Soils Consumed by Chimpanzees of the Kanyawara Community in the Kibale Forest, Uganda

Abstract

We previously reported on a study of 4 soils that chimpanzees of the Kanyawara community in the Kibale National Park, Uganda consumed on a near-daily basis. We suggested that iron was a possible chemical stimulus in association with high quantities of Si:Al = 1:1-dominated clay minerals in the consumed material. To test our initial findings, we analyzed 18 samples from the same general area including 7 samples that the chimpanzees did not eat. Among the chemical elements, As, Au, Br, Ca, Cl, Dy, Mg, Ni, Sb, Sr, and I are below detection limits. Only Fe stands out as a potentially important nutritional element present in sufficient quantity to provide a physiological stimulus for chimpanzees living at high elevations near the flanks of the Ruwenzori Mountains. Along with Fe, metahalloysite is present in high amounts in these soils. In its pure crystalline form as a pharmaceutical grade clay mineral metahalloysite may well counteract the debilitating effects of diarrhea, with an effect similar to what is achieved with kaolinite (cf. Kaopectate TM ). An unexpected result, the relatively high nitrogen and carbon in the eaten samples relative to the uneaten group, indicates the chimpanzees may have a higher threshold for organic-rich material than previously believed. Contrarily, the color of the ingested material, depicts a material with less humus than in the uneaten group, a finding that is compatible with previous work reported at other geophagy sites in Africa. Of all the choices of soil available to them, the chimpanzees appear to be selecting highly homogeneous chemical natural earths with well-leached and uniform mineralogical material similar to the uneaten group, but with higher relative amounts of clay size material.

Geophagy: soil consumption enhances the bioactivities of plants eaten by chimpanzees

“…Finally, the ingestion of clay has often been linked to anaemia (Reid 1992) and worm infection (Luoba 2005), without any clear answer as to which is the cause or the effect. Soil eating is common in Kanyawara chimpanzees in the Kibale National Park, Uganda (Mahaney et al 1997(Mahaney et al , 2005. We observed that this consumption occasionally occurred very shortly after or before plant ingestion such as leaves of Trichilia rubescens.…”

“…The geology of this area located on the East flank of the Ruwenzori Mountains, adjacent to a volcanic cone field, has been described by Mahaney et al (1997Mahaney et al ( , 2005. Chimpanzees of the Kanyawara community are fully habituated to the presence of observers since first observations started in 1983.…”

“…A coating effect of the soil on the digestive tract mucosa could also soothe digestive troubles. This suggests that health benefits may be derived from soil eating, as confirmed by analyses underlining the similarity between pharmaceutical products and clay material ingested by chimpanzees (Mahaney et al 1997(Mahaney et al , 2005. Soil eating has also been proposed to induce a sense of satiety explaining its use as a food substitute in times of famine (Laufer 1930;Johns 1996).…”

Geophagy in New World Monkeys (Platyrrhini): Ecological and Geographic Patterns

“…While mineral supplementation is widely considered to be one of the primary functions of geophagy in primates, it is almost impossible to determine which, if any, of these elements are targeted, especially as most are required in relatively minute amounts for a balanced diet. Avoidance of organic matter may also be a consideration here, considering the possible presence of harmful bacteria, although chimpanzees may not only be tolerant of such content [Mahaney et al, 2005], buy may seek it for specific medicinal properties [Ketch et al, 2001].…”

Geophagy in Brown Spider Monkeys (Ateles hybridus) in a Lowland Tropical Rainforest in Colombia

“…The most accepted hypotheses propose that soil (1) can help detoxify secondary plant metabolites and tannins [Gilardi et al, 1999;Johns and Duquette, 1991], (2) can provide supplementary minerals that might be absent or in very low concentration in an animal's diet [Oates, 1978;Brightsmith et al, 2008;Lee et al, 2009], (3) can act as an anti-diarrhoeal drug [Krishnamani and Mahaney, 2000] or (4) can be associated with the enhancement of the pharmacological properties of secondary plant compounds [Klein et al, 2008]. The higher concentration of minerals such as calcium, sodium or potassium, amongst others, from the mineral lick soils when compared to control sites [Emmons and Starck, 1979;Izawa, 1993;Montenegro, 2004;Mahaney et al, 2005], combined with the frequent use of mineral licks by many bird and mammal species, suggests that it has beneficial effects on their nutrition and health.…”