Ontogeny of trill and J-call vocalizations in the pygmy marmoset, Cebuella pygmaea

Abstract

Vocal ontogeny in primates is undescribed for most species, and no general pattern of vocal development has emerged from the studies that have been done. The development of two contact calls, trills and J-calls, was examined in the pygmy marmoset. Five litters (nine individuals) were tape-recorded from infancy to adulthod. The correlation of changes in the acoustical structure with age, whether stereotypy of acoustical structure increased with age, and changes in appropriate usage of trills were evaluated. There was considerable variation among the litters in the correlations of acoustic parameters with age, even in litters from the same parents. The duration of trills and the rate of frequency modulation correlated significantly with age in most litters. Frequency measures decreased with age, but were not consistently significant in litters. Only two variables, cycles per second and lowest crest, showed increasing stereotypy as measured by a progressive reduction of the coefficient of variation. J-calls were given less often than trills and few J-call variables showed significant correlations with age. The acoustic structure and usage of trills and J-calls in pygmy marmosets are not adult-like at birth, but develop with considerable individual variability. Increased stereotypy of call structure did not occur. Although some changes in acoustic structure took place over time, the most consistent aspect of vocal ontogeny in pygmy marmosets was the acquisition of adult usage.