Are capuchin monkeys (Cebus apella) inequity averse?

It has been reported that capuchin monkeys reject a less preferred food (LPF) when they see a partner capuchin receive a more preferred food (PF) for performing the same task. This behaviour was taken as evidence of 'inequity aversion', but an alternative hypothesis is that capuchins reject the LPF because of the mere presence of the PF. We tested this hypothesis in a paradigm, which consisted of presenting two different foods (one PF and one LPF) on a tray and allowing the capuchin to take only the LPF. Refusals to initiate the trial and refusals to take and eat the LPF were higher when the PF was hidden (hiding condition) and when the PF was accumulated in sight but out of reach of the subject (accumulation condition) compared to when two pieces of LPF were placed on the tray (control condition). Interestingly, the subject behaved as in the control condition when its partner was given and ate the PF (partner condition). We argue that capuchins' refusals were due to the frustration of seeing and not obtaining the PF, and that seeing the partner eating increases the LPF acceptance.

Relational spatial reasoning by a nonhuman: the example of capuchin monkeys

The authors review spontaneous manipulation and spatial problem solving by capuchin monkeys to illuminate the nature of relational reasoning (wherein two or more elements of a problem or situation are considered together to arrive at a course of action) that these monkeys use in goal-directed activity. Capuchin monkeys master problems with one, two, or three spatial relations, and if more than one relation, at least two relations may be managed concurrently. They can master static and dynamic relations and, with sufficient practice, can produce specific spatial relations through both direct and distal action. Examining capuchins' spatial problem-solving behavior with objects in the framework of a spatial relational reasoning model leads to new interpretations of previous studies with these monkeys and other nonhuman animals. The model produces a variety of testable predictions concerning the contribution of relational properties to spatial reasoning. It also provides conceptual linkages with neurological processes and cognitive analyses of physical reasoning. Understanding relational spatial reasoning, including tool use, in a wider view is vital to informed, principled comparison of problem solving and the use of technology across species, across ages within species, and across eras in human prehistory.

Ordinal representation of numeric quantities by brown capuchin monkeys (Cebus apella)

Using techniques established by E. M. Brannon and H. S. Terrace (2000) with rhesus macaques (Macaca mulatta), the authors tested the ability of brown capuchins (Cebus apella) to order arrays of items ranging in quantity from 1 to 9. Three monkeys were trained on a touch screen to select the quantities 1-4 in ascending order. The monkeys exhibited successful transfer of this ability to novel representations of the quantities 1-4 and to pairs of the novel quantities 5-9. Patterns of responding with respect to numeric distance and magnitude were similar to those seen in human subjects, suggesting the use of similar psychological processes. The capuchins demonstrated an ordinal representation of quantity equivalent to that shown in Old World monkeys.

Multi-stage mental process for economic choice in capuchins

We studied economic choice behavior in capuchin monkeys by offering them to choose between two different foods available in variable amounts. When monkeys selected between familiar foods, their choice patterns were well-described in terms of relative value of the two foods. A leading view in economics and biology is that such behavior results from stimulus-response associations acquired through experience. According to this view, values are not psychologically real; they can only be defined a posteriori. One prediction of this associative model is that animals faced for the first time with a new pair of foods learn to choose between them gradually. We tested this prediction. Surprisingly, we find that monkeys choose as effectively between new pairs of foods as they choose between familiar pairs of foods. We therefore, propose a cognitive model in which economic choice results from a two-stage mental process of value-assignment and decision-making. In a follow-up experiment, we find that the relative value assigned to three foods in sessions in which we tested them against each other combine according to transitivity.

Watching the best nutcrackers: what capuchin monkeys (Cebus apella) know about others' tool-using skills

The present work is part of a decade-long study on the spontaneous use of stones for cracking hard-shelled nuts by a semi-free-ranging group of brown capuchin monkeys (Cebus apella). Nutcracking events are frequently watched by other individuals--usually younger, less proficient, and that are well tolerated to the point of some scrounging being allowed by the nutcracker. Here we report findings showing that the choice of observational targets is an active, non-random process, and that observers seem to have some understanding of the relative proficiency of their group mates, preferentially watching the more skilled nutcrackers, which enhances not only scrounging payoffs, but also social learning opportunities.

Capuchin stone tool use in Caatinga dry forest

Wild capuchin monkeys inhabiting dry forest were found to customarily use tools as part of their extractive foraging techniques. Tools consisted of twigs and sticks, often modified, which were used to probe for insects and, most frequently, of stones of a variety of sizes and shapes used for cracking and digging. The use of tools for digging has been thought to be restricted to humans. These monkeys, living in a harsh dry habitat, survive food limitation and foraging time constraints through their extensive tool use.

Cooperative problem solving by tufted capuchin monkeys (Cebus apella): Spontaneous division of labor, communication, and reciprocal altruism

Using an experimentally induced cooperation task, the authors investigated whether tufted capuchin monkeys (Cebus apella) share the following 3 characteristics of cooperation with humans: division of labor, communication, and reciprocal altruism. In Experiment 1, the authors trained individual monkeys to perform the necessary sequence of actions for rewards and tested them in pairs to assess whether they could solve the task by spontaneously dividing the sequence of actions. All pairs solved this task. In Experiment 2, monkeys worked in the cooperation task and a task requiring no partner help. They looked at the partner significantly longer in the former task than in the latter, but communicative intent could not be determined. In Experiment 3, only 1 of 2 participants obtained a reward on each trial. Monkeys maintained cooperation when their roles were reversed on alternate trials. Their cooperative performances demonstrated division of labor; results suggest task-related communication and reciprocal altruism.

Reconciliation in wild white-faced capuchins (Cebus capucinus)

The likelihood of reconciliation (defined as preferential peaceful contact among former opponents following conflicts) has been predicted to vary positively with relationship value and compatibility, and negatively with relationship security. Long-term data on wild white-faced capuchins (Cebus capucinus) indicate that dyads consisting of an adult female and an alpha male have high value and compatibility, but low security. Two studies of C. capucinus postconflict (PC) behavior were carried out at Lomas Barbudal Biological Reserve, Costa Rica. One study consisted of 30-min PC and matched control (MC) follows. The second study extracted PC and MC periods from long follows, yielding PC/MC periods averaging 105 min. In study 2, but not study 1, significantly more PC/MC pairs were attracted (former opponents affiliated with each other sooner in the PC period than in the MC period) than were dispersed (former opponents affiliated with each other sooner in the MC period than in the PC period). Reconciliation in study 2 could not be explained as a by-product of former opponents' tendency to seek affiliative contact with conspecifics generally, or of the spatial proximity of opponents following conflicts. Attempted reconciliation was less likely to be followed by renewed aggression when reconciliation attempts were delayed following conflicts. The data were insufficient for a formal test of differences in conciliatory tendency (the difference between the number of attracted and dispersed PC/MC pairs, divided by the total number of pairs) among dyad types to be conducted.

Are monkeys aesthetists? Rensch (1957) revisited

Three experiments assessed whether capuchin monkeys (Cebus apella) and squirrel monkeys (Saimiri sciureus) prefer regular and symmetrical visual patterns. Pictorial representations of faces were included in 1 stimulus set. When the monkeys could pick up and manipulate small cards bearing the stimuli, all preferences expressed by capuchins and most of those expressed by squirrel monkeys were for regular stimuli. Symmetry of the patterns was influential but not essential. Some preferences were also found for faces. When images of the patterns were presented on a touch screen, capuchins continued to express preferences especially for regular and symmetrical stimuli, but they showed some avoidance of faces. Squirrel monkeys responded less discriminatingly to the touch screen stimuli. The findings provide support for B. Rensch's (1957) claim that monkeys prefer visual stimuli that humans find aesthetically pleasing.

A concept of value during experimental exchange in brown capuchin monkeys, Cebus apella

We evaluated the response of brown capuchin monkeys to two differentially valued tokens in an experimental exchange situation akin to a simple barter. Monkeys were given a series of three tests to evaluate their ability to associate tokens with food, then their responses were examined in a barter situation in which tokens were either limited or unlimited. Capuchins did not perform barter in the typical sense, returning the tokens which were associated with the reward. However, females, but not males, showed a different response, preferring the higher-value token. This may indicate that they learned to prefer one token over the other rather than to associate the tokens with their specific rewards. This sex difference parallels previous findings of greater reciprocity in female brown capuchins than in males.

Reunion displays in captive male brown capuchins (Cebus apella)

Separation and subsequent reintroduction of brown capuchins (Cebus apella) can lead to reunion displays during which individuals will embrace and emit high-pitched, loud vocalizations. These displays were investigated in three male capuchins: two adults and one juvenile. These subjects were part of a larger captive social group held at the Capuchin Laboratory, Hiram College, OH, USA. We hypothesized that males would engage in reunion displays following separation regardless of the order of reintroduction, as evidence of an affiliative bond judged by concurrent social behavior. Sixty separations were conducted as part of weekly husbandry over a period of 13 months. Occurrence of reunion displays between the males was recorded with the initiator also noted. Reunion displays among males were found to occur only between the juvenile and alpha male, and all displays were initiated by the juvenile. Displays were highly influenced by the order of reintroduction. We suggest that reunion displays operate to reaffirm social relationships, particularly during situations of social tension.

Discrimination of functionally appropriate and inappropriate throwing tools by captive tufted capuchins (Cebus apella)

A tool-throwing task was used to test whether capuchin monkeys understand the difference between functionally appropriate and functionally inappropriate tools. A group of monkeys was trained to obtain a sticky treat from a container outside their enclosure using a projectile attached to one end of an anchored line. Subsequently, these monkeys were given choice tests between functional and nonfunctional versions of tools used in training. A different feature of the tool was varied between alternatives in each choice test. The monkeys chose to use functional tools significantly more often than nonfunctional tools in early exposures to each choice test. A second experiment tested whether these subjects, as well as a second group of minimally trained participants, could distinguish between functional and nonfunctional tools that appeared different from those used in training. A new set of design features was varied between tools in these choice tests. All participants continued to choose functional tools significantly more often than nonfunctional tools, regardless of their tool-throwing experience or the novel appearance of the tools. These results suggest that capuchin monkeys, like chimpanzees studied in similar experiments, are sensitive to a variety of functionally relevant tool features.

Transport of tools to food sites in tufted capuchin monkeys (Cebus apella)

Tool use and transport represent cognitively important aspects of early hominid evolution, and nonhuman primates are often used as models to examine the cognitive, ecological, morphological and social correlates of these behaviors in order to gain insights into the behavior of our early human ancestors. In 2001, Jalles-Filho et al. found that free-ranging capuchin monkeys failed to transport tools (stones) to food sites (nuts), but transported the foods to the tool sites. This result cast doubt on the usefulness of Cebus to model early human tool-using behavior. In this study, we examined the performance of six captive tufted capuchin monkeys (Cebus apella) in a tool transport task. Subjects were provided with the opportunity to transport two different tools to fixed food reward sites when the food reward was visible from the tool site and when the food reward was not visible from the tool site. We found that the subjects quickly and readily transported probing tools to an apparatus baited with syrup, but rarely transported stones to a nut-cracking apparatus. We suggest that the performance of the capuchins here reflects an efficient foraging strategy, in terms of energy return, among wild Cebus monkeys.

Do squirrel monkeys (Saimiri sciureus) and capuchin monkeys (Cebus apella) predict that looking leads to touching?

Squirrel monkeys (Saimiri sciureus) and capuchin monkeys (Cebus apella) were tested using an expectancy violation procedure to assess whether they use an actor's gaze direction, signaled by congruent head and eye orientation, to predict subsequent behavior. The monkeys visually habituated to a repeated sequence in which the actor (a familiar human or a puppet) looked at an object and then picked it up, but they did not react strongly when the actor looked at an object but then picked up another object. Capuchin monkeys' responses in the puppet condition were slightly more suggestive of expectancy. There was no differential responding to congruent versus incongruent look-touch sequences when familiarization trials were omitted. The weak findings contrast with a strongly positive result previously reported for tamarin monkeys. Additional evidence is required before concluding that behavior prediction based on gaze cues typifies primates; other approaches for studying how they process attention cues are indicated.

Wild capuchins (cebus capucinus) fail to use tools

From September through November 2000 we conducted an experimental field study of tool use in a group of 15 wild white-faced capuchins (Cebus capucinus) in Costa Rica. The problem presented to the capuchins involved the use of wooden dowels as probes to obtain a food reward (two bananas) located inside a clear Plexiglas box. Specifically, the task required the capuchins to manually insert a dowel into any of six holes drilled into the box in order to push the bananas off a shelf. The banana could then be retrieved through a large opening at the bottom of the box. The capuchins visited the tool-use platform 702 times over the course of 55 consecutive days and under several experimental conditions. During the first 21 days of the study, they explored the box but made no attempt to touch or pick up the dowels. Even after we placed the dowels in the holes, the capuchins only occasionally manipulated them. Overall, the results indicate that the capuchins did not use a tool to solve this novel foraging problem.

A Capuchin monkey (Cebus apella) recognizes when people do and do not know the location of food

In a previous study, Kuroshima and colleagues demonstrated that capuchin monkeys (Cebus apella) learned to discriminate between a "knower" who inspected a box for food, and a "guesser" who did not. The aim of the present study was to specify whether the subjects learned a simple conditional discrimination or a causal relationship that seeing leads to knowing. In experiment 1, we introduced five types of novel containers to two subjects. Each container was of different shape and color. The subjects gradually learned to reach toward the container the knower suggested. In experiment 2, we diversified the behavior of the knower and the guesser. In experiment 3, in order to eliminate the possibility of discrimination based on differences in the magnitude and the complexity of two trainers, we equated their behaviors. One subject adapted to the novel behaviors of the knower and the guesser, successfully discriminating the two trainers. Thus this monkey clearly learned to use the inspecting action of the knower and the non-inspecting action of the guesser as a discriminative cue to recognize the baited container. This result suggests that one capuchin monkey learned to recognize the relationship between seeing and knowing.

Monkeys reject unequal pay

During the evolution of cooperation it may have become critical for individuals to compare their own efforts and pay-offs with those of others. Negative reactions may occur when expectations are violated. One theory proposes that aversion to inequity can explain human cooperation within the bounds of the rational choice model, and may in fact be more inclusive than previous explanations. Although there exists substantial cultural variation in its particulars, this 'sense of fairness' is probably a human universal that has been shown to prevail in a wide variety of circumstances. However, we are not the only cooperative animals, hence inequity aversion may not be uniquely human. Many highly cooperative nonhuman species seem guided by a set of expectations about the outcome of cooperation and the division of resources. Here we demonstrate that a nonhuman primate, the brown capuchin monkey (Cebus apella), responds negatively to unequal reward distribution in exchanges with a human experimenter. Monkeys refused to participate if they witnessed a conspecific obtain a more attractive reward for equal effort, an effect amplified if the partner received such a reward without any effort at all. These reactions support an early evolutionary origin of inequity aversion.

How do tufted capuchin monkeys (Cebus apella) understand causality involved in tool use?

Four tufted capuchin monkeys (Cebus apella) were trained to choose from 2 hook-like tools, 1 of which successfully led to collecting food, whereas the other did not because of inappropriate spatial arrangement of the tool and the food. In Experiment 1, all of the monkeys successfully learned the basic task. The monkeys performed successfully with tools of novel colors and shapes in Experiments 2-5. These results demonstrate that the monkeys used the spatial arrangement of the tool and the food as a cue. However, they failed when there were obstacles (Experiment 6) or traps (Experiment 7) on the path along which the monkeys dragged tools. These results may suggest that capuchin monkeys understand the spatial relationship between 2 items, namely, food and the tool, but do not understand the spatial relationship among 3 items, namely, food, tool, and the environmental condition. The possible role of stimulus generalization is also considered.

Abstract-concept learning and list-memory processing by capuchin and rhesus monkeys

Three capuchin monkeys (Cebus apella) touched the lower of 2 pictures (same) or a white rectangle (different), increased same/different abstract-concept learning (52% to 87%) with set-size increases (8 to 128 pictures), and were better than 3 rhesus monkeys (Macaca mulatta). Three other rhesus that touched the top picture before choices learned similar to capuchins but were better at list-memory learning. Both species' serial position functions were similar in shape and changes with retention delays. Other species showed qualitatively similar shape changes but quantitatively different time-course changes. In abstract-concept learning, qualitative similarity was shown by complete concept learning, whereas a quantitative difference would have been a set-size slope difference. Qualitative similarity is discussed in relation to general-process versus modular cognitive accounts.

Capuchin cognitive ecology: cooperation based on projected returns

Stable cooperation requires that each party's pay-offs exceed those available through individual action. The present experimental study on brown capuchin monkeys (Cebus apella) investigated if decisions about cooperation are (a) guided by the amount of competition expected to follow the cooperation, and (b) made instantaneously or only after a period of familiarization. Pairs of adult monkeys were presented with a mutualistic cooperative task with variable opportunities for resource monopolization (clumped versus dispersed rewards), and partner relationships (kin versus nonkin). After pre-training, each pair of monkeys (N=11) was subjected to six tests, consisting of 15 2 min trials each, with rewards available to both parties. Clumped reward distribution had an immediate negative effect on cooperation: this effect was visible right from the start, and remained visible even if clumped trials alternated with dispersed trials. The drop in cooperation was far more dramatic for nonkin than kin, which was explained by the tendency of dominant nonkin to claim more than half of the rewards under the clumped condition. The immediacy of responses suggests a decision-making process based on predicted outcome of cooperation. Decisions about cooperation thus take into account both the opportunity for and the likelihood of subsequent competition over the spoils.

Cone pigment variations in four genera of new world monkeys

Previous research revealed significant individual variations in opsin genes and cone photopigments in several species of platyrrhine (New World) monkeys and showed that these in turn can yield significant variations in color vision. To extend the understanding of the nature of color vision in New World monkeys, electroretinogram flicker photometry was used to obtain spectral sensitivity measurements from representatives of four platyrrhine genera (Cebus, Leontopithecus, Saguinus, Pithecia). Animals from each genus were found to be polymorphic for middle to long-wavelength (M/L) sensitive cones. The presence of a short-wavelength sensitive photopigment was established as well so these animals conform to the earlier pattern in predicting that all male monkeys are dichromats while, depending on their opsin gene array, individual females can be either dichromatic or trichromatic. Across subjects a total of five different M/L cone pigments were inferred with a subset of three of these present in each species.

Cross-site differences in foraging behavior of white-faced capuchins (Cebus capucinus)

Researchers have identified a variety of cross-site differences in the foraging behavior of free-ranging great apes, most notably among chimpanzees (Pan troglodytes) and more recently orangutans (Pongo pygmaeus), that are not due to obvious genetic or ecological differences. These differences are often referred to as "traditions." What is not known is whether this high level of interpopulation variation in behavior is limited to hominoids. In this study, we use long-term data from three Costa Rican field sites that are geographically close and similar ecologically to identify potential foraging traditions in white-faced capuchins (Cebus capucinus). Foraging traditions are predicted in Cebus because of many behavioral and morphological convergences between this genus and the great apes. The processing techniques used for the same food species were compared across sites, and all differences found were classified as present, habitual, or customary. Proximity data were also analyzed to determine if social learning mechanisms could explain variation in foraging behavior. Of the 61 foods compared, we found that 20 of them are processed differently by capuchins across sites. The differences involve pound, rub, tap, "fulcrum," "leaf-wrap," and "army ant following." For most of the differences with enough data to analyze, the average proximity score of the "matched" dyads (two individuals within a group who shared a "different" processing technique) was statistically higher than the average proximity score of the remaining "unmatched" dyads.

Capuchin monkey tool use and Léon Croizat's ideas on the evolution of human behavior

This note reviews Léon Croizat's ideas about the evolution of human behavior, based on his evaluation of the tool use capabilities of a capuchin monkey. Croizat theorized mainly on his orthogenetic view to explain such behavior. Interesting enough is the timeframe (1962) and context of his statement and the monkey's model used for such explanation. In this direction, some comments are provided considering the current knowledge of capuchin tool using and its potential implications for modeling hominid evolution.

Contexts and behavioral correlates of trill vocalizations in wild white-faced capuchin monkeys (Cebus capucinus)

Primate vocalizations that appear to occur independently of specific contexts typically are considered to be contact calls. However, results from several recent studies indicate that these calls function to facilitate social interactions. White-faced capuchin monkeys (Cebus capucinus) emit a high-frequency vocalization, termed a "trill," in social interactions and during travel. In this study, immatures emitted most trills, but adult females also trilled; by contrast, adult males rarely trilled. Infants emitted the majority of trills, and they trilled at significantly higher rates than adult females. Infants trilled most when approaching other individuals. Furthermore, infants emitted proportionately more trills than other age classes when approaching other individuals. I therefore focused on the detailed context and immediate behavioral correlates of trilling by infants. Infants that trilled when approaching others tended to interact affiliatively with them subsequently (i.e., climbing on, touching, receiving grooming, and performing food inspection) more than infants that did not trill when approaching. Therefore, infant trilling may have had an immediate effect on the recipient's behavior.

Understanding of the relationship between seeing and knowing by tufted capuchin monkeys (Cebus apella)

The ability of four tufted capuchin monkeys (Cebus apella) to recognize the causal connection between seeing and knowing was investigated. The subjects were trained to follow a suggestion about the location of hidden food provided by a trainer who knew where the food was (the knower) in preference to a trainer who did not (the guesser). The experimenter baited one of three opaque containers behind a cardboard screen so that the subjects could not see which of the containers hid the reward. In experiment 1, the knower appeared first in front of the apparatus and looked into each container; next, the guesser appeared but did not look into any containers. Then the knower touched the correct cup while the guesser touched one of the three randomly. The capuchin monkeys gradually learned to reach toward the cup that the knower suggested. In experiment 2, the subjects adapted to a novel variant of the task, in which the guesser touched but did not look into any of the containers. In experiment 3, the monkeys adapted again when the knower and the guesser appeared in a random order. These results suggest that capuchin monkeys can learn to recognize the relationship between seeing and knowing.

Do tufted capuchin monkeys (Cebus apella) spontaneously deceive opponents? A preliminary analysis of an experimental food-competition contest between monkeys

A new laboratory procedure which allows the study of deceptive behavior in nonhuman primates is described. Pairs of tufted capuchin monkeys faced each other in a food-competition contest. Two feeder boxes were placed between the monkeys. A piece of food was placed in one of the boxes. The subordinate individual was able to see the food and to open the box to obtain the bait. A dominant male was unable to see the food or to open the box but was able to take the food once the box was opened by the subordinate. In experiment 1, two of four subordinate monkeys spontaneously started to open the unbaited box first with increasing frequency. Experiment 2 confirmed that this "deceptive" act was not due to a drop in the rate of reinforcement caused by the usurping dominant male, under the situation in which food sometimes automatically dropped from the opened box. In experiment 3, two subordinate monkeys were rerun in the same situation as experiment 1. One of them showed some recovery of the "deceptive" act but the other did not; instead the latter tended to position himself on the side where there was no food before he started to open the box. Although the results do not clearly indicate spontaneous deception, we suggest that operationally defined spontaneous deceptive behaviors in monkeys can be analyzed with experimental procedures such as those used here.

Representation of serial order in humans: a comparison to the findings with monkeys (Cebus apella)

In a number of studies, serially organized behavior in humans has been examined using a procedure developed for use with pigeons and monkeys. There have been few direct comparisons, however, between the data collected with humans and that collected with nonhumans, and none with respect to the interesting latency effects noted with nonhumans. The purpose of this experiment was to make this comparison. Human subjects were trained to respond to five simultaneously presented stimuli (A, B, C, D, and E) in a specific order (A-->B-->C-->D-->E) and were then tested with all 10 pairwise combinations of the five stimuli, followed by all 10 triplet combinations of the five stimuli. Mirroring the findings with monkeys (Cebus apella), humans showed a first-item effect, a missing-item effect, and a symbolic-distance effect. These results suggest that during the course of learning the five-item serial-order task humans form an internal representation of the series and access that representation to guide their behavior.

Transport of tools and mental representation: is capuchin monkey tool behaviour a useful model of Plio-Pleistocene hominid technology?

Capuchin monkeys display greatly developed tool-using capacities, performing successfully a variety of tool-tasks. Impressed by their achievements in this respect, some investigators have suggested that capuchin tool-using behaviour could be used as a model of the tool behaviour of the first hominids. The transport of tools, a task requiring complex cognitive capabilities, is an essential ingredient in the technological behaviour of the first hominids. In this way, to qualify as another source for modelling hominid behavioural evolution, capuchins had to exhibit proficiency in the transport of tools. We investigated this problem through experiments designed to elicit the transport of objects. The results showed that the monkeys were able to transport food to be processed with the use of tools, but failed when the tools themselves had to be transported. Our hypothesis is that a limited capacity for abstract representation, together with the lack of a regulatory system ensuring that the food would not be lost and consumed by another individual during the search for and transport of the tools, were responsible for such a failure. We conclude that the tool-using behaviour of capuchins presents no functional analogy with the tool behaviour of the Plio-Pleistocene hominids, and that capuchin monkeys are a very inadequate source for modelling Plio-Pleistocene hominid's technological behaviour.

Solving a cooperation task without taking into account the partner's behavior: the case of capuchin monkeys (Cebus apella)

Four pairs of tufted capuchin monkeys (Cebus apella) were tested in a task requiring that both partners pull a handle simultaneously in order for both to be rewarded. The experimental design, an improved version of that of R. Chalmeau, E. Visalberghi, and A. Gallo (1997), aimed at assessing the extent to which a monkey that is pulling takes account of the behavior and spatial position of its partner, that is, whether the monkey understands what cooperation involves. Although all pairs succeeded, pulling was not affected by the partner's behavior, and it was affected only to a certain extent by the partner's spatial position. In addition, more experienced capuchins did not outperform naive individuals. The finding that capuchins were successful without understanding the role of the partner suggests that their cooperation is not cognitively grounded, as has been argued in descriptions of the hunting behavior of wild capuchins.

Transfer of tools and food between groups of tufted capuchins (Cebus apella)

This research examined tool and food transfer between two groups of tufted capcuhin monkeys (Cebus apella). Subjects in one group transferred stones to subjects in a second group who in turn used the stones as cutting tools and then transferred food to subjects in the first group. Aspects of the capuchins' behavior are similar to those described for food-sharing in Cebus, cooperative tool use in Papio, and tool and food exchange in Pan. We propose that tool use and food-sharing facilitate tool and food transfer between captive groups of Cebus apella.

Relationship of early infant state measures to behavior over the first year of life in the tufted capuchin monkey (Cebus apella)

Data on activity states were collected from 29 group-housed capuchin monkey (Cebus apella) infants for 3 h each week from birth to 11 weeks of age. The amounts of time spent in sleeping/drowsy, alert-quiet, and alert-active states were measured in these subjects. Videotaped observations of these infants were recorded 3 times/week in the home cage over the first year of life and were scored for a number of social and exploratory behaviors. The extent to which early infant activity state scores predicted later behavior in the home cage was examined. Infant state measures correlated significantly with home cage behavior during months 2-6 in that infants that had been more active in early infancy spent more time alone, with other animals, and in exploration and play and less time with mothers than did quieter infants. Early state measures were less successful in predicting home cage scores beyond 8 months of age, whereas differences in behavior attributable to housing variables became more salient in the latter part of the first year. There was also a negative correlation between mother and infant activity in months 2 and 3, in that more sedentary mothers tended to have more active infants.

Social context and consumption of unfamiliar foods by capuchin monkeys (Cebus apella) over repeated encounters

Visalberghi and Fragaszy [Animal Behaviour 49:1089-1095, 1995] have shown that social influences affect acceptance of novel foods. However, little is known about the temporal course on which such influences act (e.g., for how long they persist and for how many encounters they are effective). To explore this issue, 11 adult tufted capuchins were observed during ten successive encounters with eight unfamiliar foods (phase 1, in which subjects were tested in social or individual condition) and ten more encounters 6 months later (phase 2, in which all subjects were tested in social condition). A total of 680 observational sessions were carried out. Results show that during the first five encounters in phase 1, capuchins ate more when they encountered these foods in the presence of their groupmates than if they encountered them alone. Thereafter, during the second five encounters of phase 1, foods were consumed equivalently whether presented to monkeys socially or individually. In phase 2, the foods were consumed equivalently regardless of the previous circumstance of their presentation (social or alone). In phase 2, consumption was similar to that scored in a previous study for familiar foods [Visalberghi & Fragaszy, Animal Behaviour 49:1089-1095, 1995]. We conclude that 1) foods remain unfamiliar to capuchins only for the first few encounters, 2) social facilitation of consumption of unfamiliar foods is of limited duration, and 3) individuals consumed equivalent amounts of an unfamiliar food when they repeatedly encountered it alone or in the presence of groupmates. These results caution those who interpret similar feeding habits in primate groups as evidence of social influences.

Effects of upright posture on hand preference for reaching vs. the use of probing tools by tufted capuchins (Cebus apella)

This research examined the effects of task (reaching vs. tool use) and posture (quadrupedal vs. bipedal) on hand preference in tufted capuchins (Cebus apella). Regarding direction of hand preference, we found a significant main effect of posture, as the bipedal stance elicited greater use of the right hand than did the quadrupedal stance, and a significant posture x task interaction, as bipedal reaching elicited greater use of the right hand than did other postural and task conditions. Further, we found a significant main effect of task on strength of hand preference, as tool use elicited more consistent use of one hand over the other than did reaching. Our findings indicate that bipedal reaching facilitates a mild right-hand bias in intensely manipulative primates. We speculate that this moderate bias may have been pushed in the direction of nearly exclusive right-hand preference in most humans with the development of complex tool use.

Environmental enrichment of brown capuchins (Cebus apella): behavioral and plasma and fecal cortisol measures of effectiveness

No consensus exists about the quantity and variety of environmental enrichment needed to achieve an acceptable level of psychological well-being among singly housed primates. Behavioral and plasma and fecal cortisol measures were used to evaluate the effectiveness of four levels of toy and foraging enrichment provided to eight wild-caught, singly housed adult male brown capuchins (Cebus apella). The 16-week-long study comprised six conditions and began with a 4-week-long preexperimental and ended with a 4-week-long postexperimental period during which the subjects were maintained at baseline enrichment levels. During the intervening 8 weeks, the subjects were randomly assigned to a sequence of four 2-week-long experimental conditions: control (baseline conditions), toy (the addition of two plastic toys to each cage), box (access to a foraging box with food treats hidden within crushed alfalfa), and box & toy (the addition of two plastic toys and access to a foraging box). Behavioral responses to changes in enrichment were rapid and extensive. Within-subject repeated-measure ANOVAs with planned post hoc contrasts identified highly significant reductions in abnormal and undesirable behaviors (and increases in normal behaviors) as the level of enrichment increased from control to toy to box to box & toy. No significant behavioral differences were found between the control and pre- and postexperimental conditions. Plasma and fecal cortisol measures revealed a different response to changing enrichment levels. Repeated-measure ANOVA models found significant changes in both these measures across the six conditions. The planned post hoc analyses, however, while finding dramatic increases in cortisol titers in both the pre- and postexperimental conditions relative to the control condition, did not distinguish cortisol responses among the four enrichment levels. Linear regressions among weekly group means in behavioral and cortisol measures (n=16) found that plasma cortisol was significantly predicted by the proportions of both normal and abnormal behaviors; as the proportion of normal behaviors increased, the plasma cortisol measures decreased. Plasma cortisol weekly group means were also significantly and positively predicted by fecal cortisol weekly group means, but no behavioral measure significantly predicted fecal cortisol weekly group means. In sum, these findings argue strongly that access to a variety of toy and foraging enrichment positively affects behavioral and physiological responses to stress and enhances psychological well-being in singly housed brown capuchins.

Learning and limits of use of eye gaze by capuchin monkeys (Cebus apella) in an object-choice task

The ability of 3 capuchin monkeys (Cebus apella) to use experimenter-given cues to solve an object-choice task was assessed. The monkeys learned to use explicit gestural and postural cues and then progressed to using eye-gaze-only cues to solve the task, that is, to choose the baited 1 of 2 objects and thus obtain a food reward. Increasing cue-stimulus distance and introducing movement of the eyes impeded the establishment of effective eye-gaze reading. One monkey showed positive but imperfect transfer of use of eye gaze when a novel experimenter presented the cue. When head and eye orientation cues were presented simultaneously and in conflict, the monkeys showed greater responsiveness to head orientation cues. The results show that capuchin monkeys can learn to use eye gaze as a discriminative cue, but there was no-evidence for any underlying awareness of eye gaze as a cue to direction of attention.

Sleeping site preferences in tufted capuchin monkeys (Cebus apella nigritus)

The characteristics and availability of the sleeping sites used by a group of 27 tufted capuchin monkeys (Cebus apella nigritus) were studied during 17 months at the Iguazu National Park, Argentina. We tested different hypotheses regarding possible ultimate causes of sleeping-site selection. Most sleeping sites were located in areas of tall, mature forest. Of the 34 sleeping sites the monkeys used during 203 nights, five were more frequently used than the others (more than 20 times each, constituting 67% of the nights). Four species of tree (Peltophorum dubium, Parapiptadenia rigida, Copaifera langsdorfii and Cordia trichotoma) were the most frequently used. They constituted 82% of all the trees used, though they represent only 12% of the trees within the monkeys' home range which had a diameter at breast height (DBH) > 48.16 cm (1 SD below the mean DBH of sleeping trees). The sleeping trees share a set of characteristics not found in other trees: they are tall emergent (mean height +/- SD = 31.1+/-5.2 m) with large DBH (78.5+/-30.3 cm), they have large crown diameter (14+/-5.5 m), and they have many horizontal branches and forks. Adult females usually slept with their kin and infants, while peripheral adult males sometimes slept alone in nearby trees. We reject parasite avoidance as an adaptive explanation for the pattern of sleeping site use. Our results and those from other studies suggest that predation avoidance is a predominant factor driving sleeping site preferences. The patterns of aggregation at night and the preference for trees with low probability of shedding branches suggest that social preferences and safety from falling during windy nights may also affect sleeping tree selection. The importance of other factors, such as seeking comfort and maintaining group cohesion, was not supported by our results. Other capuchin populations show different sleeping habits which can be explained by differences in forest structure and by demographic differences.

Strategies used to combine seriated cups by chimpanzees (Pan troglodytes), bonobos (Pan paniscus), and capuchins (Cebus apella)

The authors investigated strategies used to combine seriated cups by apes (Pan troglodytes and P. paniscus) and monkeys (Cebus apella) using a protocol reported in P. M. Greenfield, K. Nelson, and E. Saltzman's (1972) study with children. It was hypothesized that apes would exhibit more hierarchical combinations of cups than monkeys, given apes' language capacity, and that apes would seriate the cups more efficiently than monkeys. As predicted, apes made many structures with the cups using a variety of strategies, and monkeys rarely combined the cups. After a training phase to orient monkeys to the task, the 2 genera did not differ in the strategies used to combine the cups or in efficiency in seriating the cups. Success in this task suggests that sensorimotor versions of hierarchically organized combinatorial activity are well within apes' and monkeys' abilities.

Social separation in infant Cebus apella: patterns of behavioral and cortisol response

34 infant tufted capuchins (Cebus apella) were separated from their social groups for a 2-hour period and videotaped in isolation at the ages of 6 months and 1 year. Baseline and 2-hour blood samples were measured for levels of serum cortisol. Compared to homecage baseline levels, passivity, locomotion and vocalizations increased during separation, while self-directed behavior and environmental exploration decreased. Both behavioral and cortisol responses to separation showed individual stability over the 6 month period, although both responses were somewhat attenuated at the later age. There was little correlation between cortisol and behavior during separations. Females vocalized more than did males during separations and showed greater cortisol increases at 6 months of age. The pattern of behavioral response seen in the 2 hours following separation appeared to be more passive than the typical 'protest' response described in many nonhuman primates, and may reflect either the physical circumstances of the separation or a characteristic of species with relaxed social bonds and considerable allomothering available to infants.

Object-use in free-ranging white-faced capuchins (Cebus capucinus) in Costa Rica

Chimpanzees and capuchins demonstrate greater varieties and higher rates of tool-use when compared to other non-human primates. Although capuchins have been studied extensively in captivity, data on their tool-using behavior under free-ranging conditions are limited. This is the first long-term field research to systematically study complex object manipulation in capuchins. The aims of this research are 1) to examine the types, rates, and contexts of tool- and object-use in free-ranging capuchins and 2) to determine if free-ranging capuchins' object manipulation behavior is comparable to the behavior exhibited by captive individuals. Data on 3 troops of white-faced capuchins (Cebus capucinus) were collected from February 1995 to January 1996 at Palo Verde, Costa Rica. Data were collected using focal animal and ad libitum sampling techniques. Any observed incident of tool-use and object-use was recorded. No tool-use was observed during the 11-month study. Object-use (pound, rub, and fulcrum-use) occurred at a rate of 0.19/hr and made up less than 1% of the monkeys' time (there were no differences among the age/sex classes). The results indicate that free-ranging capuchins do not exhibit the range of tool-using behavior demonstrated by their captive counterparts. This may be the result of differential motivational responses to objects, arboreal lifestyle, absence of adequate tool material, and/or absence of food resources that require extraction involving tool-use.

Why some capuchin monkeys (Cebus apella) use probing tools (and others do not)

Tufted capuchins (Cebus apella) were provided with a task that facilitated the use and modification of sticks as probing tools. It was found that subjects aged 10 years or older at initial task exposure were less likely to use tools than were younger subjects. Furthermore, juveniles whose mothers died before the subjects were aged 3 years were less likely to use tools than were juveniles whose mothers survived through this period. The ability to use tools was not related to subject sex or to access to the tool site or raw tool materials. Subjects modified tools both before and during their use, and the relative percentage of tools modified increased with subject age. Thus, it appears that capuchins most readily acquire tool use before the age of 10 years and that early disruption of the mother-infant relationship has deleterious effects on the emergence of instrumental behavior.

Pointing, withholding information, and deception in capuchin monkeys (Cebus apella)

Brown capuchin monkeys, like 4-year-old children and human-socialized chimpanzees, showed communicative and deceptive pointing in experiments in which they benefited by indicating, accurately or falsely, the location of hidden food. All 3 capuchin monkeys tested (13, 19, and 26 years old) pointed communicatively in the presence of a cooperative trainer. One human-reared monkey pointed without any training and frequently gazed at her human respondent; as with apes, extensive exposure to humans may promote some human-like responses in monkeys. Another capuchin withheld pointing when beneficial, whereas the 3rd learned to obtain the hidden food by pointing deceptively in the presence of a competitive trainer. Such deceptive pointing by one monkey and withholding of information by another suggest that primates' deceptive pointing in an experimental situation is explainable in terms of response inhibition and conditional discrimination learning.

Food transfers through mesh in brown capuchins

Capuchin monkeys (Cebus apella) share food even if their partner is behind a mesh restraint. Pairs of adult capuchins were moved into a test chamber in which 1 monkey received cucumber pieces for 20 min and the other received apple slices during the following 20 min. Tolerant transfers of food occurred reciprocally among females: The rate of transfer from Female B to A in the second test phase varied with the rate from Female A to B in the first test phase. Several social mechanisms may explain this reciprocity. Whereas this study does not contradict cognitively complex explanations (e.g., mental record keeping of given and received food), the results are consistent with a rather simple explanation: that food sharing reflects a combination of affiliative tendency and high tolerance. The study suggests that sharing mechanisms may be different for adult male capuchins, with males sharing food more readily and less discriminatingly than females.

Experimental field study of spatial memory and learning in wild capuchin monkeys (Cebus capucinus)

Despite a large body of data on diet and ranging patterns in prosimians, monkeys and apes, little is known regarding the types of information that non-human primates use when making foraging decisions. In a series of controlled field experiments, we tested the ability of wild capuchins (Cebus capucinus) at La Suerte Biological Research Station in north-eastern Costa Rica to remember the spatial positions of 13 feeding platforms and use olfactory and visual cues to identify baited (real bananas) versus sham (plastic bananas) feeding sites. The results indicate that when 'place' was predictable, the capuchins learned the spatial locations of food and non-food sites rapidly (one-trial learning). In a second experiment, the positions of baited feeding sites were random. In the absence of other information, the capuchins used the presence of a local landmark cue (yellow block) placed at reward platforms to select feeding sites. In a final experiment, there was evidence that expectations regarding the amount of food available at a platform (2 bananas vs. 1/2 banana) had a significant influence on capuchin foraging decisions. Although the capuchins were sensitive to changes in experimental conditions, when they were given conflicting cues, spatial information was predominant over other information in selecting feeding sites.

Use of olfactory cues in foraging by owl monkeys (Aotus nancymai) and capuchin monkeys (Cebus apella)

The authors tested free-ranging New World monkeys (nocturnal owl monkeys [Aotus nancymai] and diurnal capuchin monkeys [Cebus apella]) to determine the extent to which they use olfactory cues to locate food hidden in containers at 2 of 6 feeding sites within a 1 1/2-ha forested enclosure. These 2 sites were selected randomly for each trial and then were baited with banana and banana peel residue. The 4 other sites were unbaited and unscented. In trials in which the food was not visible to the monkeys, Aotus monkeys located the baited sites at a level greater than expected by chance, whereas Cebus monkeys did not. Use of olfactory information by Aotus monkeys in foraging may be an adaptation for nocturnal foraging because olfactory cues are more salient than visual cues at low light levels.

Developmental changes in manipulation in tufted capuchins (Cebus apella) from birth through 2 years and their relation to foraging and weaning

This study examined the contributions of physical and sensorimotor development to manipulation in capuchins (Cebus apella) from birth to 2 years. Between months 1-6 and 7-12, manipulation increased significantly in frequency, in the proportion that was vigorous or required fine motor control, and in the proportion directed at portable objects. Fine motor control, moving objects in relation to the body, and stamina are largely in place by 12 months, after which little changed. All elements of the manipulative repertoire have appeared, and vigorous and dexterous activities have peaked before fully independent foraging. Emergence of permanent dentition and achievement of approximately half of adult body size accompany the attainment of fully independent foraging at 15 months. Thereafter, increasing strength and specific knowledge probably contribute more to changing foraging competence in young capuchins than do stamina and sensorimotor development.