Tree bark has been reported as a minor dietary component in many primate species, from western lowland gorillas (Gorilla gorilla gorilla) (Goldsmith, 1999) to red-handed howler monkeys (Alouatta belzebul discolor) (Pinto and Setz, 2004). Barbary macaques (Macaca sylvanus) commonly strip bark from cedar (Cedrus atlantica) trees in Morocco, where research suggests they are seeking water or scarce nutrients present in the cambium tissue (see CamperioCiani et al., 2004). There is also mounting evidence of primate self-medication, the use of medicinal plants to treat a range of ailments from ectoparasites to intestinal worms (reviewed in Huffman, 1997). Increased consumption of known medicinal plants has been associated with seasonal trends of nematode infection in chimpanzees (Pan troglodytes), while non-nutritive bark and wood are used as suspected purgatives by numerous great ape populations (Huffman et al., 1997). In the Neotropics, Gottlieb et al. (1996) noted a close higher-order similarity in the taxonomic groups of plants utilized by humans and primates, and also suggested a correlation between the choice of certain plant types and the medicinal properties of their secondary compounds.

White-faced capuchin monkeys (Cebus capucinus) inhabit a wide range of low- to mid-elevation forest types from Honduras to Ecuador (Reid, 1997). Their diet and behavior are well documented at several locations (e.g., Oppenheimer, 1968; Buckley, 1983). They are known to remove tree bark in search of insects (Rose, 1994) and to occasionally ingest the bark of at least two tree species, Rhizophora mangle and Byrsonima crassifolia (Buckley, 1983). Several authors have watched C. capucinus engage in fur-rubbing, the topical application of plants with known ethnomedicinal qualities in a possible attempt to treat ectoparasites or other skin conditions (Oppenheimer, 1968; Buckley, 1983; Baker, 1996). Self-medication for intestinal parasites has not been studied, but C. capucinus hosts a wide range of intestinal worms and pathogens (Thatcher and Porter, 1968) and the barks of both R. mangle and B. crassifolia are well-documented medicinals. B. crassifolia is a common rural remedy for diarrhea (Heinrich, 2003) and has shown efficacy in treating Giardia (Peraza-Sánchez et al., 2005), while R. mangle is being studied as a treatment for gastrointestinal ulcers (e.g., Sanchez-Perera et al., 2004). Carapa guianensis Aubl. (Meliaceae) is a widespread Neotropical canopy tree, characteristic of lowland forests from Belize south to the Amazon basin (Fournier, 2002). Its bark, seeds and leaves have a wide range of ethnobotanical uses, from fever reduction to the treatment of ulcers and skin conditions (Schultes and Raffauf, 1990; Fournier, 2002). Most notably, the bark tissue is used in a tea to expel intestinal worms and parasites (Schultes and Raffauf, 1990).

On 7 March 2006, I observed an adult male C. capucinus consuming bark from the trunk of a mature C. guianensis (∼90 cm dbh) in the southwestern portion of La Reserva Indio-Maíz, Nicaragua (10°56′18.4″N, 84°19′54.3″W). At least eight other members of the troop were foraging nearby, but only a single individual was engaged in bark stripping. Balancing in the crown of a small sub-canopy tree, he used his weight to lean the tree against the straight bole of an adjacent C. guianensis, approximately 10 m above the ground. He then grasped at the smooth trunk and used his teeth to strip off long pieces of bark, chewing first the bark strips and then directly chewing the exposed inner bark and cambium of the trunk itself. In more than ten minutes of feeding he completely removed the bark from an area approximately 0.75 m by 0.5 m, leaving the cambium and sapwood exposed. The tree bore no signs of insect infestation and the individual appeared to be consuming the inner bark and cambium specifically.

Consumption of C. guianensis bark by C. capucinus has not been previously reported and authors of recent studies in Panama and Costa Rica have not observed this behavior (L. Fedigan, pers. comm.; E. Wehnke, pers. comm.). It remains to be learned whether the event described here is a local habit of the Indio-Maíz population, or a more widespread behavior that is simply unusual and rarely seen. Given the documented ethnobotanical uses of C. gutanensis bark, as well as two other tree barks eaten by C. capucinus, this behavior should be looked for in other populations as a potential new example of self-medication in primates.