Max Planck Institute for Evolutionary Anthropology
Department of Primatology
Deutscher Platz 6
D-04103 Leipzig, Germany
phone: +49 341 3550 217
e-mail: giulia_sirianni[>>> Please replace the brackets with an AT sign <<<]eva.mpg.de
TOOL USE IN CHIMPANZEES AND CAPUCHINS
One of the major hypotheses to explain the emergence of tool use is that access to food resources, that would otherwise not be exploitable by a given species, makes tool use beneficial to these species.
A number of studies from various sites describe a variety of tool-using behaviour in wild chimpanzees and, more recently, also in wild capuchin monkeys. Nut cracking is one of the most sophisticated forms of tool use, and it is restricted to west chimpanzees populations (Pan troglodytes verus) and to the northeastern brazilian capuchins living in dry habitats (Cebus libidinosus, C. xanthosternos).
NUT CRACKING: COSTS AND BENEFITS
Though previous results clearly show the enormous net energetic gain provided by nut cracking in both species (Gunther and Boesch 1993; Fragaszy et al., 2010), cracking hard nuts with a woody or stone hammer and transporting the nuts/hammer to the anvil may be very demanding. Energetic costs associated with nut cracking depend on a subtle balance of hammer weight, number of strikes necessary to open the nut and distance of transport.
If animals possess an understanding of the physical properties and spatial relationships of each item involved, they may be expected to select tools in order to maximize the net energetic gain of nut cracking sessions. Selection of tools has been demonstrated in both chimpanzees and capuchins, but the lack of a consistent experimental framework has, to date, impeded interspecific comparisons of modes of selection.
Relative importance of selective factors is expected to vary according to physical characteristics of individuals and species. Since capuchins crack nuts as hard as those cracked by chimpanzees and due to the huge difference in body size of the two species (ca. 3 kg vs ca. 40 kg) we may expect different roles of selective factors between the two species. Moreover, captive studies suggest that tempo and mode of learning may vary between chimpanzees and capuchins.
The main topic of my Phd project is to develop a consistent model of tool selection based on a common set of field experiments integrating available data on tool selection in both chimpanzees and capuchins. This will provide means to explore differences in tool selection, perception of physical properties, and modes of learning, comparing the two habitual tool-using primate species.
The work is sponsored by:
Max Planck Institute for Evolutionary Anthropology - Department of Primatology