Long-tailed macaques in Borneo (Photo by John Tomsett)

Dear Readers, when I read this piece in New Scientist this week I was transported right back to my 60th birthday special holiday in Borneo, when we watched long-tailed macaques playing alongside the river. I remember thinking how intelligent and dextrous they seemed to be. I was also very impressed that one macaque who had lost one of his hands (possibly in a snare, or from a predator attack) was doing very well, keeping up with the rest of the group and appearing to be in good condition. Clearly there are benefits from being a social animal.

Injured macaque, but doing very well.

Now, the report in New Scientist is about a group of long-tailed macaques who live in Thailand, on the island of Koh Ped. Normally these monkeys have a splendid life, as tourists visit the island by boat and often bring mangoes, cucumbers and nuts for the animals. The monkeys were also visited by a group of researchers led by Dr. Suchinda Malaivijitnond of Chulalongkorn University in Bangkok, who had been visiting the macaques for over a decade.

However, all of this came to a grinding halt in 2020, due to the Covid-19 pandemic. No mangoes! No researchers! And when the researchers were allowed back to the island in 2022, they discovered something astonishing: the macaques were using stone tools.

The macaques had discovered that they could use stones to smash the shells of the oysters that occur along the beach. According to the researchers, they were using quite a crude method, raising the stone above their heads and then throwing it at the shellfish, but 17 separate monkeys were using the method to get themselves some much-needed food. At the moment it’s not clear if the monkeys came up with the technique individually, or if they learned it from one another. Nor is it clear what will happen now that the tourists are back with their fruit and nuts, but primatologist Jonathan Reeves, of the Max Planck Institute in Leipzig, thinks that now that the oysters are part of their culinary repertoire they may well keep doing it.

Interestingly, a study on captive long-tailed macaques concluded that they couldn’t use tools. But why would they, when presumably they were getting food regardless? The monkeys on Koh Ped innovated because they had to, and because they had the intelligence and dexterity to figure it out. I think we often conclude that animals can’t do a particular thing because we didn’t offer them a big enough reward, or didn’t design the experiment well enough. For example, I remember reading a study that found that tortoises were perfectly capable of negotiating a maze provided it was wide enough for them to turn around the corners comfortably. Doh.