Experimental analysis of food detection in capuchin monkeys: effects of distance, travel speed, and resource size

JANSON, C. H.; DI BITETTI, M. S.

BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY

Springer-Verlag

Año: 1997 vol. 41 p. 17 - 24

0340-5443

Knowing how far away animals can detect food has important consequences for understanding their foraging and social behaviors. As part of a broader set of ®eld experiments on primate foraging behavior, we set out arti®cial feeding platforms (90 ´ 90 cm or 50 ´ 50 cm) throughout the home range of one group of 22 brown capuchin monkeys, at sites where they had not seen such platforms previously. Whenever the group approached such a new platform to within 100 m, we recorded the group´s direction and speed of approach, and the identity and distance from the platform of the group member that detected the platform or came closest to it without detecting it. We used logistic regression on these data to examine the e.ects of group movement speed, platform size and height, and focal individual age and sex on the probability of detecting the platform as a function of distance. Likelihood of detecting a platform decreased signi®cantly at greater distances ± the probability of detecting a platform reached 0.5 at 41 m from the group´s center and 25.5 m from the nearest group member. These results show that detectability of platforms by the entire group (9 adults, 13 juveniles) was less than twice that for single group members. Detectability at a given distance decreased severely as the group moved faster; at their fastest speed, individuals had to approach a platform to within less than 10 m to ®nd it. The large platforms were significantly more likely to be detected than the small ones, suggesting that increased use of larger food patches by wild primates may not necessarily reflect foraging preferences.´ 90 cm or 50 ´ 50 cm) throughout the home range of one group of 22 brown capuchin monkeys, at sites where they had not seen such platforms previously. Whenever the group approached such a new platform to within 100 m, we recorded the group´s direction and speed of approach, and the identity and distance from the platform of the group member that detected the platform or came closest to it without detecting it. We used logistic regression on these data to examine the e.ects of group movement speed, platform size and height, and focal individual age and sex on the probability of detecting the platform as a function of distance. Likelihood of detecting a platform decreased signi®cantly at greater distances ± the probability of detecting a platform reached 0.5 at 41 m from the group´s center and 25.5 m from the nearest group member. These results show that detectability of platforms by the entire group (9 adults, 13 juveniles) was less than twice that for single group members. Detectability at a given distance decreased severely as the group moved faster; at their fastest speed, individuals had to approach a platform to within less than 10 m to ®nd it. The large platforms were significantly more likely to be detected than the small ones, suggesting that increased use of larger food patches by wild primates may not necessarily reflect foraging preferences.