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Captured on film: wild gorilla using a walking stick

David Adam, environment correspondent
Friday September 30, 2005
The Guardian

It is an unnerving sensation that anyone who has waded into unfamiliar water 
will know well: the ground is slippy and uneven and before you know it you 
can be in up to your waist.

So when Leah the gorilla found herself in difficulty attempting to cross a 
swampy pool left by elephants in northern Congo, she grabbed a branch and 
used it as a walking stick. In doing so, she became the first wild gorilla 
seen using any kind of tool in decades of wildlife research.

Thomas Breuer of the Wildlife Conservation Society, who captured the incident 
on film and publishes the first pictures today in the journal Public Library 
of Science Biology, said: "This is a truly astounding discovery. Tool use in 
wild apes provides us with valuable insights into the evolution of our own 
species."

The scientists were watching a group of wild western gorillas last October 
from an observation platform near a forest clearing in the Nouabale-Ndoki 
national park. After staring intently at the pool from the water's edge Leah 
took a few tentative steps. The water quickly became waist deep so she 
grabbed the branch and used it to prod the water, as if testing its depth. 
She then moved further into the pool, leaned on the branch and used it as a 
walking stick.

All great apes use tools in captivity, but only chimpanzees and orang-utans 
had been seen with them in the wild. Biologists had suggested gorillas did 
not need to because they are strong enough to get food by force. While chimps 
use hammers to crack nuts and sticks to dig out termites, gorillas break nuts 
with their teeth and smash termite mounds with their fists.

The scientists also saw a second gorilla using a branch as a tool, this time 
laying it over swampy ground as a bridge and walking across.