Tool use in wild capuchin monkeys (Cebus albifrons trinitatis)

White-fronted capuchins were observed to use leaves as cups to retrieve water from tree cavities. On multiple occasions several individuals performed this behavior. Thus, these capuchins engage in habitual tool use, as defined by McGrew's classificatory scheme of tool using behavior. Am. J. Primatol. 46:259–261, 1998. © 1998 Wiley-Liss, Inc.     

Ant-Gathering with Tools by Captive Tufted Capuchins (Cebus apella)

We examined ant-gathering with tools by captive tufted capuchins (Cebus apella) via two experiments. In Experiment 1, we provided groups of subjects with sticks and small branches and an apparatus that accommodated the use of tools to gather ants. In Experiment 2, we sealed the apparatus with acetate and provided the same subjects with sticks and stones. Seven of 14 subjects used sticks and leaves as probes to extract ants from the apparatus. Six of them modified probes by detaching sticks from larger branches, breaking sticks into two or more pieces, and subtracting leaves and bark. Three subjects later used a stone and stick tool-set to penetrate acetate barriers and to extract ants. These results demonstrate the use of tools by Cebus to capture moving prey and are consistent with the idea that sensorimotor skills associated with the production and use of tools in primates evolved convergently in capuchins and great apes.     

Hand Preference in Free-Ranging White-Throated Capuchins (Cebus capucinus) in Costa Rica

I studied the hand preference patterns of individuals in three troops of white-throated capuchins (C. capucinus) in Palo Verde, Costa Rica, during 11 months from February 1995 to January 1996. I used focal and ad libitum sampling techniques and tested several frameworks that seek to explain and to predict primate hand use patterns via a variety of spontaneous tasks that differ in manipulative difficulty and required postural regulation: reach, tap, grab, carry, and object-use. The monkeys showed symmetrical hand use patterns for the easy tasks, reach and tap; strongly asymmetrical patterns for the highly manipulative task, object-use, at the individual level; and weak population-level biases for tasks requiring a degree of postural regulation, carry. The results for data on grab are inconclusive. These results do not support the available primate hand use frameworks and differ from most of the captive literature on hand preference in Cebus. The findings indicate that postural regulation may influence hand use patterns in nonhuman primates at the population level.     

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 × 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. Am. J. Primatol. 44:147–153, 1998. © 1998 Wiley-Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.     

The use of probing tools by tufted capuchins (cebus apella): evidence for increased right-hand preference with age

We examined hand preference in the use of tools by tufted capuchins (Cebus apella). We presented a colony of monkeys with an enclosed container designed to accommodate the use of probing tools. Over an 8-month period, 13 monkeys used probes to extract sweet syrup from the narrow opening of the apparatus. Five monkeys exhibited bias toward use of their right hand and eight monkeys exhibited bias toward use of their left hand. Adult monkeys exhibited a greater percentage of right-hand preferent probing sequences than did juveniles. These results are consistent with hypotheses that in tasks that involve the use of tools, nonhuman primates exhibit strong lateral asymmetries at the individual level, a moderate left-hand bias at the population level, and increased bias with age toward use of the right hand.     

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. Am. J. Primatol. 43:33–41, 1997. © 1997 Wiley-Liss, Inc.     

Vertebrate Predation and Food-Sharing in Cebus and Pan

Capuchins and chimpanzees are the only nonhuman primates apart from baboons known to prey systematically upon relatively large vertebrates. Vertebrate predation is common and well documented in Pan troglodytes, rare in Pan paniscus, and commonly reported but infrequently studied in Cebus. Food-sharing is common in both Pan species but rarely reported for wild capuchins. I present data on vertebrate predation and food-sharing by white-faced capuchins (Cebus capucinus) from ongoing field studies at Santa Rosa National Park, Costa Rica. We have observed 106 successful predation events resulting in the capture of 156 prey items during 2929 observation hr (5.35 prey per 100 hr). Squirrels and nestling coatis comprised half of the prey taken; the remainder were mainly nestling birds and eggs. Adult males took 52% of all prey and 67% of squirrels. Squirrels are actively hunted and about 65% of them are adults. I estimated that the average capuchin group kills 43–50 squirrels annually, mostly during the dry season. Capuchins hunt squirrels in groups 81% of the time, and 17% of hunts are successful. There is no evidence for cooperative hunting, but occasional collaboration is suggested. Rates of food-sharing were low (1.7 per 100 hr), and meat was the only food shared between adults. I compare predation and food-sharing in C. capucinus with published data for Pan troglodytes, primarily in Gombe and Taï National Parks. I discuss sex differences, hunting strategies, the relationship between hunting and food-sharing, and various ecological and social factors that may promote vertebrate predation in Pan and Cebus.     

Substrate optimization in nut cracking by capuchin monkeys (Cebus apella)

We conducted an experiment to examine the effect of substrate on the nut-cracking behavior of a group of semicaptive capuchin monkeys. We wanted to determine whether tufted capuchin monkeys were selective in choosing the substrate on which they pound nuts, and whether the choice of substrate affected the outcome. Eight adult females and eight juveniles were provided with nuts in the outdoor facility. We found that 1) all adult females and three young capuchins succeeded in cracking nuts; 2) they preferred the hardest substrates (concrete and stone); 3) there is a link between the substrate and the amount of time needed to crack a nut; 4) most young capuchins used various substrates, some of which were inadequate, in a haphazard manner; and 5) there are different forms of nut cracking. We conclude that adult capuchins choose the hardest substrates, and that these substrates support efficient cracking.     

Problem-Solving Strategies and Hand Preferences for a Multicomponent Task by Tufted Capuchins (Cebus apella)

We examined hand preferences in 23 tufted capuchins (Cebus apella) in 2 tasks requiring the lid of a box to be lifted before taking out a peanut. The first task, Box 1, could entail either 2 or 3 problem-solving acts, with the 3-act solution involving bimanual coordination for food retrieval. The second task, Box 2, involved only the 3-act solution. The results indicated that the types of solution employed to perform the task influenced capuchin hand preferences. In the 2-act solution, capuchins exhibited a significant right-hand bias for the final one-handed reaching action, but not for the initial lid lifting action. In contrast, in the 3-act solution, no significant asymmetry emerged for any act. We noted a significant effect of subject's sex on the strength of laterality, with males being more strongly lateralized than females. We discuss results in the light of recent models of primate laterality.     

Spatial Facilitation in a Probing Task in Wedge-Capped Capuchins (Cebus olivaceus)

Activities ordinarily performed by an animal in a given place may influence the way it behaves towards an object newly found there. We examined the use of probing tools in a group of 4 wedge-capped capuchins (Cebus olivaceus), in the home cage into which we simultaneously introduced two identical apparatuses, one at a site ordinarily used to manipulate objects, and the other at a site mainly used for visual monitoring. We expected that spatial facilitation would occur, i.e., the subjects would be more efficient at the site where manipulative behaviors were more frequently performed. Two monkeys used probing tools to extract syrup from the openings of the apparatuses. Tool use efficiency was higher with the apparatus located at the site where they had performed more manipulative and combinative behaviors. These results are consistent with the hypothesis of spatial facilitation and illustrate the fact that spatial context can be an overwhelming variable that should not be neglected in behavioral research dealing with instrumental tasks.     

Vocal Repertoire of Cebus capucinus: Acoustic Structure, Context, and Usage

Researchers studying nonhuman primate vocal repertoires suggest that convergent environmental, social, and motivational factors account for intra- and interspecific vocal variation. We provide a detailed overview of the vocal repertoire of white-faced capuchins, including acoustic analyses and contextual information of vocal production and vocal usage by different age-sex classes in social interactions. The repertoire is a mixture of graded and discrete vocalizations. In addition, there is general support for structural variation in vocalizations with changes in arousal level. We also identified several combined vocalizations, which might represent variable underlying motivations. Lastly, by including data on the social contexts and production of vocalizations by different age-sex classes, we provide preliminary information about the function of vocalizations in social interactions for individuals of different rank, age, and sex. Future studies are necessary to explore the function of combined vocalizations and how the social function of vocalizations relate to their acoustic structure, because social use of vocalizations may play an important role in shaping vocal evolution.     

Canine Dimorphism and Interspecific Canine Form in Cebus

I investigated canine dimorphism and interspecific canine form in adult specimens from 4 capuchin species (Cebus albifrons, C. apella, C. capucinus, and C. olivaceus). I used various univariate and multivariate statistics, which are based on 6 variables, to test several hypotheses that are based upon the finding that canine dimorphism is strongly associated with intermale competition in platyrrhines (Kay et al., 1988), Greenfield (1992a), Plavcan and van Schaik (1992, 1994). Results from the indices of canine dimorphism and the unpaired t-tests corroborate the prediction that males of each species possess significantly larger canines than those of females. Large male canines are especially prominent in 2 variables, maxillary and mandibular canine height. Greene's t-test (1989) does not support the prediction that Cebus apella and C. olivaceus possess a larger degree of canine dimorphism relative to C. albifrons and C. capucinus. No interspecific differences in degree of canine dimorphism are indicated by this test. Results of the discriminant function analyses (DFA) do not find that Cebus apella and C. olivaceus possess different canine form relative to C. albifrons and C. capucinus as predicted. However, Cebus apella is differentiated from the untufted capuchins (C. albifrons, C. capucinus, and C. olivaceus) by the DFA. I suggest that intermale competition is the primary selective force underlying the observed morphological patterns; however, it does not explain all the variation associated with canine dimorphism in Cebus.     

Effects of manipulatable objects on the activity of captive capuchin monkeys (Cebus apella)

The aim of this study was to evaluate simple behavioral enrichment procedures for a captive group of tufted capuchin monkeys (Cebus apella). We examined the effects of providing a manipulatable substrate (straw) and a variety of portable objects in the monkeys' home cage. The animals were observed across three conditions in two replications: 1) No portable objects were present; 2) a set of six identical portable objects was present; and 3) a set of six varied portable objects was present. The cage floor was bare in the first replication; straw was uniformly spread on the cage floor in the second replication. An 18-month period of qualitative note taking followed completion of the initial data collection phase. The presence of straw and portable objects affected patterns of affiliation by decreasing quiet contact and close proximity. Providing additional manipulative opportunities affected both the form and frequency of object-directed activities. Object contacts were directed toward a greater variety of targets, and some objects were spontaneously used as tools. Manipulation of provided objects and use of objects as tools have become routine activities in this group of monkeys. We conclude that providing straw and portable objects in an already well equipped cage is an effective means of long-term behavioral enrichment for captive capuchin monkeys. Enabling captive capuchins to express species-typical manipulative tendencies is apparently conducive to the monkeys' optimal physical and psychological well-being as well as interesting to the human observer.     

Semifree-ranging Tufted Capuchins (Cebus apella) Spontaneously Use Tools to Crack Open Nuts

Naturalistic studies on tool use by nonhuman primates have focused almost exclusively on Old World monkeys or hominoids. We studied the cracking of Syagrus nuts with the aid of stones by a group of semifree-ranging capuchins living in a reforested area (Tietê Ecological Park, São Paulo, Brazil). Our data are from direct observation and from mapping nut-cracking site utilization. All adults, subadults and juveniles (plus one infant) crack nuts, but individual differences in frequency and proficiency are marked. Juveniles do most of the nut-cracking, but adults are, on average, more efficient; the frequency of inept stone manipulation decreases with age. About 10% of the nut-cracking episodes were watched by other individuals—mostly infants and juveniles, suggesting a role for observational learning, even if restricted to stimulus enhancement.     

Hand Preferences in Different Tasks by Tufted Capuchins (Cebus apella)

We examined hand preferences in 25 tufted capuchins (Cebus apella) in three tasks. The hole task involved a single action of reaching for food in a hole. The horizontal panel and the vertical panel tasks required the alignment of two apertures, by moving or lifting a panel, to reach for food in a hole. We found a significant group-level right-hand preference for reaching actions in the hole and in the horizontal panel tasks, but not in the vertical panel task, in which the food retrieval implied the complementary use of both hands. No significant hand bias emerged for moving or lifting actions with high visuospatial components. There is a stronger hand preference in more complex manual activity—coordinated bimanual hand use for food retrieval—than in other unimanual measures. We discuss the results in the context of previous reports on primate laterality.     

Self-treatment of wounds by a capuchin monkey (Cebus apella)

A captive adult female capuchin monkey spontaneously manufactured and used tools to groom her vaginal area and four of her own wounds over a six-month period. The wounds apparently occurred during fights with other monkeys living in the same social groups. The monkey often groomed her vaginal area and wounds with tools she had coated with a sugar-based syrup. The monkey did not use tools to groom other body areas, nor did she use tools that were coated with substances other than syrup. This monkey’s unusual habit developed in the context of manufacturing and using tools in a feeding task. These observations demonstrate that the serendipitous performance of particular behaviours in appropriate contexts can lead to the discovery and practice of simple treatment of wounds by a monkey. The independent discovery of simple medicinal procedures in human cultures may have occurred in a similar manner. Such discoveries could have predated the development of sophisticated cultures in which medicinal practices were embedded and eventually recorded.     

Carrying, Sharing, and Hand Preference in Tufted Capuchins (Cebus apella)

We examined the relationship among carrying, food-sharing, and hand preference in tufted capuchins (Cebus apella). The rationale was to evaluate further the use of Cebus as an alternative primate model to Pan for behavior relevant to early hominid evolution. We first examined bipedalism and food-sharing within an established social group, and then examined the direction and strength of hand preference for food carrying in an expanded sample. Several aspects of capuchin behavior warrant discussion. First, bipedal carrying and food-sharing occurred more frequently when we provided bulky foods than when we provided smaller foods. Second, food-sharing was characterized by passive tolerance, rather than active giving, between subjects. Third, subjects shared food primarily with immatures and followed a pattern of reciprocal exchange. Finally, we found no evidence for population-level hand preference for carrying. We posit that an array of behavioral similarities among Cebus, Pan, and Homo evolved through convergent processes, and in this regard capuchins can be seen as an alternative primate model to chimpanzees for the evolution of early hominid behavior.     

Carrying and hand-use patterns in Panamanian white-faced capuchins (Cebus capucinus)

The aim of this project was to examine the potential influence of postural regulation on capuchin hand-use patterns by focusing on tasks that involved the carrying of objects. Two months were spent on Barro Colorado Island, Panama, collecting data on ten white-faced capuchins (Cebus capucicus) (four adult males/six adult females). Over 215 contact hours were spent with the monkeys, and a total of 213 carries were recorded. No hand preference bias at the population level was found for the carry task; and no detectable hand-use patterns for carry were correlated with the weight of the object carried (except a right-hand bias for carrying medium-sized objects), the plane of the monkey's movement, its locomotor pattern, or its height above the ground. Therefore, the results of this study do not support the hypothesis that the need for postural regulation while carrying an object influences hand-use patterns in free-ranging capuchins. Our results are especially important because they are contrary to the results of the only other free-ranging capuchin laterality study conducted to date (Panger, 1998).