Gorillas are classified into two main species, namely the western gorillas and eastern gorillas. The two species are named based on the location of their respective natural habitats as eastern gorillas are found in the forests of East Africa while the jungles of West Africa are home to the western gorillas. The two gorilla species are further categorized into four subspecies; western gorillas are comprised of the western lowland subspecies and the cross-river subspecies while eastern gorillas are made up of the mountain subspecies and the eastern lowland subspecies. Each of the four subspecies of the gorilla has a distinctive dietary characteristic. The different types of diets in the gorilla's subspecies are attributed to the differences in the type of vegetation found in their respective ranges of habitats. Nonetheless, all gorillas are primarily herbivores and feed mainly on leaves, shoots, barks, and fruits from the vegetation found in the respective habitats. Invertebrates also make up a small part of the diets of all gorillas subspecies. As the world’s largest great ape, adult gorillas have to consume an average of 40 pounds of food each day to sustain their large bodies.
Cross River Gorillas
One of the two subspecies which make up the western gorilla species is the cross-river subspecies which get its name from their habitat as they are found in the Cross River’s upstream area. The subspecies is the rarest in the world with its wild population being comprised of an estimated 250 individuals making it a critically endangered species. While closely related to the western lowland subspecies, the cross river gorilla has distinctive characteristics including a few morphological characteristics seen in its skull and cranial vaults. The cross-river subspecies resides in the forests of western Africa usually preferring areas found between 328 feet and 6,683 feet in altitude. However, like all other gorilla subspecies, the cross river gorilla has been struggling for sufficient space as human activity has been infringing into the gorilla’s traditional range. The cross-river subspecies is the least studied subspecies of gorilla and, therefore, little is known about the behavior or diet. Much of what is presently known about the dietary habits of the subspecies is based on analysis done on their droppings. Such studies have established that the cross river gorilla feeds primarily on fruits in periods when trees produce fruits. However, in the months between September and January when fruits are scarce, the gorillas move to a different diet made up of stems, leaves, and tree barks. These sources of food are usually derived from nutritious plants found around the gorilla’s nesting area.
Western Lowland Gorillas
The smallest subspecies of gorillas in physical size is the western lowland subspecies whose adult males average 310 pounds in weight while females have an average weight of 200 pounds. However, the subspecies has the most extensive range of all gorillas which encompasses part of Equatorial Guinea, Gabon, Cameroon, and the Republic of Congo. However, the species is still listed as critically endangered. Western lowland gorillas are exceptional in their ability to make tools from basic materials such as twigs, something that is yet to be observed in another gorilla subspecies in the wild. Adults have been observed using sticks to measure the depth of water before plunging in. The subspecies has also been studied using twigs to collect termites, ants, and other invertebrates which make up a significant portion of their diet, from holes in the ground. Like all other gorillas, the western lowland subspecies is primarily herbivorous and mainly feed on fruits. The preferred fruit for the western lowland gorillas is fleshy and rich in fiber and sugar. When fruits become scarce, the gorillas will feed on shoots, tree bark, and roots. The feeding habits of this subspecies have been well-studied, and scientists have stated that the gorillas feed on a diet that is balanced in nutrients.
Eastern Lowland Gorillas
Eastern gorillas are made up of two subspecies of mountain gorillas and eastern lowland gorillas. Eastern lowland gorillas are found in the forests of Central and East Africa and usually inhabit areas of diverse altitudes ranging from lowland forests to mountainous rainforests. Like all other gorillas, the eastern lowland subspecies is predominantly herbivorous and feed on the fruits, stems, and leaves of plants found in their habitats. Studies have established that an estimated 104 plant species make up the diet of this gorilla subspecies. Contrary to public perception, the subspecies does not feed on bananas and only destroy banana plants to feed on the pith. This dietary behavior of the subspecies puts them in constant collision with humans particularly in areas where their natural range overlaps human settlement. They are listed by the IUCN as a critically endangered species. While the eastern lowland gorilla occasionally feeds on termites and ants, the invertebrates comprise a small part of the gorilla’s diet.
As the name suggests, mountain gorillas are a subspecies of gorilla that inhabits mountainous regions of Central Africa and are found in regions between 7,200 and 14,100 feet in altitude. The remaining wild population, listed as critically endangered, is made up of an estimated 1,000 individuals and is found in the Virunga Mountains and the Albertine Rift. Due to their residency in high-altitude areas which experience cold temperatures, the mountain gorillas have a thick fur as insulation against the cold. The thick fur is characteristic of mountain gorillas and is thicker than that of any other subspecies. Mountain gorillas have 142 plant species that make up their diet. The extensive variety of plants in the mountain gorilla’s diet is the largest variety that has been recorded in any gorilla subspecies. However, due to the gorilla’s high-altitude habitat which is not conducive for the growth of fruiting plants, only three fruits comprise the mountain gorilla’s diet. The bulk of the gorilla’s diet is made up of stems and leaves which account for an estimated 86% of the mountain gorilla’s diet. The next most important parts of the plant as far as mountain gorilla’s diet is concerned are the roots (which make up about 7% of the gorilla’s diet) and flowers (which account for 3% of the gorilla’s diet). While the mountain gorilla primarily subsists on a vegetarian diet, the subspecies also occasionally feed on grubs, snails, and ants which are estimated to make up about 2% of its diet.
About the Author
Benjamin Elisha Sawe holds a Bachelor of Arts in Economics and Statistics and an MBA in Strategic Management. He is a frequent World Atlas contributor.
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