Primate Behavior Research Articles

A stealthy neural recorder for the study of behaviour in primates.

By monitoring brain neural signals, neural recorders allow for the study of neurological mechanisms underlying specific behavioural and cognitive states. However, the large brain volumes of non-human primates and their extensive range of uncontrolled movements and inherent wildness make it difficult to carry out covert and long-term recording and analysis of deep-brain neural signals. Here we report the development and performance of a stealthy neural recorder for the study of naturalistic behaviours in non-human primates. The neural recorder includes a fully implantable wireless and battery-free module for the recording of local field potentials and accelerometry data in real time, a flexible 32-electrode neural probe with a resorbable insertion shuttle, and a repeater coil-based wireless-power-transfer system operating at the body scale. We used the device to record neurobehavioural data for over 1 month in a freely moving monkey and leveraged the recorded data to train an artificial intelligence model for the classification of the animals' eating behaviours.

Dynamic modulation of social gaze by sex and familiarity in marmoset dyads.

Social communication relies on the ability to perceive and interpret the direction of others' attention, and is commonly conveyed through head orientation and gaze direction in humans and nonhuman primates. However, traditional social gaze experiments in nonhuman primates require restraining head movements, significantly limiting their natural behavioral repertoire. Here, we developed a novel framework for accurately tracking facial features and three-dimensional head gaze orientations of multiple freely moving common marmosets ( Callithrix jacchus ). By combining deep learning-based computer vision tools with triangulation algorithms, we were able to track the facial features of marmoset dyads within an arena. This method effectively generates dynamic 3D geometrical facial frames while overcoming common challenges like occlusion. To detect the head gaze direction, we constructed a virtual cone, oriented perpendicular to the facial frame. Using this pipeline, we quantified different types of interactive social gaze events, including partner-directed gaze and joint gaze to a shared spatial location. We observed clear effects of sex and familiarity on both interpersonal distance and gaze dynamics in marmoset dyads. Unfamiliar pairs exhibited more stereotyped patterns of arena occupancy, more sustained levels of social gaze across social distance, and increased social gaze monitoring. On the other hand, familiar pairs exhibited higher levels of joint gazes. Moreover, males displayed significantly elevated levels of gazes toward females' faces and the surrounding regions, irrespective of familiarity. Our study reveals the importance of two key social factors in driving the gaze behaviors of a prosocial primate species and lays the groundwork for a rigorous quantification of primate behaviors in naturalistic settings.

Measuring behavioral synchronization and spatial cohesion in the activity budgets of three adult white-handed gibbon (Hylobates lar) dyads in Huai Kha Khaeng Wildlife Sanctuary, Thailand.

Individual behavior of primates living in small groups is often seen to represent behavior of all group members due to close spatial cohesion. However, given that females expend more energy on reproduction than males (including lactation and infant carrying), females and males may exhibit different behaviors even when maintaining spatial proximity, particularly in highly seasonal or resource-poor environments. We collected 187 hours of data from three dyads (n= 6 individuals) of white-handed gibbons (Hylobates lar) living in a fruit-poor environment in western Thailand during the period of fruit scarcity. We calculated activity budgets, dyad behavioral synchronization, and dyad spatial cohesion. We hypothesized that activity budgets would differ significantly between sexes or pairs would engage in behaviors independently to provide females with an opportunity to obtain more resources. We also hypothesized that pairs would remain in close proximity. Overall, activity budgets exhibited significant variation when analyzed by sex (X2= 27.693, P ⩽ 0.001) and group (X2= 119.584, P ⩽ 0.001). Females spent less time resting and vocalizing and more time traveling compared to males. Percentages of synchronized behavior were lower than expected with only 55% of records synchronized (group B: 58.6%; group D: 58.5%; group L: 49.7%). Spatial cohesion, however, was relatively high overall with adults in the same or adjacent trees in 67.1% of paired records but significantly variable across groups (B: 89.4%; D: 73.1%; L: 48.2%; X2= 190.111, P ⩽ 0.001). We suggest that behavioral synchronization and spatial cohesion may be indicators of pair bond strength, not just the result of pair living. Given differences in activity budgets, low behavioral synchronization, and variable amounts of time pair mates spent apart, we conclude that pair mates should be considered individual actors who engage in behaviors independently from one another, particularly when coping with challenging ecological conditions.

Development of a Marmoset Apparatus for Automated Pulling to study cooperative behaviors

In recent years, the field of neuroscience has increasingly recognized the importance of studying animal behaviors in naturalistic environments to gain deeper insights into ethologically relevant behavioral processes and neural mechanisms. The common marmoset (Callithrix jacchus), due to its small size, prosocial nature, and genetic proximity to humans, has emerged as a pivotal model toward this effort. However, traditional research methodologies often fail to fully capture the nuances of marmoset social interactions and cooperative behaviors. To address this critical gap, we developed the Marmoset Apparatus for Automated Pulling (MarmoAAP), a novel behavioral apparatus designed for studying cooperative behaviors in common marmosets. MarmoAAP addresses the limitations of traditional behavioral research methods by enabling high-throughput, detailed behavior outputs that can be integrated with video and audio recordings, allowing for more nuanced and comprehensive analyses even in a naturalistic setting. We also highlight the flexibility of MarmoAAP in task parameter manipulation which accommodates a wide range of behaviors and individual animal capabilities. Furthermore, MarmoAAP provides a platform to perform investigations of neural activity underlying naturalistic social behaviors. MarmoAAP is a versatile and robust tool for advancing our understanding of primate behavior and related cognitive processes. This new apparatus bridges the gap between ethologically relevant animal behavior studies and neural investigations, paving the way for future research in cognitive and social neuroscience using marmosets as a model organism.

Development of a Marmoset Apparatus for Automated Pulling to study cooperative behaviors.

In recent years, the field of neuroscience has increasingly recognized the importance of studying animal behaviors in naturalistic environments to gain deeper insights into ethologically relevant behavioral processes and neural mechanisms. The common marmoset (Callithrix jacchus), due to its small size, prosocial nature, and genetic proximity to humans, has emerged as a pivotal model toward this effort. However, traditional research methodologies often fail to fully capture the nuances of marmoset social interactions and cooperative behaviors. To address this critical gap, we developed the Marmoset Apparatus for Automated Pulling (MarmoAAP), a novel behavioral apparatus designed for studying cooperative behaviors in common marmosets. MarmoAAP addresses the limitations of traditional behavioral research methods by enabling high-throughput, detailed behavior outputs that can be integrated with video and audio recordings, allowing for more nuanced and comprehensive analyses even in a naturalistic setting. We also highlight the flexibility of MarmoAAP in task parameter manipulation which accommodates a wide range of behaviors and individual animal capabilities. Furthermore, MarmoAAP provides a platform to perform investigations of neural activity underlying naturalistic social behaviors. MarmoAAP is a versatile and robust tool for advancing our understanding of primate behavior and related cognitive processes. This new apparatus bridges the gap between ethologically relevant animal behavior studies and neural investigations, paving the way for future research in cognitive and social neuroscience using marmosets as a model organism.

Heritability in the Rhesus Macaque (Macaca mulatta) Vertebral Column.

The vertebral column plays a central role in primate locomotion and positional behavior. Understanding its evolution, therefore, has the potential to clarify evolutionary processes that have occurred in the primate lineage as well as the specific behaviors of extinct primates. However, to understand primate vertebral anatomy, it is important to determine how much of this anatomy is heritable and how much develops as a response to environmental factors during life. We estimated heritability for vertebral counts as well as typical cervical, thoracic, and lumbar elements from 210 individuals from the pedigreed Cayo Santiago Macaca mulatta skeletal collection. We found moderate heritability of vertebral counts (h2 = 0.216-0.326), but with strong heritability of the type of variation (e.g., a tendency to meristic or homeotic change) in the vertebral count (h2 = 0.599), suggesting a possible explanation for high variability in vertebral numbers among the hominoids in particular. The moderate heritability of vertebral count also suggests that vertebral count is an unsuitable metric for estimating the ancestral state for some taxa. We found strong heritability in the morphology of cervical and upper lumbar zygapophyseal facets (h2 = 0.548-0.550) and the thoracic spinous processes (h2 = 0.609-0.761), including high heritability of the spinous process angle in the upper thoracic and upper lumbar elements (h2 = 0.649-0.752). We suggest these are related to maintaining stability in the cervical and lumbar regions, and reducing motion in the thoracic region, respectively. We propose that spinous processes may contain greater phylogenetic information, whereas transverse processes may contain greater information of function 'in life'. We also found important size effects, suggesting that size is the most heritable component of overall form and largely responsible for intertrait differences. This suggests that it is inappropriate to indiscriminately remove size effects from morphological comparisons.

Mind-body medicine and altered states of consciousness in Homo

The mind-body relationship has long been a subject of inquiry from both philosophical and scientific perspectives. Ancient Greek philosophers such as Pythagoras and Plato posited dualistic models, where the mind and body are distinct substances. In contrast, modern approaches in Mind-Body Medicine (MBM) offer integrative models that emphasize the interconnectedness of mental and physical states and the proactive role of the patient in their own healing process. This review examines the evolutionary roots of altered states of consciousness (ASC) as a precursor to current MBM techniques. By tracing ASC to early hominins and their cognitive development, it posits that the ability to enter various ASC—such as those used in rituals, meditation, and other mind-body practices—provided evolutionary advantages, influencing both individual fitness and social cohesion. Moreover, this review discusses tonic immobility in animals as a survival mechanism and explores parallels in human and non-human primate behaviors involving ASC. Additionally, neurochemical pathways that govern ASC, such as serotonergic and dopaminergic regulation, are explored for their roles in promoting social behaviors, cognitive flexibility, and emotional regulation. Furthermore, the role of the default mode network is investigated in relation to psychotropic and mood altering substances and altered states of consciousness. This integrated perspective offers new insights into the origins of MBM and underscores the significance of ASC in both evolutionary and contemporary contexts.

A brief history of primate research in the Ndoki forest.

The Nouabalé-Ndoki National Park (NNNP) in Republic of Congo has become a beacon for conservation in Central Africa. This manuscript documents the arrival of primatologists, the establishment of field stations and major discoveries in primate behavior and ecology. Field stations were strategically established to study primate behavior in a variety of different contexts from stationary platforms to forest follows of habituated groups. The implementation of new technologies and analyses have also been a hallmark of research at Ndoki. Scientists are shaping a new era in primatology at NNNP by building on past successes and promoting the next generation of Congolese conservationists to address environmental challenges. Results have proven crucial in discussions with government and industry and led to conservation gains such as the inclusion of the intact forests of the Goualougo and Djéké Triangles into the NNNP. The research stations have also become essential for developing a long-term certified sustainable international gorilla tourism program. Despite the many advancements for conservation such as increased protection of forests, development of internationally recognized protocols and large-scale capacity building initiatives, there are reasons for considerable concern in the near- and long-term for primates and their forest habitats in the Ndoki landscape. To address these concerns, we emphasize the long history of forming partnerships with local communities. We also discuss shared overlap featuring multicultural and environmental use of forest resources that is likely to be crucial in championing the conservation of the Ndoki forests for the next 25years and beyond.

Development of a Marmoset Apparatus for Automated Pulling (MarmoAAP) to Study Cooperative Behaviors.

In recent years, the field of neuroscience has increasingly recognized the importance of studying animal behaviors in naturalistic environments to gain deeper insights into ethologically relevant behavioral processes and neural mechanisms. The common marmoset (Callithrix jacchus), due to its small size, prosocial nature, and genetic proximity to humans, has emerged as a pivotal model toward this effort. However, traditional research methodologies often fail to fully capture the nuances of marmoset social interactions and cooperative behaviors. To address this critical gap, we developed the Marmoset Apparatus for Automated Pulling (MarmoAAP), a novel behavioral apparatus designed for studying cooperative behaviors in common marmosets. MarmoAAP addresses the limitations of traditional behavioral research methods by enabling high-throughput, detailed behavior outputs that can be integrated with video and audio recordings, allowing for more nuanced and comprehensive analyses even in a naturalistic setting. We also highlight the flexibility of MarmoAAP in task parameter manipulation which accommodates a wide range of behaviors and individual animal capabilities. Furthermore, MarmoAAP provides a platform to perform investigations of neural activity underlying naturalistic social behaviors. MarmoAAP is a versatile and robust tool for advancing our understanding of primate behavior and related cognitive processes. This new apparatus bridges the gap between ethologically relevant animal behavior studies and neural investigations, paving the way for future research in cognitive and social neuroscience using marmosets as a model organism.

Representing the dynamics of natural marmoset vocal behaviors in frontal cortex.

Here, we tested the respective contributions of primate premotor and prefrontal cortex to support vocal behavior. We applied a model-based generalized linear model (GLM) analysis that better accounts for the inherent variance in natural, continuous behaviors to characterize the activity of neurons throughout the frontal cortex as freely moving marmosets engaged in conversational exchanges. While analyses revealed functional clusters of neural activity related to the different processes involved in the vocal behavior, these clusters did not map to subfields of prefrontal or premotor cortex, as has been observed in more conventional task-based paradigms. Our results suggest a distributed functional organization for the myriad neural mechanisms underlying natural social interactions and have implications for our concepts of the role that frontal cortex plays in governing ethological behaviors in primates.

Commemorating the monkey bars, catalyst of debate at the intersection of human evolutionary biology and public health.

Play is an essential part of childhood, and growing attention has focused on the potential health benefits of 'risky' or 'thrill-seeking' play. Such play behavior is readily observed on any playground, where it can sometimes lead to injuries--most often from fall impacts--that require medical attention. Monkey bars account for ~7% of childhood arm fractures in the USA, an alarming statistic that raises difficult questions over its costs and benefits. Many authors view monkey bars as a public health hazard, but it is plausible that our childhood impulse toward thrill-seeking play is a result of selective pressures throughout our primate evolutionary history. Indeed, emerging evidence suggests that the developmental benefits of thrill-seeking play extend into adulthood, outweighing the occasional costs of injury. Disparate and consequential, these dueling perspectives have fueled debate among health professionals and policymakers, but with little attention to the work of biological anthropologists. Here we call attention to the hominin fossil record and play behaviors of non-human primates, providing a novel perspective that bolsters arguments for the adaptive significance of thrill-seeking play. The moment for such a review is timely, for it commemorates the centennial anniversaries of two playground icons: the jungle gym and monkey bars.

Salivary cortisol captures endocrine response to an acute stressor in captive female tufted capuchin monkeys (Sapajus apella).

Measuring glucocorticoids such as cortisol is a useful tool for exploring relationships among behavior, physiology, and well-being in primates. As cortisol circulates in blood, it moves into biological matrices such as hair, urine, feces, and saliva. Saliva sampling is a simple, noninvasive method to measure cortisol that can be easily implemented by training animals to voluntarily provide samples. The temporal lag between elevation of cortisol in the blood and elevation of cortisol in saliva likely varies by species and must be characterized to identify appropriate sampling regimens. In the present study we characterized the time course of cortisol changes in saliva following an acute psychological stressor in captive tufted capuchin monkeys (Sapajus apella). We trained eight free-moving female tufted capuchin monkeys to voluntarily produce clean saliva samples. We exposed them to the acute stressor of a veterinary catch net and observed behavior pre and post exposure. We collected salivary samples immediately pre exposure (0 min) and 30, 45, 60, 75, 90, and 120 min after exposure. Salivary cortisol was quantified using a Salimetrics kit. Behavioral and cortisol measures were compared within individuals to a control condition in which no stressor was presented. Capuchins showed a clear behavioral response to the stressor by demonstrating increased freezing and pacing, decreased feed foraging, nonsocial play, and scratching, and decreased willingness to provide saliva samples after stressor presentation. After stressor presentation, average salivary cortisol began to increase at 30 min and continued to increase through the 120 min sample period. There was individual variation in absolute cortisol levels, the timing of the cortisol increase, and the timing of the peak. Our results suggest that no single time-point can be reliably used to evaluate salivary cortisol response to an acute stressor across individuals, and instead we recommend the collection of a prolonged time series.

Bonobo geophagy at Wamba.

Geophagy, the deliberate consumption of earth materials, is widely observed in animals. While anecdotal evidence exists of bonobos (Pan paniscus) consuming soil from Cubitermes termite mounds, the functions of their geophagic behavior remains unexplored. This study aims to examine a preliminary hypothesis that termite mound geophagy of free-ranging bonobos at Wamba are helpful for iron supplementation. Here, we tested the following three predictions: (1) the soil of Cubitermes termite mounds at Wamba would have high iron content, (2) bonobos would engage in termite mound geophagy regularly across all seasons, and (3) termite mound soil would be more often consumed by (a) females than males, (b) pregnant than non-pregnant females, and (c) adolescents than adults. As predicted, soil samples collected from the pointy protrusions on the caps of the mushroom-shaped mounds, the part typically consumed by bonobos, had a much higher iron content than other food items for them. In addition, geophagic behavior was noted on 48 out of 116 days (41.3%) with full-day focal animal sampling, and was observed throughout the entire study duration without any bias in frequency toward a certain period. However, contrary to our prediction, there was no significant variation in the frequency of geophagic behavior by sex nor by pregnancy status, although it occurred more frequently among adolescents than adults. Our findings partially support the Iron Supplementation Hypothesis, suggesting that Cubitermes termite mound soils could offer a readily accessible source of iron for bonobos. However, we cannot draw definitive conclusions on the function of their geophagic behavior from our findings without in vitro studies examining whether the ingested iron is bioavailable and whether the soil does not have properties inhibiting iron absorption. Nonetheless, this study is a first step to explore the health implications of geophagy in bonobos, extending our knowledge of this behavior in primates.

Focal pharmacological manipulation of serotonin signaling in the amygdala does not alter social behavior.

Serotonin signaling plays critical roles in social and emotional behaviors. Likewise, decades of research demonstrate that the amygdala is a prime modulator of social behavior. Permanent excitotoxic lesions and transient amygdala inactivation consistently increase social behaviors in non-human primates. In rodents, acute systemic administration of drugs that increase serotonin signaling is associated with decreased social interactions. However, in primates, the direct involvement of serotonin signaling in the amygdala, particularly in affiliative social interaction, remains unexplored. Here, we examined the effects of serotonin manipulations within the amygdala on social behavior in eight pairs of familiar male macaques. We microinfused drugs targeting the serotonin system into either the basolateral (BLA) or central (CeA) amygdala and measured changes in social behavior. Surprisingly, the results demonstrated no significant differences in social behavior following the infusion of a selective serotonin reuptake inhibitor, 5-HT1A agonist or antagonist, 5-HT2A agonist or antagonist, or 5-HT3 agonist or antagonist into either the BLA or CeA. These findings suggest that serotonin signaling in the amygdala does not directly contribute to the regulation of social behavior between familiar conspecifics. Future research should explore alternative mechanisms and potential interactions with other brain regions to gain a comprehensive understanding of the complex neural circuitry governing social behavior.

A prominent vertical occipital white matter fasciculus unique to primate brains

Vision in humans and other primates enlists parallel processing streams in the dorsal and ventral visual cortex, known to support spatial and object processing, respectively. These streams are bridged, however, by a prominent white matter tract, the vertical occipital fasciculus (VOF), identified in both classical neuroanatomy and recent diffusion-weighted magnetic resonance imaging (dMRI) studies. Understanding the evolution of the VOF may shed light on its origin, function, and role in visually guided behaviors. To this end, we acquired high-resolution dMRI data from the brains of select mammalian species, including anthropoid and strepsirrhine primates, a tree shrew, rodents, and carnivores. In each species, we attempted to delineate the VOF after first locating the optic radiations in the occipital white matter. In all primate species examined, the optic radiation was flanked laterally by a prominent and coherent white matter fasciculus recognizable as the VOF. By contrast, the equivalent analysis applied to four non-primate species from the same superorder as primates (tree shrew, ground squirrel, paca, and rat) failed to reveal white matter tracts in the equivalent location. Clear evidence for a VOF was also absent in two larger carnivore species (ferret and fox). Although we cannot rule out the existence of minor or differently organized homologous fiber pathways in the non-primate species, the results suggest that the VOF has greatly expanded, or possibly emerged, in the primate lineage. This adaptation likely facilitated the evolution of unique visually guided behaviors in primates, with direct impacts on manual object manipulation, social interactions, and arboreal locomotion.

Collective decision-making in nocturnal huddling sleep: The influence of social factors on fans and fandom in Tibetan macaques

Social animals frequently exhibit huddling sleep behaviors in response to nocturnal ecological pressures. However, there remain significant gaps in our understanding of the decision-making process promoting huddle sleep. Exploring how such decision-making processes are initiated and programmed in nonhuman primates offers additional insights into various animals, with a particular focus on humans. The present research examined the social factors and individual influences involved in initiating huddle sleep among a population of wild Tibetan macaques (Macaca thibetana) at Mt. Huangshan in Anhui, China. The results showed that social rank, age, and social centrality were involved in the decision-making process for huddle sleep. Individuals with higher rank and greater social centrality not only tended to act as leaders but also frequently took on followers. Younger individuals were more inclined to be followers. If an individual consistently followed a specific member during huddles, we referred to her/him as a fan. Individuals with more fans (fandom) and those that were consistently fans of others were also more socially central in their group. Such different selection factors fostered coordination among individuals and promoted huddle formation. The study has enhanced our understanding of nocturnal huddling behavior in social nonhuman primates and the intricate mechanisms involved in decision-making. The findings provide valuable insights into the sleep behavior of wild animals, thereby increasing our understanding of how monkeys maintain long-term survival. The analysis of sleep behavior has significant theoretical and practical implications for the conservation of Tibetan macaques.

Time-mapping and future-oriented behavior in free-ranging wild fruit bats

Episodic memory and mental time travel have been viewed as uniquely human traits.1,2,3 This view began to shift with the development of behavioral criteria to assess what is referred to as "episodic-like memory" in animals.4,5 Key findings have ranged from evidence of what-where-when memory in scrub-jays, rats, and bees; through decision-making that impacts future foraging in frugivorous primates; to evidence of planning based on future needs in scrub-jays and tool use planning in great apes.4,6,7,8,9,10,11,12,13 Field studies of these issues have been rare, though there is field-based evidence for future-oriented behaviors in primates.8,10,14,15 We report evidence that free-ranging wild fruit bats rely on mental temporal maps and exhibit future-oriented behaviors when foraging. We tracked young bats as they navigated and foraged, documenting every tree they visited over many months. We prevented the bats from foraging outside for different time periods and monitored their foraging decisions, revealing that the bats map the spatiotemporal patterns of resources in their environment. Following a long period in captivity, the bats did not visit those trees that were no longer providing fruit. We show that this time-mapping ability requires experience and is lacking in inexperienced bats. Careful analysis of the bats' movement and foraging choices indicated that they plan which tree to visit while still in the colony, thus exhibiting future-oriented behavior and delayed gratification on a nightly basis. Our findings demonstrate how the need for spatiotemporal mental mapping can drive the evolution of high cognitive abilities that were previously considered exclusive to humans.

The Use of Guanfacine to Mediate Anxiety-related Reactivity and Reduce Associated Agonistic Behavior in Two Pigtail Macaques (Macaca nemestrina).

Guanfacine, an α ₂adrenoceptor agonist, has been used to successfully treat self-injurious behavior in nonhuman primates, including macaques (Macaca mulatta) and baboons (Papio anubis). It does so by facilitating a correction to the dopaminergic system that mediates a reduction in impulsivity and reactivity. Given this, we assessed the potential efficacy of guanfacine to treat socially directed agonistic behavior in primates with an apparent reactive behavioral phenotype. We present data from 2 pigtail macaques (Macaca nemestrina): an intact adult male housed in a breeding group, and an experimentally naive adult female living in a research setting with her social partner. Baseline behavioral assessments suggested that both macaques showed extreme responses to external stressors that triggered them to aggress social partners often leading to wounding that required veterinary intervention. Both animals were tracked during the course of 1 y. Once treated regularly with guanfacine, both animals showed significant reduction in their agonistic behavior and the rate at which they wounded other animals. Indeed, in the year since the female has been treated with guanfacine she has never wounded her cagemate. By collecting regular and detailed behavioral observations on the male in the breeding colony, we were able to identify triggers for his aggression and to track the behavioral changes evidenced after guanfacine treatment. These data supported our hypothesis that his aggression reflected extreme reactivity to external stressors, rather than general anxiety. Importantly, we saw only a limited and short-lived reduction in the male's affiliative behavioral rates, and thus guanfacine had no sedative effect, but did successfully reduce his reactivity and resultant agonism and wounding.

Wild capuchin monkeys use stones and sticks to access underground food

Primates employ different tools and techniques to overcome the challenges of obtaining underground food resources. Humans and chimpanzees are known to tackle this problem with stick tools and one population of capuchin monkeys habitually uses stone tools. Although early hominids could have used stones as digging tools, we know little about when and how these could be useful. Here, we report a second primate population observed using stone tools and the first capuchin monkey population to habitually use the ‘stick-probing’ technique for obtaining underground resources. The bearded capuchin monkeys (Sapajus libidinosus) from Ubajara National Park, Brazil, use ‘hands-only’ and ‘stone-digging’ techniques for extracting underground storage organs and trapdoor spiders. Males also use ‘stick-probing’ and ‘stone-stick’ techniques for capturing trapdoor spiders. Tool use does not increase success in obtaining these resources. Stone-digging is less frequent in this population than in the only other known population that uses this technique. Females use stones in a lower proportion of their digging episodes than males in both populations. Ecological and cultural factors potentially influence technique choice and sex differences within and between populations. This population has a different pattern of underground food exploration using tools. Comparing this population with others and exploring the ecological and cultural factors under which capuchin monkeys employ different tools and techniques will allow us to better understand the pressures that may have shaped the evolution of those behaviors in primates.

59. Effects of Ketamine on Anxiety-Like Behavior in Non-Human Primates

59. Effects of Ketamine on Anxiety-Like Behavior in Non-Human Primates