Capuchin Monkeys Research Articles

‘Tail-dipping’ to drink from an open water source in Cebus imitator (Primates: Cebidae) in a protected area of Costa Rica

Primate species demonstrate high levels of intelligence, innovation, and social learning. These characteristics give rise to a high likelihood of new behaviours occurring and being socially transmitted to other individuals within a group. Capuchin monkeys are group-living and are commonly considered to be among the most intelligent non-ape primates. They exhibit a large repertoire of complex behaviours and have been shown to be capable of innovating to problem solve. However, observations of new behaviours in wild populations are rare in comparison to captive populations. Here we describe Panamanian white-faced capuchins (Cebus imitator) carrying out a behaviour which has not been previously documented in capuchin species and may be related to predator avoidance. This behaviour was video-recorded and to our knowledge is the first record of a capuchin species using tail-dipping behaviour to access an open water source in the wild.

Size reduction and skull shape parallelism following the evolutionary forest-to-savanna transition in Platyrrhini monkeys.

There are strong physiological and behavioral differences that allow animals to live in forests versus savannas. For example, terrestrial forest-dwelling mammals tend to be small compared to species living in savannas. Robust capuchin monkeys (genus Sapajus) are widespread in tropical South America, occurring in both forest and savanna environments, with forest species considered basal in an evolutionary context. Whether or not skull shape and size variations are associated with variation in resource use remains unknown, particularly for the two species living in savanna (Sapajuslibidinosus and S. cay). Here we show that savanna species present convergent size and skull characteristics that may facilitate living in this new environment. Geometric morphometric methods were used to assess skull size and shape variation for 184 Sapajus specimens distributed across South America. We used phylogenetic generalized least squares to test size against environmental variables and multivariate morphological trajectories/partial least square analyses on the skull shape to detect shape differences in specimens between forest and savanna biomes. Our findings reveal Sapajus size reduction in the evolutionary transition from forest to savanna, a process related to increasing seasonality. Moreover, we found morphological parallelism in the skull (e.g., muzzle shortening) and (large) molars in the two savanna species, features that may facilitate the processing of harder food such as fallback resources. We associate these phenotypic differences to the evolutionary process of colonizing the savannas by primates (including early hominins), leading to morphological adaptations to tolerate stressful, seasonal environments, such as body size reduction and ingestion and mastication of tough foods.

Size and degree of protection of native forest remnants drive the local occupancy of an endangered neotropical primate.

Although the species-area relationship is well known, it may interact with and be augmented or cancelled out by other factors, such as local human disturbance. We used data on site occupancy of the Endangered blonde capuchin monkey (Sapajus flavius) based primarily on a standardized program of local interviews to model the influence of past human disturbance on the occurrence of this species across remaining forest patches of northeastern Brazil within the Atlantic Forest and Caatinga biomes. To do so, we assessed environmental covariates that best represent the history of human impacts. We then used single-species occupancy models to assess site occupancy, while controlling for detection error during sampling. Surprisingly, we obtained a higher occupancy rate in the more arid Caatinga remnants than in the more mesic Atlantic Forest. Habitat patch size, history of site protection, and annual precipitation were the best predictors of local occupancy. Historical human disturbance, including subsistence hunting, has exerted considerable impact on the modern distribution of the blonde capuchin, whose geographic range largely spans a region historically lacking any wildlife protection. Matrix vegetation structure across the Caatinga, which so far has averted large-scale mechanized agriculture, also creates a benign landscape that likely benefits contemporary capuchin occupancy. Local extinctions of this endangered primate will most likely continue unabated unless a ban on hunting in remaining Atlantic Forest and Caatinga fragments can be enforced.

Spontaneous object recognition in capuchin monkeys: assessing the effects of sex, familiarization phase and retention delay.

The spontaneous object recognition (SOR) task is a versatile and widely used memory test that was only recently established in nonhuman primates (marmosets). Here, we extended these initial findings by assessing the performance of adult capuchin monkeys on the SOR task and three potentially intervening task parameters-object familiarization phase, retention delay and sex. In Experiment 1, after an initial 10-min familiarization period with two identical objects and a pre-established retention delay (0.5, 6 or 24h), the capuchins preferentially explored a new rather than the familiar object during a 10-min test trial, regardless of delay length. In Experiment 2, the capuchins were again exposed to two identical objects (but now for 10 or 20 min), then a 30-min retention delay and a 10-min test trial. An exploratory preference for the new over the familiar item was not affected by the length of the familiarization interval, possibly because overall exploration remained the same. However, the amount of initial object exploration was not related to task performance, and both males and females performed similarly on the SOR task with a 10-min familiarization, 30-min delay and 10-min test trial. Therefore, male and female capuchins recognize objects on the SOR task after both short and long delays, whereas a twofold increase in the familiarization phase does not affect task performance. The results also provide further support for the use of incidental learning paradigms to assess recognition memory in nonhuman primates.

Animal behavior: Monkeys use tools for diet quality, not quantity

An enduring question in the study of human evolution is why tool use evolved. A new study has found that stone tools improve diet quality in wild capuchin monkeys. Tools may have similarly increased the nutritional security in ancestral hominins.

The Influence of Landscape Structure on the Occurrence of Neospora caninum, Toxoplasma gondii, and Sarcocystis spp. in Free-Living Neotropical Primates.

Habitat fragmentation is the main threat to primate survival in the world. Additionally, changes in the environments in which they live can also contribute to exposure to pathogens. To investigate some pathogens that free-living primates may be exposed to in Rio Grande do Sul State (RS; southern Brazil) and characterize the forest remnants in which they live, we investigated anti-Neospora caninum, Toxoplasma gondii, and Sarcocystis spp. antibodies in the serum of the animals. We analyzed 105 serum samples from 63 black howler monkeys (Alouatta caraya), 39 southern brown howler monkeys (Alouatta guariba clamitans), and 03 capuchin monkeys (Sapajus nigritus cucullatus), which were captured in forest fragments of RS. Indirect fluorescence antibody test (IFAT) and indirect hemagglutination assay (IHA) were used to detect antibodies to the agents. We then characterized the landscapes in a multiscale approach in radii from 200 to 1400m to investigate the relationship of the presence of the agents with landscape elements. In the IFAT-IgG, 13.3% (14/105) of the samples were seropositive for N. caninum, 4.8% (5/105) for T. gondii, and 5.7% (6/105) for Sarcocystis spp. In the IHA-IgM/IgG, 24.8% (26/105) were seropositive for T. gondii. The metrics that best explained exposure to agents were edge and patch density, forest cover, urban cover, and average Euclidean distance to the nearest patch. This study indicated that the primates were exposed to the agents studied, demonstrating that some landscape features are associated with exposures to the investigated pathogens.

Gross anatomical description of the extrinsic and intrinsic scapular and brachial muscles of Sapajus apella (Linnaeus, 1758).

The robust brown capuchin monkey (Sapajus apella) is a South American primate with preferences for arboreal locomotion, which requires specific thoracic limb muscle adaptations. The present investigation studied the gross anatomy of the extrinsic and intrinsic scapular and brachial muscles. Gross dissections were performed in both thoracic limbs of four formaldehyde-fixed specimens. Three rhomboideus muscles were present (capitis, cervicis, and thoracis). The trapezius muscle was divided into two parts (cervicis and thoracis). The pectoralis abdominalis and omotransversarius muscles were present. The anconeus muscle was found as an individual muscle or fused to the caput mediale of the triceps brachii muscle. The brachialis muscle had among one and two heads. The anconeus epitrochlearis was absent. These muscles of Sapajus apella are adapted for arboreal locomotion and some terrestrial habits, since these have many similarities with other primates with a similar locomotor patterns.

Female squirrel monkeys’ (Saimiri boliviensis) responses to inequity in a group context; testing a link between cooperation and inequity responses

Primates of several species respond negatively to receiving less preferred rewards than a partner for completing the same task (inequity responses), either rejecting rewards or refusing to participate in the task when disadvantaged. This has been linked to cooperation, with species that cooperate frequently refusing to participate in inequity tasks (the 'cooperation hypothesis'). However, inequity is a social response, and previous research has involved dyads, precluding studying the effects of additional social partners. While dyads allow for tighter control in experimental settings, dyadic interactions in nature do not take place in a social vacuum, so understanding the role of the social context is needed to verify that the pattern of results supports the cooperation hypothesis. Here we focus on Bolivian squirrel monkeys, Saimiri boliviensis, a highly social species that does not generally cooperate and has not responded to inequity in previous dyadic research, although they do respond to receiving a lower reward than they expected. In the current study, we provide a more nuanced test by studying female Bolivian squirrel monkeys, the demographic most likely to cooperate in both field and laboratory contexts, in a more socially relevant group setting. For some reward values, females responded in both the inequity condition, rejecting less preferred rewards when they were disadvantaged relative to their social group, and a contrast condition, wherein all animals received a lower reward than they expected, making it difficult to disentangle contrast from inequity. As in capuchin monkeys, refusals increased when monkeys were to receive low-value rewards compared to medium-value rewards. These results suggest that the relationship between cooperation and inequity responses may be more nuanced than previously suggested, with demographic, social context and reward value potentially influencing outcomes even within species.

Context-effect bias in capuchin monkeys (Sapajus spp.): exploring decoy influences in a value-based food choice task

Decision making is known to be liable to several context effects. In particular, adding a seemingly irrelevant alternative (decoy) to a set of options can modify preferences: typically, by increasing choices towards whatever option clearly dominates the decoy (attraction effect), but occasionally also decreasing its appeal and generating a shift in the opposite direction (repulsion effect). Both types of decoy effects violate rational choice theory axioms and suggest dynamic processes of preference-formation, in which the value of each alternative is not determined a priori, but it is instead constructed by comparing options during the decision process. These effects are well documented, both in humans and in other species: e.g., amoebas, ants, honeybees, frogs, birds, cats, dogs. However, evidence of decoy effects in non-human primates remains surprisingly mixed. This study investigates decoy effects in capuchin monkeys (Sapajus spp.), manipulating time pressure across different conditions, to test whether such effects require time-consuming comparative processes among available alternatives. Whereas the time-dependent nature of decoy effects is a robust finding in the human literature, this is its first investigation in non-human animals. Our results show that capuchins exhibit an attraction effect with decoys targeting their preferred food, and that this effect disappears under time pressure; moreover, we observe preliminary evidence of a repulsion effect when decoys target instead the less-preferred food, possibly due to the larger distance between decoy and target in the attribute space. Taken together, these results provide valuable insight on the evolutionary roots of comparative decision making.

The development of sex differences in play in wildwhite-faced capuchins (Cebus capucinus).

Many mammalian species display sex differences in the frequency of play behavior, yet the animal literature includes few longitudinal studies of play, which are important for understanding the developmental timing of sex differences and the evolutionary functions of play. We analyzed social play, solitary play, and grooming using an 18-year data set on 38 wild white-faced capuchin monkeys (Cebus capucinus) followed since infancy. Rates of each behavior were measured as the proportion of point samples taken during focal follows in which the individual engaged in each behavior. To determine sex differences in these rates, we ran a series of generalized linear mixed models, considering both linear and quadratic effects of age, and chose the optimal model for each of the three behavioral outcomes based on information criteria. Rates of both social play and solitary play decreased with age, with the exception of social play in males, which increased in the early juvenile period before decreasing. Male and female capuchins had different developmental patterns of social play, with males playing more than females during most of the juvenile period, but they did not display meaningful sex differences in solitary play rates. Additionally, males and females had different patterns of grooming over the lifespan: males participated in grooming at low rates throughout their lives, while adult females participated in grooming at much higher rates, peaking around age 11 years before declining. We suggest that male and female white-faced capuchins may adopt alternative social bonding strategies, including different developmental timing and different behaviors (social play for males vs. grooming for females). Our results were consistent with two functional hypotheses of play, the practice and bonding hypotheses. This study demonstrates that play behavior may be critical for the development of sex-specific social strategies and emphasizes the importance of developmental perspectives on social behaviors.

Oxytocin and social gaze during a dominance categorization task in tufted capuchin monkeys.

Visual attention to facial features is an important way that group-living primate species gain knowledge about others. However, where this attention is focused on the face is influenced by contextual and social features, and emerging evidence in Pan species suggests that oxytocin, a hormone involved in forming and maintaining affiliative bonds among members of the same group, influences social attention as measured by eye gaze. Specifically, bonobos tend to focus on conspecifics’ eyes when viewing two-dimensional images, whereas chimpanzees focus more on the edges of the face. Moreover, exogenous oxytocin, which was hypothesized to increase eye contact in both species, instead enhanced this existing difference. We follow up on this to (1) determine the degree to which this Pan pattern generalizes across highly social, cooperative non-ape primates and (2) explore the impact of exogenously administered vs. endogenously released oxytocin in impacting this behavior. To do so, we tracked gaze direction on a computerized social categorization task using conspecific faces in tufted capuchin monkeys (Sapajus [Cebus] apella) after (1) exogenously administering intranasal oxytocin using a nebulizer or (2) inducing an endogenous increase in oxytocin using fur-rubbing, previously validated to increase oxytocin in capuchins. Overall, we did not find a general tendency in the capuchins to look toward the eyes or mouth, but we found that oxytocin was related to looking behavior toward these regions, albeit not in a straightforward way. Considering frequency of looking per trial, monkeys were more likely to look at the eye region in the fur-rubbing condition as compared to either the saline or exogenous oxytocin conditions. However, in terms of duration of looking during trials in which they did look at the eye region, monkeys spent significantly less time looking at the eyes in both oxytocin conditions as compared to the saline condition. These results suggest that oxytocin did not necessarily enhance eye looking in capuchins, which is consistent with the results from Pan species, and that endogenous and exogenous oxytocin may behave differently in their effect on how social attention is allocated.

A primate model for the origin of flake technology

When and how human ancestors first used tools remains unknown, despite intense research into the origins of technology. It has been hypothesized that the evolutionary roots of stone flake technology has its origin in percussive behavior. Before intentional stone flaking, hominins potentially engaged in various percussive behaviors resulting in accidental flake detachments. We refer to this scenario as the ‘by-product hypothesis.’ In this scenario, repeated detachments of sharp stone fragments eventually resulted in intentional flake production. Here, we tested the circumstances of accidental flake production as a by-product of percussive foraging in wild capuchin monkeys (Sapajus libidinosus) from Brazil, the only nonhuman primate known to habitually produce sharp-edged flakes through a percussive behavior. We conducted field experiments where we tested the potential for accidental flake production during nut cracking. We provided three different types of stone with varied material properties as anvils to assess the circumstances in which accidental production of sharp-edged flakes occurs during nut cracking. A further freehand knapping experiment, with the raw material that exhibited accidental flake detachments, allows a direct comparison of flakes that have been intentionally produced by an experienced knapper and flakes produced during nut cracking by capuchin monkeys. Our results show that raw material quality and morphology significantly affect the rate of sharp-edged flake production as well as the resulting lithic signature of this behavior. In addition, accidental flakes produced during capuchin nut cracking on highly isotropic raw material are similar in many respects to intentionally produced flakes by a human knapper. Our field experiments highlight the fact that nut-cracking behavior can lead to the unintentional production of substantial quantities of sharp-edged flakes and therefore supports the ‘by-product hypothesis’ as a potential mechanism for the emergence of hominin flake technology.

An exploratory study of cooperation: food-sharing behaviour in wild varied white-fronted capuchin monkeys (Cebus versicolor) in Central Colombia

Abstract Food-sharing is a cooperative behaviour related to the transfer of resources between conspecifics, and it is considered a complex prosocial behaviour because of its associated costs. It is more likely that an individual cooperates with closely related kin (e.g., in food sharing), and particularly with close maternal kin. In female philopatric species, such as Cebus spp., mother–offspring bonds likely explain patterns of maternal kin biases. On the other hand, the explanation of the evolution of food-sharing among non-kin is diverse. Capuchin monkeys (genera Cebus and Sapajus) are interesting to study cooperation since this is a critical behaviour to gain and protect ecological and reproductive resources in the wild, including care of their offspring. We performed an experimental protocol to induce behavioural observations with a provisioning technique using chicken eggs in a wild group of white-faced capuchin monkeys (Cebus versicolor). We aimed to test whether this white-faced capuchin monkeys engaged in food-sharing in the wild, describing the pattern of this cooperative behaviour. Furthermore, we also described some conditions that might affect this behaviour. We observed that these capuchins shared the eggs in passive exchanges, meaning that possessors let other individuals to eat from their egg. Our results further suggest that these exchanges may be due to mainly maternal kin biases. This study offers a preliminary observation of a little-studied capuchin species in the wild and adds information about how cooperation works in the wild.

Testing for changes in rate of evolution and position of the climatic niche of clades

ABSTRACT There is solid recognition that phylogenetic effects must be acknowledged to appreciate climatic niche variability among species clades properly. Yet, most currently available methods either work at the intra‐specific level (hence they ignore phylogeny) or rely on the Brownian motion model of evolution to estimate phylogenetic effects on climatic niche variation. The Brownian motion model may be inappropriate to describe niche evolution in several cases, and even a significant phylogenetic signal in climatic variables does not indicate that the effect of shared ancestry was relevant to niche evolution. We introduce a new phylogenetic comparative method which describes significant changes in the width and position of the climatic niche at the inter‐specific (clade) level, while making no a priori assumption about how niche evolution took place. We devised the R function phylo.niche.shift to estimate whether the climatic niches of individual clades in the tree are either wider or narrower than expected, and whether the niche occupies unexpected climates. We tested phylo.niche.shift on realistic virtual species' distribution patterns applied to a phylogeny of 365 extant primate species. We demonstrate via simulations that the new method is fast and accurate under widely different climatic niche evolution scenarios. phylo.niche.shift showed that the capuchin monkeys and langurs occupy much wider, and prosimian much narrower, climatic niche space than expected by their phylogenetic positions. phylo.niche.shift may help to improve research on niche evolution by allowing researchers to test specific hypotheses on the factors affecting clades' realised niche width and position, and the potential effects of climate change on species' distributions.

Capuchin monkeys learn to use information equally well from individual exploration and social demonstration

The limited evidence of complex culture in non-human primates contrasts strikingly with human behaviour. This may be because non-human primates fail to use information acquired socially as effectively as they use information acquired individually. Here, monkeys were trained on a stimulus discrimination task with a win-stay, lose-shift (WSLS) reward structure. In a social learning condition, the experimenter performed an information trial by choosing between the available stimuli; in an individual condition, monkeys made this choice themselves. The monkeys’ subsequent test trials displayed the same stimulus array. They were rewarded for repetition of rewarded (‘win-stay’) and avoidance of unrewarded (‘lose-shift’) information trial selections. Nine monkeys reached our pre-determined performance criterion on the initial two-stimulus stage. Their ability to generalise the WSLS strategy was then evaluated by transfer to a three-stimulus stage. Minimal differences were found in information use between the social and individual conditions on two-stimuli. However, a bias was found towards repetition of the information trial, regardless of information source condition or whether the information trial selection was rewarded. Proficient subjects were found to generalise the strategy to three-stimuli following rewarded information trials, but performed at chance on unrewarded. Again, this was not found to vary by source condition. Overall, results suggest no fundamental barrier to non-human primates’ use of information from a social source. However, the apparent struggle to learn from the absence of rewards hints at a difficulty with using information acquired from unsuccessful attempts; this could be linked to the limited evidence for cumulative culture in non-human primates.

Genetic, maternal, and environmental influences on sociality in a pedigreed primate population

Various aspects of sociality in mammals (e.g., dyadic connectedness) are linked with measures of biological fitness (e.g., longevity). How within- and between-individual variation in relevant social traits arises in uncontrolled wild populations is challenging to determine but is crucial for understanding constraints on the evolution of sociality. We use an advanced statistical method, known as the ‘animal model’, which incorporates pedigree information, to look at social, genetic, and environmental influences on sociality in a long-lived wild primate. We leverage a longitudinal database spanning 20 years of observation on individually recognized white-faced capuchin monkeys (Cebus capucinus imitator), with a multi-generational pedigree. We analyze two measures of spatial association, using repeat sampling of 376 individuals (mean: 53.5 months per subject, range: 6–185 months per subject). Conditioned on the effects of age, sex, group size, seasonality, and El Niño–Southern Oscillation phases, we show low to moderate long-term repeatability (across years) of the proportion of time spent social (posterior mode [95% Highest Posterior Density interval]: 0.207 [0.169, 0.265]) and of average number of partners (0.144 [0.113, 0.181]) (latent scale). Most of this long-term repeatability could be explained by modest heritability (h2social: 0.152 [0.094, 0.207]; h2partners: 0.113 [0.076, 0.149]) with small long-term maternal effects (m2social: 0.000 [0.000, 0.045]; m2partners: 0.000 [0.000, 0.041]). Our models capture the majority of variance in our behavioral traits, with much of the variance explained by temporally changing factors, such as group of residence, highlighting potential limits to the evolvability of our trait due to social and environmental constraints.

Stone tools differences across three capuchin monkey populations: food’s physical properties, ecology, and culture

Robust capuchin monkeys (Sapajus) are known for processing mechanically challenging foods, having morphological adaptations to do so. However, several populations go beyond body limitations by using stone tools to expand their food range. Those populations use stones in a variety of ways, goals, and with different frequencies. Stone tool size correlates with the food’s resistance within some populations. However, we have no detailed comparisons to identify if this correlation is the same across populations. This study described and compared stone raw material availability, food’s physical properties (hardness and elasticity), and stone tool weight in three populations of bearded capuchin monkeys (Sapajus libidinosus), including a newly described site (Chapada dos Veadeiros National Park, CVNP). The differences we observed regarding stone tool weight selection among sites were not correlated to the food’s physical properties we analyzed. Lithic resource availability could partly explain some differences in the stone tools used. However, the tool weight differences are larger than the raw material variance across sites, meaning some distinctions are possible behavioral traditions, such as the same fruit (Hymenaea) being processed with bigger than needed tools in CVNP than in the other two sites. Capuchin monkey behavioral variability in stone tool use can be caused by several interacting factors, from ecological to cultural.

Signatures of adaptive evolution in platyrrhine primate genomes

The platyrrhine family Cebidae (capuchin and squirrel monkeys) exhibit among the largest primate encephalization quotients. Each cebid lineage is also characterized by notable lineage-specific traits, with capuchins showing striking similarities to Hominidae such as high sensorimotor intelligence with tool use, advanced cognitive abilities, and behavioral flexibility. Here, we take a comparative genomics approach, performing genome-wide tests for positive selection across five cebid branches, to gain insight into major periods of cebid adaptive evolution. We uncover candidate targets of selection across cebid evolutionary history that may underlie the emergence of lineage-specific traits. Our analyses highlight shifting and sustained selective pressures on genes related to brain development, longevity, reproduction, and morphology, including evidence for cumulative and diversifying neurobiological adaptations across cebid evolution. In addition to generating a high-quality reference genome assembly for robust capuchins, our results lend to a better understanding of the adaptive diversification of this distinctive primate clade.

Stone tools improve diet quality in wild monkeys

Tool use is a fundamental feature of human evolution. Stone tools are in the archaeological record from 3.4 Ma, even before Homo,1 and the use of stone tools probably predated the split between hominins and panins.2 Using tools (hereafter, tooling cf Fragaszy and Mangalam3) is hypothesized to have improved hominins' foraging efficiency or access to high-quality foods.4-7 This hypothesis is supported if feeding with tools positively contributes to diet quality in extant non-human primates or if foraging efficiency is increased by tooling. However, the contribution of tooling to non-human primates' foraging success has never been investigated through a direct analysis of nutritional ecology.8,9 We used multi-dimensional nutritional geometry to analyze energy and macronutrients (nonstructural carbohydrates, lipids, and protein) in the diets of wild capuchin monkeys (Sapajus libidinous) that routinely crack palm nuts with stone hammers.10,11 We show that eating nuts obtained through tooling helps monkeys to achieve more consistent dietary intakes. Tooling increased the net energy gain by 50% and decreased the proportion of fiber ingested by 7%. Tooling also increased the daily non-protein energy intake. By contrast, protein intake remained constant across foraging days, suggesting a pattern of macronutrient regulation called protein prioritization, which is also found in contemporary humans.8,9 In addition, tooling reduced dispersion in the ratio of protein to non-protein energy, suggesting a role in macronutrient balancing. Our findings suggest that tooling prior to tool making could have substantially increased the nutritional security of ancestral hominins, sowing the seeds for cultural development.5,7 VIDEO ABSTRACT.

A robust tool kit: First report of tool use in captive crested capuchin monkeys (Sapajusrobustus).

Primate tool use is of great interest but has been reported only in a limited number of species. Here we report tool use in crested capuchin monkeys (Sapajus robustus), an almost completely unstudied robust capuchin species. Crested capuchins and their sister species, the yellow-breasted capuchin, diverged from a common ancestor over 2 million years ago, so this study fills a significant gap in understanding of tool use capacity and variation within the robust capuchin monkey radiation. Our study group was a captive population of seven individuals at the Santa Ana Zoo in California. The monkeys were given no prior training, and they were provided with a variety of enrichment items, including materials that could be used as tools as well as hard-to-access resources, for open-ended interactions. In 54 observation hours, monkeys performed eleven tool use actions: digging, hammering, probing, raking, sponging, striking, sweeping, throwing, waving, wedging, and wiping. We observed tool modification, serial tool use, and social learning opportunities, including monkeys' direct observation of tool use and tolerated scrounging of foods obtained through tool use. We also observed significant individual skew in tool use frequency, with one individual using tools daily, and two individuals never using tools during the study. While crested capuchins have never been reported to use tools in the wild, our findings provide evidence for the species' capacity and propensity for tool use, highlighting the urgent need for research on this understudied, endangered primate. By providing detailed data on clearly identified S. robustus individuals, this study marks an effort to counteract the overgeneralization in the captive literature in referring to any robust capuchins of unknown provenance or ancestry as Cebus apella, a practice that obfuscates potential differences among species in tool use performance and repertoire in one of the only species-rich tool-using genera in the world.