Date of Degree


Document Type


Degree Name





Larissa Swedell

Committee Members

Janine Brown

Marina Cords

Clifford Jolly

David Lahti

Sara Stinson

Subject Categories

Biological and Physical Anthropology


chacma baboons, sociality, stress, Papio ursinus, behavioral flexibility


The physiological stress responses that animals exhibit to the myriad stressors in their environment can be used to assess the state of their health and well-being, and even survival capability. Although the stress response is adaptive in many cases, chronic stress responses may be maladaptive in some situations when it leads to dysfunction of the physiological system involved in the stress response itself, and can also cause deleterious effects on health, reproduction and survival. The stress response includes physiological responses to both environmental perturbations and psychosocial stress and anxiety associated with social perturbations. The latter factor is particularly important for social animals such as primates. One way in which primates may respond to stressors is by adjusting their social bonds as well as their behaviors so as to cope with stressors and mitigate their negative effects.

In my dissertation research, I studied the effects of three types of stressors – social, environmental and anthropogenic – on the glucocorticoid (GC) hormone levels and behavior of females in three troops of chacma baboons (Papio ursinus) in the Cape Peninsula of South Africa. I collected behavioral data from 33 females, i.e., all females that were adults at the start of the study period, and I also collected and analyzed fecal samples to determine GC levels. My study has three components, as follows:

1. Social stressors: I examined the effects of social instability caused by death and rank changes of males on GC hormone levels of females, as well as female behavioral responses to these events and their use of social bonds as coping mechanisms. In response to male instability, females increased the strength of their social relationships with other females, while focusing less of their social effort on males. Females differed in their adjustment of social relationships by reproductive state, with cycling females increasing their grooming of males and lactating females – who are at most risk of infanticide – reducing their grooming of females during the period of instability associated with the alpha male’s injury. These changes in behavior may have effectively mitigated the negative impacts of social stressors, as GC levels did not increase during periods of male instability.

2. Environmental stressors: Living on the southern tip of Africa naturally exposes the baboons to extremes of temperatures, with hot, dry summers characterized by shortened day lengths and cold, wet winters with longer day lengths. In this study, I found that females had higher GC levels in the winter months and changed their activity budgets to accommodate their seasonally varying needs. Females spent a larger proportion of time feeding in the winter, with its shorter days, while at the same time reducing their time spent on other activities such as socializing and resting. There is some indication that the baboons used behavioral mechanisms for thermoregulation, as they spent more time in open, sunny areas in the winter possibly to absorb more heat, and they spent more time in closed forested areas in the summer, possibly as a way to remain cool.

3. Anthropogenic stressors: The study population of baboons lives in close proximity to humans in the Cape Peninsula and the home range of each troop is a patchwork of natural and developed habitats. When the baboons range in the more developed and urbanized areas, they have regular interactions with humans, often of a conflict nature. I examined the effects of this anthropogenic presence on female GC hormone levels as well as on their use of self-directed behaviors (SDB). Females had higher GC levels when they spent more time ranging in areas where they interacted more with humans and more often came into conflict with them. In some troops, ranging in areas of human presence was also associated with higher rates of self-directed behaviors.

The results of this study are meaningful and timely as anthropogenic disturbance and anthropogenic climate change are significant forces acting on animal communities, changing selection pressures and potentially driving evolutionary change. This study adds to our understanding of the variation of responses among taxa, as well as the behavioral flexibility exhibited by animals, and whether and how this flexibility may be adaptive in enabling animals to survive stressors and anthropogenic change. More broadly, my research aims to contribute to an understanding of the behavioral flexibility exhibited by primates in response to social and ecological variation and the adaptive value of this flexibility.

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