Proboscis monkeys are confined to the island of Borneo; they prefer coastal regions to inland areas.
Biogeographic Regions: oriental
Other Geographic Terms: island endemic
N. l. larvatus
It has the same range as the species as a whole, with the exception of northeastern Kalimantan.
N. l. orientalis
It is restricted to northeastern Kalimantan, Indonesia.
Proboscis monkeys are sexually dimorphic. The males have a length of 70 cm and weight of between 16 and 22 kg. Females measure 60 cm and weigh between 7 and 12 kg.
Males have a large protruding nose, which enhances vocalizations through resonance. The nose of the female is smaller.
The fur of the adult proboscis monkey is pink and brown with red around the head and shoulders. The arms, legs, and tail are gray. Males have a black scrotum and a red penis. Infants are born with a blue colored face that at 2.5 months darkens to gray. By 8.5 months of age, the face has become cream colored as in the adults.
There is webbing between the digits to allow for swimming.
Range mass: 7 to 22 kg.
Range length: 60 to 70 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger; sexes colored or patterned differently; male more colorful; ornamentation
Proboscis monkeys inhabit mangrove forest along rivers and estuaries, swamp-land, and lowland rainforest.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: rainforest
Habitat and Ecology
Habitat and Ecology
The species is mostly folivorous (about 52% of all feedings) and frugivorous (about 40% of all feedings), and prefers young leaves and unripened non-fleshy fruits. Monthly diet of this species changes with availability throughout the year (Yeager 1989). Boonratana (2000) observed this species swimming across the Kinabatangan River in northern Borneo, and frequently across its tributaries. The home range size of a focal one-male group was 220.5 ha (Boonratana 2000). Boonratana (2000) reports that this species never entered agricultural lands, nor areas used intermittently as log dumps for logging operations carried out in the area before and during the study. This species returned to the river every night at the study site of Sukau, moving inland during the day (Boonratana 2000). It avoids areas with heavy deforestation, such as agricultural land (Salter and MacKenzie 1985). Where there is no hunting the species can persist in disturbed forests and secondary habitats.
Proboscis monkeys are folivores and frugivores. They prefer fruits, seeds, young leaves, and shoots of mangrove. They may also eat some invertebrates such as caterpillars and larvae. They are more frugivorous from January through May and more folivorous from June through December.
Animal Foods: insects
Plant Foods: leaves; seeds, grains, and nuts; fruit
Primary Diet: herbivore (Folivore , Frugivore )
The role of N. larvatus in the ecosystem is not well understood. As herbivores, they probably have some affect on plant populations. To the extent that predators rely on these animals for food, proboscis monkey populations may affect predators.
The anti-predator behavior of these monkeys has not been described in detail. Leopards are known to prey upon them, as are crocodiles. Adult males sometimes vocalize, apparently to scare off potential predators.
- leopards (Panthera pardus)
- crocodiles (Crocodylus)
Known prey organisms
This list may not be complete but is based on published studies.
This list may not be complete but is based on published studies.
Life History and Behavior
The proboscis monkey has several sounds for communication. Growls are made by males and are used to calm the group members. Honks are made by males as a threat or to warn of predators. Shrieks are made by females and both sexes of juveniles to show aggitation or excitement, and screams are given during agonistic encounters. Social grooming is performed, usually between females. The grooming usually last 1 to 5 minutes and is performed by both individuals.
Communication Channels: visual ; tactile ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
Only the lifespan in captivity is known; in most animals it is at least 23 years.
Status: captivity: 23 (high) years.
Status: captivity: 20.0 years.
Status: captivity: 21.0 years.
Status: captivity: 13.6 years.
Lifespan, longevity, and ageing
The basic social unit in proboscis monkeys is a single adult male with from 2 to 7 adult females. The males mate with females in their social group.
Mating System: polygynous
Proboscis monkeys give birth to a single offspring after a gestation of 166 days. Births usually occur at night. The female sits on a tree branch during the birth. After the infant is born, the mother consumes the placenta.
The breeding season is from February until November. Copulation is initiated by the female through pursing of the lips, shaking of the head from side to side, and presentation of the hindquarters to the male. Females will continue to initiate copulations even after they have conceived.
Infants stay close to their mothers for about one year. Males reach maturity at about 7 years.
Breeding interval: Females can produce offspring each year.
Breeding season: Proboscis monkeys breed from February until November
Average number of offspring: 1.
Average gestation period: 166 days.
Range weaning age: 7 (high) months.
Average time to independence: 12 months.
Average age at sexual or reproductive maturity (male): 7 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous
Average birth mass: 490 g.
Average gestation period: 166 days.
Average number of offspring: 1.25.
Average age at sexual or reproductive maturity (female)
Sex: female: 1460 days.
As is the case for most primates, newborn proboscis monkeys are fairly helpless. They must be carried by their mother until they are able to walk on their own. Mothers provide their offspring with milk, nursing them until they are about 7 months old. They also keep their infants clean through grooming. Infants stay close to their mothers for about one year.
The role of the male in parental care is less direct. Although males do not care for infants the way females do, it can be argued that they provide important protection for the young by excluding potentially infanticidal rival males from the group.
Parental Investment: no parental involvement; altricial ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Male, Female); pre-independence (Provisioning: Female, Protecting: Male, Female); extended period of juvenile learning
Evolution and Systematics
The nose of the male proboscis monkey amplifies its threatening call by serving as a resonating chamber.
"A large mobile nose, like that of the elephant, may also be known as a proboscis: hence the name of the proboscis monkey, a curious-looking primate, the male of which has a long bulbous nose that hangs over his mouth. This kind of nose is used as a resonating chamber, and is erected to amplify the male's threatening call through the forest canopy of Borneo." (Foy and Oxford Scientific Films 1982:136)
Learn more about this functional adaptation.
Molecular Biology and Genetics
Barcode data: Nasalis larvatus
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Nasalis larvatus
Public Records: 3
Specimens with Barcodes: 4
Species With Barcodes: 1
Proboscis monkeys are protected from hunting and capture in Borneo but the destruction of the mangrove forest has limited the population. They are listed as Appendix I by the Convention on International Trade in Endangered Species (CITES). (Appendix I is defined as a species threatened with extinction with trade allowed only in extreme circumstances.) They are listed as endangered by the International Trade in Endangered Species of Wild Fauna and Flora (IUCN). ('Endangered' is defined as an estimated 50% reduction in the population in the next 10 years.)
CITES: appendix i
IUCN Red List of Threatened Species: endangered
IUCN Red List Assessment
Red List Category
Red List Criteria
IUCN Red List Assessment
Red List Category
Red List Criteria
- 1994Vulnerable(Groombridge 1994)
- 1990Vulnerable(IUCN 1990)
- 1988Vulnerable(IUCN Conservation Monitoring Centre 1988)
- 1986Vulnerable(IUCN Conservation Monitoring Centre 1986)
Date Listed: 06/14/1976
Lead Region: Foreign (Region 10)
Where Listed: Entire
Population location: Entire
Listing status: E
For most current information and documents related to the conservation status and management of Nasalis larvatus , see its USFWS Species Profile
The species is relatively lethargic and easily hunted; with little effort entire populations can be hunted to extirpation. Opportunistic hunting of Nasalis larvatus for food occurs; the species is also hunted for bezoar stones, an intestinal secretion used in traditional Chinese medicine. Hunting has been felt most significantly in the Bornean interior, but is increasing in coastal areas (Meijaard and Nijman 2000).
This species is almost never seen in captivity outside of Asia, as, owing to their dietary specialization on particular leaves and other vegetable material, they are hard to keep alive (E. Meijaard pers. comm.).
Relevance to Humans and Ecosystems
There are no known adverse affects of N. larvatus on humans.
Proboscis monkeys are considered a delicacy although they are not heavily hunted. They are also desired for zoos because of their unique appearance.
Positive Impacts: food ; research and education
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. This species co-exists with the Bornean Orangutan. It belongs in the monotypic genus Nasalis, although the pig-tailed langur has traditionally also been included in this genus.
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.
- 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.
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). Further adding to the dimorphism is the large nose or proboscis of the male, which can exceed 10 cm (3.9 in) in length, and hangs lower than the mouth. 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. The underfur is light-grey, yellowish, or greyish to light-orange. 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.
Proboscis monkeys generally live in groups composed of one adult male, some adult females and their offspring. All-male groups may also exist. Some individuals are solitary, mostly males. Monkey groups live in overlapping home ranges, with little territoriality, 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. Groups gather during the day and travel together, but individuals only groom and play with those in their own group. One-male groups consist of 9–19 individuals, while bands can consist of as many as 60 individuals. One-male groups typically consist of three to 12 individuals, but can contain more. 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 between females. 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. Upon reaching adulthood, males leave their natal groups and join all-male groups. Females also sometimes leave their natal groups, perhaps to avoid infanticide or inbreeding, reduce competition for food, or elevation of their social status.
Females become sexually mature at five years old. They experience sexual swelling, which involves the genitals becoming pink or reddened. At one site, matings largely take place between February and November, while births occur between March and May. Copulations tend to last for half a minute. The male will grab the female by the ankles or torso and mount her from behind. Both sexes will encourage mating, but they are not always successful. When soliciting, both sexes will make pouted faces. In addition, males will sometimes vocalize and females will present their backsides. Mating pairs are sometimes harassed by subadults. 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. Females tend to give birth at night or in the early morning. The mothers then eat the placenta and lick their infants clean. 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. When a resident male in a one-male group is replaced, the infants are at risk of infanticide.
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. 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.
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. It is most common in coastal areas and along rivers. This species is restricted to lowland habitats that may experience tides. It favors dipterocarp, mangrove and riverine forests. 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. 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. Aside from this, the proboscis monkey is largely arboreal and moves quadrupedally and by leaps. It is known to jump off branches and descend 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 are consumed, "with a marked preference for Eugenia sp., Ganua motleyana and Lophopetalum javanicum". 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 adjacent trees. 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. Occasionally, they chew their cud to allow more efficient digestion and food intake. 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.
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 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. 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.
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