I study the evolutionary and mechanistic underpinnings of sex differences in behavior, with a special focus on same-sex aggressive behavior in birds. While the evolutionary significance and neuroendocrine mechanisms of aggression have been well studied in males, the processes promoting this behavior in females are poorly understood. In my dissertation work, I quantified the fitness costs and benefits of intrasexual aggression in female tree swallows (Tachycineta bicolor). As a postdoc, I am continuing to study aggressive behavior in females, focusing instead on underlying neuroendocrine mechanisms. Using the dark eyed junco (Junco hyemalis), I am exploring whether behavioral differences among females and between the sexes map onto variation in neural sensitivity to testosterone (e.g. androgen receptor expression). By combining techniques from behavioral ecology, neuroendocrinology, and molecular genetics, I aim to ask fundamental questions about behavior, connect behavior to physiology, and promote a better understanding of both in the process..