Mirror-image responses in pygmy marmosets (Cebuella pygmaea).

Only a few nonhuman species (chimpanzees and orangutans) have displayed mirror-image recognition of themselves by grooming at a spot that can only be seen with the mirror. Pygmy marmosets have never been observed to self-groom, but they do behave toward mirrors in a manner suggestive of the early stages of mirror-image recognition. They displayed a rapid extinction of social threat responses to their own image and of novelty responses to mirrors, but continued to show mirror-specific responses such as following their own image, playing peek-a-boo, and looking at their image throughout a 28-day period of mirror exposure. The pygmy marmosets used a mirror to locate otherwise unseen conspecifics from other groups and directed threat responses toward the real location of these animals rather than to their mirror-image. Pygmy marmosets displayed the precursor behaviors to mirror-image recognition.