Cetaceans are important ecosystem sentinels but face growing threats from major disease-related mortality events expected to intensify under climate change. Because both environmental factors and demographics influence health and disease risk, understanding these relationships is essential for effective management. Direct health assessments are challenging in cetaceans, but skin lesions can indicate active infection and tooth-rake marks reflect social stressors that increase transmission risk. Yet, traditional photographic analysis of these indicators is inefficient, creating processing bottlenecks that limit timely evaluation of population health. To address this gap, we applied machine learning to rapidly assess lesions and rake marks in Tamanend's bottlenose dolphins (Tursiops erebennus) photographed in the Chesapeake Bay, a known hotspot for disease-related die-offs. This represents the first analysis of environmental and demographic contributions to dolphin stressors in this region. We found significant negative relationships between lesion prevalence and both temperature and salinity for some lesion types. We find tooth rakes to be positive predictors of lesions, and adult males have the highest rake mark coverage. These patterns suggest dolphins in colder, fresher waters may face elevated disease risk, while adult males may be particularly vulnerable to behavioral stress and related health consequences. Our findings are consistent with prior studies, lending validity to our machine learning models, while also revealing novel patterns of vulnerability in this threatened population. More broadly, our approach demonstrates the use of automated image analysis to enable timely, non-invasive assessments of potential health indicators across cetacean populations in an era of rapid global change.

Individual variation in behaviour is the substrate for selection. In bottlenose dolphins, individuals have been shown to have repeatable behavioural strategies that persist over decades. To what extent might such persistent individual differences impact maternal care (i.e. the presence of maternal style), or is care instead determined more by calf characteristics? Based on 40+ years of study of Indo-Pacific bottlenose dolphins, Tursiops aduncus, in Shark Bay, Australia, we investigated the repeatability and demographic drivers of maternal care and their impact on postweaning survival. Using focal follow data (N = 428 follows) of 22 mothers of 68 calves, we examined maternal behaviour when calves were <2 years old. Behavioural metrics included infant position, a type of mother–infant contact and a ‘carrying’ behaviour used as a proxy for direct maternal care, time spent together (within 10 m) and behaviour while together. Maternal care metrics were not individually repeatable; rather, calf characteristics such as age and condition were more important in determining the amount of maternal care. Calves that did not survive to age 4 (average age of weaning in this population) and those who weaned later than average received more direct maternal care than those who survived, suggesting mothers try to compensate for calf condition with increased care. In summary, unlike altricial mammals where mothers have direct control over offspring (by carrying and caching), patterns of maternal care are largely driven by the attributes of the calf in this precocial species.

Infectious diseases have detrimental impacts across wildlife taxa. Despite this, we often lack information on the complex spatial and contact structures of host populations, reducing our ability to understand disease spread and our preparedness for epidemic response. This is also prevalent in the marine environment, where rapid habitat changes due to anthropogenic disturbances and human-induced climate change are heightening the vulnerability of marine species to disease. Recognizing these risks, we leveraged a collated dataset to establish a data-driven epidemiological metapopulation model for Tamanend’s bottlenose dolphins ( Tursiops erebennus ), whose populations are periodically impacted by deadly respiratory disease. We found their spatial distribution and contact is heterogeneous throughout their habitat and by ecotype, which explains differences in past infection burdens. With our metapopulation approach, we demonstrate spatial hotspots for epidemic risk during migratory seasons and that populations in some central estuaries would be the most effective sentinels for disease surveillance. These mathematical models provide a generalizable, non-invasive tool that takes advantage of routinely collected wildlife data to mechanistically understand disease transmission and inform disease surveillance tactics. Our findings highlight the heterogeneities that play a crucial role in shaping the impacts of infectious diseases, and how a data-driven understanding of these mechanisms enhances epidemic preparedness.

Although tool use offers obvious benefits to the user, the role of costs in the spread of tool use has received scant attention. Sponge tool use is a foraging technique restricted to a small subpopulation of bottlenose dolphins (Tursiops aduncus) in Shark Bay, Australia, that carry basket sponges on their beaks to probe the seafloor and flush out camouflaged fish, widening the search area and protecting the beak from abrasion. While most instances of animal tool use extend the phenotype, we hypothesized that sponges interfere with echolocation, particularly reception of echoes along the lower jaw. To evaluate how echolocation signals change while travelling through sponge tissue, we simulated echolocation using finite-element analysis based on digital models of sponge species (Echinodictyum mesenterinum and Ircinia spp.). We find that acoustic properties of the echolocation signal are changed in the presence of Ircinia spp. and, to a lesser extent, E. mesenterinum. Given distortions vary with each sponge, dolphins must adaptively and flexibly compensate during neural signal processing. This explains why sponging takes so long to learn, is strictly vertically transmitted and does not spread to others despite close association with tool users. Taken together, these findings provide a compelling look at the underlying intrinsic and extrinsic forces shaping tool use in wild populations.

Darwin ascribed fitness to individuals with a “better chance of surviving and propagating their kind”1. Subsequently, the search for the genetic basis of fitness focused on traits of the generation that had been genotyped. However, there is only scant, indirect evidence for genetic variation conferring transgenerational fitness effects to subsequent generations2-5. Specifically, there is no direct evidence for a link between parental genetic variation and offspring fitness in long-lived, natural populations. Here we show transgenerational fitness effects mediated by adaptive genetic variation of the major histocompatibility complex (MHC) in a natural population of bottlenose dolphins. Our study, spanning nearly four decades of research (1984­2022), revealed that offspring of MHC-heterozygous mothers were twice as likely to survive. The mother’s age and MHC-heterozygosity were strong predictors of offspring viability. In contrast, we found no association between neutral genetic diversity and fitness. Interestingly, MHC-heterozygous females were less sociable, perhaps an indirect effect of them being more successful mothers that prioritize offspring investment over social bonds—in contrast to other social mammals that rely on female relationships to mediate fitness6. To our knowledge, this is the first study that offers empirical evidence for MHC diversity conferring a fitness advantage across generations. This is in line with theorized, but rarely tested expectations for MHC-dependent mate choice4. Our study also underscores the crucial role of long-term studies7 in revealing the genetic basis of fitness in long-lived, natural populations.

Anthropogenic global change is occurring at alarming rates, leading to increased urgency in the ability to monitor wildlife health in real time. Monitoring sentinel marine species, such as bottlenose dolphins, is particularly important due to extensive anthropogenic modifications to their habitats. The most common non-invasive method of monitoring cetacean health is documentation of skin lesions, often associated with poor health or disease, but the current methodology is inefficient and imprecise. Recent advancements in technology, such as machine learning, can provide researchers with more efficient ecological monitoring methods to address health questions at both the population and the individual levels. Our work develops a machine learning model to classify skin lesions on the understudied Tamanend's bottlenose dolphins (Tursiops erebennus) of the Chesapeake Bay, using manual estimates of lesion presence in photographs. We assess the model's performance and find that our best model performs with a high mean average precision (65.6 %-86.8 %), and generally increased accuracy with improved photo quality. We also demonstrate the model's ability to address ecological questions across scales by generating model-based estimates of lesion prevalence and testing the effect of gregariousness on health status. At the population level, our model accurately estimates a prevalence of 72.1 % spot and 27.3% fringe ring lesions, with a slight underprediction compared to manual estimates (82.2 % and 32.1 %). On the other hand, we find that individual-level analyses from the model predictions may be more sensitive to data quality, and thus, some individual scale questions may not be feasible to address if data quality is inconsistent. Manually, we do find that lesion presence in individuals suggests a positive relationship between lesion presence and gregariousness. This work demonstrates that object detection models on photographic data are reasonably successful, highly efficient, and provide initial estimates on the health status of understudied populations of bottlenose dolphins.

Infectious diseases cause mass mortalities in wildlife populations globally, but the impact of host sociality on the spread of pathogens is often unknown. While host behaviors drive pathogen transmission, these behaviors vary individually which impacts both individual- and population-level disease outcomes. For example, delphinid species are regularly affected by serious respiratory diseases, but a lack of social behavior data means the structure of vulnerability in these ecosystem sentinels is poorly understood. To assess the role of variable social behavior on disease risk empirically, we collected behavioral data from two wild bottlenose dolphin populations (Tursiops spp.), developed network models that synthesize transmission contacts, and used an epidemiological model to predict disease consequences. We find that contacts are highly structured by age and sex, and that individuals preferentially contact others in their own demographic group. These patterns, in turn, drive heterogeneity in infection risk, which we support using empirical data from a past disease outbreak. Our work characterizes the impact of social dynamics on infectious disease risk, which can inform the structure of vulnerability for future epizootics across diverse delphinid species.

Recent work has unearthed strong relationships between aging and average sociability. Clear patterns of decreases in average sociability are observed across taxa, many of these are sex-specific. Individuals, however, generally deviate from population averages, and discounting individual variance in behaviour could disguise mechanisms of adaptation, selection, and developmental stability. Here, we leverage four decades of behavioural data on a population of Indo-Pacific bottlenose dolphins to bring new perspectives on social aging by exploring individual differences in sociability (repeatability, i.e. personality), its variance (predictability), and how sociability changes (plasticity) and its variance changes (malleability) with age. Novel analytical methods reveal a multidimensional response: individual sociability (group size) changes significantly throughout life, both in average response and underlying variance. Sociability increases for the first two decades of life, then declines with age, a trend more pronounced with males. Predictability of individual sociability, however, increases throughout life, indicating that individual social preferences strengthen (despite oscillations) with age. These patterns suggest that individuals develop social competence, defined as accruing social information via experience, presumably optimising their social relationships for a net fitness benefit. These findings provide novel insights into sex-specific social aging and illustrate how studying variance can reveal processes of competence, selection, and adaptation.

Social learning, information transmission and culture play vital roles in the lives of social animals, influencing their survival, reproduction and ability to adapt to changing environments. However, the effect of anthropogenic disturbances on these processes is poorly understood in free-living animals. To investigate the impact of anthropogenic disturbance on social learning and information transmission, we simulated individual removal from contact networks derived from long-term behavioural datasets. We simulate the effects of individual removal on network efficiency and social learning for three group-living species-yellow baboons (Papio cynocephalus), African savanna elephants (Loxodonta africana) and Indo-Pacific bottlenose dolphins (Tursiops aduncus). We reveal how removals of key network positions reduce network efficiency. However, groups with high levels of innovation may cope with changing social network structures. These findings highlight the importance of protecting key individuals to preserve group structure and the role of innovation in possibly mitigating the fitness costs of removals. Identifying and safeguarding individuals that drive innovation can reduce a group's susceptibility to anthropogenic threats and promote cultural resilience in social animals in a changing world. These emerging trends contribute to a growing understanding of the role of conservation interventions in protecting critical individuals in group-living animals.This article is part of the theme issue 'Animal culture: conservation in a changing world'.

Theory predicts that high population density leads to more strongly connected spatial and social networks, but how local density drives individuals' positions within their networks is unclear. This gap reduces our ability to understand and predict density-dependent processes. Here we show that density drives greater network connectedness at the scale of individuals within wild animal populations. Across 36 datasets of spatial and social behaviour in >58,000 individual animals, spanning 30 species of fish, reptiles, birds, mammals and insects, 80% of systems exhibit strong positive relationships between local density and network centrality. However, >80% of relationships are nonlinear and 75% are shallower at higher values, indicating saturating trends that probably emerge as a result of demographic and behavioural processes that counteract density's effects. These are stronger and less saturating in spatial compared with social networks, as individuals become disproportionately spatially connected rather than socially connected at higher densities. Consequently, ecological processes that depend on spatial connections are probably more density dependent than those involving social interactions. These findings suggest fundamental scaling rules governing animal social dynamics, which could help to predict network structures in novel systems.

Cetaceans (whales and dolphins) are important ecosystem sentinels but face growing threats from major disease-related mortality events expected to intensify under climate change. Because both environmental factors (temperature, salinity) and demographics (age, sex) influence health and disease risk, understanding these relationships is essential for effective management. Direct health assessments are challenging in cetaceans, but skin lesions can indicate active infection and tooth-rake marks reflect social stressors that increase transmission risk. Yet, traditional photographic analysis of these indicators is inefficient, creating processing bottlenecks that limit timely evaluation of population health. To address this gap, we applied machine learning to rapidly assess lesions and rake marks in Tamanend’s bottlenose dolphins (Tursiops erebennus) photographed in the Chesapeake Bay, a known hotspot for disease-related die-offs. This represents the first analysis of environmental and demographic contributions to dolphin health in this region. We found significant negative relationships between lesion prevalence and both temperature and salinity for some lesion types. Adult males also showed higher rake mark coverage than adult females and calves. These patterns suggest dolphins in colder, fresher waters may face elevated disease risk, while adult males may be particularly vulnerable to behavioral stress and related health consequences. Our findings are consistent with prior studies, lending validity to our machine learning models, while also revealing novel patterns of calf and male vulnerability in this threatened population. More broadly, our approach demonstrates the potential of automated image analysis to enable timely, non-invasive health assessments across cetacean populations in an era of rapid global change. ### Competing Interest Statement The authors have declared no competing interest. Morris Animal Foundation, https://ror.org/05pg13f04, D24ZO-425 Georgetown University, https://ror.org/05vzafd60 National Geographic Society, WW-022ER-17

Because climate change and the biodiversity crisis are driven by human actions, determining psychological mechanisms underpinning support for environmental action is an urgent priority. Here, we experimentally tested for mechanisms promoting conservation-related motivation and behavior toward a flagship species, wild Tamanend's bottlenose dolphins. Following evidence that empathy increases prosocial motivations and behavior, and that the ability to identify individual humans promotes empathy, we tested whether this relationship applied to the ability to identify individual dolphins. Participants identified dolphins from their dorsal fins at above chance levels, and better individuation correlated with higher empathy for dolphins and higher willingness to pledge environmental behaviors. Pairing a narrative with an image of an injured dolphin leads to higher donations relative to a narrative alone. Our novel finding that the ability to individually identify dolphins relates to empathy and conservation-related behavior suggests pathways for strengthening environmental attitudes and behavior.

Infectious respiratory diseases have detrimental impacts across wildlife taxa, particularly in marine species. Despite this vulnerability, we lack information on the complex spatial and contact structures of marine populations which reduces our ability to understand disease spread and our preparedness for epidemic response. We leveraged a collated dataset to establish the first data-driven epidemiological model on a cetacean species, the Tamanends bottlenose dolphin (Tursiops erebennus), whose populations are periodically impacted by deadly respiratory disease in the northwest Atlantic. We found their spatial distribution and contact is heterogeneous along the coastline and varies by ecotype, which explains differences in infection burdens observed in past outbreaks. We also determined that outbreaks beginning in northern parts of their habitat during migratory seasons have the highest epidemic risk and that dolphins in North Carolina estuaries would be the best sentinels for disease surveillance. Our mathematical model provides a generalizable, non-invasive tool that takes advantage of routinely collected marine mammal data to mechanistically understand disease transmission and inform disease surveillance tactics for marine sentinels. Our findings highlight the heterogeneities that play a crucial role in shaping the impacts of infectious diseases in wildlife, and how a data-driven understanding of these mechanisms can enhance epidemic preparedness. ### Competing Interest Statement The authors have declared no competing interest.

High population density should drive individuals to more frequently share space and interact, producing better-connected spatial and social networks. Despite this widely-held assumption, it remains unconfirmed how local density generally drives individuals' positions within wild animal networks. We analysed 34 datasets of simultaneous spatial and social behaviour in >55,000 individual animals, spanning 28 species of fish, reptiles, birds, mammals, and insects. >80% of systems exhibited strongly positive relationships between local density and network centrality, providing broad empirical evidence that local density increases connectedness at the individual level. However, >75% of density-connectedness relationships were nonlinear, and density's importance declined at higher values in >70% of systems, signifying saturating effects. Density's effect was much stronger and less saturating for spatial than social networks, suggesting population density drives individuals to become disproportionately spatially connected rather than socially. These findings reveal fundamental trends underlying societal structuring, with widespread behavioural, ecological, and evolutionary implications. ### Competing Interest Statement The authors have declared no competing interest.

Assessing trends in population abundance and demographics is crucial for managing long-lived and slow-reproducing species. Obtaining demographic data, and age-structure information, is challenging, notably for cetaceans. To address this, we combined Unoccupied Aerial System (UAS; drone) photogrammetry data with long-term (>20 years) photo identification data to assess the age-structure of the critically endangered sub-population of common bottlenose dolphins (Tursiops truncatus) of the Gulf of Ambracia, Greece. We compared our findings with two extensively studied non-endangered bottlenose dolphin populations (T. aduncus in Shark Bay, Australia, and T. truncatus in Sarasota Bay, USA). Using a log-linear model, we estimated the total body lengths (TL) of 160 known-aged dolphins between 2021 and 2023 from blowhole-to-dorsal-fin distance (BHDF) measurements collected during surfacing. Subsequently, we tested four growth models to establish an age-length growth curve. We assessed the sub-population's age-structure using three methods: (1) UAS-derived TL estimates, (2) age-length growth curve and (3) long-term monitoring data (i.e. actual age-structure). UAS-measured TL (247.6 +/- 32.2 cm) and UAS-estimated TL (246.0 +/- 34.7 cm) of the Greek sub-population showed no differences. The Richards Growth model suggested an asymptotic length of 258.5 cm. In Greece, resulting age-structure estimates across the three methods revealed no significant differences (P > 0.1). The Gulf of Ambracia and Shark Bay populations shared similar age-structures, while Sarasota had higher proportions of 2-10 year-olds and lower proportions of 10+ year-olds. All populations had a comparable proportion of 0-2 year-olds (similar to 14%), indicating a similar reproductive rate. Our findings suggest stability in the Greek sub-population; however, additional monitoring of reproductive parameters is essential before concluding its status. We demonstrated the effectiveness of UAS-photogrammetry in rapidly quantifying population age-structure, including scenarios with limited or no demographic data. This technique shows promise for enhancing precision, timeliness, cost-effectiveness and efficiency in population monitoring and informing timely conservation management decisions.

The quantity and quality of individual social relationships is a fundamental feature of social structure for group-living species. In many species, individuals preferentially associate with close relatives, which can amplify social benefits through inclusive fitness. Reproductive variation, dispersal and other factors may nevertheless impact relative kin availability, especially for species with slow life histories. As such, variation in family size can affect the social integration of the individual. Here, we investigated the effects of family size on female sociality in a population of Indo-Pacific bottlenose dolphins, Tursiops aduncus, in Shark Bay, Australia. This population exhibits high fission–fusion dynamics, with females varying widely in gregariousness and both sexes remaining philopatric, providing females with both matrilineal and nonmatrilineal kin as potential associates. We used genetic relatedness data obtained from a large single nucleotide polymorphism (SNP) panel and a spatially explicit null model to measure females' propensities to form affiliations with both related and unrelated individuals. We found that females had strong social preferences for matrilineal close (first, second and third degree) kin, but also significant preferences for nonmatrilineal close and more distant kin compared to unrelated individuals. Despite these preferences, we found only small effects of kin availability on individual social position. Stronger and more consistent effects were attributable to individual foraging ecology, although much of the variation remains unexplained. Overall, our models suggest that while female dolphins have strong kin preferences, their social connectivity is not determined by family size; rather, individual foraging strategies and high fission–fusion dynamics enable a diverse repertoire of social strategies to coexist within a population.

AbstractInfanticide by adult males is a striking example of sexual conflict; males can increase their reproductive success by killing an unrelated infant and accelerating the mother’s return to breeding condition. Reports of infanticide in cetaceans have quadrupled in the past decade, and infanticide has now been documented in six species of toothed whale, including multiple populations of common bottlenose dolphins (Tursiops truncatus). Evidence of infanticide in these species is consistent with the sexual selection hypothesis; perpetrators are predominantly adult males and targets are neonates. Toothed whales have long lactation periods that suppress estrus, making infanticide potentially adaptive for adult males. However, it remains unclear if infanticidal males are likely to sire the mother’s subsequent offspring. Here, we provide an overview of infanticide in cetaceans, evaluate the evidence for the sexual selection hypothesis, and propose a framework to predict infanticide risk in this clade. Toothed whales do not typically have dominance hierarchies, stable social groups, or monopolizable mating opportunities, all hallmarks of infanticide risk in terrestrial species. Instead, we hypothesize that infanticide risk in toothed whales is modulated by encounter rates with unfamiliar males.

Dolphin morbillivirus has caused mass mortalities in dolphin populations globally. Given their role as ecosystem sentinels, mass mortalities among these populations can be detrimental. Morbillivirus is transmitted through respiratory droplets and occurs when dolphins breathe synchronously, a variable social behavior. To assess the role of variable social behavior on disease risk empirically, we collected behavioral data from wild bottlenose dolphins ( Tursiops erebennus ), develop network models that synthesize transmission contacts, and use an epidemiological model to predict disease consequences. We find that juveniles have more contacts than adults, adult males have more contacts than adult females, and that individuals preferentially contact others in their own demographic group. These patterns translate to higher infection risk for juveniles and adult males, which we validate using data from a morbillivirus outbreak. Our work characterizes the impact of bottlenose dolphin social dynamics on infectious disease risk and informs the structure of vulnerability for future epizootics.### Competing Interest StatementThe authors have declared no competing interest.

Barnacles can reveal much about the physiology, health, and spatial ecology of their cetacean hosts. Here, we examine how temperature and hydrodynamic factors impact presence of Xenobalanus globicipitis, a pseudo-stalked barnacle that attaches exclusively to cetaceans. We hypothesized that temperature is a key environmental factor (i.e., water temperature) and physiological factor, in that X. globicipitis prefers the warmest skin temperature for attachment, possibly as a mechanism for survival in colder waters. First, we demonstrate a global relationship between spatial ecology of host species and presence of X. globicipitis. Notably, X. globicipitis is absent in the four species occupying waters with the lowest sea surface temperature (SST) year-round, but present in migratory species that likely acquire the barnacle in waters with higher SST. Second, barnacle attachment location on common bottlenose dolphin (Tursiops truncatus) dorsal fins corresponds with fin temperature and hydrodynamics. Although body temperature may influence attachment location on the body of the animal, hydrodynamic forces, as previously proposed, determine how well barnacles can remain attached during the adult stage. X. globicipitis prevalence likely provides important bioindicator, ecological, and physiological information about its host. As parasitic infestation has some cost, these results have implications for cetacean health in warming seas.