A Tree of Their Own
The most unusual thing you might notice when you see a proboscis monkey is its nose. These monkeys are sexually dimorphic -- meaning the males and females look different -- and one of the main differences is in the nose.
Photo: Danica Stark
Photo: Danica Stark
Another feature of proboscis monkeys is their large bellies, which is a result of their diet and digestive system. Proboscis monkeys are highly selective feeders, and have a specialized chambered stomach (sacculated) which allows them to eat food other primates cannot. These chambered stomachs digest leaves, an easily available but difficult to digest food source, through fermentation. However, because their digestive system is so specialized, it also means that they are restricted in what they can eat -- eating foods with high sugar (such as ripe pulpy fruits) can cause rapid fermentation and bloat, which is fatal. An improper diet can also cause the fore-stomach to become too acidic for the microflora within it to function properly; liver and blood disorders; or obstructions in the intestines or stomach, which also result in death. This specialized diet is a major cause of mortality of proboscis monkeys in zoos, and is a crucial reason why they are difficult to maintain and should not be kept in captivity.
Proboscis monkeys live in stable social groups, the sizes of which can vary from 3 to 26 individuals, and consist of one adult male, several females and their infants and juveniles; with groups of males occurring as well. These groups may also join up with other groups, and travel together in "bands" throughout the day.
In the late afternoon, proboscis monkeys congregate along the waterways to feed, play, communicate with other groups, and are where all male groups can check out their competition and the females in those groups, before settling in for the night. The following morning, after feeding, groups move away from the waterways back into the forest where they spend their day before heading back to the water in the afternoon.
Photo credit: Anna Nesbit
In my next blog, I will talk about some of the major threats proboscis monkeys are facing, why they have been labeled as Endangered, and why local extinctions of groups are expected to continue unless there are major changes made in Borneo, and by consumers all over the world.