Introduction
Tool use, the use of a free object in the environment as a functional extension of one's own body (Beck, 1980), has been reported in invertebrates, fish, birds, and mammals, including primates (Alcock, 1989). However, tool use is not common or widespread in nonhuman primates. It has been observed in a small number of species including chimpanzees, bonobos, gorillas, orangutans, some macaques and baboons, and capuchin monkeys (van Schaik et al., 1999). Captive capuchin monkeys (Cebus spp.) were long reported to use tools in a variety of contexts (Visalberghi, 1990; Urbani, 1999). Recently, however, a growing body of evidence shows that semi-captive and free-ranging capuchins in several populations and species use tools, including the use of stones as hammers and anvils to crack and open nuts (Ottoni and Mannu, 2001; Fragaszy et al., 2004; Moura and Lee, 2004; Waga et al., 2006). Tool-making is a cognitively complex process that involves an intentional modification of the tool for improving its efficiency (Beck, 1980). Reports of non-human primate tool-making have been restricted to the great apes (Boesch and Boesch, 1990; Fontaine et al., 1995; Tomasello and Call, 1997; Schick et al., 1999; van Schaik et al., 2003) with the exception of a few experimentally induced cases in captive capuchins (Westergaard and Suomi, 1994, 1995; Westergaard et al., 1995). Here we report a case of spontaneous tool-making by a captive capuchin monkey.
Methods
A group of capuchin monkeys (Cebus sp.) composed of an adult male, two adult females and three immature males living in an enriched enclosure 7.0 m long × 8.7 m wide × 2.9 m high at the Sapucaia do Sul Zoological Park, State of Rio Grande do Sul, Brazil, was opportunistically (ad libitum) observed and video-taped in January and February 2007. The enclosure included sand on the floor, trees, stones, and perches for the monkeys. For enrichment purposes, food was concealed inside ice cubes, PVC pipes, and bags.
Results
On 12 January 2007, an adult female (putative Cebus nigritus) was observed banging a twig with a piece of stone against a larger stone, licking/chewing and likely extracting something from it with her mouth. She was then observed probing an unseen structure (probably a hole in the enclosure's drinking fountain) with the modified twig (Fig. 1). This sequence of events occurred very rapidly. The latency between the end of banging and the start of probing was 3 to 4 seconds, during which time the female moved from the banging site to the probing site. After this observation, the group was monitored for 15 days and no additional cases of tool-making were observed. The capuchins, however, often used stones as hammers to crack nuts and other foods, including ice cubes containing food (Fig. 2).
Discussion
Although we do not know what happened immediately prior to this behavioral sequence and could not see whether the female acquired anything as a result of probing, the speed at which this sequence of events occurred is highly suggestive of a causal understanding during object manipulation and seems to qualify as a case of spontaneous tool-making. Future research will focus on confirming the capuchin monkeys' capability to make tools, an ability that would suggest less cognitive difference than is presently thought to exist between capuchins and the great apes (Visalberghi, 1990, 1997; Urbani and Garber, 2002). In addition to suggesting that capuchin monkeys understand cause and effect relationships during object manipulation, these findings strengthen the argument that the maintenance of captive animals in enriched environments is an important strategy to allow the expression of the species' fullest behavioral repertoire. A previous study of the same group (200 hours during 2002–2003) in this enclosure, but with minimum enrichment (paved ground, a single swing and no feeding enrichment), failed to record any case of tool use (D.B. Montano, personal observation). Environmental enrichment serves an important function in improving capuchin monkeys' welfare by reducing boredom and eliciting tool use.
Acknowledgments
We thank the staff of the Núcleo de Zoologia of the Sapucaia do Sul Zoological Park, especially Renato Petry Leal and Marcelo Linck, for the permission to conduct this study. We also thank Paul A. Garber and Bernardo Urbani for reviewing an earlier version of this manuscript.
References
Notes
[1] Tiago Scares Bortolini, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves 9500, Campus do Vale, Prédio 43323 Sala 115, Porto Alegre, RS 91501-970, Brazil, e-mail: <tbortolini@gmail.com>, and Júlio César Bicca-Marques, Laboratório de Primatologia, Faculdade de Biociências, Pontifícia Universidade Católica do Rio Grande do Sul, Avenida Ipiranga 6681 Prédio 12A, Porto Alegre, RS 90619-900, Brazil, e-mail: <jcbicca@pucrs.br>.
