Protecting the Proboscis

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Proboscis monkeys are endemic to the island of Borneo, living along rivers, coastlines and swampy forests (Image © Sylvain Cordier / Biosphoto / Corbis)

A look at conserving this charismatic species

By John Sha Chih Mun and Ikki Matsuda

The proboscis monkey has received increasing attention in recent years. Indeed, it has become a flagship species for tourism activities throughout its range, particularly in popular areas like Sukau in Kinabatangan, Sabah in East Malaysia. Tourists are almost always guaranteed to be rewarded with the sight of these enigmatic animals, as they can be easily found along rivers on a slow boat cruise in the mornings and evenings. This is due to their preference for habitats along rivers and coastlines; and their social group structure, which consists of basic one-male, multi-female or all-male groups congregating along waterways. 

Preserving the Proboscis

While on-going field studies have and will continue to reveal more information about the basic biology of this charismatic species, improved knowledge has also placed the long-term survival of the species increasingly under the spotlight. Borneo, having lost 30% of its rainforests in the last 40 years has had a particularly critical impact for the proboscis monkeys, which are adapted to swampy forest along waterways and have highly specialised diets, consisting leaves, unripe fruits and seeds found within these forests. The monkeys have quadripartite stomachs characterised by enlarged, sacculated fore stomachs for bacteria and enzymatic digestion of these hard-to-digest plants.

The proboscis monkey is a proficient swimmer, known to leap from tree limbs before hitting the water with a belly flop (Image © Martin Harvey / Corbis)

In recent years, mangroves and peat swamp forests in Malaysia and Indonesia have seen the highest rates of loss. Lowland forest habitats are also increasingly converted for land development, particularly for palm oil plantations. Unlike more generalist species of primates like macaques, proboscis monkeys are least likely to find alternative food resources in human-modified habitat and converted plantation forests.

The effects of increased tourism and human contact

The increase in proximity and interface between proboscis monkeys and humans can also lead to avoidance or habituation, neither of which are desirable. These effects can be seen in areas with high levels of tourism. Increase in boat traffic has also resulted in some populations moving further inland from their preferred habitats along river edges. In some areas, populations have become dependent on human food supplementation to survive. Increased contact with humans also mean they are more exposed to hunting pressure, where they can be easily tracked and killed.

Encroaching land development

Ten years ago, we estimated that the largest population of proboscis monkeys in Sabah, about 25% of the total population which is found along the Kinabatangan River was surviving only in an estimated 0.7% of total forested swamp habitats. As land conversion techniques improve, inland forests nearer and nearer to the waterway habitats of proboscis monkeys are being exploited. In coastal areas, the situation is even more dire as populations face a sea barrier on one side and human developments encroaching their habitats on the other. In these areas, extinctions of populations have been recorded and a decade on, this has not changed.

right The arboreal (tree-living) species travel through forest canopies by leaping from tree to tree (Image © John Sha)

However, not all is bad news. The latest evidence from the field suggests that proboscis monkey populations, at least in Sabah, have remained relatively stable over the past decade despite on-going habitat loss. Genetic studies have also shown that fragmented populations have maintained good genetic diversity, likely aided by their ability to swim across waterways. This indicates a good level of resilience to habitat loss, or at least for the moment.

A call to conservation

Many studies have shown that stable populations can operate for a period beyond their long-term carrying capacity, but eventually the ecological limitations will surface. Such a scenario has been recorded for a proboscis monkey population on an island in Kalimantan, Indonesia, where the initial density eventually collapsed due to limited food resources. With increasing land development, we fear that many populations are currently in ecological bubbles waiting to burst; effects of which would lead to catastrophic declines of populations within a very short time. More urgent conservation intervention will be needed to ensure the long-term survival of these unique monkeys.

For more stories and photos, check out Asian Geographic Issue 116.

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