The Wildly Bizarre Proboscis Monkeys Of Borneo!

Orangutans steal the spotlight from other wildlife in Borneo. When people go to Borneo to “see the Orange” they are always mystified, baffled and dazzled by so many beautiful and bizarre creatures that they never knew existed. The proboscis monkey is certainly at the top of the list. With a giant nose, pot belly, crazy voice box, and several other bizarre features, once discovered they are never forgotten.

The giant nose of the male proboscis monkey is thought to simply be attractive to females. It serves no other purpose. The bigger the better!

Physical Characteristics.
There are several features which makes these monkeys extraordinarily quirky. The local Malay name for this species is Monyet Belanda, meaning “Dutch Monkey” because their huge pot bellies and big red noses reminded them of Dutch colonists in the old days. The huge belly is actually a big fermentation vat, similar to a rumen, which is full of a soup of microbes that break down the structural cellulose in leaves and turns it into usable sugar. This “gut flora” also helps to detoxify alkaloids (plant defense poisons) so they can survive on a very low quality diet of leaves and unripe fruits, as opposed to orangutans, gibbons and macaques, which need high quality young leaves of specific trees and fruits. A proboscis monkey would never eat a ripe banana, if it did, it could die of bloat!  Another unique and attention-getting characteristic of the males is a bright red penis that is always erect and sweating. The sweat is a way for excess sodium to be released, which allows them to live in the salty, mangrove forests.

Male penises are always erect, and sweating, which is a way for them dump excess salt which they accumulate from the their salty mangrove habitat.

The social structure of proboscis monkeys is also unique. There are two types of “troops”- a “harem” consisting of a dominant male and all 20 or so female mates and their young, and a bachelor troop (or band), which consists of single males. The dominant males of harems are constantly showing off with feats of strength, like breaking a branch, which is followed by a loud grumble of affirmation by his females. The troops feed in the forest by day, and always return to the river to sleep at night. The climb out onto a branch overhanging the water, and face inland, so they cannot be ambushed by their chief predator the clouded leopard. If a leopard approaches they always jump into the water. Proboscis monkeys are excellent swimmers aided by partially webbed feet!

We spotted this proboscis monkey swimming across a stretch of the Kinabatangan River at least a half mile wide! They are vulnerable to the giant estuarine crocodiles that inhabit Borneo’s coastal mangroves and rivers

Check out this video and listen to the crazy sounds of a troop of Proboscis Monkeys at a feeding platform near Sandakan, Sabah, Borneo.

Super cute baby proboscis monkey!

To see these special primates, one must visit intact mangrove riverine forests, in an area that has been strictly protected from hunting- this is an extremely rare commodity in Borneo! Habitat loss and hunting has been heavy the last 50 years, especially along the coastal rivers.  On all our trips the viewing and photographing proboscis monkeys is always a trip highlight.

Keep Exploring! Brad

The noise is unreal. Only males have the huge noses.

Big male proboscis at Bako National Park near Kuching, Sarawak, Malaysian Borneo.

All photos copyright Brad Josephs