Stress, Sociality, and Reproduction in Female Chacma Baboons

Photo credit: Larissa Swedell

Shahrina Chowdhury (CUNY PhD Student) describes her ongoing PhD research on the effects of environmental and social stressors on the behaviour, physiology, and reproduction of female chacma baboons in the Cape Peninsula of South Africa. This project has been funded by the National Science Foundation and the Leakey Foundation and is supervised by Larissa Swedell (Queens College / CUNY).

Photo credit: Julian Saunders

The aim of this study is to determine the effects of environmental and social stressors on female behavior and reproductive output, the effect of social bonds on female fitness, and whether females exercise strategies to cope with their specific social environment. It is becoming increasingly important to understand the effects of environmental and social stressors on physiology and behavior, particularly as prolonged exposure to stress can have negative impacts on fitness (Bonier et al. 2009). Concomitant with this is an understanding of the behavioral strategies individuals employ to cope with stress. This is especially relevant to humans and other primates, who may use behavioral mechanisms and social networks to cope with stress and for whom social bonding increases fitness (Silk 2007).

Female chacma baboons (Papio hamadryas ursinus) in the Cape Peninsula of South Africa provide an ideal system in which to study the effects of stress and the importance of social bonds as coping mechanisms. Females in this population are exposed to multiple stressors in their social and physical environment. Living in close proximity to urban areas, the baboons experience frequent contact with humans, both during raiding events and during herding by the baboon monitors who are employed to keep baboons away from urban areas. Moreover, the social environment of female chacma baboons includes an array of potential stressors, including high levels of aggression and threat of infanticide from frequently changing male residence in a closed population, as well as female-female competition. Living in multi-male multi-female troops, with varying numbers of males and females in each troop over time, chacma females are dynamic in the types and numbers of partners with whom they form and maintain social bonds, in the types of stress they experience as the troops vary in the type and amount of contact with humans, and in the ways in which they might cope with stress.

This study focuses on females in three troops of chacma baboons living in the Tokai Forest and ranging in parts of the Table Mountain National Park and neighbouring suburban areas and vineyards. I am examining the effects of ‘social’ (male aggression, female competition, infanticide threat) and ‘environmental’ (conflict with humans, herding by monitors) stressors on measures of stress in females. Further I am studying whether females have coping mechanisms to mitigate stress and in particular whether they use social bonds as a coping mechanism. Using both physiological and behavioral indicators of stress, I will quantify the secretion of glucocorticoid hormones in feces and measure self-directed behaviors (SDB), such as scratching, self-grooming, yawning and body-shaking, which often occur in situations of psychosocial stress. Additionally, I am collecting daily demographic data and detailed behavioral observations on social interactions to quantify each female’s social bonds, dominance status, and reproductive parameters.

This study will contribute to our understanding of the variable behavioral strategies females use under different social circumstances, and whether and how social bonds may be used to alleviate some of the stress experienced in their specific environment. In addition, this study will provide crucial information about the effects of commensalism on stress and reproduction in female baboons, as well as the baboons’ potential ability to cope with these stressors, and can therefore inform future management plans so as to effectively control human-wildlife conflict while minimizing stress on baboons. This project can also inform management decisions regarding relocation or translocation of males among troops, currently a management strategy used in the Cape Peninsula, as the results of this study will elucidate the effects of the number of males in a troop on female stress levels and thus the ratio of males to females in a troop that is sustainable from the point of view of female physiology and reproductive output.