Dallmann, R. & Geissmann, T. 2000: Individuality in the songs of wild silvery gibbons (Hylobates moloch) of Java, Indonesia - Individualität im Gesang freilebender Silbergibbons (Hylobates moloch) auf Java, Indonesien. Folia Primatologica 71: 220 (Abstract only).
R. Dallmann & T. Geissmann
Institute of Zoology, Tieraerztliche Hochschule Hannover
All gibbon species produce loud, long and elaborate song bouts in the early morning. Gibbon songs exhibit species-, sex- and individual-specific characteristics. Silvery gibbons (Hylobates moloch) differ from other species, however, in that male singing appears to be uncommon and most song bouts are female solo songs. Individual differences easily distinguish neighbouring females in the field, and it has been suggested that female individuality is particularly high in H. moloch in order to compensate for the lack of a family-labeling male song. The present study aims to test this hypothesis by quantifying individuality in H. moloch and comparing it with data on song individuality in two other gibbon species, H. agilis and H. klossii, available from earlier studies (Haimoff & Gittins, 1985, Am. J. Primatol. 8:239-247; Haimoff & Tilson, 1985, Folia Primatol. 44:129-137). Those studies had been focussing on the great call (i.e. the most stereotypical song phrase produced by gibbon females) and had determined individual variation of several variables (such as duration and frequency range of selected great call notes). We exactly replicated each of those studies with great calls of H. moloch which were tape-recorded in Ujung Kulon and Gunung Pangrango. We chose the number of individuals, analysed the same number of great calls of each, and measured the analogous variables as the previous studies. Individuality of each variable was determined with the Kruskal-Wallis test. The resulting H-values were compared with those of H. agilis and H. klossii, with a higher H-value in a variable indicating a higher level of significance.
Conclusions: (1.) We found a statistically significant individuality in most great call variables of H. moloch, similar to those previously reported for H. agilis and H. klossii. (2.) The amount of individual differences in H. moloch is higher than that of H. klossii, but lower than that of H. agilis. (3.) Our results do not support the hypothesis that H. moloch females compensate the rarity of male song contributions with an elevated degree of individuality in their singing.
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