In some cases, pigmentation can be used as an indicator of measures of condition. In this study, I tested the relationship between reddish pheomelanin pigmentation and the amount of corticosterone, a hormone associated with stress, sequestered in the feathers. I predicted that with higher corticosterone in feathers individuals would exhibit increased brightness and reduced saturation of pheomelanin pigments in their feathers. I collected spectral data from feathers from American Kestrels (Falco sparverius), Cooper’s Hawks (Accipiter cooperii), and Sharp-shinned Hawks (A. striatus) during migration in southwestern Idaho over two years (2010-2011).
After extracting corticosterone from these same feathers, I measured concentration using radioimmunoassay and compared this measure of condition to the melanin pigment data using analysis of covariance. I determined that there was no statistical relationship between feather corticosterone and pheomelanin pigmentation. The physiological impact of circulating corticosterone on pheomelanin production during feather development was not apparent in this natural setting.