Bonobo geophagy at Wamba.

Geophagy, the deliberate consumption of earth materials, is widely observed in animals. While anecdotal evidence exists of bonobos (Pan paniscus) consuming soil from Cubitermes termite mounds, the functions of their geophagic behavior remains unexplored. This study aims to examine a preliminary hypothesis that termite mound geophagy of free-ranging bonobos at Wamba are helpful for iron supplementation. Here, we tested the following three predictions: (1) the soil of Cubitermes termite mounds at Wamba would have high iron content, (2) bonobos would engage in termite mound geophagy regularly across all seasons, and (3) termite mound soil would be more often consumed by (a) females than males, (b) pregnant than non-pregnant females, and (c) adolescents than adults. As predicted, soil samples collected from the pointy protrusions on the caps of the mushroom-shaped mounds, the part typically consumed by bonobos, had a much higher iron content than other food items for them. In addition, geophagic behavior was noted on 48 out of 116 days (41.3%) with full-day focal animal sampling, and was observed throughout the entire study duration without any bias in frequency toward a certain period. However, contrary to our prediction, there was no significant variation in the frequency of geophagic behavior by sex nor by pregnancy status, although it occurred more frequently among adolescents than adults. Our findings partially support the Iron Supplementation Hypothesis, suggesting that Cubitermes termite mound soils could offer a readily accessible source of iron for bonobos. However, we cannot draw definitive conclusions on the function of their geophagic behavior from our findings without in vitro studies examining whether the ingested iron is bioavailable and whether the soil does not have properties inhibiting iron absorption. Nonetheless, this study is a first step to explore the health implications of geophagy in bonobos, extending our knowledge of this behavior in primates.

Bonobo social organization at the seasonal forest-savanna ecotone of the Lomami national park.

Examining the relationship between food and primate social organization helps us understand how the environment shaped hominin social evolution. However, there is debate as to whether the social differences between our two closest relatives, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes), are due to differences in food availability between their respective habitats or to nonenvironmental factors. The most prominent theory is that bonobo communities have more socially cohesive, stable parties, centered on gregarious females because they evolved in food-rich habitat where individuals, especially females, are less burdened by competition with groupmates. However, more research on bonobos in habitats with seasonal variation in food is needed. This study measured food availability and bonobo social organization at Luzaka, a new site in a seasonal forest fragment. Fruit abundance and dispersion were recorded for a year at Luzaka with the same methods used at Wamba, a bonobo site in more seasonally stable habitat and terrestrial herbaceous vegetation density was measured. At Luzaka, bonobo parties were also recorded for a year using camera traps. Fruit was more seasonal and dispersed at Luzaka than at Wamba. However, the social organization of Luzaka bonobos resembled social organization of bonobos at less seasonal sites. There were minor effects of fruit clumping on party size without effects on the proportion of females in parties suggesting that at Luzaka, the clumping of fruit slightly affected social cohesiveness but does not disproportionately affect females. Bonobo social cohesiveness and female gregariousness appears consistent and compatible with seasonal habitat.