Thieving Wild Monkeys Drive Hard Bargain When Bartering to Return Purloined Loot

New research looks at the marauding macaques in Bali that swipe people's things and don't return them until the perfect food is procured.

Flip-flops, hats, glasses and even phones – nothing is safe when it comes to the little monkey jerks at the Uluwatu temple in Bali. The swiftness with which the resident long-tailed macaques (Macaca fascicularis) swoop in and snatch the sandal off a child or the glasses straight off the face is commendable to be sure, if not a bit terrifying to the unsuspecting victim.

But even more surprising is the cunning with which they barter the return of stolen goods. Soft banana? Swat. Fruit in a bag? Swat, growl. Peanuts? Swat, chew on glasses. It’s not until a favored food is offered that the monkey will grab the item and leave the ransomed item behind.

As it turns out, the behavior is unique in the wild – well not the wilds of, say, Brooklyn, but in wild animals in general. And now for the first time, a group of researchers have taken a closer look at this unusual animal strong-arming.

While monkeys in captivity have been trained in the fine art of bartering for the purposes of research, the Bali monkeys might be the only wild animals in the world to do the same.

To get a better understanding of how they came to be such expert thieves, the researchers spent four months observing the behavior of the shady monkeys. They identified four groups living around the temple, and a fifth group that moved nearby during the research.

Signe Dean reports in SceinceAlert that the team recorded 201 'robbing and bartering' events, “noting down the identity of the thief, which of the four groups the monkey belonged to, what object it tried to steal (glasses were the most popular) and whether it got a successful barter for it.”

The study concludes that the monkeys learn their nefarious ways from one another and pass the tricks down to their offspring. Their skills improve the more time they spend around their targets. Also, the more young males in the group, the more thievery there will be.

"[O]ur findings indicate that robbing and bartering is a good candidate for a new behavioural tradition defined as a group-/population-specific practice, socially transmitted among at least some group members, persistent over several generations, and possibly locally adaptive," the team writes in their paper, published in the journal Primates.

Not surprising given their observations, during a follow up visit they found that the fifth group of monkeys had become bartering robbers as well. And while nobody wants their glasses ripped off their face, the social and cultural learning is fascinating to see. The researchers agree, and hope to do more work with larger groups.

The authors conclude that robbing and bartering (RB) is a “spontaneous, customary (in some groups), and enduring population-specific practice characterized by intergroup variation in Balinese macaques.” And as such, is a candidate for a new behavioral tradition in the species.

The video below was taken by study researcher Jean-Baptiste Leca. You can really get a good taste of just how cunning these monkeys are – and who can blame them? These are smart creatures who have figured out the best way to get what they need. Monkeys with moxie for the win ... just be sure to hold onto your glasses should you happen upon a temple in Bali.