A Red Bird in a Brown Bag: The Function and Evolution of Colorful Plumage in the House Finch.—Geoffrey E. Hill. 2002. Oxford University Press, New York. xii + 318 pp., 119 figures. ISBN 0-19-514849-5. $40.00 (paper). ISBN 0-19-514848-7 $65.00 (cloth).
A journal editor recently declined to send out for review a manuscript I had submitted because I was providing the first test of an idea published 15 years previously. The editor interpreted the delay in testing the idea as evidence that the idea must not be important. Had similar reasoning been applied to Darwin's hypothesis that bright plumage evolves because female birds find colorful males attractive, Geoffrey Hill would never have produced the impressive body of research described in this book. Darwin's proposal that female choice is responsible for the evolution of ornaments in males was poorly received by his contemporaries and the source of a long-running disagreement between Darwin and Wallace. Wallace's view, that plumage was naturally, not sexually, selected, prevailed. It took more than 100 years before female mate choice began to receive serious attention from evolutionary biologists, and 131 years until Hill's work on House Finches (Carpodacus mexicanus) provided definitive experimental evidence that female birds prefer brightly colored males.
Hill's work on House Finches is impressive for reasons beyond originality—the work is both broad and deep. Methodologically, Hill has used the full arsenal of approaches available to modern evolutionary biologists, combining observation and experiment with comparative analysis, while taking advantage of technological developments for assigning paternity and quantifying color. Subjects explored range from the proximate factors underlying plumage coloration (e.g., diet, parasites) to the role that color variation plays in mate preferences expressed by females and males, to the consequences of those preferences. Depth has been achieved by Hill's unwillingness to address a particular question with one experiment and then move on. Rather, Hill typically has conducted a series of experiments, the results of which have allowed him to refine the question and to recognize the complexity that might initially have been overlooked. For example, instead of sticking with his initial approach of treating color as a one-dimensional trait (i.e., which bird is redder?), Hill systematically determined that red coloration actually consists of multiple traits: color hue and intensity, hue consistency, patch size, and patch symmetry. That approach led Hill to recognize that the proximate factors affecting expression of each of these color traits differ, as do the fitness consequences of variation in expression of each trait.
This book is first and foremost a review of work by Hill, his students, and his colleagues on plumage color variation in House Finches. Although the book provides an avenue into the broader literature on avian plumage coloration, Hill's goal was not to provide an exhaustive review of this topic. The organization of the book is effective, despite being different from what one might expect. Rather than starting with a detailed treatment of the theoretical framework for his research, Hill focuses instead on the historical interest in plumage color, the debate between Darwin and Wallace, and the simple question of whether female birds prefer brightly colored males. After a valuable review of the biochemistry and physiological ecology of carotenoids (the pigments that make birds red) Hill details his efforts to answer that simple question. Once he has vindicated Darwin, he then broadens the focus to address topics that include male preferences for color in females, the evolutionary origin of coloration in House Finches, and geographic variation in plumage color. Only later in the book does Hill delve more into sexual selection theory to illustrate how his results collectively support the hypothesis that plumage color in House Finches is an honest signal of individual quality.
Books such as Hill's, in which an author reviews his or her own body of work, are guaranteed an audience of at least those other researchers who share an interest in the subject, and Hill's book will surely interest students of avian plumage coloration. There is a feature of Hill's book, however, that makes me comfortable recommending it to a wider audience. As the whimsical title suggests, the style of the book is not that of a dry academic treatise. Hill prefaces each chapter with several quotations and a personal anecdote. The quotations are eclectic, and they both inform and amuse. The anecdotes are entertaining tales that include, among other things, an explanation of how Hill came to this study (he was unsatisfied with the maternal nostrum of “God did it”) and a description of a macabre incident involving a dentist with an unhealthy dislike for House Sparrows (Passer domesticus). (Visions of Laurence Olivier as the dentist and Geoff Hill as Dustin Hoffman were unavoidable.) These anecdotes are also informative, providing the reader with insight into why the study took the course it did, including the inevitable setbacks that are seldom evident in published papers.
Hill has greatly increased our understanding of the evolution of bright plumage in birds, but he is quick to point out how much remains to be learned. This engaging book will guide those who want to continue the study of House Finch plumage, while providing a template well worth following for research on plumage in other species, sexual selection in broader contexts, and behavioral ecology in general.