, as shown by the evident microbial differences between seawater and blow samples, confirmed also by the meta-analysis carried out comparing our results with those obtained in previous studies. Collecting exhaled air from small cetaceans using drones is a challenging process, both logistically and technically. The success in obtaining samples from small cetacean blow in this study in comparison to previous studies is likely due to the distance the sampling kit is suspended from the drone, which reduced the likelihood that the turbulence of the drone propeller interfered with successfully sampling blow, suggested as a factor leading to poor success in previous studies.

When personality matters: personality and social structure in wild bottlenose dolphins, Tursiops truncatus

There is increasing evidence that animal personality can affect many aspects of an individual's behaviour, life history and fitness. However, there have been few studies about the link between personality and social organization in the context of wild mammals in their own natural environments. This article reports on ecologically relevant data, linking experimental data from the wild to long-term social association data in a socially and cognitively complex mammal species (bottlenose dolphin, Tursiops truncatus). Here, I used behavioural data to describe personality differences between bottlenose dolphins and social network analysis to assess the relationship between personality and social structure. First, I measured the reaction of photo-identified individuals over time and across contexts as a trade-off between a novelty-seeking behaviour (boldness) and a novelty-averse behaviour (shyness). Second, I applied social network analysis to understand the link between the observed shy–bold continuum and social organization, while controlling for other factors that could contribute to affiliation. This study presents for the first time consistent individual differences in behavioural response to novelty, as a proxy for the shy–bold continuum, in wild bottlenose dolphins. Bold individuals had a central role in the social network with stronger associations than shy individuals, suggesting that bold individuals may play an important role in group cohesion, group stability and the spread of information through the network. Together, these findings provide insights into how a social network is structured by personality in wild bottlenose dolphins, with potential fitness consequences. Furthermore, this study provides additional evidence of the existence of social personalities in nonhuman animals and contributes to the understanding of the role of personality in determining the extent to which mammals associate with others.

Fine‐scale sociality reveals female–male affiliations and absence of male alliances in bottlenose dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland

AbstractKnowledge of social behavior at an individual level is central to our understanding of complex mammalian societies. In this study, we analyzed the fine‐scale sociality of wild bottlenose dolphins in the Shannon Estuary, Ireland, by examining associations between members of the whole population and between specific female and male dolphins. We carried out 51 boat‐based individual focal follows on 18 identifiable bottlenose dolphins over 90.8 hr (39 days) between 2014 and 2016. Additionally, we conducted 353 boat‐based surveys (with 607 sightings) between 2012 and 2015, and identified 121 distinct adult/juvenile dolphins. The mean group size of focal dolphin groups was 7.2 ± 4.1 (range = 1–20) and the mean fission‐fusion rate was 3.06 ± 1.35 changes/hr. The most frequent composition of within‐group affiliate pairs was female–male. Focal males spent more time with female nearest‐neighbors than male nearest‐neighbors (p = .013). Differences between female and male activity budgets were not strongly supported (p = .13). There was no evidence for male alliance formation in the Shannon Estuary population, and all of the known‐sex top‐ranked associates (7) of known males (n = 10) were females. This research reveals a distinct bottlenose dolphin society with female–male affiliations and an absence of male alliances.

Natural and anthropogenic drivers of foraging behaviour in bottlenose dolphins: Influence of shellfish aquaculture

Abstract In the coastal environment, marine mammals are exposed to one of the fastest growing food production sectors; namely, the shellfish farming industry. Identification of critical habitats, such as foraging grounds in highly human‐impacted areas, is essential to species conservation. Therefore, understanding the variables that influence a species' foraging behaviour is important for their conservation, especially for long‐lived mammals such as cetaceans. The aims of this study were (a) to identify and quantify the environmental and anthropogenic drivers of wild bottlenose dolphin (Tursiops truncatus) foraging behaviour, and (b) to investigate whether the shellfish farming industry influences the behaviour of this species. Behavioural observations were conducted along the north‐western coast of Spain, an area affected by intensive human activities, particularly the shellfish aquaculture industry. A multi‐modelling approach highlighted the importance of shellfish farm areas as a foraging ground for bottlenose dolphins. Dolphins were predicted to be more likely found foraging inside shellfish farm areas than outside (57% vs. 43%). Variability in bottlenose dolphin behaviour is likely a result of the interactions of environmental and anthropogenic drivers with prey availability and the physiological needs of the dolphins. Although shellfish farm areas provide high prey density for dolphins, they can also pose threats in a number of ways (i.e. collisions with vessels, entanglement with ropes, habitat loss, noise and water pollution). From a conservation perspective, aquaculture management should consider the presence of dolphins foraging and minimize the associated risks that this industry may pose to these coastal cetaceans.

Every scar has a story: age and sex-specific conflict rates in wild bottlenose dolphins

Social living brings competition over mates, relationships, and resources, which can translate to direct conflict. In dolphins, tooth rakes received from conspecifics are highly visible and reliable indicators of conflict. New rakes indicate recent conflicts while healed rakes suggest older instances of conflict. Here, we investigate the healing time of conspecific tooth rakes in wild bottlenose dolphins, create a demographic profile of injury risk in the population, and consider the implications for age- and sex-specific aggression. Using photographic and scarring data from the Shark Bay Dolphin Research Project spanning 31 years (N = 269 tooth rakes), healing time was analyzed using a subset of sequential photographs of the same body part over 1–12 years (N = 70 tooth rakes). Ninety percent of tooth rakes in males and 95% of tooth rakes in females were no longer visible within 400 days, with males taking longer to heal than females. Using the full sample, we examined age and sex-effects on the prevalence of new tooth rakes. A negative quadratic model best fitted tooth rake prevalence patterns from ages 0 to 13 and a positive linear regression best fitted tooth rake prevalence patterns from ages 13 to 30. Both analyses revealed significant age and sex effects, where males had more tooth rakes than females. Age differences in tooth rake prevalence may be attributed to life history events such as sexual maturity onset, male-male competition and alliance formation, and sexual coercion. These results contribute to our understanding of the relationship between social conflict and life history strategies in long-lived mammals.Significance statementIn wild dolphins, tooth rake scars indicate conspecific conflict, and the timing of such conflict clarifies the challenges faced during each life history stage. Based on > 30 years of longitudinal data, we created a demographic profile of new tooth rakes to identify patterns of age- and sex-specific received aggression. Males had more tooth rakes than females, but females healed faster than males. Juveniles had the greatest tooth rake prevalence compared to calves and adults, suggesting greater exposure to some level of conflict. Differences in patterns of tooth rake prevalence and aggression have implications regarding the costs of sexual maturity and reproduction in dolphins. To our knowledge, no study has examined the rate of received aggression across the lifespan. Our methods can be applied to other studies of wild marine mammals, where agonistic encounters are difficult to observe, but wounds are apparent.

Calf age and sex affect maternal diving behaviour in Shark Bay bottlenose dolphins

Maternal care varies across taxa from brief, minimal care to long-term, intensive care. Mammalian mothers provide extensive and energetically expensive care by definition through pregnancy and lactation, which can extend for years, resulting in behavioural trade-offs between resource acquisition and direct care. In marine environments, mammalian mothers face unique challenges, such as the inability to cache or den their offspring while diving for prey. Dolphin newborns are precocious, accomplishing shallow dives in the first few weeks of life, however, fully mature diving and breath-holding capabilities take years to develop. Consequently, mothers are faced with a trade-off between diving and foraging or remaining close to and protecting their calves at the surface. Here we examined this trade-off, specifically by investigating whether mothers change their dive durations, especially during foraging, as a function of calf age. We used a longitudinal (1988–2014) data set on wild bottlenose dolphins, Tursiops aduncus, in Shark Bay, Western Australia, which included 27 388 dive bouts from mothers (N = 26) and calves (N = 41). Our results show that maternal diving behaviour changes in response to calf age and sex. While both male and female calves increased their dive durations with age as expected, mothers were more likely to adjust their diving behaviour to accommodate female but not male calves, especially when daughters were in close proximity. This is consistent with findings that vertical social learning is more critical for daughters than for sons, and may reflect the sex-specific foraging and social tactics of the males and females more generally.

Bottlenose dolphin (Tursiops truncatus) social structure in the Shannon Estuary, Ireland, is distinguished by age‐ and area‐related associations

AbstractSocial and network analyses that incorporate information on individuals within a population enhance our knowledge of complex species. In this study, the social structure of wild bottlenose dolphins in the Shannon Estuary, Ireland, was analyzed by examining the dynamics of the whole population and then of individuals classed by sex, age, and area. One hundred and twenty‐one dolphins were identified during 522 sightings between 2012 and 2015. The mean half‐weight association index (HWI) of the population was 0.07 ± 0.02. The highest HWIs for individuals of known sex were for female‐male pairs. Mean within‐class HWI was significantly higher than mean between‐class HWI for both age and area classes. Ordinations and sociograms were used to visualize social networks. Permutation tests revealed nonrandom associations for the population overall and both between and within classes. Temporal analyses showed associations persisting for &gt;1,000 d. The whole population's best fit model was for two levels of casual acquaintances. Movement analyses demonstrated the use of the inner estuary by only 25% of the population revealing a potential community division by area. The difference between mean HWI when socializing (0.09 ± 0.03) compared to foraging (0.06 ± 0.03) was significant. These results highlight the importance of localized research, reflecting the complexity found in bottlenose dolphin societies globally.

Mating in a bisexually philopatric society: bottlenose dolphin females associate with adult males but not adult sons during estrous

In fission-fusion societies, group size and composition change dynamically, reflecting social preferences and pressures. Most notably during reproduction, intersexual group dynamics reflect a balance between female choice for optimal mates and male competition for mating access. In systems where males and females remain in their natal area for life (bisexual philopatry), females can reduce the risk of incest by avoiding mating or associating with male kin. Shark Bay bottlenose dolphins (Tursiops aduncus) live in fission-fusion societies that enable them to exercise age, sex, and kin association biases. To determine how the balance between female choice and male competition is achieved, we examined adult female association with juvenile and adult males, including sons during female receptive periods, using 30 years of longitudinal data. Adult females demonstrated an increase in adult male association just prior to known conceptions, while juvenile male association consistently remained low. A decline in male association post-conception suggests that one or both sexes detect pregnancy early on. When we examined female association with juvenile and adult sons, a distinct pattern emerged. Adult females preferentially associated with sons compared to non-sons of the same age class post-weaning. Strikingly, females rarely associated with their adult sons when cycling. Our results suggest that (1) adult males either out-compete juvenile males in gaining access to fertile females or females prefer adult to juvenile males and (2) females mitigate the risk of close inbreeding by reducing association with sons when cycling. No study has investigated behavioral strategies for reducing close inbreeding in bisexually philopatric, fluid mammal societies outside of humans. Using over 30 years of longitudinal data, we document how association dynamics change with female reproductive state. Post-weaning, mothers and sons associate, but almost never during conceptive periods. Adult male–female association is frequent during estrous, with a sharp decline after conception. Our study provides evidence for long-term kin recognition and detection of both estrous and early pregnancy among wild bottlenose dolphins. These findings have implications for the evolution of bisexual philopatry, fission-fusion dynamics, and infanticide—or lack thereof—in mammals.

The reliability of pigment pattern‐based identification of wild bottlenose dolphins

AbstractLong‐term studies often rely on natural markings for individual identification across time. The primary method for identification in small cetaceans relies on dorsal fin shape, scars, and other natural markings. However, dorsal fin markings can vary substantially over time and the dorsal fin can become unrecognizable after an encounter with a boat or shark. Although dorsal fins have the advantage in that they always break the water surface when the cetacean breathes, other physical features, such as body scars and pigmentation patterns can supplement. The goal of this study was to explore the use of dorso‐lateral pigment patterns to identify wild bottlenose dolphins. We employed photographic pigment matching tests to determine if pigmentation patterns showed (1) longitudinal consistency and (2) bilateral symmetry using a 30 yr photographic database of bottlenose dolphins (Tursiops aduncus). We compared experienced dolphin researchers and inexperienced undergraduate student subjects in their ability to accurately match images. Both experienced and inexperienced subjects correctly matched dolphin individuals at a rate significantly above chance, even though they only had 10 s to make the match. These results demonstrate that pigment patterns can be used to reliably identify individual wild bottlenose dolphins, and likely other small cetacean species at other sites.