Melanin ornament brightness and aggression at the nest in female Northern Cardinals (Cardinalis cardinalis)

Research is increasingly addressing the evolution and use of sexually selected traits in females. One strong area of interest is the display of intrasexual aggression and how female ornaments are used in intrasexual competition. One particular type of ornament focused on for its use in intrasexual aggression in both sexes is the melanin pigmented ornaments. Over the course of 2 breeding seasons in a southeastern Mississippi population of cardinals, we assessed brightness of the melanin face mask plumage ornament in female Northern Cardinals (Cardinalis cardinalis) and compared it to behavioral responses during intraspecific simulated nest intrusions (SNIs). All females responded to the SNI, but face mask brightness did not co-vary with the level of aggression shown. Our findings do not support earlier work suggesting that the face mask in female Northern Cardinals is an indicator of aggression at the nest. Potentially, differences in behavior and environmental variables between populations of cardinals could be factors in this difference and deserve further assessment. Future research should investigate other populations of cardinals to fully assess the communicative malleability of this ornament type and different selective pressures on female ornamentation and behavior.