Gender bias in probe tools' use by wild bearded capuchin monkeys (Sapajus libidinosus): opportunities for social learning? (#464)
The use of percussive tools to access defended food is widespread among savanna-dwelling bearded capuchin monkeys (Sapajus libidinosus)1. The customary use of tools (usually wooden sticks) to probe arthropod nests or dislodge prey from rock crevices, on the other hand, has only been observed, so far, in the population of Serra da Capivara National Park (SCNP, Brazil)2 , although there are a few anecdotal reports from other wild and semi-free groups.
In populations that consume hard palm nuts, the proficiency in stone-aided nutcracking is severely biased towards males, but this is easily explained by the differences in bodily mass, and the bias is much less pronounced where the items processed are easier to crack open. Differences in strength, though, can hardly explain the extreme male bias in probe tool use by SCNP capuchins: SCNP females almost never use probes3 .
In a field experiment on innovative tool use (to retrieve molasses from a Plexiglas box)4 , SCNP adult and juvenile males quickly solved the task using stick probes, but no females did it (some females and males tried without success to use stone tools to open the box). Females occasionally extracted and licked pre-inserted probes, but never re-introduced them in the box' holes (the same as males and females from another, non-probe-using, wild population). In a semi-free, urban park population facing the same task, though, after some exposure to a facilitated condition, no significant male bias was found among the successful individuals - and the most proficient one was an adult female.
Females occasionally exhibit innovative forms of tool use, as the use of projetiles during estrus displays5 ; one PNSC female used sticks as nasal probes and toothpicks.
Since the evidence does not seem to support explanations based on diet differences, strength requirements, nor on cognitive or motor limitations, we hypothesize that different opportunities for social learning may underlie the gender bias on the use of probe tools.
Funding: Fapesp, CNPq, Capes, ERC.
- Ottoni, E. B., & Izar, P. (2008). Capuchin monkey tool use: overview and implications. Evolutionary Anthropology, 17, 171–178. doi: 10.1002/evan.20185
- Mannu, M., & Ottoni, E. B. (2009). The enhanced tool-kit of two groups of wild bearded capuchin monkeys in the Caatinga: Tool making, associative use, and secondary tools. American Journal of Primatology, 71, 242–251. doi: 10.1002/ajp.20642
- Falótico, T., & Ottoni, E. B. (2014). Sexual bias in probe tool manufacture and use by wild bearded capuchin monkeys. Behavioural Processes, 108, 117–122. doi: 10.1016/j.beproc.2014.09.036
- Ottoni, E. B., & Cardoso, R. M. (2014). Tool use traditions’ effects on problem-solving in two wild bearded capuchin monkey (Sapajus libidinosus) populations. Abstracts of the XXVth Congress of the International Primatological Society, 404.
- Falótico, T., & Ottoni, E. B. (2013). Stone throwing as a sexual display in wild female bearded capuchin monkeys, Sapajus libidinosus. PLoS ONE, 8(11), e79535. doi:10.1371/journal.pone.0079535.