# Proboscis Monkey — Facts, Threats & Conservation

*Nasalis larvatus*

> A proboscis monkey is a large, reddish-brown Old World monkey found only on the island of Borneo (in Indonesia, Malaysia and Brunei), famous for the male's oversized hanging nose and for living in coastal mangrove and riverside forests; the IUCN classes it as Endangered.

**IUCN status:** Endangered (IUCN, 2020) - CITES Appendix I  ·  **WARN range:** Indonesia, Malaysia

## Quick facts
| Fact | Value |
| --- | --- |
| Lifespan | At least 23 years in captivity (~20-21 yr average); shorter in the wild |
| Weight | Males ~16-22 kg (up to ~30 kg); females ~7-12 kg |
| Length | Head-body ~66-76 cm (male), ~53-62 cm (female), plus a long tail |
| Diet | Folivore-frugivore: young leaves, unripe fruit and seeds |
| Gestation | About 166-200 days |
| Young per birth | One (single infant) |
| Baby name | Infant |
| Group name | Troop or band (one-male and bachelor groups) |
| CITES | Appendix I |
| Notable | One of the most aquatic primates; can swim and cross rivers underwater |

## Scientific classification
- **Kingdom:** Animalia
- **Phylum:** Chordata
- **Class:** Mammalia
- **Order:** Primates
- **Family:** Cercopithecidae
- **Genus:** Nasalis
- **Species:** Nasalis larvatus (Wurmb, 1787)
- **Subspecies:** Two recognised: N. l. larvatus and N. l. orientalis

## Conservation status
- **Status:** Endangered
- **Population:** Fewer than an estimated 7,000 mature individuals across Borneo (highly fragmented)
- **Trend:** Decreasing
- **Assessed:** 2020
- **CITES:** Appendix I
- Population has declined by more than 50% over roughly the last 40 years (about three generations), driven mainly by habitat loss; estimates are approximate because the range is fragmented and hard to survey.

## Key facts: Proboscis Monkey
- Proboscis monkeys are endemic to Borneo, shared by Indonesia (Kalimantan), Malaysia (Sabah and Sarawak) and Brunei - they live nowhere else in the wild.
- The IUCN Red List classifies the species as Endangered (assessed 2020), and it is listed on CITES Appendix I, the strictest trade protection.
- Males are far larger than females and grow an enormous pendulous nose; females and young have smaller, upturned noses.
- They are mangrove and riverside specialists and among the most aquatic monkeys, able to swim and even cross rivers underwater.
- Their diet is mostly leaves, unripe fruit and seeds, digested by a chambered, ruminant-like stomach full of fermenting bacteria.
- The main threats are habitat loss to oil-palm plantations, logging and coastal development, plus hunting in parts of the range.

## Why the proboscis monkey is Endangered
The proboscis monkey's fate is tied directly to Borneo's lowland forests. Because it depends on mangroves, peat-swamp forest and riverbank vegetation - exactly the flat, water-rich land that is easiest to drain and convert - it has lost huge areas of habitat to oil-palm plantations, logging, shrimp farming and coastal development. The IUCN estimates the population has fallen by more than 50% over roughly the last 40 years (about three generations) and lists the species as Endangered, with fewer than an estimated 7,000 mature individuals remaining across a highly fragmented range. Surviving groups are increasingly cut off from one another along single rivers, which makes local populations vulnerable to disturbance, hunting and isolation.

## Behaviour and ecology
Proboscis monkeys live in a flexible, fission-fusion society: typically one dominant male with a group of females and young, plus separate bachelor bands of males, which gather and split along the same stretch of river. They are highly arboreal but also remarkable swimmers - one of the few primates with partial webbing between the fingers and toes - and will leap from branches into rivers and swim across, sometimes underwater, to escape predators such as crocodiles or to reach feeding trees. Their bulging bellies house a specialised, multi-chambered stomach where bacteria ferment tough leaves, similar to a cow's digestion, allowing them to live on foliage, unripe fruit and seeds that other monkeys cannot process.

## The remarkable nose
The species is named for the male's proboscis - a fleshy, drooping nose that can hang lower than the mouth and grows larger with age. Research suggests it is shaped by sexual selection: a bigger nose acts as a resonating chamber that amplifies the male's honking calls and may signal size and dominance to females and rivals. Females prefer larger-nosed males, and nose size correlates with body mass and the number of females a male attracts. Females and infants, by contrast, have small, neat, upturned noses, making the sexes easy to tell apart.

## What rescue and protection involve
Protecting proboscis monkeys is mostly about protecting habitat. Because they cannot survive away from intact riverine and mangrove forest, conservation centres on safeguarding river corridors, restoring degraded mangroves, reducing forest conversion and maintaining connected patches so isolated groups can mix. On-the-ground work also includes monitoring populations, reducing hunting and snaring, managing wildlife tourism so it does not stress the animals, and rehabilitating individuals orphaned or displaced by land clearing. Effective action depends on local rangers, community-run reserves and sanctuary teams who know the rivers and can respond quickly.

## Male vs female proboscis monkey
| Feature | Male | Female |
| --- | --- | --- |
| Nose | Very large, pendulous, hangs over the mouth | Small and upturned |
| Weight | ~16-22 kg (up to ~30 kg) | ~7-12 kg |
| Head-body length | ~66-76 cm | ~53-62 cm |
| Coat | Brighter reddish-brown, pale rump | Similar colours, smaller build |
| Social role | Leads one-male group or joins bachelor band | Lives in one-male group with young |

## What WARN does
WARN CIC is a registered global not-for-profit animal welfare organisation that raises funds for local partner shelters, sanctuaries and rescue teams in five countries - including Indonesia and Malaysia, which together hold almost the entire wild proboscis monkey population on Borneo. For a mangrove specialist like this, the most useful support is sustained funding for the local teams who protect river corridors, monitor groups and care for displaced animals on the ground. WARN's role is to channel donor money to those in-country partners and to raise wider awareness of why Borneo's forests matter; we are honest that the long-term work of habitat protection sits with established field organisations and government reserves, which our partners support rather than replace.

Borneo's proboscis monkeys survive only where their mangroves and riverbanks do. A donation helps WARN fund the local rescue and ranger teams in Indonesia and Malaysia working to keep those forests - and the monkeys in them - standing.

## Frequently asked questions: Proboscis Monkey
### How long do proboscis monkeys live?
In captivity proboscis monkeys can live to at least 23 years, with averages around 20 to 21 years. Lifespan in the wild is less well documented and is generally shorter because of predation, hunting and habitat pressures.

### What do proboscis monkeys eat?
They are mainly leaf and seed eaters. Their diet is dominated by young leaves, unripe fruit and seeds - including those of mangrove trees - and shifts seasonally toward more fruit early in the year and more leaves later. A specialised chambered stomach ferments this tough plant material.

### How big do proboscis monkeys get?
Males are large, with a head-and-body length of about 66 to 76 cm and weights of roughly 16 to 22 kg, exceptionally up to about 30 kg. Females are much smaller, around 53 to 62 cm and about 7 to 12 kg.

### Are proboscis monkeys dangerous to humans?
No. They are shy, plant-eating monkeys that avoid people and spend most of their time in trees near water. They are not considered dangerous, though like any wild animal they should be observed at a respectful distance and never fed.

### How many proboscis monkeys are left?
The IUCN estimates fewer than around 7,000 mature individuals remain, spread across a fragmented range in Borneo, and the population has declined by more than 50% over roughly the last 40 years. The species is classed as Endangered.

### Why is the male's nose so big?
Scientists think the male's large nose is driven by sexual selection: it amplifies his honking calls and signals body size and dominance. Females prefer larger-nosed males, and nose size is linked to weight and mating success.

## Sources
- [IUCN Red List - Nasalis larvatus (2020 assessment)](https://www.iucnredlist.org/species/14352/195372486)
- [IUCN Red List assessment PDF - Nasalis larvatus](https://www.iucnredlist.org/species/pdf/17945165)
- [CITES - Appendices (Nasalis larvatus, Appendix I)](https://cites.org/eng/app/appendices.php)
- [Animal Diversity Web - Nasalis larvatus](https://animaldiversity.org/accounts/Nasalis_larvatus/)
- [Mammalian Species: Nasalis larvatus (Oxford Academic)](https://academic.oup.com/mspecies/article/47/926/84/2609392)
- [WWF - Proboscis monkey](https://www.worldwildlife.org/species/proboscis-monkey)

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Full guide: https://worldanimalrescuenetwork.org/wildlife-guides/proboscis-monkey