Factors affecting cashew processing by wild bearded capuchin monkeys (Sapajus libidinosus, Kerr 1792).

Cashew nuts are very nutritious but so well defended by caustic chemicals that very few species eat them. We investigated how wild bearded capuchin monkeys (Sapajus libidinosus) living at Fazenda Boa Vista (FBV; Piauí, Brazil) process cashew nuts (Anacardium spp.) to avoid the caustic chemicals contained in the seed mesocarp. We recorded the behavior of 23 individuals toward fresh (N = 1282) and dry (N = 477) cashew nuts. Adult capuchins used different sets of behaviors to process nuts: rubbing for fresh nuts and tool use for dry nuts. Moreover, adults succeed to open dry nuts both by using teeth and tools. Age and body mass significantly affected success. Signs of discomfort (e.g., chemical burns, drooling) were rare. Young capuchins do not frequently closely observe adults processing cashew nuts, nor eat bits of nut processed by others. Thus, observing the behavior of skillful group members does not seem important for learning how to process cashew nuts, although being together with group members eating cashews is likely to facilitate interest toward nuts and their inclusion into the diet. These findings differ from those obtained when capuchins crack palm nuts, where observations of others cracking nuts and encounters with the artifacts of cracking produced by others are common and support young individuals' persistent practice at cracking. Cashew nut processing by capuchins in FBV appears to differ from that observed in a conspecific population living 320 km apart, where capuchins use tools to open both fresh and dry nuts. Moreover, in the latter population, chemical burns due to cashew caustic compounds appear to be common. The sources of these differences across populations deserve investigation, especially given that social influences on young monkeys learning to open cashew nuts at FBV seem to be nonspecific. Am. J. Primatol. 78:799-815, 2016. © 2016 Wiley Periodicals, Inc.

Do tufted capuchin monkeys play the odds? Flexible risk preferences in Sapajus spp.

As humans, several non-human animal species avoid risk, defined as "variability in rate of gain". However, non-human primate studies revealed a more complicated picture, with different species ranging from risk aversion to risk proneness. Within an ecological rationality framework, a species' feeding ecology should influence its risk preferences, as it has been shown in bonobos and chimpanzees. Although the feeding ecology hypothesis is promising, it has not been yet verified in species other than apes. Here, we aimed to assess whether this hypothesis holds true in tufted capuchin monkeys (Sapajus spp.). Ten capuchins were presented with choices between a "safe" option and a "risky" option in three conditions differing for the probability of receiving the larger reward when selecting the risky option. Similarly to chimpanzees, capuchins were risk prone. However, capuchins' behaviour was not the result of a bias towards the choice of the risky option, since-when facing options with different probabilities of obtaining the larger outcome-they were able to flexibly modify their preferences. Capuchins' decision-making under risk mirrors their risk-prone behaviour in the wild, where they often rely on unpredictable and/or hazardous food sources, thus satisfying the feeding ecology hypothesis.

Nonhuman gamblers: lessons from rodents, primates, and robots.

The search for neuronal and psychological underpinnings of pathological gambling in humans would benefit from investigating related phenomena also outside of our species. In this paper, we present a survey of studies in three widely different populations of agents, namely rodents, non-human primates, and robots. Each of these populations offers valuable and complementary insights on the topic, as the literature demonstrates. In addition, we highlight the deep and complex connections between relevant results across these different areas of research (i.e., cognitive and computational neuroscience, neuroethology, cognitive primatology, neuropsychiatry, evolutionary robotics), to make the case for a greater degree of methodological integration in future studies on pathological gambling.

How capuchin monkeys (Cebus apella) behaviorally cope with increasing delay in a self-control task.

Displacement activities are behavior patterns apparently irrelevant to the situation in which they are performed that facilitate transitions between behavioral states. Scratching is one of the most commonly described displacement activities in primates and is related to frustration and anxiety. In chimpanzees scratching during cognitive tasks increases with task difficulty. We analyzed behavioral data obtained from video clips on nine capuchin monkeys tested in a delay choice task, a potentially stressful self-control task where subjects choose between a small immediate and a large delayed option. Scratching, response latency, and motor impulsivity scored during the delay decreased across sessions, as capuchins became indifferent between options, whereas the bias for choosing the option placed on one side of the apparatus increased. Capuchins might have found the delay choice task less stressful over time because they shifted from slower discriminatory responses in the earlier sessions to more 'automatic', faster responses in the later sessions. However, it cannot be excluded that they habituated over time to the contingencies of the task. In contrast with previous data on chimpanzees, handedness in scratching behavior or preferential scratching on one side of the body did not emerge, but further studies are needed to corroborate this finding.