Abstract: 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.

Abstract: When agonistic interventions are nepotistic, individuals are expected to side more often with kin but less often against kin in comparison with non-kin. As yet, however, few mammal studies have been in a position to test the validity of this assertion with respect to paternal relatedness. We therefore used molecular genetic kinship testing to assess whether adult female rhesus macaques (Macaca mulatta) from the free-ranging colony of Cayo Santiago (Puerto Rico) bias their interventions in ongoing dyadic aggressive interactions towards maternal and paternal half-sisters compared with unrelated females. It turned out that females supported maternal half-sisters significantly more often than paternal half-sisters or non-kin regardless of the costs associated with such interventions. Similarly, females targeted maternal half-sisters significantly less often than non-kin when this was associated with high costs. Unrelated females provided significantly higher mean rates of both high- and low-cost support to each other than did paternal half-sisters. However, females targeted paternal half-sisters significantly less often than non-kin when targeting was at low cost, suggesting that females refrain from intervening against paternal half-sisters. Our data confirm the general view that coalition formation in female mammals is a function of both the level of maternal relatedness and of the costs of intervention. The patterns of coalition formation among paternal kin were found to be more complex, and may also differ across species, but clear evidence for paternal kin discrimination was observed in female rhesus as predicted by kin selection theory.

Abstract: It was recently demonstrated that capuchin monkeys notice and respond to distributional inequity, a trait that has been proposed to support the evolution of cooperation in the human species. However, it is unknown how capuchins react to inequitable rewards in an unrestricted cooperative paradigm in which they may freely choose both whether to participate and, within the bounds of their partner's behavior, which reward they will receive for their participation. We tested capuchin monkeys with such a design, using a cooperative barpull, which has been used with great success in the past. Contrary to our expectations, the equity of the reward distribution did not affect success or pulling behavior. However, the behavior of the partner in an unequal situation did affect overall success rates: pairs that had a tendency to alternate which individual received the higher-value food in unequal reward situations were more than twice as successful in obtaining rewards than pairs in which one individual dominated the higher-value food. This ability to equitably distribute rewards in inherently biased cooperative situations has profound implications for activities such as group hunts, in which multiple individuals work together for a single, monopolizable reward.

Abstract: To what extent can animal behaviour be described as rational? What does it even mean to describe behaviour as rational? This book focuses on one of the major debates in science today – how closely does mental processing in animals resemble mental processing in humans. It addresses the question of whether and to what extent non-human animals are rational, that is, whether any animal behaviour can be regarded as the result of a rational thought processes. It does this with attention to three key questions, which recur throughout the book and which have both empirical and philosophical aspects: What kinds of behavioural tasks can animals successfully perform? What if any mental processes must be postulated to explain their performance at these tasks? What properties must processes have to count as rational? The book is distinctive in pursuing these questions not only in relation to our closest relatives, the primates, whose intelligence usually gets the most attention, but also in relation to birds and dolphins, where striking results are also being obtained. Some chapters focus on a particular species. They describe some of the extraordinary and complex behaviour of these species – using tools in novel ways to solve foraging problems, for example, or behaving in novel ways to solve complex social problems – and ask whether such behaviour should be explained in rational or merely mechanistic terms. Other chapters address more theoretical issues and ask, for example, what it means for behaviour to be rational, and whether rationality can be understood in the absence of language. The book includes many of the world's leading figures doing empirical work on rationality in primates, dolphins, and birds, as well as distinguished philosophers of mind and science. The book includes an editors' introduction which summarises the philosophical and empirical work presented, and draws together the issues discussed by the contributors.