INDIVIDUALITY BUT NOT STABILITY IN MARMOSET LONG CALLS

Individually distinct communication signals ('signatures') have been d ocumented in a variety of taxa across signal modalities and they serve a host of important functions. However, studies have rarely examined the temporal stability of these signals. Cooperatively breeding specie s, such as marmosets and tamarins, are characterized by long-term grou p membership, complex social organization, and high levels of interind ividual coordination of behaviour. These social attributes may promote complex, individually distinct and stable acoustic signals to facilit ate the expression of cooperative behaviour. In this study, the long c alls of socially housed individual Wied's black tufted-ear marmosets, Callithrix kuhli, were examined for a 'signature system' potentially i mportant in such interactions. Vocalizations were recorded at three di fferent times (1993, 1995, 1996), digitized, and then measured by spec trographic analysis. Acoustic and temporal features of the calls were examined, including number of syllables, length of syllables, intersyl lable interval, frequency range, start/stop frequency, peak frequency, and total call duration. A number of significant intra-individual cha nges in acoustic parameters were identified across the recording perio ds. Discriminant analysis revealed that many variables contributed to differentiation among individuals, and average classification accuracy for calls within a given year was high, ranging from 91.7 % to 93.5 % . However, reclassification accuracy for calls between-years was much poorer, averaging less than 50 %. In addition, classification confiden ce was higher for within-year scores in contrast to the between-year v alues. Thus, tufted-ear marmosets have an individually distinct vocali zation which is acoustically modified across time. Our finding suggest s that to the extent that the vocalization is used for individual reco gnition, recognition mechanisms must be modified over time as well.