Chimpanzees in Ugandan forests are turning to clay to meet their nutritional requirements, says a study published in the journal PLOS ONE.

Led by Vernon Reynolds, Emeritus Professor of Biological Anthropology from Oxford University, researchers described in the study how wild chimpanzees in Uganda's Budongo forest have been observed to eat and drink from termite mounds and clay pits. They believe that this diet shift may have been brought about by the widespread loss of raffia palm trees, a staple food source for chimps in the past, but further observations point to consuming clay as a means of detoxifying the body and digesting food.

Researchers from various universities participated in the study and observed that the chimps use leaves as sponges, dipping them into clay water and squeezing them to drink the liquid. Without leaf "sponges," the chimps would also simply use their fingers to scoop up clay from the ground and eat it.

When the researchers analyzed samples from the termite mounds and clay pits, they found that the clay chimps are chomping on are high in a number of minerals, particularly aluminum. This is true for kaolinite clay as well, which is consumed by a range of species to aid detoxification and digestion. The researchers attributed chimps eating clay as a way of neutralizing the high amounts of tannins they get when they consume leaves and fruits. Aside from aluminum, clay also contain potassium, magnesium, iron, calcium and sodium.

Prior to 2000, chimps eating raffia palms was a common sight. After 2005 though, the number of chimps consuming raffia palms dropped while clay-feeding increased. Because of the two coincided, the researchers concluded that chimps were substituting clay for raffia palms.

However, when raffia palm components were analyzed, it was found that it had higher levels of sodium than clay, meaning it couldn't have been a direct swap.

"Instead, we believe the low concentrations of minerals present in their normal diet of fruit and leaves suggests that the clay is eaten as a general mineral supplement," explained Reynolds.

Wild chimpanzees living in the Budongo forest have been the subject of uninterrupted studies since 1990, when Reynolds established the Budongo Conservation Field Station. This particular study received funding support from the Mohamed bin Zayed Species Conservation Fund.