The great apes (gorillas, chimpanzees, bonobos, and orangutans) exhibit remarkable diversity in their feeding habits across Africa and Southeast Asia. Their diets are highly specialized and directly influenced by the availability of food in their specific forest habitats. These large primates are selective eaters, constantly making foraging decisions to meet their high caloric needs. The mix of fruits, leaves, and animal matter consumed by each species reflects a sophisticated adaptation to its ecological niche. Understanding ape diets provides insight into their behavior, social structures, and importance to forest ecosystems.
The Major Dietary Groups
Gorillas are primarily folivores, meaning their diet is dominated by vegetation, relying on leaves, pith, and tough stems. This plant material is low in nutritional density, forcing an adult male gorilla to consume more than 18 kilograms (40 pounds) of vegetation daily. Mountain gorillas rely on leaves and shoots for up to 85% of their intake, as fruit is scarce in their high-altitude habitats. Western lowland gorillas, living in fruit-rich environments, incorporate fruit into up to 67% of their diet when seasonally abundant.
Chimpanzees and bonobos (Pan species) are omnivores with a strong preference for fruit. Ripe fruit makes up between 70% and 93% of their diet when available, supplemented by a wide array of other foods. These include seeds, nuts, tree bark, and insects such as termites and ants. Chimpanzees are known for actively hunting small mammals, including bush pigs and red colobus monkeys, which provides a significant source of protein.
Orangutans are the most solitary apes and are predominantly frugivores, relying heavily on fruit (60% to 90% of their diet). When fruit is scarce, they turn to other resources to survive periods of low availability. These fallback foods include:
- Young leaves
- Flowers
- Honey
- Bird eggs
- The cambium layer found beneath tree bark
Orangutans consume parts of up to 2,000 different plant species, demonstrating extensive knowledge of their forest food sources.
Foraging Strategies and Tool Use
The methods apes use to acquire food demonstrate complex cognitive abilities, particularly among chimpanzees. Chimpanzees in certain communities are famous for “termite fishing,” a learned behavior where they select a flexible herb stem, strip the leaves, and fray one end to create a brush-tipped tool. This probe is inserted into a termite mound to extract the insects, increasing the yield of this protein-rich snack. Other populations use heavy stones as hammers and anvils to crack open tough nuts, such as oil palm or panda nuts, a technique requiring coordination.
Chimpanzees also engage in complex cooperative hunting, especially for arboreal prey like red colobus monkeys. Groups of males coordinate their movements, taking on roles such as “chasers” to drive the monkey and “blockers” to cut off escape routes in the canopy. The success of these hunts is signaled by a specific “hunting bark” vocalization, which recruits more group members and coordinates the chase.
Gorillas, while not known for manufacturing tools, use immense physical strength and dexterity in their foraging. To access the nutrient-rich pith (soft inner core) of tough plants like bamboo or banana trees, a gorilla shreds and peels back the hard outer layers. They are highly selective foragers, using agile lips and hands to consume only a specific, palatable part of a plant, such as the stalk or the root epithelium, while discarding the rest.
Nutritional Requirements and Ecological Impact
Apes must consume vast quantities of food to fuel their large body masses, and their dietary strategies meet specific nutritional needs, particularly for protein. Gorillas achieve their protein requirements by consuming a massive bulk of leaves and stems, which contain substantial protein despite low caloric density. Their specialized digestive tract, featuring an enlarged hindgut, allows for the fermentation of this high-fiber plant matter, efficiently extracting nutrients.
Chimpanzees meet their protein and caloric needs through a mixed diet, with meat and insects providing nutrient-dense supplements to their primarily fruit-based intake. Their plant-based diet, like that of gorillas, is extremely high in fiber; neutral detergent fiber (NDF) levels in wild ape diets typically exceed 20%. This high-fiber intake is important for gut health and function across all ape species.
Apes function in maintaining the health and diversity of their forest ecosystems through seed dispersal, a process known as endozoochory. By consuming large quantities of fruit, they ingest the seeds, which then pass through their digestive tracts undamaged. Because apes have large home ranges, they transport these viable seeds over long distances in their feces. Studies show that for some tree species, like Dacryodes normandii, seeds passed through a gorilla’s gut show a high germination success rate, establishing apes as “gardeners” of the forest.