Vigilance, vocalizations, and cryptic behavior at retirement in captive groups of red-bellied tamarins (Saguinus labiatus).

Frequent references are made to presumed antipredator adaptations exhibited by callitrichids, but there are very few systematic investigations of these behaviors. One set of untested presumptions stems from observations that callitrichids become especially vigilant and cryptic prior to retirement each evening. This hypothesis was tested in the current study by quantifying the rates of vocalizations and extragroup behavior at various times of the day. Using two groups of captive red-bellied tamarins, it was demonstrated that these primates do become relatively more quiet and more attentive to the nonsocial environment prior to retirement each evening, culminating in virtual silence once the nest box has been entered. While the adaptive significance of these phenomena has not yet been tested, it is likely that the behaviors reduce vulnerability to predation.