Hand and mouth use during food acquisition and food processing under experimental condition
The design of the experiment controlled for probable confounding (food size/shape/texture, food attachment, food embeddedness) and direct variables (foraging style) that are known to affect differential use of hand and mouth during FA and their combination during FP at the species level. Conducting the experiment across a gradient of urbanization and alternately, dietary dependence on packaged food allowed independent examination of these two factors. The dietary dependence of the urban group on packaged foods as well as their tendency of tactile exploration, manipulation of artificial objects in their habitat and other undescribed adaptive constraints of urbanization possibly accentuates the use of hand over mouth during FA and FP beyond task-specific motor requirements. We speculate that the relative overrepresentation of hand use is because most objects encountered by the urban group are optimally designed for manual handling by humans (see Goodman-Deane et al., 2016; Rowson & Yoxall, 2011) and hence, are perhaps more efficient for even macaques to control/maneuver/manipulate with hand rather than the mouth. Remarkably, extractive foraging from packaged food influences the most fundamental aspect of manual action pattern and exploration, i.e., food acquisition to be biased towards hand use.