Abstract: Hormonal manipulations allow us to create novel phenotypes from which we can learn how existing phenotypes evolved and why they persist. Testosterone, a hormone that has been well studied in birds, has given us some insight into the mechanics of how hormones affect behavior and life history traits. To date, studies have focused mainly on males. Therefore, in attempt to further understand the selective forces that affect testosterone levels in birds we have focused our attention on females. We used hormone implants to study the effect of elevated testosterone on female Dark-eyed Juncos (Junco hyemalis). Testosterone was elevated to the normal spring maximum to determine its effects on nest defense, an important aspect of parental care. Nest defense was measured by quantifying the number of hits, dives, and nest checks made when a female junco was presented with a taxidermic mount of a potential predator. Results showed that testosterone had no affect on nest defense intensity and in correlation, nest defense intensity had no affect on nest success.