Proboscis Monkey
The proboscis monkey or long-nosed monkey, known as the bekantan in Malay
Malay language
Malay is a major language of the Austronesian family. It is the official language of Malaysia , Indonesia , Brunei and Singapore...

, is a reddish-brown arboreal Old World monkey
Old World monkey
The Old World monkeys or Cercopithecidae are a group of primates, falling in the superfamily Cercopithecoidea in the clade Catarrhini. The Old World monkeys are native to Africa and Asia today, inhabiting a range of environments from tropical rain forest to savanna, shrubland and mountainous...

 that is endemic to the south-east Asian island of Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....

. It belongs in the monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...

 genus Nasalis, although the pig-tailed langur
Pig-tailed Langur
The pig-tailed langur is a large, rather heavily built Old World monkey, which is adapted to climbing with its long arms. Its fur is black-brown, and its hairless face is also black. It is the only monkey in the subfamily Colobinae to have a relatively short tail; the tail is only slightly furred...

 has traditionally also been included in this genus - a treatment still preferred by some.

The monkey also goes by the Malay name monyet belanda ("Dutch monkey"), or even orang belanda ("Dutchman"), as Indonesians remarked that the Dutch
Dutch people
The Dutch people are an ethnic group native to the Netherlands. They share a common culture and speak the Dutch language. Dutch people and their descendants are found in migrant communities worldwide, notably in Suriname, Chile, Brazil, Canada, Australia, South Africa, New Zealand, and the United...

Colonization occurs whenever any one or more species populate an area. The term, which is derived from the Latin colere, "to inhabit, cultivate, frequent, practice, tend, guard, respect", originally related to humans. However, 19th century biogeographers dominated the term to describe the...

 often had a similarly large belly and nose.


Proboscis monkeys belong to the Colobinae
Colobinae is a subfamily of the Old World monkey family that includes 59 species in 10 genera, including the skunk-like black-and-white colobus, the large-nosed proboscis monkey, and the gray langurs. Some classifications split the colobine monkeys into two tribes, while others split them into...

 subfamily of the Old World monkey
Old World monkey
The Old World monkeys or Cercopithecidae are a group of primates, falling in the superfamily Cercopithecoidea in the clade Catarrhini. The Old World monkeys are native to Africa and Asia today, inhabiting a range of environments from tropical rain forest to savanna, shrubland and mountainous...

s. There are two subspecies:
  • Nasalis larvatus larvatus (Wurmb, 1787), which occupies the whole range of the species;
  • Nasalis larvatus orientalis (Chasen, 1940), restricted to north-east Kalimantan
    In English, the term Kalimantan refers to the Indonesian portion of the island of Borneo, while in Indonesian, the term "Kalimantan" refers to the whole island of Borneo....


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


The proboscis monkey is sexuality dimorphic
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...

. 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. Further adding to the dimorphism is the large nose or proboscis
A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...

 of the male, which can exceed 10cm (3.9 in) in length, dwarfing that of the female, and hangs lower than the mouth. 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. The fur is light-grey, yellowish, or greyish to light-orange ventrally. 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.

Range and habitat

The proboscis monkey is found only on the island of Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....

 and can be found on all three nations that divide the island: Brunei, Indonesia, and Malaysia. It is largely restricted to coastal areas and along rivers. The monkey lives only in lowland habitats such as coastal and riparian habitat, many of which are flooded by tides. It prefers dipterocarp, mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...

 and riverine forests. It can also be found in swamp forests, stunted swamp forests, rubber forests, rubber plantations, limestone hill forests, nipa
Nypa fruticans
Nypa fruticans, known as the attap palm , nipa palm , and mangrove palm or buah atap , buah nipah , dừa nước , Ging Pol in Sinhala in Sri Lanka and gol pata , dani . It is the only palm considered a mangrove in the Mangroves Biome...

 swamps, nibong
Oncosperma is a genus of flowering plant in the Arecaceae family.It contains the following species:* Oncosperma fasciculatum* Oncosperma platyphyllum* Oncosperma tigillaria Ridl.* Oncosperma horridum...

 swamps, and tall swamp forests, tropical heath forests and steep cliffs. 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. Aside from this, the proboscis monkey is largely arboreal and moves quadrupedally and by leaping. It is known to leap from high branches and into water.

Feeding and activities

As a seasonal folivore and frugivore, the proboscis monkey eats primarily fruit and leaves. 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
Eugenia is a genus of flowering plants in the myrtle family Myrtaceae. It has a worldwide, although highly uneven, distribution in tropical and subtropical regions. The bulk of the approximately 1,000 species occur in the New World tropics, especially in the northern Andes, the Caribbean, and the...

sp., Ganua motleyana and Lophopetalum javanicum
Lophopetalum javanicum
Lophopetalum javanicum is a species of plant in the Celastraceae family. It is found in Indonesia, Malaysia, Papua New Guinea, the Philippines, Thailand, and Vietnam.-References:...

. Young leaves are preferred over mature leaves and unripe fruits are preferred over ripe fruit. Being a seasonal eater, the proboscis monkey eats mostly fruit from January to May and mostly leaves from June to December. Groups usually sleep in one or several trees that are nearby. 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. Before dark, the monkeys move back near the river and feed again. Predators of the proboscis monkey include crocodiles, clouded leopards, eagles
The Eagles are an American rock band formed in Los Angeles, California in 1971 by Glenn Frey, Don Henley, Bernie Leadon, and Randy Meisner.With five number one singles, six Grammys, five American Music Awards, and six number one albums, the Eagles were one of the most successful musical acts of the...

, monitor lizards and pythons. Monkeys will cross rivers at narrows or cross arboreally if possible. This may serve as predator avoidance.

Social behavior

Proboscis monkeys generally live in groups consisting of one adult male, some adult females and their offspring. Other groups also exist such as all-male groups as well as less documented kinds. There are some individuals that are solitary, most of which are males. Monkey groups leave in home ranges that overlap and there is little territorial behavior. Proboscis monkeys live in a fission-fusion society
Fission-fusion society
In primatology, a fission-fusion society is one in which the social group, e.g. bonobo collectives of 100-strong, sleep in one locality together, but forage in small groups going off in different directions during the day. This form of social organization occurs in several other species of...

, 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. Groups all meet during the day and travel together, but individuals do not groom or play with those from other groups. One-male groups range from 9-19 individuals while bands can consist of as many as 60 individuals. One-male groups usually have 3-12 individuals but can be larger. Serious aggression is uncommon among monkeys but minor aggression does commonly occur. Overall, members of the same bands are fairly tolerant of each other. A linear dominance hierarchy exists among both males and females. 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. Upon reaching adulthood, males leave their natal groups and join all-male groups. Females also sometimes leave their natal groups, perhaps to avoid infanticide
Infanticide (zoology)
In animals, infanticide involves the killing of young offspring by a mature animal of its own species, and is studied in zoology, specifically in the field of ethology. Ovicide is the analogous destruction of eggs. Although human infanticide has been widely studied, the practice has been observed...

 or inbreeding, reduce competition for food or increase their dominance status.


Females become sexually mature at 5 years old. They show sexual swelling which involves the genitals becoming pink or reddened. At one site, mating peak in mid-year and births peak between March and May. Copulations tend to last for half a minute. The male will grasp the female by the ankles or torso and mount her from the rear. Both sexes will solicit mating but they are not always successful. When soliciting, both sexes will make a pouted face. In addition, males will sometimes vocalize and females will present her backside to a male. Copulating pairs are sometimes harassed by sub-adults. Proboscis monkey may also engage in non-reproductive mounting, such as playful and same-sex mounting. Gestation usually last 166-200 days or slightly more. Births tend to take place at night or in the early morning. The mother then eats the placenta and licks her infant clean. 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. When a resident male in a one-male groups is replaced, the infants are at risk of infanticide.


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. 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.


The Proboscis monkey is assessed as Endangered in the IUCN Red List
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...

 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
In English, the term Kalimantan refers to the Indonesian portion of the island of Borneo, while in Indonesian, the term "Kalimantan" refers to the whole island of Borneo....

; there are far fewer in Sarawak
Sarawak is one of two Malaysian states on the island of Borneo. Known as Bumi Kenyalang , Sarawak is situated on the north-west of the island. It is the largest state in Malaysia followed by Sabah, the second largest state located to the North- East.The administrative capital is Kuching, which...

, Brunei
Brunei , officially the State of Brunei Darussalam or the Nation of Brunei, the Abode of Peace , is a sovereign state located on the north coast of the island of Borneo, in Southeast Asia...

 and Sabah
Sabah is one of 13 member states of Malaysia. It is located on the northern portion of the island of Borneo. It is the second largest state in the country after Sarawak, which it borders on its southwest. It also shares a border with the province of East Kalimantan of Indonesia in the south...

. 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
Danau Sentarum National Park
The Danau Sentarum National Park is a national park protecting one of the world's most biodiverse lake systems, located in Borneo Island, West Kalimantan Province, Indonesia. It lies in the upper Kapuas River basin some 700 kilometres upstream from the delta. The basin is a vast floodplain,...

, Gunung Palung National Park
Gunung Palung National Park
Gunung Palung National Park lies on the island of Borneo, in the Indonesian province of West Kalimantan, north of Ketapang and east of Sukadana.- Geography:...

, Kendawangan Nature Reserve, Kutai National Park
Kutai National Park
Kutai National Park is a lowland national park located on the east coast of Borneo Island, in the East Kalimantan province of Indonesia, few minutes south of the equator.- Geography :...

, Lesan Protection Forest, Muara Kaman Nature Reserve, Mandor Reserve and Tanjung Puting National Park
Tanjung Puting
Tanjung Puting National Park is a national park in Indonesia located on the island of Borneo in the Indonesian province of Central Kalimantan. The park is famous for its orangutan conservation.- Geography :...

 in Indonesia; Bako National Park
Bako National Park
Bako National Park, established in 1957, is the oldest national park in Sarawak, eastern Malaysia, on the island of Borneo. It covers an area of at the tip of the Muara Tebas peninsula at the mouth of the Bako and Kuching Rivers. It is approximately by road from Kuching...

, Gunung Pueh Forest Reserve, Kabili-Sepilok Forest Reserve, Klias National Park, Kulamba Wildlife Reserve
Kulamba Wildlife Reserve
Kulambia Wildlife Reserve is situated in the Sabah's land area of Borneo , and covers 204km². It is an area protected under state law and is particularly significant for the conservation of orangutans -References:...

, Lower Kinabatangan Wildlife Sanctuary, Sungei Samunsam Wildlife Sanctuary and Ulu Segama Reserve in Malaysia.

External links

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