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Proboscis monkey

The proboscis monkey (Nasalis larvatus) or long-nosed monkey, known as the bekantan in Malay, is a reddish-brown arboreal Old World monkey that is endemic to the south-east Asian island of Borneo. It belongs in the monotypic genus Nasalis, although the pig-tailed langur has traditionally also been included in this genus.[3]

The monkey also goes by the Malay name monyet belanda ("Dutch monkey"), or even orang belanda ("Dutchman"), as Indonesians remarked that the Dutch colonisers often had similarly large bellies and noses.

This species of monkey is easily identifiable because of its unusually large nose.

Taxonomy[edit]

Proboscis monkeys belong to the Colobinae subfamily 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]

Physical description[edit]

Closeup of a proboscis monkey face

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).[4][5][6] Further adding to the dimorphism is the large nose or proboscis of the male, which can exceed 10 cm (3.9 in) in length,[7] and hangs lower than the mouth.[8][9] Nevertheless, the nose of the female is still fairly large for a primate. The proboscis monkey has a long coat; the fur on the back is bright orange, reddish brown, yellowish brown or brick-red.[8][9] The underfur is light-grey, yellowish, or greyish to light-orange.[8][9] The face is orange-pink. 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.[8]

Behavior[edit]

Social behavior[edit]

Proboscis monkeys generally live in groups composed of one adult male, some adult females and their offspring.[10][11][12] All-male groups may also exist.[13] Some individuals are solitary, mostly males.[14] Monkey groups live in overlapping home ranges, with little territoriality,[10][11] 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.[10][11][12] Groups gather during the day and travel together, but individuals only groom and play with those in their own group.[12] One-male groups consist of 9–19 individuals, while bands can consist of as many as 60 individuals.[10][14] One-male groups typically consist of three to 12 individuals, but can contain more.[13] Serious aggression is uncommon among monkeys but minor aggression does commonly occur.[15] Overall, members of the same bands are fairly tolerant of each other. A linear dominance hierarchy exists between females.[11] 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.[13] Upon reaching adulthood, males leave their natal groups and join all-male groups.[10][14] Females also sometimes leave their natal groups, perhaps to avoid infanticide or inbreeding, reduce competition for food, or elevation of their social status.[13][14]

Proboscis monkey pair

Reproduction[edit]

Females become sexually mature at five years old. They experience sexual swelling, which involves the genitals becoming pink or reddened.[13][16] At one site, matings largely take place between February and November, while births occur between March and May.[17] Copulations tend to last for half a minute.[11][13] The male will grab the female by the ankles or torso and mount her from behind.[11] Both sexes will encourage mating, but they are not always successful.[16] When soliciting, both sexes will make pouted faces. In addition, males will sometimes vocalize and females will present their backsides.[10][16][17] Mating pairs are sometimes harassed by subadults.[16] Proboscis monkeys may also engage in mounting with no reproductive purpose, such as playful and same-sex mounting. Gestation usually last 166–200 days or slightly more.[17] Females tend to give birth at night or in the early morning. The mothers then eat the placenta and lick their infants clean.[18] 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.[11][17][18] When a resident male in a one-male group is replaced, the infants are at risk of infanticide.[19]

Communication[edit]

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.[20] Honks, roars and snarls are made during low-intensity agonistic encounters. Nonvocal displays include leaping-branch shaking, bare-teeth open mouth threats and erection[disambiguation needed] in males, made in the same situations.[11]

Ecology[edit]

Range and habitat[edit]

Juvenile proboscis monkey in Bako National Park, Malaysia

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.[21] It is most common in coastal areas and along rivers.[10] This species is restricted to lowland habitats that may experience tides.[22][23] It favors dipterocarp, mangrove and riverine forests.[10] 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.[22] This species usually stays 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 (65.6 ft) underwater. It is known to swim across rivers.[22] Aside from this, the proboscis monkey is largely arboreal and moves quadrupedally and by leaps.[4] It is known to jump off branches and descend into water.[11]

Feeding and activities[edit]

As a seasonal folivore and frugivore, the proboscis monkey eats primarily fruit and leaves.[11] 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".[24] Young leaves are preferred over mature leaves and unripe fruits are preferred over ripe fruit.[11] Being a seasonal eater, the proboscis monkey eats mostly fruit from January to May and mostly leaves from June to December.[24] Groups usually sleep in adjacent trees.[25] Monkeys tend to sleep near rivers, if they are nearby. Proboscis monkeys will start the day foraging and then rest further inland. Proboscis monkeys' daily activities consist of resting, traveling, feeding and keeping vigilant.[11] Occasionally, they chew their cud to allow more efficient digestion and food intake.[26] As night approaches, the monkeys move back near the river and forage again. Predators of the proboscis monkey include crocodiles, clouded leopards, eagles, monitor lizards and pythons. Monkeys will cross rivers at narrows or cross arboreally if possible. This may serve as predator avoidance.[27]

Proboscis monkey sitting on tree

Conservation status[edit]

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 36–40 years to 2008 due to ongoing habitat loss and hunting in some areas. 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[edit]

  1. ^ Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M, eds. Mammal Species of the World (3rd ed.). Baltimore: Johns Hopkins University Press. pp. 168–169. OCLC 62265494. ISBN 0-801-88221-4. 
  2. ^ a b c d e Meijaard, E., Nijman, V. & Supriatna, J. (2008). Nasalis larvatus. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 4 January 2009.
  3. ^ Bradon-Jones D, Eudey AA, Geissmann T, Groves CP, Melnick DJ, Morales JC, Shekelle M, and Stewart CB (2004). "Asian primate classification". International Journal of Primatology 25: 97–164. doi:10.1023/B:IJOP.0000014647.18720.32. 
  4. ^ a b Napier, J. R. and P. H. Napier. (1985) The Natural History of the Primates. Cambridge, Mass.: MIT Press ISBN 0262640333.
  5. ^ Primate Factsheets: Proboscis monkey (Nasalis larvatus) Taxonomy, Morphology, & Ecology. Pin.primate.wisc.edu. Retrieved on 2012-08-21.
  6. ^ Up Close With Borneo Primates | Special Features. Brudirect.com (2012-07-02). Retrieved on 2012-08-21.
  7. ^ Ellis D. (1986) "Proboscis monkey and aquatic ape". Sarawak Mus J 36(57):251-62.
  8. ^ a b c d Ankel-Simons F. (2007) Primate Anatomy: an introduction, 3rd Ed. San Diego: Academic Press ISBN 0080469116.
  9. ^ a b c Payne J, Francis CM, Phillips K. (1985) A field guide to the mammals of Borneo. Kuala Lumpur (MY): World Wildlife Fund Malaysia & The Sabah Society ISBN 9679994716.
  10. ^ a b c d e f g h Bennett EL, Gombek F (1993) Proboscis monkeys of Borneo. Sabah (MY):Koktas Sabah Berhad Ranau
  11. ^ a b c d e f g h i j k l Boonratana R. (1993) The ecology and behaviour of the proboscis monkey (Nasalis larvatus) in the lower Kinabatangan, Sabah. PhD dissertation, Mahidol University.
  12. ^ a b c Boonratana R (2002). "Social organisation of proboscis monkeys (Nasalis larvatus) in the lower Kinabatangan, Sabah, Malaysia". Malay Nat J 56 (1): 57–75. 
  13. ^ a b c d e f Murai T (2004). "Social behaviors of all-male proboscis monkeys when joined by females". Ecol Res 19 (4): 451–4. doi:10.1111/j.1440-1703.2004.00656.x. 
  14. ^ a b c d Boonratana R (1999). "Dispersal in proboscis monkeys (Nasalis larvatus) in the lower Kinabatangan, Northern Borneo". Tropic Biodiv 6 (3): 179–87. 
  15. ^ Yeager CP (1992). "Proboscis monkey (Nasalis larvatus) social organization: nature and possible functions of intergroup patterns of association". Am J Primatol 26 (2): 133–7. doi:10.1002/ajp.1350260207. 
  16. ^ a b c d Murai T (2006). "Mating behaviors of the proboscis monkey (Nasalis larvatus)". Am J Primatol 68 (8): 832–7. doi:10.1002/ajp.20266. PMID 16847976. 
  17. ^ a b c d Rajanathan R, Bennett EL (1990). "Notes on the social behaviour of wild proboscis monkeys (Nasalis larvatus)". Malay Nat J 44 (1): 35–44. 
  18. ^ a b Gorzitze AB (1996). "Birth-related behavior in wild proboscis monkeys (Nasalis larvatus)". Primates 37 (1): 75–8. doi:10.1007/BF02382922. 
  19. ^ Agoramoorthy G, Hsu MJ (2004). "Occurrence of infanticide among wild proboscis monkeys (Nasalis larvatus) in Sabah, Northern Borneo". Folia Primatol 76 (3): 177–9. doi:10.1159/000084380. PMID 15900105. 
  20. ^ Messeri P, Trombi M (2000). "Vocal repertoire of proboscis monkey (Nasalis larvatus, L.) in Sarawak". Folia Primatol 71 (4): 268–87. 
  21. ^ Brandon-Jones D, Eudey AA, Geissmann T, Groves CP, Melnick DJ, Morales JC, Shekelle M, Stewart C-B (2004). "Asian primate classification". Int J Primatol 25 (1): 97–164. doi:10.1023/B:IJOP.0000014647.18720.32. 
  22. ^ a b c Sebastian AC (2000). "Proboscis monkeys in Danau Sentarum National Park". Borneo Res Bull 31: 359–71. 
  23. ^ Kawabe M, Mano T (1972). "Ecology and behavior of the wild proboscis monkey, Nasalis larvatus (Wurmb) in Sabah, Malaysia". Primates 13 (2): 213–28. doi:10.1007/BF01840882. 
  24. ^ a b Yeager CP (1989) Feeding ecology of the proboscis monkey (Nasalis larvatus)). "Feeding ecology of the proboscis monkey (Nasalis larvatus)". Int J Primatol 10 10 (6): 497–530. doi:10.1007/BF02739363. 
  25. ^ Yeager CP (1990). "Proboscis monkey (Nasalis larvatus) social organization: group structure". Am J Primatol 20 (2): 95–106. doi:10.1002/ajp.1350200204. 
  26. ^ 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.  edit
  27. ^ Yeager CP (1991). "Possible antipredator behavior associated with river crossings by proboscis monkeys (Nasalis larvatus)". Am J Primatol 24 (1): 61–6. doi:10.1002/ajp.1350240107. 

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