SICB Division of Ecology and Evolution (DEE)

DEE Researchers Database Entry

Kevin 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 individual's 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.