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.