Thesis (Ph.D.) - Indiana University, Psychology, 2015Variation in reproductive behavior is essential to selection. Despite this, researchers know very little about the social factors shaping the development of such variation. Social niche construction reflects the ability of an individual to shape its social environment. A social niche reflects an individuals place within the larger social network of the group. Some niches reflect high levels of connectedness with others, whereas other niches reflect more selective connections. The early niche will shape the quality and frequency of social interactions, and may have a cascading influence onto later reproductive performance. In this dissertation I explored the sex differences in social niche construction within Brown-headed Cowbirds (Molothrus ater). Male and female cowbirds face divergent challenges when navigating the social environment. In this dissertation I investigated the different niches occupied by males and females over development, and how different niches predict later reproductive behavior. Female cowbirds construct predictable niches, whereas males construct more plastic niches. During the fusion of two novel flocks females maintain stronger connections with familiar females in contrast to males. The ability to form reliable networks with familiar conspecifics may influence the predictability of individual behavior across contexts. Across changes in group size and composition both adult and juvenile females maintain correlated patterns of both social approach and affiliative head-down displays, whereas males did not. Such variation is able to predict a female's reproductive behavior across long timescales. More frequent and closer interactions during the fall predict courtship behavior and pair bonds in juvenile females, and egg production in adult females. Such results suggest that the early niches and individual constructs may have evolutionary consequences by shaping the development of functionally relevant courtship and reproductive abilities.