Gorillas, the largest primates on Earth, possess incredible strength and complex social structures. Their dietary habits are as fascinating as the animals themselves, varying based on species, habitat, and seasonal availability. This article delves into the intricate world of gorilla nutrition, exploring what these gentle giants eat in the wild and in captivity, as well as the crucial role their diet plays in their overall health and the ecosystem.
A Day in the Life: Feeding Gorillas at the Smithsonian National Zoo
At the Smithsonian National Zoo, the daily routine for gorillas begins with a small cup of yogurt. This serves as a clever method for administering medications to gorillas that require them. As they enjoy this pre-breakfast snack, zookeepers conduct a thorough wellness check, observing their alertness, behavior, and movement within their habitat.
While the gorillas wake up indoors, the outdoor habitat is prepared, weather permitting. A meticulous inspection ensures the habitat's security, removing any potential hazards like fallen tree limbs and checking for unwanted critters, particularly snakes, which gorillas strongly dislike.
Once deemed safe, the habitat is enriched with puzzle feeders and food scattered around to encourage foraging behavior, mimicking their natural instincts in the wild. Upon entering the outdoor space, some gorillas immediately seek out the scattered snacks, while others engage with the enrichment items or play with each other. Moke, a three-year-old gorilla, particularly enjoys rummaging through the toys.
While the gorillas are outside, their indoor enclosures are cleaned and further enrichment is added. After a few hours of outdoor activity, the gorillas are typically ready for a change of scenery, returning to find puzzle feeders filled with food indoors. These feeders provide both physical and mental stimulation, requiring the gorillas to figure out how to extract the treats inside.
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Lunchtime involves another foraging session outdoors. Adult male gorillas can consume upwards of 45 pounds of food per day, while adult females eat approximately two-thirds of that amount. The gorillas at the Smithsonian National Zoo enjoy a varied diet consisting of browse (fresh tree trimmings), leafy greens, vegetables, and fruits, all carefully prepared by the Nutrition Science team.
After the gorillas have foraged for the last scraps of food in the yard, Calaya, a 19-year-old female and mother to Moke, usually encourages the troop to head inside for the evening.
In the early afternoon, husbandry training sessions are conducted with each western lowland gorilla. Through verbal cues and hand signals, the gorillas are guided to present their body parts for examination. For instance, they may place an ear against the mesh for temperature taking or present an arm for injection or blood draw training using a blunted needle. This voluntary participation in healthcare minimizes the need for anesthesia during routine procedures. The gorillas seem to enjoy these interactions, receiving positive reinforcement in the form of favorite foods like fruit or mixed nuts for correct behaviors. The sight of the training buckets often elicits excited grumbles from the gorillas.
Each gorilla receives special enrichment at the end of the training session, such as a PVC tube filled with peanut butter, which they must use a tool, like a piece of browse, to fully enjoy.
Wild Diets: A Tale of Two Gorillas
The dietary habits of gorillas in the wild are heavily influenced by their habitat and the time of year. Mountain gorillas primarily consume green plant parts, while lowland gorillas consume a substantial amount of fruits. However, during the dry season, when fruits are scarce, lowland gorillas supplement their diet with seeds and tree bark.
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Gorillas of all ages climb trees to harvest fruits, which typically grow on trees. Shoots, stems, and leaves constitute approximately 85% of a gorilla's diet, but they also consume larvae, ants, rotting wood, snails, roots, and bark. Western gorillas have a broad food range, with the ability to feed on over 200 plant species, including those from the arrowroot and ginger families. Mountain gorillas, on the other hand, consume about 142 different plant species, including thistles, gallium, nettles, and celery.
Mountain gorillas spend most of their day feeding on the shoots, leaves, and stems of plants, which make up about 86% of their diet. They are selective feeders, consuming various parts of plants, including roots, stems, leaves, and fruits. Mountain gorillas inhabit the wild, specifically in Uganda, Congo, and Rwanda. Due to their high-altitude habitat, they have limited access to fruits compared to their lowland counterparts. They occasionally consume snails, ants, and grubs, which account for 2% of their diet. A mature mountain gorilla can consume over 18 kg of food daily.
Mountain gorillas use their strength to break up vegetation to access their preferred plant parts. Gorillas play an important role in their ecological niche as selective feeders, never completely depleting vegetation in one area, allowing for regrowth as they move from place to place.
Western lowland gorillas are able to feed on over 97 different plant species parts, while Eastern lowland gorilla subspecies consume parts of over 104 species of plants. The diet of the Cross River gorilla (Gorilla gorilla diehli) consists of leaves, fruits, stems, piths, and sometimes invertebrates. A mature Grauer's gorilla male can consume over 30 kg of plants each day, while a female adult can consume 18 kg.
Gorillas possess strong chewing muscles and teeth similar to those of humans, although their teeth are longer with pointed canines. They chew plant material to aid in digestion. Eastern lowland gorillas primarily inhabit the Democratic Republic of Congo, particularly Kahuzi-Biega National Park and Maiko National Park. Western gorillas predominantly occupy West African countries, including the Central African Republic, Gabon, Equatorial Guinea, the Republic of Congo, Cameroon, and the Democratic Republic of Congo.
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Infant gorillas, like all mammals, rely on their mother's milk for nourishment as they are born without teeth. Gorillas primarily follow a vegetarian diet, consuming stems, bamboo shoots, and fruits. However, western lowland gorillas also consume termites and ants, breaking open termite nests to eat the larvae.
Like most apes and humans, gorillas rely on their senses, particularly sight, touch, taste, smell, and hearing, to locate food and survive in the wild. Smell and sight are especially important when searching for food.
Subspecies and Dietary Variations
There are two species of gorilla: the eastern gorilla (Gorilla beringei) and the western gorilla (G. gorilla). Each species is further divided into two subspecies: the eastern lowland gorilla (G. b. graueri) and the mountain gorilla (G. b. beringei), and the western lowland gorilla (G. g. gorilla) and the cross river gorilla (G. g. diehli). These subspecies exhibit dietary variations based on their geographic location and available resources.
The western lowland gorilla consumes parts of at least 97 plant species, while the mountain gorilla consumes parts of at least 142 plant species and only three types of fruit due to the limited availability at high altitudes. The diet of the Cross River gorilla is less studied compared to other subspecies.
Gorillas are able to survive on vegetation such as leaves, stems, roots, vines, herbs, trees, and grasses, despite their relatively low nutritional quality. They use their strength to break apart vegetation and are selective foragers, often consuming only specific parts of a plant, such as the leaves, pith, stalk, or roots. Gorillas do not overexploit an area for food.
General Gorilla Facts
Gorillas share 98.3% of their DNA with humans, making them our closest relatives after chimpanzees and bonobos. Adult male gorillas, known as silverbacks, can weigh up to 440 pounds and reach a height of six feet when standing on two legs.
Gorillas are generally gentle and peaceful animals, avoiding conflict under normal conditions. They live in tight-knit family groups led by a dominant silverback, who directs the group's daily activities and protects them from threats. One of their most iconic behaviors is chest-beating, which can signal aggression but is also used in playful contexts.
The Role of Gorillas in Seed Dispersal
Gorillas are the largest primates, with a huge appetite for leaves, shoots, stems, roots, and fruit. An adult consumes 18â20kg of food daily, mainly foliage, and will swallow many large seeds intact. Crucially, gorillas like to build sleeping nests in areas with an open canopy, and next morning tend to poop in the vicinity before heading off. So gorillas not only disperse trees but also encourage them to grow, thereby playing a key role in maintaining West and Central Africaâs tropical forests.
Threats to Gorillas
Diseases such as Ebola, habitat destruction, and poaching threaten the four gorilla subspecies. These include the western lowland gorilla (Gorilla gorilla gorilla), found in the forests of Central Africa, the Cross River gorilla (Gorilla gorilla diehli), a critically endangered subspecies living in a small region along the Nigeria-Cameroon border, the eastern gorilla lowland gorilla, or Grauerâs gorilla (Gorilla beringei graueri), which inhabits the forests of the eastern Democratic Republic of Congo, and the mountain gorilla (Gorilla beringei beringei), famous for living in the high-altitude forests of the Virunga Mountains and Bwindi Impenetrable Forest. Most gorillas live outside of protected areas. WWF works with partners, including logging companies, to assure gorilla protection, both inside and outside formally protected areas. new gorilla sanctuaries, such as in the Congo.