How very cool

Spear-wielding chimps snack on skewered bushbabies

17:00 22 February 2007 by Rowan Hooper
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In a revelation that destroys yet another cherished notion of human uniqueness, wild chimpanzees have been seen living in caves and hunting bushbabies with spears. It is the first time an animal has been seen using a tool to hunt a vertebrate.

Many chimpanzees trim twigs to use for ant-dipping and termite-fishing. But a population of savannah chimps (Pan troglodytes verus) living in the Fongoli area of south-east Senegal have been seen making spears from strong sticks that they sharpen with their teeth. The average spear length is 63 centimetres (25 inches), says Jill Pruetz at Iowa State University in Ames, US, who observed the behaviour with Paco Bertolani, of the University of Cambridge, UK.

And the method of procuring food with these tools is not simply extractive, as it is when harvesting insects. It is far more aggressive. They use the spears to hunt one of the cutest primates in Africa: bushbabies (Galago senegalensis).

Bushbabies are nocturnal and curl up in hollows in trees during the day. If disturbed during their slumbers - if their nest cavity is broken open, for example - they rapidly scamper away. It appears that the chimps have learnt a grisly method of slowing them down.

Take a look at the chimps in action, in these three videos

Cave life

Chimps were observed thrusting their spears into hollow trunks and branches with enough force to injure anything inside the holes, Pruetz's research team says. The chimps used a "power grip" and made multiple downward stabs - much the same way as a human might wield a dagger.

Ten different chimps in the population were observed to perform this behaviour in 22 bouts. In one case the researchers saw a chimp remove a dead bush baby and eat it. Here is the chimp enjoying his grisly meal, and cleaning his small spear (5MB, Requires QuickTime).

And, in what is thought to be another first for chimps, the Fongoli population have taken up aspects of cave living. They use the the shady interiors for socialising, taking siestas and picnicking, the researchers say. Pruetz jokes that she would not be surprised if the chimps began making cave drawings.

The Fongoli chimps inhabit a mosaic savannah - patches of grass and woodland - where there are no red colobus monkeys. The absence of these monkeys, which are the favoured prey of several other chimp populations, may explain the Fongoli chimps' unique spear-hunting behaviour.

"Given the lack of opportunity, Fongoli chimps have come up with a way to get around the problem of how to get protein in their particular environment...using tools to hunt," says Pruetz.

Secret snacks

Intriguingly, the behaviour is mostly confined to females and immature chimps. Adults hunt and eat green monkeys, but males have priority over access to the meat. Pruetz suggests that Fongoli juveniles and females get around this by exploiting a niche that is relatively ignored by adult males - and spearing little bushbaby snacks for themselves.

"Immatures and females are innovative in solving the problem of feeding competition," she says.

Chimps regularly seem to be discovered doing things once thought unique to humans (see Stone Age chimps were handy with a hammer). "Back to the drawing board again in terms of trying to define how humans are special," says Pruetz.

Journal reference: Current Biology, DOI: 10.1016/j.cub.2006.12.042