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PubMed1976

Neurohistologic observations of the Cebus apella monkeys soft palate mucosa.

A neurohistological observation was done in the solf palate mucosa of the Cebus apella monkey. Six mucosa were employed and were removed after perfusion of each animal, with 10% formalin solution, through the external carotid artery of the right side. The mucosa was removed together with the muscular layer and salivary glands. The histologic analysis was performed and therefore the pieces were prepared by the "De Castro" technic of silver impregnation. The material was embedded in the vertical sense to allow frontal sections with the thickness of 8 micra. Our findings allow the following conclusions: a) the mucosa innervation of the soft palate is essencially done by the branches of the lesser palatine nerve; b) the free nerve endings of the soft palate mucosa have a great variation in the form and size and are abundant; c) the superficial fibres are related to the general sensibility and the deepest are directly connected to the innervation of the salivary glands.

Animals↗
PubMed1998

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.

Animals↗
PubMed1998

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.

Animals↗
PubMed2000

Prehension in infant capuchins (Cebus apella) from six weeks to twenty-four weeks: video analysis of form and symmetry.

We analyzed the spontaneous prehensile activity of two infants living with their mothers in social groups, using videotapes taken once weekly from weeks 5 to 24. Prehensile activities were laterally symmetric. Unimanual activity predominated, although bimanual activity appeared at the same ages as unimanual activity. In most bimanual activity the two hands performed the same action, but complementary actions occurred from the onset of bimanual activity. Extrusion of the tongue towards objects out of reach was observed occasionally, as was precision grasping. Early prehension in capuchins is organized, as in human infants, in a matrix of exploratory activity integrated with vision and oral exploration. Capuchins present a useful model system for the study of manipulative development.

Animals↗
PubMed2004

Wild capuchin monkeys (Cebus libidinosus) use anvils and stone pounding tools.

We conducted an exploratory investigation in an area where nut-cracking by wild capuchin monkeys is common knowledge among local residents. In addition to observing male and female capuchin monkeys using stones to pound open nuts on stone "anvils," we surveyed the surrounding area and found physical evidence that monkeys cracked nuts on rock outcrops, boulders, and logs (collectively termed anvils). Anvils, which were identified by numerous shallow depressions on the upper surface, the presence of palm shells and debris, and the presence of loose stones of an appropriate size to pound nuts, were present even on the tops of mesas. The stones used to crack nuts can weigh >1 kg, and are remarkably heavy for monkeys that weigh <4 kg. The abundance of shell remains and depressions in the anvil surface at numerous anvil sites indicate that nut-cracking activity is common and long-enduring. Many of the stones found on anvils (presumably used to pound nuts) are river pebbles that are not present in the local area we surveyed (except on or near the anvils); therefore, we surmise that they were transported to the anvil sites. Ecologically and behaviorally, nut-cracking by capuchins appears to have strong parallels to nut-cracking by wild chimpanzees. The presence of abundant anvil sites, limited alternative food resources, abundance of palms, and the habit of the palms in this region to produce fruit at ground level all likely contribute to the monkeys' routine exploitation of palm nuts via cracking them with stones. This discovery provides a new reference point for discussions regarding the evolution of tool use and material culture in primates. Routine tool use to exploit keystone food resources is not restricted to living great apes and ancestral hominids.

Animals↗
PubMed2005

Behavioral indicators of ovarian phase in white-faced capuchins (Cebus capucinus).

In many primate species, conspicuous behavioral and/or morphological changes are indicators of the fertile phase of the female cycle. However, several primate species, such as the white-faced capuchin, lack these cues. This is referred to as "concealed ovulation," and is argued to be a reproductive strategy that confuses paternity and lowers the risk of infanticide. We studied 10 adult female white-faced capuchins in Santa Rosa National Park, Costa Rica, from January to June 2002. We determined their ovarian cycling patterns by analyzing fecal ovarian hormones, and compared simultaneously collected behavioral data to determine which, if any, cues females use to signal their fertile phases. We found that four females cycled during the study period but ceased to cycle without becoming pregnant. We considered several explanations for the lack of conception during our study, including reproductive seasonality. We found that female C. capucinus showed only small increases in rates of affiliative/proceptive behaviors directed toward adult males during their periovulatory phases. The best indicator of cycle phase was a significant increase in male affiliative behaviors (e.g., following and grooming bouts) and sexual behaviors (e.g., copulations and courtship displays) directed toward females during the periovulatory phase compared to the nonovulatory phase. Our finding that females exhibit little proceptive behavior, but that copulations and male courtship are nonetheless concentrated in periovulatory phases suggests that even though females do not provide behavioral and morphological cues to ovulation, males are still able to detect it. Infanticide occurs with some frequency in these monkeys, and there is evidence for postconceptive mating as a female strategy to lower risk of infanticide via paternity confusion. However, despite this occurrence of nonconceptive mating and the absence of female cues to ovulation, truly concealed ovulation does not appear to be characteristic of this study population of white-faced capuchins.

Animals↗
PubMed2006

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.

Animals↗
PubMed2007

Response toward novel stimuli in a group of tufted capuchins (Cebus libidinosus) in Brasília National Park, Brazil.

We investigated responses toward novel foods and novel objects by wild capuchins that routinely exploit visitors' foods in Brasília National Park. Given the capuchins' daily exposure to human foods and objects, we expected them to be more explorative toward novel foods and objects compared to capuchins that are not habituated to visitors. However, since the safety and palatability of potential foods have to be learned, we also expected the capuchins to be cautious about eating novel foods, as has been reported for wild and captive capuchins. Stimuli were presented on a platform in four experimental conditions: familiar food (FF), novel food (NF), familiar food plus novel object (FF+O), and novel food plus novel object (NF+O). Latencies to approach and contact the platform, and to approach and to ingest food did not differ across conditions. Nevertheless, the capuchins were significantly more responsive (measured in terms of interest, manipulation, etc.) toward familiar foods than novel foods, and ate significantly more of the former. In other words, their explorative response toward novel foods led to little consumption. Our results do not support the "readiness to eat" hypothesis, according to which a lower readiness to eat and food neophobia are the consequences of the presence of a distracting novel object. The finding that capuchins explore novel stimuli but remain cautious about eating novel foods supports the view that neophilia and neophobia are motivationally independent responses.

Analysis of Variance↗
PubMed2007

Characteristics of hammer stones and anvils used by wild bearded capuchin monkeys (Cebus libidinosus) to crack open palm nuts.

Capuchins living in Boa Vista (Piauì, Brazil) crack open hard palm nuts on hard, level surfaces (anvils) using stones (hammers) as percussive tools. This activity leaves diagnostic physical remains: distinctive shallow depressions (pits) on the surface of the anvil, cracked shells, and stone hammers on the anvil. To initiate comparison of percussive stone tool use and interpretation of the artifacts it produces across capuchins, chimpanzees, and hominins, we describe a sample of the anvils and hammer stones used by capuchin monkeys at our site. Anvils (boulders and logs) were located predominantly in the transition zone between the flat open woodland and ridges, in locations that offered some overhead coverage, and with a tree nearby, but not necessarily near palm trees. Anvils contained shallow, hemispherical pits with smooth interiors. Hammers represent a diverse assemblage of ancient rocks that are much harder than the prevailing sedimentary rock out of which they eroded. Hard stones large enough to serve as hammers were more abundant on the anvils than in the surrounding area, indicating that capuchins transport them to the anvils. Capuchins use hammers weighing on average more than 1 kg, a weight that is equivalent to 25-40% of the average body weight for adult males and females. Our findings indicate that capuchins select stones to use as hammers and transport stones and nuts to anvil sites. Wild capuchins provide a new reference point for interpreting early percussive stone tool use in hominins, and a point of comparison with chimpanzees cracking nuts.

Animals↗
PubMed1989

Activity states and motor activity in an infant capuchin monkey (Cebus apella) from birth through eleven weeks.

Behavioral states and motor activity of an infant capuchin monkey reared by its mother in a social group were studied for 11 weeks after birth. Manipulative activity was infrequent through the first four weeks after birth; what little occurred was mediated by other animals interacting with the infant. The rate of manipulation increased the most between weeks 8 and 9. At the same time, the most frequent targets of manipulation shifted from the infant's own body and the bodies of others to surfaces and inanimate objects in the cage. Large increases in the proportion of time in an Alert/active state and improvement in postural control also occurred at the end of the second month. The data suggest that major organizational changes in motor coordination and the regulation of behavioral state occurred jointly over a short period of time at about 8 weeks of age. In comparison to other species of monkeys, the capuchin infant displayed later development of manipulation, postural control, and independent locomotion, and greater dependence on social contacts for early interaction with its environment. These characteristics are in accord with the greater neurological immaturity of the capuchin infant at birth compared to other monkeys.

Aging↗
PubMed2003

Joystick acquisition in tufted capuchins (Cebus apella).

A number of nonhuman primate species have demonstrated the ability to use a joystick to control a cursor on a computer screen, yet the acquisition of this skill has not been the focus of systematic inquiry. Here, we examined joystick acquisition in four tufted capuchins under two directional relationships of joystick movement and resultant cursor displacement, isomorphic and inverted. To document the natural history of the acquisition of this skill, we recorded the development of visual tracking of the cursor and body tilting. Rates of acquisition were comparable between the two conditions. After mastering the task in one condition, subjects remastered the task at an accelerated rate in the opposing condition. All subjects significantly increased or maintained high proportions of cursor tracking throughout acquisition. All subjects demonstrated a postural tilt while moving the cursor from the mid-phase of acquisition through task mastery. In the isomorphic condition, all subjects tilted significantly more often in the direction of goal location than in the opposite direction. In three of the four series of tilting that were scored for subjects in the inverted condition, tilting occurred significantly more often toward the direction of goal location than the direction of required hand movement. Together these findings suggest that body tilting participates in the organization of directional movement of the cursor rather than reflecting merely the motoric requirements of the task (to manipulate a joystick).

Animals↗
PubMed2004

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.

Animals↗
PubMed2005

Redundant food searches by capuchin monkeys (Cebus apella): a failure of metacognition?

This study investigated capuchin monkeys' understanding of their own visual search behavior as a means to gather information. Five monkeys were presented with three tubes that could be visually searched to determine the location of a bait. The bait's visibility was experimentally manipulated, and the monkeys' spontaneous visual searches before tube selection were analyzed. In Experiment 1, three monkeys selected the baited tube significantly above chance; however, the monkeys also searched transparent tubes. In Experiment 2, a bent tube in which food was never visible was introduced. When the bent tube was baited, the monkeys failed to deduce the bait location and responded randomly. They also continued to look into the bent tube despite not gaining any pertinent information from it. The capuchin monkeys' behavior contrasts with the efficient employment of visual search behavior reported in humans, apes and macaques. This difference is consistent with species-related variations in metacognitive abilities, although other explanations are also possible.

Animals↗
PubMed2006

I know you are not looking at me: capuchin monkeys' (Cebus apella) sensitivity to human attentional states.

The present study asked whether capuchin monkeys recognize human attentional states. The monkeys requested food from the experimenter by extending an arm (pointing) toward the baited one of two transparent cups. On regular trials the experimenter gave the food immediately to the monkeys upon pointing but on randomly inserted test trials she ignored the pointing for 5 s during which she displayed different attentional states. The monkeys looked at the experimenter's face longer when she looked at the monkeys than when she looked at the ceiling in Experiment 1, and longer when she oriented her head midway between the two cups with eyes open than when she did so with eyes closed in Experiment 2. However, the monkeys showed no differential pointing in these conditions. These results suggest that capuchins are sensitive to eye direction but this sensitivity does not lead to differential pointing trained in laboratory experiments. Furthermore, to our knowledge, this is the first firm behavioral evidence that non-human primates attend to the subtle states of eyes in a food requesting task.

Animals↗
PubMed2002

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.

Animals↗