Field assistants monitor chimpanzee ranging, diet, and habitat use within an approximately 50km² study area. Data are collected on chimpanzee beds as well as observations of chimpanzees. Habituation of this chimpanzee community is in progress, and diet data are based on analyses from fresh fecal samples. Currently 5 individual chimpanzees have been identified, but opportunities for behavioral observations are limited. However, research assistants have been able to remain with chimpanzee parties for up to 9 hours when they are attracted to dry season water sources. The rainy season begins in June-July, while the extensive dry season begins in November-December.

Chimpanzees share their range with baboons (Papio hamadryas papio), green monkeys (Cercopithecus sabeus), and patas monkeys (Erythrocebus patas). People of the Malinke, Bassari, Bedik, and Diahanke groups also share this area with the chimpanzees and do not hunt them. Much of the large mammalian fauna has been eliminated from the area, but ungulates such as warthog and bushbuck remain at low densities.

Since April 2001, over 400 fecal samples have been analyzed to determine the dietary habits of Fongoli chimpanzees. In addition to recording the number of seeds and their plant species within feces, data are also collected on the percent fiber contained per fecal sample and other characteristics, such as the presence of insect and vertebrate parts and leafy vegetation. Eighteen samples have been identified as indicative of leaf swallowing behavior.

Fecal samples thought to be indicative of leaf swallowing were observed to contain a large amount of undigested and unchewed leaves with some leaf fragments also included. Five samples were collected during the late rainy season that contained these unchewed leaves:

Several fecal samples also indicated that Fongoli chimpanzees swallow whole large amounts of grass leaves belonging to the species Andropogon chevalieri Reznik. During the beginning of the rainy season, on July 22, 2002, a fecal sample was collected that was made up almost entirely of wadded grass leaves. Over two months later, near the end of the rainy season, on Sept. 27, Oct. 25, and on Nov. 14, more samples were found that also contained large amounts of unchewed grass leaves. The grass leaf sections were up to 25 cm long and around 1 cm wide. The leaf surfaces are scabrous (rough) and the leaf margins are fringed with short hairs. Three other samples were collected that contained small amounts of unchewed grass leaves (between 1 and 2 leaves present per sample). Similarly, on June 18 and 19, 2003 two fecal samples were observed to contain >5 entire grass leaves measuring over 10 cm in length and 4 mm in width that may also belong to the same species.

On 31 December 2002, during the early part of the dry season, 18 entire or mostly entire leaf fragments were found contained in one fecal sample collected within a small strip of gallery forest. Leaves and leaf fragments averaged 56.9 mm in length (range: 40-102 mm) and 19.8 mm in width (range: 13-27 mm) (N=18). A number of smaller leaf fragments were also found in the dung sample. Leaves were folded/wadded when sieved from the fecal sample, but no evidence of chewing or any digestion was evident on the leaves. Leaves were identified as Ficus asperifolia after comparison with a series of plants in the study area. Less than 30 m from where the fecal sample was collected, a recent ground bed made from two F. asperifolia saplings was recorded. This particular plant is characterized by very coarse leaf surfaces. Six other instances of whole leaf swallowing were observed at Fongoli (between 1 and 2 leaves per sample). These leaves were different than the F. asperifolia, legume, and grass leaves. Similarly, the surfaces of some of the leaves were rough.

A study of parasite loads of Fongoli chimpanzees as well as future studies of feeding behavior here will provide a test of the hypothesis that Fongoli chimpanzees use plants medicinally. We hypothesize that Fongoli chimpanzees swallow whole leaves in a manner conducive to their medicinal use as reported for plants such as Aspilia and F. exasperata in the Kibale Forest, Uganda and at other sites (2). Chimpanzees fold and ingest physically irritating leaves whole, and analyses suggest such behavior helps to eliminate gut parasites (3). Chimpanzee fecal samples had not yet been collected for analyses of parasite load, save for the June 2003 samples. Adult parasites have been observed in at least 3 different fecal samples.

Given the aridity of the study site and the significant differences between the vegetation here and that characterizing other sites where chimpanzees have been assumed to use plants medicinally, this report of possible medicinal plant use has important implications for the universality of this aspect of chimpanzee behavior and ecology and, perhaps, cultural implications as well.

Thanks to the Republic of Senegal, the Direction des Parcs Nationaux, Departement des Eaux et Forets, Bill McGrew, Peter Stirling, Clayton Clement, Philip Fulton, Tom LaDuke, Dondo Kante, Mboule Camara, Kaly Camara, and the people of Fongoli, Petit Oubaji, and Djendji for their assistance in the project.

References

1. Pruetz JD, Marchant LF, Arno J, McGrew WC 2002. Survey of savanna chimpanzees (Pan troglodytes verus) in southeastern Senegal. Am J Primatol 58: 35-43.
2. Huffman MA 1997. Current evidence for self-medication in primates: a multidisciplinary perspective. Yb Phys Anthrop 40: 171-200.
3. Huffman MA, Caton JM 2001. Self-induced increase of gut motility and the control of parasitic infections in wild chimpanzees. Int J Primatol 22: 329-346.