Why do we see sex-biases in tool use in some primate groups but not in others? The second chapter of my PhD in American Journal of Primatology, which you can read here, explores this question in an unique island system where white-faced capuchins use stone tools.
Capuchins on the islands of Coiba and Jicarón in Panama have been studied since 2017, in our study we explore why females on Jicarón do not use tools while those on Coiba do.
We placed more camera traps in streambeds and “random” locations (including a grid of 24 camera traps) and leveraged over 5 years of data. This allowed us to first show that female tool use on Jicarón is absent or incredibly rare, rather than being missed by our sampling. Furthermore, we demonstrate that common hypotheses for sex differences in tool use cannot explain the absence of female tool use. First, adult female capuchins are physically capable of using tools (females on Coiba use tools without issue, as do juveniles on both islands).
Second, females have opportunity to use tools. They are present on the ground at similar rates to males, and competition over anvil sites is incredibly low. Lastly, adult females rarely scrounge on food items opened by males, who mostly use tools to consume sea almonds, suggesting that females are not being provisioned by males. This also points at the possibility of diet difference driving the observed sex-bias in tool use.
Unfortunately, at the moment it remains a mystery why exactly adult female capuchins on Jicarón do not use tools. However, our results show how such sex-biases in socially learned behavior can arise even when there are no clear physical, environmental or social constraints
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