Urbanization accentuates hand use in the foraging activities of primates

Objectives: How a species uses its anatomical manipulators is determined by anatomy and physiology at a proximate level and by phylogeny and ecology at an ultimate level. Primates are often distinguished by their prehensile capabilities and manual dexterity. Theoretical explanations for intraspecific variation in the use of mouth and hands by nonhuman animals is non-existent. In the context of intense pressures of urbanization on natural habitats, we examined if hand and mouth use differed across the rural-urban gradient in food retrieval and food processing under experimental conditions and under naturalistic conditions in cercopithecids. Results: The use of hands in acquisition and processing food increased with urbanization and the converse was true for mouth use under experimental conditions. Even under naturalistic settings, all examined species of urban primates showed a bias in hand use during food acquisition. Discussion: Thus, it appears that the adaptive pressures of urbanization, like the manual constraints of extracting packaged food and perhaps the need for visual-haptic exploration of novel objects accentuates hand use in even simple tasks among synanthropic groups of nonhuman primates. Additional research is needed to determine specific factors of urbanization influencing the trend observed and to ascertain similar patterns in other primates occupying forest-urban niches. Materials and Methods: We observed acquisition and processing of peanuts under standardized conditions across groups of bonnet monkey (Macaca radiata) differing in their dietary dependence on packed food items. Next, we coded acquisition and processing behaviors in bonnet macaques, Japanese monkey and vervet monkey in a similar habitat gradient. The supplementary materials (Folder: Supplementary information) presents supplemental figures and supplemental table. The data file for each primate species is included in 'Mined Info-R data files'. These data files have been used for analyses in R. The excel file contains all the data used in the study and data description is provided in the text file titled,'Data usage details'.