There is no mistaking these monkeys, mainly because of the male’s protruding nose. Troops may occasionally be seen walking upright like people, along forest paths. These leaf-eating monkeys became known locally as Monyet belandas or Dutch monkeys, caricaturing the Dutch settlers who colonized this part of Southeat Asia.
Scientists are not sure why proboscis monkeys, particularly older males, have evolved such strange noses, but they may be involved in attracting females or even used to radiate excess heat. The male is considerably larger than the female, perhaps twice her weight. When he makes his loud, honking call, the nose straightens out. The female has a much smaller nose and a quieter cry. Proboscis monkeys are very social and sometimes feed together in bands of up to 60 or more animals. Usually they live in smaller groups of 2 - 27 animals, consisting of a single dominant male, a harem of 1 - 9 females and their young. They are most active in the morning, when they feed on leaves and shoots of mangrove and pedada trees, as well as on the fruit and flowers of other trees. Much of the rest of the day is spent basking in the tree tops, where they also sleep at night.
Proboscis monkeys have peculiar protruding noses that become particularly long and bulbous in old males. The infants have blue faces.
Young females stay with the group, while young males move away to join bands of bachelor males. Proboscis monkeys rarely move more than 1 - 2 km (0.6 - 1.2 miles) away from fresh water. They sleep close to rivers or in mangrove trees in coastal areas. The sturdily built proboscis monkey lives in the tree-tops of mangrove swamp jungles, where the trees are strong and rigid and do not attain enormous heights. It is an agile animal and runs and leaps in the branches, using its long tail as a counterbalance; its long fingers and toes aid grip.
Proboscis monkeys are among the best swimmers of all primates. They even have partially webbed feet, which help them to paddle or walk across soft mud. They drop off branches into water to escape predators such as clouded leopards, but are vulnerable to crocodilians. Proboscis monkeys are difficult to keep in captivity. Habitat clearance has meant that the numbers of this primate have fallen in recent years.
Distribution: Populations are restricted to Southeast Asia, found on the island of Borneo. Here they occur at low altitude, in areas of forest, mangrove and swamp.
Habitat: Lowland rainforest and mangroves.
Weight: 10 - 20 kg (22 - 44 lb); males are twice as heavy as females.
Length: 135 - 147 cm (53 - 58 in) overall; tail is longer than the body.
Maturity: Females 4 years; males 4 - 7 years.
Gestation Period: 166 days.
Breeding: 1; weaning occurs at around 8 months.
Diet: Young leaves in the first part of the year, followed by unripe fruit.
Lifespan: Up to 23 years.
Up to 18 cm (7 in) long, this swells with blood if the male feels threatened, and amplifies his calls.
Large and rounded, the chambered stomach houses microbes to break down vegetation.
These monkeys use their hands to pick the voting leases from the trees.
Webbing between the toes help these monkeys to swim.
The difference in size between the male (foreground) and female proboscis monkey is greater than in any other primate. The male’s nose attracts mates.
Even when drinking, proboscis monkeys rarely descend to the ground.