for National Geographic News
The first evidence has been found that chimps use tools to dig for tubers, roots, and bulbs to eat.
The discovery may shed light on how early human ancestors survived the transition from food-rich forests to drier habitats, a new study says.
Anthropologist Adriana Hernandez-Aguilar observed chimpanzees digging in the Ugalla Forest Reserve of western Tanzania. The arid woodland savanna is home to a small population of chimps that have adapted to life beyond their species' typical forest habitat.
Chimps were never directly observed using the food sources. But at 11 dig sites—10 of them directly below chimp nests—Hernandez-Aguilar, of the University of Southern California, found chimp knuckle prints, feces, and chewed wads of fibrous tubers.
And three of the sites contained dirt-caked sticks. Wear patterns suggested the sticks had been used to dig up the foods, which are often protected by a hard crust of earth.
What's more, the chimps are using tubers in the rainy season, when other foods are presumably abundant. This challenges a long-standing theory that chimps use tubers only as backup food sources.
Chimps are known to use potato-like tubers for the nutrients and then spit out wads of fiber. People also use some of the plants as food or medicine.
"Adriana's find was a delightful surprise," said Jim Moore of the University of California, San Diego, in an email. Moore, one of the study's co-authors, has coordinated chimp research in the Ugalla savanna for 18 years.
"The discoveries that they sometimes use tools [to access the underground foods], do so in the wet, resource-rich season, and that some of the plants may have medicinal properties—those were real surprises," Moore added.
The paper appears online this week in the journal Proceedings of the National Academy of Sciences.
Some experts believe access to underground foods helped enable the expansion of early human ancestors into dry, relatively food-poor habitats like the African savanna.
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