Proboscis monkey

Taxonomy

The proboscis monkey belongs to the subfamily Colobinae of the Old World monkeys. The two subspecies are:

• N. l. larvatus (Wurmb, 1787), which occupies the whole range of the species excluding northeast Kalimantan
• N. l. orientalis (Chasen, 1940), restricted to north-east Kalimantan However, the difference between the subspecies is small, and not all authorities recognise N. l. orientalis.

The genus name Nasalis comes from the Latin word nasus meaning "nose".

This animal was made known to Westerners by Baron Friedrich von Wurmb in 1781, he later sent specimens of it to Stamford Raffles in Europe.

Description

The proboscis monkey is a large species, being one of the largest monkey species native to Asia. Only the Tibetan macaque and a few of the gray langurs can rival its size.

Sexual dimorphism is pronounced in the species. Males have a head-body length of 66 to and typically weigh 16 to, with a maximum known weight of 30 kg. Females measure 53.3 to in head-and-body length and weigh 7 to, with a maximum known mass of 15 kg. The male has a red penis with a black scrotum.

The proboscis monkey has a long coat; the fur on the back is bright orange, reddish brown, yellowish brown or brick-red. The underfur is light-grey, yellowish, or greyish to light-orange. Both sexes have bulging stomachs that give the monkeys what resembles a pot belly. Many of the monkeys' toes are webbed.

Nose

Further adding to the dimorphism is the large nose or proboscis of the male, which can exceed 10.2 cm in length, and hangs lower than the mouth. Theories for the extensive length of their nose suggest it may be sexual selection by the females, who prefer louder vocalisations, with the size of the nose increasing the volume of the call.

The nose is smaller in the female and is upturned in the young. Nevertheless, the nose of the female is still fairly large for a primate. The skull of the proboscis monkey has specialized nasal cartilages that support the large nose.

Proboscis monkey (Nasalis larvatus) male head.jpg|Male Proboscis monkey (Nasalis larvatus) female Labuk Bay.jpg|Female Proboscis monkey (Nasalis larvatus) juvenile Labuk Bay.jpg|Juvenile Nasalis larvatus Paris 150110.jpg|Nasal cartilages that were left intact in a specimen skull in order to show the structures that support the nose

Distribution and habitat

The proboscis monkey is endemic to the island of Borneo and can be found in all three nations that divide the island: Brunei, Indonesia and Malaysia. It is most common in coastal areas and along rivers. This species is restricted to lowland habitats that may experience tides. It favors dipterocarp, mangrove and riverine forests.

Behavior and ecology

Social behavior

Proboscis monkeys generally live in groups composed of one adult male, some adult females and their offspring. Some individuals are solitary, mostly males. Monkey groups live in overlapping home ranges, with little territoriality, One-male groups consist of 3 to 19 individuals, Overall, members of the same bands are fairly tolerant of each other. A linear dominance hierarchy exists between females. Males of one-male groups can stay in their groups for six to eight years. Replacements in the resident males appear to occur without serious aggression. Upon reaching adulthood, males leave their natal groups and join all-male groups. Females also sometimes leave their natal groups, perhaps to avoid infanticide or inbreeding, reduce competition for food, or elevation of their social status.

In Sabah, Malaysia, proboscis monkeys have been observed in mixed-species groups with silvery lutungs, and interspecific mating and a possible hybrid has been observed.

Reproduction

Females become sexually mature at the age of five years. They experience sexual swelling, which involves the genitals becoming pink or reddened. Copulations tend to last for half a minute. When soliciting, both sexes will make pouted faces. In addition, males will sometimes vocalize and females will present their backsides and shake their head from side to side. The young begin to eat solid foods at six weeks and are weaned at seven months old. The nose of a young male grows slowly until reaching adulthood. The mother will allow other members of her group to hold her infant.

Communication

Proboscis monkeys are known to make various vocalizations. When communicating the status of group, males will emit honks. They have a special honk emitted towards infants, which is also used for reassurance. Males will also produce alarm calls to signal danger. Both sexes give threat calls, but each are different. In addition, females and immature individuals will emit so-called "female calls" when angry. Honks, roars and snarls are made during low-intensity agonistic encounters. Nonvocal displays include leaping-branch shaking, bare-teeth open mouth threats and erection in males, made in the same situations.

Feeding and activities

As a seasonal folivore and frugivore, the proboscis monkey eats primarily fruit and leaves. Groups usually sleep in adjacent trees. Monkeys tend to sleep near rivers, if they are nearby. Proboscis monkeys will start the day foraging and then rest further inland. Their daily activities consist of resting, traveling, feeding and keeping vigilant. As night approaches, the monkeys move back near the river and forage again. Predators (potential or confirmed) of the proboscis monkey include crocodilians like false gharials and saltwater crocodiles, the Sunda clouded leopard, sun bears and reticulated pythons as well as, for probably young or sickly monkeys, large eagles (such as the crested serpent eagle or black eagle), large owls, and monitor lizards. Monkeys will cross rivers at narrows or cross arboreally if possible. This may serve as predator avoidance.

Conservation status

The proboscis monkey is assessed as endangered in the IUCN Red List of Threatened Species and listed in Appendix I of CITES. Its total population has decreased by more than 50% in the past 36–40 years to 2008 due to ongoing habitat loss because of logging and oil palm plantations, and hunting in some areas due to the species being treated as a delicacy, as well as its use in traditional Chinese medicine. The population is fragmented: the largest remaining populations are found in Kalimantan; there are far fewer in Sarawak, Brunei and Sabah. The proboscis monkey is protected by law in all regions of Borneo. In Malaysia, it is protected by a number of laws including the Wildlife Protection Act (federal law), the Wildlife Protection Ordinance 1998 (Chapter 26) and Wildlife Conservation Enactment 1997 (Sabah state law).

The proboscis monkey can be found in 16 protected areas: Danau Sentarum National Park, Gunung Palung National Park, Kendawangan Nature Reserve, Kutai National Park, Lesan Protection Forest, Muara Kaman Nature Reserve, Mandor Reserve and Tanjung Puting National Park in Indonesia; Bako National Park, Gunung Pueh Forest Reserve, Kabili-Sepilok Forest Reserve, Klias National Park, Kulamba Wildlife Reserve, Lower Kinabatangan Wildlife Sanctuary, Sungei Samunsam Wildlife Sanctuary and Ulu Segama Reserve in Malaysia.

References

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