Behaviour 2019
Stone affordances shape the expression of object play in long-tailed macaques (Macaca fascicularis)
Camilla Cenni1, Jessica Bess Agnes Christie1, Danielle Hazel Lucy Van der Pant2, I Nengah Wandia3, Jean-Baptiste Leca1,4. 1Department of Psychology, University of Lethbridge, Lethbridge, AB, Canada; 2Department of Psychology and Neuroscience, University of St. Andrews, St. Andrews, , United Kingdom; 3Primate Research Center, Udayana University, Denpasar, Bali, Indonesia; 4School of Natural and Engineering Sciences National Institute of Advanced Studies, Bangalore, , India

Objects’ physical properties (i.e., affordances) limit and enhance the form that actions available to an individual takes, possibly generating instrumental solutions. We tested the “Object Affordance” hypothesis in stone handling (SH) behavior, a type of socially-mediated object play, in free-ranging long-tailed macaques. This hypothesis holds that object’s features associated with stone size afford different stone-directed actions in a playful context. We predicted that higher SH versatility (i.e., total number of different SH actions expressed) and higher duration of the SH action “Pound” would be associated with the manipulation of medium-sized stones, followed by small stones and then large stones.
Our data partly supported these predictions. Both medium and small stones afforded the highest SH versatility, and a higher duration of “Pound” than large stones. As expected, duration of “Pound” was higher with medium than small stones, but the difference was not statistically significant. The relaxed selective pressures acting on object play may provide a behavioral reservoir that facilitates the acquisition of functional object-assisted actions, through affordance learning.