Abstract: For small, arboreal marmoset monkeys, antipredator vigilance is essential to ensure survival. However, since antipredator vigilance is incompatible with some other behaviours, such as feeding in a head-down position, it has to be regulated efficiently within individuals and perhaps even at the group level. To investigate what drives individual differences in vigilance and feeding behaviour in common marmosets, Callithrix jacchus, and whether they adjust these behaviours to each other, we collected behavioural data on 14 marmosets in contexts where feeding and vigilance were mutually exclusive. The presence of infants resulted in higher overall vigilance and less feeding. Moreover, individuals increased their vigilance when the pair mate was feeding and thus could not be vigilant itself. They thus adjusted their own vigilance to the risk level of their pair mate, which resulted in a turn taking-like pattern of feeding and being vigilant in the pair. This flexibility of vigilance is consistent with marmosets' sensitivity to other's needs in another context, food sharing, when sharing is increased when food is more difficult to obtain. Together, these results suggest considerable awareness of the current state of group members in common marmosets.