Gorillas feed on trees, up to 30 m above the ground. Animals adopt sitting and standing positions for feeding. They twist the branches within reach, often without breaking them. The fruits and leaves are picked with the lips or picked by hand and transferred to the mouth.
When fruit abundance is low, adults also bend and break saplings to access foliage, fruit, or vines. When foraging on the ground, group members spread over distances of up to 500 m. Animals will cross swamps to feed on aquatic weeds and will sit in chest-deep water for up to 2 hours. T
Gorilla gorilla eats fruit, seeds, leaves, petioles, bracts, tendrils, invertebrates and terrestrials, stems, bark, shoots, and roots. The average food diversity is 148 food species (range 100-180). The food strategy of G. g. gorilla requires it to consume leaves to meet protein needs, even when the fruit is abundant.
Staple foods are the pith of Aframomum spp. and leaves and shoots of Marantaceae(primarily Haumania spp.), abundant, accessible, and available all year round. The western lowland gorilla is highly selective; for example, animals eat the easily digestible stem- and the leaf bases of Megaphrynium macrostachyum and Haumania liebrechtsiana, but discard the rest of the plant.
They consume protein-rich leaves, ripe succulent fruits rich in soluble sugars and low in tannins, and freshwater grasses high in protein and minerals such as sodium and potassium. Unripe fruits and leaves high in digestive inhibitors are avoided.
Fruit is widely available in lowland habitats, thus G. g. gorilla eats fruits from up to 100 species. Fruit is the most diverse food category across all sites studied (range 44-70% of food species).
Fruit remains recorded in 90-100% of fecal samples. The seeds of ripe fruits are ingested with the pulp, but rarely digested, so G. g. gorilla is an important seed disperser. An exception is in Likouala, where G. g. gorilla feeds heavily on Gilbertiodendron dewevrei seeds during mast fruiting, but the processing of seeds takes time, and individuals have difficulty collecting small seeds from the ground.
In Gabon, immature seeds of Dialium lopense are reingested by coprophagy. In Gabon, the gorilla forages sporadically in streams and semi-aquatic swamps Marantaceae, Marantochloa cordifolia, M. purpura and Halopegia azurea.
In Congo, animals extensively exploit flooded or permanently flooded swamp forests, preferred foods are aquatic Hydrocharis chevalieri and sodium-rich sedges Rhynchospora corymbosa and Cyperus sp. In Likouala and Lac Téléswamps, staple foods are Raphia sp. palm leaves and Pandanuscan delabrum respectively.
Fallback foods are always available but tend to be lower quality (pith, leaves, bark, and fibrous fruit) and are ignored when ripe, succulent fruit is available. There are hard, dry fruits, eaten in large quantities only when other fruits are not available.
Western gorilla consumes >20 species of invertebrate, mostly social ants and Cubitermes termites. Weaver ants Oecophylla longinodaare ingested in convenient nests, containing eggs, larvae, pupae, and adults. Remains of ants have been recorded in 31% of feces.
The gorillas are more insectivorous in areas dominated by secondary forests, where Crematogaster (ants) and Thoracotermes (termites) are also eaten. Insectivory seems to occur at about the same rate at four sites: Lopé, Belinga, Ndoki, and Dzanga-Sangha.
Termites are the most commonly observed food item and are eaten on 91% of days. Geophagy has been observed in natural salt ponds with high sodium concentrations. The diet of G. g. gorilla varies seasonally. The amount of fruit consumed is positively related to rainfall and the availability of mature fruit trees. When fruits are abundant, they constitute the majority of the diet (68%), but only 30% in the dry season. During the dry season, more fibrous plant material is consumed, including shoots, young leaves, and bark. Milicia excelsa bark is eaten only during the dry season.
Little is known about the diet of cross river gorilla G. g. diehli. The diet includes fruits, leaves, stems, pith, invertebrates, and soil, but fruits are preferred when available. The habitat of G. g.diehli is distinguished by its strong seasonality, with a prolonged dry season (45 months) during which the fruits become rare and the diet shifts to the bark, leaves, and pith of terrestrial grasses.
Range patterns are shaped by the availability of particular foods. Gorilla adopts a low-cost energy strategy in times of fruit shortage by decreasing in diurnal range and shifting of diet to abundant but lower quality leaves and woody vegetation.