female_bluebird_aggression
Description
Studies investigating the integration of ornamental signaling, aggression, and their hormonal mediation have focused on male birds but there has been a more recent shift to females. The change is being driv-en by increasing evidence for direct selection on female aggression and ornamental traits despite their increased sensitivity to androgens. In male eastern bluebirds (Sialia sialis), ultra-violet blue structural coloration signals aggression and larger melanin pigmented patches are associated with higher quality parental care. While less pronounced, female bluebirds display similar ornamentation. Although less research has focused on the signaling potential of the ornaments of female bluebirds, evidence suggests plumage color is associated with body condition and reproductive output. We provide evidence that female ornaments may signal hormonal profiles after aggressive encounters. In the wild, we presented females with simulated territorial intrusions of unfamiliar females prior to egg-laying and measured aggression, testosterone, corticosterone, and ornamental plumages. We found that females with greater corticosterone and less-ornamented melanin plumage had greater levels of circulating testosterone after exposure to social intrusion. Interactions between corticosterone and melanin suggest that to-gether they limit high levels of testosterone. Our data supports the hypothesis that ornamentation sig-nals hormone profiles after aggressive encounters. Further research during molt is necessary to under-stand the mechanisms whereby social interactions may influence hormone profiles, sensitivity of tis-sues to hormones, and the development of ornaments in female bluebirds.