The mountain gorilla, Gorilla beringei beringei, is a large primate adapted to the high-altitude, dense cloud forests of Central Africa. Their habitat, spanning the Virunga Massif and Bwindi Impenetrable National Park, dictates a specialized diet. Due to their massive body size and the low energy density of available food, mountain gorillas must consume a high volume of plant matter daily. This necessity shapes their physical adaptations and daily routines, making their nutritional strategy distinct among great apes.
Core Diet Composition
The diet of the mountain gorilla is overwhelmingly herbivorous, consisting almost entirely of fibrous plant parts available year-round. Leaves, stems, and shoots form the majority of their intake, accounting for an estimated 86% of their total diet. They consume over 140 different plant species, frequently targeting nettles, thistles (Carduus spp.), and Galium vines.
The diet is supplemented by smaller proportions of roots, bark, and flowers, which make up about 7% and 3% respectively. Mountain gorillas are adept at peeling the tough outer layers of thick stalks, such as bamboo, to access the soft, nutrient-rich inner pith. This selection process allows them to target the most digestible and nutrient-dense parts of large, woody plants.
Fruit constitutes a very small part of their diet, typically less than 2%, unlike their lowland gorilla relatives who consume significantly more. This scarcity is due to the high-altitude environment, where fruit-bearing trees are less common. Occasionally, they consume invertebrates, such as ants, snails, and larvae, which provide a minor protein boost. An adult male silverback must consume over 30 kilograms (66 pounds) of vegetation daily to sustain its size.
Foraging Behavior and Daily Routine
Mountain gorillas dedicate a substantial part of their waking hours to finding and consuming food. They begin foraging early in the morning, often around 6:00 am, and spend approximately four to six hours each day actively feeding. This prolonged feeding time is necessary for processing the sheer volume of low-quality forage required to meet their energy demands.
Foraging is highly selective; they rarely eat an entire plant. They use their hands to strip leaves from stems and their agile lips to manipulate vegetation, ingesting only the preferred portion, such as the soft pith or young shoots. This method allows the plant to quickly recover, avoiding overexploitation of the area.
The daily routine involves periods of intense feeding interspersed with rest and short travel periods. Since their primary food source is widely distributed, groups do not typically have to travel large distances daily.
Mountain gorillas rarely drink standing water. The vegetation they consume is extremely succulent, often containing between 50% and 90% water. They obtain virtually all necessary moisture directly from their diet and from dew collected on leaves.
Nutritional Requirements and Fiber Intake
The massive quantity of herbaceous material results in extremely high levels of dietary fiber. Gorillas overcome this digestive challenge through a specialized biological adaptation: they are hindgut fermenters, possessing an enlarged large intestine that acts as a fermentation vat.
This adaptation houses microbes that break down indigestible cellulose and tough plant fibers. The fermentation process yields short-chain fatty acids (SCFAs), which are absorbed and used as a primary energy source. This microbial energy extraction accounts for a significant portion of their daily metabolizable energy.
Mountain gorillas easily meet their protein needs through the selective consumption of high-protein leaves and stems. Their diet provides a protein concentration of 17–20%, comparable to the intake of human athletes. By prioritizing young leaves and shoots, which are higher in protein and lower in fiber, they ensure the amino acids needed to maintain their large, muscular physique.