Abstract
Capuchin monkeys at Serra da Capivara National Park (SCNP) usually forage on the ground for roots and fossorial arthropods, digging primarily with their hands but also using stone tools to loosen the soil and aid the digging process. Here we describe the stone tools used for digging by two groups of capuchins on SCNP. Both groups used tools while digging three main food resources: Thiloa glaucocarpa tubers, Ocotea sp roots, and trapdoor spiders. One explanation for the occurrence of tool use in primates is the “necessity hypothesis”, which states that the main function of tool use is to obtain fallback food. We tested for this, but only found a positive correlation between plant food availability and the frequency of stone tools’ use. Thus, our data do not support the fallback food hypothesis for the use of tools to access burrowed resources.
Highlights
Fallback food is constantly proposed as an important selective force that could determine primate anatomy, influence grouping and ranging behavior, and trigger adaptation processes in primate evolution[9, 10]
Low quality food requires more processing and anatomical adaptations, and high quality food depend more on the behavioral adaptations for foraging the food[13]. It was thought chimpanzees could be a good model for the use of Underground Storage Organs (USOs) as fallback food by primates, because they dig for the USOs of some plants, in some cases using tools[14,15,16]
The typical use of the stones was as Digging Stone Tools (DST) to loosen the soil, using the stone tool as a percutor to do so; some stones were used to pull the dirt from the digging site, as “hoes”
Summary
Fallback food is constantly proposed as an important selective force that could determine primate anatomy, influence grouping and ranging behavior, and trigger adaptation processes in primate evolution[9, 10]. Low quality food (leaves, bark) requires more processing and anatomical adaptations, and high quality food (eg fruits and seeds) depend more on the behavioral adaptations for foraging the food[13] Until recently, it was thought chimpanzees could be a good model for the use of USOs as fallback food by primates, because they dig for the USOs of some plants, in some cases using tools[14,15,16]. Capuchin monkeys (Sapajus spp and Cebus spp) are New World primates that have a large area of occurrence in Central and South America, inhabiting diverse environments, from rainforests to dry-bush forest, and semi-arid areas[17] In tropical forests, they do not usually forage for roots or USOs18, 19, but there are reports of crop raid on cassava tubers in groups of Sapajus nigritus[20]. Koops et al.[27] tested the “necessity hypothesis” for tool-assisted insectivory in chimpanzees, but found that the termites and ants caught with tools were present during times of scarcity, they were not used as fallback food, and nuts cracked with stone tools were not available during food shortage periods
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