American Journal of Primatology

Nonhuman primates (NHP) are crucial models of human health and disease and offer the opportunity to bridge the gap between basic research and the clinic. Given the ethical considerations, high costs, and logistical constraints associated with NHP studies, careful planning is essential to maximize scientific rigor while minimizing animal use. Statistical power calculations, to determine optimal sample size, require knowing the expected number of animals at each timepoint, a challenge for longitudinal studies that must account for natural deaths or disease during a study. Here, we leveraged data from a recent study detailing NHP life- and healthspans to develop a web-based NHP study design tool, available at midas.wakehealth.edu. For 11 NHP species relevant to biomedical research, users can provide study details to generate estimates of sample counts based on natural healthspan trajectories. We envision this tool being used by colony managers and investigators for both study design and monitoring colony health over the course of a study.

Primates are central to both human evolutionary research and ecosystem functioning, serving as seed dispersers, predators, pollinators, and prey. Despite their value to human and ecosystem science, global primate populations continue to decline, with [~]65% of species currently threatened with extinction. Conservation biology increasingly recognises that survival depends not only on protecting habitats and populations, but also on safeguarding the microbial communities that underpin host health, nutrition, and resilience. The gut bacterial microbiome plays a critical role in digestion, immune function, and adaptation to environmental change, making it an important dimension of primate conservation. Here, we systematically and quantitatively assessed the taxonomic and geographic coverage of primate gut bacterial microbiome research to identify key knowledge gaps relevant to primate conservation. Between 2001 and 2025, 261 articles were published across 100 journals. While taxonomic coverage is high at the family level, it declines substantially at the finer taxonomic scales. Currently, [~]34.5% of species have been studied, leaving gut bacterial biodiversity undocumented for 344 species. Moreover, approximately one-third of studied species have exclusively been studied in captivity, limiting insights into natural microbiome variation and reducing the conservation relevance of these findings. Geographic biases further hinder conservation applications, with megadiverse countries such as Brazil, the Democratic Republic of Congo, and Indonesia underrepresented. In addition, study methodology and reporting standards remain inconsistent. To address these challenges, a framework for the standardised reporting of a minimum set of data for primate gut bacterial microbiome research is included in this review. Adoption of this framework will improve transparency, comparability, and data accessibility, thereby enhancing the utility of microbiome research for primate conservation. By integrating microbial ecology into conservation biology, we highlight the microbiome as a potential critical frontier for safeguarding primate health, evolutionary potential, and long-term survival.

Humans are widely regarded as unusually slow to develop, exhibiting prolonged childhood and extended dependence on caregivers. However, this view is based primarily on comparisons with other primates, leaving unresolved whether humans remain distinctive within the broader diversity of mammals. We addressed this question by situating human development in a comparative framework using gestation length, weaning age, and age at sexual maturity for both sexes across 462 mammalian species representing 25 orders. Each trait was examined both as an absolute value and as a proportion of the longest verified captive lifespan. In absolute terms, human developmental traits fell within the upper range of mammalian variation. When expressed relative to lifespan, however, gestation shifted toward the lower end of the distribution, whereas weaning age and sexual maturity occupied intermediate positions, indicating that human developmental timing largely follows general mammalian scaling patterns rather than representing a pronounced outlier. These findings suggest that key features of human dependency are better understood as extensions of broader evolutionary trends than as uniquely human life-history characteristics.

Across different modalities, signals play a core role in attracting mates and influencing mating success. In several non-human primate species, females produce calls during mating that are thought to promote male competition over receptive females. The extent to which social system characteristics modulate the function of copulation calls remains less clear. We studied copulation calls in wild Guinea baboons (Papio papio), who live in a multilevel society structured around units in which females associate and mate almost exclusively with a single male. We hypothesised that females use copulation calls as an indirect form of mate competition, with competition increasing in larger units. In addition, we hypothesised that females are more likely to mate again after calling. We analysed 6116 copulations between 2014 and 2025, involving 99 reproductively active females and 78 subadult and adult males. Females produced copulation calls in 72.7% of copulations, with large inter-individual variation. Neither unit size nor its interaction with the female's swelling size or the presence of simultaneously receptive females affected the probability of calling. A survival analysis with a subset of the data (2353 copulations) revealed no effect of calling on the latency to the next mating. Our results render the hypothesis that female Guinea baboons use calls in indirect mate competition unlikely. Yet, the probability of calling varied with sexual swelling size, suggesting that calls signal female fertility. Possibly, Guinea baboon copulation calls represent an evolutionary remnant, no longer under selective pressure, and can be considered index signals of female fertility.

Early life adversity (ELA) causes lasting psychological and behavioral consequences in humans, with parallel stress and fear responses observed in captive animals. How naturally occurring ELA shapes behavior in non-captive animals remains poorly understood. Investigating these effects across socioecological environments is important for identifying the evolutionary pressures shaping early life sensitivities, and determining whether these behavioral syndromes have deep evolutionary roots. Here, we tested the effects of eight forms of ELA on adult behavior using a large dataset (N=313 males, 346 females) from a free-ranging population of rhesus macaques (Macaca mulatta). We measured adult behaviors indicative of stress and the tenor of social interactions, including agonism, vigilance, self-directed behaviors, and affiliation. Individuals exposed to more ELA received more aggression and less grooming, were more submissive, and were less vigilant. While high status buffered the effects of ELA on grooming, it amplified effects on aggression. Our findings demonstrate that in a large sample of a free-ranging primate, early life environments impact behavior into adulthood. While some behaviors are consistent with patterns in humans and captive animals, suggesting an evolutionarily conserved ELA syndrome, other findings add new insights into the various ways individuals interact with their environment as a function of ELA.

Approaching conspecifics is a fundamental component of social interactions. Such decisions are typically investigated through the study of social relationships (e.g., kinship, dominance, affiliation) and their impact. In the framework, the role of social affordances, i.e., interaction opportunities arising from the immediate social environment, remains poorly understood. We investigated how context-dependent factors shape approach decisions in wild crested macaques (Macaca nigra) in North Sulawesi, Indonesia. From September 2024 to May 2025, we collected data on 27 adults (20 females, 7 males) using focal observations and an approach-specific protocol recording neighbours identities and behaviours at the initiation of close-proximity approaches (<1 body length). We first compared data collected during approaches with focal data, then conducted within-approach analyses contrasting approached partners and bystanders. We further tested the effects of behavioural state, subgroup size and composition, including infant presence. Bayesian models revealed that affiliative, neutral, and grooming behaviours were more frequent in approach contexts than in general observations. Within approaches, individuals avoided congeners already engaged in grooming and approached individuals in neutral or affiliative states (e.g., lip-smacking, embracing). Macaques globally approached more isolated individuals or dyads. When multiple subgroups were present (i.e., multiple choices), the likelihood of being approached increased with subgroup size and was higher in subgroups containing infants. These findings indicate that macaques use behavioural cues and local social density as affordance signals, adjusting approach decisions to maximize interaction opportunities and navigate complex social environments.

Non-human primates are crucial animal models in biomedical research including neurosciences. Legal frameworks ensure that participation of monkeys in biomedical research follows an ethical assessment, driven by specific guidelines for ensuring animal well-being. Those guidelines promote continued refinement of practices to improve animal wellbeing, yet quantitative data to inform such refinements is limited. In this context, we investigated the impact of modifications to the housing that created either navigational complexity or visual access to neighbouring animals on the behaviour of rhesus macaques. Then we quantified the value of different enrichment programmes based on manipulable objects. We showed that making navigation within a modular housing more complex, or adding transparent separations between housing units is associated with significant reduction of severe aggression, stereotypical behaviours and a significant increase of appeasing behaviours. We also observed a positive effect of manipulable objects with an increase in the expression of appeasing behaviours and a decrease in abnormal or stereotypical behaviours. Finally, our study revealed significant inter-individual variability that was not explained by sex, age, social network size or social status. Overall, our results point to the importance and benefits of environmental changes and enrichment protocols, and of the critical need for personalised enrichment programmes.

Behavioral thermoregulation allows animals to reduce the physiological costs associated with variation in the thermal environment, yet little is known about how chimpanzees respond behaviorally to the cool and humid conditions of tropical montane forests. We examined how microclimatic conditions influenced resting posture, sun/shade use, substrate use, vertical position within the canopy, and day nest use in eastern chimpanzees (Pan troglodytes schweinfurthii) in Nyungwe National Park, Rwanda. From March 2024 to February 2025, we collected 5,661 individual behavioral records during 486 contact hours and paired behavioral observations with measurements of ambient temperature, water vapor pressure, wind speed, and rainfall. Bayesian mixed models showed that temperature was the most consistent climatic correlate of resting behavior. Under cooler conditions, chimpanzees were more likely to adopt heat conserving postures, particularly curled and huddled postures, and to use day nests. As temperature increased, chimpanzees increased their use of shade, shifted from arboreal to terrestrial resting, and used lower canopy strata more frequently. Higher wind speed was also associated with reduced use of the upper canopy, whereas rainfall, water vapor pressure, and fruit availability generally showed weaker or behavior-specific associations. These findings indicate that chimpanzees in a cool montane forest flexibly adjust posture, solar exposure, substrate use, vertical position, and day nest use in relation to local thermal conditions. Resting behaviour may therefore provide an important context for behavioral thermoregulation, extending our understanding of chimpanzee thermal ecology beyond the warmer lowland and savanna habitats that have received most previous attention.

Classic socio-ecological theory predicts that males and females experience different sources and mechanisms of social competition. Whether these differences translate into sex-specific structural properties of dominance hierarchies remains unclear. Here, we compiled 156 dominance interaction matrices from 80 published studies and extracted three commonly used metrics - hierarchy steepness, linearity and the directional consistency index - to investigate the structural characteristics of male and female dominance hierarchies across primates. All three metrics were strongly affected by methodological and demographic variables. Steepness increased with the number of recorded interactions and group size, linearity decreased as matrices became sparser, and directional consistency declined with increasing numbers of interactions. Steepness covaried positively with both linearity and directional consistency, indicating that groups with steeper hierarchies also exhibited more linear and more directionally consistent relationships. We found no sex differences in steepness, linearity or directional consistency. These results suggest that current metrics primarily reflect variation in the sampling effort and the rate of interaction of the recorded behaviour and appear therefore not to capture potential sex differences in the forms of competition. Our findings highlight the need for alternative measures of power asymmetries that are less confounded by sampling effort and demographic variation to better understand how competition and conflict are structured across primate societies.

Adult sex ratios in mammals are usually female-biased, but the northern mole vole (Ellobius talpinus) (Pallas, 1770), a cooperatively breeding subterranean rodent, shows a persistent male bias that increases with age. Combining four years of capture-mark-recapture data with radiographic age estimation and genetic parentage data, we modeled apparent survival and state transitions (young-of-the-year, breeder, non-breeder) separately by sex. Young individuals showed significantly lower apparent survival than adults in both sexes, consistent with dispersal occurring predominantly in the first year of life. Within each age class, females showed consistently lower apparent survival than males, and this pattern held within breeding and non-breeding status groups alike, with female breeders showing lower apparent survival than male breeders. These results point to female-biased natal dispersal, an atypical pattern for mammals. We propose that faster turnover of reproductive females than males, in combination with singular breeding, favor female dispersal in search of vacant breeding positions, while promoting male philopatry and facultative polyandry.

Predation is a major selective force shaping lemur behaviour and population dynamics, yet direct observations remain rare, particularly for small nocturnal species. Here, we document predation on mouse lemurs (Microcebus spp., Cheirogaleidae) in Andohahela National Park, south-eastern Madagascar, and using complementary evidence from radio-telemetry and owl pellet analyses. Two radio-collared individuals were confirmed as prey of endemic snakes, Ithycyphus oursi and Madagascarophis meridionalis (both Pseudoxyrhophiidae), representing the first documented records of Microcebus predation by these species. Examination of owl pellets and prey remains from three sites and from three owl species revealed a single predation event by Asio madagascariensis (Strigidae), likely involving M. tanosi, no evidence of mouse lemur predation by Tyto alba (Tytonidae) despite high local prey availability, and a single and first predation record from Athene superciliaris (Strigidae). Material from A. superciliaris roosts was otherwise dominated by invertebrates, indicating that primate predation is likely opportunistic. Together, these findings expand the known predator guild of mouse lemurs and suggest that snake predation is rarely detected, and its contribution to mouse lemur mortality and population dynamics is likely underestimated. Our findings demonstrate how combining behavioural field observations with dietary evidence can uncover otherwise undetected predation events and clarify predator prey relationships in nocturnal primates.

Risk-taking behaviour permeates daily decision-making across many taxa and has significant impact on fitness outcomes. Previous research finds that individuals display consistent tendencies in their propensity to take risks, often labelled as a "Boldness-Shyness" personality trait. In this experimental study, we investigated repeatability in risk-taking behaviour in 241 wild vervet monkeys by measuring their responses to capture threat (via human-initiated darting procedure) and predation threat (via two predator models). We further examined the influence of socio-demographic, group identity and hormonal factors on risk-taking behaviour. We found that multiple behavioural responses, including the likelihood of approaching a food source under threat, were consistent across contexts. Risk-taking behaviour was influenced by age, sex, dominance rank, and hormonal profiles: juveniles, males, and higher-ranking individuals were more likely to approach food under (perceived) predation risk. Additionally, we observed significant among-group differences, suggesting that individuals within the same social group exhibit similar risk sensitivities, potentially due to social facilitation or shared environmental effects. The findings contribute to our understanding of animal personality and the ecological and social drivers underlying variation in risk-related behaviours.

Zoological gardens strive to prioritize excellent animal care and adhere to the highest standards of animal welfare, ensuring that the conditions of animals` social and physical environment are as close as possible to those in the wild. This study investigates the effects of group split and relocation to the new enclosure on the behaviour of western lowland gorillas (Gorilla gorilla gorilla) (N = 7) living in Prague Zoo, Czech Republic. We conducted over 289 hours of behavioural observations focusing on daily activities, social interactions, and behaviours that serve as potential stress and welfare indicators. The group split led to establishment of two groups in two separate enclosures; the old enclosure consisted of a "bachelor group" (i.e. three males) and a new enclosure consisted of a mixed-sex group (i.e. three females and one juvenile male). The behavioural comparisons across different study periods were conducted using linear mixed models (LMMs). The changes led to an increase in time spent moving, feeding, being in social proximity, and higher rates of approaches among the gorillas, as well as to a decrease in rates of self-directed and "undesirable" behaviors. Our findings indicate that the gorillas effectively adapted to the changes, most likely by relying on social support, to navigate new conditions. This study contributes to our understanding of how socio-cognitively complex species cope with necessary alterations in captive animal care programs. Furthermore, these observations may inform strategies to enhance the welfare of zoo-housed animals and to improve their captive care.

Long-term studies of isolated animal populations have greatly improved the understanding of various evolutionary processes. However, potentially elevated inbreeding in those compared to wild populations is a common concern. Conventionally, inbreeding has been investigated using reconstructed pedigrees, but nowadays it can be done directly at the genomic level. Here, we utilize genomic data from an intensively studied isolated rhesus macaque (Macaca mulatta) population on the small island Cayo Santiago (Puerto Rico), which was founded in 1938 with wild animals from India. We quantified inbreeding levels by inferring runs of homozygosity (ROH), i.e., long identical haplotypes inherited from both parents. We identified ROH in 97 ~5x-coverage genomes from Cayo Santiago and, for comparison, in 79 rhesus macaque genomes from five wild populations from China. Notably, this conventionally considered low-coverage data proved sufficient to infer ROHs >4 centimorgans long after imputing the genomes using a reference panel. Our results revealed that the ROH-derived effective population size on Cayo Santiago, 420 individuals, falls within the ranges we inferred in wild populations. Moreover, a general scarcity of individuals with long ROH in both the Cayo and wild populations indicates very few cases of close-kin breeding, suggesting that mechanisms to avoid close-kin breeding operate in rhesus macaques, both in wild and isolated populations. Taken together, our results suggest that Cayo Santiago remains a representative study population.

As wolves (Canis lupus) recolonize diverse environments, the extent to which ecological and individual factors shape their spatial behaviour remains insufficiently understood. Italy, where wolf recovery began earlier than elsewhere in Europe and spans highly heterogeneous landscapes, offers an opportunity to explore patterns relevant to future European scenarios. We analysed variation in home range size and movement patterns using GPS data from 19 wolves monitored between 2019 and 2025 across five study areas representing a broad environmental gradient. Continuous-time movement modelling was used to estimate home range size and distance travelled. Home range size varied markedly among areas, with annual averages for pack-member wolves ranging from 35 to 185 km2. The smallest ranges occurred where wolves had been established for longer and/or where prey availability was higher, suggesting that both intraspecific competition and resource abundance influence space use. Wolves expanded their ranges in winter and in more urbanized landscapes. Pack members consistently had smaller home ranges than floaters, and among floaters, females showed slightly larger ranges than males. Distance travelled also differed significantly across areas (local averages 25-53 km/day) but showed no significant association with individual traits. Three dispersal events were documented, two of which resulted in successful pair formation and subsequent reproduction. Overall, our results provide a broad overview of wolf spatial behaviour in contemporary Italian landscapes and offer insights relevant to the management of wolf populations across Europe.

Understanding how closely related species coexist in highly seasonal and unpredictable environments is central to studies of ecological differentiation and niche partitioning. We investigated the feeding ecology of sympatric populations of Microcebus murinus and M. griseorufus within a contact zone in Andohahela National Park, southeastern Madagascar, across dry and wet seasons. Using a combination of direct behavioral observations (1,611 feeding records), fecal sample analyses (n = 56), and vegetation phenology surveys, we quantified dietary composition, seasonal shifts in resource use, and habitat-related variation. Seasonal changes in diet were pronounced, with dry-season feeding dominated by exudates and wet-season diets incorporating greater proportions of fruit and flowers, closely tracking phenological patterns at both sites. Diets of both species were dominated by plant resources, but consistent interspecific differences in dietary strategy were evident. Although both species consumed comparable proportions of insect prey, M. murinus showed pronounced wet-season increases in the use of high-sugar, carbohydrate-rich floral resources (15.9%) and hemipteran-associated honeydew (30.6%). In contrast, M. griseorufus relied more consistently on predictable exudates throughout the year. Fecal analyses supported observational data but revealed differences in the detectability of dietary components, with increased representation of invertebrates in the wet season and seeds in the dry season. These results indicate substantial dietary overlap but consistent differences in resource use, suggesting that coexistence is facilitated by fine-scale trophic differentiation within a broadly shared omnivorous niche. Such subtle but persistent differences in feeding strategy likely reduce competitive overlap and enable continued sympatry in a climatically variable and resource-limited system.

Among Madagascar primates, the sportive lemurs (family Lepilemuridae) have seen their species diversity increase from eight in 2005 to 26 in 2009 mostly by applying the phylogenetic species concept to DNA barcode data. Despite the genus being speciose, only one case of sympatry is known from northern Madagascar, where two sportive lemur species described based on low mtDNA divergence, Lepilemur ankaranensis and Lepilemur milanoii, were found to co-occur at the center of their joint distribution range. Here, to clarify the taxonomy of these two species and examine their sympatry, we apply an integrative taxonomic framework to genomic and morphological data from 84 individuals of L. ankaranensis and L. milanoii, encompassing their entire distribution range and the forest of Analafiana, beyond their southernmost limit. Using clustering, multivariate, and isolation by distance analyses, we find no evidence of a sympatric zone and show that despite clear genetic differentiation between regions, the genomic and morphological diversity of the L. ankaranensis, L. milanoii-Analafiana group is clinal and explained by geographic distance. These results clarify that L. milanoii is a junior synonym of L. ankaranensis and that the Analafiana forest population belongs to L. ankaranensis, extending its distribution. It further implies that the 'sympatric' zone, the Andrafiamena forest, hosts conspecific individuals with slightly differentiated mtDNA backgrounds, rather than slightly differentiated sympatric species. Lastly, we re-evaluate the IUCN conservation metrics of L. ankaranensis, which continue to qualify as Endangered (EN) under the B1ab(i-v) criteria.

The concept of "wild" is poorly defined when applied to non-human animals, despite its central role in conservation, wildlife management and environmental policy. Despite numerous attempts to define "wildness", the distinction between "wild" and "non-wild" remains inconsistently applied. A shared, empirically grounded understanding of wildness would strengthen communication, support policy and legislation, and clarify human attitudes towards wildlife and nature. We assessed whether a shared understanding of wildness exists within the research community. A total of 358 professionals from different fields completed an online survey comprising 44 wildness-related statements along established measures of attitude and acceptability toward wildlife (AATW) and nature-relatedness (NRS). . Exploratory Factor Analysis revealed six components (19 statements): Human-mediated animal availability, Urbanisation, Independence from humans, Human-wildlife perceived conflict, Individual history of wildness, and Feralisation. These factors explained 43.91% of the variance. Mediation analysis showed that urbanisation and human-wildlife perceived conflict shape nature-relatedness by influencing attitudes and acceptability towards wildlife. Respondents demographic and professional backgrounds influenced their conceptualisation of wildness. While there is a shared latent structure of wildness across fields, it is multidimensional. This has implications for developing working definitions applicable to research, policy and practice.

Resource scarcity prompts animals to adjust their space use in ways that enhance their survival. In wild herbivores, seasonal habitat shifts are well studied; however, little is known about how large herbivores navigate human-dominated landscapes under fluctuating resource conditions. In Hong Kong, feral water buffalo (Bubalus bubalis; henceforth buffalo) experience declines in body condition score during the dry season. While buffalo expand spatial ranges in the dry season, whether this expansion reflects access to improved ecological conditions, and how key anthropogenic factors (like distance to roads and human density) further influence space use, remains understudied. We observed six buffalo herds (n=92 known individuals) across one wet (July-September 2023) and one dry (January-March 2024) season. We recorded herd locations and extracted remotely sensed habitat and environmental data. We used Normalized Difference Vegetation Index (NDVI) as a proxy of vegetation productivity and included elevation, distance to roads, and human density as additional predictors. We hypothesized that dry-season space use would shift toward higher vegetation productivity, and that anthropogenic factors would have weak influence on space use due to the adaption of buffalo in human-dominated landscapes. We found that buffalo used areas with higher vegetation productivity and higher elevation in the dry season than in the wet. Distance to roads and human density had no detectable effect. Our findings reveal that space use by a large herbivore like buffalo in human-dominated landscapes is strategic and resource driven, and that these seasonal shifts may have important implications for local biodiversity and human-animal interactions.

Animals face a fundamental trade-off between food-related competition and predation risk in how they allocate time and behavior. Nocturnal mammals offer a particularly tractable system for testing this trade-off because moonlight creates a natural, quantifiable gradient in both predation risk and the visibility needed for safe movement. We used minute-by-minute focal observations of nine kinkajous (Potos flavus; 4 female, 5 male) in Panama to test how fruit abundance and moonlight predicted nocturnal activity budgets (percent time traveling, feeding, resting) and nightly travel distance. Beta-family generalized linear mixed models and a linear mixed model of log travel distance showed that fruit abundance was positively associated with percent time traveling and with nightly travel distance, and negatively associated with percent time feeding: kinkajous traveled more and fed less per hour when fruit was abundant, consistent with movement between many nearby productive trees rather than prolonged feeding at a few. Males traveled less as moonlight increased, while females traveled more. Rainfall had no independent effect. We interpret the sex-reversed moonlight response as evidence that moonlight elevates predation risk for males while facilitating movement for the more food-limited females of this frugivorous carnivore.