Wild Capuchins Show Male-Biased Feeding Tool Use

Relatively few studies have explored sex differences in the use of foraging tools among primates other than apes. Although male primates are thought to be more innovative, researchers have reported a female sex bias in the use of feeding tools in wild chimpanzees. We investigate here the nature and extent of sex differences in foraging tool use over 12 mo in a free-ranging group of bearded capuchins (2 males, 5 females, and 3 juveniles) living in the dry Caatinga forests of the Serra da Capivara National Park, Piaui, Brazil. These capuchins used 3 major types of feeding tools: 1) tools for probing; 2) tools for pounding/cracking; and 3) digging stones to extract tubers or roots. Adult males performed 63% (n=134) of all events of tool use and used tools significantly more frequently than did females, although male bout lengths across all tools (57 s±7.9 SE) were equivalent to those of adult females (47.3 s±12.6 SE). Both sexes used digging and cracking tools, although at different rates, whereas adult males used sticks to probe for prey and other rewards far more than females. Differential opportunities to use tools were not apparent: >71% of tool-use events occurred on the ground, and males and females spent equal time on the ground. We suggest that sex differences in tool use may function as opportunities for male signaling of investment quality

A Comparative Assessment of Hand Preference in Captive Red Howler Monkeys, Alouatta seniculus and Yellow-Breasted Capuchin Monkeys, Sapajus xanthosternos

There are two major theories that attempt to explain hand preference in non-human primates-the 'task complexity' theory and the 'postural origins' theory. In the present study, we proposed a third hypothesis to explain the evolutionary origin of hand preference in non-human primates, stating that it could have evolved owing to structural and functional adaptations to feeding, which we refer to as the 'niche structure' hypothesis. We attempted to explore this hypothesis by comparing hand preference across species that differ in the feeding ecology and niche structure: red howler monkeys, Alouatta seniculus and yellow-breasted capuchin monkeys, Sapajus xanthosternos. The red howler monkeys used the mouth to obtain food more frequently than the yellow-breasted capuchin monkeys. The red howler monkeys almost never reached for food presented on the opposite side of a wire mesh or inside a portable container, whereas the yellow-breasted capuchin monkeys reached for food presented in all four spatial arrangements (scattered, on the opposite side of a wire mesh, inside a suspended container, and inside a portable container). In contrast to the red howler monkeys that almost never acquired bipedal and clinging posture, the yellow-breasted capuchin monkeys acquired all five body postures (sitting, bipedal, tripedal, clinging, and hanging). Although there was no difference between the proportion of the red howler monkeys and the yellow-breasted capuchin monkeys that preferentially used one hand, the yellow-breasted capuchin monkeys exhibited an overall weaker hand preference than the red howler monkeys. Differences in hand preference diminished with the increasing complexity of the reaching-for-food tasks, i.e., the relatively more complex tasks were perceived as equally complex by both the red howler monkeys and the yellow-breasted capuchin monkeys. These findings suggest that species-specific differences in feeding ecology and niche structure can influence the perception of the complexity of the task and, consequently, hand preference