Proboscis monkey

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

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 - a treatment still preferred by some.^[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 a similarly large belly and nose.

Taxonomy

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

• Nasalis larvatus larvatus (Wurmb, 1787), which occupies the whole range of the species;
• Nasalis larvatus 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]

Description

Closeup of a Proboscis monkey face

The proboscis monkey is sexuality dimorphic. Males have a head-body length averaging 75.5 cm (29.7 in) and weigh on average 20kg (44.1 lb). Females average 62 cm (24.4 in) in length and weigh half as much as the males.^[4] Further adding to the dimorphism is the large nose or proboscis of the male, which can exceed 10cm (3.9 in) in length^[5], dwarfing that of the female, and hangs lower than the mouth.^[6][7] Nevertheless, the nose of the female is still fairly large for a primate. The proboscis monkey has a nearly long coat. Dorsally, the fur is bright orange, reddish brown, yellowish brown or brick-red.^[6][7] The fur is light-grey, yellowish, or greyish to light-orange ventrally.^[6][7] The face is orange-pink. The male has a red penis with a black scrotum. Both sexes have over-sized stomachs that protrude and give the monkeys what resembles a pot belly. Many of the monkey’s toes are webbed.^[6]

Ecology

Range and habitat

Proboscis monkey in the trees at dawn

The proboscis monkey is found only on the island of Borneo and can be found on all three nations that divide the island: Brunei, Indonesia, and Malaysia.^[8] It is largely restricted to coastal areas and along rivers.^[9] The monkey lives only in lowland habitats such as coastal and riparian habitat, many of which are flooded by tides.^[10][11] It prefers dipterocarp, mangrove and riverine forests.^[9] It can also be found in swamp forests, stunted swamp forests, rubber forests, rubber plantations, limestone hill forests, nipa swamps, nibong swamps, and tall swamp forests, tropical heath forests and steep cliffs.^[10] This species is rarely found more than a kilometer from water sources. It is perhaps the most aquatic of the primates and is a fairly good swimmer, capable of swimming up to 20m (65.6 ft) when completely submerged. It is known to swim across rivers.^[10] Aside from this, the proboscis monkey is largely arboreal and moves quadrupedally and by leaping.^[4] It is known to leap from high branches and into water.^[12]

Proboscis monkey sitting on tree

Feeding and activities

As a seasonal folivore and frugivore, the proboscis monkey eats primarily fruit and leaves. ^[12] It also eats flowers seeds and insects to a lesser extent. At least 55 different plant species have been recorded used as food sources, with a marked preference for Eugenia sp., Ganua motleyana and Lophopetalum javanicum.^[13] Young leaves are preferred over mature leaves and unripe fruits are preferred over ripe fruit. ^[12] Being a seasonal eater, the proboscis monkey eats mostly fruit from January to May and mostly leaves from June to December.^[13] Groups usually sleep in one or several trees that are nearby.^[14] In habitats near rivers, monkeys sleep near the river. Proboscis monkeys will start the day feeding and then move further inland. Proboscis monkeys spend most of the daily resting, traveling, feeding and keeping vigilant.^[12] Before dark, the monkeys move back near the river and feed 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.^[15]

Life history

Social behavior

Proboscis monkey pair

Proboscis monkeys generally live in groups consisting of one adult male, some adult females and their offspring.^[9][12][16] Other groups also exist such as all-male groups as well as less documented kinds.^[17] There are some individuals that are solitary, most of which are males.^[18] Monkey groups leave in home ranges that overlap and there is little territorial behavior.^[9][12] Proboscis monkeys live in a fission-fusion society, with groups coming together at sleeping sites at the end of the day. There exist bands which are formed with the fission and fusion of groups.^[9][12][16] Groups all meet during the day and travel together, but individuals do not groom or play with those from other groups.^[16] One-male groups range from 9-19 individuals while bands can consist of as many as 60 individuals.^[9][18] One-male groups usually have 3-12 individuals but can be larger.^[17] Serious aggression is uncommon among monkeys but minor aggression does commonly occur.^[19] Overall, members of the same bands are fairly tolerant of each other. A linear dominance hierarchy exists among both males and females.^[12] Male of one-male groups can stay in their groups for 6-8 years. Replacements in the resident males appear to occur without serious aggression.^[17] Upon reaching adulthood, males leave their natal groups and join all-male groups.^[9][18] Females also sometimes leave their natal groups, perhaps to avoid infanticide or inbreeding, reduce competition for food or increase their dominance status.^[18][17]

Juvenile Proboscis monkey in Bako National Park, Malaysia

Reproduction

Females become sexually mature at 5 years old. They show sexual swelling which involves the genitals becoming pink or reddened.^[17][20] At one site, mating peak in mid-year and births peak between March and May.^[21] Copulations tend to last for half a minute.^[17][12] The male will grasp the female by the ankles or torso and mount her from the rear.^[12] Both sexes will solicit mating but they are not always successful.^[20] When soliciting, both sexes will make a pouted face. In addition, males will sometimes vocalize and females will present her backside to a male.^[20][9][21] Copulating pairs are sometimes harassed by sub-adults.^[20] Proboscis monkey may also engage in non-reproductive mounting, such as playful and same-sex mounting.^[21] Gestation usually last 166-200 days or slightly more.^[21] Births tend to take place at night or in the early morning. The mother then eats the placenta and licks her infant clean.^[22] The young eat their first solid foods at 6 weeks and are weaned at 7 months. The nose of a young male grows slowly until reaching adulthood. The mother will allow other members of her group to hold her infant.^[12][21][22] When a resident male in a one-male groups is replaced, the infants are at risk of infanticide.^[23]

Communication

Proboscis monkey are known to make various vocalizations. When communicating information on group cohesion, male will emit honks. They have a special honk emitted towards infants, which has the same function and is also used for reassurance. Males will also emit alarm calls to signal danger. Males and females both give threat calls, but each are different. In addition females and immature individuals will emit so called "female calls" calls when agitated.^[24] Honks, roars and snarls are made during low intensity agonistic encounters. Non-vocal displays include leaping-branch shaking, bare-teeth open mouth threats and the erect penis of males, made during agonistic encounters.^[12]

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 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 is known to occur 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. (2005). Wilson, D. E., & Reeder, D. M, eds. ed. Mammal Species of the World (3rd ed.). Baltimore: Johns Hopkins University Press. pp. 168–169. OCLC 62265494. ISBN 0-801-88221-4. http://www.bucknell.edu/msw3/browse.asp?id=12100619. 
2. ^ ^{a b c d e} Meijaard, E., Nijman, V. & Supriatna, J. (2008). Nasalis larvatus. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 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 23: 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.
5. ^ Ellis D. (1986) "Proboscis monkey and aquatic ape". Sarawak Mus J 36(57):251-62.
6. ^ ^{a b c d} Ankel-Simons F. (2007) Primate Anatomy: an introduction, 3rd Edition. San Diego: Elsevier Acad.
7. ^ ^{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.
8. ^ 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.
9. ^ ^{a b c d e f g h} Bennett EL, Gombek F. (1993) Proboscis monkeys of Borneo. Sabah (MY):Koktas Sabah Berhad Ranau.
10. ^ ^{a b c} Sebastian AC. 2000. "Proboscis monkeys in Danau Sentarum National Park". Borneo Res Bull 31:359-71.
11. ^ Kawabe M, Mano T. (1972) "Ecology and behavior of the wild proboscis monkey, Nasalis larvatus (Wurmb) in Sabah, Malaysia". Primates 13(2):213-28.
12. ^ ^{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.
13. ^ ^{a b} Yeager CP. (1989) Feeding ecology of the proboscis monkey (Nasalis larvatus). Int J Primatol 10(6):497-530.
14. ^ Yeager CP. (1990) "Proboscis monkey (Nasalis larvatus) social organization: group structure". Am J Primatol 20(2):95-106.
15. ^ Yeager CP. (1991) "Possible antipredator behavior associated with river crossings by proboscis monkeys (Nasalis larvatus)". Am J Primatol 24(1):61-6.
16. ^ ^{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.
17. ^ ^{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.
18. ^ ^{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.
19. ^ 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.
20. ^ ^{a b c d} Murai T. (2006) "Mating behaviors of the proboscis monkey (Nasalis larvatus)". Am J Primatol 68(8):832-7.
21. ^ ^{a b c d e} Rajanathan R, Bennett EL. (1990) "Notes on the social behaviour of wild proboscis monkeys (Nasalis larvatus)". Malay Nat J 44(1):35-44.
22. ^ ^{a b} Gorzitze AB. (1996) "Birth-related behavior in wild proboscis monkeys (Nasalis larvatus)". Primates 37(1):75-8.
23. ^ Agoramoorthy G, Hsu MJ. (2004) "Occurrence of infanticide among wild proboscis monkeys (Nasalis larvatus) in Sabah, Northern Borneo". Folia Primatol 76(3):177-9.
24. ^ Messeri P, Trombi M. (2000) "Vocal repertoire of proboscis monkey (Nasalis larvatus, L.) in Sarawak". Folia Primatol 71(4):268-87.

External links

• John C.M. Sha, Ikki Matsuda & Henry Bernard (2011) The Natural History of the Proboscis Monkey
• ARKive - images and movies of the Proboscis monkey (Nasalis larvatus)
• Primate Info Net Nasalis Factsheets
• Save the Proboscis Monkeys Petition and weblog with info on the rare, endangered species.
• National Geographic video