Monkey tool use threatens prey numbers, say researchers

Using tools to search for food is affecting primate prey numbers and could potentially lead to prey species extinction, new Oxford research suggests.

Once thought to be a skill unique to humans, recent studies have shown that some animals, such as monkeys, apes, birds and otters, are able to use tools to find food that would otherwise be inaccessible to them.

Tool use has been a gift and a curse for human society, on the one hand allowing people to progress to become one of the most successful species on the planet, but on the other endangering and pushing many prey species to the brink of extinction, particularly in the case of ocean overfishing.

In new research published in the journal eLife and funded by the European Research Council, scientists from the Department of Anthropology and Archaeology at Oxford University have assessed whether tool use can negatively affect prey species in the same way it does in human society. Using the primate species macaques (Macaca fascicularis) as an example, the findings reveal that these monkeys not only use tools but experience the same adverse effects, such as prey decline, which could eventually lead to a loss of tool skills. The paper was presented today at the British Science Festival.

Led by Dr Lydia Luncz, a postdoctoral researcher at Oxford, the team used archaeological evidence to demonstrate that the macaques’ use of tools to forage for shellfish in Khao Sam Roi Yot National Park in Thailand is affecting prey availability.

The researchers compared the availability, size and maturation stages of groups of shellfish between two islands inhabited by different-sized macaque populations against the stone artefacts uncovered on the island. In doing so, they were able to show how tool use has affected prey reproductive biology over time.

The findings show that this foraging behaviour has caused the monkeys to enter an ‘ecological feedback loop’, influencing both the size and amount of prey available over time. The evidence revealed an emerging pattern: both the size of the shellfish and the tools used to open them were found to be smaller on the island with many predators. If it continues, the researchers have speculated that these prey populations are likely to decline.

Without prey to forage on, the monkeys will also have no need to use the technique so might even experience a social regression and ‘unlearn’ how to use tools altogether.

Dr Luncz said: ‘People often say that practice makes perfect – the more you do something the better you get at it. But the less you do it, the harder it becomes and the more you are likely to forget that skill completely. Our study shows that it is the same for monkeys. With no need to use the stones for foraging, the technique might be lost.

‘As this is a learned social behaviour, in the long term there will be a generation of macaques that do not know how to use tools, and any associated benefit or trade with other species will be lost. Potentially, one day tool use might get reinvented by later generations, and it will be interesting to see how the skill is discovered and who they learn it from.

‘This has interesting parallels to the evolution of human stone use, where stone technology might also have been lost and reinvented throughout history.’

The team will next build on this knowledge by visiting islands with monkey populations that do not currently use stone tools to dig for evidence that they may have done in the past.

Dr Luncz said: ‘In archaeology, generally the deeper you dig the further you go back in time. The same methods used for human artefacts can tell us a lot about how species have evolved and adapted to environmental change over time.’

For further information and images, please contact Stuart Gillespie in the University of Oxford press office at [email protected] or Lydia Luncz: [email protected]