Do chimpanzees know what conspecifics know?

We conducted three experiments on social problem solving by chimpanzees, Pa n troglodytes. In each experiment a subordinate and dominant individual com peted for food, which was placed in various ways on the subordinate's side of two opaque barriers. In some conditions dominants had not seen the food hidden, or food they had seen hidden was moved elsewhere when they were not watching (whereas in control conditions they saw the food being hidden or moved). At the same time, subordinates always saw the entire baiting proced ure and could monitor the visual access of their dominant competitor as wel l. If subordinates were sensitive to what dominants did or did not see duri ng baiting, they should have preferentially approached and retrieved the fo od that dominants had not seen hidden or moved. This is what they did in ex periment I when dominants were either uninformed or misinformed about the f ood's location. In experiment 2 subordinates recognized, and adjusted their behaviour accordingly, when the dominant individual who witnessed the hidi ng was replaced with another dominant individual who had not witnessed it, thus demonstrating their ability to keep track of precisely who has witness ed what. In experiment 3 subordinates did not choose consistently between t wo pieces of hidden food, one of which dominants had seen hidden and one of which they had not seen hidden. However, their failure in this experiment was likely to be due to the changed nature of the competition under these c ircumstances and not to a failure of social-cognitive skills. These finding s suggest that at least in some situations (i.e. competition with conspecif ics) chimpanzees know what conspecifics have and have not seen (do and do n ot know), and that they use this information to devise effective social-cog nitive strategies. (C) 2001 The Association for the Study of Animal Behavio ur.