Long-tailed macaques of Bali have learned to steal high-value goods from tourists

A few years ago, the scientific news broke of a group of long-tailed macaque monkeys in Bali, Indonesia who would steal stuff from people and hold it ransom for food. You want your hat back? Gimme an apple.

Researchers kept studying the monkeys, and discovered something even more wild: The animals learn which items humans regard as high-value, and which will produce superior ransoms.

Stealing a low-value item, like an empty phone case? That won't get much food. Steal someone's glasses, or a wallet? Now that is gonna get a human to cough up a high-end ransom. The monkeys demonstrate "unprecedented economic decision-making processes", as the researchers write in their paper, online here.

What's more, the behaviors are socially learned, and the monkeys get better at judging high-value items with experience. The older ones, researchers found, tended to steal higher-value items.

The Guardian spoke to the researchers, who said …

"These monkeys have become experts at snatching them from absent-minded tourists who didn't listen to the temple staff's recommendations to keep all valuables inside zipped handbags firmly tied around their necks and backs," said Leca. [snip]

Bargaining between a monkey robber, tourist and a temple staff member quite often lasted several minutes. The longest wait before an item was returned was 25 minutes, including 17 minutes of negotiation. For lower-valued items, the monkeys were more likely to conclude successful bartering sessions by accepting a lesser reward. [snip]

Robbing and bartering is an expression of cultural intelligence on the part of the monkeys, said Leca. "These behaviours are socially learned and have been maintained across generations of monkeys for at least 30 years in this population."

(CC-2.0-licensed photo of long-tailed macaques in Bali courtesy the Flickr stream of Ron Knight)