Search

Among animal societies, dominance is an important social factor that influences inter-individual relationships. However, assessing dominance hierarchy can be a time-consuming activity which is potentially impeded by environmental factors, difficulties in the recognition of animals, or disturbance of animals during data collection. Here we took advantage of novel devices, machines for automated learning and testing (MALT), designed primarily to study non-human primate cognition, to additionally measure the dominance hierarchy of a semi-free-ranging primate group. When working on a MALT, an animal can be replaced by another, which could reflect an asymmetric dominance relationship. To assess the reliability of our method, we analysed a sample of the automated conflicts with video scoring and found that 74% of these replacements included genuine forms of social displacements. In 10% of the cases, we did not identify social interactions and in the remaining 16% we observed affiliative contacts between the monkeys. We analysed months of daily use of MALT by up to 26 semi-free-ranging Tonkean macaques (Macaca tonkeana) and found that dominance relationships inferred from these interactions strongly correlated with the ones derived from observations of spontaneous agonistic interactions collected during the same time period. An optional filtering procedure designed to exclude chance-driven displacements or affiliative contacts suggests that the presence of 26% of these interactions in data sets did not impair the reliability of this new method. We demonstrate that this method can be used to assess the dynamics of both individual social status, and group-wide hierarchical stability longitudinally with minimal research labour. Further, it facilitates a continuous assessment of dominance hierarchies in captive groups, even during unpredictable environmental or challenging social events, which underlines the usefulness of this method for group management purposes. Altogether, this study supports the use of MALT as a reliable tool to automatically and dynamically assess dominance hierarchy within captive groups of non-human primates, including juveniles, under conditions in which such technology can be used.

When exploiting the environment, animals have to discriminate, track, and integrate salient spatial cues to navigate and identify goal sites. Actually, they have to know what can be found (e.g. what fruit), where (e.g. on which tree) and when (in what season or moment of the year). This is very relevant for primate species as they often live in seasonal and relatively unpredictable environments such as tropical forests. Here, we review and compare different approaches used to investigate primate spatial foraging strategies: from direct observations of wild primates to predictions from statistical simulations, including experimental approaches on both captive and wild primates, and experiments in captivity using virtual reality technology. Within this framework, most of these studies converge to show that many primate species can (i) remember the location of most of food resources well, and (ii) often seem to have a goal-oriented path towards spatially permanent resources. Overall, primates likely use mental maps to plan different foraging strategies to enhance their fitness. The majority of studies suggest that they may organise spatial information on food resources into topological maps: they use landmarks to navigate and encode local spatial information with regard to direction and distance. Even though these studies were able to show that primates can remember food quality (what) and its location (where), still very little is known on how they incorporate the temporal knowledge of available food (when). Future studies should attempt to increase our understanding of the potential of primates to learn temporal patterns and how both socio-ecological differences among species and their cognitive abilities influence such behavioural strategies., (© 2018 Cambridge Philosophical Society.)

Foraging in seasonal environments can be cognitively demanding. Comparative studies have associated large brain size with a frugivorous diet. We investigated the ability of three semi-free-ranging primate species with different degrees of frugivory (Ntrials: Macaca tonkeana = 419, Macaca fascicularis = 197, Sapajus apella = 346) in developing a mental representation of the spatio-temporal distribution of food using foraging experiments. Forty-two boxes were fixed on trees, and each week ("season"), some of them were filled with fruits which were either highly preferred, or less preferred. Spatial (geometrical panels) and temporal (peel skin of the available fruit) cues were present at each season to indicate where (food location), what (which food) was available, and when. To test the flexible use of the cues in primate foraging behaviour, we first removed the spatial and temporal cues one at a time, and then, we manipulated the "seasonal" order of the available fruit. We compared the foraging performances in the absence and the presence of the cues and during the usual and unusual seasonal order. The average proportion of baited boxes chosen by the subjects in presence of both cues was high (between 73% and 98%) for all species. The primates seemed to remember the spatio-temporal food availability (or used other cues) because no difference was found between trials with or without our spatial and temporal cues. When the usual seasonal pattern was changed, they flexibly adjusted the feeding choice by using the provided temporal cues. We discuss these results also in view of a possible experimental bias. [ABSTRACT FROM AUTHOR]

Many primates intentionally consume earth. This geophagy has probable health benefits, such as mineral supplementation or gastrointestinal tract protection, and is likely to be an important behavior for a species' ecology, health, diet, and conservation. We investigated geophagy in the Critically Endangered yellow-tailed woolly monkey (Lagothrix flavicauda). We collected observational data and camera trap records over 2 years at La Esperanza study site, northern Peru. Geophagy was rare, with 67 events recorded during the study. All age/sex classes engaged in geophagy, but adult males spent significantly less time consuming earth in situ than adult females did. Geophagy occurred predominantly during the dry season and was a solitary behavior. The forest floor is presumably a high-risk environment for these predominantly arboreal primates and our study animals employed various strategies to minimize predation risk. These included using a single route to access and leave geophagy sites, displaying increased vigilance behaviors before and during geophagy events, and minimizing the time spent on the forest floor (mean: 15 ± SD 9 s). They also maximized the benefits of being on the forest floor by removing earth to consume ex situ. These findings provide the first steps in the systemic approach required to understand the role geophagy plays in our study species, whose almost exclusive arboreality, coupled with the increased predation risk associated with terrestriality, suggests that geophagy confers an important benefit. [ABSTRACT FROM AUTHOR]

Awareness of one's own mental states, also known as metacognition, is an important component of human self-awareness. In recent decades, several studies have investigated nonhuman metacognition and evidence of this ability has notably been gathered in catarrhine primates. Conversely, numerous studies on capuchin monkeys have reported mixed or negative results. Because it has been suggested that the failure of capuchins may be due to species-related limitations of classical metacognition tasks, we tested metacognition in the brown capuchin, Sapajus apella , using a novel experimental paradigm adapted from a study of human infants. In this experiment, capuchins had to choose between two boxes, one of which had previously been baited with a treat under their gaze, before searching the hidden content of the chosen box. As the treat was surreptitiously removed, the time capuchins were willing to search the box for the treat could be used as a nonverbal postdecision indicator of metacognitive confidence, with longer persistence times indicating greater confidence in remembering which box was baited and expecting to find the treat in the chosen box. Consistent with the possibility that capuchins possess metacognitive abilities, capuchins persisted longer in their search after a correct versus incorrect choice. This result suggests that metacognition in primates is not restricted to catarrhines. Although nonmetacognitive explanations are possible, experimental paradigms involving a postdecision indicator of confidence, such as persistence, have advantages over classical paradigms and offer promising perspectives for investigating metacognition in a wide range of animals. • An experimental paradigm based on persistence was adapted from a human study. • Capuchin monkeys persisted longer after correct choices than after incorrect choices. • This aligns with the possibility that capuchins have metacognitive abilities. • Alternative explanations of the results are discussed. [ABSTRACT FROM AUTHOR]

Research methods in cognitive neuroscience using non-human primates have undergone notable changes over the last decades. Recently, several research groups have described freely accessible devices equipped with a touchscreen interface. Two characteristics of such systems are of particular interest: some apparatuses include automated identification of subjects, while others are mobile. Here, we designed, tested and validated an experimental system that, for the first time, combine automatization and mobility. Moreover, our system allows autonomous learning and testing of cognitive performance in group-living subjects, including follow-up assessments. The mobile apparatus is designed to be available 24 h a day, 7 days a week, in a typical confined primate breeding and housing facility. Here we present as proof of concept, the results of two pilot studies. We report that rhesus macaques ( Macaca mulatta ) learned the tasks rapidly and achieved high-level of stable performance. Approaches of this kind should be developed for future pharmacological and biomedical studies in non-human primates. [ABSTRACT FROM AUTHOR]

The understanding that the perceptual appearance of the environment can differ in several ways from the reality underlies the ability to discriminate appearance from reality. Being able to realize when a misperception can lead us to behave in inappropriate ways confers an evolutionary advantage and may be a prerequisite to develop a Theory of Mind. Understanding that our own perception can differ from reality seems indeed necessary to attribute to others perceptions or beliefs different than ours. This appearance-reality discrimination ability has recently been demonstrated in great apes but no information is currently available regarding this ability in other nonhuman species. In a comparative study, we tested Tonkean macaques (Macaca tonkeana), an Old World primate species, and brown capuchins (Sapajus apella), a New World primate species. We provided monkeys with two experiments using visual illusions of size and quantity to test their ability to discriminate appearance from reality, with an experimental setup similar to the one developed by Krachun et al. (2016) on chimpanzees. A large number of brown capuchins, from different ages and both sexes, as well as two Tonkean macaques succeeded in the two experiments. By ruling out all alternative explanations (i.e. visual tracking or associative learning), our study brings the first evidence that some Old World and New World monkeys are able to discriminate appearance from reality. Our results suggest moving the evolutionary apparition of this cognitive ability earlier in time. Finally, it suggests that humans could share more Theory of Mind components with more nonhuman species than we previously thought. [ABSTRACT FROM AUTHOR]