Geophagy by Sanje Mangabeys (Cercocebus sanjei) of the Udzungwa Mountains, Tanzania: Patterns of Soil Consumption in a Highly Frugivorous Primate

Geophagy, defined as the deliberate consumption of soil, has been observed in several primate species. However, its aetiology and function(s) remain poorly understood. The major adaptive hypotheses for the role of geophagy are “protective” to alleviate gastrointestinal distress due to the consumption of plants, parasites and/or pathogens, or a source for “dietary supplementation.” In this study, we investigated patterns and potential drivers of soil consumption in the Sanje mangabey, an endemic monkey from Tanzania, by analysing the events of geophagy in relation to temporal and dietary variation. We found that the mangabeys consumed significantly more soil during periods of high ripe fruit availability (November to May; GLM: F = - 0.00175, df = 33, p = 0.032). Conversely, unripe fruit availability did not impact the occurrence of geophagy (GLM: F = 0.000158, df = 33, p = 0.225); however, unripe fruit made up only 1% of the annual diet, whereas, ripe fruit comprised the majority of the annual diet from 71 to 85%. Rainfall and elevation of soil sites did not impact geophagic behaviour. Highly frugivorous diets are characterised by high soluble carbohydrate concentrations and low fibre. A combination of high fructose diets and reduced polysaccharides has been associated with gastrointestinal (GI) distress in human-provisioned groups of primates; hence, the results of this study suggest that geophagy in the Sanje mangabeys may function in relieving dietary GI distress.