Bali’s thieving monkeys deliberately target most valuable items to trade for food

Long-tailed macaques have sophisticated understanding of value of objects they steal

Macaques had a preference for which reward they were given in exchange for valuables (GABRIEL BOUYS/AFP via Getty Images)

Long-tailed macaques who live around the Uluwatu temple in Indonesia deliberately steal the most valuable items from tourists in order to exchange them for better food, research shows.

Researchers found the enterprising monkeys have sophisticated knowledge of which items tourists consider most valuable and which are likely to net them the best returns when bartered for food.

The team from the University of Lethbridge in Canada spent 273 days at the temple in Bali and recorded over 2,000 interactions between the monkeys and tourists.

They established the relative values of food rewards for the monkeys, by observing their preference between three rewards offered by temple staff for tourists who want their property returned: raw eggs, bags of fruit and crackers. They found individual monkeys have different preferences between the rewards.

From their video recordings they observed that the monkeys have a sophisticated understanding of the value of the objects they steal, and would often hold out for greater or more preferred rewards when stealing items such as mobile phones, wallets and cameras.

While previous laboratory experiments had shown monkeys attach value to non-food items such as plastic containers and can learn by experience that such tokens can be exchanged for food, this study looked at the free-roaming monkeys around the Hindu temple.

In a paper published in the journal Philosophical Transactions of the Royal Society, Dr Jean-Baptiste Leca, an associate professor in the University of Lethbridge’s psychology department, said his team also found the monkeys seemed to learn the value of tourists’ items as they grew up, as they observed that younger macaques made no distinctions between the value of items.