Observations of termitarium geophagy by Rylands’ bald-faced saki monkeys ( Pithecia rylandsi ) in Madre de Dios, Peru

Geophagy, or soil consumption, has been documented in diverse animal taxa, including many primates. Physiological functions such as mineral supplementation, detoxification of secondary compounds, and antacid properties are possible causes for this behavior. We report on observations of geophagy at arboreal termitaria by free-ranging Pithecia rylandsi at La Estación Biológica Los Amigos (EBLA) in Perú between 2008 and 2015. Characteristics of geophagy events, including saki monkey behavior at the termitaria, were recorded and geochemical analyses were conducted on consumed termitaria, nearby topsoils, and unvisited termitaria. We observed 76 feeding bouts at 26 different termitaria by two groups of P. rylandsi during 1125 observational hours (0.07 bouts/obs. h). Geophagy occurred throughout the year, but rates peaked in January during the rainy season. All age and sex classes visited both active and inactive mounds. Feeding bouts were brief (171 ± SD 154 s), and no differences were observed in time spent feeding at active or inactive termitaria. Analyses showed that consumed soils contained higher concentrations of phosphorous, potassium, calcium, and magnesium than did topsoil. Consumed soils also contained a higher total cation exchange capacity than topsoil. Our analysis of consumed versus control termitaria revealed no differences in their chemical composition. We discuss these results in the context of the two primary hypotheses proposed for geophagy in pitheciins: mineral supplementation and toxin adsorption. Our data are consistent with the interpretation that P. rylandsi consume soils from arboreal termitaria to aid in adsorption of toxins found in immature seeds, which are a year-round component of their diet.