Proboscis monkey

The proboscis monkey (Nasalis larvatus) or long-nosed monkey is an arboreal Old World monkey with an unusually large nose, a reddish-brown skin color and a long tail. It is endemic to the southeast Asian island of Borneo and is found mostly in mangrove forests and on the coastal areas of the island.^[3]

Proboscis monkey
Conservation status
Endangered (IUCN 3.1)^[2]
CITES Appendix I (CITES)^[2]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Primates
Suborder:	Haplorhini
Infraorder:	Simiiformes
Family:	Cercopithecidae
Subfamily:	Colobinae
Tribe:	Presbytini
Genus:	Nasalis É. Geoffroy, 1812
Species:	N. larvatus^[1]
Binomial name
Nasalis larvatus^[1] Wurmb, 1787

This species co-exists with the Bornean orangutan and monkeys such as the silvery lutung.^[4] It belongs in the monotypic genus Nasalis.^[5][6]

Taxonomy and names

Proboscis monkeys belong to the subfamily Colobinae of the Old World monkeys. The two subspecies are:^[2]

• N. l. larvatus (Wurmb, 1787), which occupies the whole range of the species
• N. l. orientalis (Chasen, 1940), restricted to north-east Kalimantan

However, the difference between the subspecies is small, and not all authorities recognise N. l. orientalis.^[2]

The species is known as monyet belanda in Malaysia^[7][8] or bekantan in Indonesia.

Description

 

Male

 

Female

The proboscis monkey is a large species, being one of the largest monkey species native to Asia. Only the Tibetan macaque and a few of the gray langurs can rival its size. Sexual dimorphism is pronounced in the species. Males have a head-body length of 66 to 76.2 cm (26.0 to 30.0 in) and typically weigh 16 to 22.5 kg (35 to 50 lb), with a maximum known weight of 30 kg (66 lb). Females measure 53.3 to 62 cm (21.0 to 24.4 in) in head-and-body length and weigh 7 to 12 kg (15 to 26 lb), with a maximum known mass of 15 kg (33 lb).^[9][10][11] Further adding to the dimorphism is the large nose or proboscis of the male, which can exceed 10.2 cm (4.0 in) in length,^[12] and hangs lower than the mouth. Theories for the extensive length of their nose suggest it may be sexual selection by the females, who prefer louder vocalisations, with the size of the nose increasing the volume of the call.^[13][14][15] The nose is smaller in the female and is upturned in the young.^[16] Nevertheless, the nose of the female is still fairly large for a primate. The skull of the proboscis monkey has specialized nasal cartilages that support the large nose.^[3] The proboscis monkey has a long coat; the fur on the back is bright orange, reddish brown, yellowish brown or brick-red.^[14][15] The underfur is light-grey, yellowish, or greyish to light-orange.^[14][15] Infants are born with a blue coloured face that at 2.5 months darkens to grey. By 8.5 months of age, the face has become cream coloured like the adults.^[17] The male has a red penis with a black scrotum. Both sexes have bulging stomachs that give the monkeys what resembles a pot belly. Many of the monkeys' toes are webbed.^[14]

 

Nasal cartilages that were left intact in a specimen skull in order to show the structures that support the nose

Behavior

Social behavior

 

Jumping (composite image, from right to left), Labuk Bay, Sabah, Borneo, Malaysia

Proboscis monkeys generally live in groups composed of one adult male, some adult females and their offspring.^[18][19][20] All-male groups may also exist.^[21] Some individuals are solitary, mostly males.^[22] Monkey groups live in overlapping home ranges, with little territoriality,^[18][19] in a fission-fusion society, with groups gathering at sleeping sites as night falls. There exist bands which arise when groups come together and slip apart yet sometimes groups may join to mate and groom.^[18][19][20] Groups gather during the day and travel together, but individuals only groom and play with those in their own group.^[20] One-male groups consist of 3 to 19 individuals,^[21][18] while bands can consist of as many as 60 individuals.^[18][22] Serious aggression is uncommon among the monkeys but minor aggression does occur.^[23] Overall, members of the same bands are fairly tolerant of each other. A linear dominance hierarchy exists between females.^[19] Males of one-male groups can stay in their groups for six to eight years. Replacements in the resident males appear to occur without serious aggression.^[21] Upon reaching adulthood, males leave their natal groups and join all-male groups.^[18][22] Females also sometimes leave their natal groups, perhaps to avoid infanticide or inbreeding, reduce competition for food, or elevation of their social status.^[21][22]

In Sabah, Malaysia, proboscis monkeys have been observed in mixed-species groups with silvery lutungs, and interspecific mating and a possible hybrid has been observed.^[6] Researchers believe this may be a result of the two species being confined to a small patch of riverine forest due to deforestation in order to plant oil palm trees.^[6]

Reproduction

Females become sexually mature at the age of five years. They experience sexual swelling, which involves the genitals becoming pink or reddened.^[21][24] At one site, matings largely take place between February and November, while births occur between March and May.^[25] Copulations tend to last for half a minute.^[19][21] The male will grab the female by the ankles or torso and mount her from behind.^[19] Both sexes will encourage mating, but they are not always successful.^[24] When soliciting, both sexes will make pouted faces. In addition, males will sometimes vocalize and females will present their backsides and shake their head from side to side.^{[18][24][25][17]} Mating pairs are sometimes harassed by subadults.^[24] Proboscis monkeys may also engage in mounting with no reproductive purpose, such as playful and same-sex mounting, and females will attempt to initiate copulation even after they have conceived.^[17] Gestation usually last 166–200 days or slightly more.^[25] Females tend to give birth at night or in the early morning. The mothers then eat the placenta and lick their infants clean.^[26] The young begin to eat solid foods at six weeks and are weaned at seven months old. The nose of a young male grows slowly until reaching adulthood. The mother will allow other members of her group to hold her infant.^[19][25][26] When a resident male in a one-male group is replaced, the infants are at risk of infanticide.^[27]

Communication

Proboscis monkeys are known to make various vocalizations. When communicating the status of group, males will emit honks. They have a special honk emitted towards infants, which is also used for reassurance. Males will also produce alarm calls to signal danger. Both sexes give threat calls, but each are different. In addition, females and immature individuals will emit so-called "female calls" when angry.^[28] Honks, roars and snarls are made during low-intensity agonistic encounters. Nonvocal displays include leaping-branch shaking, bare-teeth open mouth threats and erection in males, made in the same situations.^[19]

Ecology

Range and habitat

The proboscis monkey is endemic to the island of Borneo and can be found on all three nations that divide the island: Brunei, Indonesia, and Malaysia.^[29] It is most common in coastal areas and along rivers.^[18] This species is restricted to lowland habitats that may experience tides.^[30][31] It favors dipterocarp, mangrove and riverine forests.^[18] It can also be found in swamp forests, stunted swamp forests, rubber forests, rubber plantations, limestone hill forests, nypa swamps, nibong swamps, and tall swamp forests, tropical heath forests and steep cliffs.^[30] This species usually stays within at least a kilometer from a water source. It is perhaps the most aquatic of the primates and is a fairly good swimmer, capable of swimming up to 20 m (66 ft) underwater. It is known to swim across rivers.^[30] Aside from this, the proboscis monkey is largely arboreal and moves quadrupedally and by leaps.^[9] It is known to jump off branches and descend into water.^[19]

Feeding and activities

As a seasonal folivore and frugivore, the proboscis monkey eats primarily fruit and leaves.^[19] It also eats flowers, seeds and insects to a lesser extent. At least 55 different plant species are consumed, "with a marked preference for Eugenia sp., Ganua motleyana and Lophopetalum javanicum".^[32] Young leaves are preferred over mature leaves and unripe fruits are preferred over ripe fruit.^[19] Being a seasonal eater, the proboscis monkey eats mostly fruit from January to May and mostly leaves from June to December.^[32] Groups usually sleep in adjacent trees.^[33] Monkeys tend to sleep near rivers, if they are nearby. Proboscis monkeys will start the day foraging and then rest further inland. Their daily activities consist of resting, traveling, feeding and keeping vigilant.^[19] Occasionally, they chew their cud to allow more efficient digestion and food intake.^[34] As night approaches, the monkeys move back near the river and forage again. Predators (potential or confirmed) of the proboscis monkey include crocodilians (likely false gharials and saltwater crocodiles), clouded leopards, sun bears and reticulated pythons as well as, for probably young or sickly monkeys, eagles (possibly larger Nisaetus, Haliaeetus, crested serpent eagle or black eagles), large owls and monitor lizards.^[35][36] Monkeys will cross rivers at narrows or cross arboreally if possible. This may serve as predator avoidance.^[37]

•  

  Juvenile, Labuk Bay, Sabah, Borneo, Malaysia

Conservation status

The proboscis monkey is assessed as endangered in the IUCN Red List of Threatened Species and listed in Appendix I of CITES. Its total population has decreased by more than 50% in the past 36–40 years to 2008 due to ongoing habitat loss because of logging and oil palm plantations, and hunting in some areas due to the species being treated as a delicacy, as well as its use in traditional Chinese medicine.^[17] The population is fragmented: the largest remaining populations are found in Kalimantan; there are far fewer in Sarawak, Brunei and Sabah.^[2] The proboscis monkey is protected by law in all regions of Borneo. In Malaysia, it is protected by a number of laws including the Wildlife Protection Act (federal law), the Wildlife Protection Ordinance 1998 (Chapter 26) and Wildlife Conservation Enactment 1997 (Sabah state law).

The proboscis monkey can be found in 16 protected areas: Danau Sentarum National Park, Gunung Palung National Park, Kendawangan Nature Reserve, Kutai National Park, Lesan Protection Forest, Muara Kaman Nature Reserve, Mandor Reserve and Tanjung Puting National Park in Indonesia; Bako National Park, Gunung Pueh Forest Reserve, Kabili-Sepilok Forest Reserve, Klias National Park, Kulamba Wildlife Reserve, Lower Kinabatangan Wildlife Sanctuary, Sungei Samunsam Wildlife Sanctuary and Ulu Segama Reserve in Malaysia.^[2]

References

1. Groves, C. P. (2005). "Order Primates". In Wilson, D. E.; Reeder, D. M (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 168–169. ISBN 978-0-8018-8221-0. OCLC 62265494.
2. Boonratana, R.; Cheyne, S.M.; Traeholt, C.; Nijman, V. & Supriatna, J. (2021). "Nasalis larvatus". IUCN Red List of Threatened Species. 2021: e.T14352A195372486. doi:10.2305/IUCN.UK.2021-1.RLTS.T14352A195372486.en. Retrieved 17 January 2022.
3. "Proboscis monkey". Animal Diversity Web. December 2019. Retrieved 11 December 2019.
4. "Economics, Ecology and the Environment: "Conservation of the Proboscis Monkey and the Orangutan in Borneo: Comparative Issues and Economic Considerations"" (PDF). March 2007. {{cite journal}}: Cite journal requires |journal= (help)
5. Bradon-Jones D., Eudey A. A., Geissmann T., Groves C. P., Melnick D. J., Morales J. C., Shekelle M., Stewart C. B. (2004). "Asian primate classification". International Journal of Primatology. 25: 97–164. doi:10.1023/B:IJOP.0000014647.18720.32. S2CID 29045930.{{cite journal}}: CS1 maint: uses authors parameter (link)
6. Lhota, S.; Yap, J.L.; Benedict, M.L.; et al. (26 April 2022). "Is Malaysia's "mystery monkey" a hybrid between Nasalis larvatus and Trachypithecus cristatus? An assessment of photographs". International Journal of Primatology. 43 (3): 513–532. doi:10.1007/s10764-022-00293-z. PMC 9039274. PMID 35498121.
7. Rosmah Dain (14 September 2011). "Sabah 'benteng' terakhir Proboscis". Utusan Malaysia.
8. "Bertemu monyet belanda dan Orang Utan di Kinabatangan". Sinar Harian. 29 January 2013.
9. Napier, J. R. and P. H. Napier. (1985) The Natural History of the Primates. Cambridge, Massachusetts: MIT Press ISBN 0262640333.
10. Primate Factsheets: Proboscis monkey (Nasalis larvatus) Taxonomy, Morphology, & Ecology. Pin.primate.wisc.edu. Retrieved on 2012-08-21.
11. Up Close With Borneo Primates| Special Features. Brudirect.com (2012-07-02). Retrieved on 2012-08-21.
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14. Ankel-Simons F. (2007) Primate Anatomy: an introduction, 3rd Ed. San Diego: Academic Press ISBN 0080469116.
15. Payne J., Francis C. M., Phillips K. (1985) A field guide to the mammals of Borneo. Kuala Lumpur (MY): World Wildlife Fund Malaysia & The Sabah Society ISBN 9679994716.
16. "proboscis monkey". www.britannica.com. Encyclopedia Britannica Inc. 19 Feb 2020. Retrieved 11 Feb 2022.
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19. Boonratana R. (1993) The ecology and behaviour of the proboscis monkey (Nasalis larvatus) in the lower Kinabatangan, Sabah. PhD dissertation, Mahidol University.
20. Boonratana R. (2002). "Social organisation of proboscis monkeys (Nasalis larvatus) in the lower Kinabatangan, Sabah, Malaysia". Malay Nat. J. 56 (1): 57–75.
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22. Boonratana R. (1999). "Dispersal in proboscis monkeys (Nasalis larvatus) in the lower Kinabatangan, Northern Borneo". Tropic Biodiv. 6 (3): 179–187.
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25. Rajanathan R., Bennett E. L. (1990). "Notes on the social behaviour of wild proboscis monkeys (Nasalis larvatus)". Malay Nat. J. 44 (1): 35–44.{{cite journal}}: CS1 maint: uses authors parameter (link)
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27. Agoramoorthy G., Hsu M. J. (2004). "Occurrence of infanticide among wild proboscis monkeys (Nasalis larvatus) in Sabah, Northern Borneo". Folia Primatol. 76 (3): 177–179. doi:10.1159/000084380. PMID 15900105. S2CID 20111145.{{cite journal}}: CS1 maint: uses authors parameter (link)
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29. Brandon-Jones D., Eudey A. A., Geissmann T., Groves C. P., Melnick D. J., Morales J. C., Shekelle M., Stewart C. B. (2004). "Asian primate classification". Int. J. Primatol. 25 (1): 97–164. doi:10.1023/B:IJOP.0000014647.18720.32. S2CID 29045930.{{cite journal}}: CS1 maint: uses authors parameter (link)
30. Sebastian A. C. (2000). "Proboscis monkeys in Danau Sentarum National Park". Borneo Res. Bull. 31: 359–371.
31. Kawabe M., Mano T. (1972). "Ecology and behavior of the wild proboscis monkey, Nasalis larvatus (Wurmb) in Sabah, Malaysia". Primates. 13 (2): 213–228. doi:10.1007/BF01840882. S2CID 20269823.{{cite journal}}: CS1 maint: uses authors parameter (link)
32. Yeager C. P. (1989). "Feeding ecology of the proboscis monkey (Nasalis larvatus)". Int. J. Primatol. 10 (6): 497–530. doi:10.1007/BF02739363. S2CID 23442969.
33. Yeager C. P. (1990). "Proboscis monkey (Nasalis larvatus) social organization: group structure". Am. J. Primatol. 20 (2): 95–106. doi:10.1002/ajp.1350200204. PMID 31963992. S2CID 85675872.
34. Matsuda, I.; Murai, T.; Clauss, M.; Yamada, T.; Tuuga, A.; Bernard, H.; Higashi, S. (2011). "Regurgitation and remastication in the foregut-fermenting proboscis monkey (Nasalis larvatus)". Biology Letters. 7 (5): 786–789. doi:10.1098/rsbl.2011.0197. PMC 3169055. PMID 21450728.
35. Feilen, K. L., & Marshall, A. J. (2014). Sleeping site selection by proboscis monkeys (Nasalis larvatus) in West Kalimantan, Indonesia. American journal of primatology, 76(12), 1127-1139.
36. Stuebing, R. B., Bezuijen, M. R., Auliya, M., & Voris, H. K. (2006). The current and historic distribution of Tomistoma schlegelii (the False Gharial)(Müller, 1838)(Crocodylia, Reptilia). The Raffles Bulletin of Zoology, 54(1), 181-197.
37. Yeager C. P. (1991). "Possible antipredator behavior associated with river crossings by proboscis monkeys (Nasalis larvatus)". Am. J. Primatol. 24 (1): 61–66. doi:10.1002/ajp.1350240107. S2CID 84996963.

External links

 

Wikispecies has information related to the proboscis monkey.

 

Wikimedia Commons has media related to the proboscis monkey.

• ARKive –
• Primate Info Net Nasalis Factsheets
• Save the Proboscis Monkeys Petition and weblog with info on the rare, endangered species.
• A Video about proboscis monkeys by National Geographic
• John C. M. Sha, Ikki Matsuda & Henry Bernard (2011)
• John C. M. Sha, Henry Bernard, and Senthival Nathan (2008) Status and Conservation of Proboscis Monkeys in Sabah, East Malaysia