Blue Grosbeak (Passerina caerulea) Science Article 1
Plumage blueness in Blue Grosbeaks (Passerina caerulea) is related to nutritional conditionduring molt, and bluer males hold larger territories with more food resources. We tested the hypothesis that females use male plumage brightness as a criterion in choosing mates. In a mate-choice aviary, we presented females with a choice between males whose feathers were either brightened with blue marker or dulled with black marker. Treatment resulted in an increase in the plumage intensity (reflectance at peak wavelength) of blue-treated males and a decrease in the intensity of black-treated males within the natural range of variation, while the wavelength of peak reflection (hue) remained unchanged.
BARBARA BALLENTINE AND GEOFFREY E. HILL, The Condor 105:593-598