Vocal behaviour of the common marmoset : structure and function of selected calls.
The vocal behaviour of the captive common marmoset, Callithrix jacchus
jacchus, was investigated with particular reference to three call types; phee,
twitter and trill calls. The aim of the study was to determine the functional
significance of these vocalizations by relating the behavioural and social
contexts of calling to the detailed acoustic structure of each call type.
The study first examined the effects of housing environment and social
status within family groups on vocal and related behaviours. Each call type
was found to be given in distinctly different circumstances and at differing
rates according to the status of the vocalizer and the social and physical
environment in which the call was given.
The role of vocal communication in the establishment and maintenance
of male-female pairs was also examined. Newly formed pairs were
monitored for the initiation of vocal contact and subsequent call exchange.
Changes in levels of interaction were most evident in measures of vocal
behaviour. Partners in both new and established pairs appeared to exchange
trill calls when in close proximity and exchange phee calls when separated.
Finally, the study examined vocalizations for individual, gender and
contextual differences in acoustic structure. Quantitative analysis revealed
individual differences in phee, twitter and trill call structure indicating that
these calls carry information on the identity of the vocalizer. Phee and trill
calls also showed considerable intra-individual variation under changing
social conditions, suggesting that these vocalizations may also convey
information on the caller's internal state. In addition, differential responses
to playbacks of twitter calls demonstrated the recognition of structural
differences present in this call type.
These results indicate that the functions of vocal signals in the common
marmoset are complex and confirm that vocal communication plays an
important role in influencing social interactioris in this species.