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The Depletion of the Proboscis Monkey

Figure 1: Proboscis Monkeys in Borneo (New England Primate Conservatory, 2015)


The Proboscis monkey is an incredibly unique and distinct species, recognized for their large, probe-like noses. Nicknamed the “Cows of the Canopy” (BBC, 2015), this species resides in the Borneo forest, located on the Equator in Southeast Asia. Unfortunately, over the years, Proboscis monkeys have become an endangered species. With only about an estimated 20,000 left in the forests of Borneo, (New England Primate Conservancy, 2015) with the depletion of Proboscis monkeys comes the depletion of its habitat and an imbalance in the relationship between predators and prey. Before learning about how to prevent the extinction of Proboscis monkeys, it is important to recognize their characteristics, roles and abilities as complex primates.

Figure 2: The Proboscis Monkey eating leaves (Hakai Magazine, 2020)

The Biology

Nasalis lavartus, also known as the Proboscis monkey, are mammals, apart of the primate family. They are widely recognized for their probe-like noses, a physical trait only male Proboscis monkeys possess. They are omnivores, with their diet mostly consisting of leaves, seeds, unripe fruits and occasionally, insects. Spanning between 24 and 28 inches, (New England Primate Conservancy, 2015) Proboscis monkeys have a unique digestive system consisting of 8 stomachs (Hakai Magazine, 2020). The design of their digestive system allows them to digest and chew the cud within the leaves. In comparison to most monkeys, they are good swimmers, diving into nearby waters to travel in search of food. Their ability to swim comes from their evolved trait of webbed feet. This makes the Proboscis monkey an efficient animal, whether they’re on land or in water.

Predators and Deforestation

As the number of Proboscis monkeys continues to deplete, three factors can be attributed to the reducing number: deforestation, illegal hunting and a surplus of predators. Deforestation in Borneo sustains at a rate of 1.7%, although in mangrove forests, the rate increases up to 7.92% (New England Primate Conservancy, 2015). The extermination of rainforests in Borneo are caused by the production of timber, palm oil plantations and settlements, depleting massive regions of the proboscis monkey’s habitat. Without a habitat, Proboscis monkeys are vulnerable to illegal hunting and predators. Humans hunt Proboscis monkeys as a delicacy or in some cases, for the bezoar stones found in their stomachs to produce traditional Chinese medicine (New England Primate Conservancy, 2015). While they are vulnerable to humans, with the depletion of their habitat, they are vulnerable to nearby predators such as the crocodile and jaguar. Proboscis monkeys are “forced to descend from trees more frequently and often must travel perilously long distances to find food” (BBC, 2015).

Figure 3: The Proboscis Monkey travelling from place to place (World Land Trust)


The Proboscis monkey is officially listed as an endangered species under the IUCN Red List of Threatened Species. The IUCN Red List is prominent for reporting about the several endangered and extinct species of mammals, amphibians, reptiles and more. An estimate of about 20,000 Proboscis monkeys are still left in the wild (IUCN, 2015). Organizations such as the WWF are dedicated to saving and protecting endangered species such as the Proboscis monkey, urging people to cut back on deforestation and donate money to their conservation and protection (WWF, 2023). Government legislation is necessary to protect Proboscis monkeys but as of now, Indonesia has not spoken up about protecting Borneo forests.


The Proboscis monkey is one of the most uniquely evolved species in the forests of Borneo. From their probe-like noses to their complex digestive systems to their ability to swim and thrive in rainforest environments, they are incredibly gifted in their ability to thrive as a species. With the loss of their habitat and surplus of predators, however, the global population could be saying a permanent farewell to this species of primate. To protect, conserve and ensure the survival of Proboscis monkeys, the push for wildlife organizations and governments for mandates and support are necessary.

(Proboscis Monkey) References
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