INDIVIDUAL-DIFFERENCES IN VOCALIZATIONS OF YOUNG BARBARY MACAQUES (MACACA-SYLVANUS) - A MULTI-PARAMETRIC ANALYSIS TO IDENTIFY CRITICAL CUESIN ACOUSTIC SIGNALING

It had been shown that Barbary macaque (Macaca sylvanus) mothers are a ble to individually recognise their offspring by its vocal signals, bu t it remained unclear which acoustical cues may account for such an ab ility. In order to address this issue from a basic perspective, about 1800 calls of infants and yearlings (N = 10) were investigated. The in vestigation applied a method of signal analysis which allowed to deter mine a large number of parameters (N = 84) for each vocal signal. The application of discriminant and cluster analyses provided the followin g results: (1) Animals differed in almost all call parameters. However , individuals were best identified by specific parameters which formed an individually characteristic parameter set. (2) Those parameters th at facilitated the assignment of vocal patterns to a given individual usually were different among individuals. (3) Infants and yearlings ac hieved the same maximum value of correct assignment. However, infants achieved a reasonable assignment at a much small er number of call par ameters. (4) Cluster analysis of vocalisations revealed that Barbary m acaques uttered individual versions of common call types. (5) When the discriminant analysis was rerun on the call clusters, the correct ass ignment could be improved from 81% to 94% for infants and from 80.5% t o 96% for yearlings. Our findings suggest that Barbary macaque mothers can recognise their offspring by more than one signal cue, and such a strategy may improve the recognition system's robustness against poss ible distortions caused by the environment. The pronounced differences in vocal patterns of young Barbary macaques may help mothers or other group members to readily learn and recognise the individually specifi c signal features. The methodological procedures described in this pap er provide a powerful tool for an assessment of signal parameters also in other areas of vocal interactions.