Geissmann T., 1987: Songs of hybrid gibbons (Hylobates lar x H. lar). International Journal of Primatology 8: 540 (Abstract only).
Anthropological Institute, University Zürich-Irchel
In a previous publication, inheritance of song characteristics was demonstrated in two captive hybrid gibbons (Hylobates pileatus x H. lar) (Geissmann, 1984: Folia primatol. 42: 216). The results appear to be corroborated by studies on natural hybrid populations in Thailand and Kalimantan. One problem encountered in free-living hybrid gibbons is, however, that for most individuals the number of hybrid generations and the extent of admixture of the two hybridizing species are not known. This report documents singing behaviour in 3 female and 2 male first-generation hybrids (Hylobates pileatus x H. lar), observed and tape-recorded during 1987 in several zoos in West Germany. The song structure of all hybrids corresponds to the previous observations, showing that the F1-hybrids have a characteristic song repertoire which is different from that of both parental species. This song structure can now be shown to have remained stable over six years in one female. In addition, one female is reported to have displayed male-like behaviour and songs for several years while in her natal group. One hybrid male mated with a H. lar female was observed to sing (albeit unfrequently and always in synchrony with his lar mate) a phrase most similar to the great calls of female gibbons during his otherwise typical male songs. Although this male has never heard other great calls than those of H. lar females, his great call-like vocalizations were virtually identical to those of female F1-hybrids. These observations have implications for the interpretation of the evolution of duetting in gibbons. In addition, sex-specific behaviour (at least in these hybrids) may be less rigidly determined than is generally assumed.
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