The Proboscis Monkey (Nasalis larvatus), also known as the Monyet Belanda (in Malay), the Bakantan (in Indonesian) or simply the Long-nosed Monkey, 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 traditionally also has been included in this genus – a treatment still preferred by some.
A distinctive trait of this monkey is the male’s large protruding nose, from which it takes its name. The big nose is thought to be used in mating and is a characteristic of the males, reaching up to 7 inches in length. The females also have big noses compared to other monkey species, but not as big as the males. Besides attracting mates, the nose serves as a resonating chamber and works by amplifying their warning calls. When the animal becomes agitated its nose swells with blood, making warning calls louder and more intense. Proboscis monkey belong to the order of Primates, from the family Cercopithecidae and subfamily Colobinae (Bennett & Gombek, 1993). According to Bennett & Gomber (1993), in the Old World, monkey divided into two groups known as cercopithecines and colobines. Proboscis monkey are colonines. Males are much larger than females, reaching 72 cm (28 inches) in length, with an up to 75 cm tail, and weighing up to 24 kg (53 pounds). Females are up to 60 cm long, weighing up to 12 kg (26 lb). This large sexual dimorphic difference is greater than in any other primate.
The Proboscis monkey can be found in island of Borneo in South-east Asia but they are not even found throughout all of Borneo. Proboscis monkey’s main habitats are mangrove, peat swamp and riverine forests (Bennett & Gombek, 1993). Monkey also has a large belly, as a result of its diet. Its digestive system is divided into compartments, with bacteria that digest cellulose and neutralize toxins from certain leaves. This lets the monkey eat leaves and remain in the forest canopy. The contents of their stomach weigh about a quarter of their whole body. A side-effect of this unique digestive system is that it is unable to digest ripe fruit, unlike most other simians. The diet consists mainly of seeds, leaves, mangrove shoots and unripe fruit.
The Proboscis Monkey is endemic to Borneo’s low elevation mangrove forests, swamps, and lowland riparian forests It lives in small groups of 10 to 32 animals. Group membership is very flexible, and animals are known to move from group to group quite often.
The Proboscis Monkey lifestyle is both arboreal and amphibious, with its mangrove swamp and riverine environment containing forest, dry land, shallow water allowing wading, and deep water requiring swimming. Like other similar monkeys, the Proboscis Monkey climbs well. It is also a proficient swimmer, often swimming from island to island, and has been picked up by fishing boats in open ocean a mile from shore. While wading, the monkey uses an upright posture, with the females carrying infants on their hip. Troops have been filmed continuing to walk upright, in single file, along forest trails when they emerge on land, the only non-human mammal, with the exception of gibbons and giant pangolins, known to use this form of locomotion for any length of time.
Due to ongoing habitat loss and hunting in some areas, only about 7000 are known to still exist in the wild. In Sarawak, the population of this species has declined from 6500 in 1977 to only 1000 in 2006. The Proboscis Monkey is evaluated as Endangered on the IUCN Red List of Threatened Species. It is listed on Appendix I of CITES.
While the official Indonesian name for this monkey is Bakantan, an Indonesian nickname is ‘monyet belanda’, meaning ‘Dutch monkey’ or ‘Orang Belanda’, the Indonesian word for ‘Dutchman’, as Indonesians noticed the Dutch colonisers often also had a large belly and nose.
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