Factors affecting mirror behaviour in western lowland gorillas, Gorilla gorilla.

To date, it has proven difficult to demonstrate mirror self-recognition in gorillas. However, gorillas display pronounced gaze aversion that may prevent them from spending a sufficient amount of time exploring their mirror images to understand that they are the source of their reflections. It has also been suggested that the presence of observers may inhibit gorillas from engaging in mark-directed behaviours. To overcome the problem of gaze aversion, we used an angled-mirror apparatus developed by Anderson & Roeder (1989, Primates, 30, 581-587) that prevented two gorillas at the National Zoological Park from making direct eye contact with their reflections. To counter the observer inhibition hypothesis, we conducted mark tests on these animals using video cameras. Despite addressing these and other concerns in a series of four experiments, the gorillas did not show compelling evidence of self-recognition, even after over 4 years of mirror exposure. Copyright 1999 The Association for the Study of Animal Behaviour.