Big Nose, Big Problems: The Future of the Proboscis Monkey

By Nadine Galle and Aleksandra Dragozet

Figure 1. The bigger the nose, the louder the call. See here a male proboscis monkey calling out in warning (Source: Arkive)


Who is the Proboscis Monkey?

The proboscis monkey (Nasalis larvatus), also known as the long nosed monkey, has one of the most unusual appearances in the family Cercopithecidae. The local people of this species’ home, which ranges throughout Borneo, including Brunei, Kalimantan (Indonesia), and Sabah and Sarawak (Malaysia), used to refer to these monkeys as “Dutch monkeys” since they resembled Dutch colonialist sailors and plantations owners of the region with their long noses and overweight pot bellies[i]. Apart from having long noses, this species is also known to exhibit great sexual dimorphism with a difference in size between sexes, as the males are much larger than the females with a visible bright red penis and black scrotum[i]. These monkeys are excellent swimmers with partially webbed feet and can often be seen jumping into waters to cross rainforest rivers.

Figure 2. Note the male proboscis monkey’s red penis and black scrotum. Another indiction of high sexual dimorphism (Source: Arkive)

Figure 3. Note the high level of sexual dimorphism in the sizes between the two sexes. See female on the left, male on the right (Source: Arkive)

Where are they?

Sarawak has less than 1,000 proboscis monkeys remaining, which are patchily disturbed throughout, while Brunei has only one population in their estuaries[ii]. Kalimantan supports the largest population, which has fluctuated from 1000 to less than 100 over the years depending on the threats the species they exposed to. East Kalimantan used to have populations in the thousands until the early 1990s when the coastal swamps were turned into shrimp farms[ii].

Figure 4. The proboscis monkey is listed as “endangered” on the IUCN Red List (Source: IUCN)


What is their habitat like?

The habitat of this species includes riparian-riverine forest, coastal lowland forest, peat swamp, freshwater swamp forest, and mangroves. The diet of this species is mostly folivorous and frugivorous, as it prefers unripened non-fleshy fruits and young leaves but it does fluctuate throughout the year depending on local availability[ii].

Figure 5. Proboscis monkeys being social in their typical mangrove habitat (Source: Arkive)

Proboscis Monkey vs. Habitat Destruction

Unfortunately, this species is listed as endangered mainly due to mass habitat destruction. Having a riverine and coastal habitat makes this species especially vulnerable to habitat destruction, as these areas are used for cultivation and logging, which has lead to the recent population decline. In addition, the Malaysian population is under continued threat of deforestation to make room for increased oil-palm plantations[i]. Proboscis monkeys are unable to cross the plantations, greatly disrupting their foraging, social structure, mating patterns, and wild habitat.

Proboscis Monkeys vs. Poachers

The rather lethargic behavior of this species makes it more vulnerable to poaching, which can lead to whole populations going extinct with little effort by hunters. Along with being hunted for food as bush meat this species is also hunted for bezoar stones, which are masses usually stuck in the stomach believed to have healing powers in traditional Chinese medicine. Due to all of these threats, in the past 35-40 years, the populations have declined by more than 50 %[ii].

VIDEO: Proboscis Monkeys Threatened by Malaysia Oil-Palm Plantations


Proboscis Monkeys and the Law

The threats the proboscis monkey faces are clear and imminent. Fortunately, several conservation efforts are underway. In the global conservation of the proboscis monkey, the species is listed under CITES Appendix I. Appendix I lists the species which are most endangered among CITES-listed plants and animals and are therefore prohibited from all international trade. In addition to its listing under CITES, the proboscis monkey is also protected by law throughout its native Borneo range. Prevalent in both the Malaysian and Indonesian regions of Borneo, it is protected through a multitude of nature reserves totaling sixteen protected regions.

Zoo Keeping for Conservation

Keeping the proboscis monkey in captivity, however controversial, can be extremely valuable in the study and conservation of this unique primate species. Since 1998, Singapore Zoo has been most successful in proboscis monkey captivity, and now houses one of the largest collections of the species in the world. The program owes its success mostly to a well-substituted diet, as the primate is highly adapted to eat slow-growing mangrove leaves. The proboscis monkey is highly sensitive to digestive complications, human interference, noise pollution, disease, and stress related illnesses when kept in captivity so Singapore’s success is seen as a successful, but by no means easily achievable, accomplishment. Instead of the development of further zoo exhibitions, these resources should be invested locally in proboscis monkey sanctuaries in Borneo. Currently, the Labuk Bay proboscis monkey sanctuary (established in 1994) and the Kinabatangan Wildlife Sanctuary (established in 2005) in Sabah, Borneo play an important role in the conservation of the wild populations by providing a safe reserve, free from illegal poaching and habitat destruction. Now critically acclaimed attractions, tourists can observe the semi-wild monkeys and take meaningful action for their conservation through donations and volunteer work.

Figure 6. Proboscis monkeys enjoying fruit at the Labuk Bay Proboscis Monkey Sanctuary (Source: Sabah Tourism)

Protecting their Habitat

Conservation actions are also being implemented to protect the ever-diminishing proboscis monkey habitat. Heavy habitat fragmentation hinders their ability to disperse, mate, interchange its gene pool, and acquire adequate food resources. To combat this, Sabah Forestry Department (SFD) has put forward its strategic plan for forest resource development. Sha et al.’s paper[iii] on the status and conservation of proboscis monkeys in Sabah suggests greater efforts must be dedicated to restoring remnant habitat patches as well as re-establishing corridors along fragmented river systems, preferably linking major populations through a protected area network, as part of a conservation strategy that extends beyond borders for the protection of the species across its range. It is clear the future conservation of the proboscis monkey in the wild heavily depends on the reestablishment of proper habitat.

Figure 7. Motion camera shot of three proboscis monkeys capturing the importance of the newly implemented forest corridor that links two forest fragments in the Lower Kinabatangan Wildlife Sanctuary in Sabah, Borneo (Source: Sabah Wildlife Department and the Danau Girang Field Centre)

Translocation Controversy

The most controversial conservation strategy to protect the proboscis monkey is the translocation of wild populations. The increasing and seemingly inevitable (unless immediate action is taken) loss of suitable habitat could lead to the translocation of individuals who are at risk of local extinction. However, as seen in zoo translocation failures, this species is highly sensitive and tend to have high mortality rates when moving. Translocation can also introduce new diseases and parasites to once unaffected areas, disrupt the ecosystem and food resources, and unsettle the monkey’s social structure[iv]. Even if these risks are avoided, the real problem lies in the translocation destination. Borneo’s rainforest, like so much other tropical rainforest in the region is under constant threat of destruction. If translocation were deemed absolutely necessary, the specie’s final home should not only be appropriate to the monkey’s various needs – but entirely safe from habitat destruction. With its many risks, this debatable method is extremely irresponsible unless the necessary precautions have been considered.

Figure 8. Will YOU take my conservation seriously? (Source: QuickMeme)


What Conservation Actions Should Be Used?

Through analysis of the conservation actions, it is clear the monkey’s long-term survival is dependent on the protection given by gazetted parks and wildlife sanctuaries. Borneo’s governing parties must enforce better protection, establish stricter regulations on land use, and minimize environmental damage to the specie’s natural habitats, in order to make a lasting impact on the conservation of the proboscis monkey. In addition, forest corridors can assist in the movement of individuals and genetic material through undisturbed landscapes, enhance meta-population survival through improving individual survival, and supplement population growth. Also, wildlife sanctuaries which provide extra food, healthcare, and a safe haven for the monkeys may be valuable especially when tourist admission fees help fund further conservation efforts, but their questionable impacts on the monkeys must be researched further. However, each conservation action has risks associated with it, and none can be used on their own. But in combination with one another, despite their risks, this combined conservation action is realistic and effective. Furthermore, while the proboscis monkey may not be the most charismatic, it’s “ugly” charm may in fact benefit its conservation efforts. All in all, the likelihood of success with this joint conservation action is high so long as it is implemented soon, effectively, and maintained by good governance and regulation. Do this, and do it well, and the proboscis monkey may have a very bright future after all.

VIDEO: A Day in the Life of the Proboscis Monkey



[i] Richardson, M. (2006). Proboscis monkey videos, photos and facts – Nasalis larvatus – ARKive. ARKive – Discover the world’s most endangered species. Retrieved April 1, 2013, from

[ii] Meijaard, E., Nijman, V. & Supriatna, J. (2008). Nasalis larvatus in IUCN 2012. IUCN Red List of Threatened Species (2). Retrieved April 12, 2013, from

[iii] Sha, J., Bernard, H., & Nathan, S. (2008). Status and conservations of Proboscis monkeys (Nasalis larvatus) in Sabah, Malaysia. Primate Conservation International 23 (1), 107-120.    Retrieved April 1, 2013, from

[iv] Yeager, C. and Silver, S. (1999). Translocation and rehabilitation as primate conservation tools: are they worth the cost? The Non-Human Primates, 164-169.

Pictures Cited

Figure 1: Male proboscis monkey. (2005). Retrieved April 5, 2013 from

Figure 2: Male proboscis monkey scrotum. (2005). Retrieved April 5, 2013 from

Figure 3: Male and female proboscis monkey. (2005). Retrieved April 5, 2013 from

Figure 4: Nasalis larvatus endangered status. (2012). Retrieved April 10, 2013 from

Figure 5: Proboscis monkey in mangrove habitat. (2005). Retrieved April 5, 2013 from

Figure 6: Proboscis monkeys feeding at Labuk Bay Proboscis Monkey Sanctuary. (2009). Retrieved April 11, 2013 from

Figure 7: The endangered proboscis monkey. (2011). Retrieved April 15, 2013 from

Figure 8: Proboscis monkey meme. (2012) Retrieved April 16, 2013 from

Videos Cited (in order of appearance)

1) Noteworthy News. (2012, January 11). Proboscis monkeys threatened by malaysia oil-palm plantations [Video file]. Retrieved from

2) National Geographic Wild. (2012, July 11). World’s Weirdest: Proboscis Monkey [Video file]. Retrieved from

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