Scientists photographed for the first time ever that wild gorillas used a stick to test the depth of a pool before wading into it, according to a study appearing in Friday's journal Public Library of Science (PLoS) Biology.
Up to this point, all other species of great apes including chimpanzees and orangutans, have been observed using tools in the wild, but never gorillas. Scientists said this new finding is "astounding."
"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," Thomas Breuer, lead researcher of the Wildlife Conservation Society, said in a statement.
On two separate occasions in the northern rain forests of the Republic of Congo, researchers observed and photographed individual western gorillas using sticks as tools, according to the study.
The observations were made in Mbeli Bai, a swampy clearing located in Nouabale-Ndoki National Park where monitoring has been ongoing since February 1995. The first instance occurred when a female gorilla nicknamed Leah by scientists attempted to wade through a pool of water created by elephants, but found herself waist deep after only a few steps.
Climbing out of the pool, Leah then retrieved a straight branch from a nearby dead tree and used it to test the depth of the water. Keeping her upper body above water, she moved some 10 meters out into the pool before returning to shore and her wailing infant.
Then another female gorilla named Efi used a detached trunk to support herself with one hand while digging for herbs with the other. As she moved from location to location, she used the stick for one last job, a bridge over a muddy patch of ground.
Gorillas had been observed using tools in zoos, but not in the wild. And, while most other observed instances of tool-usage in great apes are related directly to processing food, such as cracking of nuts with rocks or extracting termites with long sticks, these two examples of using tools for postural support were triggered by other environmental factors.
"Information on tool use and factors favoring tool use in wild apes helps us to understand its importance in the evolution of our own species," the researchers wrote in the paper.
The gorillas live in a protected area, where scientists can conduct long-term observation and study of the big apes, according to the paper.
"These protected areas 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.
"Places like Nouabale-Ndoki, and the nearby Goualougo Triangle, are places where we see the process unfolding before our very eyes. "