The Monkey Mafia is acting up in Indonesia.

“Hey boss, you got something good for me?” Image credits: McKay Savage.

Researchers have identified and described a nasty but fascinating behavior of monkeys. By themselves, they’ve learned to steal the valuables of tourists and then sell it back for a profit.

The long-tailed macaques (Macaca fascicularis) living near the Uluwatu temple in Indonesia are not picky — they’ll steal anything: wallets, cash, hats, cameras, anything that looks like it’s valuable. Then, they’ll run off to the temple staff to sell their ill-gotten goods for a tasty treat. This behavior has been discussed anecdotally for years, but it hasn’t been properly studied. So Fany Brotcorne, a primatologist at the University of Liège in Belgium, set out to see how the macaques act, and what drove them to act this way.

“It’s a unique behaviour. The Uluwatu Temple is the only place in Bali where it’s found,” she says, which suggests it is a learned behaviour rather than an innate ability.

She spent four months around the temple, documenting the monkeys’ behavior — which I can only imagine was a unique experience in itself.

She learned that it’s a learned behavior because when a new group of macaques moved to the area, they too observed the other monkeys and soon copied the behavior. There were other clues as well. Aside from monkeys learning from one another, young males (who are more prone to taking risks) were observed to exhibit this behavior more than others. Basically, this appears to be a cultural behavior, transmitted from generation to generation and from monkey to monkey. In other words, it’s more like a human behavior than an animal behavior.

“This indicates that it can indeed be a new behavioural tradition in primates and one that teaches us that new traditions can involve robbing and bartering with a different species,” he says.

In fact, Brotcorne believes that this could actually help us understand a thing or two about ourselves and how our own cognitive abilities developed.

“Bartering and trading skills are not well known in animals. They are usually defined as exclusive to humans,” she says.

Amusingly, she also said that she herself fell victim to the monkeys — not once, but several times.

“Oh, so many times,” she says. “The monkeys were always trying to steal my hat, my pen, even my research data!”

It’s not the first time monkeys exhibit a surprising behavior. In a separate experiment, researchers taught monkeys the concept of money. Not long after, the first prostitute monkey appeared.

Journal Reference: Fany Brotcorne, Gwennan Giraud, Noëlle Gunst, Agustín Fuentes, I. Nengah Wandia, Roseline C. Beudels-Jamar, Pascal Poncin, Marie-Claude Huynen, Jean-Baptiste Leca — Intergroup variation in robbing and bartering by long-tailed macaques at Uluwatu Temple (Bali, Indonesia). DOI: 10.1007/s10329-017-0611-1