xx, 229 p. : ill. (some col.) / Reproductive effort is a central element of human biology and ecology. Particularly for females, reproduction is energetically demanding, with elevated metabolic costs during pregnancy and lactation, followed by high child care costs. To satisfy energetic needs, women can adopt various physiological and behavioral strategies. On a physiological level, the energetic requirements of offspring may be met by adjusting metabolic allocation and/or drawing on maternal bodily reserves. On a behavioral level, women may reduce energy expenditure and/or increase energy intake. This study examined reproductive trade-offs in activity and skeletal health among the indigenous Shuar forager-horticulturalists of Ecuadorian Amazonia and had two main objectives. First, this research examined trade-offs in energy use during female reproductive states and behavioral adjustments made by females and males to meet high reproductive demands. Second, this study investigated skeletal health profiles among Shuar, as well non-Shuar Colonos, to identify the relationships between female reproductive factors and skeletal health. Research was conducted among adults in four Morona-Santiago communities. Skeletal health was measured using calcaneal ultrasonometry, and physical activity was measured using accelerometry. Extensive information on sociodemographics and reproduction was assessed through structured interviews. Age-related declines in bone mineral density (BMD) were observed for Shuar and Colonos, while Shuar BMD was significantly higher than that of other populations. These results suggest that normative data from developed countries may reflect suboptimal bone density levels. Regarding reproductive effects on skeletal health, results indicate that earlier menarcheal age and greater stature are associated with better bone health in postmenopausal life. These conclusions suggest the importance of the timing of early developmental stages in establishing bone status in adulthood. Results demonstrate that physical activity levels were similar between pregnant/lactating (P/L) and other women. However, P/L women appear to compensate for elevated energetic demands by relying on a male partner who has increased his energy expenditure, suggesting greater participation in subsistence activities. Overall, this study demonstrates the importance of biocultural strategies among women to meet high reproductive costs. Further, it emphasizes the utility of a life history framework for identifying trade-offs in physiology and behavior. This dissertation contains previously published and unpublished co-authored material. / Committee in charge: Dr. J. Josh Snodgrass, Chair; Dr. Lawrence S. Sugiyama, Member; Dr. John Lukacs, Member; Dr. John Halliwell, Outside Member