Proboscis Monkey

Proboscis Monkey facts at a glance

How big is a proboscis monkey?

An adult proboscis monkey measures 75 cm long — about 43% of the height of an average adult person (1.73 m) — and weighs around 20 kg, about 29% of an average adult’s body weight (70 kg).

What is a group of proboscis monkeys called?

Explore more animal collective nouns and baby animal names .

The remarkable nose

The proboscis monkey takes its name from the enormous, pendulous nose of adult males, which can hang down past the mouth. This oversized nose is thought to amplify the male's honking calls and to signal health and status to females. Females and young have much smaller, upturned noses by comparison. No other primate carries a nose quite like it, making the species instantly recognisable.

Found only on Borneo

Proboscis monkeys live nowhere else on Earth but the island of Borneo, shared by Malaysia, Indonesia, and Brunei. They keep to lowland habitats close to water, favouring coastal mangroves, peat-swamp forest, and forest along rivers. Rarely straying far from the water's edge, they gather in the trees overhanging rivers and estuaries. This tight link to waterside forest makes them especially sensitive to the loss of these habitats.

Leaf-eating and the pot belly

Proboscis monkeys are herbivores, feeding mainly on young leaves and unripe fruit, along with seeds and flowers. To digest this tough, leafy diet they have a large, chambered stomach full of bacteria that ferment the plant material, giving them a distinctly pot-bellied appearance. This specialised gut means they generally avoid sweet ripe fruit, which can ferment too quickly and upset their digestion. They feed mostly in the morning and late afternoon, resting during the heat of the day.

Swimming and moving through the forest

Unusually among monkeys, proboscis monkeys are excellent swimmers, with partially webbed fingers and toes that help them cross rivers. They can move at up to 24 km/h and will leap dramatically from trees into the water to escape predators such as crocodiles or to reach the far bank. In the trees they travel by climbing and leaping through the canopy. This swimming ability lets them exploit the flooded, waterlogged forests that many other primates avoid.

Social structure

Proboscis monkeys live in harem groups made up of one dominant male, several females, and their young, alongside separate bachelor groups of males. At night, many groups gather in trees along the same stretch of river, coming together in loose communities before dispersing to feed by day. Males are much larger than females, weighing up to around 24 kg, and use their size and honking calls to hold their group together. Young males eventually leave to join bachelor bands before trying to win a harem of their own.

Why it is endangered

The proboscis monkey is listed as Endangered by the IUCN, and its population continues to fall. Its waterside forests are being cleared rapidly for palm-oil plantations, logging, and shrimp farming, destroying the mangroves and riverine trees it depends on. Because the species is confined to Borneo and tied to a narrow band of habitat, it has little room to retreat. Protecting mangrove and riverside forest is critical to its future.

Did you know? Proboscis Monkey facts

• Proboscis monkeys are endemic to Borneo, recognised by males' large pendulous noses and pot bellies.
• Sexual selection — larger noses correlate with higher rank in males.
• Borneo river cruises at dawn often spot troops in mangroves.
• Conservation: Endangered.

Diet & feeding

Proboscis Monkey feeds primarily as a leaves, unripe fruit, seeds.

Adaptations

• The nose amplifies honking calls and may signal mate quality.
• Webbed feet help proboscis monkeys escape crocodiles by crossing water.

Behaviour & ecology

• The nose amplifies honking calls and may signal mate quality.
• Webbed feet help proboscis monkeys escape crocodiles by crossing water.

Communication

• Proboscis Monkey uses scent, posture, and vocal signals to mark territory and coordinate social behaviour.
• Communication intensity often peaks during breeding seasons and territorial disputes.

Habitat & range

Borneo mangroves and riverine forest

Ecological role

Proboscis Monkey plays a recognised ecological role in borneo mangroves and riverine forest.

Conservation status of the Proboscis Monkey

Sources & references

This guide is compiled and reviewed against established zoological and conservation references. Key sources for the Proboscis Monkey:

• IUCN Red List of Threatened Species

  Conservation status (Endangered) reflects the IUCN Red List category for Nasalis larvatus, most recently assessed in 2021.

• iNaturalist — observations & photos

  Search citizen-science observations and community IDs for Nasalis larvatus. Useful for range checks and recent sightings — not a substitute for formal Red List status.

• GBIF — occurrence data

  Global Biodiversity Information Facility species search for Nasalis larvatus. Explore published occurrence records used in range research.

• IUCN Red List — Nasalis larvatus.

  Conservation status (Endangered) and population trends.

• Animal Diversity Web — Nasalis larvatus. University of Michigan Museum of Zoology.

  Life history, morphology, and range.

• Global Animal Guide editorial standards

  How we research, source, review, and update every guide for accuracy.