Kopp, K. S., Ebel, S. J., Wittig, R. M., Haun, D. B. M., & Crockford, C.  (2021). Small mirrors do the trick: A simple, but effective method to study mirror self-recognition in chimpanzees. Animal Behavior and Cognition, 8(3), 391-404.  https://doi.org/10.26451/abc.08.03.05.2021

Mirror self-recognition (MSR) is considered an indicator of self-awareness. Standardized mirror tests reveal compelling evidence for MSR in a few non-human species, including all great apes. However, substantial inter-individual variation of MSR within species resulted in an ongoing methodological controversy, questioning the appropriateness of standard MSR tests for cross-species comparisons. Lack of motivation, in particular, is discussed as one possible cause for false negative results. Here, we compare the spontaneous behavioral response of 47 zoo-housed chimpanzees (Pan troglodytes) to (i) standard body-sized, stationary mirrors and (ii) small, portable hand mirrors. We predicted that the monopolizability and maneuverability of small mirrors increase the chances of identifying MSR across a larger proportion of individuals. Chimpanzees both revealed a substantially higher frequency of general mirror-related behaviors and engaged in significantly more and longer behaviors specifically indicating MSR when provided with small mirrors compared to a large mirror. Handheld mirrors provide a more sensitive measure for MSR within and likely between primate species than the traditional large mirrors, and thereby are a potentially valuable tool for studying self-awareness across species.

Mirror self-recognition, Comparative cognitive research, Primates, Self-awareness, Mirror test, Cognition