Infant survival among free-living bonnet macaques (Macaca radiata) in South India

In our research, carried out in two groups of free-living bonnet macaques in the middle of the in the southern India, we assessed whether the characteristics of age, dominance rank and experience of mothers, as well as their age and sex of children, had an impact on the survival rate of offspring in the first year of life. Our observations showed that the offspring of older and more experienced females survived more often until the first year of life. Moreover, regardless of the age of the mother, infant males were more likely to die than infant females. Our research shows the importance of social and anthropological factors on reproduction and survival of wild bonnet macaques, which may help protect this endangered species. Female reproductive success depends to a large extent on infants’ ability to survive to maturity. While most studies of female reproductive success have focused on the effects of individuals’ sociodemographic factors (e.g. age/parity, dominance rank) on offspring survival among wild primates living in less disturbed habitats, little research has focused on offspring survival in urban or peri-urban animals.

In our study we assessed the social, demographic, and anthropogenic determinants of infant survival in wild bonnet macaques (Macaca radiata) living in peri-urban environments in Southern India. Fifty infants were born across two birth seasons. 29.2% of infants died or disappeared in 2017 and 26.9% died or disappeared in 2018. We found that infant survival was strongly influenced by the female’s experience: infants of older mothers had a better chance of survival than those of first-time mothers. We also found that sons had less chances to survive up to the first year of life, than daughters. However, we found no effects of mothers’ dominance rank, or of frequency of mothers’ interactions with people and time spent foraging on anthropogenic food, on infant survival. Our results, consistent with findings from other wild primate species, show that even in challenging human-impacted environments, experienced bonnet macaque mothers have greater success than inexperienced ones.

Our study has implications for the conservation of bonnet macaques, because understanding sociological and ecological factors that affect reproduction and survival are important in increasing our ability to effectively protect populations threatened with extinction. The fact that naïve mothers in particular, may be more vulnerable to losing offspring in unpredictable anthropogenic environments suggests that the Thenmala bonnet macaque population remains vulnerable. As a species, bonnet macaques are restricted to peninsular Southern India, where an expanding human population is associated with a decreasing population trend. It will therefore be important to design and implement cost-effective tools for monitoring population health, gain more insights into the mortality of bonnet macaques, and more generally better distinguish the effects of social, ecological and anthropological stress on reproduction and infant survival.