With its big, bulbous hooter, the proboscis monkey is one of the most recognisable primates in the world. In the past, it was said that their noses were so big, they had to hold them to one side to eat, but this isn’t true. They eat just fine.
Endemic to the southeast Asian island of Borneo, these Old World monkeys are social and easygoing. They live in troops; harem troops contain a large, dominant male with his females and their youngsters, while bachelor troops are made up of males with the occasional female.
They hang out in the forests by mangrove swamps and rivers, where they forage for fruits, seeds and leaves. Unripe fruits are preferred as the higher sugar content of ripe fruit can cause their already plump bellies to distend even further.
They’re the only primate known to regurgitate their food and chomp it twice (aka, chewing the cud) and have a cow-style stomach with multiple chambers. Symbiotic bacteria living in the chambers help to break down and detoxify their hard-to-digest food.
Everything about these monkeys is large. Their stomachs are large, comprising up to a quarter of their body weight. They have long limbs and tails. They’re physically large – males can weigh up to 24kg (about 52lbs). And of course, their noses are large. As large, apparently, as those of the Dutch colonists who came to Borneo in the 19th century, prompting the local Malay people to nickname the monkey ‘Orang Belanda’ or ‘Dutch guy’.
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Not that the monkeys minded, because it turns out that lady proboscis monkeys dig a big conk. The sizeable schnoz, which is specific to the males and grows up to 17cm (6.5in) long, is a sexually selected trait. Females prefer males with big noses and science helps to explain why.
Studies show that males with bigger noses have bigger bodies and testes, and that nose size affects the quality of the males’ vocalisations. Their noses are, essentially, a proxy for reproductive fitness and, in keeping with this, males with bigger noses tend to have more females in their harems.
Oddly, males with bigger noses also tend to have smaller canine teeth. This is unexpected because males of other monkey species often use their canines for fighting and self-defence. But longer canines can make it harder to forage and proboscis monkeys are remarkably chilled – they’re not very territorial and rarely fight.
Members sometimes drift between groups and troops will often come together at night to sleep in the same area.
Proboscis monkeys are also good swimmers, with partially webbed hands and feet. Adults aspire to a splash-free doggy paddle that discourages attention from the crocodiles lurking in the waters where they live. Their biggest threat, however, is from us.
Populations have plummeted in recent years, due to the destruction of their native forests for timber, settlement and oil palm plantations. So, it’s as plain as the nose on their faces. This needs to stop.
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