A group of chimpanzees has been observed eating clay. Scientists think that they’re after the clay because it contains a very important element that helps neutralize problematic parts of their diet.

A group of chimpanzees living in Budongo Forest in Uganda have spent at least part of their days visiting clay pits. Once they’re there, they scoop up clay and eat it, or use leaves as “sponges” for the muddy water. They will chew the leaves, then dip the leaves in the water and bring them back up to their mouths, wringing the liquid from the wet leaves before bringing the leaves down to the pools once again.

A lot of animals, including humans, are driven to eat clay, mud, or dirt once in a while. In this case, the chimpanzees are probably trying to deal with the many tannins in their diet. Tannins come in many varieties, but they all bind to and precipitate proteins, including amino acids. Tannins are usually used as plant self-defense. Their bitter or astringent taste puts animals off their feed. Other animals develop a tolerance for tannins, or even a taste for them in small quantities. Wine, tea, and chocolate all have different kinds of tannins in them, and do us no harm, but we only eat small amounts of each. The chimpanzees eat fruits and leaves filled with tannins all day long, and they’ve developed another way of dealing with them.

Aluminum binds to tannin. It’s naturally present in a lot of different kinds of soil, including the clay from the pits at which the chimps were eating. The chimps probably have always made stops by the clay pits to neutralize the tannins in their diet.

But the clay also contains other minerals—minerals which are also found in the decaying pith of the forest palm tree. Lately, humans have been eliminating many of the forest palm trees in the park where the chimps live, and the chimps are visiting the clay ponds and clay termite hills more frequently. Scientists think that, in addition to detoxing themselves with aluminum, they might be seeking minerals in the clay that they can’t get in their regular diet anymore.


[Source: Mineral Acquisition from Clay by Budongo Forest Chimpanzees.]