After the orang-utan, the proboscis monkey is the best known primate of Sarawak. It is easy to understand why: the huge nose (which their English and Latin names refer to) and large bellies of the males make them instantly recognisable, and give them a somewhat comical appearance. (The Malay name "orang belanda" literally means "Dutchman" - not entirely complimentary to the Dutch!) Proboscis monkeys are also the largest of the monkey species in Sarawak, with males weighing about 20kg. The females are about half this size, and have tiny little noses. It's not certain what purpose the large male nose serves, but it is thought that it may be attractive to the females (just like people - or maybe not!).
Proboscis monkeys live near the water, mainly in mangrove and coastal riverine forests. These forest types only occur in very small and isolated patches, hence the rarity of the monkeys. Although they live mainly in the trees, proboscis monkeys are excellent swimmers, and even have slightly webbed hind feet!
Proboscis monkeys eat mainly seeds, non-sweet fruit and young leaves. This diet explains the large stomachs, which are compartmentalised like cow's stomachs, allowing bacteria to break down the tough foods. The poor quality of the food also means that proboscis monkeys have to move around quite a lot to find food. During the wet season, when there is less fruit in riverine forest, they are more likely to come down into the mangroves to look for food.
Proboscis monkeys live in loose social groups of 8 to 10 individuals. They are found in two types of group: an adult male with a harem of females and children; and all-male groups. But different groups meet at different times, and individuals move between them.
Best places to see
Unlike the orang-utan, which also occur in northern Sumatra (Indonesia), proboscis monkeys are only found in a few scattered locations, all in Borneo. And the best of these locations to see them is Bako National Park, in the area around the park headquarters, in the early morning and at dusk. Check with the staff about where the most recent sightings have been - if you're lucky, you may not have to walk more than 50m from your cabin door!
You'll usually hear proboscis monkeys before you see them - crashing around in the canopy and issuing loud honking ("Ngonk!") and grunting sounds. The males, being larger and more brightly coloured, are easier to spot - particularly their red backs and long white tails, which hang straight down.