Proboscis Monkey

The proboscis monkey's fate is tied directly to Borneo's lowland forests. Because it depends on mangroves, peat-swamp forest and riverbank vegetation - exactly the flat, water-rich land that is easiest to drain and convert - it has lost huge areas of habitat to oil-palm plantations, logging, shrimp farming and coastal development. The IUCN estimates the population has fallen by more than 50% over roughly the last 40 years (about three generations) and lists the species as Endangered, with fewer than an estimated 7,000 mature individuals remaining across a highly fragmented range. Surviving groups are increasingly cut off from one another along single rivers, which makes local populations vulnerable to disturbance, hunting and isolation.

Proboscis monkeys live in a flexible, fission-fusion society: typically one dominant male with a group of females and young, plus separate bachelor bands of males, which gather and split along the same stretch of river. They are highly arboreal but also remarkable swimmers - one of the few primates with partial webbing between the fingers and toes - and will leap from branches into rivers and swim across, sometimes underwater, to escape predators such as crocodiles or to reach feeding trees. Their bulging bellies house a specialised, multi-chambered stomach where bacteria ferment tough leaves, similar to a cow's digestion, allowing them to live on foliage, unripe fruit and seeds that other monkeys cannot process.

The species is named for the male's proboscis - a fleshy, drooping nose that can hang lower than the mouth and grows larger with age. Research suggests it is shaped by sexual selection: a bigger nose acts as a resonating chamber that amplifies the male's honking calls and may signal size and dominance to females and rivals. Females prefer larger-nosed males, and nose size correlates with body mass and the number of females a male attracts. Females and infants, by contrast, have small, neat, upturned noses, making the sexes easy to tell apart.

Protecting proboscis monkeys is mostly about protecting habitat. Because they cannot survive away from intact riverine and mangrove forest, conservation centres on safeguarding river corridors, restoring degraded mangroves, reducing forest conversion and maintaining connected patches so isolated groups can mix. On-the-ground work also includes monitoring populations, reducing hunting and snaring, managing wildlife tourism so it does not stress the animals, and rehabilitating individuals orphaned or displaced by land clearing. Effective action depends on local rangers, community-run reserves and sanctuary teams who know the rivers and can respond quickly.