Kevin J. McGraw
Behavioral Ecology, Animal Behavior, Sexual Selection, Biochemical and Physiological Mechanisms of Bright Coloration in Birds
We use field and laboratory studies to identify the mechanisms and functions of colorful ornaments in birds. These colors often serve as indicators of an individuals worth as a mate or their ability to compete for access to mates. We are interested in how color signals reliably communicate this information. Bright coloration often reveals the nutritional condition, health state, or aggressive ability of birds, and we employ a variety of biochemical, nutritional, physiological, immunological, and behavioral methods to determine the factors that control color intensity. Techniques such as high-performance liquid chromatography (HPLC), for example, allow us to track the types and amounts of pigments that birds accumulate and the physiological causes and consequences of variability in pigmentation.
One of the major thrusts of our work is that the different types of pigmentary and structural colors that birds display incur different costs and benefits as they are produced or maintained, send different messages to conspecifics, and ultimately serve different social and sexual functions. The red, orange, and yellow carotenoid-based colors of birds commonly serve to attract mates and signal the nutritional or health state of individuals. Black and brown melanin-based colors, in contrast, are less sensitive to nutrition and health and are more likely to be linked to an individuals hormonal state and their competitive ability. Preliminary studies of structural colors show their dependence upon adequate nutrition for maximal expression, but their behavioral significance is still in question. We are also now investigating the nature and significance of other, less common types of colors in birds, including the red and yellow psittacofulvins in parrot feathers and the pterin pigments in the colorful eyes of certain birds. Last, we have recently identified new forms of pigmentary coloration in birds like penguins and wood ducks, and in the coming years it will be interesting to see how the mechanisms and functions of these understudied forms of coloration fit into our current system that is becoming an ideal model for understanding why such a diversity of exaggerated features have evolved in animals.
Brilliant colors are by no means restricted to birds, and we are anxious to expand our focal studies on birds to other vertebrates and invertebrates to determine if, how, and why other animal colors play valuable roles as visual signals of quality.
Selected Publications
Hill, G. E. and K. J. McGraw . 2006. Bird Coloration. Volume II. Function and Evolution. Harvard University Press, Cambridge , MA .
McGraw, K. J. 2006. The mechanics of uncommon colors: pterins, porphyrins, and psittacofulvins. In: Bird Coloration. I. Mechanisms and Measurements (G. E. Hill and K. J. McGraw, eds.). Harvard University Press, Cambridge , MA , pp. 354-398.
McGraw, K. J. 2006. The mechanics of carotenoid coloration. In: Bird Coloration. I. Mechanisms and Measurements (G. E. Hill and K. J. McGraw, eds.). Harvard University Press, Cambridge , MA , pp. 177-242.
McGraw, K. J . 2006. The mechanics of melanin coloration. In: Bird Coloration. I. Mechanisms and Measurements (G. E. Hill and K. J. McGraw, eds.). Harvard University Press, Cambridge , MA , pp. 243-294.
Safran, R. J., C. R. Neuman, K. J. McGraw , and I. J. Lovette. 2005. Dynamic paternity allocation as a function of male plumage color in barn swallows. Science 309:2210-2212.
McGraw, K. J. and M. C. Nogare. 2005. Distribution of unique red feather pigments in parrots. Biology Letters 1:38-43.
McGraw, K. J. , J. Hudon, G. E. Hill, and R. S. Parker. 2005. A simple and inexpensive chemical test for behavioral ecologists to determine the presence of carotenoid pigments in animal tissues. Behav. Ecol. Sociobiol. 57:391-397.
McGraw, K. J. ,G. E. Hill, and R. S. Parker. 2005. The physiological costs of being colourful: nutritional control of carotenoid utilization in the American goldfinch ( Carduelis tristis ). Anim. Behav. 69:653-660.
McGraw, K. J. 2004. Antioxidant function of many animal pigments: consistent health benefits of sexually selected colorants? Anim. Behav. 69:757-764 .
McGraw, K. J. , R. J. Safran, M. R. Evans, and K. Wakamatsu. 2004. European barn swallows use melanin pigments to color their feathers brown. Behav. Ecol. 5:889-891 .
McGraw, K. J., K. Wakamatsu, S. Ito, P. M. Nolan, P. Jouventin, F. S. Dobson, R. E. Austic, R. J. Safran, L. M. Siefferman, G. E. Hill, and R. S. Parker. 2004. You cant judge a pigment by its color: carotenoid and melanin content of yellow and brown feathers in swallows, bluebirds, penguins, and domestic chickens. Condor 106:390-395.
McGraw, K. J. 2004. Multiple UV reflectance peaks in the iridescent neck feathers of pigeons. Naturwiss. 91:125-129.
Hill, G. E. and K. J. McGraw . 2004. Correlated changes in male plumage coloration and female mate choice in cardueline finches. Anim. Behav. 67:27-35.
McGraw, K. J. and D. R. Ardia. 2003. Carotenoids, immunocompetence, and the information content of sexual colors: an experimental test. Am. Nat. 162:704-712.
McGraw, K. J., A. J. Gregory, R. S. Parker, and E. Adkins-Regan. 2003. Diet, plasma carotenoids, and sexual coloration in the zebra finch ( Taeniopygia guttata ). Auk 120:400-410.
McGraw, K. J. 2003. Melanins, metals, and mate quality. Oikos 102:402-406.
Hill, G. E and K. J. McGraw . 2003. Melanin, nutrition, and the lion's mane. Science (Letter) 299:660.
McGraw, K. J., J. Dale, and E. A. Mackillop. 2003. Social environment during molt and the expression of melanin-based plumage pigmentation in male house sparrows ( Passer domesticus ). Behav. Ecol. Sociobiol. 53:116-122.
McGraw, K. J., E. A. Mackillop, J. Dale, and M. E. Hauber. 2002. Different colors reveal different information: how nutritional stress affects the expression of melanin- and structurally based ornamental coloration. J. Exp. Biol. 205:3747-3755.
McGraw, K. J., G. E. Hill, R. Stradi, and R. S. Parker. 2002. The effect of dietary carotenoid access on sexual dichromatism and plumage pigment composition in the American goldfinch. Comp. Biochem. Physiol. B 131:261-269.
Badyaev, A. V., Hill, G. E., Beck, M. L., Dervan, A. A., Duckworth, R. A. , McGraw, K. J., N olan, P. M., and Whittingham, L. A. 2002. Sex-biased hatching order and adaptive popul ation divergence in a passerine bird. Science 295:316-318.
McGraw, K. J., G. E. Hill, R. Stradi, and R. S. Parker. 2001. The influence of carotenoid acquisition and utilization on the maintenance of species-typical plumage pigmentation in male American goldfinches ( Carduelis tristis ) and northern cardinalis ( Cardinalis cardinalis ). Physiol. Biochem. Zool. 74:843-852.
McGraw, K. J., A. M. Stoehr, P. M. Nolan, and G. E. Hill. 2001. Plumage redness predicts breeding onset and reproductive success in the house finch: a validation of Darwin's theory. J. Avian Biol. 32:90-94.
Stoehr, A. M. and K. J. McGraw . 2001. Ultraviolet reflectance of color patches in male Sceloporus undulatus and Anolis carolinensis . J. Herpetol. 35:168-171.
McGraw, K. J. and G. E. Hill. 2000. Plumage brightness and breeding-season dominance in the house finch: a negatively correlated handicap? Condor 102:457-462.
McGraw, K. J. and G. E. Hill. 2000. Differential effects of endoparasitism on the expression of carotenoid- and melanin-based ornamental coloration. Proc. R. Soc. Lond. B. 267:1525-1532.
McGraw, K. J. and G. E. Hill. 2000. Carotenoid-based ornamentation and status signaling in the house finch. Behav. Ecol. 11: 520-527.