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.