Despite a major delay in the fieldwork due to restrictions to international travel caused by the Covid19 pandemic, the action accomplished most of the planned objectives.
Aim 1
We tested our approach on the previously unstudied population of bearded capuchins (Sapajus libidinosus) living in the Ubajara National Park (UNP), Ceará, Brasil.
When monkeys use stones to crack-open encased food items, often re-using the same tools year after year, they leave abundant evidence in the form of cracked shells and worn stones, the latter used as both hammers and anvils. We used surveys and camera-trapping to assess the presence and distribution of nut-cracking behavior in the UNP. We observed 209 nut-cracking sites, measuring 270 stone hammers. Two species of palm nuts were processed: babaçu (Acrocomia aculeata) and macaúba (Attalea speciosa). Macaúba had never been previously reported to be processed by capuchins using tools.
Six hammers used by capuchins to process macaúba were analyzed with an archeological approach at Sapienza University of Rome, Italy. Microscopic analyses of food residues showed that fibers were organized in bundles and oriented, suggesting that capuchins exerted a rotational movement after striking the nut, probably to detach the gluey pulp from the stones This behavior was confirmed by the analysis of camera trap video recordings. Before our study, wear marks on nut-cracking hammers had only been characterized in tools used by capuchins to process the relatively weak cashews nuts. Our study suggests that stones used to crack open the hard macaúba nuts bear marks more like those observed on stones used to fracture other stones (so to lick salt) than those observed on stones used to crack open soft cashew. We also found that nut-cracking by capuchins at UNP produces the detachment of stone flakes.
We used archeological excavations to trace the temporal development of nut-cracking behavior at UNP. We excavated a total area of 5 m2 surrounding a currently used nut-cracking anvil at a maximum depth of 75 cm. We identified four stratigraphic units containing a total of 376 potential stone artefacts: 13 hammers and 66 flakes. Morphological and functional analysis is ongoing to confirm the preliminary identification and characterize wear traces and food residues. Charcoal samples will be employed for radiocarbon dating.
We tested the application of field experiments to reveal tool use behaviors that are naturally present in the behavioral repertoire of unhabituated populations but are difficult to detect by indirect methods (because they leave no permanent traces in the environment) or camera trap monitoring (because they are rare or occur at unpredictable locations). From the only two long term study sites of wild robust capuchins, we know that monkeys can use stone tools (Serra da Capivara, SCNP) or exclusively their hands (Fazenda Boa Vista, FBV) to dig the soil. We designed a field experiment to reveal tool digging in unhabituated population and successfully tested it in SCNP and FBV. The “positive control” capuchins (SCNP) readily collected the provided stones using them for digging the soil and retrieve food items, while those from FBV (“negative control”) only used their hands to dig in a total of 11 h 10 m of observation. The experiment in UNP is still ongoing.
Aim 2
We tested whether individual personality traits (neophobia), social status, and previous experience with tools impacted performance in solving four experimental tasks (foraging boxes). Experiments were performed on the captive Sapajus colony held at ISTC-CNR, Rome, Italy.
We preliminarily tested the effect of sex, social status and lifetime exposure to experiments involving the presentation of novel food items on the neophobic attitudes of individual monkeys towards novel food. Higher-ranking individuals appeared less neophobic than lower-ranking ones, and female were less neophobic than males, while previous lifetime experience did not influence levels of neophobia.
Analyses of results from the four foraging boxes experiments are ongoing and were, so far, only completed for the water-tube task. In this experiment, subjects had to insert sticks into a water-filled tube so to raise the water level and reach a floating food item. A non-functional, sand-filled tube was also presented. If an individual’s long-term experience enhances his ability to solve a novel task, more experienced individuals would outperform individuals with less extensive experience with tool use. We found that the probability of inserting tools in the functional tube increased with short-term experience and a weak effect that it also increases with an individual’s long-term experience with tools.
The action produced one published peer-reviewed paper and three manuscripts to be submitted soon. Results have been presented in 4 international scientific conferences. Outreach activities included 4 seminars at universities, laboratory activities in 5 schools, and 1 exhibition at the European Researcher’s Night.
