Tool-use learning in Tonkean macaques (Macaca tonkeana)

The transmission of tool use is a rare event in monkeys. Such an event arose in a group of semi-free-ranging Tonkean macaques (Macaca tonkeana) in which leaning a pole against the parks fence (branch leaning) appeared and spread to several males. This prompted us to test individual and social learning of this behavior in seven young males. In the first experiment, three males learned individually to obtain a food reward using a wooden pole as a climbing tool. They began using the pole to retrieve the reward only when they could alternatively experience acting on the object and reaching the target. In a second experiment, we first tested whether four other subjects could learn branch leaning after having observed a group-mate performing the task. Despite repeated opportunities to observe the demonstrator, they did not learn to use the pole as a tool. Hence we exposed the latter subjects to individual learning trials and they succeeded in the task. Tool use was not transmitted in the experimental situation, which contrasts with observations in the park. We can conclude that the subjects were not able to recognize the target as such. It is possible that they recognized it and learned the task individually when we alternated the opportunity to act upon the object and to reach the reward. This suggests that these macaques could then have associated the action they exercised upon the pole and the use of the pole as a means to reach the reward.     

Following and joining the informed individual in semifree-ranging tonkean macaques (Macaca tonkeana)

The authors investigated whether Tonkean macaques (Macaca tonkeana) can distinguish between 2 group mates with different knowledge and improve their foraging performance. The subjects were 8 young individuals belonging to a group raised in a 2-acre park. The authors carried out 192 tests in which subgroups of 3 individuals were released in a food search situation. Two leaders could be informed about 2 different food sites. A naive follower could choose to follow 1 leader or another. The follower could find the correct site when 1 leader was informed about food location. There was no evidence that the follower identified the best leader, however. The less well-informed leader generally joined the other leader, prompting the follower to follow them. The followers' pathways were mainly determined by the interactions of leaders.     

Tonkean macaques ( Macaca tonkeana) find food sources from cues conveyed by group-mates

It is possible that non-specialised cues transmitted by conspecifics guide animals' food search provided they have the cognitive abilities needed to read these cues. Macaques often check the mouth of their group-mates by olfactory and/or visual inspection. We investigated whether Tonkean macaques (Macaca tonkeana) can find the location of distant food on the basis of cues conveyed by group-mates. The subjects of the study were two 6-year-old males, who belonged to a social group of Tonkean macaques raised in semi-free-ranging conditions. In a first experiment, we tested whether the subject can choose between two sites after having sniffed a partner who has just eaten food corresponding to one of the sites. We found that both subjects were able to choose the matching site significantly above the chance level. This demonstrated that Tonkean macaques are capable of delayed olfactory matching. They could associate a food location with an odour conveyed by a partner. In a second experiment, the same subjects were allowed to see their partner through a Plexiglas window. Both subjects were still able to choose the matching site, demonstrating they could rely on visual cues alone. Passive recruitment of partners appears possible in macaques. They can improve their foraging performances by finding the location of environmental resources from olfactory or visual cues conveyed by group-mates. Electronic Publication     

The use of the bared-teeth display during play fighting in Tonkean macaques (Macaca tonkeana): sometimes it is all about oneself

Play signals are viewed as important means by which animals inform each other that bites, strikes, and throws that occur during play fighting are indeed playful rather than serious. One such signal is the open mouth play face that is common in primates and many other mammals. Unfortunately, as most play fighting involves biting, it can be ambiguous as to whether any instance of opening the mouth is performed to communicate playful intent or is simply a preparation for biting. In this study, open mouths co-occurring with the bared-teeth display (teeth-baring) in Tonkean macaques were used to assess the context in which facial gestures only relevant for signaling (i.e., teeth-baring is not necessary for biting) are used during play. Two predictions arising from the hypothesis that play signals are used to facilitate playful contact were tested: that the open mouth with teeth-baring should (1) be most frequent preceding contact, and (2) that it should be performed most often when bites are directed at orientations that is visible to the recipient. The data only partially support these predictions. The open mouth with teeth-baring is also frequently used when a monkey withdraws from playful contact. Moreover, it is associated with bites to body targets, such as the rump, that offer little prospect for detection by the recipient; this supports the possibility that play signals may sometimes be emitted not to communicate with the partner but with the performer itself. Thus, play signals serve multiple functions during play fighting.     

Object individuation using property/kind information in rhesus macaques (Macaca mulatta)

Around 1 year of age, infants develop the ability to individuate objects in the absence of spatiotemporal information. Some have proposed that this capacity relies on the emergence of language and, in particular, that comprehending an object's label is required to individuate it as a particular kind. One approach to testing this hypothesis is to conduct experiments on pre-linguistic human infants. A second is to test non-linguistic animals. We followed the second approach, exploring whether semi-free-ranging rhesus macaques can individuate objects using property/kind information. To make the results most directly comparable, we adapted a reaching paradigm used to examine property/kind individuation in infants. Results from three experiments demonstrate that, like 12-month-old infants, adult rhesus macaques can use both spatiotemporal and property/kind information to individuate food objects. In a fourth experiment designed to examine which properties are used to individuate food objects, results revealed that rhesus use color, but not shape. These results, together with experiments involving different procedures, provide support for the conclusion that in the absence of linguistic abilities, some non-human primates spontaneously use property/kind information to individuate objects.     

Cued repetition of self-directed behaviors in macaques (Macaca nemestrina)

Two macaques (Macaca nemestrina) were trained to perform 3 self-directed behaviors on signal and to repeat behaviors after a 'repeat' signal. The cognitive processes underlying the monkeys' repeat performance were evaluated via multiple repetitions of the repeat signal, extended delay periods between target behavior and repeat signal, and by transferring the repeat signal to novel behaviors. The monkeys seemed to use representations of their own past behaviors as a basis for repetition performance, but they mostly failed to correctly repeat target behaviors after extended delays and during transfer tasks. Implications for episodic memory abilities are discussed.     

Lion-tailed macaques (Macaca silenus) manufacture and use tools

Lion-tailed macaques (Macaca silenus) in captive social groups spontaneously manufactured and used tools to extract syrup from an apparatus that was designed to accommodate probing behavior. An attempt to replicate these findings with mandrills (Mandrillus sphinx) was unsuccessful. This report is the first to describe spontaneous manufacture of tools in any group of Old World monkeys and provides evidence of greater continuity among primates for the expression of complex cognitive abilities. These data are consistent with hypotheses that lion-tailed macaques have extensive propensities for advanced sensorimotor skills and that omnivorous, extractive foraging is associated with the manufacture and use of tools. I present a proximate model that integrates sensorimotor and social factors to account for diverse expression of tool-related behavior.     

Retrospective and prospective metacognitive judgments in rhesus macaques (Macaca mulatta)

A growing body of research suggests that some non-human animals are capable of making accurate metacognitive judgments. In previous studies, non-human animals have made either retrospective or prospective judgments (about how they did on a test or how they will do on a test, respectively). These two types of judgments are dissociable in humans. The current study tested the abilities of two rhesus macaque monkeys to make both retrospective and prospective judgments about their performance on the same memory task. Both monkeys had been trained previously to make retrospective confidence judgments. Both monkeys successfully demonstrated transfer of retrospective metacognitive judgments to the new memory task. Furthermore, both monkeys transferred their retrospective judgments to the prospective task (one, immediately, and one, following the elimination of a response bias). This study is the first to demonstrate both retrospective and prospective monitoring abilities in the same monkeys and on the same task, suggesting a greater level of flexibility in animals’ metacognitive monitoring abilities than has been reported previously.     

Weber's Law influences numerical representations in rhesus macaques (Macaca mulatta)

We present the results of two experiments that probe the ability of rhesus macaques to match visual arrays based on number. Three monkeys were first trained on a delayed match-to-sample paradigm (DMTS) to match stimuli on the basis of number and ignore continuous dimensions such as element size, cumulative surface area, and density. Monkeys were then tested in a numerical bisection experiment that required them to indicate whether a sample numerosity was closer to a small or large anchor value. Results indicated that, for two sets of anchor values with the same ratio, the probability of choosing the larger anchor value systematically increased with the sample number and the psychometric functions superimposed. A second experiment employed a numerical DMTS task in which the choice values contained an exact numerical match to the sample and a distracter that varied in number. Both accuracy and reaction time were modulated by the ratio between the correct numerical match and the distracter, as predicted by Weber's Law.     

Time preferences in long-tailed macaques (Macaca fascicularis) and humans (Homo sapiens)

Rosati et al. (Curr Biol 17(19):1663–1668, 2007) found in a self-control test in which choice was between a smaller, immediately delivered food and a larger, delayed food, that chimpanzees preferred the larger reward (self-control); humans, however, preferred the smaller reward (impulsivity). They attributed their results to a species difference in self-control. In Experiment 1, monkeys (long-tailed macaques) were exposed to a self-control task in two conditions: where the food was hidden under differently colored bowls and where it was visible. When these two conditions were compared, choice shifted from greater preference for the impulsive alternative in the hidden condition to greater preference for the self-control alternative in the visible condition. Additionally, in both conditions, preference shifted from self-control to impulsivity over sessions. These results were explained in terms of the reversed-contingency effect (a propensity to reach for more over less when rewards are visible) and not to a capacity for self-control. In Experiment 2, humans that demonstrated preference for more over less in choice preferred the impulsive alternative when choice to either alternative was followed by the same intertrial interval—a preference that accelerates trial rates relative to preference of the self-control alternative. When trial rates were equated so that neither choice accelerated session’s end, humans demonstrated self-control. These results suggest that Rosati et al.’s demonstration of impulsivity in humans was due to participants’ desire to minimize session time.     

Rhesus macaques (Macaca mulatta) monitor uncertainty during numerosity judgments

Two rhesus macaques (Macaca mulatta) judged arrays of dots on a computer screen as having more or fewer dots than a center value that was never presented in trials. After learning a center value, monkeys were given an uncertainty response that let them decline to make the numerosity judgment on that trial. Across center values (3-7), errors occurred most often for sets adjacent in numerosity to the center value. The monkeys also used the uncertainty response most frequently on these difficult trials. A 2nd experiment showed that monkeys' responses reflected numerical magnitude and not the surface-area illumination of the displays. This research shows that monkeys' uncertainty-monitoring capacity extends to the domain of numerical cognition. It also shows monkeys' use of the purest uncertainty response possible, uncontaminated by any secondary motivator.     

Ordinal judgments of numerical symbols by macaques (Macaca mulatta)

Two rhesus monkeys (Macaca mulatta) learned that the arabic numerals 0 through 9 represented corresponding quantities of food pellets. By manipulating a joystick, the monkeys were able to make a selection of paired numerals presented on a computer screen. Although the monkeys received a corresponding number of pellets even if the lesser of the two numerals was selected, they learned generally to choose the numeral of greatest value even when pellet delivery was made arrhythmic. In subsequent tests, they chose the numerals of greater value when presented in novel combinations or in random arrays of up to five numerals. Thus, the monkeys made ordinal judgments of numerical symbols in accordance with their absolute or relative values.     

Come with me: experimental evidence for intentional recruitment in Tonkean macaques

Animal Cognition - Recruitment is a process by which animals can initiate collective movements: the action of an individual prompts conspecifics to follow. Although it has been hypothesized that...     

Patterns of agonistic interactions in three species of macaque (Macaca mulatta,M fascicularis,M tonkeana)

Patterns of aggression and response to aggression were studied in three groups of macaques living in semiliberty, each group representing a different species: Macaca mulatta, M fascicularis, and M tonkeana. In Macaca mulatta, intensity of aggression is high (biting is frequent) and symmetry in aggression is low: the aggressee most often flees or submits. In Macaca tonkeana, in contrast, biting is exceptional, aggression is very often bidirectional, and appeasement behaviors are frequently observed. Intermediate patterns are found in Macaca fascicularis with, in addition, especially frequent mild forms of submission. It is argued that relationships exist between intensity of aggression, symmetry in aggression, and development of behaviors controlling aggresssion. Whether balances between these variables are species-specific is discussed.     

Recognition of heterospecific alarm vocalizations by bonnet macaques (Macaca radiata)

Recognition of heterospecific alarm vocalizations is an essential component of antipredator behavior in several prey species. The authors examined the role of learning in the discrimination of heterospecific vocalizations by wild bonnet macaques (Macaca radiata) in southern India The bonnet macaques' flight and scanning responses to playbacks of their own alarm vocalizations were compared with their responses to playbacks of vocalizations of Nilgiri langurs (Trachypithecus johnii), Hanuman langurs (Semnopithecus entellus), and sambar deer (Cervus unicolor). The study was conducted in 3 regions that differed in the frequency with which bonnet macaques encountered these species and included an urban setting. Call recognition was highest in adults and in regions where individuals were frequently exposed to the calling species; calls were not recognized by urban monkeys. Thus, age and experience are important factors in heterospecific call recognition by bonnet macaques.     

Signals use by leaders in Macaca tonkeana and Macaca mulatta: group-mate recruitment and behaviour monitoring

Animals living in groups have to make consensus decisions and communicate with each other about the time, or the direction, in which to move. In some species, the process relies on the proposition of a single individual, i.e. a first individual suggests a movement and the other group members decide whether or not to join this individual. In Tonkean (Macaca tonkeana) and rhesus macaques (Macaca mulatta), it has been observed that this first individual displays specific signals at departure. In this paper, we aimed to explore the function of such behaviours, i.e. if these behaviours were recruitment signals or only cues about the motivation of the first departed individual. We carried out temporal analyses and studied the latencies of the first departed individual’s behaviours and of the joining of other group members. We also assessed whether the social style of a species in terms of dominance and kinship relationships influenced the patterns of signal emissions. We then analyzed how the first departed individual decided to make a pause or to stop it according to the identities of group members that joined the collective movement. Results showed that Tonkean macaques and rhesus macaques seemed to use back-glances to monitor the joining of other group members and pauses to recruit such individuals. This was especially the case for highly socially affiliated individuals in Tonkean macaques and kin-related individuals in rhesus macaques. Moreover, back-glances and pauses disappeared when such individuals joined the first departed individual. From these results, we suggested that such behaviour could be considered intentional. Such findings could not be highlighted without temporal analyses and accurate observations on primate groups in semi-free ranging conditions.     

Sequential responding and planning in chimpanzees (Pan troglodytes) and rhesus macaques (Macaca mulatta)

Chimpanzees (Pan troglodytes) and rhesus macaques (Macaca mulatta) selected either Arabic numerals or colored squares on a computer monitor in a learned sequence. On shift trials, the locations of 2 stimuli were interchanged at some point. More errors were made when this interchange occurred for the next 2 stimuli to be selected than when the interchange was for stimuli later in the sequence. On mask trials, all remaining stimuli were occluded after the 1st selection. Performance exceeded chance levels for only 1 selection after these masks were applied. There was no difference in performance for either stimulus type (numerals or colors). The data indicated that the animals planned only the next selection during these computerized tasks as opposed to planning the entire response sequence.     

Affiliative vocalizations in infant rhesus macaques (Macaca mulatta).

In Experiment 1, infant rhesus monkeys (Macaca mulatta) were separated and then reunited with mothers, united with a male, or placed in an empty cage. Infants girned more when with mothers or the male than when alone. Girns declined over time when infants were united with the male. Coo rates were high when the infant was alone or with the male. Shrieks, barks, and fear-related behavior were higher with the male. In Experiment 2 the vocalizations of infants were examined during separation when alone or when mothers or a male were in the same room. Infants cooed more when mothers or a male were present. Cooing increased over time, with a greater increase in the mothers' presence. Girns were given to both mothers and males, but more were given to mothers. Coos and girns are both affiliative vocalizations but are differentially modulated as infants cease cooing when they receive contact comfort.