Agricultural habitat use affects infant survivorship in an endangered macaque species

Infant survival is a major determinant of individual fitness and constitutes a crucial factor in shaping species' ability to maintain viable populations in changing environments.¹ Early adverse conditions, such as maternal loss, social isolation, and ecological hazards, have been associated with reduced rates of infant survivorship in wild primates.^2,3,4 Agricultural landscapes increasingly replacing natural forest habitats may additionally threaten the survival of infants through exposure to novel predators,⁵ human-wildlife conflicts,^6,7 or the use of harmful chemicals.^8,9 Here, we investigated potential links between agricultural habitat use and high infant mortality in wild southern pig-tailed macaques (Macaca nemestrina) inhabiting a mosaic landscape of rainforest and oil palm plantation in Peninsular Malaysia. Longitudinal data revealed that 57% of all infants born during the study period (2014-2023) died before the age of 1 year, far exceeding mortality rates reported for other wild primates.^{10,11,12,13,14} Importantly, prolonged time spent in the plantation during infancy decreased the likelihood of infant survival by 3-fold, likely caused by increased exposure to the threats inherent to this environment. Further, mortality risk was elevated for infants born to primiparous mothers and predicted by prolonged maternal interbirth intervals, suggesting potential long-term effects attributed to the uptake and/or accumulation of pesticides in mothers' bodies.^15,16,17 Indeed, existing literature reports that pesticides may cross the placental barrier, thus impacting fetal development during pregnancy.^18,19,20 Our findings emphasize the importance of minimizing anthropogenic threats to wildlife in agricultural landscapes by establishing environmentally friendly cultivation practices that can sustain wildlife populations in the long term.