WASHINGTON -- Two female gorillas have been photographed using sticks as tools to get through swampy areas, the first time the apes have been seen doing so in the wild, researchers reported yesterday.
''This is a truly astounding discovery," said Thomas Breuer of the Wildlife Conservation Society and the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the study.
The findings can help shed light on how human beings came to use tools, and also broaden the understanding of how animals use them, the researchers said.
''Although there are reports of tool use by captive gorillas, including object throwing and use of tools in feeding, there has been to our knowledge no reported case of tool use by wild gorillas, despite decades of field research," they wrote in their report, published in the Public Library of Science Biology, an online journal.
All great apes use tools in captivity, but scientists have worried this does not necessarily reflect natural behavior, just something copied from humans.
''Tool usage in wild apes provides us with valuable insights into the evolution of our own species and the abilities of other species. Seeing it for the first time in gorillas is important on many different levels."
They described the two instances in the rain forests of the Republic of Congo.
''We first observed an adult female gorilla using a branch as a walking stick to test water deepness and to aid in her attempt to cross a pool of water at Mbeli Bai, a swampy forest clearing in northern Congo," Breuer and his two colleagues wrote.
In the second case, they saw another pull up a dead shrub. ''She forcefully pushed it into the ground with both hands and held the tool for support with her left hand over her head for two minutes while dredging food with the other hand," they wrote. ''Efi then took the trunk with both hands and placed it on the swampy ground in front of her, crossed bipedally on this self-made bridge, and walked quadrupedally towards the middle of the clearing."
Chimpanzees and other apes have been seen using tools in the wild-- for instance, to catch termites. But never wild gorillas.
The gorillas live in protected areas that ''are not only important for the conservation of species they contain, they also hold the key to comparing our own development as a species with our next of kin," Breuer said in a statement.