Male Proboscis monkey
The females are far more modest being about half the weight of the males and with much smaller noses. Younger females have reasonably short stubby noses and even when fully mature they do not reach the huge dimensions of the males. Baby proboscis monkeys look very different from their parents but are equally striking with slightly blackish fur, blue faces and short upturned noses. By the time they reach about 4 months their fur has changed colour similar to that of an adult. Their face slowly changes too but they do not completely lose the blueish tinge until their are about 1 year old. Proboscis monkeys have a very limited distribution and they are not found in the rain forests of central Borneo. It is not completely understood why they choose peat and mangrove swamps but it is probably due to the richer alluvial soils that occur in these areas. The inland forests of Borneo grow on particulary poor soil and an animal of this size needs a good supply of digestible food which they seem to be unable to find there. Proboscis monkeys have quite complicated stomachs divided into several parts which contain large amounts of bacteria to ferment their food. This bacteria helps to break down cellulose which is the main structural part of leaves enabling these monkeys to exist on a very green diet. They miss out on more digestable foods such as forest fruits as these would cause a huge build up of acid in their stomachs. The forests around the mangrove and peat swamps of Borneo are always lush and green so it would seem that they are perfect for a leaf eating monkey. However most of the mature leaves are extremely tough which means they are not available as a food source and they need to find large quantities of young leaves to survive. They can also eat non sweet fruits such as nutmeg along with seeds but these are not available all year round. This forces proboscis monkeys to travel long distances to find enough young leaves and seeing them leap through the trees is always very special. They tend to live in groups containing one adult male and his harem of several females and their offspring. The average size of a harem is about 10 animals but occasional you see larger groups. Many primates live in such social groups but proboscis monkeys are unusual in that they do not stay apart to avoid rival harems. In fact they frequently come together by riversides in the evenings meaning it is not unusual to see large groups of them. Tanjung Puting national park in Borneo has an important population of proboscis monkeys along with its more famous orangutans. If you'd like to come to Borneo to see them have a look at my trips I run here.