To accurately replicate the wild diet in a sanctuary setting, it is necessary to understand not just the broad categories of food consumed, but the composition of the diet. Wild gibbons utilise an extraordinarily diverse array of plants: long-term ecological studies have routinely recorded individual gibbon groups consuming parts from 100-150 distinct plant species throughout an annual cycle.
In the wild, gibbons show a strong preference for ripe, fleshy forest fruits that offer a very different nutritional profile compared to the domesticated fruits cultivated for human consumption. Rather than being saturated with simple sugars and water, these preferred wild fruits, which include a diverse array of tropical forest berries, and pulpy tree fruits, are significantly higher in complex carbohydrates, structural fiber, and vital minerals such as calcium. Many of the specialised fruits they actively seek out are also relatively lipid-rich, providing concentrated sources of dietary fat that serve as an energy source. Because gibbons maintain a highly active, arboreal lifestyle with elevated metabolic rates, they selectively target these ripe, energy-dense wild fruits for their easily digestible nutrients, allowing for quick processing and rapid energy extraction during foraging.
Trees from the genus Ficus (family Moraceae), encompassing the wild figs, occupy a uniquely important role in gibbon nutrition. Unlike most tropical trees, which have seasonal fruiting tied to monsoon patterns, Ficus species fruit asynchronously. This continuous, staggered availability ensures that fig trees provide a reliable food source even during the dry seasons when other fleshy fruits are mostly absent. In other words, figs function as the primary “fallback food” for almost all gibbon species. When preferred fruits are abundant, gibbons actively select them over figs. However, when overall forest productivity drops, fig consumption increases significantly. In fragmented habitats where tree diversity has been compromised, Ficus trees alone can account for over 1/3 of a gibbon group’s total annual feeding time, sustaining populations that would otherwise face starvation. Figs are much higher in fibre and lower in simple sugars than the preferred fruits gibbons eat. As such, they have an important contribution to digestive fibre intake.
Flowers and young leaves function as additional fallback foods. Flowers from lianas and emergent trees offer a rapid influx of simple sugars via nectar, alongside easily digestible proteins in the pollen, requiring minimal digestion. Leaves are very low in simple sugars and high in fibre, making them more difficult to digest. Most gibbon species prefer fresh leaves, which contain smaller amount of poorly digestable fibres compared to more mature leaves. Siamangs and some gibbons species, however, readily consume larger amounts of leaves when other food are not available.
The ingestion of animal prey, while insignificant as a proportion of the diet, provides important micronutrients. However, gibbons do not actively hunt in the manner of some other apes, instead, their invertebrate consumption is largely opportunistic. They eat caterpillars, spiders, and orthopterans from the undersides of leaves, or selectively ingest figs that have been heavily parasitised by fig wasps, thus inadvertently acquiring a source of dietary protein. This protein intake is relatively modest, the vast majority of the protein consumed by gibbons is from plants.