The Proboscis Monkeys of Sukau

Female proboscis monkey (Nasalis larvatus)

Dear Readers, on our first evening at Sukau, with the sun bathing the trees in golden light, we took a boat down the river to see what we could see. These boats have electric engines and so we glide along silently. We didn’t have far to go before we saw a troop of proboscis monkeys. I had seen them on wildlife documentaries, but was unprepared for how subtly beautiful they are, their fur patterned in grey and cream, gold and russet. They have long, elegant fingers and magnificent white tails. However, they also have those noses – huge in males (and a sign of dominance), and upturned in females and youngsters.

Male proboscis monkey

Proboscis monkeys look a little like strange woodland folk from some lost book by Tolkien, but they are animals who are superbly adapted to their habitat. They eat mainly leaves, and are very particular about choosing the youngest, tenderest shoots. This fibre-heavy diet adds to their somewhat comical appearance by giving them enormous round tummies. The male pictured above has the same concentrated expression on his face that my Nan used to wear when she was trying to work out a complicated knitting pattern.

The babies start life with completely black fur – I suspect that, like the little white tuft of tail on a baby chimpanzee, it gives them licence to misbehave in a way that older animals would never get away with. Alas, if a new alpha male moves into a troop he may kill any existing youngsters, and some studies seem to think that the new male will deliberately target male babies who might grow up to be a threat. This is one reason that female proboscis monkeys with youngsters often vote with their feet when a new male takes over the harem. Fortunately¬† I don’t think anyone will be messing with this male any time soon.

Mother proboscis monkey with young baby (Photo by Jan Young)

Male with a bit of a mouthful (Photo by John Tomsett)

Proboscis monkeys form groups of females, young and a single alpha male – the male defends his females from other males, but doesn’t defend a feeding territory, and you will often find proboscis monkeys, langurs and macaques all feeding from the same trees. The males are twice the size of the females, and in addition to their fine schnozzles, they also sport a bright-red, permanently-erect penis, just to make the point about who is the Big Man. I do have a photo of this but have decided to spare the monkey in question’s blushes. Here, instead, is one just looking a little guilty.

Male proboscis monkey by Caroline Hooper

The main predators of proboscis monkeys (except for humans, naturally) are clouded leopards, pythons and saltwater crocodiles. When travelling, male proboscis monkeys always bring up the rear, and they are the only members of the troop big enough to fight one of these beautiful cats off. Fragmentation of habitat puts the monkeys at greater risk from crocodiles – you might remember a sequence in a recent BBC wildlife documentary in which the proboscis monkeys had to cross a river that was home to a very large saltwater crocodile in order to reach fruiting trees on the other side. The monkeys are excellent climbers and swimmers (they have partially webbed feet), and while the babies are particularly athletic, the male often puts on a quick display of his leaping prowess to demonstrate how strong he is before settling back to eat more tasty leaves.

Youngster displaying his magnificent tummy

We only saw a couple of tiny saltwater crocodiles, but they can grow to 6m long, and are described as ‘hypercarnivorous apex predators’ on that fount of all knowledge, Wikipedia.

Baby saltwater crocodile. Not big enough to do anyone any damage (yet)


As with all of Borneo’s wildlife, the planting of oil palm plantations has presented considerable problems for the proboscis monkey. Many populations are now isolated along the mangrove forests on the coast, and although this is currently protected in Sabah, the areas are under considerable development pressure. In the Labuk Bay area around Sandakan, workers on the local oil palm plantation noticed that starving proboscis monkeys were coming into the kitchen to steal food, and so they started to feed the animals, giving them green beans, cucumbers and sugar-free pancakes. Apparently this dietary supplement meant that the animals began to thrive, and the population expands year after year. There are also plans to reintroduce proboscis monkeys to areas of protected forest in the west of Borneo. Let’s hope that this magnificent, unique monkey has the opportunity to expand its range and to survive into the future.

Photo by John Tomsett







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