By Matt Walker
Editor, Earth News
Poni, a chimp who likes to chop his food
For the first time, chimpanzees have been seen using tools to chop up and reduce food into smaller bite-sized portions.
Chimps in the Nimba Mountains of Guinea, Africa, use both stone and wooden cleavers, as well as stone anvils, to process Treculia fruits.
The apes are not simply cracking into the Treculia to get to otherwise unobtainable food, say researchers.
Instead, they are actively chopping up the food into more manageable portions.
Observations of the behaviour are published in the journal Primates.
PhD student Kathelijne Koops and Professor William McGrew of the Leverhulme Centre for Human Evolutionary Studies, University of Cambridge, UK, studied a group of chimps living wild in the Nimba Mountains.
Ms Koops research is focused on the use by the chimps of elementary technology, such as the use of tools while foraging.
"Chimpanzees across Africa vary greatly in the types of tools they use to obtain food. Some groups use stones as hammers and anvils to crack open nuts, whereas others use twigs to fish for termites," she says.
The apes' use of such tools can be surprisingly sophisticated.
Cleaver and smashed fruit (shown by arrow)
"For example, nut-cracking in the Bossou chimpanzee community in Guinea involves the use of a movable hammer and anvil, and sometimes the additional use of stabilising wedges to make the anvil more level and so more efficient," explains Ms Koops.
"Termite fishing in some chimpanzee communities in the Republic of Congo involves the use of a tool set, i.e. different tool components used sequentially to achieve the same goal.
"These chimpanzees were found to deliberately modify termite fishing probes by creating a brush-end, before using them to fish for termites."
But together with Prof McGrew and Prof Tetsuro Matsuzawa of the Primate Research Institute at Kyoto University in Japan, Ms Koops has discovered another startling use of tools not previously recorded.
During a monthly survey of chimps (Pan troglodytes) living in the mountain forests, she came across stone and rocks that had clearly been used by the apes to process Treculia fruits.
Treculia fruits need to be cut down to size
These fruits, which can be the size of a volleyball and weigh up to 8.5kg, are hard and fibrous.
But despite lacking a hard outer shell, they are too big for a chimpanzee to get its jaws around and bite into.
So, instead, the chimps use a range of tools to chop them into smaller pieces.
Ms Koops found stone and wooden cleavers, as well as stone anvils used to fracture the large fruits.
All were covered by the remains of smashed fruit and seeds.
The cleavers were clearly used to pound the fruit, rather than the fruit pounded upon the stones.
And the anvils were made from immoveable rocky outcrops.
This is the first account of chimpanzees using a pounding tool technology to break down large food items into bite-sized chunks rather than just extract it from other unobtainable sources such as baobab nuts, Ms Koops told the BBC.
Smashed fruit and anvil, with seed residue on it (shown by arrow)
"And it's the first time wild chimpanzees have been found to use two distinct types of percussive technology, i.e. movable cleavers versus a non-movable anvil, to achieve the same goal."
Surprisingly, neighbouring chimps living in the nearby region of Seringbara do not process their food in this way, reinforcing how tool use among apes is culturally learnt.