Proboscis Monkey
Nasalis larvatus – The proboscis monkey was once fortunate enough to live in one of the world’s most inaccessible and undisturbed areas. Today, despite government protection, the species is endangered because of destruction of its mangrove forest habitat. Until quite recently the extraordinary-looking proboscis monkey was relatively common on its native island of Borneo. Even while other native primates-such as the orang utan were suffering dramatic population declines, the proboscis monkey appeared to be holding its own.
The main reason for its success was its inaccessible habitat; the species lives in some of the most impenetrable places on the island, namely, the dense mangrove forests that once lined many of the region’s rivers. Mangroves form a dense mass of branches and stems, standing in water and soft mud. It is virtually impossible to walk around in mangrove thickets, which may extend unbroken for many miles. Animals living there are fairly safe and have adapted to climb and scramble around with ease. While the stable rain forest of Borneo’s interior was being felled for timber and wood pulp, or cleared for agriculture, the mangroves remained inaccessible to machinery, and the space they occupied was unsuitable for agriculture. The waterlogged forest had little commercial value and was left to the proboscis monkeys and other specialized mangrove wildlife.
A Life Near Water
Proboscis monkeys are the most aquatic of all the primates. Their partially webbed feet make them excellent swimmers, and they sometimes use the water as a convenient emergency escape route. Alarmed monkeys will readily plunge 50 feet (15 m) from a treetop to the relative safety of the water. Such a jump onto dry land would result in serious injury, even for an agile primate. The monkeys tend not to feed in the water, surviving instead on a diet of leaves plucked from the trees. The leaves are generally tough and not nutritious, so they have to be eaten in large quantities. It has been estimated that the contents of an adult proboscis monkey’s stomach accounts for about a quarter of its body weight. The huge meals pass slowly through the monkey’s digestive system and are broken down by special gut dwelling bacteria. The bacteria also break down some of the toxic chemicals produced by mangroves and many other forest plants, enabling the proboscis monkey to take advantage of food that other animals have to avoid.
A Nose for Success
The large nose of the mature male proboscis monkey is what gives the species its name, but its precise purpose is unknown. Being much larger than females, males are more prone to overheating: One theory is that the nose acts as a cooling device, radiating excess body heat. It may also be that the large nose is a badge of success, since it continues to grow throughout a male’s life; the males with the largest noses are the oldest and presumably, therefore, the fittest and most successful breeders. In choosing a suitable male to father her offspring, a female may use the size of a male’s nose as an indicator of his genetic desirability.
Reduced Circumstances
It would be a tragedy if proboscis monkey numbers were reduced by so much that the species became more famous for being rare than for its other unique characteristics. However, its future is uncertain. The mangroves that provide its home are now harvested for wood, and modern drainage technology has meant that the watery world of the proboscis monkey is being invaded by developers. The rivers that once flooded the forests-creating natural refuges for wildlife-have been tamed, and in just a few decades well over half of Borneo’s mangrove forest has disappeared. Previously extensive mangrove swamps have been reduced to narrow fringes along rivers and no longer supply adequate habitat for the monkeys. There are a few proboscis monkeys in captivity. However, the species is considered difficult to keep in zoos, perhaps because it is not easy to re-create its natural mangrove habitat in artificial conditions. With the entire wild population confined to one island, the priority must be the preservation of its habitat. The male proboscis monkey’s extraordinary nose makes it one of the most easily recognized of all primates. Females and youngsters have small, upturned noses.
Statistic of Proboscis monkey (Nasalis larvatus)
- Family: Cercopithecidae
- Diet: Mostly leaves of pedada trees; some fruit seeds; also flowers
- World population: About 260,000 (1986 estimate); now likely to be considerably fewer
- Distribution: Borneo
- Habitat: Freshwater mangrove and lowland rain forest
- Size: Length head/body: 21-30 in (53-76 cm); tail: 22-30 in (56-76 cm); males twice as big as females. Weight: 17-30 lb (7-22 kg)
- Form: Large, long-tailed monkey with variable red-brown fur that fades to white on underside. Feet partially webbed. Nose is small and snub in juveniles and females; large and pendulous in males
- Breeding: Single young born at any time of year after 24 week gestation. Life span unknown; probably at least 10 years
- Related endangered species: No close relatives, but at least 35 other species of Old World monkey family Cercopithecidae are classified as Vulnerable or Endangered
