Planning abilities of wild chimpanzees (Pan troglodytes troglodytes) in tool-using contexts

Abstract

Planning is a type of problem solving in which a course of future action is devised via mental computation. Potential advantages of planning for tool use include reduced effort to gather tools, closer alignment to an efficient tool design, and increased foraging efficiency. Chimpanzees (Pan troglodytes troglodytes) in the Goualougo Triangle use a variety of different types of tools. We hypothesized that procurement strategy (brought to the termite nest, manufactured or acquired at the termite nest, or borrowed from others) reflects planning for current needs, with tool transport behavior varying by tool type and by age and sex class. It is also possible that chimpanzees anticipate the need for tools at future times, which would be evidenced by transporting multiple tool types for a sequential task. One year of video recordings at termite nests were systematically screened for tool procurement; data comprised 299 tool procurement events across 66 chimpanzees. In addition, we screened video recordings of leaf sponging and honey gathering, which resulted in another 38 procurement events. Fishing probes, which are typically used during a single visit, were typically transported to termite nests, while puncturing tools, which are durable and remain on site, were more often acquired at termite nests. Most tools transported in multiples were fishing probes, perhaps in anticipation that a single probe might not last through an entire foraging bout or might be transferred to another chimpanzee. We further documented that chimpanzees transported tool sets, comprising multiple different tool types used in sequence. Mature chimpanzees transported tools more often than did immatures. These observations suggest that chimpanzees plan tool use flexibly, reflecting the availability of raw materials and the likelihood that specific tool types will be needed for particular tasks. Developmental studies and further integration of behavioral, spatial, and archaeological data will help to illuminate the decision making and time depth of planning associated with tool technologies in living primates and hominin ancestors.

Keywords: Cognition; Termite fish; Tool manufacture; Tool set; Tool use.

Fig. 1

Tool sets to gather termites at epigeal (left) and subterranean (right) nests. A subadult male clears a termite exit hole with a perforating twig a before using a fishing probe b to extract termites. An adult female tunnels into the earth with a woody puncturing stick c; the brush-tip fibers are visible on the end of the fishing probe d she holds in her mouth

Fig. 2

Tool origin varied according to tool type. Chimpanzees usually transported fishing probes to nests, while puncturing sticks were most often acquired after arrival. Perforating twigs were never transported in advance; instead, chimpanzees picked up or made these tools once at the nest

Fig. 3

Fishing probe origin varied across age classes. While adults, subadults, and juveniles most often arrived with fishing probes, this strategy was significantly more likely for mature (adult and subadult) compared with immature (juvenile and infant) chimpanzees. Juveniles’ procurement strategy was more diverse, most notably with a greater proportion of these tools procured via transfer

Fig. 4

A juvenile male uses a leaf sponge to gather water from a tree basin. For this arboreal tool task, chimpanzees gather leaves from within arm’s reach of a water basin, without preference for specific plant species. Photo credit: Kyle de Nobrega, Goualougo Triangle Ape Project, Wildlife Conservation Society

Fig. 5

An adult female with a clinging infant transports a beehive pounding club to an arboreal beehive. In the present study, most observations of beehive pounding club transport were documented among mature females. Photo credit: Sean Brogan, Goualougo Triangle Ape Project, Wildlife Conservation Society