Context-specific tool use by Sus cebifrons

Abstract Tool use has been reported in a wide range of vertebrates, but so far not in Suidae (the pigs). Suidae are widely considered to be "intelligent" and have many traits associated with tool use, so this is surprising. Here, we report the first structured observations of umprompted instrumental object manipulation in a pig, the Visayan warty pig Sus cebifrons, which we argue qualifies as tool use. Three individuals were observed using bark or sticks to dig with. Two individuals, adult females, used the sticks or bark, using a rowing motion, during the final stage of nest building. The third individual, an adult male, attempted to use a stick to dig with. Stick and branch manipulation was observed in other contexts, but not for digging. Our observations suggest the hypothesis that the observed use of stick to dig with could have been socially learned through vertical transmission (mother-daughter) as well as horizontal transmission (female-male). When used by the females, it altered their digging affordance, and had a specific placement in the nest-building sequence. In addition to its context-specificity and its role in a functional sequence, the observed tool use is distinguished by an ambiguous function or effectiveness as a digging behaviour, and the participation of the male in a female action pattern. Observations of unprompted tool use represented for the first time in a phylogenetic family are rare. These open new possibilities for research on tool use and social learning in Suidae.