The adaptive function of melanin based coloration is poorly known in birds, although in one study the amount of melanin color in feathers correlated with the abilities to produce antibodies. I will test the idea that the redness of raptor feathers is an honest signal of immunocompetence by examining the relationship between the reddish pheomelanin pigments and body condition, as determined by morphological and immunocompetence measurements. I propose that if the redness of feathers in hawks and falcons is an honest signal of fitness, then birds with redder feathers will have more robust immune systems and this will be reflected in the amount of bacteria killed by exposure to their blood in a bacteria killing assay (BKA).
Additionally, I predict that the blood parasite count will be lower in birds with redder feathers, which I will investigate by making blood smears. I also will use the blood smears to count white blood cells and will determine the heterophil:lymphocyte ratio, a measure of stress in birds. I will capture raptors at the Idaho Bird Observatory, a migration trapping station near Boise, ID, and along roadsides throughout the state during non-migratory periods. Standard morphological measurements will be collected, along with a blood sample (ca. 1 ml, jugular vein), and a blood smear. A cloacal swab will be taken to determine the bacterial flora already in the bird’s system. At the lab, the plasma will be harvested and stored in a -80° C freezer until BKAs are run, In BKA, a known number of bacteria colony forming units is exposed to a particular concentration of whole blood or plasma and then plated on an agar petri
dish. A spectrophotometer will be used to measure reflectance of red color in the feathers.
Literature
Chakarov, N., M. Boerner, and O. Krüger. 2008. Fitness in common buzzards at the cross-point of opposite melanin–parasite interactions. Functional Ecology. 22: 1062-1069.
Gasparini, J, Bize, P, Piault, R, Wakamatsu, K, Blount, JD, Ducrest, A, and Roulin, A. 2009. Strength and cost of an induced immune response are associated with a heritable melanin-based colour trait in female tawny owls. Journal of Animal Ecology. 78: 608-616.
Matson, KD, Tieleman, BI, and Klasing, KC. 2006. Capture stress and the bactericidal competence of blood and plasma in five species of tropical birds. Physiological and Biochemical Zoology. 79: 556-564.
Roulin, A. 2009. Melanin-based coloration covaries with ovary size in an age-specific manner in the barn owl. Naturwissenschaften. 96: 1177-1184.