Department of Anthropology, Stony Brook University
Saturday All day, Park Concourse
Although decreased individual investment in vigilance is frequently posited as a benefit of sociality, the increased within-group competition for food and mates associated with living in groups may promote increased levels of individual vigilance. Rather than serving an anti-predator function, vigilance in this case is used for social monitoring. In this study, we assess the correlates of vigilance among tufted capuchin monkeys (Sapajus [Cebus apella] nigritus) at Iguazú National Park, Argentina. Previous studies of capuchins at Iguazú indicate that duration of vigilance increases with neighbor density, suggesting that social monitoring is more important than predation risk as a means of driving vigilance in this popualtion. Yet in avoiding predators, frequency – and not duration – of vigilance may be more important. We conducted instantaneous focal animal samples (N = 592 hr) of all adult individuals in four habituated groups, recording individual activity, spatial position, and vigilance behavior. We used generalized linear mixed effects models to examine the factors predicting the occurrence of vigilance. Consistent with the intense within-group feeding competition observed among tufted capuchin monkeys, vigilance is more common during feeding and resting, when individuals may benefit most from monitoring the activity of group mates. Yet increased vigilance is also associated with decreased neighbor density and height in the canopy, contexts associated with increased predation risk. These results suggest vigilance in this population is used in both an anti-predator and a social context, and support previous suggestions that these two types of vigilance behavior may be qualitatively different.
This study was supported through grants from the Leakey Foundation, National Geographic Society, the National Science Foundation (BCS-0752683 to C. H. Janson and C. J.S.), and the Wenner-Gren Foundation.