A tool worth keeping : efficiency and multifunctionality in great ape tool use

This dissertation includes three studies with wild and captive non-human apes to explore the structure and scope of great ape tool representation. In the first study, I test whether captive orangutans can combine two separately learned tool functions into a multifunctional tool-use sequence. The results suggest that combining tool functions is highly challenging for a test-experienced orangutan (Pongo abelii) even after mastering each sub-action. For the second study, I tested captive chimpanzees’ tool choice under uncertain task demands. Most captive chimpanzees (Pan troglodytes) learned to choose multifunctional tools when they were unsure which task would be presented, but they also generalised this preference to open trials where single-function tools would have been more efficient. My third chapter targets tool transport behaviour while nut gathering in wild nutcracking chimpanzees. My analysis suggests that wild chimpanzees combine social and physical information to make transport decisions: the more adult individuals were nearby, the more likely they were to carry their tool while gathering, but only when they were using medium-sized stone hammers. This preference appears to be driven by cultural factors or a preference for more versatile tool materials, since carrying rates for wooden hammers were significantly lower despite equal or higher tool efficiency. Both captive and wild apes, therefore, appear ready to develop preferences for more versatile tools and use tools in multifunctional ways, even in the absence of efficiency benefits or clear evidence for multifunctional tool representations.