Palm oil plantations change the social behavior of macaques

19-MAY-2021

Researchers spent months observing groups of southern pig-tailed macaques

UNIVERSITÄT LEIPZIG



A macaque eats a palm oil fruit on the edge of the plantation.

CREDIT
Photo: Anna Holzner

Due to the extensive clearing of their habitat, these primates sometimes turn to palm oil monocultures while foraging. This often leads to conflicts with farmers. The macaques do not damage the palm oil fruits to any great extent. On the contrary, they can even benefit palm oil cultivation, as they are excellent hunters of the masses of rats found on plantations, the main pest found there. As a new study has now been able to prove, however, regularly visiting the plantations has a significant impact on macaques' social behaviour. This was shown by researchers from the Max Planck Institute for Evolutionary Anthropology (MPI-EVA), Leipzig University (UL), Universiti Sains Malaysia (USM) and the German Centre for Integrative Biodiversity Research (iDiv). The new findings may help to develop appropriate measures for protecting the primate species, which is listed as vulnerable by the IUCN, and to promote peaceful coexistence between humans and wild animals.

It is well known that human-induced disturbances can affect the behaviour of various wildlife species, including primates. Previous studies have mainly focused on changes in the activity patterns or feeding behaviour of animals living in urban or tourist areas and fed by humans. "We, on the other hand, wanted to look at how different habitats, including anthropogenically highly modified habitats such as palm oil plantations, affect social behaviour in macaques," said Anna Holzner, first author of the study, which was recently published in Scientific Reports. "For most primate species social interactions within the group are particularly essential for successfully surviving in large, complex social groups in their natural habitat."

Two groups of southern pig-tailed macaques observed over a period of months

To find out, the scientists spent several months observing 50 individuals of two social groups of southern pig-tailed macaques (Macaca nemestrina) in Segari (Malaysia). Dr Nadine Ruppert (USM), head of the local research station, stressed: "This is the first population of this shy species to be habituated to scientific observers. Every day, the groups walk for about three hours from the rainforest to the neighbouring plantation." The researchers were interested in the differences in the animals' social behaviour between the rainforest - whose dense vegetation provides protection for the macaques - and two habitats within the palm oil plantation, the interior of the plantation and its edge. These both have an abundance of food in the form of palm oil fruits and rats, and also an increased potential for conflict with humans, but only the plantation edge provides cover in the form of a safe avenue of retreat into the adjacent forest. The study focused on aggressive interactions, relationship-promoting behaviours such as grooming and juvenile social play, social networking within the group, and mother-infant relationships.

As expected, the macaques use the plantation mainly as an additional food source. Both inside the plantation and at its edge, they spent about two-thirds of the time foraging and eating. Aggressive behaviour in the macaques was significantly increased in the plantation interior compared to the other habitats - a well-known phenomenon, especially in connection with foraging. However, this was not only triggered by the monkeys' increased feeding activity in the plantation, but rather the plantation itself played a major role: according to the scientists, the interior of the plantation, unlike the rainforest and the edge of the plantation, offers little protection from potential attackers and puts the animals under stress, which may in turn trigger the increased rates of aggression.

More:
https://www.eurekalert.org/pub_releases/2021-05/ul-pop051921.php