Dr. Kevin McGraw

My research programme centers on the control and function of animal colors, particularly in birds. The Darwinian theory of sexual selection coined over 125 years ago remains the cornerstone of biological explanations for the evolution of exaggerated ornamental traits. Brilliant colors, for example, evolve particularly in male animals in response to intense competitions for mates. Only the most colorful males can out-compete their rivals and serve as suitable, attractive mates for females.

While there is now much empirical evidence to support this basic tenet of sexual-selection theory for many ornament types (e.g. large body-size, colorful plumage, elongate tails), biologists have become particularly interested in why females pay particular attention to these male traits when making their mating decisions. What information are males communicating to females with their color? What advantages do females gain by mating with the most colorful male? It is with a mechanistic approach to studying the particular factors that mold the development of colorful plumage in birds that we have begun to understand the costs to males in developing bright colors and the benefits accrued by females who acquire the sexiest mate.

My advisor during my M.Sc. degree, Dr. Geoffrey Hill, helped revolutionize many of the ways in which biologists perceive ornamental traits as mating signals. Following the theoretical framework offered by Zahavi, Williams, Fisher, and of course Darwin, he pursued the means by which males communicate their worth to females in a colorful species of songbird from North America, the house finch (Carpodacus mexicanus). Males derive their colorful plumage, which ranges from bright red to drab yellow, from carotenoid pigments, the same pigments that are responsible for the yellow color of corn, the orange color of carrots, and the redness of autumn leaves. Only photosynthetic organisms like plants and algae can manufacture these molecules, so birds and other vertebrates can only display carotenoids in feathers by first acquiring them in their diet. In a series of elegant field and laboratory experiments, Geoff demonstrated that the more brightly colored males are preferred as mates by females, but also obtain the largest quantities of carotenoids in their diet, are in the best nutritional condition, help provision females with food as she prepares for breeding, and have the highest survival rates. Thus, males use their color to demonstrate to females their foraging abilities, general health, and willingness to provide parental assistance. Only with this foundation of research in place have we begun to explore the ways in which carotenoid-derived plumage is controlled and functions in other songbirds as well as the information contained within other types of color signals in animals.

In fact, these two areas of research have been the focal points of my dissertation work at Cornell University. To dive deeper into the world of carotenoid-signaling in birds is to understand these pigments at the biochemical and physiological levels. Animals certainly acquire these molecules in the diet, but also use a complex physiological processing system to transport carotenoids through the body to the site of deposition at the growing feather. Thus, we must consider these physiological steps as potentially costly components of pigment utilization and thus a direct means by which male birds can communicate their nutritional, physiological, and genetic quality to females. Preliminary work has in fact shown that certain male songbirds (e.g. American goldfinches) develop differently colored plumage when fed the same diet (McGraw and Hill 2001), suggesting a role for physiological regulation of color development. In collaboration with Dr. Bob Parker in the Nutritional Sciences division at Cornell, we are using high-performance liquid-chromatography (HPLC) as a biochemical tool for identifying the carotenoid pigments acquired by these animals in their diet and the degree to which they circulate them through the body bound to lipoprotein particles and deliver them to peripheral tissues for pigmentation. Birds are also capable of metabolically altering the structure of carotenoids, often times rendering them more desirable as feather colorants. It appears that certain metabolic pathways may be favored over others en route to the development of the most brightly colored feathers (McGraw et al. 2002). There is no doubt that this new, mechanistic approach to evaluating the production of color signals will offer many unique insights into the costliness and signal content of carotenoid-based colors in birds.

Carotenoid pigments are by no means the only source of color in animals, however. Melanin pigments are responsible for most of the black, gray, brown, and earth-toned colors in nature (e.g. in insect cuticles, animal fur, lizard scales, and bird feathers), and are found in two primary forms, eumelanin (blacks and grays) and phaeomelanin (rust, olive). Many birds display sexually dimorphic patches of black color in their feathers, and this has been the focus of a great body of literature over the past 25 years. These eumelanic colors appear to serve unique functions as signals of social status in populations of songbirds, often times in non-breeding contexts (e.g. in a winter foraging flock). Again, to understand why these ornaments reliably reveal the aggressive intentions or dominance ability of individuals is to delve into the mechanisms underlying the production and maintenance of these signals. I have accumulated evidence that nutritional input has little impact on the development of eumelanic plumage colors in certain species (e.g. American goldfinch, house sparrow; see McGraw and Hill 2000, McGraw et al. 2002). Instead, it seems that physiological regulation occurs via steroid-hormone circulation (e.g. testosterone) and its corresponding link to aggressive behavior in animals. We are currently considering the role that social factors themselves play on the androgenic responsiveness of individuals and the associated development of melanin-based plumage.

Lastly, an altogether different form of color has captured the attention of behavioral ecologists over the past few years. Rather than having a pigmentary origin, structurally colored feathers have unique microstructural arrangements of feather tissues and layers that often reflect iridescent, blue, or ultraviolet wavelengths of light. Human-vision is limited for short light-wavelengths, and as such many of the structural plumage colors in songbirds have been historically ignored as signals of mate quality. Recent advances in spectrophotometric technology, however, have allowed more objective and quantitative means of assessing structural-color. In fact, many songbirds exhibit sexually dichromatic patterns of structural color that function as targets of female mate-choice. Much less is known of the proximate factors that shape the production of these carefully arranged feather tissues, and this has been the subject of a series of studies in collaboration with fellow graduate students in and around our department here at Cornell (McGraw et al., 2002).

In all, my biological research is deeply rooted in integrative approaches, as the only means by which we can understand how and why animals communicate with the signals they do and can provide unique sets of information with the diversity of ornaments that exist. Continued progress at the biochemical, physiological, molecular, and genetic levels will bring us that much closer to identifying the true fitness benefits that females reap from securing a colorful mate, in currencies that not even Darwin could have imagined.

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Publications^*

Edited books

Hill, G. E. and K. J. McGraw. 2006b. Bird Coloration. Volume II. Function and Evolution. Harvard University Press, Cambridge, MA. Catalog advertisement, Table of Contents, Purchase now, Read an excerpt, Wingspan (review), Times Literary Supplement (review), Science (browsing), Trends in Ecology and Evolution (review), Nature (review), Condor (review), Quarterly Review of Biology (review), ISBE newsletter (review)

Hill, G. E. and K. J. McGraw. 2006a. Bird Coloration. Volume I. Mechanisms and Measurements. Harvard University Press, Cambridge, MA. Catalog advertisement, Table of Contents, Purchase now, ASU Insight feature (on last page), Condor (review), Auk (review)

Journal Publications or Book Chapters

96. McGraw, K. J. and J. D. Blount. 2009. Control and function of carotenoid coloration in birds: a review of case studies. In Carotenoids: Physical, Chemical, and Biological Functions and Properties (J. T. Landrum, ed.). CRC Press, Boca Raton, FL (in press).

95. Toomey, M. B. and K. J. McGraw. 2008. Season, sex, and quality related variation in retinal carotenoid accumulation in house finches. Funct. Ecol. (in press).

94. Cohen, A. A. and K. J. McGraw. 2008. No simple measures for antioxidant status in birds: Complexity in inter- and intraspecific correlations among circulating antioxidant types. Funct. Ecol. (in press).

93. McGraw, K. J. and A. L. A. Middleton. 2008. American Goldfinch (Carduelis tristis). The Birds of North America Online (A. Poole, Ed.). Ithaca, NY: Cornell Laboratory of Ornithology.

92. Rowe, M. and K. J. McGraw. 2008. Carotenoid pigments in the seminal fluid of wild birds: interspecific variation in fairy wrens (genus Malurus). Condor (in press).

91. McGraw, K. J. 2008. Visual signaling in animals. In: New Encyclopedia for Neuroscience (L. R. Squire, ed.). Elsevier Ltd., Oxford, in press. Uncorrected galley proofs

90. McGraw, K. J., E. A. Tourville, and M. W. Butler. 2008. A quantitative comparison of the commonly used methods for extracting carotenoids from avian plasma. Behav. Ecol. Sociobiol. (in press). Online pre-print

89. Cohen, A. A., K. J. McGraw, P. Wiersma, J. B. Williams, W. D. Robinson, T. R. Robinson, J. D. Brawn, and R. E. Ricklefs. 2008. Interspecific associations between circulating antioxidant levels and life-history variation in birds. Am. Nat. 172:178-193. PDF

88. Piault, R., J. Gasparini, P. Bize, M. Paulet, K. J. McGraw, and A. Roulin. 2008. Experimental support for the make-up hypothesis in nestling tawny owls (Strix aluco). Behav. Ecol. 19:703-709. PDF

87. Safran, R. J., J. Adelman, K. J. McGraw, and M. Hau. 2008. Sexual signal elaboration affects physiological state in a social vertebrate. Current Biology 18:R461-R462. PDF, over 300 newspaper and online articles written on this paper, plus Good Morning America, CNN, and several local radio interviews (e.g. San Francisco, Houston, Rockford, IL, New York)

86. Deviche, P., K. J. McGraw, and J. Underwood. 2008. Age-, sex- and season-specific accumulation of plasma carotenoid pigments in white-winged crossbills. J. Avian Biol. 39:283-292. PDF

85. Blount, J. D. and K. J. McGraw. 2008. Signal functions of carotenoid colouration. In: Carotenoids. Volume 4: Natural Functions (G. Britton, S. Liaaen-Jensen, and H. Pfander, eds.). Birkhauser, Switzerland. Uncorrected galley proofs (due March 2008)

84. McGraw, K. J. 2008. An update on the honesty of melanin-based color signals in birds. Pigment Cell Melanoma Res. 21:133-138. PDF

83. Schaefer, H. M., K. J. McGraw, and C. Catoni. 2008. Birds use fruit colour as an honest signal of dietary antioxidant rewards. Funct. Ecol. 22:303-310. PDF

82. Juola, F. A., K. J. McGraw, and D. C. Dearborn. 2008. Carotenoids and throat pouch coloration in the great frigatebird (Fregata minor). Comp. Biochem. Physiol. B. 149:370-377. PDF

81. Safran, R. J., Pilz, K. M., McGraw, K. J., Correa, S. M., and Schwabl, H. 2008. Are yolk androgens and carotenoids in barn swallow eggs related to parental quality? Behav. Ecol. Sociobiol. 62:427-438. PDF

80. Jouventin, P., K. J. McGraw, M. Morel, and A. Celerier. 2008. Dietary carotenoid supplementation affects orange beak but not foot coloration in gentoo penguins. Waterbirds 30:573-578. PDF

79. Clotfelter, E., Ardia, D., and McGraw, K. J. 2007. Red fish, blue fish: trade-offs between pigmentation and immunity in Betta splendens. Behav. Ecol. 18:1139-1145. PDF

78. Toomey, M. B. and K. J. McGraw. 2007. Modified saponification and HPLC methods for analyzing carotenoids from the retina of Japanese quail (Coturnix japonica): implications for its use as a nonprimate model species. Invest. Ophthalmol. Vis. Sci. 48:3976-3982. PDF

77. Taylor, L. A. and K. J. McGraw. 2007. Animal coloration: sexy spider scales. Curr. Biol. 17:R592-R593. PDF

76. McGraw, K. J., M. B. Toomey, P. M. Nolan, N. I. Morehouse, M. Massaro, and P. Jouventin. 2007. A description of unique fluorescent yellow pigments in penguin feathers. Pigment Cell Res. 20:301-304. PDF, Supplementary Material

75. Bezzerides, A. L., K. J. McGraw, R. S. Parker, and J. Husseini. 2007. Elytra color as a signal of chemical defense in the Asian ladybird beetle (Harmonia axyridis). Behav. Ecol. Sociobiol. 61:1401-1408. PDF

74. McGraw, K. J. and D. R. Ardia. 2007. Do carotenoids buffer testosterone-mediated immunosuppression?: an experimental test in a colorful songbird. Biol. Letters 3:375-378. PDF, Electronic Supplementary Material, Biology Letters Highlighted Paper, ASU Headline, ASU News, School of Life Sciences News, Science Daily, Innovations Report, Biology News Net, PhysOrg.com, Eureka Alert, DentalPlans.com, United Press International, ImediNews, Earth Times, Monsters and Critics, New Kerala, Post Chronicle, News-Medical.net, Associated Content, Medical News Today, MediLexicon, Nutrition Horizon, ASU Research Magazine, Softpedia

73. Hofmann, C. M., K. J. McGraw, T. W. Cronin, and K. E. Omland. 2007. Melanin coloration in New World orioles I: carotenoid masking and pigment dichromatism in the orchard oriole complex. J. Avian Biol. 38:163-171. PDF

72. McGraw, K. J., W. Medina-Jerez, and H. Adams. 2007. Carotenoid-based plumage coloration and aggression during molt in male house finches. Behaviour 144:165-178. PDF

71. Steffen, J. and K. J. McGraw. 2007. Patterns of carotenoid and pterin pigmentation in the colorful dewlaps of two anole species. Comp. Biochem. Physiol. B. 146:42-46. PDF

70. McGraw, K. J. 2007. Dietary mineral content influences melanin-based ornamental coloration. Behav. Ecol. 18:137-142. PDF

69. McGraw, K. J. 2006. The mechanics of uncommon colors in birds: 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.

68. McGraw, K. J. 2006. The mechanics of carotenoid coloration in birds. In: Bird Coloration. I. Mechanisms and Measurements (G. E. Hill and K. J. McGraw, eds.). Harvard University Press, Cambridge, MA, pp. 177-242.

67. McGraw, K. J. 2006. The mechanics of melanin coloration in birds. In: Bird Coloration. I. Mechanisms and Measurements (G. E. Hill and K. J. McGraw, eds.). Harvard University Press, Cambridge, MA, pp. 243-294.

66. Shawkey, M. D., G. E. Hill, K. J. McGraw, and W. R. Hood. 2006. An experimental test of the contributions and condition-dependence of microstructure and carotenoids in yellow plumage colouration. Proc. R. Soc. Lond. B. 273:2985-2991. PDF

65. McGraw, K. J., O. L. Crino, W. Medina-Jerez, and P. M. Nolan. 2006. Effect of dietary carotenoid supplementation on food intake and immune function in a songbird with no carotenoid coloration. Ethology 112: 1209-1216. PDF

64. McGraw, K. J. and K. C. Klasing. 2006. Carotenoids, immunity, and integumentary coloration in red junglefowl (Gallus gallus). Auk 123:1161-1171. PDF

63. McGraw, K. J. 2006. Carotenoids mediate a trade-off between egg quantity and quality in Japanese quail. Ethol. Ecol. Evol. 18:247-256. PDF

62. McGraw, K. J. 2006. Sex-steroid dependence of carotenoid-based coloration in female zebra finches. Physiol. Behav. 88:347-352. PDF

61. McGraw, K. J., P. M. Nolan, and O. L. Crino. 2006. Carotenoid accumulation strategies for becoming a colorful house finch: analyses of plasma and liver pigments in wild molting birds. Funct. Ecol. 20:678-688. PDF, Cover Image

60. McGraw, K. J., S. M. Correa, and E. Adkins-Regan. 2006. Testosterone upregulates lipoprotein status to control sexual attractiveness in a colorful songbird. Behav. Ecol. Sociobiol. 60:117-122. PDF

59. McGraw, K. J. and L. Hardy. 2006. Astaxanthin is responsible for the pink plumage flush of Franklins and Ring-billed gulls. J. Field Ornithol. 77:29-33. PDF

58. McGraw, K. J. and R. S. Parker. 2006. A novel lipoprotein-mediated mechanism controlling sexual attractiveness in a colorful songbird. Physiol. Behav. 87:103-108. PDF

57. Deviche, P., K. McGraw, and E. Greiner. 2005. Interspecific differences in hematozoan infection in Sonoran Desert Aimophila sparrows. J. Wild. Dis. 41:532-541. PDF

56. McGraw, K. J., E. Adkins-Regan, and R. S. Parker. 2005. Maternally derived carotenoid pigments affect offspring survival, sex ratio, and sexual attractiveness in a colorful songbird. Naturwiss. 92:375-380. PDF

55. McGraw, K. J., R. J. Safran, and K. Wakamatsu. 2005. How feather colour reflects its melanin content. Funct. Ecol. 19:816-821. PDF

54. 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. PDF, Cover image, Cornell University, Arizona State University, ASU Insight, ASU homepage, BBC, Cornell Daily Sun, Cornell Lab of Ornithology, American Association for the Advancement of Science, ABC News, ABC News Online, AOL News, Belleville News Democrat, Biology News Net, Cherry Bomb, CLAS Alumni Magazine, EurekAlert, East Valley Tribune (AZ), East Valley Tribune homepage, Melbourne Herald Sun, Innovations Report, Independent Online, Live Science, MSNBC, National Geographic, National Wildlife Federation Magazine, New Haven Herald, New Kerala, New Scientist, New York Times, Newswise, Noorderlicht, NPR, OptusNet, Pet Talk Radio, Planet Ark, Red Nova, Reuters, Salem Statesman Journal, Science Daily, School of Life Sciences (ASU), Science News, Telegraph, The Age, The Oregonian, Times Online, Unison, Virtual Life Sciences Library, Web India, World News Australia, Yahoo News, AAAS radio clip, CLAS News (ASU), 10,000 Birds

53. McGraw, K. J. 2005. Interspecific variation in dietary carotenoid assimilation in birds: links to phylogeny and color ornamentation. Comp. Biochem. Physiol. B 142:245-250. PDF

52. McGraw, K. J. and M. C. Nogare. 2005. Distribution of unique red feather pigments in parrots. Biology Letters 1:38-43. PDF, Arizona State University homepage 1, Arizona State University homepage 2, Arizona State University press release 1, Arizona State University press release 2, Arizona State University video interview, ASU Insight Newspaper, The Arizona Republic, Innovations Report, The Biochemist, Windy City Parrot, Wissenschaft, EurekaAlert (AAAS), ChemLin, ParrotSuperCenter, Yahoo Korea, Noorderlicht, ScienceDaily, LiveScience, ParrotScience.com, The Oregonian, Farbimpulse, Futura Sciences, El Correo Digital, Vigyan Prasar, Precious Fids, Girl Scientist, Science News, Aviary & Cage Bird Society of South Florida, ASU Insight (Summer Highlights), ASU Alumni Magazine (Spring 2005), eNewsSource, BBC Wildlife, BirdTalk Magazine, Grade Winner, Planned Parrothood, Chemical and Engineering News, Birdwatchers Digest

51. McGraw, K. J. 2005. The antioxidant function of many animal pigments: are there consistent health benefits of sexually selected colorants? Anim. Behav. 69:757-764. PDF, Top 10 article in Animal Behaviour

50. McGraw, K. J. and D. R. Ardia. 2005. Sex differences in carotenoid status and immune performance in zebra finches. Evol. Ecol. Res. 7:251-262. PDF

49. 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. PDF

48. 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. PDF

47. McGraw, K. J. 2004. Not all red, orange, and yellow animal colors are carotenoid-based: the need to couple biochemical and behavioral studies of color signals. Proc. Ind. Natl. Sci. Acad. B 70:593-598. PDF

46. McGraw, K. J., K. Wakamatsu, A. B. Clark, and K. Yasukawa. 2004. Red-winged blackbirds Agelaius phoeniceus use carotenoid and melanin pigments to color their epaulets. J. Avian Biol. 35:543-550. PDF

45. McGraw, K. J. 2004. Colorful songbirds metabolize carotenoids at the integument. J. Avian Biol. 35:471-476. PDF

44. McGraw, K. J. and A. J. Gregory. 2004. Carotenoid pigments in male American goldfinches: what is the optimal biochemical strategy for becoming colourful? Biol. J. Linn. Soc. 83:273-280. PDF

43. McGraw, K. J. and J. G. Schuetz. 2004. The evolution of carotenoid coloration in estrildid finches: a biochemical analysis. Comp. Biochem. Physiol. B 139:45-51. PDF

42. McGraw, K. J. 2004. Winter plumage coloration in male American goldfinches: do reduced ornaments serve signaling functions in the non-breeding season? Ethology 110:707-715. PDF

41. McGraw, K. J., G. E. Hill, K. J. Navara, and R. S. Parker. 2004. Differential accumulation and pigmenting ability of dietary carotenoids in colorful finches. Physiol. Biochem. Zool. 77:484-491. PDF

40. McGraw, K. J. and K. Wakamatsu. 2004. Melanin basis of ornamental feather colors in male zebra finches. Condor 106:686-690. PDF

39. Horak, P., L. Saks, U. Karu, I. Ots, P. F. Surai, and K. J. McGraw. 2004. How coccidian parasites affect health and appearance of greenfinches. J. Anim. Ecol. 73:935-947. PDF

38. 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. 15:889-891. PDF, Confirmatory reply by Stradi

37. McGraw, K. J. and G. E. Hill. 2004. Plumage color as a dynamic trait: carotenoid pigmentation of male house finches (Carpodacus mexicanus) fades during the breeding season. Can. J. Zool. 82:734-738. PDF

36. McGraw, K. J. and M. C. Nogare. 2004. Carotenoid pigments and the selectivity of psittacofulvin-based coloration systems in parrots. Comp. Biochem. Physiol. B 138:229-233. PDF

35. Safran, R. J. and K. J. McGraw. 2004. Plumage coloration, not length or symmetry of tail-streamers, is a sexually selected trait in North American barn swallows. Behav. Ecol. 15:455-461. PDF, Nature Australia

34. 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. PDF

33. McGraw, K. J. 2004. Multiple UV reflectance peaks in the iridescent neck feathers of pigeons. Naturwiss. 91:125-129. PDF

32. Mays Jr., H. L., K. J. McGraw, G. Ritchison, S. Cooper, V. Rush, and R. S. Parker. 2004. Sexual dichromatism in the Yellow-breasted Chat (Icteria virens): spectrophotometric analysis and biochemical basis. J. Avian Biol. 35:125-134. PDF

31. McGraw, K. J. and G. E. Hill. 2004. Mate attentiveness, seasonal timing of breeding and long-term pair bonding in the house finch (Carpodacus mexicanus). Behaviour 141:1-13. PDF

30. McGraw, K. J. and D. R. Ardia. 2004. Immunoregulatory activity of different dietary carotenoids in male zebra finches. Chemoecol. 14:25-29. PDF

29. 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. PDF

28. 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. PDF

27. Saks, L., K. J. McGraw, and P. Horak. 2003. How feather colour reflects its carotenoid content. Funct. Ecol. 17:555-561. PDF

26. McGraw, K. J., M. D. Beebee, G. E. Hill, and R. S. Parker. 2003. Lutein-based plumage coloration in songbirds is a consequence of selective pigment incorporation into feathers. Comp. Biochem. Physiol. B. 135:689-696. PDF

25. McGraw, K. J., G. E. Hill, and R. S. Parker. 2003. Carotenoid pigments in a mutant cardinal: implications for the genetic and enzymatic control mechanisms of carotenoid metabolism in birds. Condor 105:587-592. PDF

24. 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. PDF

23. McGraw, K. J. 2003. Melanins, metals, and mate quality. Oikos 102:402-406. PDF

22. Hill, G. E and K. J. McGraw. 2003. Melanin, nutrition, and the lions mane. Science (Letter) 299:660. PDF

21. McGraw, K. J., J. Dale, and E. A. Mackillop. 2003. Social environment d