Extractive Foraging and Grasping Postures in Sanctuary-Housed Chimpanzees (Pan Troglodytes)

Several primate species use tools for a wide variety of functions, such as probing or obtaining out-of-reach food, both in captivity and in the wild. Given the ubiquitous presence of plants, the study of plant tool use may serve as a proxy to reconstruct archeologically invisible aspects of early human behavior. Chimpanzees (Pan troglodytes) are the most prolific non-human primate tool users. We evaluated the use of two artificial mounds filled with food in two groups of sanctuary-housed chimpanzees (N = 14) at Fundació Mona (Girona, Spain). We assessed how the group, the use and size of tools, posture, and the type of substratum affected chimpanzee behavior during an enrichment task that replicated termite fishing observed in wild chimpanzees. We also focused on the grasping postures and explored the manual laterality of individuals performing the task. We analyzed 290 min of video footage, including 5736 bouts of extractive foraging. Our results showed that individuals mainly performed the task alone, sitting on the ground, and probing with larger, rather than smaller, tools. Ten individuals showed manual preference: two showed a preference for using the left hand, while eight showed a preference for the right. Additionally, chimpanzees tended to use a variety of unimanual grip strategies. This study highlights the impact that enrichment activities that mimic realistic scenarios can have on the manual capacities of captive chimpanzees, enhancing the opportunity to develop further comparative studies with wild chimpanzees to understand the evolution of the manual abilities in human and non-human primates.