Chimpanzees eating clay 'as mineral supplement'

A study suggests that chimpanzees in Uganda are eating clay to boost their mineral intake.

Writing in the journal PLoS One, an international team of researchers described the animals eating clay and drinking clay water, often by using leaves as sponges.

This behaviour, shown in the footage above, increased after 2005, at the same time as the animals started to feed much less on raffia palms, which became scarce because they were used by local tobacco farmers.

"Raffia is a key source of sodium, but to our surprise the sodium content was very low in the clay so this does not appear to be the main reason for the new clay-bingeing," said Vernon Reynolds, an emeritus professor at Oxford University and the study's first author.

"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."

Eating earth, which scientists call "geophagy", is a known habit among chimpanzees as well as other animals.

A different community of the animals elsewhere in Uganda has been shown to self-medicate using a particular combination of soil and leaves with anti-malarial properties.

Footage courtesy of Brittany Fallon, University of St Andrews