Behavior of Mothers after Infant Loss in Bonnet Macaques (Macaca radiata)

Abstract Mother–offspring bonds in primates often last for life and shape the behavior of both mother and offspring. Therefore, the death of an infant may trigger an emotional response from its mother akin to human grief, which is characterized by active distress and passive depression. Our goal was to investigate whether the behavior of female bonnet macaques ( Macaca radiata ) changed after the loss of their infants. In the Thenmala area, southern India, between 2020 and 2022, we observed 18 mothers in two groups who lost, in total, 19 infants and three juveniles aged < 18 months. We compared affiliative, aggressive, and stress-related behavior of females before and after the death of their infants. We also examined individual variation in responses to infant loss. After the death of their infants, females withdrew socially, stayed on the periphery of the group, and had fewer companions. Bereaved females were less involved in grooming and hugging and initiated aggressive behavior more frequently than before they lost their infants. Moreover, females who lost infants showed frequent stress-related behaviors, such as self-scratching and yawning compared with when their infants were alive. Our results suggest that female bonnet macaques react to deaths of their infants in a manner that is consistent with the interpretation of grief in humans and other primates.