Balinese temple monkeys are sophisticated thieves

IF YOU VISIT Uluwatu temple in Bali, beware. The long-tailed macaques there are well-known thieves. Since time out of mind they have made a living by robbing visitors of their possessions and then holding those objects hostage until a ransom in the form of food is paid. That is quite clever. But Jean-Baptiste Leca of the University of Lethbridge, in Canada, wondered whether these monkeys are cleverer still. Sometimes, they do not accept the first offer and hold out for more. He therefore asked himself whether they are able to assess how valuable an object is to its owner, and factor that into their negotiations.Laboratory experiments conducted in the past with various species of monkey and ape suggest such primates can indeed attach a value to something intrinsically worthless to them, like a coloured plastic counter, by learning that tokens of this sort may be exchanged for food, and that different types of token bring different rewards, not all of them equally valued by the animal (a desirable grape versus an undesirable piece of cucumber, for example). That, though, is an artificial protocol in an artificial setting. The macaques of Uluwatu are true wild animals, albeit ones that are familiar with, and comfortable in the presence of, human beings.