Temporal and structural features of infant calls in relation to caregiving behaviour in common marmosets, Callithrix j. jacchus.

The role of infants in the communal rearing system of marmosets and tamarins has received little attention although their demands may not be complied by inadequate helpers. As acoustic signalling plays an important role in their social communication, it is expected to be an effective way for infants to signal their demand for care. As a first approach, this study focussed on the use and quality of 'tsik' calls given by infants of common marmosets (Callithrix j. jacchus) in the context of caregiving. The acoustic and non-acoustic behaviour of a group of common marmosets were recorded during the first two weeks of the life of two infants (twins). Vocalizations were classified, and the structure of the infants' 'tsik' calls was quantified by measuring specific signal parameters. Infants gave 'tsik' calls in close temporal relation to caregiving behaviour. Specific parameters covaried with the subsequent behaviour of potential caretakers. Values of call duration, start frequency, peak frequency, and range were lower when infants' calls were followed by no reaction or an approach of group members, whereas these parameters showed higher values when followed by a transfer of infants. Our results suggest that the actual demand of infants is encoded in the variations of 'tsik' calls.