EXPERIMENTAL-ANALYSIS OF FOOD DETECTION IN CAPUCHIN MONKEYS - EFFECTSOF DISTANCE, TRAVEL SPEED, AND RESOURCE SIZE

Knowing how far away animals can detect food has important consequence s for understanding their foraging and social behaviors. As part of a broader set of field experiments on primate foraging behavior, we set out artificial feeding platforms (90 x 90 cm or 50 x 50 cm) throughout the home range of one group of 22 brown capuchin monkeys, at sites wh ere they had not seen such platforms previously. Whenever the group ap proached such a new platform to within 100 m, we recorded the group's direction and speed of approach, and the identity and distance from th e platform of the group member that detected the platform or came clos est to it without detecting it. We used logistic regression on these d ata to examine the effects of group movement speed, platform size and height, and focal individual age and sex on the probability of detecti ng the platform as a function of distance. Likelihood of detecting a p latform decreased significantly at greater distances - the probability of detecting a platform reached 0.5 at 41 m from the group's center a nd 25.5 m from the nearest group member. These results show that detec tability of platforms by the entire group (9 adults, 13 juveniles) was less than twice that for single group members. Detectability at a giv en distance decreased severely as the group moved faster, at their fas test speed, individuals had to approach a platform to within less than 10 m to find it. The large platforms were significantly more likely t o be detected than the small ones, suggesting that increased use of la rger food patches by wild primates may not necessarily reflect foragin g preferences.