American Journal of Primatology

ABSTRACTAnthropogenic landscapes are rapidly replacing natural nonhuman primate habitats. Yet, the access to anthropogenic resources on primate biology, health, and fitness remain poorly studied. Given their ubiquity across a range of human impacted landscapes, from cities to national parks, savanna monkeys (Chlorocebus spp.) provide an excellent study system in which to test these effects. We compared body condition and reproductive maturation in vervets (Chlorocebus pygerythrus) inhabiting a private farm in !Gariep Dam, with ample access to anthropogenic foods, and wild-foraging vervets in Soetdoring Nature Reserve, South Africa. Overall, vervets in !Gariep show significantly thicker skin folds, and higher BMI and body mass, than those in Soetdoring, suggesting increased fat deposition. Males in !Gariep have larger relative testis volumes at peri-pubescent ages compared to those in Soetdoring, suggesting early reproductive maturation associated with age-specific increases in body mass. Females from !Gariep showed evidence of an earlier onset of reproduction than those in Soetdoring, based on parity status as assessed by nipple length and evidence of lactation. Parity status at sub-adult dental ages was also strongly associated with body mass. These results are consistent with a positive effect of anthropogenic food-enhancement on body fat deposition, potentially linked to an earlier onset of reproductive maturation. Further investigation into primate responses to cultivated resources will inform our understanding of the broader effects of food enhancement on developmental plasticity.Competing Interest StatementThe authors have declared no competing interest.View Full Text

Human development is marked by extended immaturity, necessitating extended care throughout infancy and childhood, facilitating advanced cognitive, social, and cultural skill acquisition. Parallels of extended development are also present in our closest living relatives, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). The Self-Domestication Hypothesis (SDH) suggests that human uniqueness stems from selection against aggression. Bonobos are also considered self-domesticated, exhibiting lower aggression and greater social tolerance, which are linked to delayed development and prolonged maternal dependence compared to chimpanzees. However, systematic, quantitative comparisons of the two species developmental patterns are limited and conflicting. This study addressed this gap by examining behavioural development in bonobo and chimpanzee infants aged 0-5.5 years living in two populations (Kokolopori community, Kokolopori Bonobo Reserve, DRC, N=21; Ngogo community, Kibale National Park, Uganda, N=22) in their natural environments. We specifically focused on (i) general behaviours (travel, feeding, grooming), and (ii) spatial independence. By systematically comparing developmental data and using consistent methods, we tested whether bonobo development aligns with SDH predictions. Our results showed similar developmental trajectories, with no species differences concerning ventral riding, nipple contact, or grooming. However, we found species differences regarding travel and proximity patterns, with chimpanzees exhibiting prolonged dorsal riding, bonobos travelling independently more often and maintaining greater distances from their mothers. Age, sibling presence, and maternal parity influenced behavioural patterns, but no sex differences were observed. These findings challenge assumptions of slower bonobo maturation, and highlight the importance of systematic, collaborative research on primate behavioural diversity in natural environments.

Object play - seemingly non-functional interactions with objects - can promote the development of foraging skills, tool use, and behavioral innovation. Among Catarrhine monkeys, it was described in macaques and baboons. Wild geladas, although closely related to baboons, have been described as lacking object play (observed only in captivity) linked to their specialized grazing ecology. Here, we provide the first evidence of both social and solitary object play in a wild gelada population (NOMUs=13) at Debre Libanos (Ethiopia) and compare it with object play in sympatric olive baboons (Nindividuals=42). Notably, immature geladas engaged in object play both socially and solitarily, but the latter case was most frequent also with novel objects introduced by researchers. Solitary object play occurred at levels comparable to those of baboons, challenging previous reports of limited object interest in geladas. This finding aligns with the occurrence of object play in phylogenetically related species and with the retention in wild geladas of arboreal behavior and fruit consumption and hand morphology enhancing fine manipulation. Hence, object play in geladas under certain environmental conditions may reflect a biologically rooted capacity and underscores the importance of ecological variability, as distinct behavioral ecotypes can emerge across different populations of the same species.

Percussive tool use for extractive foraging allows animals to access otherwise inaccessible resources and forage more efficiently, with potentially important implications for their fitness. The development of tool use proficiency has been well-documented in nut-cracking chimpanzees and robust capuchins, and in shellfish-cracking long-tailed macaques, where mothers and proficient tool users are the most important models for social learning. However, little is known about how tool use develops in populations where opportunities for social learning are scarce. White-faced capuchins (Cebus capucinus imitator) on Jicaron Island, Panama, provide a unique case to consider this question: stone tool use is entirely male-biased, meaning juveniles cannot learn from their mothers, and reduced group cohesion further limits social learning opportunities. Here, we investigate the acquisition and development of stone tool proficiency in this population using a year-long dataset from camera traps placed at two experimental anvils. We assess differences in proficiency between age classes, examine the development of tool use proficiency over time, and explore patterns of social attention during tool use. We show that juvenile capuchins are less proficient than subadults and adults, but their proficiency remains stable over the course of one year, suggesting that skill development may require prolonged practice or physical maturation. In contrast to other primates, social learning opportunities on Jicaron appear limited and scrounging is rare, yet when social attention occurs, we find robust patterns. Social attention to tool use mostly comes from juveniles too young to use tools themselves, who observe proficient subadults that tolerate scrounging. Our results contribute to the understanding of how complex tool use behaviours are acquired and maintained in primates. They highlight that even when tool use is largely solitary, directed social attention and social tolerance play an important role in the development of tool use proficiency. HighlightsO_LIJuvenile white-faced capuchins are less proficient tool users than (sub)adults C_LIO_LIDevelopment of capuchins tool use proficiency is a slow process C_LIO_LISocial learning opportunities on Jicaron island are limited and social attention rare C_LIO_LIAttention was selective, juveniles to proficient sub(adults) who tolerated scrounging C_LIO_LINon-tool-using juveniles paid most attention, so likely important for acquisition C_LI

Quantitative acoustic analysis has been used to decipher individual differences, population structure, and taxonomic diversity in numerous primate species. We previously described three distinct call types in wild Aotus nigriceps, and now assess acoustic differences in two of these call types between social groups and spatially distinct populations. Acoustic parameters for both analyzed call types exhibited significant variability between groups. Similarly, geographically distant field sites were acoustically distinct from one another. Several groups also used a variation of a common call: a triplet Ch Ch instead of a duplicate. Other groups made use of ultrasonic frequencies which have not previously been reported in Aotus. Our results suggest that Aotus nigriceps exhibits substantial acoustic variability across sites that could potentially be useful for taxonomic classification, although additional geographically distant populations still need to be sampled. The possibility of individual signatures also exists and will require recording vocalizations from known individuals.

Chimpanzees, amongst other primates, are characterized by the large variability of habitats they can be found in as well as a large behavioral, sometimes cultural diversity. Such observations have launched a decades-long debate on the roots of behavioral diversity, stressing the need to document this behavioral variability in context, such as by connecting closely related populations through localized analyses. This study presents the first comprehensive description of feeding ecology from the Mwera South chimpanzee (Pan troglodytes schweinfurthii) community in the Bugoma Central Forest Reserve, in Uganda, establishing a valuable baseline for this previously unstudied population and providing a comparative perspective on the populations of Western Uganda and Eastern Democratic Republic of Congo. By employing multiple methodological approaches, including direct observation and fecal analysis, we describe dietary composition, seasonal patterns, and environmental influences on feeding behavior. Characterizing the feeding ecology of this previously unstudied population is critical for examining how ecological factors might influence how feeding patterns evolve depending on resource availability or chimpanzee behavior, in particular by favoring analyses at the regional level. In addition, we can better evaluate to what extent behavioral differences between chimpanzee communities stem from ecological constraints and/or cultural transmission pathways. Our findings suggest that the Bugoma chimpanzees seat at the location of a historic cultural junction, opening a large array of questions about historic movements and cultural diffusion in Eastern chimpanzees.

ObjectivesMost primate species live in groups, and temporal and spatial coordination of activities of individuals is essential for maintaining group cohesion, and there is still considerable debate to which degree social organization, the extent of despotism, and resource distribution shape group coordination processes. As different baboon species exhibit considerable variation in all of these factors, they constitute an excellent test case to resolve this debate.\n\nMaterials and MethodsWe analyzed group departures and progressions of Guinea baboons, Papio papio, in the Niokolo Koba National Park in Senegal. Guinea baboons live in a multi-level society with strong male bonds and a lack of a clear dominance hierarchy between males.\n\nResultsTwo-thirds of departures were initiated by adult males, and one third by adult females. Although initiators were more likely to signal than followers, signaling did not affect the initiation success. During group progression, males that were not affiliated with females were predominantly found in the front, while affiliated males, females and young were observed more frequently closer to the center of the group, and no preferences for rear positions. Overall, affiliated subjects were more likely to depart and travel together.\n\nDiscussionThe group departures in Guinea baboons differed strikingly from the elaborate negotiation behaviors among male hamadryas baboons, Papio hamadryas. We did not observe that specific individuals dominated the group coordination. Neither social organization, variation in despotism, nor resource distribution alone explain variation between species. Future studies should test whether specific combinations of factors promote the occurrence of negotiation processes.\n\nResearch HighlightsO_LIIn wild Guinea baboons, both adult males and females initiated group departures\nC_LIO_LIInitiators signaled during departures, but this did not affect initiation success\nC_LIO_LISolitary males were predominantly found at the front during group progression\nC_LI

ObjectivesBonobos (Pan paniscus) are unique among non-human primates in that females exhibit prolonged sexual receptivity to males during the postpartum infertile stage. Although high synchrony in female sexual receptivity has been hypothesized to constrain dominant males monopolization of reproductive success, recent genetic studies indicate pronounced male reproductive skew in this species. We investigated how prolonged sexual receptivity in female bonobos affects male behavioral patterns. Materials and MethodsBehavioral observations were conducted on a free-ranging bonobo group at Wamba in the Luo Scientific Reserve, Democratic Republic of the Congo. Periovulatory periods (POPs) were estimated from the timing of detumescence marking the end of the maximal swelling phase, following Ryu et al. (2022). For each male, we calculated the proportion of copulations with POP females. Using all-day focal follows targeting mature males, we tested for rank-related bias in their copulation rates and evaluated the effects of the party-level operational sex ratio (OSR; the ratio of mature males to sexually receptive females) on the focal males probability of copulation and intermale aggression. ResultsHigher-ranking males were more likely to copulate with POP females, yet males of all ranks engaged in copulation on most of focal observation days (twice per day, on average). Lower party-level OSR values increased the focal males probability of copulations while reducing intermale aggression. DiscussionProlonged sexual receptivity in female bonobos--yielding a pool of sexually receptive but non-POP females--may broaden male copulation opportunities beyond dominance rank and reduces intermale mating competition, even when POPs are detectable.

Wild chimpanzees possess diverse cultural repertoires, representing the richest example of non-human animal cultures. However, traditional methods, which investigate culture at the group level, have likely underestimated the full extent of chimpanzee cultural repertoires. In particular, the cultural relevance of everyday behaviors has remained largely unexplored. Here, we investigated evidence for social transmission of everyday behaviors to assess the breadth of individuals cultural repertoires in a population of wild eastern chimpanzees (Pan troglodytes schweinfurthii). First, we validated whether peering (i.e. close-range observation of a conspecific) serves as an indicator of social (i.e., cultural) learning. We then examined the contexts in which chimpanzees engage in peering to determine the range of behaviors that may be culturally transmitted. Finally, we explored potential motivations and additional functions of peering behavior. Our results indicate that chimpanzees use peering for targeted social information seeking in learning-intensive contexts. Peering rate was highest during immaturity, for complex or rare food items, and when observing older, more experienced conspecifics. Overall, wild chimpanzees peered at a wide range of everyday skills, such as feeding and grooming, and directed peering towards various conspecifics from an early age. We found no evidence supporting peering as a begging or submissive "gesture", but our findings indicate that it may function as a signal to initiate affinitive interactions. Our findings suggest that wild chimpanzees use peering to learn a broad variety of skills, thereby highlighting unrecognized cultural potential in everyday skills. Furthermore, our findings suggest that peering may have multiple functions and underlying motivations.

A major challenge in managing captive-bred rhesus macaque social groups is mitigating deleterious aggression before it escalates to social instability. Prior work at the California National Primate Research Center (CNPRC) showed that fragmentation of matrilineal structure--reflected in lower average kinship among female kin--is associated with weakened cohesion in grooming networks and higher rates of intense aggression. We tested the generality of these findings by analyzing data from 105 matrilines across 16 social groups at CNPRC and Emory NPRC (ENPRC), which differ in group size, natal male management, and housing. Using generalized linear models, we found that matrilines with lower mean kinship coefficients showed greater grooming fragmentation, even after accounting for network density. Threshold analyses identified a mean kinship of 0.16 as the point at which grooming cohesion declined most consistently across both centers, highlighting a biologically meaningful level of relatedness for maintaining kin-biased social bonds. Patterns of severe aggression differed by target and center: across both centers, matrilines with lower mean kinship directed proportionally more severe aggression toward kin. However, for aggression toward all group members, lower kinship predicted more severe aggression only at ENPRC; at CNPRC, this effect emerged only when natal male aggression was included. Our results demonstrate that mean matrilineal kinship is a robust indicator of family cohesion and latent social instability across management settings. Nepotistic threshold analysis provides a practical tool for managers to identify matrilines at risk for social fragmentation and implement interventions before intra-family aggression emerges.

The hypothesis that dangerous snakes served as evolutionary selective pressures on traits characterizing the Order Primates (Snake Detection Hypothesis, SDH), specifically vision and aspects of the brain, has received recent attention. We provide data on 52 encounters between chimpanzees (Pan troglodytes verus) in a savanna landscape and snakes and other large reptiles at the Fongoli site in Senegal, over the course of eight years. These encounters yielded data on 178 interactions between identified individual chimpanzees and reptiles. The majority of encounters with identified reptiles (62%) involved potentially deadly snakes. Constrictors of the family Pythonidae were encountered more frequently than any other reptile. Chimpanzees exhibited a variety of reactions to reptiles, ranging from attacking with objects to ignoring them. Even reptiles other than snakes were met with some degree of alarm when they were in water or moving quickly. We assessed variables that may affect apes reactions, as well as the age-sex class of chimpanzees. As a test of Isbells snake detection hypothesis, we examined chimpanzees reaction intensity to venomous versus constricting snakes but found no difference. We did find significant age-sex differences in chimpanzees reactions to snakes, with adolescent males exhibiting higher-intensity reactions than adult males and females and adolescent female chimpanzees. Chimpanzees reacted at significantly higher intensities when snakes were arboreal in location, but reptile species, size, and activity did not significantly influence individuals reactions to snakes. We also report one inferred encounter between an adult female chimpanzee and a venomous snake, which led to her death. Our data suggest that snakes are significant threats to chimpanzees in savanna environments and support the hypothesis that danger from snakes could have exerted significant evolutionary pressure on the Order Primates.

The concept of the alpha female has become widely accepted as a form of female identity in the West. Though relationships between hormone concentrations and alpha-related traits have been demonstrated in alpha nonhuman primates, this has not been examined in the case of the human alpha female. The present study examined the associations of testosterone and cortisol, as well as 3 other hormones, estradiol, oxytocin, and progesterone derived from hair samples, with 11 variables related to the expression of the alpha female identity in a small non-random sample (N=126) of self-identified alpha and non-alpha women in North America. The results revealed statistically significant differences between these groups. When compared to non-alpha women, alpha women scored higher than non-alphas in measures for masculinity, leadership, low introversion, self-esteem, and exhibited lower hair cortisol levels. Alphas exhibited slightly lower estradiol and oxytocin levels than non-alphas though these differences were non-significant. Similar non-significant differences were also found in the case of sexual experience, sexual dominance, testosterone, and progesterone. Though cortisol was not associated with masculine traits, it was positively and significantly associated with leadership. Cortisol was also negatively and significantly associated with strength and a measure for femininity. Progesterone, testosterone, and oxytocin were positively and significantly associated with enjoying sex, as was oxytocin with playing a dominant role in sexual encounters. Surprisingly, testosterone was not associated with alpha status nor with the measure of masculinity, and estradiol was not associated with any of the variables. The results imply that women who identify as alpha may experience less physiological stress than non-alpha females as measured by their lower cortisol levels.

The ability to scan visual scenes to gather information is a critical adaptive skill across primates. The common marmoset, a small-bodied New World monkey and emerging model of social and visual neuroscience, relies heavily on rapid head movements in addition to eye movements to orient (Pandey et al., 2020; Singh et al., 2025). Previous studies have found a relatively restricted oculomotor range extending out about 10 visual degrees from the central position of rest (Mitchell et al., 2014; Singh et al., 2025). However, previous studies have either used empty arenas for exploration (Singh et al., 2025), or in head-fixed animals used exploration of images potentially biased centrally with posed stimuli (Mitchell et al., 2014). This leaves open questions about whether this restricted oculomotor range is due to physical constraints or a lack of attention-drawing stimuli in the periphery. Understanding marmosets oculomotor range is important for applying modern methods that use marker-less pose tracking of the head as a proxy for gaze direction, under the assumption eye gaze is relatively restricted and can be ignored (Meisner et al., 2025). Using high-precision eye tracking and free-viewing of a natural image and video with objects of interest placed in the periphery, we quantified the oculomotor range of head-fixed marmosets. Our results show limited changes in the range reported from previous studies, even with naturalistic stimuli including moving animals that were optimized to encourage peripheral viewing.

Social tolerance, defined as the probability of individuals maintaining proximity with minimal aggression, is essential for the functioning of social groups. This study investigates social tolerance in wild vervet monkeys (Chlorocebus pygerythrus), with a focus on co-feeding tolerance. Previous research has highlighted that social tolerance varies both between and within species, influenced by stable group-specific and temporally variable factors. However, it remains unclear how these differences manifest in wild primates, particularly among vervet monkeys. To address this, we employed a novel experimental co-feeding paradigm adapted for field conditions, presenting a fake grass carpet with a fixed density of corn and a plot area proportional to group size to measure group-level co-feeding tolerance. The study was conducted with two habituated groups of wild vervet monkeys at the iNkawu Vervet Project in South Africa. Results revealed significant group differences in co-feeding tolerance despite similarities in the groups demographics and environments. The presence of mothers with infants was associated with higher levels of co-feeding tolerance, though this effect differed by group. These findings highlight the need for further research to elucidate the factors driving group-specific social tolerance levels and the mechanisms behind these differences.

2AO_SCPLOWBSTRACTC_SCPLOWQuantifying energy expenditure in free-living primates is fundamentally important yet challenging. Acceleration-based metrics such as Dynamic Body Acceleration (DBA), obtained from accelerometers, are potential proxies for energy expenditure, yet have not been previously validated in primates. Here, we validated DBA in black lion tamarins (Leontopithecus chrysopygus) by comparison to doubly labelled water (DLW) in 10 captive tamarins housed at the Rio de Janeiro Primate Centre. Individuals were equipped over 48 hours with a backpack with a tri-axial accelerometer and received an intra-peritoneal DLW injection at the beginning of the experiment, with blood samples taken 1 and 48h later. Daily Energy Expenditure by DLW was 326 (SD=66) kJ/day, close to expected values for primates of their size. The accelerometers recorded at 40 Hz, collecting >6.9 million records per axis for each individual. Individual DBA metrics were calculated and regressed against DLW daily energy measures. From this regression, we found a consistent and significant linear relationship (R2 = 0.46) between DLW and DBA, which could be improved by the incorporation of activity and resting time information (R2 = 0.52). Our results provide the first estimates of total daily energy expenditure for black lion tamarins and a validation of the method for estimating energy expenditure through accelerometers. Given the similar levels of total energy expenditure of captive and wild primates, this method can now be used in the field to estimate the energy cost of black lion tamarin movements in its natural environment. 1 SO_SCPLOWUMMARYC_SCPLOWO_SCPCAP C_SCPCAPO_SCPLOWSTATEMENTC_SCPLOWDynamic body acceleration was validated against doubly labelled water in black lion tamarins, showing it is a useful tool for measuring free-living energy demands.

The physiological mechanisms of the responses toward stressors are the core of ecophysiology studies to understand the limits of an organisms flexibility and better predict the impact of environmental degradation on natural populations. However, little information is available when we question inter-individual variability of these physiological responses, even though they can be particularly important. Some observations of intersexual differences in heterothermy raised the question of a difference in energy management between sexes. Here we assess male and female differences in a mouse lemur model (Microcebus murinus), a highly seasonal Malagasy primate, studying their physiological flexibility toward caloric restriction, and examining the impact on their reproductive success. These animals are adapted for naturally changing food availability and climate conditions, and can express deep torpor, allowing them to spare their energy expenses over the dry and cold season. We monitored body mass and body temperature on 12 males and 12 females over winter, applying a chronic 40% caloric restriction to 6 individuals of each group. Our results showed variability of Tb modulations throughout winter and in response to caloric treatment depending on the sex, as females entered deep torpor regardless of food restriction, while only CR males had a similar response. The use of deep torpor, however, did not translate into better body condition either in females, or in response to CR, and did not clearly affect reproductive success. The favorable captive context potentially buffered the depth of torpor and minimized the positive effects of using torpor on energy savings. However, our results may emphasize the existence of other benefits of heterothermic responses than fat reserves.

1.The objective of this study was to examine the impact of visitors on the behavior of chimpanzees at a sanctuary. We hypothesized there wouldnt be an increase in abnormal, agnostic, or self-directed behaviors during visits, nor a decrease in affiliative behaviors when visitors are present. The study examined the effects of visitor presence on chimpanzee behavior at Fundacio MONA, a rescue center. Key findings includeO_LINo significant changes in abnormal or self-directed behaviors or agonistic behaviors were observed with visitor presence. C_LIO_LIAffiliative behaviors (excluding grooming) showed a slight decrease during visits. C_LI These results indicate that guided visitor interactions do not adversely affect chimpanzee behavior and may even enhance their welfare. The study supports the implementation of structured visitor programs for public education and funding, without compromising animal well-being. This contrasts with some previous research in zoo settings, suggesting that controlled visits can be beneficial in primate sanctuaries.

The growing field of comparative thanatology aims to shed light on how and why the understanding of death evolved. Observations across different nonhuman primate species have reported care-taking behaviour of dead infants, but also cannibalism. Various hypotheses have been put forward to explain these infant-directed behaviours, ranging from responses to infantile cues to an understanding of death. To aid comparative analyses and test some of these hypotheses, we report behaviours directed at dead infants in a wild population of Guinea baboons (Papio papio) living in the Niokolo-Koba National Park, Senegal. During 12 years of field observations (2014-2025), 67 infants died before reaching 1 year of age. In 4 cases, we could not establish when the infants had died because the field station was closed due to the COVID-19 pandemic. In 22 of the remaining 63 cases, mothers, but occasionally also other group members, carried, protected, groomed, and dragged dead infants. In 6 cases, cannibalism occurred. None of the mothers expressed any signs of emotional distress in response to infant death. We suggest that a concept of death in Guinea need not be invoked to explain the observed behaviours. Instead, selection appears to have favoured post-mortem caretaking behaviours to avoid abandoning an infant that might temporarily be unresponsive. The lack of infant responses to maternal behaviour and the disintegration of the corpse may drive the transition from perceiving the infants as an object that evokes caretaking to one that resembles food, which ultimately facilitates occurrences of cannibalism.

Using tools to access hard-to-reach and high-quality resources, such as termites, honey, and nuts, initiated a fundamental adaptive shift in human and nonhuman primate cognitive and behavioural evolution. Variation in the efficiency of extracting calorie-rich and nutrient-dense resources directly impacts energy expenditure, and potentially has significant repercussions for cultural transmission where model selection biases are employed during skill acquisition. Assessing variation in efficiency is key to understanding the evolution of complex behavioural traits in primates. Yet, individual-level differences beyond age- and sex-class in primate extractive foraging efficiency have never been investigated. Here, we used 25 years (1992- 2017) of video data of the Bossou chimpanzee community (Guinea), to investigate whether individual differences in nut-cracking efficiency exist across the life span of chimpanzees aged [≥] 6 years. Data from 3,882 oil-palm nut-cracking bouts from over 800 hours of observation were collected. We found long-term stable and reliable individual differences in four (out of five) measures of efficiency. We found no sex effect, challenging previous research on a female bias in chimpanzee tool use. These life-long differences in extractive foraging impacts daily energy budgets, which potentially have significant individual fitness and life history consequences. Additionally, the establishment of long-term individual variation in chimpanzee stone tool use has implications for interpreting archaeological records of hominins. Our findings highlight the importance of longitudinal data from long-term field sites when investigating underlying cognitive and behavioural diversity across individual lifespans and between populations.

Chimpanzee pant-hoots are frequently produced long-distance vocalisations that serve a number of social functions, such as to indicate coordinate travelling, food discovery, or social status. Calling often triggers replies by others, offering potential for some form of group-level decision-making through vocal exchanges. However, despite important physiological and social differences between male and female chimpanzees, pant-hoot research has traditionally focused on males, with very little known about female use. To address this gap, we collected all-occurrence behavioural data from wild adult female and male Eastern chimpanzees (Pan troglodytes schweinfurthii) in two communities in the Budongo Forest Reserve, Uganda. We show that females pant-hooted regularly, but less frequently than males and, when they did so, mostly in response to others. Response pant- hoots were more common than initiating pant-hoots in both sexes (females: 90.1%; males: 69.5%), and male and female chimpanzees responded to pant-hoots heard at a similar rate (females: 14.1%, males excluding alpha: 15.8%). Both sexes were more likely to respond to pant-hoots from within their own party, but this effect was stronger for females. The likelihood of male chimpanzees pant-hooting in response was inhibited in larger party sizes, while females response pant-hoots were not. Finally, female response pant-hoots were less common during periods of maximal oestrous as compared to other stages of their reproductive cycle. Overall, our findings demonstrate that response pant-hoots are subject to social factors, such as within-sex social competition and between-sex reproductive strategies, which affect male and female chimpanzees in different ways, a further demonstration of the high degree of audience awareness in this primate species. HighlightsO_LIChimpanzees use pant-hoots in both sex-specific and sex-non-specific ways C_LIO_LIIndividual and social factors impact likelihood of pant-hoot production C_LIO_LIOur findings suggest pant-hoots are important flexible elements of vocal behaviour for male and female chimpanzees. C_LI