ABOVE: North Borneo Gibbons  Hylobates  funereus feeding on ripe F. sundaica figs at the Danum Valley Field Center in Sabah.  In most parts of Borneo gibbons rely on figs to provide their staple diet.  Other types of preferred fruit are only seasonally or intermittently available whilst there is almost always at least one fig fruiting at any one time in a gibbon family territory.  Thus the density of figs in most areas of lowland forest determines the density of the gibbon population. The exception to this rule is in areas of peat swamp forest in Kalimantan  (e.g Sabangau) where the fig density is low  and the majority of  trees fruit  throughout the year.

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Note the large oblong leaves with a re-curved (back pointing) drip tip and the very prominent basal veins  all distinctive features of Ficus sundaica  a common forest strangler in Borneo.
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North Borneo Gibbons live in small family groups of a male, a female and one or two offspring. Gibbon territories  average c. 40 ha and are fiercely defended  by both sexes. Early morning gibbon territorial calls  are a characteristic sound of Borneo’s forests.