Meeting Abstract
Elaborate traits often serve as honest signals of aggression and fighting ability or motivation to potential competitors. Historically, studies on such traits have focused on the more aggressive male sex. However, the American goldfinch (Spinus trusts) is unique in that females exhibit an orange bill, which serves as a dynamic carotenoid-based status signal to mediate aggressive interactions over food resources. Although testosterone (T), a hormone well known to mediate aggression in males, is known to affect female aggression in some species, the relationship between female aggression and T appears to vary between species, and the link between this hormone and female contest behavior is not fully supported. The unique relationship between bill color and aggressive outcome in American goldfinches appears to be limited to females, as a similar hypothesis was not supported for male bill color. This suggests a unique sex-specific divergence of ornamental function, and the potential for T to play a different role in mediating bill color between the sexes. In this study, the effects of T on both dominance and bill color of female American goldfinches was analyzed. Female birds were administered T or control treatments via subcutaneous injections for 5 subsequent days. On the fifth day, birds novel to each other were placed into dyads after being deprived of food to analyze dominance. T was administered so that each in each dyad a T bird was competing against a control bird. Winners were determined as the individual that won at least 80% of the supplants and hold-offs at the feeding station. T plasma levels and spectrometer measurements of bill color were taken before and after T administration to determine the influence of T on rank and bill color. Analyses will reveal if dominance and bill color were greater in the T-augmented females compared to the control females.
