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

Self-handicapping behaviors evolved as honest signals that reliably reflect the quality of their performers. In playful activities, self-handicapping is described as intentionally and unnecessarily putting oneself into disadvantageous positions and situations. Self-handicapping during play may allow individuals to learn to cope with unexpected events by improving sensori-motor coordination, as well as function as a play solicitation signal. One such self-handicapping behavior involves moving about while deliberately covering one's eyes. We conducted a quantitative study of object-assisted eye-covering (OAEC) in a population of free-ranging Balinese macaques. After evaluating the frequency, form, distribution, and context of OAEC, we measured the responses this behavior elicited (1) in the performers with a focus on sensori-motor self-handicapping, and (2) in their conspecifics, with an emphasis on whether, and if so how, OAEC may facilitate social play. Our data provided some support for several hypotheses: OAEC is a sensori-motor self-handicapping behavior, an attention-getting cue, a social play signal, and a socially self-handicapping tactic during social play. We discuss our results from the perspective of tool-assisted self-handicapping behavior, propose a scenario to account for the emergence of this behavioral innovation, and speculate on the cultural nature of OAEC.