A tool to act blind? Object-assisted eye-covering as a self-handicapping behavior and social play signal in Balinese long-tailed macaques

Animal Cognition - Self-handicapping behaviors evolved as honest signals that reliably reflect the quality of their performers. In playful activities, self-handicapping is described as...     

Complexity in object manipulation by Japanese macaques (Macaca fuscata): a cross-sectional analysis of manual coordination in stone handling patterns

Defined as a spontaneous stone-directed noninstrumental manipulative behavior, and comprised of multiple one-handed and (a)symmetrical/(un)coordinated two-handed patterns, stone handling (SH) is a good candidate for the study of complexity in object manipulation. We present a cross-sectional developmental analysis of SH complexity in Japanese macaques (Macaca fuscata), through the combined investigation of bimanuality, coordination, and symmetry in hand use. Bimanual SH patterns were more frequent than unimanual patterns. Among bimanual patterns, coordinated actions were more frequent than uncoordinated ones. We recorded five asymmetrical coordinated SH patterns with manual role differentiation, a form of hand use reminiscent of complex actions involving the use of tools in monkeys and apes. Bimanuality in SH was affected by body posture. Aging individuals performed less bimanual and less coordinated SH patterns than younger individuals. Our result on senescent males performing less bimanual patterns than senescent females was consistent with sex differences found in the late deterioration of complex manual movements in other species. Although some SH patterns represent a high degree of behavioral complexity, our results suggest that SH behavior is not as complex as tool-use or tool-manufacture in other nonhuman primates and hominids.     

Social influence on the expression of robbing and bartering behaviours in Balinese long-tailed macaques

Animal Cognition - Animals use social information, available from conspecifics, to learn and express novel and adaptive behaviours. Amongst social learning mechanisms, response facilitation occurs...