Bimodal temporal organization of specific vigilance behaviors in captive black tufted-ear marmosets (Callithrix penicillata)

The aerial/terrestrial scan and glance behaviors of 20 captive adult black tufted-ear marmosets (Callithrix penicillata), kept undisturbed in their own familiar social environments, were assessed at 07:00, 09:00, 11:00, 13:00 and 15:00 h, as little is known on the temporal organization of their vigilance repertoire, particularly under normal social and stress-free conditions. For each time point, four 20-min observation sessions were held. Although general high vigilance rates were observed, significantly more time was spent scanning the upper part of the home-cage, particularly during the earliest and latest hours of the day. Significantly higher terrestrial than aerial glance frequencies were also seen, yet both remained constant throughout the day. Therefore, the observed pattern not only varied significantly according to the specific vigilance behavior and time of day, but also seemed associated with eco-physiological factors, such as the search/intake of food, sleep site selection and higher risk of air-born threats.