Visibility, group size, vigilance, and drinking behavior in coati ( Nasua narica ) and white-faced capuchins ( Cebus capucinus ): experimental evidence

Abstract

I studied the role of visibility on the vigilance behavior of coatis Nasua narica and white-faced capuchins Cebus capucinus in a dry tropical forest in Costa Rica. Vigilance and drinking behavior were observed at a waterhole where the water surface was 2–3 m below ground level for 5 days. Then I provided an artificial water pan of similar size adjacent to the natural waterhole, but level with the ground, and observed the same behaviors. Animals drinking at the natural waterhole had to descend below ground where they could not see above ground, while those drinking from the experimental pan could see approaching predators. Variations in drinking and vigilance behavior were accounted for by site (natural vs. experimental water source) and group size, with site contributing most significantly to variations. Both coatis and capuchins decreased their time to wait at the forest edge before emerging to drink, had more drinking bouts, had longer bout lengths, and decreased their vigilance behavior when they drank at the ground-level waterhole compared to the one below the surface, where their visibility was obscured. For both species, total drinking time increased, and vigilance decreased, with group size. This study demonstrated experimentally that visibility and group size influence drinking and vigilance behaviors.