Abstract
Descriptions of novel tool use by great apes in response to different circumstances aids us in understanding the factors favoring the evolution of tool use in humans. This paper documents what we believe to be the first two observations of tool use in wild western gorillas (Gorilla gorilla). 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. In the second case we saw another adult female using a detached trunk from a small shrub as a stabilizer during food processing. She then used the trunk as a self-made bridge to cross a deep patch of swamp. In contrast to information from other great apes, which mostly show tool use in the context of food extraction, our observations show that in gorillas other factors such as habitat type can stimulate the use of tools.
Highlights
Tool use is defined as ‘‘the employment of an unattached environmental object to alter more efficiently the form, position, or condition of another object, another organism, or the user itself when the user holds or carries the tool during or just prior to use and is responsible for the proper and effective orientation of the tool’’ (p. 10 of [1])
It has been argued that gorilla tool use in captivity is less extensive than that shown by other apes [10], but it has recently been demonstrated that captive western gorillas (Gorilla gorilla) showed tool-using skills similar to those of orangutans (Pongo pygmaeus) [11], who frequently use tools in the wild [12]
One possible explanation for the absence of observed tool use in wild gorillas is that they are less dependent on extractive foraging techniques that might require the use of tools, since they exploit food resources differently than chimpanzees (Pan troglodytes) [2,13]
Summary
Tool use is defined as ‘‘the employment of an unattached environmental object to alter more efficiently the form, position, or condition of another object, another organism, or the user itself when the user holds or carries the tool during or just prior to use and is responsible for the proper and effective orientation of the tool’’ (p. 10 of [1]). One possible explanation for the absence of observed tool use in wild gorillas is that they are less dependent on extractive foraging techniques that might require the use of tools, since they exploit food resources differently than chimpanzees (Pan troglodytes) [2,13]. Whereas chimpanzee feeding ecology involves tools such as hammers to crack open nuts and sticks to fish for termites, gorillas access these food resources by breaking nuts with their teeth and smashing termite mounds with their hands. Mountain gorillas (Gorilla beringei) possess food-processing skills of comparable complexity and logical organization to chimpanzee termite fishing [14], which give them access to additional herbs in their habitat [15]
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