The Proboscis monkey is an Old World monkey with a characteristic long nose that distinguishes this animal from other monkeys. As a matter of fact, another name of this primate is 'Monyet belanda' monkey, literally meaning 'long-nosed' monkey. When first seeing this animal, people didn't suppose it was a monkey because of its rather unusual appearance. Thus, males of this species exhibit extremely long noses of up to 7 inches, which are likely to attract females whose noses are usually shorter. Another important characteristic of Proboscis monkeys is their diverse color patters, varying from bright orange to yellow or pink. Additionally, newborn Proboscis monkey display blue faces that turn to cream color as they grow up.
These animals are native and endemic exclusively to the island of Borneo in the southeastern Asia, where they generally live in coastal areas, covered with mangroves and swamp forests. Other suitable habitats include lowlands along rivers as well as riparian forests and rainforests. Proboscis monkeys typically live in close proximity to water bodies of their home range.
Proboscis monkeys are highly social animals, forming troops of 2 - 30 animals, typically consisting of a single dominant male and multiple (up to 10) females with their offspring. Males defend their group by exposing their teeth and emitting loud, honking signals, while females are responsible for foraging and caring for infants. In areas with sufficient food or close to the water these troops may occasionally unite in larger aggregations. During these times, groups of Proboscis monkeys rest and sleep among mangroves at the edge of the water. The presence of freshwater bodies such as swamps or rivers is the primary life condition for these animals. Proboscis monkeys are accomplished swimmers. Moreover, when foraging or fleeing from a threat, they are able to take deep dives.
Proboscis monkeys have a polygynous mating system, where the dominant male mates with females in a troop. They breed between February and November. Gestation period lasts for 166 days, yielding one infant, typically during the nighttime hours. The newborn baby exhibits deep blue face and sparse, almost black coat, which changes its color within 3 - 4 months after birth. Collective rearing is common in this species: females of a troop help raise each other's offspring. They can also suckle another female's young when needed. During the first year of its life, the infant is constantly with its mother. However, soon the female produces another baby, after which young females usually continue living with their natal group, whereas males disperse, joining all-male bachelor groups. The age of reproductive maturity is 4 years old in females and 4 - 5 years old in males.
Currently, the biggest threat to this species is loss of their natural habitat as a result of forest fires and cutting of mangrove trees, growing along riverbanks. Meanwhile, those in coastal areas lose their range due to development of human settlements and shrimp farms. Another serious concern is localized hunting for food and intestinal bezoar stones, used in traditional medicine. This threat is compounded by the docile nature of these animals, making them 'easy prey' for hunters.
The IUCN Red List and other sources don’t provide the number of the Proboscis monkeys’ total population. However, according to the IUCN Red List, specific populations have been estimated in the following areas: Indonesia - population number in this country is associated with past and current threats, varying from less than 100 to more than 1,000 individuals; and Sarawak - population in this region is estimated to be less than 1,000 Proboscis monkeys. Overall, Proboscis monkeys’ numbers are decreasing today, and the animals are classified as Endangered (EN) on the IUCN Red List.