Proboscis Monkey

The Proboscis Monkey (Nasalis larvatus), also known as the Long-nosed Monkey, is a reddish-brown arboreal Old World monkey. It is the only species in monotypic genus Nasalis.

Appearance
A distinctive trait of this monkey is the male's large protruding nose. The purpose of the large nose is unclear, but it has been suggested that it is a result of sexual selection. Another explanation is an adaptation to the facial structure to diving, the same as bipedalism might be an adaptation to wading, as proposed in the aquatic ape hypothesis.

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).

The Proboscis 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 fruits, seeds, leaves and mangrove shoots.

Ecology
The Proboscis Monkey is distributed and endemic to the coastal mangrove, swamps and riverine forests of Borneo. 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.

Status
Due to ongoing habitat loss and hunted 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.

Other names
While the official Indonesian name for this monkey is Bekantan, 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.