Monkeys know the value of stolen goods

A long-tailed macaque holding a pair of stolen sunglasses

Summer! Many of us will, after a two-year break, travel year again this year. But crowded touristic places are heaven for pickpockets. And sometimes the robbers are not humans but animals.

At the Uluwatu Temple in Bali (Indonesia) long-tailed macaques are the guilty party. But luckily, the monkeys are willing to return the stolen goods… if you pay them enough.

Uluwatu Temple

On a nice day at the Uluwatu Temple

Imagine that on a warm and sunny day you walk among this Hindu temple complex. You admire the old buildings, the view from the cliff and also the cute monkeys running around or resting among the trees. They don’t seem to be bothered by people and you can watch them from really close by.

At some point, it’s time for a small break in the shade. You lean against the stone fence, prop your sunglasses on the top of your head to grab your water bottle. Suddenly, you feel that, in a split second, someone grabs the glasses off your head. Turning around you see a monkey running away with them. However, it doesn’t get far and it looks at you. But if you try to get too close it will keep its distance. You won’t outrun the monkey. Your only chance to get your glasses back is to offer something in exchange.

But be prepared. These monkeys (at least the older ones) are experienced barterers.

Toke exchange economy in a wild animal

Long-tailed macaques living near the Uluwatu Temple have been studied extensively as they seem to be the only wild animals that learned by themselves the ins and outs of token exchange economy*. For them humans’ objects are just tokens that by themselves are not very useful (even if they might be interesting to these curious animals). But these monkeys have learned that humans are willing to give them food in exchange for stolen items and that some items are more valuable than others.

With time comes shrewdness

Like any other skill, stealing and bartering need practice to perfect. Young individuals are not as successful at robbing as older ones. With age, their stealing abilities improve, reaching a peak with adulthood. This may be linked not only with increased muscle strength and control, but also cognitive skills and experience in, for example, target selection, stealth and self-control.

Juvenile animals also don’t seem to recognize the different value people give to different objects. Where value doesn’t necessarily mean the financial cost. Tourists value different items differently. For example, they are less likely to try to negotiate with the monkey for an empty phone case or hair pins, but are very likely to barter for shoes, glasses and electronic devices. Juvenile macaques not only indiscriminately steal objects of all values but are also not very successful at bartering and they will in general accept less food for stolen items than their elders do.

In contrast, adolescent and older monkeys already know the value given to things by humans and are fierce barterers. They steal more valuable objects and are less likely to give them back if not enough food or less-preferred food is offered (monkeys have a specific “turning down” hand/arm gesture – a way of saying “are you kidding me?”). The more valuable the object the fiercer the macaques will barter.

Experience it yourself?

So, if you have a chance to go for holidays to Bali, do visit Uluwatu Temple and maybe instead of guarding your sunglasses, let them be stolen and experience the full phenomena of the monkey exchange market (tip: ask one of the temple guides to do the bartering for you). The monkeys know that only undamaged goods will be exchanged for food, so you have a good chance to get your glasses back in one piece.

And if you don’t go to Bali, tell the story of the long-tailed macaques next time you haggle on the local market.


* There are numerous studies in the lab showing that various non-human primate species can learn to use tokens in exchange for goods.


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Photos: Macaque by Mx. Granger – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=82945951; Temple by Paskuu – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=62017662

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