Are Oil Palm Plantations killing Baby Macaques?

James Peng

Professor Joseph Feldblum

Are Oil Palm Plantations killing Baby Macaques? 

Did an Orangutan Try To Fight a Bulldozer Razing a Forest? | Snopes.com
An orangutan trying to fight a bulldozer razing a Forest

In Southeast Asia, the rapid expansion of oil palm plantations has always been criticized for its impact on biodiversity. For instance, according to the Orangutan Foundation International, the establishment of palm oil plantations is a major cause of habitat loss for these great apes. Moreover, they are often brutally killed as agricultural pests by people inhabiting the plantations.


A recent Current Biology study demonstrated another alarming consequence of these plantations the high mortality rate of infant southern pig-tailed macaques (Macaca nemestrina) in Peninsular Malaysia.

Over a 10-year longitudinal study at the Segari Melintang Forest Reserve, which covers both rainforest and oil palm plantations, researchers found that more than half (57%) of infant macaques born in the study group died before one year old. Using correlation analysis, they determined that infants spending more time in plantations were three times more likely to die than those with lower exposure. Additionally, researchers observed that many infants were underweight or had facial malformations, leading them to suspect pesticides as a contributing factor. Chemicals such as herbicides glyphosate and paraquat can lead to low fertility and thus increase the long birth interval. This study found that mothers with longer birth intervals had higher infant mortality, further supporting concerns about pesticide exposure.

A southern pig-tailed mother with infant.

During our class discussions, we have talked about how deforestation and habitat loss can lead to devastating impacts for primates. However, this study suggests that primates that adapt to fragmented landscapes such as these macaques living alongside human plantations are still at great risk. The findings highlight the need for wildlife-friendly agricultural practices, such as reducing chemical use. It also raises ethical concerns such as how can oil palm companies be held accountable for the ecological damage they cause? Nevertheless, it is important to keep in mind that this correlation study does not establish that pesticides are the direct cause of infant mortality. Therefore, further research is needed to confirm their physiological role while considering other factors that negatively impact the macaques, such as behavioral stress from human activities.


Citation:

Holzner, A., Mohd Rameli, N. I. A., Ruppert, N., & Widdig, A. (2024). Agricultural habitat use affects infant survivorship in an endangered macaque species. Current biology : CB, 34(2), 410–416.e4. https://doi.org/10.1016/j.cub.2023.12.002 (Raman & Esterman, 2024)

Raman, S., & Esterman, I. (2024, February 27). 'Shocking' mortality of infant macaques points to dangers of oil palm plantations. Mongabay. Retrieved March 7, 2025, from https://news.mongabay.com/2024/02/shocking-mortality-of-infant-macaques-points-to-dangers-of-oil-palm-plantations 

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