AbstractInfant pygmy marmosets (Cebuella pygmaea) are extremely vocal with much of their calling occurring in long sequences of mixed call-types that appears to have several parallels to the babbling of human infants (Elowson et al., 1998b). We refer to this vocal behaviour as Pygmy Marmoset Babbling (PMB) (Elowson et al., 1998a). We followed several of our original subjects beyond infancy to adulthood. Babbling bouts continued to appear through the age of puberty though at a reduced rate from that seen in infancy, but babbling was rarely observed in adults. With increasing age the vocal bouts contained a greater diversity of call types per bout and a decrease in call series duration. In addition, with increasing age there were decreasing proportions of calls that were Adult Variant and Infant calls and an increase in Adult calls. Structural analyses of trills, the most common call type found in vocal bouts, showed increased proportions of well-formed trills and decreased proportions of poorly formed trills with increased age, with different features reaching adult form at different ages. Babbling by juvenile marmosets was associated with increased social interactions with other group members as we had observed with infants. 'Babbling' in both infant and juvenile marmosets might provide vocal practice as well as attract attention from other group members.
