Testosterone elevation and response to gonadotropin-releasing hormone challenge by male Northern Cardinals (Cardinalis cardinalis) following aggressive behavior

► We examined if male cardinals significantly elevate testosterone levels in aggressive contexts. ► Males were injected with gonadotropin-releasing hormone (GnRH) following aggressive behavior. ► Testosterone levels of birds subject to STIs were not significantly higher than passive captures. ► Males captured in aggressive contexts could elevate testosterone in response to GnRH injection.