Choosing and Using Tools: Capuchins (Cebus apella) Use a Different Metric Than Tamarins (Saguinus oedipus).

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Abstract
Cotton-top tamarins (Saguinus oedipus) selected canes positioned so that a straight inward pull brought food within reach (M. D. Hauser, 1997). Tamarins failed to retrieve food with canes in other positions, and they did not reposition these canes. In this study, tufted capuchin monkeys (Cebus apella) preferred canes they could pull straight in when these were present, but they also repositioned canes in individually variable ways, and their success at obtaining food with repositioned canes improved with practice. In accord with predictions drawn from ecological psychology, capuchins discovered affordances of canes through exploratory actions with these objects, whereas tamarins did not. Ecological theory predicts these differences on the basis of species-typical manipulative activity, and it provides a useful approach for the study of species differences in tool-using behavior. Nonhuman primates are well represented among species that spontaneously use objects as tools, with capuchins (a genus of New World monkeys) topping the list of monkeys as frequent and varied tool users (Anderson, 1996; Fragaszy, Visalberghi, & Fedi- gan, 2004; Tomasello & Call, 1997). One theoretical perspective on tool use in nonhuman primates seeks to explain the observed patterns in terms of causal reasoning (Hauser, 1997; Povinelli, 2000; Visalberghi & Limongelli, 1994; Visalberghi & Tomasello, 1998; Visalberghi & Trinca, 1989). In this perspective, members of a species share a species-normative pattern of reasoning about the physical world. For example, Hauser (1997) presented cotton- top tamarins with a choice between two canes to pull in a food treat. The tamarins preferentially chose canes of a certain size and shape, and they chose canes on the basis of the location of the food (i.e., inside the crook of the cane vs. outside the crook). They did not choose canes on the basis of familiarity, color, or texture. Hauser concluded that the tamarins selected canes on the basis of functionally relevant properties for their intended use (to pull in the food). In Hauser's view, the tamarins seemed to have a grasp of at least some of the causal relations involved in using the canes as tools. Hauser's (1997) interpretation of the tamarins' behavior with canes is couched in terms of the tamarins' possession of concepts about objects. This argument stipulates that conceptual knowledge about objects guides action and that such knowledge is, in part,