A Red Bird in a Brown Bag: The Function and Evolution of Colorful Plumage in the House Finch

Auk, The, Jan 2004 by Andersson, Staffan

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, xiv 318 pp. ISBN 0-19-5148487. Cloth, $65.00. -Why are star-forming galaxies red? Because enormous dust clouds absorb light of shorter wavelengths that is then re-radiated at longer wavelengths. By analyzing that phenomenon, one can learn about the origin and behavior of stars and galaxies and, ultimately, the universe. Why are male House Finches (Carpodacus mexicanus) red? Because carotenoid pigments, acquired through the diet and deposited in the feathers, absorb the shorter wavelengths of the white daylight, whereas longer wavelengths are reflected. By analyzing that phenomenon, one can learn about the origin and behavior of birds and other living creatures including, ultimately, ourselves.

There are people (and funding agencies) that find the first of those questions fascinating and worth the enormous cost of a VLT (Very Large Telescope), while considering the second question uninteresting, even at the minor expense of RFB (Regular Field Binoculars). But there are also many people that, like me, would argue that the red forehead of a backyard bird has more interesting things to teach us than does 10-billion-year-old starlight.

I start this review in a somewhat confrontational way because the title of Geoffrey Hill's book, A Red Bird in a Brown Bag, implies the almost apologetic attitude that many behavioral ecologists have towards their study topics as compared to "real science" like astronomy or biochemistry (try to imagine an astrophysics book entitled A Red Dot in a Huge Telescope...). Luckily, there is nothing apologetic inside this tribute to the fascinating puzzle of evolutionary biology in general, and animal coloration in particular. Let us just hope that, despite its title, this book reaches the broad readership it deserves.

Geoffrey Hill takes us on an enjoyable personal and scientific journey, from how he first decided on House Finch plumage coloration as a Ph.D. project 16 years ago, through the many aspects of this problem that he and his students have tackled over the years, to the current frontiers in the study of avian plumage coloration. As a matter of fact, the House Finch is the frontier in many ways: Looking back at all the mechanisms of avian color signaling for which these little birds, in the hands of Hill and his collaborators, have been the first (and quite often the only) model system, it is no exaggeration to say that the field would be seriously set back if the House Finch proves to be an exception rather than a general example. Then again, even if the House Finch turns out to be one of a kind in some features, it has still provided a large number of novel hypotheses and testable predictions.

Personal memories and stories make great spices in scientific monographs, but there is always a risk of diluting or even concealing the scientific message. Hill has solved this nicely by keeping the ingredients apart, starting each chapter with a short, amusing anecdote (I especially liked the one about the merciless Terminator working undercover as a suburban dentist), before switching to focused and nicely illustrated accounts of the chapter topics -from pigment physiology and nutrition to sexual and social behavior, ending with comparative tests of sexual selection theory in the chapter, "Why red?". The book is a pleasure to read from start to finish, but it also has enough repetitions of results and conclusions between chapters to allow readers with a more narrow interest to dive straight into the section of their choice.

The first chapter, on Darwinism and "Wallacism," describes how the views of dazzling bird colors have changed from divine creation (a "part of God's plan," as young Geoffrey was told by his mother) to the current models of sexual selection and visual signaling. The important contribution of Alfred Russell Wallace is emphasized. Although he rejected, almost ridiculed, Darwin's idea of female mate choice, he identified several of the other currently discussed adaptive significances of plumage coloration. Ironically, Wallace was also the first to suggest the link between color intensity and vigor that is now a central assumption of the sexual selection theory he dismissed.

After a chapter on general "housefinchology" and methods, filling in useful details for which there has been no or too little space in journal papers, the third chapter is devoted to color vision and color quantification. This is an important foundation for the chapters to come, not least to make sure that younger students, brought up in the age of portable spectrometers, do not dismiss the early House Finch research as flawed by its subjective color scoring. Hill makes a good case for the relevance and repeatability of his use of human color space, in the first years with color charts and more recently via tri-stimulus values measured with a miniature and rather low-resolution (10 nm segments) spectrophotometer, the Colortron. However, in my opinion (colored, of course), this chapter could have been a few pages longer and even more convincing. Why not use reflectance analyses directly to demonstrate in what way and how well the human color scoring captures objectively measured and computed parameters. Researchers familiar with spectrometry and colorimetry will know this, but there might be many readers (not to mention reviewers and editors) that dogmatically reject any animal color study without reflectance. (Somewhat reminiscent of how every comparative result without phylogenetic control was treated 10 years ago.)