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Proboscis Monkey

Nasalis larvatus

Photo: Monkey in tree

Photo: Monkey in tree (View larger version)

Photograph by Tim Laman

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It may seem hard to believe, but male proboscis monkeys use their fleshy, pendulous noses to attract mates. Scientists think these outsize organs create an echo chamber that amplifies the monkey’s call, impressing females and intimidating rival males.

Proboscis monkeys are endemic to the jungles of Borneo, never straying far from the island’s rivers, coastal mangroves, and swamps. They are a highly arboreal species and will venture onto land only occasionally to search for food. They live in organized harem groups consisting of a dominant male and two to seven females and their offspring. Various groups often congregate near water at night to sleep.

Proboscis monkeys are the primate world’s most prolific swimmers, frequently leaping from tree limbs and hitting the water with a comical belly flop. They’ve evolved webbed feet and hands to help them outpace the crocodiles that are some of their main predators.

Among the largest of Asia’s monkeys, male proboscis specimens can reach 50 pounds (23 kilograms), although females attain only about half that size. Adults wear a coat of light brown fur that turns red around the head and shoulders and gray at the arms, legs, and tail. Only males develop the namesake nose.

Proboscis monkeys survive mainly on a diet of leaves, seeds, and unripe fruits but will occasionally consume insects as well. They have complex, chambered stomachs that rely on a host of symbiotic bacteria for digestion.

Unfortunately, Borneo’s most threatened landscapes are home to these highly specialized primates. The rampant clearing of the region’s rain forests for timber, settlement, and oil palm plantations has depleted huge tracts of their habitat. The fragmentation of the monkeys' range means they are being forced to descend from the trees more frequently and often must travel perilously long distances to find food. Their land predators include jaguars and some native peoples who consider proboscis monkey a delicacy.

Over the last 40 years, proboscis monkey populations have plummeted. They are currently protected from hunting or capture in Borneo and are listed as an endangered species.

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