Geophagy in the yellow-tailed woolly monkey (Lagothrix flavicauda) at La Esperanza, Peru: site characterization and soil composition.

Geophagy is the intentional consumption of soil and has been observed in various animal taxa including human and nonhuman primates. Among the numerous adaptive hypotheses proposed to explain this behavior, two of them stand out: soil either protects the gastrointestinal tract from secondary plant compounds, parasites and pathogens, and/or supplements micronutrients in the diet. Few studies have characterized the physical and chemical characteristics of soils consumed by nonhuman primates. Here, we describe the composition of soils consumed by yellow-tailed woolly monkeys (Lagothrix flavicauda) in comparison with soils taken from surrounding areas. We also studied the physical aspects of geophagy sites in terms of accessibility, dimensions and vegetation density. This study took place at the La Esperanza field site, in northern Peru, between 2016 and 2018. We conducted focal follows, placed camera traps at geophagy sites and sampled soils. In total, we recorded 77 geophagy events. Our results highlight some aspects of soil and site selection in these arboreal primates, who face an increased predation risk when descending to the ground. Animals preferred smaller sites with denser surrounding vegetation. Composition of consumed soils was similar between geophagy sites. Soils were poor in micronutrients, but contained around 20% clay. High clay content, coupled with the fact that geophagy was performed significantly more in the dry season, when leaf consumption is highest, lends support to geophagy as a mechanism for protection of the gastrointestinal tract in L. flavicauda.