Hand and mouth use during food acquisition under naturalistic
conditions
Analyses beyond a controlled setting and across species in similar
ecological condition allowed much broader and critical examination of
the strength of urbanization and encounter with packaged food on
hand/mouth use during FA. Though we could include only 3 primate species
in our preliminary analyses, we obtained identical trends of hand/mouth
use in FA across every cercopithecid species along the gradient of
urbanization and encounter with packaged food. The trend in hand use
remained conserved even when analyses were carried out at the level of
food types. The results obtained on hand use in vervet monkeys offered a
numerical estimate of the effect of urbanization and dependence on
packaged food, which lends credence to the near-universal impact of
urbanization on cercopithecid foraging and perhaps on other urban
species with phylogenetic and/or anatomical similarities.
Analogous to our previous proposition on the role of artificial object
exploration on hand use biases in FA and FP, recent neurobiological
studies (e.g. Fleming et al., 2015; Goda et al., 2014, 2016; Hiramatsu
et al., 2011; Pasupathy et al., 2019) on perception of material
properties of objects have found the role of long-term visual and haptic
(crossmodal) experience with objects ‘for neural representation of
non-visual object properties’, which is essential for object
categorization (Hiramatsu & Fujita, 2015). Object categorization is
believed to be an essential adaptive behavioral feature of urban animals
since it allows animals to ‘adjust their response to novel items in
their environment” (Barrett et al., 2019). We reasoned that since urban
primates are perpetually exposed to novel objects/foods and haptic
experience is critical for developing object familiarity and
consolidating object categorization, they are biased towards hand use
during food acquisition as a result of frequent manual
exploration/manipulation. However, our study is limited by a number of
factors, like inadequate statistical representation of food types across
an urban gradient, unavailability of data from all habitat types and
foraging evaluation of just 3 cercopithecid species. We intend the
article to prompt research efforts towards verifying and validating
trends observed in the study along with bridging the gaps mentioned
above. Of great interests are also determinations of additional
proximate factors within urbanization that seem to be driving concerted
adaptive pressures on urban foraging behaviors.