Did You Know? The proboscis monkey has the 'Endangered' status in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, and is listed in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

Information About Proboscis Monkeys

Bulbous Nose of an Old Male

Classification

✦ Kingdom: Animalia ✦ Phylum: Chordata ✦ Class: Mammalia ✦ Order: Primates ✦ Family: Cercopithecidae ✦ Subfamily: Colobinae ✦ Genus: Nasalis ✦ Scientific name: Nasalis larvatus ✦ Length: 73 - 76 cm (males), 54 - 64 cm (females) ✦ Average Weight: 44 pounds (males), 22 pounds (females) ✦ Feet: Partially-webbed toes ✦ Tail Length: 66 - 75 cm (males), 52 - 62 cm (females) ✦ Gestation Period: 166 - 200 days ✦ Age of Sexual Maturity: 5 years (Females) ✦ Breeding Season: February to November ✦ Lifespan: 15 - 20 years

Habitat

The proboscis monkey is endemic to the island of Borneo in Southeast Asia. As far as their habitat is concerned, these monkeys seem to have a preference for coastal mangrove forests, but they can also be found in mixed diterocarp-kerangas forests or lowland rainforests that lie close to freshwater rivers. They rarely move farther than a kilometer from water. The availability of food is a determining factor, when it comes to the choice of habitat. They avoid deforested areas. The deforestation of the rainforests for timber has been the reason behind their declining numbers or their endangered status.

Diet

These monkeys are folivores (leaf eaters) and frugavores (fruit eaters). It is believed that they are more likely to consume fruits from January through May, and leaves from June through December. Their diet mainly comprises tender leaves, shoots of mangrove, fruits, seeds, flowers, and unripened fruits. However, they might occasionally consume caterpillars or larvae.

Interesting Facts About Proboscis Monkeys

Pendulous Nose of a Male

Nose of a Juvenile

✦ Only the males have a very long nose. Though the nose of the females is larger in comparison to monkeys belonging to other genera, it is considerably shorter than that of the males. The juveniles or young monkeys have small, upturned noses. ✦ When excited or angry, the nose of the male monkeys turns red and swells up. The nose acts as a resonating chamber during vocalizations. During vocalizations, the nose extends and amplifies the sounds. It is believed that females get attracted to monkeys with a longer nose, as the long nose helps them make louder calls. ✦ Loud honking calls are made by adult males of the group to warn others about the presence of a predator or to threaten other members of the group. Adult males might also growl for calming or reassuring the members of a group. Males protect the young ones from predators, which might include false gavial, pythons, crested serpent eagles, estuarine crocodile, and clouded leopards. ✦ These monkeys are social by nature. They live in groups, with a group comprising a male with a harem of around six females and their offspring. The dominant male protects the group. While the group feeds, the adult might climb a tall tree to look out for predators. ✦ The females compete with other females for the attention of the dominant male. Usually, females pout or shake their heads to express their desire to mate. ✦ Several harems or groups might even join together to form troops, which can have as many as 50 males and females. Young females might move from one harem to another. ✦ Several groups might come together at night to sleep. They prefer to sleep near water. ✦ Births mostly occur during the night. The mother cleans the offspring by licking, and is also known to consume the placenta. ✦ The offspring stays with the mother for the first few years. After 18 months, juvenile males leave the group for joining all-male groups. ✦ These monkeys are born with blackish blue fur on their face. Within 3-4 months, the color of the fur changes. ✦ Adults have light brown fur, with red-colored fur on the crown and the shoulders. The fur on the underparts and the tail is gray in color and there are cream patches on the throat. The fur on the back is reddish brown in color. They have cream-colored fur around the neck, which looks like a collar. ✦ Their diet comprises unripe fruits and leaves, which are rich in cellulose. The colonies of bacteria present in their digestive tract helps in the digestion of cellulose. ✦ Both males and females have a large belly, which accounts for about one-fourth of their body weight. Their stomach is divided into chambers like cows. Symbiotic bacteria in the first two chambers help in the digestion of cellulose, whereas the enzymes present in the other two chambers digest these bacteria. ✦ The partially-webbed feet of these monkeys helps them swim. Usually, these monkeys resort to swimming for crossing rivers. They can walk upright in the water. They have been known to leap from high branches into rivers. ✦ These monkeys vocalize in different ways. The males may honk to communicate territorial information. They might honk for reassuring infants. In case of an impending threat, the males give an alarm call. Threat calls are given by both males and females. When agitated, the females and offspring are known to shriek.