Heine, A. & Geissmann, T. 2000: Gibbon ethograms: What makes the difference? - Gibbon Ethogramme: Woher kommen die kleinen Unterschiede? Folia Primatologica 71: 228 (Abstract only).

Gibbon ethograms: What makes the difference? - Gibbon Ethogramme: Woher kommen die kleinen Unterschiede?

A. Heine & T. Geissmann

Institute of Zoology, Tieraerztliche Hochschule Hannover

Few elaborate ethograms are available for gibbons (only one has apparently been published) and most of them refer to two gibbon species only, H. lar and H. syndactylus. The present study offers an ethogram for H. leucogenys, an examination of the differences among existing gibbon ethograms, and an assessment of the reasons for these differences.

Four groups of H. leucogenys with group sizes ranging from two to four animals were observed in the zoological gardens of Amsterdam, Beekse Bergen and Hannover. All groups were kept on islands. Behavioral data were collected with the focal animal sampling method using continuous recording. Total observation time amounted to 77-90 hours per group. Observation time was equally distributed over the animals' activity period.

A total of 74 different behaviour elements were described. The observed animals exhibited significant individual differences. Most differences were due to the individual-specific characteristics or differences in the keeping conditions. Males of all groups had higher values for the behaviour element observe and various dynamic types of locomotion (brachiate, jump), all of which mainly occurred in the context of territorial behaviour. Male H. leucogenys possibly invest more time and energy into guarding and defending particular resources (territory, partner) than females. In addition, the songs of H. leucogenys, which also serve a territorial function, have been shown to be clearly male-dominated. Possibly, this higher investment compromises energy intake. Females tended to show higher values than males in several behaviour elements of the feeding and foraging context.

The ethogram of the present study was compared with previous gibbon ethograms. Many behaviour elements show similarities with those of other gibbon species. Behavioural differences between groups as well as between ethograms appear to result from individual differences or external conditions and do not appear to reflect phylogenetic differences between the species. In this respect, most gibbon behaviour elements differ from vocalisations - in particular from territorial songs - which have previously been shown to be relatively stereotypic, species-specific and largely genetically determined.