Thieving Monkeys Steal Expensive Items to Trade for Better Food, Study Says

The monkeys hold onto the stolen item until they receive the food they think to be of corresponding value.
Derya Ozdemir
A thieving monkey on the job.Freiheitsjunkie/Pixabay

Uluwatu Temple in Indonesia is home to long-tailed macaques (Macaca fascicularis) who are famous for their intelligent nature and highly skillful hands which tend to find their way into unsuspecting tourists' pockets.

This crime ring of monkeys has become infamous over the years when the sight of macaques stealing from tourists and holding the random until they were paid in food became popular, and now, a new study has shown that some of these monkeys intentionally steal expensive items that are valued by their owners in order to barter for better food.

A team of researchers at the University of Lethbridge in Canada and Udayana University in Indonesia spent 273 days at the temple in Bali and recorded more than 2,000 interactions between the monkeys and tourists, showing that some of the monkeys carried out "unprecedented economic decision-making processes." 

The paper has been published in a Royal Society science journal. 

Economic decision-making among monkeys

It was previously known that monkeys attach value to non-food items such as plastic containers and can learn that such items can be exchanged for food. In this study, free-roaming monkeys around the Hindu temple was explored. 

It was investigated whether the macaques were using stolen objects as a bartering tool to get food. The researchers also examined whether they discriminated in what they took from the visitors. While such behavior has never been recognized in a free-roaming population of non-human animals, per the paper, researchers suspected that monkeys' living with humans and their belongings may have inspired such behavior.

Thieving events were observed with macaques' age, degrees of success, and whether or not the monkeys used the stolen item as a bartering tool being noted down.

Researchers staged robberies

These observations and their analyses revealed that the bartering behavior had to be learned at a young age with their likelihood of success increasing with age and experiences.

The researchers also staged fake robberies where the monkeys were presented with the perfect opportunity to steal from a person carrying medium or high-value items. Some scenarios included shoe versus glasses and hat versus phone.  

It was seen that low-valued items were seldom bartered for by humans, while the medium-valued were often bartered for. High-valued items were almost always bartered for by humans. 

The results showed that older monkeys were better at identifying and stealing the high-value items. They also refused measly offerings and hold out for bigger trades. After stealing the item which had the highest value to the visitor, such as an electronic item, the older monkeys would hold onto it until they received the food they thought to be of corresponding value.


The researcher wrote that this "population-specific, prevalent, cross-generational, learned and socially influenced practice may be the first example of a culturally maintained token economy in free-ranging animals."

“Further experimental research on the Uluwatu macaques should make future cross-species comparisons of economic decision-making and symbolic tool use more relevant from an evolutionary perspective and may ultimately lead to a better understanding of the origins of autonomous monetary systems in humans.”

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