Capuchin monkeys from different areas of Brazil have shown that distinct populations feed differently, suggesting historic cultural behaviour is at play
Capuchin monkeys (Sapajus spp.) are among only a few primates that use tools in day-to-day activities. In the Cerrado and Caatinga regions of Brazil, they use stones as hammers and anvils to crack open cashew nuts, seed pods of Hymenaea courbaril, and other hard foods.
Brazilian researchers show that food hardness and tool size do not always correlate as closely as has been thought.
In their study, the researchers observed three populations of bearded capuchin monkeys (Sapajus libidinosus), measuring food hardness, tool size and weight, and the local availability of stones. They concluded that culture, defined as information passed on from one generation to the next by social learning, can also influence behaviour in this regard.
Tiago Falótico, a researcher at the University of São Paulo’s School of Arts, Sciences and Humanities (EACH-USP), said: “In one of the populations we analysed, even when they have stones that are suitable for use on a particular food resource, they may use disproportionately heavy tools, possibly evidencing a cultural trait of that group.”
The population to which he referred lives in Chapada dos Veadeiros National Park in Goiás, a state in Brazil’s Centre-West region. In the study, this population was compared with capuchins living in Serra das Confusões National Park, in Piauí, a state in the northeast, and another population that lives in Serra da Capivara National Park, about 100km away in the same state.
The tools are pieces of quartzite and sandstone found in places referred to as processing sites. The animals frequent these sites solely to look for these stones for use as hammers and anvils. One stone is used to pound a nut or seed resting on another stone used as an anvil.
Falótico said: “In Serra das Confusões, they use smaller tools to open smaller and softer fruit but use large, heavy hammers to crack coconut shells, which are very hard. In Chapada dos Veadeiros, where there are stones of varying sizes to choose from, they use the heaviest ones even for fragile foods.”
Not by chance, it was in this latter park that the researchers recorded the heaviest stone lifted by capuchins. An adult male monkey weighs 3.5kg on average, and they filmed an individual lifting a hammer stone that was later found to weigh 4.65kg.
The researchers documented the kinds of food most frequently found in the processing sites, such as babassu (Attalea speciosa), West Indian locust, cashew, and wild cassava (Manihot spp). They also documented the stones available, as well as the sizes and weights of the tools they found, measured the hardness of each type of food, and observed and filmed tool usage in each study area.
Falótico said: “We expected to find a very close correlation between the type of food and the size and weight of the tool, but the population in Chapada dos Veadeiros mainly used the larger ones even though stones of all sizes are plentiful and they can choose a smaller size. They probably inherited this habit from their ancestors. It’s a cultural difference compared with the other populations.”
The cultural learning hypothesis is reinforced by the fact that studies in other areas, such as Serra de Itabaiana in Sergipe and Chapada Diamantina in Bahia (both states in the northeast), involving Sapajus capuchins, stones and the same kinds of fruit and seed have not found processing sites or the use of stone tools for this purpose. In Serra das Confusões, the capuchins use tools to crack open several kinds of food except cashew nuts, which are nevertheless abundant.
Falótico stated. “Their behaviour isn’t due to the availability of resources but to cultural heritage.”
The researchers are now analysing the genomes of all three populations to see if the cultural differences can be linked to genetic differences.
The article is published in Scientific Reports.
Image: The coconut-like shell containing the edible kernels is very hard and has to be cracked open with a stone tool. Not all capuchin populations have adopted this innovation. © Tiago Falótico/ EACH-USP).