Proboscis monkeys are found exclusively on the island of Borneo in Southeast Asia. They live nowhere else on Earth, making them one of the few primate species restricted to a single island. Their range spans three countries that share Borneo: Malaysia, Indonesia, and Brunei.
Three Countries, One Island
Borneo is divided among Malaysia (the states of Sabah and Sarawak), Indonesia (the region of Kalimantan), and the small nation of Brunei. Proboscis monkeys live in all three territories, though not evenly. Sabah holds an estimated 5,907 individuals, while Sarawak supports roughly 9,586. Indonesian Kalimantan is home to around 7,500, though those populations are scattered and fragmented. Brunei’s population is smaller and less well documented.
Even within these regions, the monkeys aren’t spread across the whole island. They concentrate along coastlines and riverbanks, so large stretches of Borneo’s mountainous interior have no proboscis monkeys at all. Inland, they follow rivers that wind through the lowlands, sometimes appearing over 200 km from the coast.
Coastal Lowlands and Flooded Forests
Proboscis monkeys are tied to water. They live in mangrove forests along estuaries, peat swamp forests, and riverine forests that flood with the tides. These are acidic, waterlogged environments in coastal lowlands, generally below 200 meters above sea level. You won’t find them in upland or mountain forests.
This preference for soggy, low-lying habitat shapes everything about the species. Their fingers and toes are partially webbed, an adaptation that makes them strong swimmers. They regularly cross rivers and channels, sometimes diving from tree branches into the water. Few other primates are as comfortable in the water as proboscis monkeys are.
What They Eat in These Habitats
Their diet reflects the forests they live in. About 80% of what proboscis monkeys eat consists of young leaf shoots from coastal and swamp tree species, including mangrove apple trees, sea hibiscus, and sea ferns. The remaining 20% comes from small fruits, particularly from fig trees and a shrub called buas-buas. They’re leaf specialists with a complex, chambered stomach that ferments tough plant material, similar to the way a cow digests grass.
Why Their Range Is Shrinking
The IUCN classifies proboscis monkeys as Endangered, and the reason is straightforward: the specific habitats they depend on are the same ones humans want. Riverbanks and coastal mangroves are prime land for farming, logging, housing, and palm oil plantations. Clearing these areas eliminates proboscis monkey habitat entirely, because the species cannot simply relocate to drier upland forest.
Forest fires have compounded the problem. The devastating 1997-1998 fires across Borneo destroyed a larger share of proboscis monkey habitat than that of any other primate in Kalimantan. Fires along rivers and in peat swamps burn through the exact corridors these monkeys use to travel and feed.
Hunting is another pressure. Proboscis monkeys are relatively slow-moving and easy to spot in the trees along riverbanks. They’re hunted opportunistically for food and also targeted for bezoar stones, intestinal secretions used in traditional Chinese medicine. Because they live in small, concentrated groups along waterways, a single hunting campaign can wipe out an entire local population.
Where to See Them
If you’re hoping to see proboscis monkeys in the wild, the most accessible locations are in Malaysian Borneo. The Kinabatangan River in Sabah is one of the best-known spots, where boat tours along the river regularly encounter groups feeding in riverside trees at dusk. The Klias Peninsula, also in Sabah, supports populations in its remaining mangrove and swamp forests. In Sarawak, Bako National Park is a popular destination where proboscis monkeys are habituated enough to human presence that sightings are common.
In Indonesian Kalimantan, Tanjung Puting National Park offers sightings, though populations there are more dispersed due to habitat fragmentation. Brunei’s Ulu Temburong National Park also falls within the species’ range, though encounters are less predictable.
In all of these locations, the pattern is the same: look near water. Proboscis monkeys sleep in trees along riverbanks at night, typically within a few dozen meters of the water’s edge, and fan out into the surrounding forest during the day to feed before returning to the riverside by evening.