EXPERIMENTAL-EVIDENCE FOR SPATIAL MEMORY IN FORAGING WILD CAPUCHIN MONKEYS, CEBUS-APELLA

Obtaining convincing evidence for spatial memory of natural food sourc es in wild animals is hard because the observer rarely knows as much a bout the available food as does the animal, and the ability of the ani mal to detect novel food sources is usually not measured. In this stud y, I took advantage of the scarcity of natural fruit sources in the su btropical winter to present a wild group of brown capuchin monkeys wit h a large-scale array of 15 feeding platforms spaced ca 200 m apart. W ith this array, I could control the location, productivity and renewal schedule of the major fruit sources used by these animals. Combining an independent measurement of their detection held for these platforms with the known locations of the platforms, I calculated the expected patterns of movement among platform sites by the group under various m odels of 'random' foraging. These expected patterns were compared to t he actual spatial movements of the group. The capuchin group moved sig nificantly more often toward closer platforms and in straighter lines than expected by any random search model using their observed detectio n field of 82 m, although their behaviour did agree with such models f or unrealistically large search fields of 225-350 m. I infer that the movements of this study group are likely to be guided by spatial memor y. However, straight-line movement and a preference for closer platfor ms are in general not convincing evidence for spatial memory unless th e detection field of the forager for the resources is known. (C) 1998 The Association for the Study of Animal Behaviour.