Geissmann, T. & Nijman, V. 2000: Do male silvery gibbons have anything to say? - Haben männliche Silbergibbons etwas zu sagen? Folia Primatologica 71: 225 (Abstract only).
T. Geissmann1, V. Nijman2
1Institut für Zoologie, Tierärztliche Hochschule Hannover
2Institut Systematics and Population Biology, Zoological Museum
All gibbon species are known to produce loud, long and well patterned morning songs which, among others, serve a territorial function. In mated pairs, male and female song contributions are sex-specific. The following song patterns occur among gibbon species: (1.) Duet song bouts only (7 species); (2.) duets and male solo songs (3 species); (3.) female solo songs and male solo songs (1 species: Hylobates klossii); (4.) female solo songs only (1 species: H. moloch). Only one behavioural study has previously been carried out on wild silvery gibbons (H. moloch). Kappeler (1984) observed the species in Ujung Kulon (the western-most tip of Java). During 130 full days of listening, he never heard any male songs of the resident groups in his study area and concluded that territorial male gibbons do not sing.
We monitored gibbon singing activity around Linggo Asri in central Java on a daily basis during 19 consecutive days (October 1998). We recorded location and sex of the singer, and starting and ending time of all song bouts we heard. We compare our results with those from Ujung Kulon [Kappeler, M. in The lesser apes. Evolutionary and behavioural biology (Preuschoft et al., eds.) 376-389 (Edinburgh University Press, Edinburgh, 1984)].
We heard a total of 125 song bouts of at least 9 groups. Most groups could be individually identified by individualospecific song characteristics. No duet songs were heard. Most of the song bouts (n=108, 86%) were female solo songs. In contrast to an earlier study in western Java, males in central Java also produced songs, albeit less frequently than females (n=13, 10%). Males prefer to sing before dawn (05:20), whereas females sing later in the day: Most male songs (62%) started between 04:20-04:40. All female songs, in contrast, started after 05:00 and female singing activity peaked around 06:00. Similarly separated periods of male and female solo songs were also observed in Kloss gibbons (H. klossii) on the Mentawai Islands. This may represent a derived characteristic shared by H. moloch and H. klossii.
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