The Endangered Proboscis Monkey Is Easily Identifiable By One Physical Trait: Its Supersized Schnoz

If Cyrano de Bergerac had been a proboscis monkey, he might not have needed poetry. For this furry primate, found only on the island of Borneo, a prominent nose is an asset. Males with the biggest snouts, up to nearly seven inches long, usually have the largest bodies overall. And, because their noses are an indicator of both status and reproductive fitness, these fellows attract more mates than their lesser-endowed competitors.

Proboscis monkeys can be seen and heard, thanks to the males’ deep nasal honks, in the forests along Borneo’s inland waterways and coastal mangroves, where they survive on young leaves and unripe fruit. Perhaps the world’s most aquatic primates, they swim across crocodile-patrolled rivers in search of fresh foliage, aided by partially webbed fingers and toes. Every night, the monkeys return to trees at the water’s edge to socialize and sleep. Researchers think the water makes it harder for predators such as tree-climbing clouded leopards to sneak up on them.

But this dependence on Borneo’s waterfront forests has put the species in danger, as humans have destroyed much of their habitat in the past several decades. In some areas of Kalimantan, the Indonesian part of the island, the monkeys are also hunted for food and traditional medicine. Combining regional estimates based on scant data puts the current population at 20,000 to 25,000. The International Union for Conservation of Nature has classified the proboscis monkey as “endangered” since 2000, calculating in 2015 that the population had declined by more than 70 percent over roughly four decades.

The Kinabatangan River floodplain, in the Malaysian state of Sabah, has lost approximately 80 percent of its natural forest to agriculture and logging, leaving the proboscis monkey and other wildlife in isolated fragments. To heal the landscape, the Malaysian conservation organization Hutan has planted more than 246,000 native trees since 2008, rebuilding forest corridors along the riverbanks in government-protected areas and private lands secured by Hutan and its partners. Hutan is also working with farmers to plant native trees on their lands. 

A few years after the group helped an oil palm plantation add native trees to its riverside land, monkeys returned to the area. “Today, we have a couple of proboscis families we see regularly,” says Marc Ancrenaz, a wildlife veterinarian who co-founded Hutan with primatologist Isabelle Lackman in 1998. 

In an area with so much degraded forest, small sites like this one offer Ancrenaz hope. “These monkeys don’t need a perfect, pristine forest,” he says. “With even a little restoration, the forest can become usable for proboscis monkeys again. This gives us a tremendous opportunity to link together habitat fragments with agroforestry and restoration work to help rebuild this population.”