Abstract
Visual scanning of the environment was studied in two captive groups of red-bellied tamarins (Saguinus labiatus). The tamarins scanned throughout the day, but rates of scanning were highest just after arising and just prior to retiring. Scanning increased following the presentation of threatening stimuli, and hidden objects were more likely to be discovered at times when scanning rates were high. These data support the contention that visual scanning is a form of vigilance which has important anti-predator functions for red-bellied tamarins.