Anim Cogn (2006) 9: 110–117 DOI 10.1007/s10071-005-0007-2 ORIGINAL ARTICLE Annika Paukner · James R. Anderson · Kazuo Fujita Redundant food searches by capuchin monkeys (Cebus apella): a failure of metacognition? Received: 15 March 2005 / Revised: 3 July 2005 / Accepted: 5 July 2005 / Published online: 24 September 2005 C  Springer-Verlag 2005 Abstract This study investigated capuchin monkeys’ un- derstanding 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 experimen- tally manipulated, and the monkeys’ spontaneous visual searches before tube selection were analyzed. In Exper- iment 1, three monkeys selected the baited tube signifi- cantly 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. Keywords Metacognition . Metacognitive awareness . Capuchin monkey . Visual search behavior When humans are aware that they are missing important information for correctly completing a task, or when they are unsure about what to do, they often react predictably. For example, if they realize that a piece of information is not sufficiently known to pass an exam, students may de- cide to study further (Nelson and Narens 1990). Seeking information or declining a response in a situation of uncer- tainty are indicative of metacognitive awareness, which is A. Paukner () · J. R. Anderson Department of Psychology, University of Stirling, Stirling, FK9 4LA, UK e-mail: ap14@stir.ac.uk Tel.: +44-1786-467640 Fax: +44-1786-467641 K. Fujita Department of Psychology, Faculty/Graduate School of Letters, Kyoto University, Yoshida-honmachi, Sakyo, Kyoto 606-8501, Japan defined as knowing about one’s own cognitive states (Smith et al. 1995). Metacognitive awareness has been investigated in several non-human species, including dolphins, pigeons and a few species of primates (e.g. Smith et al. 1995; Inman and Shettleworth 1999; Hampton 2001; for a review, see Smith et al. 2003). For example, Hampton (2001) found that rhesus macaques (Macaca mulatta) may decline a memory trial that they are unlikely to complete correctly and opt for a new, easier trial instead. This behavior suggests that rhesus macaques are capable of accurately monitoring their own memory contents (Hampton 2001). Griffin (2003) argued that all animals face uncertainty, for example, when deciding whether a movement in the veg- etation is a predator or simply wind, or whether an object on the ground is edible or not. Decisions regarding these uncertainties can be crucially important for survival of an animal. Therefore, a system for accurately monitoring un- certainties and controlling the animal’s behavior in terms of either seeking more information or deciding on the point of certainty sufficient for making an adaptive response would appear advantageous. It is therefore conceivable that natu- ral selection has led to metacognitive awareness evolving in many species. Regarding primates, chimpanzees (Pan troglodytes) and orangutans (Pongo pygmaeus) will efficiently seek additional information. Call and Carpenter (2001) showed hollow tubes to these apes, one containing a food reward, and the apes were allowed to look into the tubes before selecting one. They received the reward only if they selected the baited tube. Call and Carpenter (2001) found that both species were more likely to search for the reward when they had not witnessed the baiting procedure and thus did not know where the bait was. In addition, searching the tubes led to more correct tube selections. Apes behave similarly to 2.5-year-old children in this respect; the latter also engage in visual searches when they do not know the correct location of a desirable objects (Call and Carpenter 2001). Recently, Hampton et al. (2004) adapted the tube paradigm to test rhesus macaques. Like humans and apes, the macaques searched more when they had not witnessed the baiting, and selection accuracy increased when they