Meeting Abstract
Signal honesty is an essential component of stable communication systems, but exposure to novel conditions associated with anthropogenic change has the potential to alter relationships between signals and phenotype, disrupting signaling systems. Previously, we showed that different aspects of melanin-based coloration in male song sparrows related to territorial behavior in urban and rural habitats. Here, we experimentally reduced and enlarged the badge in both habitats, in a balanced design, to determine if associations between badge size and phenotype were plastic across habitats. We assessed the behavioral response to a simulated territorial intrusion prior to manipulation and again two weeks post-manipulation. We also measured body mass and initial corticosterone and testosterone pre and post-manipulation. Based on our previous results, we predicted that males with reduced badges would increase or maintain territorial aggression, have lower body mass, and have greater corticosterone and testosterone concentrations than males with enlarged badges. We found that males with experimentally reduced badges were more aggressive than males with enlarged badges, and that this was particularly the case for urban males. Urban males with reduced badges also lost mass while rural birds and urban males with enlarged badges maintained body mass. However, we found no effect of the manipulation on initial corticosterone or testosterone. Together, these results suggest that melanin ornamentation in male song sparrows mediates territorial interactions and that urbanization influences this response to some extent. However, these behavioral changes are unrelated to initial corticosterone and testosterone concentrations, suggesting an alternative physiological mechanism mediates this relationship.
