Do chimpanzees anticipate an object’s weight? A field experiment on the kinematics of hammer-lifting movements in the nut-cracking Taï chimpanzees

Abstract

When humans are about to manipulate an object, our brains use visual cues to recall an internal representation to predict its weight and scale the lifting force accordingly. Such a long-term force profile, formed through repeated experiences with similar objects, has been proposed to improve manipulative performance. Skillful object manipulation is crucial for many animals, particularly those that rely on tools for foraging. However, despite enduring interest in tool use in non-human animals, there has been very little investigation of their ability to form an expectation about an object’s weight. In this study, we tested whether wild chimpanzees use long-term force profiles to anticipate the weight of a nut-cracking hammer from its size. To this end, we conducted a field experiment presenting chimpanzees with natural wooden hammers and artificially hollowed, lighter hammers of the same size and external appearance. We used calibrated videos from camera traps to extract kinematic parameters of lifting movements. We found that, when lacking previous experience, chimpanzees lifted hollowed hammers with a higher acceleration than natural hammers (overshoot effect). After using a hammer to crack open one nut, chimpanzees tuned down the lifting acceleration for the hollowed hammers, but continued lifting natural hammers with the same acceleration. Our results show that chimpanzees anticipate the weight of an object using long-term force profiles and suggest that, similarly to humans, they use internal representations of weight to plan their lifting movements.Electronic supplementary materialThe online version of this article (10.1007/s10071-017-1144-0) contains supplementary material, which is available to authorized users.

Sooty mangabeys scavenge on nuts cracked by chimpanzees and red river hogs—An investigation of inter‐specific interactions around tropical nut trees

“…The use of camera traps to systematically study detailed aspects of behavior in wild animals is still restricted to a few studies (e.g., De Moraes, Da Silva Souto, & Schiel, ; Estienne, Stephens, & Boesch, ; Kühl et al, ; Sirianni et al, ). Here we took advantage of camera traps to investigate interspecific interactions involving unhabituated foragers.…”

“…From 2012 to 2015, a total of 170 camera traps (Bushnell Trophy Cam™; model #119576C and model #119476) were placed in Taï and Guiroutou (Ivory Coast) during a biomonitoring study (Després‐Einspenner, Howe, Drapeau, & Kühl, ; Pan African Project), and a behavioral study on chimpanzees (Sirianni, Wittig, Gratton, Schüler, & Boesch, ). For all the studies, cameras were placed in either a systematic manner, using a grid of cells of 1 km 2 , or a targeted manner, at locations frequently visited by chimpanzees, or both, according to the specific study (see details in Després‐Einspenner et al, ; Sirianni et al, ). For this study, we selected 73 cameras (Taï: n = 66, and Guiroutou: n = 7, Figure ).…”

Percussive tool use by Taï Western chimpanzees and Fazenda Boa Vista bearded capuchin monkeys: a comparison

“…B 370: 20140351 together with the mass of the hammer). An ongoing study [35] will provide data for the kinematics of nut cracking in wild chimpanzees with a much larger sample of nut-cracking sessions recorded by remote camera traps.…”

“…Hence, capuchins' stone tool use has become a reference point for those studying the evolution of tool use in hominins, as is chimpanzees' stone tool use [30]. The last common ancestors of living stone tool-using nonhuman primate species and Homo lived 7-8 Ma for Pan and Homo [31], 25 Ma for Macaca and Homo [32] and 35 Ma for Cebus/Sapajus and Homo [33]. The phylogenetic distance among these taxa makes the argument that their common ancestor also used tools unlikely; instead, it suggests that stone tool use has emerged independently in capuchins, macaques and hominids.…”

“…At present, research involves three neighbouring habituated chimpanzee communities [23,34]. Ecological surveys have been regularly conducted in the past ca 30 years, and recently field experiments on nut-cracking have started [35]. Capuchins in FBV have been studied during a much shorter period.…”