Chimpanzees know what conspecifics do and do not see

We report a series of experiments on social problem solving in chimpanzees, Pan troglodytes. In each experiment a subordinate and a dominant individua l were put into competition over two pieces of food. In all experiments dom inants obtained virtually all of the foods to which they had good visual an d physical access. However, subordinates were successful quite often in thr ee situations in which they had better visual access to the food than the d ominant, for example, when the food was positioned so that only the subordi nate land not the dominant) could see it. In some cases, the subordinate mi ght have been monitoring the behaviour of the dominant directly and simply avoided the food that the dominant was moving towards (which just happened to be the one it could see). In other cases, however, we ruled out this pos sibility by giving subordinates a small headstart and forcing them to make their choice (to go to the food that both competitors could see, or the foo d that only they could see) before the dominant was released into the area. Together with other recent studies, the present investigation suggests tha t chimpanzees know what conspecifics can and cannot see, and, furthermore, that they use this knowledge to devise effective social-cognitive strategie s in naturally occurring food competition situations. (C) 2000 The Associat ion for the Study of Animal Behaviour.