Proboscis Monkey

About the Proboscis Monkey

Unmistakable and endemic to Borneo. Males carry a large pendulous nose thought to amplify their honking alarm calls and signal dominance to rivals; females have smaller, upturned noses. Both sexes have a notable pot belly, housing a specialised chambered stomach that ferments the leaves and unripe fruit that make up most of their diet.

Strictly tied to riverine, mangrove and swamp forest, rarely straying far from water — they are strong swimmers with partially webbed feet and will readily leap from overhanging branches into rivers to escape predators or cross channels. Kinabatangan and Trusan Sugut offer the most reliable river-based sightings, especially at dawn and dusk when troops gather at the water's edge.

Endangered, with numbers declining across most of their range due to loss of riverine and coastal forest.

How to recognise a proboscis monkey

A large monkey with a reddish-brown back, paler grey limbs and tail, and a round pot belly. The adult male's long, fleshy nose is unmistakable, and he is also much heavier than the female, at roughly twice her weight. Females and young have smaller, upturned noses. If you see a big monkey with a droopy nose sitting in a riverside tree, it is this species.

How proboscis monkeys live

Proboscis monkeys live in two kinds of group. A harem group has one dominant male with several females and their young. Bachelor groups are made up of males only. Males that are not in a harem, usually young ones, join a bachelor group, so a troop of big-nosed males without any females or babies is a bachelor group, not a harem.

Where to see proboscis monkeys in Borneo

Kinabatangan is the classic site. Troops sleep in tall trees along the riverbank and come to the water's edge at dawn and dusk, so early-morning and late-afternoon boat trips are the best times to look. On a two-night stay, seeing proboscis monkeys is close to certain.

Bako National Park, a short trip from Kuching in Sarawak, is the best-known site outside Sabah. The Telok Delima trail, about 45 minutes' walk from park headquarters, ends in mangroves where proboscis monkeys feed, and early morning and the hours before dusk are the best times. Listen for grunts or crashing branches, then scan the canopy. The park's population is small, with surveys estimating a few hundred animals, so allow time and expect a shy troop. Trusan Sugut offers river-based sightings too.

Frequently asked questions

Where do proboscis monkeys live?

Only on Borneo, in mangrove, riverside and peat swamp forest in the coastal and river lowlands. They are rarely found far from water.

Why do proboscis monkeys have big noses?

Only males grow the large pendulous nose. It is thought to amplify their honking alarm calls and to signal dominance to rival males.

How do proboscis monkeys live in groups?

In two kinds of group: harem groups, with one dominant male, several females and their young, and bachelor groups made up of males only.

Can proboscis monkeys swim?

Yes. They are strong swimmers with partially webbed feet and will jump from overhanging branches into rivers to escape predators or cross channels.

What do proboscis monkeys eat?

Mainly young leaves, unripe fruit and seeds. A chambered stomach ferments the leaves, which is why they have a pot belly.

Are proboscis monkeys endangered?

Yes. They are classed as Endangered, and numbers are falling across most of their range because riverside and coastal forest is being lost.