Mirror inspection varies with age and tool-using ability in tufted capuchin monkeys (Cebus apella)

We examined mirror inspection in tufted capuchin monkeys (Cebus apella). Capuchins were presented with a non-reflective surface for 30 minutes and then a mirror for 3 hours. Inspection of the non-reflective surface did not vary significantly as a function of tool-using ability, age, or sex. Mirror inspection was lowest in older animals, and was greater in animals that used tools than in animals that did not use tools. Mirror-aided self-inspection was not observed. These results indicate that mirror inspection varies with age and tool-using ability in tufted capuchin monkeys. We hypothesize that psychological capacities associated with mirror inspection correspond with those related to the use of tools, and that these capacities facilitate the emergence of self-recognition in some primate species.     

Sex differences in play behavior in juvenile tufted capuchin monkeys (Cebus apella)

According to the motor training hypothesis, play behavior in juvenile primates improves motor skills that are required in later adult life. Sex differences in juvenile play behavior can therefore be expected when adult animals assume distinct sexually dimorphic roles. Tufted capuchin monkeys show sexually dimorphic levels of physical antagonism in both inter- and intra-group encounters. Accordingly, it can be predicted that juvenile capuchins also show sex differences in social play behavior. To test this hypothesis, the play behavior of nine juvenile and two infant capuchins was examined. As predicted, juvenile males showed significantly higher levels of social play (wrestle, chase) than juvenile females, but no differences were found in nonsocial play (arboreal, object). Levels of infant play behavior were comparable to that of juveniles. These results lend support to the motor training hypothesis and highlight the need for more detailed investigations of individual differences in play behavior. An erratum to this article can be found at     

Use of a tool-set by capuchin monkeys (Cebus apella)

The purpose of this study was to examine the use of a tool-set by capuchin monkeys (Cebus apella). Capuchins were presented with an apparatus designed to accommodate the use of pounding tools to crack walnuts and the use of probing tools to loosen and extract the inner meat. Three capuchins used stones and sticks sequentially for these purposes. The capuchins' behavior was similar in form and function to behavior that has been reported for chimpanzees in analogous situations. These results provide further evidence of the extensive tool-using capabilities of capuchin monkeys and are consistent with a hypothesis of cross-species continuity in the skillful use of tools by primates.     

Hierarchical complexity of combinatorial manipulation in capuchin monkeys (Cebus apella)

The purpose of this study was to examine the hierarchical complexity of combinatorial manipulation in capuchin monkeys (Cebus apella). Two experiments were conducted. In Experiment 1 capuchins were presented with an apparatus designed to accommodate the use of probing tools. In Experiment 2 the same capuchins were presented with sets of nesting containers. Five of the ten subjects used probing tools and seven subjects placed objects in the containers. The capuchins' behavior reflected three hierarchically organized combinatorial patterns displayed by chimpanzees and human infants. Although the capuchins sometimes displayed the two more complex patterns (“pot” and “subassembly”), their combinatorial behavior was dominated by the simplest pattern (“pairing”). In this regard capuchins may not attain the same grammar of manipulative action that has been reported for chimpanzees and young human children. © 1994 Wiley-Liss, Inc.     

Male reunion displays in tufted capuchin monkeys (Cebus apella)

When males in captive tufted capuchin monkey (Cebus apella) groups separate and come together within their group, they have been observed to embrace and vocalize upon reunion. This display has not been observed in any other age/sex class. To investigate this, we deliberately separated six animals, including the only two adult males, from each of two social groups. We hypothesized that only the adult males would embrace upon reintroduction. When two males were consecutively reintroduced to their group, they typically ran to each other and came together in a frontal embrace, emitting stereotyped vocalizations. No other combination of animals showed this “reunion display.” Though dramatic, this behavior was in no way associated with incidents of aggression. We argue affiliative bonds may exist in these tufted capuchin male dyads. © 1996 Wiley-Liss, Inc.     

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.     

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.     

Response to novel housing in two groups of captive tufted capuchin monkeys (Cebus apella)

The influence of age, maternal status, and the presence of a group male on use of space was assessed in two groups of captive tufted capuchin monkeys that underwent a move from indoor housing to a larger outdoor facility. Both groups originally contained two adult males, but only one group retained a male after the move. Following the move, mothers spent less time on the ground when carrying their infants than they did when not carrying their infants. In the group with no male (1) individuals decreased time spent on the ground relative to pre-move levels, whereas no such difference was noted in the group with the male; (2) females spent more time carrying their infants than did females in the group with a male. In the group with the adult male, juveniles spent less time on the ground than did non-mother adult females, whereas no difference had existed prior to the move. Grooming rates dropped from pre-move to post-move, but the mean number of partners with which each animal was in contact increased. Measures of social behavior varied across post-move observation periods inversely to time spent on the ground. These results are consistent with the view that an individual's relative vulnerability influences behavioral conservatism in novel environments, and suggests a relatively profound role for males in promoting exploration of new space in this species.     

Responses to urine odor in the tufted capuchin (Cebus apella)

When the tufted capuchin urinates, it frequently performs “urine-washing”. Previous studies have proposed several hypotheses about this behavior. This study investigated 1) whether the tufted capuchin can distinguish the urine odor of conspecific individuals from other groups, and 2) whether the capuchins can distiguish conspcific urine odor of from that of other species. When an odor bar that had been prepared in conspecific other group's cage was presented, the response (sniffing, licking, or biting) was significantly greater than that to any other odors, including that of the home group, 5 other species, or a neutral odor. This tendency was stronger in males than in females. and suggests that the tufited capuchin is able to discriminate its home group's urine odor from that of the other groups. This monkey may also discriminate its own species from others by urine odor. The sex difference of the response to the odor bar may be the result of differences in social role between males and females. These results support the idea that the tufted capuchin may use olfaction for social communication.     

Response to changes in food palatability in tufted capuchin monkeys, Cebus apella

Palatability of plant foods may change over time in relation to the concentration of toxic secondary metabolites. We investigated the behavioural response of capuchin monkeys to this type of change and assessed the influence of social conditions. Twenty-seven tufted capuchin monkeys were presented in Social or Individual conditions with a familiar palatable food (phase 1), with the same familiar food to which pepper had been added, making it unpalatable (phase 2), and with the same familiar palatable food of phase 1 (phase 3). Five sessions were carried out in each phase. The capuchins adapted quickly to the change in food palatability by reducing (phase 2) and increasing (phase 3) the amounts of food eaten. The unpalatable food prompted an increase in olfactory exploration and in food processing. The experimental conditions (Social versus Individual) did not influence consumption, or any of the other behaviours. In addition, capuchins were more often near subjects with food in phases 2 and 3 in which palatability changed than in phase 1. These findings show that capuchins readily adjust to changes in flavour and palatability of a familiar food and that sudden unpalatability has no carry-over effects. Therefore, capuchins behave differently towards a familiar food whose palatability has changed than they do towards novel foods. Copyright 2000 The Association for the Study of Animal Behaviour.     

Response to neighbors and strangers by capuchin monkeys (Cebus apella)

Capuchin monkeys in the laboratory were observed when another monkey was introduced to their group. The introduced monkey was either from a hostile neighboring group; from a completely strange group, or from the host group. Attacks were directed primarily toward strange males but were rare. The results were discussed in terms of the neighbor effect, mere exposure theory, and species differences in responses to strangers.     

Olfactory discrimination of urine odors from five species by tufted capuchin (Cebus apella)

Urine collected from New World monkeys (tufted capuchin, squirrel monkey, cotton-top tamarin) and Old World monkeys (rhesus macaque, Japanese macaque), was used as the odor stimuli. Two adult tufted capuchins were trained on a successive odor-discrimination task with two odors, 30 trials each, in one session per day. Responses to one of the two odors (S+) were reinforced by sweet water. The monkeys failed to discriminate between the urine from the two species of macaques but could discriminate among the urine from the three species of New World monkeys. Furthermore, similarity of urine odors was analyzed by multi-dimensional scaling (MDS) and a cluster analysis. These analysis suggested that the tufted capuchin can distinguish differences among New World monkeys but not between the macaques. The natural distribution of the tufted capuchin overlaps with that of other New World monkeys, but it does not overlap with those of Old World monkeys. Consequently, it can be concluded that this difference in olfactory recognition in the tufted capuchin reflects their sympatric and allopatric relationships with other species.     

Influence of a skilled model on the behavior of conspecific observers in tufted capuchin monkeys (Cebus apella)

We analyze how the presence of a skilled juvenile capuchin monkey interacting with a mechanical puzzle requiring sequential actions affected the behavior of group-mates towards the puzzle. Using this study as an example, we suggest a methodological approach to the evaluation of social enhancement of activity and imitation. We suggest that this design could be useful in determining if social and demographic factors influence the occurrence of these phenomena. © 1995 Wiley-Liss, Inc.     

Social after-effects of fur rubbing in tufted capuchin monkeys (Cebus apella): increased antagonism and reduced affiliation

Fur rubbing is widely believed to have a social bonding function in capuchin monkeys, yet a recent study of tufted capuchins revealed increased levels of aggression and reduced levels of affiliation after fur-rubbing bouts. This observed decrease in group cohesion may be attributable to increased intragroup competition for fur-rub material rather than being a direct effect of fur rubbing itself. To test this hypothesis, we separated individual tufted monkeys (Cebus apella) from their social group and provided them with fur-rub material or control material, thereby avoiding intragroup competition. After engagement with materials, we released subjects back into their social group and observed their subsequent interactions with group members. We found that subjects were more likely to encounter aggression and less likely to receive affiliation from others in the fur-rub condition than in the control condition. These results support the idea that fur rubbing carries social after-effects for capuchin monkeys. The precise mechanisms of the observed effects remain to be clarified in future studies.     

Modification of Clay Forms by Tufted Capuchins (Cebus apella)

We examined modification of clay forms by tufted capuchins (Cebus apella) by presenting groups of subjects with clay, paint, stones, leaves, and sticks. In Experiment 1, 7 of 10 subjects reshaped portable forms with their hands and with stones, and decorated them with leaves and paint. In Experiment 2, 9 subjects marked clay slabs manually and with stick and stone tools. The manipulative propensities of Cebus can help us to understand psychological processes that underlie artistic expression in Homo and Pan.     

A multi-task assessment of hand lateralization in capuchin monkeys (Cebus apella)

Eight tasks were presented to ten tufted capuchin monkeys and hand preferences were recorded for each subject on each task. The strength of hand preferences varied accross tasks. Although no significant population-level left- or right-hand bias emerged for any of the tasks, there was a tendency toward greater left-hand use in a task requiring the use of probing tools. The data also confirm that simple reaching is of limited value as a measure of hand preference. Hand preferences in capuchin monkeys appear to be determined by a number of individual, species, and environmental factors.