Monkeys were caught eating rats in a palm oil plantation in Malaysia

A macaque devouring a rat. | Anna Holzner
Pig-tailed macaques (family Cercopithecidae) feed mainly on sweet fruits and other vegetables. But, to the surprise of the scientists who made this intriguing discovery, they can also eat an astronomical amount of ... rats. Indeed, macaques were caught eating rats in a palm oil plantation in Malaysia.

The researchers found that, far from being seen as pests, monkeys could ultimately be prime guests in Malaysian oil palm plantations, compensating more than the few fruits they steal by reducing a threat well. more important: rodents.

Over the last six years, scientists from Malaysia and Germany have closely monitored two populations of Pig-tailed Macaques (here in particular Macaca nemestrina) from the south of Segari Melintang Forest Reserve, Malaysia. The monkeys spent a lot of time relaxing in the palm oil plantation surrounding the reserve, which represents about one-third of their living area.

Farmers may not have been happy with the intrusion of monkeys, but for macaques, the palm oil plantation was like a supermarket: indeed, although monoculture encroaches on their habitat, it offers them "cheap" food. Note that these macaques spend several hours a day in the plantations, about half of their total feeding time. As a result, it is not surprising to see them busy eating palm fruit.

What was a little more surprising though, even shocking when scientists discovered it, is the main dish of macaques: rats. " I was stunned when I saw that macaques were feeding on rats in plantations, " says Nadine Ruppert, an ecologist at Universiti Sains Malaysia. " I did not expect them to hunt these relatively big rodents or eat so much meat. They are widely known to be frugivorous primates, which only feast on small birds or lizards from time to time  , "she added.

An adult male pigtailed macaque consuming a rat in oil palm plantations. Credits: Anna Holzner
This observation leads to interesting questions: Are monkeys really the enemies of farmers? Is their presence a lower cost for them, since they perform a service for the least practical fight against rats? Why do these monkeys eat so many rats?

Through their research, scientists have found that monkeys eat more than 12 tons of palm fruit a year. It may sound like a lot, but you should know that this amount is only a little over half a percent of the total production of the plantation area covering their home range ... This is nothing compared to the damage caused by rats, which they can potentially nibble up to 10% of the products of the plantation.

Of course, if the monkeys ate only a few rats from time to time, it certainly would not make a big difference. But it turns out that they can consume very large quantities ... " In discovering cavities in oil palm trunks, where rats seek refuge during the day, a group of pig-tailed macaques can capture more than 3000 rats a year!  Said Anna Holzner, an anthropologist at the University of Leipzig, Germany.

As a result, if a primate-hungry population feeds on rats that cause havoc on the plantations, their damage could be reduced to only 2% (instead of 10%). Of course, there is still the 0.56% damage caused by the monkeys. But the total would represent a loss of less than 3%, which is always more advantageous than the 10% caused only by rats ...

However, in this calculation, one must also consider ethics. Indeed palm oil plantations are important activities in Southeast Asia, but their cost to the environment is more than considerable.

As a result, finding ways to turn these plantations into non-hostile areas for the surrounding wildlife could help to save, in part, the industry's terrible reputation for its impact on wildlife.

" We hope that our results will encourage private and public plantation owners to consider protecting these primates and their natural forest habitat in and around existing and newly established oil palm plantations ," said Anja Widdig. , lead author of the study, also from the University of Leipzig.


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