Burmese long-tailed macaques' use of stone tools is being threatened by human activity in Thailand

Burmese long-tailed macaques (Macaca fascicularis aurea) are a rare variety of the common long-tailed macaques of Southeast Asia, found only in Myanmar and bordering areas of Thailand. In a few locations, these monkeys use stone tools along the coasts to crack hard-shelled invertebrate prey, such as rock oysters, sea snails, and crabs.

The research team, comprising Assistant Professor Michael D. Gumert from Nanyang Technological University's Division of Psychology, Professor Yuzuru Hamada of Kyoto University's Primate Research Institute, and Professor Suchinda Malaivijitnond of Chulalongkorn University' Primate Research Unit, discovered that human activities are showing signs that the persistence of the macaques' stone-use tradition may be in jeopardy at Laem Son National Park, a marine national park along the western coast of Thailand.

"Macaques easily change their feeding behaviour when influenced by humans, and we are concerned stone-using macaques will lose their traditional feeding behaviour if illegitimate development continues within the protected park," said Assistant Professor Gumert, who is based at the Nanyang Technological University in Singapore.

On Piak Nam Yai Island, the team's research site within the Laem Son National Park, they have found that human impact is altering the macaques and the island's ecosystems. Of highest concern is the illegal development of rubber farms and oil palm plantations within the park that is clearing portions of forest. Humans are also competing with the macaques for food, by their harvesting of bivalves, such as clams and oysters, at the protected coasts.

Another major concern is harassment by domestic dogs that have been released to protect the farms. The dogs are repelling macaques from the shores, which inhibits their tool-using activity. As these macaques are forced to become more vigilant and to constantly keep a look out for dogs on the coast, they are paying less attention to learning tool-using patterns from their seniors.

"Traditions need safety and stability to properly develop, otherwise, the coasts just become a danger area that macaques must learn to avoid, rather than a stable learning ground for developing tool-use," laments Dr Gumert.

"If these changes continue, the macaques could alter their foraging strategies, and potentially limit further development of their stone-using traditions in future generations," stressed Dr Gumert.

"Generally, when we think of conservation, we think of species preservation, but I think we must also be concerned with the preservation of rare and interesting behaviour produced by animals' cultures as well. Many animal species have unique traditions, and these traditions are fragile to disturbance. They require good conservation management of the habitats that foster these traditions," he added.

The researchers, who have studied the Burmese long-tailed macaques living on Piak Nam Yai Island since 2007, found that the island's macaque population had 192 individuals in nine groups and 88% of all adults there use stone tools. Tool-use is a part of the everyday life of these long-tailed macaques. "They have a fascinating lithic culture," noted Dr Gumert.

"These Burmese macaques are the only monkeys in Asia that use stone tools. Only two other primate species, out of several hundred in the world use stone tools -- the chimpanzees in Africa and capuchin monkeys in South America. Knowing about primate stone tool use has important implications to compare with early hominine tool use, as well as the origins of cultural behaviour. Studying traditions allow us to investigate the cultural capacity of animals," he added.

"We need to have better protection for these macaques. Otherwise, I am worried they will lose their natural foraging behaviour, like many macaques in Singapore and other parts of Southeast Asia already have."

A major environmental problem currently affecting Southeast Asia is the large portion of the long-tailed macaque population that has acclimated to living around humans and using our food sources. Voicing concern, Dr Gumert said, "This is directly the consequence of human development, and we don't want these rare stone-using macaques going the path of so many other macaques whose natural behaviour has been destroyed by our actions. Piak Nam Yai Island, should be fully protected from human activity because it is a national park and therefore legally protected land for natural resources and wildlife."

Looking ahead, the researchers hope to develop a long-term research programme in Thailand on tool-using long-tailed macaques that is based out of NTU and Chulalongkorn University. Dr Gumert plans to build permanent research sites around these animals, and bring in students and other scientists to study the behaviour and ecology of these macaques.

"We should also explore into Myanmar, because we think the behaviour may be more common there. Macaque stone tool-use was first reported back in the 1880's in the journal, Nature, by Alfred Carpenter, an English seaman. He saw tool-using monkeys in the Myeik Archipelago of then Burma, which has hundreds of islands in the chain. Laem Son National Park is at the southern part of that island chain and probably represents the southern boundary of this behaviour. We need to get into Myanmar and see how the macaques have changed since a century ago," Dr Gumert added.

"These monkeys are extraordinary and a natural treasure to the Southeast Asian region. I believe stone-using macaques will become a symbol of coastal preservation here, a symbol for protecting Thailand and Myanmar's wonderful coastal ecosystems, and all that depends on them," Dr Gumert said.